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How flat can I surface grind 2x18x27" plate A36?

Lazyman

Aluminum
Joined
Nov 28, 2016
I have no experience surface grinding and will mill a A36 2x18x27" and will get it surface ground after. I got a quote from a surface grinder saying they can get it flat and parallel to.002" and I was really hoping for .001". Thickness tolerance is very loose it could be plus/minus .05" but I want it as flat and parallels as possible are my expectations too high?
 
I would think you could have it Blanchard ground and easily hold 0.001" However the material may be your enemy as hot rolled A36 may move like crazy. I don't have much experience grinding A36. That could be why they didn't quote better than 0.002"

May want to choose a stress-relieved material.


Best Regards,
Bob
 
I was under the impression A36 was hot rolled and not too bad as far as stresses but I could have it stress relieved. Is cast iron plate something that's not too hard to get in that size?
 
I machine a lot of A36, and it is almost always stress free. I've had some 4" plate that came in with a 1/4" bow over 36" that moved around a bit as we brought it in, but anything under 3" has always been pretty nice.

Blanchard shops usually hold about 1/2 the tolerance they quote IME, and I think as long as you are dealing with a reputable place, you will be happy with the result.

Unless it is for a machine tool app, then you better plan on scraping it in the rest of the way, or finding a shop with a Mattison in good condition.
 
If you can split it into 2x pieces 9" wide you may get some more quotes. I have a pretty large surface grinder, but it only has 16" of Y travel.
 
Never will come out right, It will stress relieve on every pass of the grinder, can you weld a grid under the plate to make it stiff?...Phil

I've done a lot of 2-3" x 20x36ish A36 plates that are flat and parallel within .005", usually better. You know A36 is hot rolled right? It's normally not too bad, unless you get some odd ball import material.
 
Never will come out right, It will stress relieve on every pass of the grinder, can you weld a grid under the plate to make it stiff?...Phil

Nonsense. I used to blanchard plates in this size to within .001". It just takes patience. Might be excessivley expensive though.... Curious as why .002" isn't good enough? That's pretty good in that size...
 
To clarify guys. The shop is going to surface grind with a Mattison Horizontal Spindle Surface Grinder, not a blanchard grinder which I assume is more accurate. The plate is for a small machine base that needs to be quite accurate and I was hoping for .001" fatness and parallel The material doesn't have to be A-36 I just picked it cos its cheap and readily available. I don't really know what's realistic in general for a thinner plate. Perhaps I can use a 2.5" thick plate to help keep it more accurate. How the heck are they making things like your mill table for example so accurately? I know Haas just mills many of their mill tables without even grinding, I wonder what spec they are reaching on those?
 
Don't confuse thickness with flatness, its not hard to get the thickness within .oo1 easy, now flatness is a whole new deal, its flat until you release the plate from the grinder chuck, and stress re-leaves , no more flatness...only deep bracing or a real good stress relieved steel will work, this is my every day work...Phil
 
He might be able to get it, with a lot of flipping and shimming if necessary. It will depend on the individual piece of material. If it's mission critical just get it stress relieved before grinding.

And yes, it's a very important distinction, that between "flat" and "parallel."
 
What kind of a machine needs a base that flat? Is the plate part of the machine? Or just the base?
Could make a difference in what you need.

And I will point out that over the years I've had better luck with 44W plate than with A36. Both are
hot-rolled "mild steel" but I've generally found that 44W is a little better quality as a starting point
if I want something to be flat and (relatively) stable. Just a thought...
 
What kind of a machine needs a base that flat? Is the plate part of the machine? Or just the base?
Could make a difference in what you need.

And I will point out that over the years I've had better luck with 44W plate than with A36. Both are
hot-rolled "mild steel" but I've generally found that 44W is a little better quality as a starting point
if I want something to be flat and (relatively) stable. Just a thought...

It's for some small automation platform . It will have linear guides and balls crews mounted to it and needs to be fairly accurate. I'm considering going to 2.5 inches thick.
 
I'd suggest trying to find a shop with a Blanchard over a surface grinder. That size of plate is more typically done on a BG, and good shops will know how to shim, flip, and lower the mag field strength to get the best outcome.

But you still should get the plate stress relieved before final milling and sending to the grinder. Or, just plan to rough mill, stress relieve, finish machine, and scrape in the linear way mounting area. That takes its own expertise, and perhaps isn't ideal for you.
 
I agree, Blanchard would be the way to go and if the shop is worth a darn and they have a good machine .001" is possible. If they are going to use a H. surface grinder. Have them set plate on 3 points and support the center and edges with slight pressure sharp topped leveling jacks and block around the plate to keep it put. If they set it on the chuck it will bend to the chuck even if you use low magnetism. Also you can only grind on as close as the machine your using. One advantage of a Blanchard the pate spins under the same point unlike a table that moves back and forth. If your not familiar with a Blanchard check into it and it will surprise you.
Mattison Made that style too.
 
Is cast iron plate something that's not too hard to get in that size?

How many are you making?

Might be doable, even from salvage and in "better than the average CI" as well.

The 9" would be an issue, but I've got the better part of ten feet of it left out of two five-foot sections of detachable rectangular bed off a G&L hor-bore optional rig.

And you MIGHT not even have to grind it at all? It wasn't the "main" bed, so doesn't have much wear. Might be able to just polish it then shim and/or scrape-in the linear-rail support pads?

3" X 8" but .. each five-footer already sawed so Igor could palletize it to 2-foot and 3-foot lengths.

Drilled and tapped on a grid at the back for the attach bolts, too.

But it IS "the right stuff", given its origin and the long years it has had to stabilize.

That's why I bought the whole 980-odd pounds of it in one go to begin with!

Coupla projects.

And trading material.

:D
 
Just occurred to me that you might be able to use a cast iron surface plate. Google the term and you
get lots of results. Will probably cost quite a bit more than a slab of mild steel but it should be pretty flat
right off the shelf. If you don't have to grind it the project will still be cheaper overall...
 
Just occurred to me that you might be able to use a cast iron surface plate. Google the term and you
get lots of results. Will probably cost quite a bit more than a slab of mild steel but it should be pretty flat
right off the shelf. If you don't have to grind it the project will still be cheaper overall...

It isn't actually any BETTER than ribbed CI, but the 'go to' for a LOT of small chow and metrology fixturing and system "bench" mounts is granite.

For its easily shape-selected feature. Already has a billion years or so of stress relief "baked-in".... literally, and on the grandest of scale...as well. It CAN be broken, but still... worried about that?

Just go thicker. Strong enough to hold entire Continental land masses together ain't it? Even if hit with am atom bomb! Mind "thicker" is... kinda "relative?"

:D

It will not NEED any further grinding at all. And yes, one can bolt stuff to it.
It now and then shows-up as salvage on ebay, even. With holes in it! Where the "whatever' had been mounted. But still, not ordinarily very MANY holes.

Grave monument makers can cut it to shape. Among the earliest users of water jets, they are. And wet-worked Diamond saws.

Herman surface plates CAME from a monument-maker. That was also "Rock of Ages" main line, historically... before granite surface plates were resurrected.

Ancient Egypt made them. Herman being "the first" is a joke by easily five thousand years!
 








 
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