Magnetic chucks.. do they pull out of true from the mag

woodchucker

woodchucker

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I have a small Delta tool maker grinder. it has a Walker Chuck on it. I have ground it flat twice. I can say it was true the last time a few years ago.
I had a parallel that needed to be ground. I noticed that when I went to pull this parallel the grind was poor on it, and it was not square, it was trapazoidal. Anyway, I just put them on my chuck together, and used some magnetic blocks to hold them upright. I had swept by hand the chuck first.
After grinding, I double checked them, and found them to be 5 thou off from end to end. The chuck no longer feels like it did when I surfaced it years ago, it's rougher, where the lead (assuming lead) lines are things don't feel as smooth as years ago. I have left things chucked up on the chuck with the mag on many times.... So do the chucks pull themselves apart, is me leaving something chucked contributing?

This is a coarse pole mag, only about 9 inches long by 5.

Thanks.
 
I've never heard of a chuck warping due to it being left in the on position. I have however seen them warp from either being tightened excessively to the table or having uneven mounting platforms, or rust or debris between the table and the bottom of the chuck.

I have a 5" x 10" and a 6" x 12" coarse poll magnetic chuck. I did a dusting on both in about 2016. The 6 x12 lives on the grinder while the 5 x10 sits on a shelf most of the time. The 6 x 12 is the original that came with the surface grinder when it was built in 1956. Neither show signs of warping nor going out of square. Both of my chucks have brass dividers. I do know aluminum dividers were used on some brands, but I've never heard of lead.
 
Just ran a test indicator over the chuck. It does dip on the al separators but the chuck is true otherwise. I re ground the parallels and they are now correct, blame it in the idiot at the controls.
 
Still would like to understand the dips. That should be flat. It had been.
 
Heat is your enemy also . I don't think those little Deltas have coolant at least I've never seen one that does . .005 seems like a lot , did the wheel possibly break down while grinding ?
 
If the chuck is square and true and the part came out tapered. it is one of 2 things.
1. There was dirt on the chuck that held one end of the part up.
2. There was a burr on the part when you put it down holding one end up. (0.005 is pretty small to see by eye.)
3. You said that the non magnetic lamination were lower than the steel lamination, If the part is parallel to the lamination it could have had one end in a low spot. (Ok so I can't count. :drunk:)
 
I run a mister, and also have flood if I need it.... I prefer the mister, the flood leaves a mess. I have to redesign my pan..

Yea, I figured maybe when I put it down I picked up something, everything has a lot of magnetism even when off.
still don't understand why it has dips when it was ground flat years ago. Those no magnetic areas should still be the same height as the metal.
 
When you ground it it was warmer. Aluminum has a lot more thermal expansion than steel, near double. While still warm maybe it was flat but now that it is cool the AL has shrunk more than the steel so it is low. Just a WAG based on some physics.
My chuck is all steel and brass. It has not changed since I ground it in. The brass did grind a tiny bit deeper than the steel. I don't think it was due to thermal expansion, I only did one pass per day to avoid heat build up. I think it was just due to the brass being a lot softer than the steel.
 
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