Toolpost Grinding

[Gray62Participant @gray62]

I am in the process of designing and building a toolpost grinder and was wondering what the opinion is on the direction of rotation of workpiece to grinding wheel.

Some documentation I have found shows it as below however, others state that the work should rotate in the opposite direction to that shown

[Gray62Participant @gray62]

[Billy MillsParticipant @billymills]

Perhaps a reversing switch might be handy!

 

Regards,

Alan.

[JDEngParticipant @jdeng]

There was some debate on this subject on this forum about two months or so ago. Opinion seemed to be divided.

 

When we were apprentices we were always told that the work and the wheel should rotate so that the point where the two met was going in opposite directions. IE. using the above diagram as a guide, for external grinding both should be going clockwise (or anti-clockwise); for internal grinding on the left hand edge of the job, the wheel should go clockwise and the job anti-clockwise.

 

I’ve never known exactly why but just accepted it however, after the previous debate, I’ve spoken to a one or two people who have done a lot of universal grinding. The consensus of opinion seemed to be that contra rotation prevents any potential backlash or slackness in drive belts or gears affecting the relative speeds which could mar the finish.

 

John.

 

 

 

[TerrydParticipant @terryd72465]

Hi Coalburner,

 

A long time ago, in a toolroom far,far away I was taught the above method. As stated the work should rotate slowly, but the grinder should rotate at a relatively high speed, say 10,000rpm for such a small wheel. The speed of the rotating work and grinder should be added or subtracted depending on the relative rotation. So if your workpiece is rotating at say 250 rpm the relative speeds of the two will be either 10,250 or 9,750 rpm, not a great deal of difference really. Of course if you rotate the work at 50 rpm there is essentially no difference.

 

I would agree with John’s last paragraph above, depending on the quality of your equipment.

 

By the way the instructions above are wrong I believe. For external work it shows the two shafts contra-rotating and claims that the speeds are thus added. It doesn’t take a great intellectual exercise to show that in fact the speeds are subtracted in this mode. Think of a workpiece of the same diameter as the grindstone and imagine that you could increase the lathe to the same speed as that grinder. The two surfaces would simply roll together with no relative movement between the surfaces, so no grinding action. The same holds for their internal grinding assuming that you are grinding at the rear of the workpiece so that you can see what’s happening.

 

Best regards

 

Terry

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

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