# Surface plate info?



## astjp2 (Dec 14, 2013)

I found a granite surface plate in the local classifieds, its a Herman that has 4 ledges and is a 36x48x8 inches.  Can anyone tell me when it was made or what class it might be?  I think it might be fairly nice, there was only a few nicks in the edges and I need to get a stand.  I hope to get it checked for flatness during Christmas break.  Did I get a good deal for 300?  Tim


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## Ray C (Dec 14, 2013)

A brand new Grade B or A plate that size is running about 550 to $600 but, delivery fees will be about another $100.  I don't know what grade yours is but, in a home shop environment, B-grade is more than adequate.


Ray


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## astjp2 (Dec 14, 2013)

I am seeing 1200-1950 for that size for new ones...

http://precisiongraniteusa.com/pdffiles/PGPRICELIST.pdf


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## Ray C (Dec 14, 2013)

Try here...




http://www.shars.com/products/view/2345/Grade_A_36quot_x_48quot_Black_Granite_Surface_Plate


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## astjp2 (Dec 15, 2013)

Well after doing some reading, this plate has the original 3 mounting pads, now I have to make the stand that uses the mounting pads.  :thinking:


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## DaveSohlstrom (Dec 15, 2013)

Get in touch with Don Roberts (bebop) on PM forum. He is in Ogden and can check you surface plate for you and tell you what grade it is also I think.

Dave


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## astjp2 (Dec 15, 2013)

I was talking with Don yesterday, he is busy for a while.  I will get him to look at it sometime in the future.  Tim


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## astjp2 (Dec 24, 2013)

Well I got my stepson to use the MIG today, a friend gave me a steel table that was very short and with a few modifications and addition of adjustable feet, I now have a table that I can level and the 3 point pads for the surface plate fit on.  I also got my stepson to use the bandsaw to cut new bases for the feet, he drilled and tapped them all, and cut a few of the braces.  He did some of the initial welding then I did some of the finish welding.
	

		
			
		

		
	









	

		
			
		

		
	
  All in all a good day.  Tim


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## Tony Wells (Dec 24, 2013)

Very nice, Tim. Going to make a cover for it I hope.


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## xalky (Dec 24, 2013)

Nice job on the table and bringing those struts down to the corners, She should be rock solid now(literally).)


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## astjp2 (Dec 25, 2013)

Tony Wells said:


> Very nice, Tim. Going to make a cover for it I hope.


I am planning on making a wood top for it that will be suspended above the granite, if I do it right, it will have supports that slide into the square tubes and then the wood top will be supported above it by a couple of inches.  I have a maple top that needs a little work but should fit fine.  Tim


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## Ray C (Dec 25, 2013)

Nice job...  -Man that thing looks heavy!


Ray


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## astjp2 (Dec 25, 2013)

Ray C said:


> Nice job...  -Man that thing looks heavy!
> 
> 
> Ray



Starrett says that theirs is 1400# in this size.  Put on a mill table or lathe bed and you are looking at up to 1800#.  I hope the 1/2x13 threads on the feet will be strong enough.  Tim


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## Ray C (Dec 25, 2013)

Yeah, that's heavy!   You're fine with 1/2"-13.  One bolt could handle that.  Four is even better.


Ray




astjp2 said:


> Starrett says that theirs is 1400# in this size.  Put on a mill table or lathe bed and you are looking at up to 1800#.  I hope the 1/2x13 threads on the feet will be strong enough.  Tim


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## astjp2 (Dec 25, 2013)

Ray C said:


> Yeah, that's heavy!   You're fine with 1/2"-13.  One bolt could handle that.  Four is even better.
> 
> 
> Ray


We used 3/4" plate for the feet to screw into, it made welding real easy with the MIG.  It made tapping and drilling real fun!hew:  Didn't break a tap either!


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## Ray C (Dec 25, 2013)

astjp2 said:


> We used 3/4" plate for the feet to screw into, it made welding real easy with the MIG.  It made tapping and drilling real fun!hew:  Didn't break a tap either!




Oh yes, tapping a 3/4" hole actually requires a little beef on the tap handle...  BTW:  a single 1/2-13" (Grade 2) bolt with 3/4" thread engagement is good for 1100lbs (max safe static working load) and the threads won't tear off until you get around 1600lbs.  Since the weight is spread across 4 bolts, you're well within a safe range -especially since that's a static setup.  You can put another ton on that table and you're OK as long as you don't bounce it -which you're unlikely going to do since it's a precision surface...

BTW, when you look-up things like this, make sure to read the tables for thread root strength, not bolt strength.  Also, the standard charts assume a thread engagement equal to the diameter bolt (which is why, for example, a standard nut that fits a 1/2" bolt will always be 1/2" wide).  As you increase thread engagement, strength increases linearly until you get to about 5 diameters of engagement -at which point, thread root strength is about equal to bolt tensile strength (roughly).


Ray


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## toag (Dec 25, 2013)

Thats a nice size plate.  I have seen them go for 50 to 500 depending on the auction.  if it is in good shape then I think you made out well.  Seems smaller ones go for more, but I am a huge fan of bigger. Nice work on the stand should be easy to level and use.


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## astjp2 (Dec 26, 2013)

Well I got it to within .002 over 12" of level, but I was not able to get even pressure on all of the feet because my wife was getting cold.  I am not keeping the heat on in the shop because my door is not insulated.  I also cleaned the plate with some Dykem cleaner, it got most of the debris and discoloration off but someone used an indelible marker on one corner and it didn't clean up.  My shop must have a lot of dust, I kept feeling small granules of grit on it even after I wiped the plate off.  It may take some time to get it clean enough to start scraping.  I hope to make progress tomorrow.  Tim


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## Tony Wells (Dec 27, 2013)

Over the years working in QC/QA, I have used just about everything for cleaning plates. From Windex type ammonia cleaners to MEK. And lots in between. Probably best all around is Fantastik or Formula 409, lots of paper towels and a good rinse with clean water and more paper towels. This will generally be sufficient unless there are marks left by solvent based agents. Then out come the tough stuff, like Toluene, Xylene, and MEK. PLEASE TAKE PROPER PRECAUTIONS if you have to use any of those. Extremely flammable, toxic and carcinogenic. But there isn't much they won't remove. And they leave the plate very dry, and that has always been my preference. I worked for an older guy once you wanted me to use GoJo, and after I cleaned it my way, I did....looked very nice, colors in the granite showed nicely, but I really never liked the lanolin residue.

As far as the dust goes, if you have the plate in an open shop, you can hardly stop that. That's one reason I asked about a cover. Not really a nice wooden top like you are doing, but I was thinking of something just to keep it clean. Yours will do that as well. Dust is your enemy though, so you should wipe it down before you use it. That's about all you can do in an open environment. 

Realistically, being level is secondary (by far) to having it certified and lapped flat to whatever specification needed. Or at least lapped. In a home shop, a cert isn't all that useful, unless you do commercial work where you have to keep records of all calibrations. Granted, having it level makes some things easier, but it isn't absolutely necessary. And 0.0002/12" should be more than adequate. And if it's on casters ad gets moved, that's out the window anyway.


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## astjp2 (Dec 27, 2013)

Does it hurt the plate if I use shop air to blow off the dust?  Wiping it down just does not seem to work, if I take my hand and wipe it after using a rag, I still feel grit.  Tim


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## Tony Wells (Dec 27, 2013)

No. If your shop air isn't dry, you will be adding moisture/oil to the surface. Odd as is may sound, if the dust really bothers you, use a Swiffer or equivalent.


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## Ray C (Dec 27, 2013)

It occurs to me that blowing air on something is a good way to build-up the static charge.  In the right environment, that will make your dust problem worse.  And BTW, I don't have a plate as big as yours but, it's almost impossible to run your hand over it and not feel something.

Anyhow, whenever I use it, I'm not too concerned about minor flecks of dust...  It's a fact of life and for the most part, I don't recall measurements ever being wildly off based on the stuff I do...


Ray


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## astjp2 (Dec 27, 2013)

I will try a microfiber cloth and some more of the Dychem cleaner.  I am just worried about when I am scraping that the debris will scratch my amateur work....anic:


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## Tony Wells (Dec 27, 2013)

I really wouldn't stress over it. In an open shop, you will never get rid of airborne particles. And truthfully, nothing that is likely to settle on your plate will be hard enough to damage either the plate itself or the work. That is, unless you are running a dry grinding operation in the shop. THAT'S what covers are for, to be sure. Wipe it down just prior to a test if you must, but really, I wouldn't worry about it too much.


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