Surface Plate Resurfacing

[SouthernChap]

I'd have it on three points.. I would personally put tiny (oiled) soft wood shims on one of the short sides, at or near the corners of that stand, and let it sit on those. Just thin ones. If you've got an old wooden yardstick that needs to be gotten rid of, that's the "scale" of shim I'm thinking. They're pre marked so you can cut off just what you need and paint stores sell 'em cheap. And on the other short side, a single shim in the middle. Maybe a little longer to spread the weight over the unsupported angle. Maybe even six or eight inches. Wide enough to keep it from rocking (if that's an issue), but short enough to concentrate some weight so it'll "bed into" the shim, and find it's own happy place, without being influenced tangibly by the stand.

Yep, the frame is distinctly sup-par and your suggestion of a three point support sounds a great one. I'll definitely do that.

That'd be an excellent use case for a "precision ground stone"

Those are on my shopping list. Your suggestion just moved them the list.

 

[AllenV]

Can folks supply specific recommendations for "precision ground stone(s)"?

I have a mill table with a ding in it as well as a cast iron flat plate.

 

[RaisedByWolves]

Are you saying that, on cast iron, the impact of a hard, sharp point/corner won't raise a "donut" around the divot?
What is your definition of a "boo boo"?

That is the reasoning behind them being made out of cast iron vs any other metal. Cast iron is porous and the deformed metal will flow into the voids rather than raise a donut.

If you're asking about hitting it with a ball peen hammer were having two different conversations.

Its a precision instrument and should be treated and thought of as such.

 

[RaisedByWolves]

This is an apposite topic to have turned up.

I laid my hands on a 36"×24" "surface plate" pretty cheaply from Charter Auctions.

It was on this stand:

View attachment 500819

(The frame's inner 'shelf' is now a lot cleaner than it was when I first got it) and it's currently resting on some blocks of wood on the floor. Here it is before it was lowered onto the wood:

View attachment 500820
It has some surface corrosion and a couple of minor dinks close to a couple of the corners.

So the consensus is that a bit of evaporust and some delicate stoning to to take any high spots down is the way to go?

While that frame is a mess, its probably good enough.

Id rather see the whole frame designed around 3 points, but if you do as described above and also put the frame on 3 points (I would go long ways on that) you will be better than good.

As to the stoning, less is more. If its bad enough that you need to "WORK" at cleaning it up, send it out.


The important thing to remember in this thread is your space agency cannot have an X in the name, that's already taken.

Point of reference: I "Made" my own surface plate out of a 12"x9"x4" hunk of steel during my apprenticeship, and it served me well during my formative years in the trade. I ground it to within .0002 flat and parallel. Thick as it is it never had a rack, Never bothered with 3 points, it just sat happily on a steel table.

Once it got dinged a little, it was right about the time I moved into this house and it has sat ever since, 18ish years. Its got rust on one side now and has been resurrected as a seriously heavy duty bench block for my basement mini shop as all of my table tops down there are reclaimed butcher block.

 

[extropic]

That is the reasoning behind them being made out of cast iron vs any other metal. Cast iron is porous and the deformed metal will flow into the voids rather than raise a donut.

If you're asking about hitting it with a ball peen hammer were having two different conversations.

Its a precision instrument and should be treated and thought of as such.

My point is that he bought a "used" item and , unless he bought it from you, neither of us have any idea of how it was cared for.
That's why I suggested he "search out" any high spots. Your apparent assumption that his purchase is in pristine condition seems overoptimistic to me.

Filling voids . . .

 

[SouthernChap]

While that frame is a mess, its probably good enough.

Worse than you know. I had to get the chaps at Charter Auctions to cut the bottom legs off to fit it in my car! I have just ground down the mess the plasma cutter left and have welded four plates to the corners to take some levelling casters.

Id rather see the whole frame designed around 3 points, but if you do as described above and also put the frame on 3 points (I would go long ways on that) you will be better than good.

I can put in an M12 bolt in the middle of one of the bottom lengths of angle iron between one pair of casters to act as a third point with the opposing pair of casters acting as the other two points. Would that be okay?

Actually, I have some M24 threaded rod (Allthread do you chaps call it?), so I could use that instead.

I can use the casters flanking the third point just to stop any wobble.

Which would be the better length to choose for the single point, the longer side or shorter side?

The important thing to remember in this thread is your space agency cannot have an X in the name, that's already taken.

I should point out that this 3'x2' plate and shonky frame (even shonkier now I've welded on it) cost me less than the fuel I used to go collect it. I have no pretensions of great precision. I just got fed up looking for something 2'x1'

 

[extropic]

Attached is some information about 3 point mounting a granite surface plate. I didn't find anything about cast iron.
I expect that your cast iron plate has 3 mounting bosses prominent on the bottom.

http://www.precisiongraniteusa.com/images/4919-INSTALLATION-INSTRUCTIONS-FOR-SURFACE-PLATES.pdf

 

[SouthernChap]

I expect that your cast iron plate has 3 mounting bosses prominent on the bottom.

I'll check. Thank you.

 

[Jake M]

I can put in an M12 bolt in the middle of one of the bottom lengths of angle iron between one pair of casters to act as a third point with the opposing pair of casters acting as the other two points. Would that be okay?

If you've got the plate sitting on the stand, on three points, and the stand is on four points, the stand can be free to bugger off and twist in whichever direction it wants, and the plate will remain flat. I wouldn't loose too much sleep over that until an issue presents it's self. Although if it's EASIER to do it with the stand... That stand looks "flexy" enough that if you had "something" on three points, it'd probably be fine either way. But there's not much sense in making the three point mount twice. That's just making the whole thing floppier than it needs to be.

Also, good call from "someone above here", do look at the bottom of the plate for built in feet. I didn't think of that, but it's a plausible possibility. If so, there'd really be no call to make your own.

 

[dwall174]

I expect that your cast iron plate has 3 mounting bosses prominent on the bottom.

Mine has the 3 mounting bosses, I just got finished cleaning it up & repainted the base.

I didn't get any pictures of the top after cleaning it up, but it came out pretty good.
I don't have a really good precision straight edge, but I do have a 24" ruler for my Starrett combination square. Using the ruler & some feeler gauges, I had a hard time getting a 0.002" gauge under the ruler. Way better than I expected & good enough for the type of work I'll be laying out with it.

I'm also going to be making a new stand for the plate since the one that came with it is not that square, plus those big wheels are way overkill for this surface plate & they're not locking swivels.