If you were to build up to 24" bowl lathe

[Bart Leetch]

With belt drive only what speeds with a five step pulley system would you choose to build into the system?

[robo hippy]

Knowing what I know now, after 8 years on a PM3520A and 2 years on a Robust American Beauty, I would not make it without a 3 phase motor, and probably one in the 5 hp range. For large turnings, especially if they are unbalanced, you really NEED variable speed. It is that much better. I would want speeds from minimum 10 rpm for sanding up to 2000 or more for bowls.

robo hippy

[Dave Moore]

I don't understand why, if I were building up from scratch, I would want to restrict my options with a five (or whatever) step speed range.
That said, a speed range that does not give speeds quite high enough is a smaller problem than a range that does not go low enough, most especially for large work.
I would absolutely not want to be trapped into not being able to slow my speeds down enough for large work, and with a five speed range this might mean that I would suffer a lack of speed capacity at the upper range.
I routinely trim the high spots off large unbalanced work at slow speeds, maybe 100-200 rpm, and then gradually increase the speed as the work will tolerate it.
I'm with Robo, VS really is that much better.

If you're working with parts you already have on hand, and money is too tight for a variable speed setup, then I would go with clustering the speeds toward the low end rather than high. I could live with a top speed of 1000 rpm if I had to, or even less in a pinch, but I could not live without the flexibility at the low end. Not on a 24 inch lathe that I would want to use at full capacity that's for sure.
I would then save my pennies and upgrade to EVS as soon as possible.

[Bill Boehme]

Hooo boy, Bart, you are about to embark on an exciting adventure. If I could have my druthers, I would like to have a minimum speed of about 240 RPM and a maximum speed of about 1800 RPM. However, you will soon find out that there are so many deign constraints that once you look at the practical mechanical configuration, there is really not much leeway in what you are able to choose.

The first thing that I will recommend is that you get ahold of some engineering design manuals for belts and pulleys. Many of the manufacturers such as Gates Rubber Company have them available online in PDF format. Sometimes they are a part of their product manuals. Don't worry, the engineering stuff is not too difficult -- it mostly consists of a lot of tables and graphs along with a few simple equations and design guidelines. This will be invaluable information.

Here are a few examples of some design limitations and other considerations:

• All of the various types of belts have operating restrictions such as maximum linear feet per second velocity, minimum wrap radius as a function of velocity, maximum distance between sheaves, and minimum contact wrap angle to prevent slipping.
• Pulleys also have design limitations such as maximum rim speed to maintain a safe angular momentum. For the very expensive machined cast iron multi-V sheaves, this limitation is typically 6,000 feet per minute, if memory serves me right. Without actually doing the math, I think that keeps you below about eight inches diameter. Machined aluminum sheaves might allow a slightly greater rim speed, but they are harder to find and more expensive. As you can probably already see, my desired minimum spindle speed of 240 RPM is not achievable because of belt and pulley operating limitations. The flimsy cast aluminum pulleys that you see in hardware stores are not suitable for this type of project.
• Good pulleys are not cheap. They run at very high speed and so they must be perfectly balanced or else your machine will vibrate all to heck. Generally these pulleys are two piece affairs which have a tapered hole into which a hub is inserted to fit the arbor on which the pulley is mounted.
• Everything becomes a juggling act -- you pick a belt length and then size the pulleys for the minimum speed -- next you try to come up with pulley sizes for the other speeds that will work with that belt length -- next you change the belt length and start over, etc. This sounds like an exaggeration, but it really isn't. In addition, you have some practical limitations on how the motor is mounted and how much throw to allow for locking it down. Ideally, it would always lock down at the same position for each speed, but it won't quite work out that way. And remember that you can't have the belt too long or else the wrap angle will be too large.

I found that the best solution for me was to use an Excel spreadsheet and then create graphs to help me design the drive system. Having a CAD program is also invaluable.

This may be a case where you are better off with an electronic variable frequency drive because the cost of the mechanical components such as pulleys and hubs can get out of hand rather quickly unless you are able to machine them yourself (such as what Brent English does). I am sure that he probably looked at the cost of buying machined pulleys and hubs from some company like Gates and quickly decided that it was too expensive. Something else to consider is that having five cast iron pulleys is not possible on most motor shafts -- first there is not enough room and even if there was, the moment of inertia of the iron pulleys may be excessive. So far, I have not located a good source of machined aluminum pulleys.

Your project certainly is feasible and I would say to go for it, but I just wanted to let you know that it is a bit more than picking your five favorite speeds. That is fine for a starting point, but once you get into it, there will necessarily be some design trade-offs.

[Joe Greiner]

+1 for spreadsheet and CAD. I went on a similar adventure several years ago, to add more speeds to my 1929 Delta, armed only with Machinery's Handbook treatment of V-belt drives. Power transmission suffers with too-small belt contact on the smaller pulley, e.g. ~70% correction for 90 degrees. You can add an outside idler pulley to correct that, but it increases the flex in the belt and shortens its life; also need to ensure that the belt doesn't contact itself on the inside. I avoided the problem with better geometry

Most motor shafts are too short to mount a four or five step pulley, maybe two steps at best. In the original configuration, the motor slides axially to mate with the step pulley on the lathe. I added a jackshaft (aka countershaft) to increase the number of combinations. I folded the drive train, so that the motor was fixed, and the jackshaft was movable in two directions. You'll need enough adjustment to accommodate belt stretch over time.

In the event, I got a good deal on a lathe with Reeves drive, and the old Delta is in storage. And that lathe probably isn't my last one (with EVS), if I live long enough. In fact, I got a clone of the Reeves with an even better deal.

Designing and building your own lathe can be fun in itself. BTW, Bill's "belt too long" vs "wrap angle too large" doesn't conjure a good mental image for me. I think the worst thing about having a belt too long might be the belt whipping about at high speed.

FWIW, you can make odd-sized step pulleys in wood, but it might not be worth the effort; even Nawm and Roy would probably pass on that one.

[Bill Boehme]

I think that the main problem occurs when a large wrap angle like 180° is when combined with a very long belt. The belt is coming out of a wedge and then whips back to set up a flutter. A short belt is not nearly as likely to set up any kind of flutter. I really like the J-section belts. Their efficiency usually runs around 95 - 98% and they are quiet.

I had also considered an outside idler, but kept running into the possibility of the belt contacting itself and I also found out that there is a limit on the amount of reverse flex that should be applied to a belt. Use of outside idlers can also lower the efficiency a bit. I finally discarded the whole idler idea and decided to go with the motor on a hinged mount and using a jackscrew to adjust the belt tension.

[Dave Ogren]

You are getting all of the great and accurate comments.
Why not copy a VB 36 ???
The VB has a 3 step pulley system and variable speed, This could be inproved on also such as their lowest speed is 50 RPM. I would try to get it down to about 10 RPM for sanding.
The thin timing belts appear to be able to go down to a smaller radius. I have not checked it out but that is what it appears because of the thickness of the belts.
Good Luck, I am waiting for the project to start. Please keep us informed.
By the way I have seen a lot of home built lathes for sale in the last 2 years, some of them seem to be very well built and also have surprisingly low asking prices. Or buy an old Vega and retrofit the variable speed controls.

Dave

[Bart Leetch]

I would go with a VFD If I knew which control to put with which 2 hp motor. Preferably it would come pre-wired as I’m afraid I would fowl it up. Maybe it could even go on my current Delta lathe which has step pulley’s starting at 750 RPM & topping out plenty high enough. Obviously I am trying to keep cost down by using my current lathe. This enables me to later build a bigger lathe similar to a Vega & swap the VFD/motor system over to it at a later time.

Right now I just can justify buying a lathe & don't have the time or room to build one. But trying to ruff bowls at 750 RPM is not making me happy at all.

Ignorance was bliss back in the day both Dad & I turned on a Craftsman tube style way lathe using a 1/2 hp washing machine motor & stepped pulleys. Granted we used kiln dried material for the most part. Dad & I were talking about it this morning & when I explained a little about green wood & natural edge turnings & hollow turnings & that you never know what is in a piece of wood & it could explode are any number of things go wrong spinning it at such a high speed he understood what I was saying.

[Bill Boehme]

Originally Posted by Bart Leetch

Dad & I were talking about it this morning & when I explained a little about green wood & natural edge turnings & hollow turnings & that you never know what is in a piece of wood & it could explode are any number of things go wrong spinning it at such a high speed he understood what I was saying.

Always keep your ear tuned to the sound of the wood. If it starts to make a different sound, it is time to stop. It usually means that a crack has developed somewhere. One of our club members showed a good example of this at our last meeting where most of what he was turning flew off the lathe.

With a bit more experience, you can "read" a piece of wood fairly well and discard obvious bad pieces, but even those that appear to be good can have hidden faults. This applies equally to green and dry wood.

[Bart Leetch]

Originally Posted by Bill Boehme

Always keep your ear tuned to the sound of the wood. If it starts to make a different sound, it is time to stop. It usually means that a crack has developed somewhere. One of our club members showed a good example of this at our last meeting where most of what he was turning flew off the lathe.

With a bit more experience, you can "read" a piece of wood fairly well and discard obvious bad pieces, but even those that appear to be good can have hidden faults. This applies equally to green and dry wood.

Good advice. Do you have any recommendations for a VFD & 2 hp motor
that will work together & where to purchase them?