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Tool Post Grinder Design Questions

xplodee

Hot Rolled
Joined
Oct 14, 2013
Location
Allentown, PA
Hi All-

As a fun project I'd like to design a tool post grinder while making my own spindle for it and supplying my own motor. At work we design and manufacture brushless DC pumps so I have plenty of access to BLDC motors and some really advanced motor drivers.

  1. What is the average power of a tool post grinder motor for use on a south bend lathe? 50w? 200w?
  2. Also, what speed do these typically run at?
  3. If you could have a speed range, what would the minimum and maximum speed desirable be?


Thank you all!
 
All depends on the intended application and the maximum size wheel. I have a Dumore tool post grinder. It has a 3/4 HP AC motor (that will be some 600W) and speeds 3,000-45,000 using wheels up to 6". For internal grinding with very small wheels I am sometimes using an air turbine. It can reach 100,000 rpm and probably develops 200W or more.
So as for speed - it is the rated speed of the wheel and I see no advantage running lower speeds. Power...not less than 200W even for a small device.
 
Also, what speed do these typically run at?

A good grinding wheel speed used to be stated to be a "mile and minute" - or 5280 feet per minute at the surface of the wheel's OD

Naturally this requires a rotational speed based on wheel diameter.

If your proposed grinder has a 3" wheel, it would need to turn about 6700 RPM.

Since such wheels are often belt driven, this is not necessarily the motor speed
 
Thanks guys, this is ideal.

So I guess the proper question then is not speed and power, but wheel size. What sizes of wheels do you typically use on a TPG? From that and the surface speed quoted above, I can then determine what kind of motor and pulley setup I might need.

Thank you!
 
Probably smaller than swing. My #4 B&S Universal is a "real" grinder, but lighter duty than a plain cylindrical grinder. Its 14" swing uses a 14" wheel. A plain this size could easily use a 24 or 30" wheel.

I imagine a TPG would trend the other way - some fraction of the swing diameter.

I would guess a TPG for a 9" lathe would max out at about a 4 1/2" wheel. You have to think about the room available and cross slide travel involved, and naturally size or diameter of part to be ground.


Thanks guys, this is ideal.

So I guess the proper question then is not speed and power, but wheel size. What sizes of wheels do you typically use on a TPG?

Thank you!
 
Get yourself a Dumore TPG catalog and study. They've been doing it pretty well for a long time. No doubt, your will be better.
 
There's also practical limits to the utility of TPG's, especially if you're talking about putting them on older lathes. To me, an ideal grinder starts with rigidity, and if you've got a SBL then presumably the compound, cross slide, and Z ways will all have some level of wear and looseness. If you're starting from scratch, think about how you can minimize the problems that come from this (chatter/wheel bouncing, inaccuracy, etc.) by at least bypassing the compound - mount directly to the cross slide if you can.

If I were doing this, and was feeling nuts, I'd mount a new cross slide to one of the saddle wings, with a servo control on the slide drive that was coupled to a linear readout output for Z. There would be only one "old" axis to worry about (the most stable and rigid), and you could make any taper you wanted by driving the servo to slave to changes in Z.

Tell us more about your motor drives and such - can we buy parts from you? ;)
 








 
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