Cutting a granite surface plate into straight edges

I have found many threads talking about cutting a granite surface plate down, but have not found any that have actually done it. I hope this thread does not suffer a similar fate.

Background:

After taking the 3 day Maryland / Tuckahoe scraping class with Richard King (which was well worth it, although regretfully I could not stay for the full 5 days), I ended up with a mill table that was fairly well documented to be worn in the middle (big surprise there). Not having a large surface plate or straight edge long enough for the table, I have been on a search for said items in order to finish up the work. This is not my day job, so picking up the phone and ordering was not in the cards.

After looking for a while, I came across a Craigslist 'find', the past history of which is a bit foggy as to how things got into the state they are. It involves some aircraft part shop in western Maryland, a retiring machinist, who then later passes away, and the cleaning out of the shop which resulted in the plates sitting under a rollback in the drive. That's about all I know there.

Two Scherr-Tumico Ultra-Flat surface plate, one 24x36x4, and one 18x24x2 3/4. They are both, well, let's say far from pristine.

I do not know if sitting buried down 1" in mud counts as being well supported at their airy points. Maybe. Kind of like grouting something in place?
Number of chips on their edges and sides (which are beveled).
Many chips in the surfaces, along with some rust stains and grease.
Many scratches of all depths for most of the surface.

Neither sticker had an accuracy or grade listed. Whatever they might have been, they are not any longer.

As a rough start, I plan on trying to print one against the other, just for grins, not sure if anything can be learned from that.


Now, as to the question:

I will probably keep the 18x24 plate, and try to qualify it in some way.

The 24x36" plate however... I have a local stone shop that has a 18" blade automated saw. In first discussions, they gave the impression that slicing it up into pieces is not a big deal, and they can price it per cut pretty easily. Their first guess was reasonable. They also have the ability to grind the surface, but with a 1.5" stone on a robot arm, and would have to make several passes, but could do it. They of course cannot give any sort of accuracy numbers, since they go for 'shiny and smooth'.

I will take the plate over to them, and get firm costs, but if it actually does pan out, is there any market for straight edges made from slicing a surface plate? I was going to go with around 10 pieces, 35" long (clean off the bevel end), 4" high and either 1.5 or 2" wide. Maybe with two holes, each on center line about 30% in, about 1" diameter? Just one surface, the top, would be original, others saw cut, but still fairly nice finish.

Again, I have not found any results from anyone actually trying this, so if someone has, please let me know the results.

Would there be any interest in 'rough' granite straight edge blanks? I know the price would vary with how accurate / good they turn out, but I could print groups of three to get an idea of accuracy (so some level at least).

Thoughts?

Comments?

Flames?

Thanks in advance for any and all.


I have not found much on the Scherr-Tumico plates, don't seem to be too common, but in general the company made good quality.

Matt

And the mandatory photos.

If they won't/can't certify straightness, what's the point?

Just like buying a raw casting or milled surface cast iron straight edge. You need to do the final work yourself. Just need to lap it in, rather than scrape.

Hopefully Richard will comment on the sensibility of finishing a granite straight edge, but other than a different technique to remove metal should be the same principle.

Except perhaps, 'ringing out the stresses' by hammering it wouldn't be such a good idea.

You only need one flat side, use the original ground flat side. I would guess a 2" thick chunk may be alittle unstable. That's why there 4" , I'm just guessing, hopefully a knowledge person will post. Good luck.

OK, they are granite. So they can crack, chip, scratch, and wear. Of those, only crack and wear are going to destroy the flatness or straightness of the surface. Cutting them should not change the straightness of the "flat" surface. Granite does not distort like a metal would.

And storing them, a loose use of the term, without proper support is not going to have any effect on the flatness. They only need to be properly supported while in use, not in storage or shipping. But, the flatness was originally figured and certified while they were properly supported so when you cut them into strips for straight edges, you destroy that method of support and they will not be as flat or straight as the original certification. In lay terms, they will sag differently. I would not trust such a straight edge unless it was certified.

There are services that will come to your site and re-figure and certify a surface plate. But in the sizes you are talking about, it would probably be less expensive to just buy new ones.

As for that local stone shop re-grinding them, that will probably result in their being FAR less flat then they are now. As said above, they go for shiny. They can not even begin to measure flatness much less produce it.

If you could find a third plate or a scrap of granite from one of those local stone companies, you possibly could lap all three together until they are flat. But it is going to be some work. If you value your time even at minimum wage, it is probably less expensive to just buy new plates.

You would be far ahead to go get a part time job at Mcdonalds for a couple of months and just go and buy a straight edge.

Sawing them up is the easy part, surface plate granites are very easy to work with. The granite used is picked for stability and wear resistance so they may not distort when sawed into strips. I would think it is worth a try and then just measure them for flatness. I'm also in the camp of only have them saw the rails, nothing else.

Matt,

Get them resurfaced, put them on points and then find e piece of iron you can scrape to it. Ask on the metrology page who does surface plate reconditioning in MD. It is like 300 to 400 bucks to get them to AA level for both, maybe less if you are willing to drive it there drop it off and pick it up. And it is certified. Someone like these guys in York PA can give you a quote

Surface Plates | Calibration Resurfacing

If you have the room having an AA 24x36 plate can be invaluable. You can pick up a 36" granite SE for pittens, or you can just make one out of almost anY old lathe bed.

dee
;-D

dcsipo said:

...You can pick up a 36" granite SE for pittens, or you can just make one out of almost anY old lathe bed.

dee
;-D

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Maybe a use for that "forbidden brand"..... It has flat ways, and so starts out right..... Saw that sucker down the middle and who knows?

Buying a decent SE seems a tad more reasonable though.... Time is money.

I did once make a right angle reference the hard way using 3 and scraping them to each other. Just little ones about 5" on a side, and it was a pain... I only did it to see how it went, and once I started I had to finish it.

Turned out OK, and I use the piece, but my advice is definitely "don't go there".

dcsipo said:

Matt,

Get them resurfaced, put them on points and then find e piece of iron you can scrape to it. Ask on the metrology page who does surface plate reconditioning in MD. It is like 300 to 400 bucks to get them to AA level for both, maybe less if you are willing to drive it there drop it off and pick it up. And it is certified. Someone like these guys in York PA can give you a quote

Surface Plates | Calibration Resurfacing

If you have the room having an AA 24x36 plate can be invaluable. You can pick up a 36" granite SE for pittens, or you can just make one out of almost anY old lathe bed.

dee
;-D

Click to expand...

I say give it a try. if you can get them lapped locally. call that company and ask them if they can lap them. You could cut a 45 deg. on one end and see if the can lap the side and top. The top is probably straighter then the side, but I bet the side is within .005"

I have often thought about doing the same thing and even using a diamond concrete saw. Get a price and I would be willing to toss in a hundred or 2 just to see if it can be done.

Maybe they could make you a good set of parallels too. I was also think Polao lives up near you and maybe you could take one of his scraped straight-edges over to the stone cutter and blue up one of the head-stones and see how flat they can get them.

I think it would be well worth finding this out as you can buy used granite plates super cheap. Rich

It wasn't to long ago there was a thread here where someone tested a counter top granite and found it a straight area gauge straight and it also a dip that was off in another area. So I think this a good idea to try, but it would have to be tested before trusted. But one side flatness might be made easier then opposite sides being dead parallel. I could likely grind a 20" or 24" granite parallel within .0002 on my B&S. Perhaps give it a try next summer.

Other options get it ripped into strips, lay them nicely together supported on airy point and call for your 20 strip surface plate to be lapped :-)

My only concerns the effort your putting into old plates, granite plates are pretty cheap new, buying a good one and sawing up is only going to add like $40 raw material cost per straight edge. Why use a knackered plate to start?

I could cut them all day long since that's what I do for a living. Shipping might be a bit tasty though

Peter. said:

I could cut them all day long since that's what I do for a living. Shipping might be a bit tasty though

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How about telling and showing us with pictures us more about how you cut them? It would be interesting as heck knowing more and do you grind and lap them too. Use them for precision surface plates? Or headstones??

adama said:

Other options get it ripped into strips, lay them nicely together supported on airy point and call for your 20 strip surface plate to be lapped :-)

My only concerns the effort your putting into old plates, granite plates are pretty cheap new, buying a good one and sawing up is only going to add like $40 raw material cost per straight edge. Why use a knackered plate to start?

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Our plate guy said the time and diamonds to save a bad plate made some a throw away.. I don't remember the number.

Seeing this thread again, and recalling some responses, emphasized my thought that the whole deal is not worth dicking with.

Why go to trouble to do that, when you can buy a certified one for the same sort of total money after all the stuff AFTER doing the sawing up?

Richard King said:

How about telling and showing us with pictures us more about how you cut them? It would be interesting as heck knowing more and do you grind and lap them too. Use them for precision surface plates? Or headstones??

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Beg your pardon Rich I cut concrete for a living, but I have on occasion had to cut granite and it's no different in the process.

This week I have been saw cutting on the foundation of the largest brick building in Europe.

Granite is not as rigid as you might think. Copper is about twice as rigid as granite, cast iron three times, and steel four times as rigid. Carbide is 10x as rigid as granite.

In terms of cheapness versus rigidity versus corrosion resistance, cro-moly is probably the best material for a straightedge. No idea why people don't make straightedges out of cro moly.

michiganbuck said:

Our plate guy said the time and diamonds to save a bad plate made some a throw away.. I don't remember the number.

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Time maybe, diamond grits so cheap its akin to irrelevant, a tea spoon of 60 grit diamond would easily remove a square foot of granite a good 1" thick or probably a lot more. Would not want to do that by hand. a Sintered 5" diamond grinding disc will easily take a 1/8" of 240 square feet of concrete and not be far short of that in granite. Wet grinding concrete i can easily do flat within a mm over a couple of feet with my free hand wet diamond polisher, bit more care and i could easily get a typical 3x4' surface plate to less than that and in under a hour too. Diamond chews through granite and concrete fast, yeah technically the granites a lot harder, but you would be surprised how little difference there is in cutting speed.

Would not want to have to take off even half a mm of granite with a hand lap on a 3x4' plate though!