Grinding over-long parts on a surface grinder

When you have a part that's too long for the chuck, is there a rule of thumb about how to overhang it off the chuck and grind it in stages?

I ask, because this weekend I ground some 600mm (24") parts for a friend, on my J&S 540 surface grinder (long traverse 450mm = 18"). I had to grind each part in two passes, shifting and blending.

At first I had the parts hanging off the left side of the chuck. So when the table was at the far right, the grinder reversed direction on the part. But when I was done, I found that the "reverse points" had dug a hole about 20 microns (0.0008") deep in the part. Fortunately I had no spec for total thickness, so I shifted the part so it overhung on the right side of the chuck, and did it again. This time, all went fine, the reverse on the part happened when the table was at the far left, and it did not "dig a hole".

I'm wondering if there is some effect like climb cutting that happens when you reverse on a part on one end of the long traverse that causes the wheel to dig in, but not if you reverse at the other end.

May be weight causing a slight shift when the table is at its extreme end of travel on that one side. I've read about that issue before when grinding longer than travel parts in multiple setups but never had to deal with it myself. Adding weight on the table in the correct place is said to help.

Running into the arc of the wheel diameter at the end of long travel is a big increase of forces, and an extreme more at the climb side. I would put the overhang to the left side so to have no climb grinding at the travel end…and drop a shim at the travel stop every few travels (.025 to .050) and grind part to just under my high limit. Then with my ground portion of to the right grease pencil mark my ground and set the to- be-ground in position to grind… I know with a CNC grinder the long travel end of travel is not easy to change every few travels. A rubber block can also be good at the long travel stop so to not bump the stop hard. softer wheel and a lot of coolant is good.
The old-fashioned grease pencils were made of grease like material and would begin to smear at about .003 to go thinner and allow almost a zero height to ground and spot location of the last grind. Nowadays a dark crayon is good. The modern ceramic markers don't smear/melt very will so are not a good as the old grease pencils

I have set parts on the chuck angle wise to long travel so with down grinding I could go off the part with long travel. with the back rail off you can hang a little length off chuck to the front and back. down grind for speed and then increment for finish.

I have tried to grind a notch at across part long ways center/mid section to near the finish size but often that can cause a warp...

Good that you reminded me of that , I will add it to me book notes.

Grind with the parts on an angle off the chuck and don't reverse direction with the wheel contacting the part. Still a pain if things need to be flat over the entire part.
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