Making granite parallels and squares - is any granite sufficient?

jccaclimber · Apr 9, 2021

To start with, this is more an exercise in gaining some experience than it is a need for calibrated tools. I do regularly use some shop made steel parallels, but it's a bit more work to keep them from rusting than I'd like, being magnetic is inconvenient for some of my work, and occasionally I find an inconvenient couple micron tall ding that has to be stoned out.

I have a surface grinder, diamond wheel, curiosity, and some time. I also have the ability to measure error better than I want to make it (1 to 2 µm would make me happy). Not set up to lap granite, but I'll work on that as needed.

The question is where to get stock. I could buy a few small import surface plates and cut them up for material, or I could try the local counter shop. What I'm wondering is if one granite is well close enough to the next, if a large vein of different quartz content is going to matter, etc. If both of these are a bad idea and I need to wait for second hand block from a more reputable manufacturer I'll do that.

I dug up an old thread here: <<https://www.practicalmachinist.com/vb/general-archive/granite-surface-plate-comparison-97695/#post300234>> that makes it sound like there's more variation in west coast vs. east coast "granite" varieties than I'm likely to find from one quarry to the next within an area. That makes me think seconds from the counter shop (assuming I can find them thick enough) will be just fine, but I figured I'd ask here first.

eKretz · Apr 9, 2021

I've gotten some scrap granite at counter shops to make a few things and there are some varieties that you would not want to make a surface plate accessory out of and some that look just like the stuff used for surface plates. Generally I'd avoid any granite that isn't very regularly grained and any that has a lot of coarse particles and large quartz inclusions. Look for uniform fine grained stuff.

And I don't know about your local places, but the place I mainly go to has a huge yard full of granite slabs, and wouldn't take payment for letting me look through and pick from their offcuts and cutouts piles, which were also monstrous. They let me take as much as I want at no charge. After I get some there I always give the counter guy a 10-spot anyway to get a couple beers or coffee and doughnuts at his preference. They always welcome me back so I guess the arrangement works both ways.

Milland · Apr 9, 2021

You can always check out local monument (grave stone) makers, they may have offcuts or spoiled pieces available.

And yes, the actual stone matters. New Hampshire is nicknamed "The Granite State", but much of our stone is "rotten", too gaseous and fragile to make ideal structural items from. We do have (or did have) active quarries, so there must be some good veins around, but it's not "dig anywhere and use what you find".

DavidScott · Apr 9, 2021

North of 95% of the "granites" at countertop shops is not granite, not enough quartz. You will have better luck at a monument shop. If it were me I would just cut up a surface plate for parallels, then you know you will have good granite for what you are making. Setting up to hand lap is easy, a flat and some loose diamond. Nice thing about granite is it will be real stable when surface grinding, just make sure the temperature of everything is the same, grinder, granite, and coolant. It will cut like warm butter with a diamond wheel, way easier than any metal.

M.B. Naegle · Apr 9, 2021

I have no experience in the matter, but it seems to me that most counter-top places like all the different patterns and quartz inclusions as it gives more character and color to the piece, while monument shops prefer more uniform material since it's a background and needs to not detract from the etchings they add, so I'd start with monument off-cuts.

Please post your progress with this project. IMO granite surface plates are not something to DIY given the amount of labor to hand lap every dimension and the material errors can compound on a larger piece, but smaller granite parallels and such is an interesting endeavor.

Mark Rand · Apr 9, 2021

Gabbro isn't granite. it has a much more consistent and finer texture than most granites. It's used for surface plates. On the plus side, it's stiffer than almost all granites, on the minus sure, the lack of quartz makes is more liable to abrasive wear.

On the gripping hand, it laps pretty quickly.

Kingbob · Apr 9, 2021

I've been to a few shop auctions and have seen lots of granite surface plates go for very little money. I've seen chipped and out of calibration 2' x '3 plates go for about $50. For what you are talking about doing I imagine one old plate would be a lifetime supply, it would be a shame to spoil your labor with poor material.

jccaclimber · Apr 9, 2021

Additional question, I was planning on slicing this up on a tile saw as I think that would make straighter cuts than on my (very small) diamond blade bandsaw. However, there is a waterjet sitting 20' from the grinder. Any reason not to just slice them up on that? I'll need to clean and square the surfaces regardless, so I don't know that the kerf will be a bigger issue with one method vs. the other. Normally I don't like removing a ton of stock on the grinder, but if granite grinds anything like the sharpening stones I've ground it will be a very fast process.

Orbital77 · Apr 9, 2021

jccaclimber said:
Additional question, I was planning on slicing this up on a tile saw as I think that would make straighter cuts than on my (very small) diamond blade bandsaw. However, there is a waterjet sitting 20' from the grinder. Any reason not to just slice them up on that? I'll need to clean and square the surfaces regardless, so I don't know that the kerf will be a bigger issue with one method vs. the other. Normally I don't like removing a ton of stock on the grinder, but if granite grinds anything like the sharpening stones I've ground it will be a very fast process.

I do make parallels from time. My advice would be to let a properly tooled business to cut and polish your parallels. It's dead easy for them and you'll get one side close to "done". You do not mention the size of the parallels you wnt to make - that's going to matter.
Unless they're very short it'll take quite a bit of time and A LOT of irritation to bring them into 1 or 2 microns per meter. If that's what you're shooting for. That's much easier to get with the right kind of ceramics and it's "better" all around.

jccaclimber · Apr 9, 2021

Orbital77 said:
I do make parallels from time. My advice would be to let a properly tooled business to cut and polish your parallels. It's dead easy for them and you'll get one side close to "done". You do not mention the size of the parallels you wnt to make - that's going to matter.
Unless they're very short it'll take quite a bit of time and A LOT of irritation to bring them into 1 or 2 microns per meter. If that's what you're shooting for. That's much easier to get with the right kind of ceramics and it's "better" all around.

Unless I'm misreading the standard a grade A parallel is closer to 8 microns/meter than it is 1 to 2, and that will likely exceed my needs. I'm planning on making these in the 6" to 9" range, although I could see making a 12" set if it's convenient at the time.

I have realized that while measuring parallelism in the long direction will be straight forward, measuring it in the short direction is a bit less straightforward. Also likely less important, but I'm open to ideas here.

jccaclimber · Apr 9, 2021

There are quite a few monument shops a few miles from here, unfortunately they are all appointment only due to the pandemic. Calling them all I didn't find any willing to sell even scraps. I did find out the supplier from one. They are unfortunately a bit over an hour away, so I don't want to just drop by. I was able to get them on the phone, but insisted they don't sell scraps and price for the smallest pieces they will sell are priced the same as an import surface plate delivered to my door. If they were closer/more open I suspect I might get a different answer, so I'll probably revisit if I decide to try this again in the future.

It's probably a function of my left coast location, but the local used surface plate market is also higher than the price of imports. I have no doubt that visiting auctions would net me a great deal eventually, but in the name of keeping this moving forward and not spending my weekends at auctions this may end up coming from an import surface plate.

There is one surplus building supply place nearby, so if I have an excuse to head in their direction I'll see if they have better options.

Orbital77 · Apr 9, 2021

jccaclimber said:
Unless I'm misreading the standard a grade A parallel is closer to 8 microns/meter than it is 1 to 2, and that will likely exceed my needs. I'm planning on making these in the 6" to 9" range, although I could see making a 12" set if it's convenient at the time.

I have realized that while measuring parallelism in the long direction will be straight forward, measuring it in the short direction is a bit less straightforward. Also likely less important, but I'm open to ideas here.

I am not familiar with American standards but 2 microns in 10" shouldn't be a problem. Perfectly doable. I never needed to measure on the width - the errors there would be simply too small. Keep an eye on humidity - can be an issue.

jccaclimber · Apr 9, 2021

Orbital77 said:
I am not familiar with American standards but 2 microns in 10" shouldn't be a problem. Perfectly doable. I never needed to measure on the width - the errors there would be simply too small. Keep an eye on humidity - can be an issue.

Does granite shift significantly with humidity or water absorption? I was planning to grind with a water based coolant to keep the wheel cool and dust down, but have not considered drying the parts before measuring? I always assumed moisture wasn’t an issue as many surface plate cleaners are water based, but I’ve never given it much thought.

EmanuelGoldstein · Apr 9, 2021

jccaclimber said:
... in the name of keeping this moving forward and not spending my weekends at auctions this may end up coming from an import surface plate.

Search craigslist for a pink one ? I know, shipping, but the color .... the pink ones look waycool.

TGTool · Apr 9, 2021

I was in a shop once that had a pink granite plate you could park a Volkswagen on. Shop was in the basement of an old industrial building and I inquired about how they'd got it in. The freight elevator was no where near qualified to lift it, but the brake was good enough to let it go down slowly. Once, at least.

Mr_CNC_guy · Apr 9, 2021

There are guys that grind granite in the field (cemetery

. They are the
guys that add the second name to grave stones after they are placed, that is
when the spouse dies. They have portable sand blasters in their truck to
do their work. Get a hold of one of them and they will surely know where
to get scrap granite.

woodchuckNJ · Apr 9, 2021

jccaclimber said:
Additional question, I was planning on slicing this up on a tile saw as I think that would make straighter cuts than on my (very small) diamond blade bandsaw. However, there is a waterjet sitting 20' from the grinder. Any reason not to just slice them up on that? I'll need to clean and square the surfaces regardless, so I don't know that the kerf will be a bigger issue with one method vs. the other. Normally I don't like removing a ton of stock on the grinder, but if granite grinds anything like the sharpening stones I've ground it will be a very fast process.

so water jetting definetly works. I was at a shop that was cutting counters a few years ago to talk to them about a bathroom vanity.

next, I polished my nook shelf and shower pan step using simple diamond polishing pads.. The stuff cuts easily. So I would think that you will have no problem with heavy machinery. Mine was with a hand held low speed grinder and my wife spraying water with a pressurized container.

I know that surface plate can be harder , but I don't think it will matter to the diamond grinding wheel.

obviously black granite softer, pink harder... I know that my black granite surface plate is slightly magnetic it an old Sherr plate. if you are bothered by magnetic, I would find out if others using pink find it magnetic. I find strong magnets slightly adhere to mine.

Orbital77 · Apr 10, 2021

jccaclimber said:
Does granite shift significantly with humidity or water absorption? I was planning to grind with a water based coolant to keep the wheel cool and dust down, but have not considered drying the parts before measuring? I always assumed moisture wasn’t an issue as many surface plate cleaners are water based, but I’ve never given it much thought.

I think it does, I noticed differences but I know not the mechanism. A geologist could be of help here. I know one and I will ask in a couple of days.

Rob F. · Apr 10, 2021

I got several headstones at a funeral home years ago, they were by the dumpster and had typos or something similar wrong. Funeral people did not want to lift them up into the can so they sat until I asked about them.

Also years ago I used to work building precision polishing machines, many of which had granite tables, most used water coolant, I dont think water should a worry.

Where in Ca are you? I think I still have 1 or 2 of those headstones....

jccaclimber · Apr 10, 2021

Rob F. said:
I got several headstones at a funeral home years ago, they were by the dumpster and had typos or something similar wrong. Funeral people did not want to lift them up into the can so they sat until I asked about them.

Also years ago I used to work building precision polishing machines, many of which had granite tables, most used water coolant, I dont think water should a worry.

Where in Ca are you? I think I still have 1 or 2 of those headstones....

I’m in the SF Bay Area.

Making granite parallels and squares - is any granite sufficient?

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