Motor for a Shop-Built Lathe

      Pros discuss torque, RPMs, cooling, and other technical issues for the motor of a custom-designed lathe. May 27, 2006

Question
I am in the process of designing a ww lathe for my furniture business. Hope to use a 3hp, 3 phase motor, 1800 rpm with a VFD, input power is 220V AC single phase. It will be a direct drive lathe similar to the old Hall and Brown lathes of the 20's (see OWWM website). Will it have sufficient torque at low rpm to turn a 15" diameter top, without a pulley system? I know it has plenty of torque as speed increases. I plan on overspeeding the motor for high speeds. I believe it will need 83Hz for 2500 rpm, which is okay. My second question is: how can I mount a Oneway chuck directly onto a 1 1/8" motor shaft with 1/4" keyway?

Forum Responses
(Solid Wood Machining Forum)
From contributor H:
I believe that the old Brown & Hall lathes and Olivers (I had one) were driven by DC motors. His allowed variable speed with no loss of torque at low speed. Variable speed with AC is possible, but maintaining torque? And for mounting the face plate/chuck. My old Oliver's shaft was threaded. Both inboard and out board sides. Talk to a machine shop.



From contributor L:
There are a variety of VFDs out there and some of them are designed for torque at low RPMs. You just have to buy what you are looking for. A 3 phase motor has more torque than a single phase motor to start with. How slow do you plan on turning the lathe?


From contributor R:
Based on my VFD experience, I think you should have a step pulley to insure torque at the lower speeds. There's a few companies that are making lathes, so look at what they did and call them up and ask technical questions about the specs. You don't need to reinvent the lathe, just copy what's already been done. Oneway lathes have 2 pulleys. You can read the manual online.


From contributor J:
I recently built my own lathe and used a 1" diameter shaft with a 1/4" keyway for the drive. Oneway chucks are held in place by a taper lock - they are sold in several standard sizes and can be custom machined by Oneway to meet your specific needs. I had a local machinist mill and broach mine, and it works very well. And without getting off on too much of a sales tangent, I do like Oneway products - I occasionally use a friend's 2436 and that is a great lathe.


From contributor E:
The inverter should have enough torque at the lower speeds. One problem with slowing an ac motor down is the fan mounted on the motor will not move enough air to keep it cool and it may overheat. This can be addressed by mounting a small round fan on the end of the motor. McMaster Carr has them for about $60.


From Dave Rankin, forum technical advisor:
One question: Are you using an inverter duty rated motor? If so, they are normally set up to run well at low RPM without overheating and burning up the windings.


From contributor T:
As Dave said, an inverter duty or at least a continuous duty motor would be a good idea. I like your idea of using an 1800 rpm motor if you can overspeed it, safely, to 2500 rpm for spindles. I like turning small spindles like 1 1/4" balusters at my lathe's top speed of 2800 rpm. I don't feel the desire to spin them any faster.

At lower rpm's, if you're profiling edges of a 15" table top, you are not removing a lot of wood for extended periods. The amount of time you are putting a heavy load on the motor is relatively short compared to the time the motor has to cool when it is stopped or under no load. For spindles and small tops, I think you're on the right track. You should be very concerned, however, about low speed torque and overheating the motor if you want to start making huge piles of shavings hollowing out large vessels and bowls.



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