Can a granite plate be calibrated vs another granite late?

I am going to purchase an 18x12 pink granite grade A starrett plate. I have a 6x18 black stone plate that I am using now. I would like to "check" my current black stone (its not the real granite, its the cheap crappy black stone (Woodriver brand), what ever it's called) plate against the starrett, to continue using the 6x18 plate as my working plate and use the starrett as an inspection only plate. Is there a "proper" technique to checking one plate vs the other. My worry would be the 6x18 plate scratching the 12x18 starrett, since it is also a "hard" rock rather than "soft" metal...

If I am crazy and this should not be done, just say so. I admit, I am a total newb.

When I want to check the flatness of a surface, the simplest way is to invert the second surface and set it on risers above your calibrated surface plate. Use whatever you have for height, and adjust or shim as necessary to get matching height. I had 2-3-5 blocks I usually used, but jacks, 1-2-3 blocks, or parallels can work as well. You just have to be able to get your instruments and hand in the space.

As GBent states, using the Starrett plate as the reference for indicating the surface of the black plate is a good way to start out. I would use a .0001 indicator on a height gage or transfer stand to give the indicator a stable large footprint. There are also methods for using bluing to check the surfaces by direct contact, although this is typically done in machinery reconditioning processes with granite plate and the cast iron machine parts. Reading info in the "machinery Reconditioning" forum may provide some ideas in this regard. Cleanliness is key in this arena.

specfab said:

As GBent states, using the Starrett plate as the reference for indicating the surface of the black plate is a good way to start out. I would use a .0001 indicator on a height gage or transfer stand to give the indicator a stable large footprint. There are also methods for using bluing to check the surfaces by direct contact, although this is typically done in machinery reconditioning processes with granite plate and the cast iron machine parts. Reading info in the "machinery Reconditioning" forum may provide some ideas in this regard. Cleanliness is key in this arena.

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The problem is that the blue contact will be very hard to see on the black granite. If i were doing it i would use a light colored transfer media like yellow Canode. You need not to worry about scratching the stone if you keep things clean, because you have the slippery transfer ink between the surfaces touching. You could also look for some very fine Titanium white powder pigment and mix it with some way oil to a fine paste consistency a bit thicker than latex paint and thinner than toothpaste. I do not know the stuff amazon sells but it is cheap.

Amazon.com: Titanium Dioxide / Fine Powder / 4 Ounces / 99.9% Pure / SHIPS FAST FROM USA: Sports & Outdoors


If you want to work your black stone you will need a lap and diamond abrasives.


If you just want to check the black stone to see if it is within a tenth or so. you can do it with a surface gage and tent indicator. read this thread...good educamtion....http://www.practicalmachinist.com/vb/general-archive/granite-flat-calibration-lapping-89744/
dee
;-D

dcsipo said:

The problem is that the blue contact will be very hard to see on the black granite. If i were doing it i would use a light colored transfer media like yellow Canode. You need not to worry about scratching the stone if you keep things clean, because you have the slippery transfer ink between the surfaces touching. You could also look for some very fine Titanium white powder pigment and mix it with some way oil to a fine paste consistency a bit thicker than latex paint and thinner than toothpaste. I do not know the stuff amazon sells but it is cheap.

Amazon.com: Titanium Dioxide / Fine Powder / 4 Ounces / 99.9% Pure / SHIPS FAST FROM USA: Sports & Outdoors


If you want to work your black stone you will need a lap and diamond abrasives.


If you just want to check the black stone to see if it is within a tenth or so. you can do it with a surface gage and tent indicator. read this thread...good educamtion....http://www.practicalmachinist.com/vb/general-archive/granite-flat-calibration-lapping-89744/
dee
;-D

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Thank you all for great suggestions. I have plenty of abrasive compounds of different grits and hardnesses ranging from 6o grit SiC to fine grit AlOx to diamond nano-powders; so no worries there. My biggest worry was scratching pink plate with my other one.

pcm81 said:

Thank you all for great suggestions. I have plenty of abrasive compounds of different grits and hardnesses ranging from 6o grit SiC to fine grit AlOx to diamond nano-powders; so no worries there. My biggest worry was scratching pink plate with my other one.

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IIRC the pink granite is said to be more wear resistant and black granite stiffer. So in the question of who is messing with who, I think your Starrett plate should be safe.

Which reminds me of the Dick Gregory quip (back when he was still funny). He said if whites are worried about black men messing with their women, just look at what's happening to the races. The white race isn't getting blacker. The black race is getting whiter.

Doh!

dcsipo said:

The problem is that the blue contact will be very hard to see on the black granite. If i were doing it i would use a light colored transfer media like yellow Canode. You need not to worry about scratching the stone if you keep things clean, because you have the slippery transfer ink between the surfaces touching. You could also look for some very fine Titanium white powder pigment and mix it with some way oil to a fine paste consistency a bit thicker than latex paint and thinner than toothpaste. I do not know the stuff amazon sells but it is cheap.





;-D

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Would canode yellow work well? I see it labeled as a "contact fluid rather than transfer fluid... is there a difference? Yesterday was the first time i got a chance to play with pursian blue; so i am a total newb...

pcm81 said:

Would canode yellow work well? I see it labeled as a "contact fluid rather than transfer fluid... is there a difference? Yesterday was the first time i got a chance to play with pursian blue; so i am a total newb...

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And that was supposed to be prussian blue, not pursian blue...

pcm81 said:

Would canode yellow work well? I see it labeled as a "contact fluid rather than transfer fluid... is there a difference? Yesterday was the first time i got a chance to play with pursian blue; so i am a total newb...

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I use Canode blue in combination with canode yellow for my scraping projects. The blue transfers very well. I assume the yellow is the same formula, so it should transfer well too. Not terribly expensive stuff. give it a try.


dee
;-D

The 'black rock' may well be gabbro. It's a similar hardness to granite, but stiffer and stronger. Don't knock it, it doesn't have Starrett's advertising budget behind it, but it's used for high grade surface plates by companies tha care about their reputation..

pcm81 said:

And that was supposed to be prussian blue, not pursian blue...

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LOL! Could use "Persian Orange". The classical Allis-Chalmers tractor paint.

More seriously... if neither plate shows discoloration, such a 'graying' on the black one, or worn areas obvious to a standard-issue Mark One human Eyeball, they are probably flatter than you - or MOST of us, really - have the skills or equipment - and above all borderline insane levels of patience and dedication - to make them.

My tiny 9" X 12" 1959 vintage 50-millionths flat Do All sez that is one-half the wavelength of visible AKA 'white' light. It is only used to vet other metrology goods, kept covered and protected for sometime several years between uses.

Workaday used B&S "B" grade 18" x 24" has obvious wear. If prepping a transfer straight edge, I simply avoid those areas.

The Herman 30" X 48" left the factory a very long time ago as a 4-ledge grade A. I'm happy the last calibration stickers show it was still such when the company as owned it went tits-up and it went off to a used equipment dealer, thence to me. Still and all, "perfect all over" it no longer is.

BFD. Once again - just avoid the dodgy coloration spots, and use the better areas.

When it even matters.

Which - for most of us, is damned seldom for the work we actually DO, not dream about.

Now.. if you actually have a NEED, then get a pro to make a service call with his Planikator, magical pixie dust collection, and half a lifetime of doing SP touch-up and issuing certs, all day, every day.

BTW: Any surface plate has to have set and stabilized for 'a while' before you even consider that. Closer to 24 days than 24 hours, that is.

No certs to be had, or no NEED of certs in your environment == no justification for the spend.

DIY?

Well.. have you done this before? Under expert on-site supervision? Flown off and taken a course in it?

Based only on 'interest', wish-for, and internet advice, even a fair-decent craftsman who has-never can f**k-up an average decent plate faster and more easily than improve it.

You just bought a decent Starrett? JF use it.

pcm81 said:

I am going to purchase an 18x12 pink granite grade A starrett plate. I have a 6x18 black stone plate that I am using now. I would like to "check" my current black stone (its not the real granite, its the cheap crappy black stone (Woodriver brand), what ever it's called) plate against the starrett, to continue using the 6x18 plate as my working plate and use the starrett as an inspection only plate. Is there a "proper" technique to checking one plate vs the other. My worry would be the 6x18 plate scratching the 12x18 starrett, since it is also a "hard" rock rather than "soft" metal...

If I am crazy and this should not be done, just say so. I admit, I am a total newb.

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Itd be a slight assumption but you could use the Starrett as a standard, and take a zero off it using a decent height gauge or indicator stand, on 3 feet over 5" would be ideal. Stick the indicator out 5", place it on the Starrett an set a zero, carefully remove and place on the 6x18 blackstone and see what you have. After youre, done carefully place your indicator back on the Starrett and check your zero. A lot depends you being savy enough to create a repeatable set up on the indicator.
GL

gbent and Deamon43 are on the right track. The surface plates should be flat enough that if put together with a marking medium you will have a great deal of difficulty separating them without sliding them apart, and sliding them will likely smear any markings. Even if you get reliable markings, you will not know how far out they are.

You will learn a lot more with an indicator. I would suggest using a magnetic base on a race from a tapered bearing- but not using the rollers or other end of the race. The idea is to have the ground face of the bearing on the plate, with the indicator set off to the side as Deamon73 has drawn out. Rotate the base in place 360 degrees, and the reading should be the same all the way around. Because the bearing face is a disk, the rotation will continue to contact the same part of the plate. As Deamon73 suggests, calibrate on the Starrett- after you check it using the assembly and are able to get repeatable results. Be sure and pick it up by the bearing race or the magnet portion, never the arm.

It is also possible to do an inspection with a sensitive level. Commercially this is done with electronic levels and software. It can be done with a sensitive bubble level if you have the time and patience. One thing to remember about levels, is that the sensitivity is stated for a given base length. A Starret 98-12 with a ground vial is marked for .005 in per foot. You can check this by putting a .003 feeler gage under one end, and a .008 gage under the other (.005 difference), and the bubble should have moved 1 graduation. Now move both feeler gages in 3 inches, so they are 6 inches apart, To have the bubble move 1 graduation, you have to have .a .0025 difference in feeler gages ( .004 and .0015). Suppose you have a 199 level, sensitive to .0005 per foot. That is .00004166 inches per inch. Set it on supports 7 inches apart, and each graduation is showing .00029. If you can estimate 1/3 of a graduation, you are in the .0001 ballpark. If you can estimate 1/10th of a graduation, you are looking at .00005 inches in a foot. I do not mean to imply that you can easily or casually measure to these numbers using a level- but if you set things up properly, you can find low or worn areas on your plate. If you decide to try this- take a close up picture of the bubble/graduations, then go online and print some graph paper with 10 graduations between the main lines. Put the graph paper on the image, with main lines on the graduations (angled so they will fit, and use the 10th lines to "read" the bubble location to 1/10th of a graduation.

Ooo bubble levels and surface plates, a controversial match here on PM . Im a believer, thats a very interesting method of reading the bubble . Could think of situations where it could come in very handy.

pcm81
If youve not already, give this video a watch. Lots of great info in there including a smaller plate being evaluated with a repeat meter / indicator.