Woodturning Class and Speed

[Ed Brekke]

I had the great pleasure last week to take a one week class in woodturning at the JC Campbell Folk School in Brasstown, North Carolina. First of all what a great place. There are dedicated studios for every craft. Maximum class sizes are 10. The Woodturning studio has 11 Powermatics with each station set up with a work bench and tool rack with all the tools and chucks you may need. (You can bring your own tools if you prefer.) A lot of emphasis was given to tool sharpening, tool selection and specifically how to ride the bevel and use the bevel to achieve a surface without tear out.
We also spent time discussing turning speed. A subject on which there are so many different opinions. Basically our instructor summarized it this way: low speed for sanding higher speeds for turning. And by higher speeds he defined it as turning at a speed you are comfortable with. He did the majority of his turning at speeds between 1200 and 1700 rpm’s. His work was beautiful! As someone who typically turned between 800 - 1000 rpm this was a revelation to me. A second key learning was his preference for mortises over tenons. And his mortises varied from 3/16 - 5/16 max. This made finishing a bowl with a completed bottom so easy. I had always been digging out mortises as deep as the jaws would go. And I used tenons much more frequently than mortises because they seemed easier to me. Here are some photos of work I completed in the class.

 

[Kevin Jenness]

Sounds like a great class.

On the subject of speed, rpms have to be considered relative to diameter. There is a rule of thumb stating that rpms x diameter in inches should be 6000-9000. It's not written in stone, but it's a useful reference. At the upper end (rpms x D = 9000) the rim speed is about 27 miles per hour. The more mass and the higher the rim speed, the more energy is embodied in the spinning wood and the more damage it can do if something breaks loose.

You probably know all this, and everyone can make their own judgments about shop safety. My tolerance for getting hit by speeding objects is pretty low. I tend to regulate the speed by perceptible vibration and adjust my tool feed rate to match.

I was showing my friend how to use his McNaughton coring system on a 8.5" walnut bowl blank last Monday. It looked quite sound to me. He called me later that day to say he had blown the piece up at 1700 rpm, about 2/3 faster than I would have spun it. He's getting to be a good turner, but he's only been doing it for a year, usually wears only safety glasses, and had never heard of my rule of thumb. I worry that he is going to get beaned one day.

 

[Lennart Delin]

I usually go as fast as seems comfortable to me. If I get vibrations, giving undulating surface I reduce a little. I like small feet, so mostly a tenon, but on large bowls, say 30 cm and above, I often use mortice. I always finish the outside completely, including sanding, before turning the inside. I never go back to return the foot. These are typical tenons and mortice I use for turning the inside. I also strive for a uniform wall thickness and bottom thickness.

 

[robo hippy]

I don't think I have ever used a tenon on a bowl. Not positive though. I do use a NRS for the inside of the recess, and it gives a nice protected place for my signature. Mine are at most maybe 1/8 inch. The trick is to make sure you have enough shoulder on the recess to support the turning loads. I think Mike Mahoney on his platters, generally turned from dry or drier wood, goes 1/16 inch deep on his. When our club first formed, there was a discussion about which to use for bowls. I was pretty new at turning back then, and every problem the others mentioned with their recesses, I had solved, so I didn't have those problems.

robo hippy

 

[Alan Weinberg]

after a couple classes with Jimmy Clewes, who was constantly saying, “faster, faster, faster.” I have turned up the rpm a bit. I’ve alternated between tenon and recess, depends on the wood. That adequate shoulder on a recess is definitely needed.

 

[Ed Brekke]

Sounds like a great class.

On the subject of speed, rpms have to be considered relative to diameter. There is a rule of thumb stating that rpms x diameter in inches should be 6000-9000. It's not written in stone, but it's a useful reference. At the upper end (rpms x D = 9000) the rim speed is about 27 miles per hour. The more mass and the higher the rim speed, the more energy is embodied in the spinning wood and the more damage it can do if something breaks loose.

You probably know all this, and everyone can make their own judgments about shop safety. My tolerance for getting hit by speeding objects is pretty low. I tend to regulate the speed by perceptible vibration and adjust my tool feed rate to match.

I was showing my friend how to use his McNaughton coring system on a 8.5" walnut bowl blank last Monday. It looked quite sound to me. He called me later that day to say he had blown the piece up at 1700 rpm, about 2/3 faster than I would have spun it. He's getting to be a good turner, but he's only been doing it for a year, usually wears only safety glasses, and had never heard of my rule of thumb. I worry that he is going to get beaned one day.

I have read about that rule of thumb in the past but having struggled with 9th an 10th grade algebra, it does not make sense to me. Basically, the formula goes: RPM X Diameter = Speed But the "speed" on my lathe is a measure of RPM's. So the rule of thumb equation would look like this: RPM X Diameter = RPM which is an unsolvable equation. Unless, of course, the RPM's on my machine is a measure of the motor RPM, not the spindle speed.

Like most of you have said: It depends. Are you turning a bowl or a spindle? What type of wood are you turning? I think the "formula" I like best is: "The proper speed is a balance between safety and turning quality" and what you are comfortable with.

 

[Ed Brekke]

I usually go as fast as seems comfortable to me. If I get vibrations, giving undulating surface I reduce a little. I like small feet, so mostly a tenon, but on large bowls, say 30 cm and above, I often use mortice. I always finish the outside completely, including sanding, before turning the inside. I never go back to return the foot. These are typical tenons and mortice I use for turning the inside. I also strive for a uniform wall thickness and bottom thickness.
View attachment 75183

I am feeling very comfortable now that I have started using the mortise like in your live edge piece. By the way, I take note that your diagram is in Swedish. Personally, I prefer Utvendig grip.

 

[Ed Brekke]

I don't think I have ever used a tenon on a bowl. Not positive though. I do use a NRS for the inside of the recess, and it gives a nice protected place for my signature. Mine are at most maybe 1/8 inch. The trick is to make sure you have enough shoulder on the recess to support the turning loads. I think Mike Mahoney on his platters, generally turned from dry or drier wood, goes 1/16 inch deep on his. When our club first formed, there was a discussion about which to use for bowls. I was pretty new at turning back then, and every problem the others mentioned with their recesses, I had solved, so I didn't have those problems.

robo hippy

Mike Mahoney is a legend here in San Diego. I missed him last time he visited our local association here but his videos are awesome.

 

[Brian Gustin]

I have read about that rule of thumb in the past but having struggled with 9th an 10th grade algebra, it does not make sense to me. Basically, the formula goes: RPM X Diameter = Speed But the "speed" on my lathe is a measure of RPM's. So the rule of thumb equation would look like this: RPM X Diameter = RPM which is an unsolvable equation. Unless, of course, the RPM's on my machine is a measure of the motor RPM, not the spindle speed.

If you really wanted, it is as simple as March 14th (Pi Day) Circumference = Pi times radius squared (I.E. Diameter) so a 10 inch bowl at the rim, using Pi you have 31.4 inches, multiply that by RPM , say 1200 RPM's and you can figure your bowl at the rim is travelling at 37,680 inches per minute, or 3,140 feet per minute (Which obviously is why you can figure sharp edges and burrs can dull relatively quickly, no?)

 

[John K Jordan]

I had the great pleasure last week to take a one week class in woodturning at the JC Campbell Folk School in Brasstown, North Carolina. First of all what a great place. There are dedicated studios for every craft…. A second key learning was his preference for mortises over tenons.

Hey Ed! You sure had a productive week!

Isn’t JCC a great place. When I go I wander around and visit the metalworking, carving, fabric, paper craft, and other crafts. You meet the most wonderful people! And it’s an easy drive from where we live. (I’ve never taught there but assisted with a Mike Stafford box class.)

I didn’t see if you mentioned - who was the instructor? One of the pieces (the square plate with glued up strips) looks like one of Frank Pentas designs - maybe the instructor was one of the many teachers that Frank trained and mentored.

I almost always use a recess/mortice rather than a tenon. It’s surprising to some how shallow the recess can be. The one on this platter (I made in one of Frank’s platter classes) is only about 1/8” deep, and with the way I executed the off-axis base (all cuts on a single plane) the only thing for the chuck to expand into was inside the three small triangular pieces - doesn’t take much! (no catches allowed, of course) The piece held well with no problems. Properly sizing and shaping the recess is important!

(Sorry, I’ve posted these at least once before in other threads)

Sapele.



For me, the big advantage of not using a recess/mortice is the simplicity: mount by the top, turn/smooth/finish the bottom, reverse and in the recess and turn the top - done. No second reverse or sometimes tricky holding to turn away the tenon.

I’ve done many pieces like this, bowls and platters, some with quite shallow recess, and not once has one come off the lathe. (another factor to consider fir recess depth is the strength and quality of the wood.)

JKJ

 

[Holmes Anderson]

I find an out-of-round long tenon much easier to use than an out-of-round shallow mortise for remounting rough turned bowls.

 

[Kevin Jenness]

I have read about that rule of thumb in the past but having struggled with 9th an 10th grade algebra, it does not make sense to me. Basically, the formula goes: RPM X Diameter = Speed But the "speed" on my lathe is a measure of RPM's. So the rule of thumb equation would look like this: RPM X Diameter = RPM which is an unsolvable equation. Unless, of course, the RPM's on my machine is a measure of the motor RPM, not the spindle speed.

Like most of you have said: It depends. Are you turning a bowl or a spindle? What type of wood are you turning? I think the "formula" I like best is: "The proper speed is a balance between safety and turning quality" and what you are comfortable with.

The product of D x rpm is just an easily calculated number, not denominated in units, that gives an idea of the rim speed of the turning. The rule suggests that a 10" bowl should be turned at 600-900 rpm. 900 x 31.4" = 28,260 inches/minute. 28,260/12=2355 feet/minute. 2,355/5,280 = .446 miles/minute. .446 x 60 =26.76 miles/hour.

As an analogy, let's say the 9000 number represents a highway speed of 65 mph. A lot of people, including me, go faster than that, but there's no getting around the fact that hitting an abutment at 80 will cause more damage than at 65.

 

[Tom McDonnell]

I've seen a more detailed chart with weight of object vs rpms but, can't find it now. Anyway I always have this in the back of my mind when turning.

 

[R Henrickson]

I've seen a more detailed chart with weight of object vs rpms but, can't find it now. Anyway I always have this in the back of my mind when turning.

I think the important aspect of this is *weight* so it thus applies more to bowls and hollow forms. Spindle turning tends to be at higher rpms but with lesser diameters and weights. Spindles tend to drop toward the floor at rpm well over 1000.

 

[john lucas]

I'm a tenon guy. I don't likevtonbe limited in my final size by a presized mortiss. I work on the foot design when I first start the piece. I always reverse turn my bowls and I finish off the foot to the size and shape I want.
Platters are different. I do use mortiss fir them.
Speed. Whatever is comfortable. I don't believe speed gives a cleaner cut. A clean cut is all about using the tool correctly and not pushing the tool faster than the wood wants to be cut.

 

[John K Jordan]

I find an out-of-round long tenon much easier to use than an out-of-round shallow mortise for remounting rough turned bowls.

But don't you reshape a warped tenon or mortise before mounting for final turning? Making an oval tenon round is easy; I made a special tool to reshape a warped recess/mortise.

JKJ

 

[Lennart Delin]

For me, the big advantage of not using a recess/mortice is the simplicity: mount by the top, turn/smooth/finish the bottom, reverse and in the recess and turn the top - done. No second reverse or sometimes tricky holding to turn away the tenon.



JKJ

I never reverse to turn away the tenon. See my example

 

[Bill Alston]

I'm a tenon guy. I don't likevtonbe limited in my final size by a presized mortiss. I work on the foot design when I first start the piece. I always reverse turn my bowls and I finish off the foot to the size and shape I want.
Platters are different. I do use mortiss fir them.
Speed. Whatever is comfortable. I don't believe speed gives a cleaner cut. A clean cut is all about using the tool correctly and not pushing the tool faster than the wood wants to be cut.

I don’t turn many bowls but an experienced turner suggested to me that using a tenon gives you far more design possibilities.
I thoroughly agree about thinking about the foot design early on.

One other minor point. I’ve never seen a tenon fail. On the other hand I’ve seen a mortise fail due to either too much pressure being applied by the chuck Jaws, or the turner having a catch.

I did use a mortise a few times early in my turning but it’s not something I intend to do now unless there’s a very compelling reason to do so.
Perhaps turning a thin platter where there is not enough material to accommodate a tenon.

 

[Holmes Anderson]

But don't you reshape a warped tenon or mortise before mounting for final turning? Making an oval tenon round is easy; I made a special tool to reshape a warped recess/mortise.

JKJ

No, I remount the rough-out using the warped tenon, true the rim and cut a shallow mortise in the interior, reverse the bowl and mount using that mortise, and then true-up the tenon and finish turn the outside. Then I use the trued-up tenon to reverse mount and finish turn the inside. Then reverse again with a vac and finish the base. Finish turning without a tailstock or faceplate in the way and no speed limits of anything other than a solid chuck-to-mortise and chuck-to-tenon mount is a joy.

 

[David Wyke]

I turn a lot of bowls and have around 200 drying on the shelf and always use a tenon because it’s what I prefer. All my bowls are twice turned and I find it easier to true the tenon up and shape the foot when reversed. Mortise is fine but I prefer the tenon except for platters.
I turn at a speed that is comfortable for me, large bowls 12-18” are usually between 750 and 950 rpm’s. The gouge is sharp and moves at a slow advance when doing finished cuts. Smaller bowls are usually around 850 - 1200 rpm’s.
My rpm setting is determined by the wood and any vibration I feel. I slow the lathe speed down if I feel the slightest vibration since I find that to make a big difference in the quality of cut. I keep two bowl gouges razor sharp when turning and switch when I feel the slightest resistance to the cut and always have a fresh gouge for the last pass. I sharpen my gouge before it gets dull, do the same with my chainsaw.
I don’t push the gouge except when green turning and the not that much but green turning to me is fun time!

 

[robo hippy]

If I twice turned my bowls, I might switch to a tenon, mostly for convenience. I did find Tomislav's video about his twice turned bowls where he turns a recess on the inside of a dried rough out, then expands into that, and then trues up the tenon. That seems to make a lot of sense. If I was to do it that way, then I would be able to use a recess. I can get a good enough grip on my "ovaled" recesses to be able to sand them out, so that may mean that I could very gently turn an inside recess to expand into to be able to return my bottom recess.

robo hippy

 

[John K Jordan]

I can get a good enough grip on my "ovaled" recesses to be able to sand them out, so that may mean that I could very gently turn an inside recess to expand into to be able to return my bottom recess.

I designed and ground this tool. Mount the roughed bowl (or dry bowl/platter blank) between centers to suit, then use this to reach in front of the live center and clean up a warped recess or create one if needed. It can dovetail the recess if I want.

Easily shaped and sharpened on CBN wheels with square "corners" and grit on the flat side.
Made from an old scraper.




I don't usually use this to make recesses in dry bowl and platter blanks (with parallel top/bottom) but will work if needed.
I usually hold with a screw chuck in the top then turn the base, recess, bottom/outside, smooth and apply finish, then reverse to turn the top/inside.

JKJ

 

[Holmes Anderson]

If I twice turned my bowls, I might switch to a tenon, mostly for convenience. I did find Tomislav's video about his twice turned bowls where he turns a recess on the inside of a dried rough out, then expands into that, and then trues up the tenon. That seems to make a lot of sense. If I was to do it that way, then I would be able to use a recess. I can get a good enough grip on my "ovaled" recesses to be able to sand them out, so that may mean that I could very gently turn an inside recess to expand into to be able to return my bottom recess.

robo hippy

A mortise is definitely more efficient for once-turned bowls. The vac chuck doesn't like heavily warped bowls, so to remove a tenon you're left with some form of jamb operation or donut which takes too much time. Back to twice-turned, Tomasic and Raffen seem to favor footed bowls with perfect circle grip points (either mortise or tenon). That may be the most efficient way but it requires extensive sets of jaws and chucks. Cleaning up jaws marks from an otherwise finished foot with the bowl mounted by a vac chuck doesn't take much more time. I used mortises more often before I had the vac system. For turning bowls quickly with minimum tooling the mortise is the better option because reverse chucking is avoided entirely. Maybe that is what the OP was being taught.

 

[Jon Rista]

The only thing from the OP's instructor I disagree with, is mortises. I will use a mortise on platters, most of the time, as I generally then convert the mortise into a recessed foot for the piece. I will usually thin the recess out, though, so its not so deep. Depending on the design of the bowl, I may even create a soft transition from the inside edge of teh foot into the recess. or maybe even just produce a curved recess in the bottom. Basically, I use a mortise when I have the intent of having some kind of interesting foot on a bowl or platter, where the foot is part of the design.

This is mostly fine on platters, as their design tends to be different than bowls where the thickness of the walls of the bowl matter. With bowls, I pretty much always opt for a tenon. With a mortise, unless your intent is to turn the excess outside wood of the bowl away, you have this necessity of thickening the bottom of the bowl, to accommodate the mortise. If you finish the outside of your bowls before flipping, then removal of a mortise requires a lot of extra work, on top of the extra thickness of teh base. But, that thickness is inconsistent, and you have a thinner bottom in the middle of the mortise.... I've just never quite liked that. For most of my bowls, I generally prefer to have a fairly consistent thickness throughout the walls and the base. I will allow the base to be slightly thicker, usually, but not enough to accommodate a mortise...even a "shallow" one of say only 3/16". The thing about a shallow mortise, is you have to be even more concerned about expansive force from the chuck, ripping your bowl apart from the bottom. The thinner the mortise, the less force you can use, and I've had bowls with mortises pop off the lathe WAY more than bowls with tenons, where I can really crank the compressive force down.

Still, there are occasions, where I want a foot on my bowls as well. I can convert a tenon or a mortise to a foot, and unless the design really calls for a mortise, I'll still usually use a tenon. Someone mentioned that with a tenon, you often have to jamb chuck to turn the tenon off. Sometimes this is true. I picked up a longworth+doughnut chucking set, oh, I guess it was 2021. I like that for cleaning up the bottom of bowls. Most of them, I'll try to use the doughnut, as its much more secure, however its a bit more prone to damaging the finished bowl surfaces. The longworth works well when you don't need a ton of clamping force to hold the bowl or platter for bottom cleanup. Still, I don't often have to jamb chuck bowls/platters for bottom cleanup regardless...most of the time I doughnut them.

Finally, with a tenon...aside from the beautiful work of @John K Jordan in the platter he showed O) when using a mortise...you can "erase" a tenon entirely from existence really easily. You can then leave everyone else wondering: "How the heck did you make this beautiful thing?" There is no evidence left of how it was ever attached to a lathe, and it kind of seems a bit more magical when that mystery is left in tact.