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Glass surface plate

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Camnefdt

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#1
Hey guys

I am needing some parts to be made as flat, parallel and square as possible.

Here in South Africa it is just not economical to purchase a surface plate, cast iron or granite.

They start at around R16000 zar for a small one which is around 1000 usd

I can get a piece of laminated glass free and was wondering if anybody has actually used or tested the accuracy of glass in general as a surface plate.

I have searched for it and found a couple people talking about it, but none having actually done it yet.

I don't need accuracy to the millionths but looking at getting within 0.01mm of flat, parallel and square
 

T Bredehoft

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#2
The theory is that you start with three equal sized plates, heavy laminated glass will do. Number them on the back with something permanent, 1, 2, 3. Using lapping compound, work them together, 1 and 2 then 1 and 3 then 2 and 3. repeat until all three are equally flat. Check with blue (whatever its called). Then you have three fairly good surface plates. Not easy, but surely cheaper than buying. They will get you flat. Parallel and square are different.
 

pstemari

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#3
Glass is pretty flexible. Laminated safety glass is not going to give you a decent degree of flatness in the usual thicknesses. There's some architectural stuff that's thick enough to be decently rigid, but I don't know how flat it really is.

Sent from my Pixel XL using Tapatalk
 

Camnefdt

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#4
The theory is that you start with three equal sized plates, heavy laminated glass will do. Number them on the back with something permanent, 1, 2, 3. Using lapping compound, work them together, 1 and 2 then 1 and 3 then 2 and 3. repeat until all three are equally flat. Check with blue (whatever its called). Then you have three fairly good surface plates. Not easy, but surely cheaper than buying. They will get you flat. Parallel and square are different.
Can only get one piece, roughly 500x500mm so wont even be able to cut it smaller.

Parallel and square I can do, ive got DTI for that. I can even do flat, but not to the accuracy that I want and can get with a surface plate.
 

Bob Korves

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#5
Plate glass is ground pretty flat, depending on the quality of the grind. It is usually polished after grinding, which does not often improve the flatness, and often makes it worse (but shiny.) It is, however, quite flexible unless it is seriously thick. It is expensive.

Float glass is floated on melted Zinc or similar:
https://en.wikipedia.org/wiki/Float_glass
It is usually done in a continuous process where it is lifted off the molten metal onto rollers, which provide the surface finish and accuracy, which is less flat and parallel than plate glass.

Machinists also ask about using granite counter tops, or the imitation ones for flat surfaces. Sorry, they test quite poorly.

I hate to rain on your parade, but none of those approaches is going to get you something reliably flat from other than metrology supply sources, at similar prices or higher than granite surface plates.

Metrology is not about "how do I get something cheap to work?" It is about carefully controlled standards, careful testing with the proper equipment and well honed technician skills. and careful comparison with known standards. Quick and dirty is not the equivalent of carefully testing to a reliably known result.

Also, the three plate method is quite a bit more complicated than Tom's simple overview. It is often undertaken, but almost never completed to true and metrology standards. If they had the standards, they would not need to make them... and, how do you test them without standards?

How big are the parts you want to make flat, what materials are they, and what official standard do they need to meet, if any?

Why are granite surface plates not available in South Africa? What makes them so expensive there?
 

Camnefdt

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#6
Plate glass is ground pretty flat, depending on the quality of the grind. It is usually polished after grinding, which does not often improve the flatness, and often makes it worse (but shiny.) It is, however, quite flexible unless it is seriously thick. It is expensive.

Float glass is floated on melted Zinc or similar:
https://en.wikipedia.org/wiki/Float_glass
It is usually done in a continuous process where it is lifted off the molten metal onto rollers, which provide the surface finish and accuracy, which is less flat and parallel than plate glass.

Machinists also ask about using granite counter tops, or the imitation ones for flat surfaces. Sorry, they test quite poorly.

I hate to rain on your parade, but none of those approaches is going to get you something reliably flat from other than metrology supply sources, at similar prices or higher than granite surface plates.

Metrology is not about "how do I get something cheap to work?" It is about carefully controlled standards, careful testing with the proper equipment and well honed technician skills. and careful comparison with known standards. Quick and dirty is not the equivalent of carefully testing to a reliably known result.

Also, the three plate method is quite a bit more complicated than Tom's simple overview. It is often undertaken, but almost never completed to true and metrology standards. If they had the standards, they would not need to make them... and, how do you test them without standards?

How big are the parts you want to make flat, what materials are they, and what official standard do they need to meet, if any?

Why are granite surface plates not available in South Africa? What makes them so expensive there?
They are available here but i have no idea why they are so expensive. Everything fun here is expensive haha.

Biggest piece i will need to work on is 200mm x 300mm and made from cast iron. Its a project that im busy planning out which the parts need to align together as flat and accurate as I can get but dont need to be extreme.

Will only start properly planning parts if I can figure out a reasonable way of getting a flat surface to work from
 

Camnefdt

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#7
One of the main reasons for asking about the glass is that its something i can get for free and with my extreme space constraints, can be stored easily
 

Bob Korves

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#8
They are available here but i have no idea why they are so expensive. Everything fun here is expensive haha.

Biggest piece i will need to work on is 200mm x 300mm and made from cast iron. Its a project that im busy planning out which the parts need to align together as flat and accurate as I can get but dont need to be extreme.

Will only start properly planning parts if I can figure out a reasonable way of getting a flat surface to work from
Well, try some plate glass, the thicker the better, or even two thicknesses. Use it and store it carefully, glass is pretty soft and it will warp if not stored vertically or on an equally flat surface.

Here in the U.S., we can get machinist stuff shipped direct from China from sites like Banggood and AliExpress for incredibly cheap prices and amazingly low shipping costs. Is that not a possibility in SA? Unfortunately, neither sells surface plates.
Maybe something through Alibaba? https://www.alibaba.com/showroom/surface-plate.html
 

Camnefdt

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Well, try some plate glass, the thicker the better, or even two thicknesses. Use it and store it carefully, glass is pretty soft and it will warp if not stored vertically or on an equally flat surface.

Here in the U.S., we can get machinist stuff shipped direct from China from sites like Banggood and AliExpress for incredibly cheap prices and amazingly low shipping costs. Is that not a possibility in SA? Unfortunately, neither sells surface plates.
Maybe something through Alibaba? https://www.alibaba.com/showroom/surface-plate.html
I can get through all those chinese places too, shipping isn't too bad. But as you say, they dont have surface plates.

Im still searching for a possible import, but like I tried shars cause their prices are reasonable, but for their $22 9" x 12" plate its $1000 in shipping to get it to me.
 

fvdbergh

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#12
Hey guys

I am needing some parts to be made as flat, parallel and square as possible.

Here in South Africa it is just not economical to purchase a surface plate, cast iron or granite.

They start at around R16000 zar for a small one which is around 1000 usd

I can get a piece of laminated glass free and was wondering if anybody has actually used or tested the accuracy of glass in general as a surface plate.

I have searched for it and found a couple people talking about it, but none having actually done it yet.

I don't need accuracy to the millionths but looking at getting within 0.01mm of flat, parallel and square
I bought a 300x300x70mm granite plate from Gem tool company in Pretoria (https://www.gemtool.co.za) about three years ago for only about R500. The inspection certificate claims it has a maximum deviation of 2.6 micron, which is probably good enough for the average hobbyist.
 

Camnefdt

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I bought a 300x300x70mm granite plate from Gem tool company in Pretoria (https://www.gemtool.co.za) about three years ago for only about R500. The inspection certificate claims it has a maximum deviation of 2.6 micron, which is probably good enough for the average hobbyist.
Oh nice! Ill check them out and see!
 

Round in circles

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#14
They are available here but i have no idea why they are so expensive. Everything fun here is expensive haha.

Biggest piece i will need to work on is 200mm x 300mm and made from cast iron. Its a project that im busy planning out which the parts need to align together as flat and accurate as I can get but dont need to be extreme.

Will only start properly planning parts if I can figure out a reasonable way of getting a flat surface to work from
Can you get a weld reinforced 3/4 "2 thick steel plate ? Fly cut the face on a warmed up milling machine of reasonable accuracy . It wont matter if the reinforcing is not dead parallel to the fly cut face as it's just the single cut plane you're wanting to use. Perhaps set the fly cut part in a 4 " slab of mesh reinforced concrete & use an engineers spirit level to get it true all round if you need it nearly true flat in all planes
 

Camnefdt

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Can you get a weld reinforced 3/4 "2 thick steel plate ? Fly cut the face on a warmed up milling machine of reasonable accuracy . It wont matter if the reinforcing is not dead parallel to the fly cut face as it's just the single cut plane you're wanting to use. Perhaps set the fly cut part in a 4 " slab of mesh reinforced concrete & use an engineers spirit level to get it true all round if you need it nearly true flat in all planes
Unfortunately all my projects have been placed on hold, going to be moving soon. Will have to see if i can get this done. But I'm also moving to a bigger city which will have more chance to find a second hand surface plate from somewhere.

To get a shop to mill off a plate will be just as expensive as buying. But will see what I dan do once ive moved and set up again!
 

brino

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#16
Unfortunately all my projects have been placed on hold, going to be moving soon.
Best of luck with the move. I hope everything goes smoothly and according to plan.

I'm also moving to a bigger city which will have more chance to find a second hand surface plate from somewhere.
I hope you find a bigger pool of both new and used equipment.....and a bigger shop to enjoy it in!
-brino
 

Camnefdt

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#17
Best of luck with the move. I hope everything goes smoothly and according to plan.


I hope you find a bigger pool of both new and used equipment.....and a bigger shop to enjoy it in!
-brino
Thanks!

Moving back with my parents to start studying again, will have full and sole use of a 2.5 car garage.

Will also be on the look out for auctions, hopefully get some good deals there! Would be over the moon if i could find a milling machine within budget haha
 

Richard King 2

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#18
Have you checked with Granite Grave Stone Markers, They are pretty close. I had a student make a surface plate from one. It was 36" x 36" and 4" thick. He made a stand with set it on 3 points. We used a precision level to test it looking for the flat part of the plate and we found a section that was with-in .0002"
 

Camnefdt

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#19
Have you checked with Granite Grave Stone Markers, They are pretty close. I had a student make a surface plate from one. It was 36" x 36" and 4" thick. He made a stand with set it on 3 points. We used a precision level to test it looking for the flat part of the plate and we found a section that was with-in .0002"
Will have a look around once the move is done
 
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