re:re: ground plates

On Tue, Jul 09, 2002 at 08:59:15PM +0000, bjammin@... wrote:
> At 04:24 AM 7/10/02 -0000, you wrote:
> >Dave,
> >
> >To get plate that'll end up flat after grinding is a two step process.
> >First it needs to be stress relieved by a heat treater, then ground.
>
> Actually, this won't do it. Mag chuck will flatten it, then when it's
> released it will spring back some. To get flat, you need to suppport it on
> chuck so it isn't stressed in any way.
>
> Regards, Hoyt
>

>I had a vertical bandsaw table Blanchard ground. I wanted to get it
>flat because some idiot had tipped it over and the table had a distinct
>bend in it. The mag chuck pulled it flat for grinding and, when I got
>it back, it still had the bend in it. But at least it was pretty.

> Paul

I also have had things Blanchard ground. A cheap chinese 6" joiner bed,
about 40" long, was visibly out of flat.
The Blanchard guy flipped it upside down, supported the working surface from
the magnet with a few carefully chosen shims so that it was resting at three
points and level, then leveled the four mounting feet.
He then flipped it over and carefully removed metal from the table surface.
Worked great, and its still quite flat.

I should put the autocollimator on it to make sure, though.

This technique could be used in other applications if the metal being ground
was moderately stiff, maybe not the case for 1/2" thick 15" long steel.

The trick would be to evenly support it.

Maybe a bed consisting of a couple of layers of bb's?

Some sort of pin device like they sell in novelty stores might work, a block
of metal with lots of holes, pins through the holes. The block sits on the
chuck, the spring loaded pins support the work, when the magnet goes on the
pins are frozen in the block.

Other ideas?

Elliot Burke