The trouble with "muscle lathes"..........

[odie]

In a recent discussion, the desirability of, and trend for manufacturers to offer more increasingly powerful motors has led me to some casual thinking on the side.......(Uh, oh.......here comes trouble! Ha!)

First, I must say that I have never had more than 1 1/2hp to work with, so my input here is strictly theoretical on my part.........

It seems to me there are only two main reasons why more horsepower is desireable........the most important consideration it seems, would be that it allows turners to take massive cuts in a single pass, and the other will be related to the size/weight of the block of wood mounted.

Nobody could deny that horsepower is needed for both applications, but I am questioning whether massive cuts is desireable......except for the obvious!

I'm sure everyone here has experienced hot shavings on their hands. The act of cutting wood, and bevels rubbing creates heat, right? The heavier the cut, the more heat created. OK, so how many of you understand that the heat you create is drying the wood quickly, if only on the surface?

Drying wood too quickly is the most common cause of cracking in wood. Let's just say that a very tiny hairline crack, one you may not, or cannot notice at the time, and even though it is, at this point, only on the surface.......could become a major crack later on during the seasoning process. It just may be that sometimes, some of us have no idea we are actually initiating cracks that will only be realized later on.....when it's too late!.......

Even though I have less power than some turners, I have noticed some surface cracking on my turnings during the roughing stage. These tiny cracks may only be visible momentarily, and then close up when the surface cools. (I have seen this phenomenon with my own eyes!) I wonder if I've caused cracks that I never did realize were there, until later on.......?

Generally, even though I process lots of very wet bowls, I'm not very much plagued by cracking, and I think my drying techniques are contributing to that.....but, once in awhile, I do get them. I just have to consider all the possibilities, and surface heat in the roughing stage is one to consider. Even though I only have 1 1/2hp on tap, I can take some pretty big bites......and create a lot of heat.....but obviously not to the extent that someone else who has a more powerful motor can make.

Sooooooo........if any of the above is credible, and true........then it could be reasonable to suspect some of us are causing our own cracking problems without realizing why. It could also be true that, unless we are putting monster blocks of wood on our lathes, then the craving for horsepower and taking massive cuts, isn't something that is ultimately desireable........

It cannot be questioned that market sales determines the evolution of lathes, and I can see where the manufacturers are simply responding to the demands of those buying their products.......and, those buying lathes are overwhelmingly inexperienced turners. Maybe I've been on the right track all along by not having more power available to me........because it forces me to make more passes with less aggressive cuts! :cool2:

If I drive my SS396 Chevelle at the same speed as everyone else does, I won't get those tickets......but, man is it ever impressive to have all that raw power! I only get into trouble when I actually use it! Heh,heh,heh........!

ooc

 

[Gynia]

It could be said that the heavier the cut the cooler the cut. The cooling comes from the wood. There is no heat in the wood. The heat comes from friction and pressure. Some turners ride the bevel very hard and that pressure will generate heat. Dull tools will also increase heat as there is more friction with a dull tool than a sharp tool. However a big shaving will cary away more heat than a small shaving. So more horse power enable bigger cuts and cooler cuts.

I have 3 HP but I very much doubt that I use more than 1/2 HP for the vast majority of the turning that I do.

 

[Jarred Hoffpauir]

Ohh Business theory!

So like all other industries the lathe industry is out to maximize their market share of pure dollars. If the market will sustain 3hp lathes then you will simply drop off the less expensive options and only produce the more expensive options thus increasing your overall profit. See profits below,
$2500 lathe with 1.5hp motor @ 15% profit = $375.00
$3500 lathe with 3hp motor @ 15% profit = $525.00
Saome $3500 lathe with 3hp motor even at increased cost to the manufacturer @12% profit = $420.00

Either way the more the final product sells for the more the company makes. Once the general market starts to deflate and the consumers in your demographic start to shop for better deals the formula need to change. Right now the market will not support the "Cadillac" model in the same volume as before though everyone still wants all those options but for the bare bones price. So we start to see things like a 2.5hp model made with cheaper parts for the same price as the old 1.5hp model sold for. This makes it sound like a great deal right? They will sell lots of these cheaper machines because they are exactly what the market wants.

When those machines are in use for a few years and the cheaper parts start to break or wear down the market will start to demand more quality part and will gladly sacrifice that 3hp motor for the 1.5hp motor and the 2.5hp motor in place of quality parts. Thus starting the cycle again.

The misnomer in the minds of consumers of products in a niche market, like the Lathe market is quite simply that the change of motors is in the interest of the consumer. Truth be told it is simply in the interest of sales and companies will always give you exactly what you want. Sad part is that the consumer never knows whats good for them and because "the customer is always right" they will continue to get what they deserve.

In reality each lathe in any part of that cycle is going to be perfectly serviceable for a large section of the consumers because the 1.5hp is going to sit in the corner of the garage just as well as the 3hp model.

 

[davidwalser]

I learned to drive in a '68 VW bug. At the time, the car always seemed to have plenty of power. It was in the days of the 55mph speed limit, so I could keep up with traffic (except on fairly steep grades) and I could merge onto the freeway without problems (except on short on-ramps). I was sure the VW had all the power a reasonable driver could desire. This belief was reinforced by my first few chances to drive my parents' Ford LTD with its 400ci V8. That thing had way too much power! If you weren't careful, the LTD could easily zoom right past a stop sign or you'd find yourself at the end of the on-ramp before you were ready to merge into traffic. When driving up the canyon, the car could easily obtain speeds that were too fast for comfort. Such power was not only not needed, it was dangerous! Such were my perceptions as a learning driver.

Of course, now that I've been driving a few years, my perceptions have changed. I don't find the additional power of my pickup's V8 to be a danger. I am comfortable with the power and feel I can harness it for my productive use, convenience, and safety. (Truth be told, within a few weeks of getting my license, I found my parent's LTD to be under-powered. But, that wasn't because the car lacked power, it was because I was young and stupid.)

Returning to woodworking, I learned shop skills in a furniture mill. All our equipment was industrial. The tablesaw had a 5hp motor. My home shop has a Craftsman tablesaw with a 1.5hp motor. Can I do with my Craftsman tablesaw what I used to do with the saw I learned on? For the most part, yes. Both saws use 10" blades, so the capacity of both saws is basically the same. One saw is a lot easier to use than the other. It cuts quicker, with less burning, and leaves a better surface than the other saw. I won't leave you in suspense. The saw that is easier to use is the one with more horsepower. Usually, I can get the same result with either saw -- but my home saw requires a lot more effort on my part. The feed rate has to be just right to keep from overpowering the saw (too fast a feed rate) and to keep from burning the wood (too slow a feed rate). The "feed rate margin of error" is much finer on my home saw and, with thick hardwoods, the margin of error might not exist at all.

I suspect that most would find the same to be true with lathes. More power is nice to have. It may not be essential, but for some operations -- such as roughing out a bowl -- the extra power might be awfully nice. I know turners who occasionally stall a 3hp lathe when roughing out a bowl. They have sharp tools and excellent technique. Their turning skill just enables them to take a larger bite than their lathe can handle with that particular blank. So, they back off a little on their cut and everything's fine. What would happen on a 1.5hp lathe? They'd have to back off more and more often. For a lot of turners, that'd be a real pain.

 

[john lucas]

Odie It's interesting that you bring up the point of heat. I remember early on that I had to wear a glove because of the heat coming from turings. I don't any more. Not sure why but I can speculate.
First off, I know my tools are sharper. Second, I make my main bevel very short now. It varies with my tools but my bevel is less than 1/4" and on some tools more line 1/8". Maybe this is producing less friction. 3rd, I now I use less pressure on the bevel than ever before. I know because at the end of turning sessions the only thing that hurts is my feet (and that's just old age). I think that is because I am so much more relaxed in my cuts and at the same time use less muscle partly because I'm not pushing the tool.
I do take fairly large cuts at first. It's just a time saving thing. I don't force the tool I let it do the cutting but with the proper horsepower and proper tool orientation the lathe and tool are doing all the work.

 

[dbonertz]

Interesting thread but I think it has more to do with how you use the lathe/tool. I am a hobbyist turner but I will get into production mode turning when I am roughing bowl blanks for a friend. It really helps to have my vl300 3hp when roughing for the speed at which I can rough turn on it. When I use smaller lathes (helping others in their shops) I cannot cut the same as I do on mine. I do not mean technique wise but rather speed due to bogging the lathe down. I am a professional contractor and can make a job go faster and smoother with the right equipment. That is why I purchase heavier duty tools for my business. They can handle the daily heavy use and they make the job go easier thus faster. I have tried lighter duty tools and end up frustrated. I started woodworking in a wood window and door manufacturing business and am also used to industrial woodworking equipment. Heavier duty equipment not only make the work easier but also since easier they are also safer due to not having to force, push harder or slower and etc. to make the cuts. They (equipment) just do there job with ease. Lighter equipment have there place for the hobbyist woodworker or home owner or weekend warriors but for professional turners or production turners of larger items they need to go for muscle tools.

 

[Harry Robinette]

I have a 2HP Vega 2600 and USE the 2 horse POWER allot of the time. When I put a piece 25" dia. and 12" deep and green I need the power. I also do most of my turning under 14" on a General 160-18 with a 1HP DC drive hooked to the reeves drive and have plenty of power. I believe that we all will use the power we have and we all want more power then we need. Lathes,Car's whatever, it's
all the nature of the beast.
Just my $.02

 

[Gretch Flo]

If I drive my SS396 Chevelle at the same speed as everyone else does, I won't get those tickets......but, man is it ever impressive to have all that raw power! I only get into trouble when I actually use it! Heh,heh,heh........!

ooc

Boys with their toys!!!!!! Gretch

 

[Gretch Flo]

I have noticed some surface cracking on my turnings during the roughing stage. These tiny cracks may only be visible momentarily, and then close up when the surface cools. (I have seen this phenomenon with my own eyes!) I wonder if I've caused cracks that I never did realize were there, until later on.......?
.
ooc

These cracks that open and then close. I have seen this too. Would you superglue these if at final thickness?. Is it loss/gain of bound or unbound water????? Gretch

 

[Dale Miner]

I think part of the need for higher horsepower lathes is a result of switching away from a belt change model, or a reeves drive model to the electronic variable speed lathes.

With a belt drive, and even the much maligned reeves drive system, as the lathe is slowed down, the torque available at the spindle goes up by the factor of speed reduction. Much like a truck using granny gear to start a load and switching to higher gears as the speed increases. Since the motor is running at a constant nameplate rpm, the available horsepower is never reduced, while available torque at the spindle does change inversely to the spindle speed.

With an electronic variable system, assuming constant torque from the motor, as the speed is reduced, available horsepower is reduced. Some electronic VFD's have the ability to increase the torque from the motor to some extent as speed is reduced, but there is a limit to that increase. My guess is that the torque increase would max out at about a 33% increase. If so, a 2 hp 1800 rpm motor running at 900 rpm would only be able to produce 1.33 horsepower.

I've a 3520B, and stalling it in low range roughing a 12" blank can be done, but not easily. With an 18" blank, stalling the lathe with the same cut taken on a 12" blank will cause stalling or at least slowing down necessitating backing off on the cut.

I've not noticed the small cracks you mention on fresh cut wood. Since freshly cut wood is usually throwing water, heat is not a problem. I have noticed heat and small cracks on wood that is partly dry and does not release water when turned. This is especially true when the tools are less than sharp. Roughing partly dry wood seems to take more power and stalling the lathe can occur with lighter cuts.

On second turnings with the harder woods (oak, osage, sugar maple, pear, etc.), hot shavings do happen, as well as the gouge becoming hot even with light bevel contact and freshly sharpened tools. I have not seen any cracking develop on fully dry pieces while second turning. Lighter cuts and fewer rpms reduce the heat issue. Stalling on the second turning hasn't been a problem.

 

[Steven Antonucci]

If I drive my SS396 Chevelle at the same speed as everyone else does, I won't get those tickets......but, man is it ever impressive to have all that raw power! I only get into trouble when I actually use it! Heh,heh,heh........!

ooc

98% of the time, you probably used 10% of the power that your 396 could put out. I think I read somewhere that an average engine cruises at 40hp?

On the times when you mash the pedal, it is fun to realize that you have WAY MORE HP than you need. Odds are that if you are a law abiding citizen, you have about 5 or 6 seconds to enjoy that power before quickly becoming a menace to society. I know that I enjoyed my 350 4-barrel Chevelle, but the reality is that if you add 4 seconds to full throttle, you could easily kill yourself.

I understand your point. I suspect that a lot of folks are looking at lathes the same way that they look at cars. Having a car that can go 150mph and being able to drive it are two different things. Most of the time, we're only going to the grocery store.

I do not lust after more HP, but I wouldn't say no to better bearings, more metal holding the lathe to the floor, and a larger capacity for the occasional large work that I do. (if you've ever done a clean-up after turning large work, you know why it is occasional...)

Still, it's nice to know that you've got the ability to unleash the beast, huh?

 

[odie]

It could be said that the heavier the cut the cooler the cut. The cooling comes from the wood. There is no heat in the wood. The heat comes from friction and pressure. Some turners ride the bevel very hard and that pressure will generate heat. Dull tools will also increase heat as there is more friction with a dull tool than a sharp tool. However a big shaving will cary away more heat than a small shaving. So more horse power enable bigger cuts and cooler cuts.

I have 3 HP but I very much doubt that I use more than 1/2 HP for the vast majority of the turning that I do.

Gynia.......

Yes, correct......sharp tools will reduce the amount of heat generated, but will not eliminate it.........

I did a test yesterday on a Brazilian Cherry bowl I was currently working on.......took a heavy cut and immediately stopped the lathe and felt the wood. I was surprised to feel less heat on the wood than the heat which was felt in the shavings being created.

You are also correct that the heat transfer is mostly with the shavings, but there was some felt heat transferring to the wood surface. Even though it may not have been as much as the heat in the shavings (probably from the cooling effect of the solid wood you mention) there was some obvious heat transfer to the wood itself........which brings us back to the whole point of this thread.......

The heat transfer to the surface of a wet bowl blank will necessarily evaporate moisture at the surface. Because drying wood too quickly is the most prevalent cause of cracks, it's my thought that very small, or microscopic cracks could have their genesis with the heat produced during the roughing out phase of bowl making. Even though they may be too small to notice at this point, the process of seasoning the bowl to a stabilized moisture content will likely make that microscopic beginnings of a crack into something that ultimately ruins the bowl.......:mad:

Is anyone here going to disagree that larger capacity cuts will produce more heat than smaller lighter cuts? What I'm trying to convey here, is that it's possible that taking smaller cuts with more passes yields a benefit to the turner that some of us didn't realize we were enjoying in the first place.

The only disadvantage to the whole process is lighter cuts will mean more passes of the tool to accomplish the same volume of wood removed.......and, for me this does not make much difference in the time element, because, for example, 30 passes as opposed to 20 passes is pretty insignificant time wise.........

Yes, of course, horsepower is a convenience. If I were in the market for a new lathe, I'd probably go for the bigger motor......but not for the ability to make bigger cuts......that would stay pretty much the same as it is now. If I ever did opt for a more powerful motor, it would be to manage heavier, larger blocks of wood......


ooc

 

[Gynia]

There is the other consideration of more horse power which hasn't been mentioned. Taking a heavy cut on green wood is a joyous activity. Shavings flying, the humidity in the shop going up, the smell of wet wood, the spray of water off the spinning blank. There is nothing in woodturning which is more glorious. The trap to this basic joy is bogging down the lathe so that you need to take a lighter cut. Talk about a buzz kill...

 

[robo hippy]

Having done concrete work for 30 years, I prefer things over built to being under built. I prefer a bigger heavier lathe to a smaller one. Case in point, a Nova DVR 1 1/2, 110 volt (the demo lathe at our local Woodcraft store), to my Robust American Beauty. The ability to absorb and dampen vibration from the wood and related stresses of applying heavy cuts is a huge benefit. The Beauty does an excellent job, the DVR a fair job. Both are good lathes, but.....

I am surprised to hear about the micro cracks that you have seen open up, then close back up. The only times I have had those micro glazing cracks are from sanding with dull abrasives, and applying too much pressure. If those cracks occur in green wood, as it drys, they would open back up again. I have never seen cracks get smaller, only bigger.

It would be interesting to take one of those thermal sensor things that can read temperatures of surfaces into the turning shop and see where the heat is being generated and dissipating. I would guess very little heat on the bowl, but more on the tool and shavings.

I have had more problems with the abrasive quality of the shavings going across my hand than the heat. One advantage to using a scraper for roughing cuts is the shavings go more up and over your hand rather than across the top of your hand. I no longer have a bowl turner's callous on my pinky finger.

robo hippy

 

[odie]

These cracks that open and then close. I have seen this too. Would you superglue these if at final thickness?. Is it loss/gain of bound or unbound water????? Gretch

Hello Gretch.......

I've had such poor luck with the super glues, insta-bond, etc., that I avoid using them anymore, unless there is nothing else to avoid a complete failure. When I saw these "disappearing" cracks.....and, I believe this had to be more than five years ago, it would be my standard procedure to try and remove them completely and go for an alternate bowl shape. If that isn't an option, then you might as well go for it.....couldn't hurt to give it a go after the wood has stabilized!

It's possible that the momentary cracks I saw were the result of taking more "bite" than I do now......memory a little foggy on that one. Anyway, at some point, I decided to take smaller cuts and more passes. I am in a continual state of change when it comes to my woodturning, so my success rate probably can't be pinned down to that one element, but I'm pretty sure it has helped.......

Also, along that point in time, I also converted from wet grinding and slipstones of my turning tools (as a follow-up to the initial 80gt Norton SG wheel), to impregnated diamond hones and slipstones. My tools were as sharp as those methods can provide, but the diamond hones are the superior alternative.......sharpER......

PS: Don't tell anyone, but I don't own a SS396 Chevelle.........I wish! That was just added in there to give a little perspective to the post! (I did have a '67 GTO with an optional 400 (as opposed to the 389) engine, though......but, that one is long since history!

ooc

 

[odie]

I think part of the need for higher horsepower lathes is a result of switching away from a belt change model, or a reeves drive model to the electronic variable speed lathes.

With a belt drive, and even the much maligned reeves drive system, as the lathe is slowed down, the torque available at the spindle goes up by the factor of speed reduction. Much like a truck using granny gear to start a load and switching to higher gears as the speed increases. Since the motor is running at a constant nameplate rpm, the available horsepower is never reduced, while available torque at the spindle does change inversely to the spindle speed.

With an electronic variable system, assuming constant torque from the motor, as the speed is reduced, available horsepower is reduced. Some electronic VFD's have the ability to increase the torque from the motor to some extent as speed is reduced, but there is a limit to that increase. My guess is that the torque increase would max out at about a 33% increase. If so, a 2 hp 1800 rpm motor running at 900 rpm would only be able to produce 1.33 horsepower.

I've a 3520B, and stalling it in low range roughing a 12" blank can be done, but not easily. With an 18" blank, stalling the lathe with the same cut taken on a 12" blank will cause stalling or at least slowing down necessitating backing off on the cut.

I've not noticed the small cracks you mention on fresh cut wood. Since freshly cut wood is usually throwing water, heat is not a problem. I have noticed heat and small cracks on wood that is partly dry and does not release water when turned. This is especially true when the tools are less than sharp. Roughing partly dry wood seems to take more power and stalling the lathe can occur with lighter cuts.

On second turnings with the harder woods (oak, osage, sugar maple, pear, etc.), hot shavings do happen, as well as the gouge becoming hot even with light bevel contact and freshly sharpened tools. I have not seen any cracking develop on fully dry pieces while second turning. Lighter cuts and fewer rpms reduce the heat issue. Stalling on the second turning hasn't been a problem.

Good post, Dale.........

I suppose I must clarify what I would call a "wet bowl"......and may not be in line with what every has concluded........for the purposes of this discussion, my use of the term was meant to be any wood that is above stabilization moisture content. You're right that it would be difficult to produce enough heat to be considered on wood that is above, say, 20 percent MC, or more.

When on second turning, or final turning.......at that point, moisture content should have stabilized. Even though heat can be produced, the moisture content is so low (in my area, stabilization occurs at around 10-12 percent MC, but I often received bowl blocks from outside this area that are below that number) that I'm certain it would never be an issue with suddenly appearing cracks, like under discussion. If I were to take a guess at the MC range where this kind of cracking can occurr......around 12-20 percent would be my estimate.......

You are probably right about the changeover from belt, and Reeves drives to the more current DC VS drives of today being the inspiration for more HP, I think!. When I first got my Australian Woodfast, it was offered with 1 1/2hp belt drive and 1hp VS.......I chose the belt drive step pulleys..........and eventually converted to the 1 1/2hp Leeson/Minarik drive that I have now. (It took me way too long to make that decision! )

ooc

 

[Gretch Flo]

If I drive my SS396 Chevelle at the same speed as everyone else does, I won't get those tickets......but, man is it ever impressive to have all that raw power! I only get into trouble when I actually use it! Heh,heh,heh........!

Notice Odie that there is MY]S396 Chevelle- Is this "Man talk"???? What lathe should I "own" up to????, Maybe back to hand carving chisels!!!!! Gretch

 

[odie]

If I drive my SS396 Chevelle at the same speed as everyone else does, I won't get those tickets......but, man is it ever impressive to have all that raw power! I only get into trouble when I actually use it! Heh,heh,heh........!

Notice Odie that there is MY]S396 Chevelle- Is this "Man talk"???? What lathe should I "own" up to????, Maybe back to hand carving chisels!!!!! Gretch

Heh,heh,heh......yeah, I guess it's "man talk", Gretch.......

Kinda like wishful thinking, along with some trying to impress the guys sort of thing!......all under the pretense of making the point!

Later, lady........

ooc

 

[David Wilkins]

For what it is worth, I have a nova dvr xp wired to 220 and a general maxi vs for demo's and teaching. I've turned on a 2436 with a 3hp motor and a vb36. I used to have a 1440 knockoff and before that a craftsman tube lathe. The craftsman outpowered the 1440 3/4 hp knockoff by a wide margin. The general I demo with is great for a small portable lathe it'll do just about anything. The extra power the dvr has makes rough work easier, no bog and you can run things a bit faster too. When you get to a vb36 or the oneways, it is about removing even the minute restrictions previous lathes had. They are a luxury of sorts, because you can do the same projects on smaller and cheaper lathes. I had a vb36 savings account, and I was 3/4 of the way there when my wife delivered our baby. Now it's the second car in the driveway

 

[n7bsn]

I have to admit that when I read the subject line I thought the OP was talkign about a REAL muscle lathe

Like my foot powered treadle lathe

 

[john lucas]

Mine does about 90 rpm and is powered by about 4 donuts per hour. I will admit the friction is pretty low but the heat (on my body) is pretty high.

 

[Bill Boehme]

Not as much "muscle" as some might think.

In a recent discussion, the desirability of, and trend for manufacturers to offer more increasingly powerful motors has led me to some casual thinking on the side.......(Uh, oh.......here comes trouble! Ha!)

Here a few things that many turners may not know about "muscle lathes":

First some background. Before the days of electronic variable speed in woodturning lathes, the choice was between a "stepped cone" pulley drive or variable spacing split pulleys, AKA Reeves pulleys. The advantage of both of the mechanical arrangements is that the available output power at the spindle is the same as the the motor shaft output power times the efficiency of the drive train which is in the neighborhood of 80 to 90 percent (around 75% for Reeves drives). What this means is that regardless of the spindle speed, the available power is constant and nearly equal to the motor output power. Cost is also a factor that favors these simpler all-mechanical machines.

Now, along comes these fancy new lathes with electronic variable speed control at the touch of a knob and touting larger horsepower motors -- seems like "goodness squared" minus the somewhat higher cost. When we hear sales buzzwords like "constant torque" and "constant horsepower", we're now ready to retire the old lathe and get one of these newfangled toys.

Just in case anyone is wondering if there a downside to a lathe with electronic variable speed, the answer would be "it depends". If money is a scare commodity around your neck of the woods, then the bad news is that these new toys are quite a bit more expensive than their all-mechanical counterparts. The good news is that you will eventually get over the extra money spent on one of these "muscle lathes" with electronic variable speed control. The larger motors aren't there just for show -- there are valid technical reasons for the larger horsepower motors (I won't deny that the "muscle factor" has also entered the picture, but the issue gets somewhat muddied by the fact that there is also a trend for larger swing in lathes which necessitates higher horsepower motors).

So, on to the nitty-gritty. One of the first things that we might notice is that many of these fancy pants variable speed lathes also have two or three stepped pulley positions. A reasonable question would be what is the reason for that? Isn't the purpose of electronic variable speed control to get away from the need to change drive belt position from one pulley to another? Ideally, yes, but with electronic variable speed control, the motor is not able to deliver full mechanical power below "base" speed (base speed is the normal nameplate speed when connected directly to 60 Hz AC power -- typically around 1750 RPM).

As the lathe speed approaches zero, so does the motor's mechanical output power. There are two options to solving this problem. One option that is almost always implemented is to use a bigger motor in order to have reasonable power at slower speeds. However, you can only go so far with the bigger motor idea before running into much more expensive motors and controllers. This leads to the other option which is to also have two or three pulley drive ratios. Many, if not most, "muscle lathes" implement a combination of the two options.

If you are really alert, you might be wondering, "how does changing the pulley drive ratio give us more power?" Ordinarily, it doesn't, but with electronic variable speed control, we need to remember that available output power is a direct function of motor speed. Therefore, changing to a drive ratio that allows the motor to run faster results in more available power at the lathe spindle. My lathe has a maximum spindle speed of about 1000 RPM in the low speed range which is the range that provides the greatest power output at the spindle for any given spindle speed that is within the range of the other belt settings.. My experience is that I don't need a lathe speed faster than 1000 RPM except for turning pens and small spindles.

Here are a couple performance restrictions for the design engineer creating a new lathe. The standard TEFC induction motor doesn't like to run much below base speed because the cooling fan runs at the same speed as the motor shaft. The slower that the motor runs, the faster that it overheats. This is another criterion for selecting the optimal pulley drive ratios. At the other end of the speed range, motors don't like to run much faster than base speed. The bearings may not be designed to withstand constant operation much above about 125% of base speed. Additionally, windage loss (basically aerodynamic drag between the rotor and stator) increases very rapidly with increases in speed. Also, the cooling fan may "stall" (i.e., stop creating lift because the angle of attack is too high) at excessively high speeds. Pulleys and belts also have speed limits. For pulleys, it is the centrifugal force that makes it want to fly apart. For belts, it is the efficiency loss in the rubber from wrapping and unwrapping around a pulley as well as the aerodynamics of forcing air out of the grooves as the belt wraps around the pulley and the vacuum created when the belt unwraps.

What about "constant torque" and "constant horsepower", you ask? Those terms are not important unless you are a design engineer developing a variable speed drive or control system. It is also good fodder for marketing types who like to say impressive sounding words. All that "constant torque" means is that below base speed, a motor is capable of constant torque, but decreasing horsepower as speed is decreased (this assumes that we are using an electronic drive capable of providing the necessary motor current. Torque, by itself, doesn't mean anything. A motor can be stalled and providing full torque, but the power output would be zero because no work is being done. Above base speed the motor operates in the constant horsepower regime. As speed increases, the horsepower is constant, but torque and, therefore, efficiency are decreasing. The drive poops out when windage and other losses leave no available power to drive the load.

In summary, the higher horsepower motors on "muscle lathes" more or less compensates for the loss of power resulting from operating the motor below base speed. There aren't many direct comparisons available for mechanical vs. electronic variable speed lathes when talking about horsepower, so these discussions necessarily involve making generalizations.

By the way, I did once turn a pen on a "real" muscle lathe -- a Velocipede pedal lathe. It takes a bit of coordination to pedal and turn, but I finally got the hang of it just before falling off the little "tractor seat" balanced on a single metal rod to the floor. This made the whole thing sort of like riding a unicycle while turning. I flunked the coordination test just before completing my pen. The whole experience gave me a much greater appreciation for electric motors.

 

[hockenbery]

Pulleys give more speed control. On the lower pulleys.

In addition to more torque the low range pulley on the variable speed lathe gives you a finer control of speed.
A 1/4 turn of the dial on the slow range pulleys might change speed 200 to 250 RPM
While on the fast pulley a 1/4 turn on the dial will be a change of 700 to a 1000 RPM depending on the lathe.

Much easier to dial in optimal roughing speeds on the low pulley.

For me that optimal speed is a little bit of vibration. With the variable speed lathe this little bit of vibration is often a bit faster than the first vibration point. This can be really hard to dial in on the high pulley setting where small turns of the dial make big changes.

I tend to go to the lower pulleys more for the speed control advantage than the torque. I have a 2HP motor and it will spin s a 14" bowl blank on the high pulley. I can't dial into the right speed without risking going way too fast as I hunt for it. On the low pulley getting too fast is in a fine adjustment and easy to. Back off.

Going from 250 to 500 is controllable if go from 250 to 1000. I'm asking for troubles.

Al

 

[Gretch Flo]

2 points of vibration

. With the variable speed lathe this little bit of vibration is often a bit faster than the first vibration point.

Al

Is there a "simple" explanation of 2 vibration points on the lathe speeds?? Same explanation (whatever that is) of a car that vibrates at 40 MPH and slower or faster it smooths out? (tires? alignment) Gretch

 

[hockenbery]

Simple?..

Lots of stuff is vibrating. Each vibration has it's own number of vibrations per second.

At some speeds these vibrations occur at the same time making bigger vibration.
At other speeds they are offset in time and cancel each other.
A sand. Bag on a lathe reduces vibration more than a concrete block because all the sand grains vibrate independently and cancel each other out while the concrete block vibrates a unit.

Athletes are taught to run on their toes because running on the heels causes the head to vibrate. A good outfielder seems to glide because the toes take up the vibration an the head doesn't bounce. Running on the heels each foot step is an added vibration causing the head and eyes to bounce the brain has too much work to do matching up the location of the ball and the glove. Catching fly balls is about running

Al

 

[john lucas]

Bill As my skills have improved over the years I find I am turning at faster speeds than ever before. I do rough out pretty slow but I'm over 1000 rpm pretty fast and find myself turning closer to 2000 rpm or more for most turnings now. I think it's a combination of taking smaller bites per revolution which lets me relax more, and at the same time I'm able to make my body move over a smoother arc which really helps control the accuracy of the arc.
I have noticed that several other turners do the same. Stewart Batty and Jimmy Clewes come to mind.
I noticed last night when turning my mirror handles I'm running probably 3/4 or more speed on the high pulley. I'd have to look at the RPm's because mine doesn't read out direct rpm but this has to be well up there.
I'm not trying to rush things and be aggressive I just find that I have better control and can make smoother curves on my pieces.

 

[MichaelMouse]

Gynia.......

The heat transfer to the surface of a wet bowl blank will necessarily evaporate moisture at the surface. Because drying wood too quickly is the most prevalent cause of cracks, it's my thought that very small, or microscopic cracks could have their genesis with the heat produced during the roughing out phase of bowl making. Even though they may be too small to notice at this point, the process of seasoning the bowl to a stabilized moisture content will likely make that microscopic beginnings of a crack into something that ultimately ruins the bowl.......:mad:

Is anyone here going to disagree that larger capacity cuts will produce more heat than smaller lighter cuts? What I'm trying to convey here, is that it's possible that taking smaller cuts with more passes yields a benefit to the turner that some of us didn't realize we were enjoying in the first place.

You are correct in assuming that heating helps produce those brief checks on the surface. Wood shrinks as it dries, (re)expands as it readsorbs moisture. Moisture can come from within or without. In this case it comes from within, exactly as is the case with air drying. If the surface dries too fast for replenishment from within, it might check. If it checks it might crack. Except on the inside!

"Larger capacity cuts?" I'm a slicer, which means I remove shavings as broad as a half inch or more, but they're generally fairly thin at a 16th or a bit more. That's a pretty good rate of stock reduction. As rapid, if not moreso than the guy who presses and rips a thicker but narrow shaving, producing the heat that pressure will. It's independent of area, as the heat is from friction, so the length of the bevel is immaterial. A longer one is better at shaving, actually, so it produces less heat in proper application.

The old story about the hikers and the bear comes to mind again. You just have to have more power than it takes to remove a shaving, not enough to stall the lathe.

 

[MichaelMouse]

Simple?..

Lots of stuff is vibrating. Each vibration has it's own number of vibrations per second.

At some speeds these vibrations occur at the same time making bigger vibration.
At other speeds they are offset in time and cancel each other.
A sand. Bag on a lathe reduces vibration more than a concrete block because all the sand grains vibrate independently and cancel each other out while the concrete block vibrates a unit.

What's vibrating, and why? Answer is the wood - NOT the 3/4" metal cylinder - and the reason it's vibrating is because you are not shaving it, but hogging so that the easy stuff allows the motor to speed up as it departs and the tough upgrain parts slow down as you rip uphill. Cutting across the grain and down hill will even the cycle and reduce vibration, producing a long shaving.

Like to state one again that lathe oscillation, created by advocates of excess rpm and controlled by footprint or counterweight, is NOT vibration. That's caused by the wood chattering. Answer to both centrifugal wobble and vibration is to slow down and re-present the tool, not to speed up. I know I can't feed the tool fast enough to get a continuous shaving much above 800 under the best conditions, and I imagine others have noticed that as well. If you're ripping chips, you're creating vibration. Slow down for safety and control and reap the additional benefit of a good surface.

 

[-e-]

In a recent discussion, the desirability of, and trend for manufacturers to offer more increasingly powerful motors has led me to some casual thinking on the side.......(Uh, oh.......here comes trouble! Ha!)

First, I must say that I have never had more than 1 1/2hp to work with, so my input here is strictly theoretical on my part.........

It seems to me there are only two main reasons why more horsepower is desireable........the most important consideration it seems, would be that it allows turners to take massive cuts in a single pass, and the other will be related to the size/weight of the block of wood mounted.


ooc

First, let's talk torque -- if you are going to core, you need sufficient torque no matter what size mounted the chunk of wood. i'm sure others can supply the ratio of torque to horsepower.

Secondly, there seems here the assumption that horsepower equates to speed -- i hope we all agree that speed has little to do with horsepower.

torque, however, the key to a pain-free tomorrow :>)

 

[Bill Boehme]

Is there a "simple" explanation of 2 vibration points on the lathe speeds?? Same explanation (whatever that is) of a car that vibrates at 40 MPH and slower or faster it smooths out? (tires? alignment) Gretch

Sounds like it may be time to take your car in for some maintenance.

It depends on what you mean by "simple". Here is my version of "simple" -- any given mass attached to the end of a spring of a given stiffness has a natural frequency of vibration. If you change either the mass or the spring then that frequency also changes. If you want more, then ....

Suppose that we "excite" this spring-mass system by poking on it with something (a bowl gouge, for instance), the spring-mass system will respond by vibrating back and forth (or perhaps, to and fro) at its natural frequency until the vibrations eventually die down. (The vibrations die down because there is a third component to this system that we initially overlooked called a damper that is absorbing the energy of the vibration).

Now, suppose that we decide to poke this spring-mass-damper with our blunt instrument at exactly the same rate as the system's natural frequency of vibration. We will see that the amplitude of the vibrations grows ever larger until something breaks (mass comes loose from spring, smacks our investigator holding the blunt instrument and then rolls around on the floor.

Seeing that our previous action was a bad idea, we decide to find out what happens if we poke the spring-mass-damper system with the same blunt instrument at a rate that is slightly slower or faster than the system's natural frequency of vibration (a.k.a., "resonant" frequency). We discover after much wear and tear on our investigator that as our chosen exciting frequency approaches the resonant frequency of the system, the amplitude of the oscillations (i.e., the to and fro vibrations of the mass on the end of the spring) grow in magnitude. We also discover that when we excite the system at a frequency sufficiently removed from the system's natural frequency that the exciting frequency no longer has much of an effect on the amplitude of vibration of the system.

In the real world we find that masses, springs, and dampers rarely look like the classic examples seen in freshman physics textbooks. We can often identify a mass, but the spring and damper may not be as obvious. To make the picture even muddier, these systems rarely live in isolation. Most everything around us (a woodturning lathe, for example) consists of a large collection of masses, springs, and dampers that all interact with each other to some degree. An out-of-balance hunk of wood spinning on a lathe is both a source of excitation and a mass coupled to another mass which consists of the lathe body through a rather stiff spring consisting of the drive train. At the same time, the drive train itself is a spring mass-damper-system consisting of the spindle, bearings, belt, and motor. And the motor itself when being powered under load is working to maintain a certain slip frequency by changing the current through the field windings to provide the needed torque. When the load (i.e., the out of balance spinning hunk of wood being intermittently cut with with a blunt bowl gouge) is not reasonably constant then the drive train reaction also becomes part of the overall system stability. The most obvious dampers in this overall system might be your bags of sand, cement, or deer corn on the bottom shelf of the lathe, but the complex geometry of the lathe body itself usually provides most of the damping.

-e-, where have you been? Good to see that you are still alive.

 

[AlanZ]

As long as we're talking about power delivered by lathes, it's worth mentioning the Nova DVR motor. I believe it is unique in that it monitors the spindle rotation and compares it to the desired speed, adding and removing power as necessary.

The video on the Nova DVR motor page shows this by watching the power draw during cuts. Aside from the savings in electricity, this does demonstrate the intelligent power management. Also, you can set the lathe so that it stops briefly when you get a catch (and how much of a catch is necessary to invoke the stop)

Cool stuff (and no belts or pulleys to mess with)

 

[Bill Boehme]

As long as we're talking about power delivered by lathes, it's worth mentioning the Nova DVR motor. I believe it is unique in that it monitors the spindle rotation and compares it to the desired speed, adding and removing power as necessary.

The video on the Nova DVR motor page shows this by watching the power draw during cuts. Aside from the savings in electricity, this does demonstrate the intelligent power management. Also, you can set the lathe so that it stops briefly when you get a catch (and how much of a catch is necessary to invoke the stop)

Cool stuff (and no belts or pulleys to mess with)

I see that they, like most the others, don't mind slinging bull (but only when it is actually needed) as in their video proclaiming that the motor only delivers power when it is actually needed. The proper response would be, "of course and the same thing is true of every other AC induction motor whether operated straight from the power line or through a variable speed controller".

 

[Bill Boehme]

i'm sure others can supply the ratio of torque to horsepower.

It's simple for a conventional drive (fixed speed motor and stepped cone pulleys to control spindle speed).

torque = power / speed

and, if you want torque in LB-FT, power in horsepower, and speed in RPM, use the constant 5252 as follows:

torque = HP X 5252 / RPM
​

We shouldn't think of these as as unrelated parameters. Knowing any two components tells us the third.

i hope we all agree that speed has little to do with horsepower.

Well, not all of us agree. As shown in the equation above, speed has everything to do with horsepower. In order to determine the mechanical output power of a motor, we measure the torque and the speed. A motor that is not turning can provide full torque, but there is no work being done, therefore the power output is zero. Torque, by itself doesn't do anything. An angular velocity is also needed. The product of these two parameters gives us the power output.

 

[AlanZ]

Bill,

Forgive me if I don't understand your point here, or if I'm misunderstanding something fundamental.

I was under the impression that the Nova's motor design actually tries to maintain a set RPM by monitoring the spindle in real-time. It then adjusts the power to the motor in order to accomodate changes due to the resistance of the cut. Aside from energy savings, this should make for smoother cuts as the motor is less likely to bog down from heavier cuts.

Are you implying that other variable speed systems also monitor the spindle speed and are trying to do the same thing? I thought this was unique to the DVR.



Thanks for your insight into this.

 

[n7bsn]

I see that they, like most the others, don't mind slinging bull (but only when it is actually needed) as in their video proclaiming that the motor only delivers power when it is actually needed. The proper response would be, "of course and the same thing is true of every other AC induction motor whether operated straight from the power line or through a variable speed controller".

Em, Bill. I suggest you don't understand the difference between a conventional motor and a DVR motor

 

[robo hippy]

We have a DVR for our club demo lathe, courtesy of our local Woodcraft store. I have pushed it a bit, and I think it is supposed to supply more juice with higher resistance (heavy tool cuts) so the rpm stays fairly constant. I know there is a 'Vector Drive' type of motor that Robust is using on the 16 inch lathe that is supposed to do the same thing. I have no idea how they work, but the DVR is different than my big Robust. Maybe I should really push the DVR.

robo hippy

 

[AlanZ]

Though it comes from Teknatool, here are a few more items that indicate that the DVR motor is not your typical variable speed motor.

DVR motor advantages page

What is DVR page

Interesting stuff.

I've had the DVR for about 2 years, and it is a pretty cool device.

I especially like it when it beeps at me when I forget to release the spindle lock (yet again). That's all it does, beeps... the motor doesn't strain against the lock... it just sits there and giggles quietly to itself.

 

[hockenbery]

What's vibrating, and why? Answer is the wood - NOT the 3/4" metal cylinder - and the reason it's vibrating is because you are not shaving it, but hogging so that the easy stuff allows the motor to speed up as it departs and the tough upgrain parts slow down as you rip uphill. Cutting across the grain and down hill will even the cycle and reduce vibration, producing a long shaving.

I always set the lathe speed with no cutting.
The lathe tools should never vibrate. I cannot control a vibrating tool.
Any vibration from the lathe tools needs to be corrected. Tool vibration is most often too much bevel drag, dull tool, tool rest too low, tool rest too far from the wood, or too heavy a cut, In general corrections for tool vibration don't involve lathe speed.

A sharp side ground gouge will throw a 1/2 to 3/4 wide shaving with no vibration of the tool. All the force goes into the tool rest. A thumb and forefinger guide the tool. These heavy cuts will stop an underpowered lathe. A 1/2 HP mini demands the shavings be in the 3/8 inch range.

DVR - I'm impressed with it's power and stability for roughing bowls. I've done several demos on DVRs including rough turning a couple of 14-15 inch bowls with some bark on. No complaints on the power. I don't care for the DVR in general. For me, I prefer the controls, tool rests, bed, and tailstock a 16" jet over those on the DVR. The Jet would vibrate more and I would have to turn a bit slower than I would on the DVR.

Al

 

[Dale Miner]

An ac induction motor windings have very little resistance. When the line voltage is applied, without the armature spinning, the current through the windings is very high. But, when the armature is spinning at a speed that is synchrounous (or nearly so) the armature spinning in the magnetic field of the windings, generates a voltage in the windings in opposition to the line voltage. This generated voltage is called Counter Electro Motive Force (CEMF). The CEMF is usually within a few volts of the line voltage, and the current through the windings is reduced to what would occur without the rotor spinning if only a volt or two was applied. An example, a 10 HP 3 phase 220 Volt motor draws about 30 amps at full load (1780 rpm), about 120 amps with a locked rotor, and about 2 amps when running unloaded (1795 rpm). The cooling fan on the motor contributes to the two amps.

When a load is applied to the motor, and the armature slows, the rotor cuts fewer lines of magnetic force, the CEMF is reduced, and the current through the windings increases as a result. The drop in speed to cause the increase in current needs to be very slight, typically only one or two percent drop in speed will cause the current to go from an unloaded value to a full load value. This happens automatically without any sensors. The motor does not (can not)produce more power than needed at any time. If the motor was producing more power than needed, then the speed would run away until the motor self destructed (running away can happen to series wound DC motors, but they are a different animal).

I've no knowledge of how the DVR motor works, but from reading the info on the links, it sounds similar to a stepper motor with computer control and monitoring. Quite a different system than an induciton motor.

 

[Bill Boehme]

Em, Bill. I suggest you don't understand the difference between a conventional motor and a DVR motor

Em, N7BSN, I am thoroughly familiar with variable reluctance and just about any other type of motor that exists. However, it looks like you missed my point that all motors deliver only the amount of horsepower needed to maintain constant speed -- within the performance capability of the motor -- it is not something unique to VR motors. The "bull" part had to do with their implied message that their VR motor was unique in that respect. Perhaps you misread what I wrote and erroneously assumed that I meant that their VR motor didn't do what they claimed.

To Robo: I believe that there are a number of other lathes besides Robust that use controllers with sensorless vector feedback for speed regulation. Brent advertizes it as vector control and I gently corrected him about that since true vector control requires the use of a velocity or position feedback device -- most typically an incremental position optical encoder. With true vector control there is no slip under changing load and speed regulation is typically within 0.1 Hz. However, I am impressed with the smoothness of the Toshiba "Tosvert" line of controllers. Even at the minimum speed of about 38 RPM, speed regulation is quite good.

About sensorless vector: Sensorless vector attempts to indirectly measure motor speed by sensing current. Motor current determines torque output which equals load torque plus torque losses in the motor and drive train. Given the control frequency, and applied voltage which limits available horsepower (the voltage has to be reduced at lower speeds to prevent magnetically saturating the iron), an intelligent estimation of motor speed is computed. The biggest problem with the whole scheme is getting a good measurement of motor current. The current measurement is always very noisy especially with pulse-width modulation to synthesize the applied AC voltage. The Tosvert line of controllers does some clever shaping of the applied PWM voltage that greatly reduces the noise level.