How to center a part on a circular magnetic chuck?

What's the right way to center parts on a circular magnetic chuck like this:



Only way I could find was to set up a dial indicator so it wobbled around zero, then use a plastic-faced hammer to tap the part to zero. Can't be good for the part or for the chuck to be sliding against each other while clamped, but I don't see any alternative.

Thats the3 way I saw it beeing done
They used a 0.002mm dial indicator
They used a piece of copper though

Peter

That is the common way most guys do it. You can make a centering gauge and pencil mark the part with using a Starrett center foot to set the part much closer at start.

tc grinder centering height gauge photo - Yahoo Image Search Results

starrett center square foot photo - Yahoo Image Search Results

of the ones i have used, they all had spigots.

However if you can alter the speed of the chuck to very slow, just leave the power off and use a roller bearing mounted on a stick that you force onto the part to push it around, ideally with some sort of screw adjustment bring it in till it bumps it then has a full contact all around and turn on the power to the chuck and remove bearing attachment.
Bring it up to speed and do whatever you have to do.
This is with the chuck laying flat, obviously it won't work with a horizontal chuck centreline.

This can be done to quickly get faces to run true in a conventional lathe you do it slow and leave the jaws with moderate pressure not too much, enough so you can move it, the bearing this time is mounted in the tool post and forced against the face with the cross slide not power force just wind it by hand.

then lock up the chuck tight.
For quick repeat jobs its ok, but you can always check it with a dial to see how close you actually are.

ballen,
I have a similar magnetic chuck on a cylindrical grinder, a bit smaller in diameter. Mine is a permanent magnet not an electro. By slowly engaging the magnet I am able to stop a little before half way and the part will stick to the face and can easily be indicated to run true. Then fully engage the magnet and check and adjust as needed. I also have a magnetic sine plate that works the same way.
spaeth

michiganbuck said:

That is the common way most guys do it.

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OK, makes me feel better to know that.

tc grinder centering height gauge photo - Yahoo Image Search Results

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That's a good idea. The next couple of yard sale squares are going to make one of these for my lathe and one for my circular grinder.

Just thinking out loud. I wonder if you could measure what your going to chuck up and then measure from center out 1/2 and use a Sharpie when it is turning and mark the mag chuck to get it close and then use the indicator and copper punch as Peter said. I've been looking on Vintage Machinery to see if there is some instruction manual, but can't find anything. Rich

Many of those chucks have shallow circular grooves in them to centre the workpiece rougly
You could do that on yours
If it can you can also use the centre from the tailstock

peter

you could install an collet holder or even a chuck in the tailstock.

dian said:

you could install an collet holder or even a chuck in the tailstock.

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The idea with a magnetic chuck is to dail in with a accuracy of ± 0.001mm
Not possible with a chuck and even with a collet it is whishfull thinking in most cases
Also with a magnetic chuck one can centre a feature that is excentric with the chucked feature
And bigger pieces too
Very usefull tool on a OD /ID grinder

Peter

I think Richard has the best plan. Fire up the mag work head and with your hand on a block of sorts hold a pencil to make lead pencil circles on the chuck, then eyeball the part to be near center. Might get 1/16 close that way. Soft tapping down way so gravity has the bearings tight at bottom, tapping in to needing tolerance...Mag not on full at the start so easy to move abouit.

I had a friend who did ID and OD work with using a round mag in his head stock. I believe he had a head end center and a chuck that he would set on his mag.
He would ask me to make odd and special mandrills that I would make on the B&S 13 grinder and on a Parker.
I don’t know how close his work needed to be, likely much .0001/.0002 or how often he dressed his mag chuck. Most are mild steel ans so would not last long with Knocking parts to into center,
He had to throw a tarp over his machine when it rained because the shop roof at where his machine was leaked.
He did a lot on one-ups and few-ups and his machine space lease was doing parts for the building owner..

(OT) a bit I used to rebuild machines for SIFCO in Minneapolis who made jet engine blades and they had a rotary mag chuck that looked like a rotary table in the tool room and they would use it on their horizontal surface grinders to grind bearing races and other circular parts. They could get super accurate grinds as the part only was being ground in one spot under the wheel, A bit of a portable Heald Rotary Grinder.

Richard King said:

(OT) a bit I used to rebuild machines for SIFCO in Minneapolis who made jet engine blades and they had a rotary mag chuck that looked like a rotary table in the tool room and they would use it on their horizontal surface grinders to grind bearing races and other circular parts. They could get super accurate grinds as the part only was being ground in one spot under the wheel, A bit of a portable Heald Rotary Grinder.

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Friend of mine did that on his Kellenberger 600U
On that machine you can set the stone at 90 ° to the frontplate on the workpiece head
With a raiser he did grind 600mm or so thrust bearing races
Those races were premachined on a Caseneuve HB725 conventional lathe
Then after hardening turned to net shape on the same machine Also the radius And then to the Kellenberger
Whole stacks of it

Peter