[How do I?] Need Help With Lathe Speed!

[blaser.306]

I have a king 10x22 lathe ( same set up ) as a Grizzly G0602 min speed now is 150 rpm, I am trying to determine what kind of pulley sizes I need to reduce to 50-60 rpm for reaming work . I saw the on line calculators and must be doing something wrong as I am getting wild variances in required diameters. Thanks in advance if anyone can point me in the correct direction.

 

[rgray]

60 rpm is 2.5 times slower. If you shot for 2 x slower that would mean doubling the size of your large pully. That gives 75 rpm.
reducing the size of the small pully would help to not need such a large pully but the smaller the pully the less grip to drive the belt.
Maybe a cone pully in the middle like a drill press wit htwo belts to get the reduction with out running a great big pully.

 

[Terrywerm]

I am assuming that your lathe does not have a back gear?? Most lathes with a back gear can get down into that 50 or 60 RPM range. If it does not have back gear then you have two options: Fiddle with pulley sizes as Russ mentioned, but you will probably have to add a jack shaft somewhere in the power train. Another option (but more expensive) would be to switch your machine over to a 3 phase motor and a VFD.

 

[Baithog]

Terry - there is no back gear, nor is there a reverse tumbler.

Blaser - There have been a number of articles on converting the 602 to either a treadmill or 3 phase motor to get variable speed, including a lower speed like you want. A forum member has done a mod that will do speed reduction with pulleys, without hacking up the lathe and still letting you access the normal pulley set up. The thread is at http://www.hobby-machinist.com/threads/grizzly-g0602-belt-drive-speed-reducer.36419/#post-373240

 

[John Hasler]

I have a king 10x22 lathe ( same set up ) as a Grizzly G0602 min speed now is 150 rpm, I am trying to determine what kind of pulley sizes I need to reduce to 50-60 rpm for reaming work . I saw the on line calculators and must be doing something wrong as I am getting wild variances in required diameters. Thanks in advance if anyone can point me in the correct direction.

To calculate speed reduction you need pitch diameter, not pulley diameter. Also, standard A belts are inefficient on small pulleys (2'' or smaller). Cogged (not toothed) belts are better. Consider a 3/8" belt if it can handle the power.

A bit about pirch diameter: http://ww2.gates.com/IF/facts/documents/Gf000209.pdf

 

[Terrywerm]

Terry - there is no back gear, nor is there a reverse tumbler.

Blaser - There have been a number of articles on converting the 602 to either a treadmill or 3 phase motor to get variable speed, including a lower speed like you want. A forum member has done a mod that will do speed reduction with pulleys, without hacking up the lathe and still letting you access the normal pulley set up. The thread is at http://www.hobby-machinist.com/threads/grizzly-g0602-belt-drive-speed-reducer.36419/#post-373240

BINGO!!! I knew that I had seen such a project somewhere, but could not remember when or where or for what lathe. To me that mod would handle the task at reasonable cost and would be an excellent solution.

 

[blaser.306]

That is just the info I needed! Now to start amassing parts and squirrel away some time. The mods shown will get me to a "safe" speed for chamber reaming. Thanks for all the replies.