Not-so-perfect mounting table for granite surface plate

[Crashcup]

Hey, couldn't really find much in a search, so here I am. Just last weekend I picked up a 36" x 24" x 6 1/2" granite surface plate from an auction. $5, which seems to be a decent deal. The calibration sticker on the side shows it's a grade A plate, but hasn't been calibrated since 2001.

I don't really need a high-precision inspection plate... possibly someday, but for now my use of the plate will be for things like checking a steel straightedge or square for flatness. Flattening wood plane soles. Flattening gasket surfaces on motorcycle side cases.

So I've read about how these should be mounted (and cleaned and covered, etc). to keep them in good shape. But given my use of it, I may just build a simple stand that provides many points of support. Or possibly even have plate steel on the top with a rubber cushion under to even out the support.

Anyone have any thoughts on...
1) How far off could these go in 18 years without calibration?
2) Would the way I'm considering mounting it do any irreversible harm to the stone? Or would I still be able to mount it properly 5, 8, 10 years from now, get it calibrated and have a grade A plate again?

Thanks!
Keith

 

[pi_guy]

Go look at a standard stand for a surface plate at MSC. Sometimes the price is cheaper than the material. I built mine on wheels using 2" angle iron. I store heavy tools on bottom shelf and have an table extension that slides into hitch receivers that I build gearboxes on and a vice on other side attached by hitch receiver.

 

[PT Doc]

If you move the plate from the original stand, then the calibration is no longer valid. Should be mounted on 3 points. Hopefully those are obvious on the underside.

 

[rsanter]

At my last job we put the small surface plate we bought on the top of a toolbox that we stored the measuring tools in.
Put a soft rubber mat on the box and then the plate on that

 

[ddawg16]

$5? You really ****.

But that ***** is going to be heavy.

And I echo the thoughts above.

At that size....it's still manageable. It's going to be a god place to sit a beer.

 

[fsae0607]

Great price, but good luck moving that mofo!

It'll be good enough for your use. I have a 12"x18"x3" Chinese surface plate eBay special. It's more than good enough for my uses which are similar to yours. I keep mine on top of one of my toolbox chests.

 

[Crashcup]

Go look at a standard stand for a surface plate at MSC.

$294 is what i'm seeing there. I have a seemingly endless supply of 30mm square steel tubing, so I'll probably build something from that. Biggest cost to me may be casters.

The 30mm I'm not positive about, but it measures 1.18 inch on the outside - bigger than 1 1/8, yet smaller than 1 1/4. And when I convert that to metric it comes pretty dang close to 30mm.

 

[Crashcup]

But that ***** is going to be heavy.

Yup, I'm thinking around 500 lb or so. The auction place loaded it into my trailer, now I need to get it out and up on a stand. Prob rent an engine hoist.

I heard one other guy comment that it "must be a tombstone"... so between those who though that and others who know how heavy it is, I was the only one who wanted it!

Haven't heard any comments in the negative about just putting it up on something other than the official 3-point support, so I'm hoping that means I can't really hurt it. It would be good to know that if I get into machining someday and want to use it for precision measurements, I could then give it the proper mounting and get it calibrated.

 

[ddawg16]

Yup, I'm thinking around 500 lb or so. The auction place loaded it into my trailer, now I need to get it out and up on a stand. Prob rent an engine hoist.

I heard one other guy comment that it "must be a tombstone"... so between those who though that and others who know how heavy it is, I was the only one who wanted it!

Haven't heard any comments in the negative about just putting it up on something other than the official 3-point support, so I'm hoping that means I can't really hurt it. It would be good to know that if I get into machining someday and want to use it for precision measurements, I could then give it the proper mounting and get it calibrated.

At 6 1/6" thick? No, not really. What ever you put it on would have to be really off.

If it was me, I'd use a support table with rubber pads against the granite. That will compensate for a slight non-plumb table.

 

[bugnut]

HF Hydraulic Lift table adjustable height, rolls and holds 500lbs, your stone calculates to ~510lbs

Used toolbox from craigs

to lift off the trailer I'd make a ramp with boards to a ladder and shove it on there then raise the boards to the top of its final resting place and shove it over

 

[jimy]

I heard one other guy comment that it "must be a tombstone"... so between those who though that and others who know how heavy it is, I was the only one who wanted it!

In a local graveyard there is a gravestone made from a surface plate. If I recall correctly (according to the inscription) it is from General Electric and the man worked there as a machinist...

Jim

 

[matt_i]

My free advice is to make your stand so it accepts a pallet jack so you can move it later, easily, when and if that time comes. They are tricky to rig, flat web-straps work well because if things go correctly they can be pulled out of the gap that the rubber pads (see below) provide. Cook up a load-spreader out of angle iron, channel, or flat bar so the straps don't slip towards the center if using a single crane hook. Important to work very slowly as its all friction.

The typical 3pt rubber-pad is the proper suspension at roughly 1/3-2/3 of the entire length and width to minimize deflection from the weight itself.

Most "calibration" for a surface plate is just a traceability thing that eventually leads to NIST (nat institute of standards) so a company can corroborate their quality policy is something that has stability and is not on a dimensional drift. But at the end of the day its a precision-finished stone that's very rigid due to the thickness, the Young's modululs of the stone is high and its crystal structure is stable and the surface is hard enough not to be worn away by setting stuff on it.....so....unless it was roughly handled or has obvious pocks or chips out of it from poor handling its going to be great for your uses. I would trust it to 0.001" in all directions. You can of course go spend the money and have it calibrated, the process uses a laser-leveling process more or less and the high spots are mechanically scrubbed lower by hand until the plate is within planarity spec.

An excellent use for a surface plate in a home shop is layout, if you can source a 6" height gage (dial or digital, hell even vernier has a place) with a scriber-point, its very easy to lay out lines and hole centers just by scribing the part as its clamped to an angle plate. Another good use is if you ever need to bend something straight or flat you can use a test indicator on the same height gage to asses "how much" bend is needed an incremental way. If you ever get into machine scraping you have a reference for printing parts.

 

[NC Rick]

I have a 4” thick 18x20 on a stout wooden workbench with three wood blocks under the “points” and shimmed up to make the plate level using a precision level, that way round stuff won’t roll off. I know it’s an inferior setup but it is all I need in my shop. I also have an old 12x12 which gets used for quick markups and measurements as well as sandpaper *gasp*

If I had a beauty plate like yours, I’d build a steel stand and pay to have it calibrated. I’d only do that because it was cool, not from my real need.

I have to agree with others; you ****!

 

[isb cornbinder]

Keith Rucker of Vintage Machinery. Org made a stand. He is on YouTube.

 

[Crashcup]

Keith Rucker of Vintage Machinery. Org made a stand. He is on YouTube.

Hey, yes, that's one that came up in a search. Super heavy duty stand for a big plate.

 

[Crashcup]

My free advice is to make your stand so it accepts a pallet jack so you can move it later, easily, when and if that time comes. They are tricky to rig, flat web-straps work well because if things go correctly they can be pulled out of the gap that the rubber pads (see below) provide. Cook up a load-spreader out of angle iron, channel, or flat bar so the straps don't slip towards the center if using a single crane hook. Important to work very slowly as its all friction.

The typical 3pt rubber-pad is the proper suspension at roughly 1/3-2/3 of the entire length and width to minimize deflection from the weight itself.

Most "calibration" for a surface plate is just a traceability thing that eventually leads to NIST (nat institute of standards) so a company can corroborate their quality policy is something that has stability and is not on a dimensional drift. But at the end of the day its a precision-finished stone that's very rigid due to the thickness, the Young's modululs of the stone is high and its crystal structure is stable and the surface is hard enough not to be worn away by setting stuff on it.....so....unless it was roughly handled or has obvious pocks or chips out of it from poor handling its going to be great for your uses. I would trust it to 0.001" in all directions. You can of course go spend the money and have it calibrated, the process uses a laser-leveling process more or less and the high spots are mechanically scrubbed lower by hand until the plate is within planarity spec.

An excellent use for a surface plate in a home shop is layout, if you can source a 6" height gage (dial or digital, hell even vernier has a place) with a scriber-point, its very easy to lay out lines and hole centers just by scribing the part as its clamped to an angle plate. Another good use is if you ever need to bend something straight or flat you can use a test indicator on the same height gage to asses "how much" bend is needed an incremental way. If you ever get into machine scraping you have a reference for printing parts.

Thanks for the detailed and on-point reply Matt. Interesting idea on using it for layout, I will have to remember that.

 

[Crashcup]

Thanks guys, for all the great info! I have a project to finish up in the wood shop, then I think next week I'll get to taking that big rock out of the trailer.


Almost forgot I snapped a couple of pics. Here's my new acquisition in the trailer.

(Behind it is a cider press. I've been planning to build a nice one with some silver maple I have that came down in a storm, but that hasn't even been cut into boards yet. My wife talked me into bidding on this one. Also $5 for the press, including a home-made apple shredder. We can get some experience with pressing apples with this one before I make my own.)

Last calibrated by a company in Blaine, MN 18 years ago. I'm going to call and get a price on calibration just for fun. Don't really need it, but I'm curious.

 

[Robert Haas]

Interesting that you can still see saw marks on the side of your stone. My surface plate has polished calibrated sides to allow calibration of my angle plates by using a straight edge projecting below the top along the sides.

Wonder of your plate was cut down???

 

[Robert Haas]

FYI there is a surface plate at a local industrial shop that came from Boeing Aircraft. It is 12 feet long, 8 feet wide and 3 feet thick. They have tried to sell it a couple times but the cost to transport it could run tens of thousands not to mention what a real estate eater it is.

 

[2oolhound]

1st off YOU ****!!!

I'd do what you're planning, build the wheeled table with your 30mm tubing but use 1/4 wall for the top. That way you can thread the sides for removable retainer plates so it can never work it's way off and it will be easy to load off and on if you ever need to. You can then thread 3 vertical bolts into the top for the contact points that level and support the plate. Those threads should be tapped on a drill press or mill so they are square and the tops sit flat level. (also use bolts with no markings on the top or mill them smooth. Do it right the 1st time and it's done.

 

[matt_i]

FYI there is a surface plate at a local industrial shop that came from Boeing Aircraft. It is 12 feet long, 8 feet wide and 3 feet thick. They have tried to sell it a couple times but the cost to transport it could run tens of thousands not to mention what a real estate eater it is.

Internet suggests 168 #/ft^3. So just short of 50k# to move. I think the typical semi makes out around 40k payload....

I'm sure the riggers would want to bring out their medieval Tri-Lifter for exercise

 

[MushCreek]

Don't overthink this. Three points of contact, and it can't teeter. How much do you think a piece of rock that thick is going to sag? As for calibration- unless people were lapping stuff directly on it, the wear will be minute. You can have them re-lapped, although I have no idea what that costs today.

I used to work in a high-precision tool shop. Our surface plates were in constant use, all day long. We'd have them calibrated every year. Sometimes, they'd find a wear spot where a guy used the same exact spot over and over. It might be low .0001-.0002". IIRC, it was $50 to have one re-lapped to AAA tolerance, but that was many years ago, and they'd do a number of them on one visit.

 

[Crashcup]

FYI there is a surface plate at a local industrial shop that came from Boeing Aircraft. It is 12 feet long, 8 feet wide and 3 feet thick. They have tried to sell it a couple times but the cost to transport it could run tens of thousands not to mention what a real estate eater it is.

Whew! At 170 lb/cu ft, that thing would be over 24 tons!

 

[Crashcup]

Designing my stand in Fusion 360. And trying Google photo for image sharing.

Influenced heavily by a stand design I found online... might have been here on GJ.