Questions About My New/old Lathe.

If I don't quickly replace the two parts I referred to earlier then I lose the 55 rpm to 463 rpm range provided by back gear drive but I still have the 380 rpm to 3050 rpm range provided by direct drive. Smaller lathes work on small diameter stock and need higher speeds. How badly will I miss the back gear rpm range?

For the ~$450 could I switch the lathe over to a DC motor and controller? I assume if I did I could leave out the countershaft assembly. Any examples of this type of conversion that you guys have done?
 
you know, I bet you could fix that back gear - a 2-56 tap, some 2-56 set screws and a dremel with a cut off disk would work. drill and tap a couple of holes per tooth that needs fixing, loctite in set screws, grind with dremel to mesh with bull gear. It won't be super pretty, but I've seen it on other machines and it works fine. You're still welcome to my spare bull gear, which is in decent enough shape - hard to tell though if you don't post up pics.

I've added a treadmill DC motor to my 618 for little money and you'd still want the back gears. The back gears don't just slow the spindle down, they allow you to run the motor at a speed where it makes power and torque (i've heard that back gears "amplify" torque, but I'm not sure if that's correct). So while you may be able to run a DC down to 100rpm or so direct drive, using the countershaft, you won't be able to turn large or hard objects as the motor will stall or the belt will slip.
 
Your back gears are history. Your best bet is to pick up a used set off eBay.

If you never need to thread anything, you can probably live without the slow speeds. If you do, you can't. Except for very fine pitch threads, you will want to set the spindle RPM based more on your reaction time than much else. Especially with relatively coarse pitches. You don't want the carriage moving very fast, or you will run the cutter into something.

I'm not a fan of variable speed DC motors on lathes. People always assume that because they can slow them down to a crawl, they will work fine at a crawl. But they don't. Available torque is lower, and they will overheat. If you really want to go variable speed, use a 3-phase motor and a VFD. Don't run the motor faster than about 120% or slower than about 40% of it's nominal rated speed. And it will neither explode nor overheat. If you still have the back gears, you might be able to get away with a single step motor pulley and large countershaft pulley. Although I haven't run the numbers to confirm that.
 
wa5cab said:
I'm not a fan of variable speed DC motors on lathes. People always assume that because they can slow them down to a crawl, they will work fine at a crawl. But they don't. Available torque is lower, and they will overheat.
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that's why you keep the countershaft and the back gears :)
 
The part should be here Saturday. Now I'll look for the bull gear. If you happen to see a good one around please let me know.

This forum (you guys) is (are) great. Thanks guys!
 
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