Granite Surface Plate - AA, A, or B

So I'm referring to Starrett's crystal pink series here (seems to be desirable since they claim the pink granite surface to be very long wearing).

There are a whole set of specs here

Crystal Pink

But just to abbreviate, in 24x36, AA = .0001" unilateral flatness, A = .0002" unilateral flatness, and B = .0004" unilateral flatness.

Looking at MSC prices, the B-grade is currently around $1100, A is $200 more and AA is $400 more in round numbers.

Not suggesting that I have a pile of cash around to hand to Mr. MSC for his finest, if my cast iron plate can't get qualified easily, it looks like there are some "used B" plates out there locally that I could potentially acquire.

I realize that the easy answer is nothing but the finest AA Lab grade will do, but I'm actually using this in a minimally temp controlled shop and not in a CMM metrology room.

I'm wondering what some of the thoughts are out there about what grade of plates everyone else is running for scraping purposes and what kind of detriment there is to using one bought with personal shop budget thinking in mind

Keep in mind the higher grade plate is a thicker plate. It has to do with the deflection of the plate at the specified loading. IIRC, the plate can't deflect more than 1/2 the flatness tolerance. You can always refinish a plate to a higher grade, but it won't have the thickness. It seems like E for the pink granite is higher than the black so Starrett can make their plates thinner for a given accuracy requirement.

I know Prussian Blue will permanently stain a Crystal Pink plate. I don't know if the water based Canode will be completely removable. It would suck to spend the longer dollar for the pink plate and then stain it the first time you use it.

gbent said:

I know Prussian Blue will permanently stain a Crystal Pink plate. I don't know if the water based Canode will be completely removable. It would suck to spend the longer dollar for the pink plate and then stain it the first time you use it.

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Why would it suck ?????
stain it all over if you want a nice uniform look

peter from holland

peterve said:

Why would it suck ?????
stain it all over if you want a nice uniform look

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Maybe someone should make Prussian Pink... Mary Kay might carry it.

honestly if you want a big'un if you can find one on local auction you'll be in luck. I have seen big plates struggle to get a bid,, even a 6' x 12' granite AA plate at one sale that went for about $75.00.... but you have to move it. Freight is the biggest player in granite.

Milacron said:

Maybe someone should make Prussian Pink... Mary Kay might carry it.

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it is probably very funny but who the hell is Mary Kay

But don't bother I just did a googlesearch


Peter from holland

Maybe a good sealer for granite would help protect it from staining? One of the semi permanent ones. I can't see how it would be detrimental.

My granite plate is G1 (DIN standard). Better would be G0 and G00.
My guess is, that AA and G00 are kinda the same. G1 is already for calibration, G2 would be "shop use" So the decision was already easy.
The other point is, that I know that Planolith doesn't go to the upper allowable limit. I had one that in fact was quite close to the lower limit.
So I played the gamble again and was right. Just a bit (I would have to look it up) off of G0.

The other thing is, that you can have an upgrade when doing inspection of the plate. Most of what you pay are travel expenses, not the lapping.

Nick

gbent said:

I know Prussian Blue will permanently stain a Crystal Pink plate. I don't know if the water based Canode will be completely removable. It would suck to spend the longer dollar for the pink plate and then stain it the first time you use it.

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Canode Blue stained my white granite plate.

WILLEO6709 said:

honestly if you want a big'un if you can find one on local auction you'll be in luck. I have seen big plates struggle to get a bid,, even a 6' x 12' granite AA plate at one sale that went for about $75.00.... but you have to move it. Freight is the biggest player in granite.

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Around here, 3X4 plates are giveaways, apparently. I was given one, it was even dropped off at my shop. The second one I had to pick up. The shop tried to sell it for 6 months, finally called me and asked me to take it away- has a few nicks but was recently calibrated. Both were on rolling stands. I tried to trade one to a dealer, got an emphatic NO.

BTW, Gallery of Machines in Marathon NY has a truckload of plates to sell cheap, like $200 for a 2X3. Said they came from IBM. Lots of sizes.

To start just find a used one and have it resurfaced. I bought a used DoAll Grade B (originally .0002" flat) 9"x12" and had it resurfaced by United Standards Lab. Now it's a Grade A, flat to 40 millionths, and it's cost me a total of $55. That's just to have around the shop.

Here's a good one right in your area: Starrett 24 x 36 Pink Granite Surface Table

Speaking of stains, at one time Starrett did offer an option of staining the pink plates black..

I have a pink Starrett Straight-edge and use Canode on it all the time and it does not get stained. I have a grey surface plate that doesn't get stained, I am wondering what you using it to clean the ink off? I use Windex or Simple Green. I have seen where some uses Acid-tone of alcohol used and it might stain it. When we use to use Dykem High spot bluing that really stained everything especially you fingers we used cream Go-Go (not the kind with grit) and would use paper towels and red rags rub it in and off. It took a lot of elbow grease too. Rich

matt_isserstedt said:

I'm wondering what some of the thoughts are out there about what grade of plates everyone else is running for scraping purposes and what kind of detriment there is to using one bought with personal shop budget thinking in mind

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My first thought is outside of checking your parallels what good is a 24x36 plate for working on machines?
Seems small for even checking a 6x18 grinder table or a toolmakers sized B-port.

For heavy use, yes the pink plates are worth the money but I may be biased as I used to sell them.
My use has shown that they do not wear out as fast as most black plates. A undocumented guess would be 3 times the life.

For light use, it's hard to beat the cheapo black imports.
You can buy much larger and when they go bad they are useful for landscaping around the house.
I like using these and consider them "throwaways" , in the smaller sizes they make great workbench tops for your rollaround toolbox.
(Yes, I am not nice to my plates, they work fine with a few chips here and there.)

All plates need to be supported correctly, pay attention to this.
It's amazing how much even a 24" thick 60,000 lb. one bends. (the kind you drive cars and trucks onto to check them)
They are only flat when supported in the right spots and on a body checker you have to fire supports or do crazy compensation as the arm moves.

Used plates are such a crap shoot.
Most will have been used in only a few convenient areas and will have hollow spots where used.

Nothing like a "AA" pink if you have GM style funding behind you.
Two and four ledge plates can also be very handy if you need to clamp a guide plate down.
Spending your own money one can buy cheap black and maybe get into something that works fine and won't break the bank.

OTOH, since you have budgeted it buy a pink and at least a "A" and maybe one step up in size if you can move and fit it.
Given a choice for small machine scrapping I'd buy a pink "A" in a 36x48 two ledge. A darn nice thing to have.
Spread the use around it and you will get a long life between relaps and you can will it to the grandkids.
It will get stained (which you can remove with some effort) but I have no idea how that is a concern at all.
Bob

I think I paid $75.00 for my last AA Grade 48" x 72" plate I bought at an auction. It had a inspection tag on it and it was spot on. It wasn't a surface plate so to speak, but I used it as one. It was an obsolete CMM that the computer died so no one bid on it. I brought it back to the shop and took off the bridge and gave it to a guy. It came on a 3 point stand and I saved kept the steel beam that was straight so I could measure parallelism of ways of machine tables, lathe beds I would check on the plate. You will be surprised as to how cheap CMM's are and how accurate they are. Rich

My Ottavino black granite plate was covered without washing, left sitting for a prolonged time, and the blue area shows clearly. I assumed black wouldn't show any discoloration but was wrong. In the scheme of things it doesn't matter much, though I suppose if I'd paid for pink granite it might. I really am concerned about support placement though, I just put three supports in the areas that looked like they shared the weight best. Now I'm told there is data available on exactly where they should be.

BTW, one black granite plate maker says this; "We produce our granite products from several types of granite, depending on the customer's needs. Laboratory tests have shown that fine-grained black granites are stronger, denser, and less absorbent than other granites. For this reason precision machine bases, air-bearing surfaces and accessories are best made from black granite."
I guess their claim is more about strength under load rather than hardness or wear resistance, but it goes to show that every type of granite has some kind of claim of excellence.
In a related thread a poster mentioned cast iron laps being used on rock plates, I always wondered how they were brought true.

Don't know, but that pink sounds more like sales speech to me. And looks gay for me.

Planolith, the mayor maker of surface plates in Germany doesn't use granite, but some very fine grained hard stone from Africa that gets imported as raw slabs. As we do have granite here in Germany, they must have reason to import it.
The color is a very dark blue.

I once asked a technician of Planolith how they make their plates. They come off the grinder and get inspected. If it fits their request, they don't hand lap it. Only if they need more of the better quality, they hand lap them.


Nick

I would love to have a 48 x 96 but it just is not going to work in this shop space unless I start moving out other valuable piece of working iron. Sort of settled on a 24x36 as I already have that sized CI plate but just haven't figured out how to qualify it yet. The diagonal would be around 43" and that would let me qualify a 48" dovetailed straightedge. Really love the extra non-inked clean space when spotting to find the highest shiny points when trying to refine a surface, so for those reasons bigger would be better....but I think this would achieve what I need for the machines I plan to get into at this time.

It wouldn't be completely out of the realm of possibilities that a surface plate is impregnated with some sort of sealer on the working surface as part of the manufacturing process...if you look at the rough machined bottom its pretty porous.

I always thought the tradeoff was that pink was harder-longer wearing but had lower E=Youngs modulus thus had to be thicker to preserve planarity under load. The black was stiffer and so could be made thinner = lower weight, important for those sizes going via ground shipping...

@Nick:

Would you be so kind to tell me what is the lower allowable limit for DIN 876/1? I was only able to find the upper limit (20 µ for a 1000 mm plate). It's be also interesting to know the price difference between G1 and G0 (at least as far as Planolith is concerned). Thanks.

Mauro,
Old price, but good as a scale:
1000 * 630 G1: 760.- €, G0: 860.- €, G00: 980.- €

There is no lower limit for any accuracy. Usually, it is sold as what it is.


Nick

Great, thank you very much Nick. 760 euros for a 1000 mm plate is quite an attractive price.
I take that G1 is enough for general scraping work, as well? Must be, given that you said your plate is G1 and we all know what you can do as far as scraping is concerned.

Mauro