How to align Tool Post Grinder?

Ralphxyz · Mar 21, 2018

The previous owner of my lathe somehow managed to mess up a jaw on the three jaw chuck.

I was thinking about building a tool post grinder when I found one at a tool swap.

So I ground the jaws with a internal 1" course grinding wheel and then a fine 3/8" internal wheel.

I "thought" the jaws looked really nice. I actually only ground down about .005" the hole was another 015".

And then I tested the grind.

The jaws are making contact only on the rear.

So how would I align the grinder?
I can see where just eyeballing it probable would work for external grinds but not for internal grinds.

I would like to be able to do straight and taper internal grinds but cannot see I would do this.

Well I suppose I could do progressive grinds on a test piece until I got it aligned and then do actual project.

I know some people really dislike the idea of using a tool post grinder in their shop but I have a good setup to control the mess for easy cleanup.

Thanks for the help.

Leg17 · Mar 21, 2018

Are the jaws clamped tight while grinding?

grafox · Mar 21, 2018

Go to www.youtube.com and enter "grinding chuck jaws" in the search box. You will find a wealth of information on how to do it. ATB Grafox

cyanidekid · Mar 21, 2018

there is a crapton of stuff on the web about regrinding chuck jaws, but based on what I see in the pic, you either didn't review what's out there, or..well I just don't know how the hell you did that, if the taper we see is from your regrind.

just a suggestion, toss that chuck in the scrap bin.

crazygoat · Mar 21, 2018

Pic #3 looks to be a whole lot more .015. You do know to have the chuck tightened up on an ring on 1 of the steps when you grind the i.d., don't you?

L Vanice · Mar 21, 2018

crazygoat said:
Pic #3 looks to be a whole lot more .015. You do know to have the chuck tightened up on an ring on 1 of the steps when you grind the i.d., don't you?

And it needs to be tightened in the proper direction for the part of the jaws you want to grind. In other words, do not expand the jaws outward against a ring to grind the inner gripping surface. There are good commercial jaw preloading devices available for two-piece jaws, usually used for boring soft top jaws. Preloading one-piece jaws so that the entire inner surface can be ground is more difficult. Here is a crude but effective device I made from four big flat washers to grind the one piece jaws of a 5 inch 3-jaw chuck. The small washers grip the tops of the jaws as the jaws are tightened, but leave the inner gripping surface exposed to the grinding wheel for the entire length of the jaws.

Getting back to the title question, I set the height of tool post grinders by getting the tailstock center into the center hole of the grinder spindle. Now, if I am using my engine lathe with the grinder on the compound slide on the carriage, I eyeball the grinder spindle parallel with the lathe bed. Then I true the wheel with a diamond clamped to a bar in the headstock. Dumore makes a clamp-on truing device that works nicely.

If you miss any of the above steps, you will get a mess.

Larry

Bill in PA · Mar 21, 2018

When I grind hard jaws, I remove them from the chuck, and grind them clamped in a precision vise on the surface grinder. The wheel is dressed to the correct radius. I grind the jaws with a bit of taper so the jaw contacts the work at the front edge first. The jaws in a worn chuck need more taper than those of a tight one.

When I am happy with how the jaws close, I then clamp a ground bar and indicate run out. The offending jaw(s) are ground to make the bar run true. .001" is easy to get and plenty good for a scroll chuck. I just did two 10" chucks last week.

A 3/8" wheel would be too small. I have found that the radius on the jaws is around the size of the through hole in the chuck. Some jaws may have a larger radius than that.

Bill

crazygoat · Mar 21, 2018

L Vanice said:
And it needs to be tightened in the proper direction for the part of the jaws you want to grind. In other words, do not expand the jaws outward against a ring to grind the inner gripping surface. There are good commercial jaw preloading devices available for two-piece jaws, usually used for boring soft top jaws. Preloading one-piece jaws so that the entire inner surface can be ground is more difficult. Here is a crude but effective device I made from four big flat washers to grind the one piece jaws of a 5 inch 3-jaw chuck. The small washers grip the tops of the jaws as the jaws are tightened, but leave the inner gripping surface exposed to the grinding wheel for the entire length of the jaws.

Getting back to the title question, I set the height of tool post grinders by getting the tailstock center into the center hole of the grinder spindle. Now, if I am using my engine lathe with the grinder on the compound slide on the carriage, I eyeball the grinder spindle parallel with the lathe bed. Then I true the wheel with a diamond clamped to a bar in the headstock. Dumore makes a clamp-on truing device that works nicely.

If you miss any of the above steps, you will get a mess.

Larry

View attachment 223832 View attachment 223833

Now that is genuis! I would have never dreamed that up. Very good idea.

art.h · Mar 21, 2018

Picture 2, is this the stock your using to verify the contact your jaws are ground true? Some of the turning galls might be getting in the way. That aside I always pre-ground the jaws to an equal dim using a mic. off the outside internal clamping faces. If you have access to a good wire EDM you can make a hold fixture like L Vance made out of flat stock--- or on a mill boring three clearance holes for the jaw holes in place and then the larger grind access hole.

Ralphxyz · Mar 21, 2018

No, I " thought of doing it statically with just the tool post grinder spinning and closing the jaws onto the wheel, is that what you mean by clamped tight while grinding?

I have seen other YouTubes and they all had the jaws open with both the spindle and the grinder spinning bringing the wheel into the jaws.
Which is what I did. It did a very nice job grinding but the jaws are not aligned.

Ralph

Ralphxyz · Mar 21, 2018

Thanks Grafox, I have looked at some grinding videos I will watch more.

Ralph

Ralphxyz · Mar 21, 2018

cyanidekid, that is a possibility but I am on a limited (SS) budget so I do not tend to throw away things.

Ralph

Ralphxyz · Mar 21, 2018

crazygoat, not sure exactly what you are saying.

Ralph

SilveradoHauler · Mar 21, 2018

Chances are with that much jaw damage the scroll is out to lunch also.

New chuck time. Sell something to fund the chuck purchase if necessary.

Ralphxyz · Mar 21, 2018

L Vanice, I had to read and reread your post and look at the pictures at least four times before I understood what you are saying.

Tightening the chuck out, with your device, would load the jaws so that they could not move away from the grinding wheel.

that is really cool but does not address the alignment problem if the grinder spindle is off by 2° the jaw will not be straight.

This makes sense, "set the height of tool post grinders by getting the tailstock center into the center hole of the grinder spindle"
I did not do this, in fact sometime during the operation I noticed that the tailstock was not aligned with the grinder spindle.

If I had a diamond dresser aligned with the ways I could true up the wheel, that is interesting.

Ralph

Ralphxyz · Mar 21, 2018

Bill, first I would need a surface grinder.
I like the idea of a taper to the front edge.

Interesting on the radius observation.

Ralph

Ralphxyz · Mar 21, 2018

Sorry the stock pictured is just some rough stock I threw in because it was at hand.

I have a ground test bar.

Now lets see first I needed a surface grinder now a EDM would be handy.

Thanks everyone for all of the help.

I "think" I can at least get it closer.
I am going to watch some more chuck jaw grinding videos.

Ralph

Mark Rand · Mar 21, 2018

If you pass the toolpost grider wheel all the way through the jaws with the carriage feed (chuck turning while doing the grinding), the alignment won't matter because you'll be cutting all of the jaws with the 'highest' part of the wheel. Larry's fixture is needed in order to take up any clearance and slack between the jaws and the scroll and between the jaws and their slots in the chuck. If you don't use something like that, you will never get a good result, even on an un-worn chuck.

JohnMartin · Mar 21, 2018

Ralph:

You simply closed the jaws on the grinding wheel.

As noted in the At**s group, you don't do that. The grinder has to move from side to side, using the carriage feed. The cross feed is used to increase the amount you remove. The chuck should be spinning slowly.

Ralphxyz · Mar 21, 2018

Thanks everyone, it is "sloooowly" sinking in.

I had moved the grinding wheel in and out but still managed to get the taper. I will try again.

Ralph

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