# Surface plate



## Rudy (Oct 5, 2017)

I havent owned or used a surface plate before. I found this one on aBay. Its of cast iron, hand scraped. Believe most surface plates are granite, but this one ships from China and will be a lot less expensive.
Anyone know if this type of surface plate is adequate for model engineering?
http://www.ebay.com/itm/202036207677


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## kvom (Oct 5, 2017)

Model engineering doesn't often require micron level tolerances, and many people have used things like plate glass.  That chinese one should be more than adequate.


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## Blogwitch (Oct 5, 2017)

Like Kvom has stated, unless you are working in a high precision laboratory, then almost any near flat surface will do. I used a glass platten out of a copying machine for many years until I realised they don't like heavy bits of steel dropping on them.

If you are just going to be using it for marking out or measuring somewhere near (5/10ths), then bear in mind that a scribed line will be about 0.002" wide, so making a mockery of quoted 1 or 2/10ths flatness.

John


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## Sansspaceship (Oct 5, 2017)

Hi Rudy,

Went through this process recently myself as I had granite plate that i had inherited. I was looking at getting it restored as it had been damaged. Rang around and was told just to buy a new one, as not worth the effort. Ended up with one 45cmx45cmx7.5cm @45kg and think it was $300aud which would be circa $216usd. Think it was out of India as well (although bought from Australian supplier), came with a calibration (map) certificate and think it was better than 0.0001.

I actually think it is a good tool to have in the shop, for those times u need something measured accurately and for checking square and 

parallelism.  That said Kvom does make a point, could be done other 
ways. But like everything a nice to have when u want a dead nuts flat 
surface, and for the $$ the reality is probably have more expensive tools 
in the shop that get used less.

Just a make sure u keep it covered when not in use.

Cheers,
Adrian


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## bazmak (Oct 5, 2017)

I bought a sink offcut of 40mm granite for $10,he even polished the edges
Works well for me The ground surface is as accurate as you will ever need
for marking out and even scraping etc. About 700x 400.I have even cut off 
a couple of pieces as a base to mount a model on


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## Wizard69 (Oct 5, 2017)

I picked up a small "granite" one from Grizzly a few years ago and it cost me less than $50, if I remember correctly $39.    So my first thought is that that is one expensive surface plate for what most model engineers are likely to need.   I suppose the value of the plate will vary a bit with your intended usage but for me I have many other things to buy if I'm ever to get a shop together to pursue this sort of hobby.




Rudy said:


> I havent owned or used a surface plate before. I found this one on aBay. Its of cast iron, hand scraped. Believe most surface plates are granite, but this one ships from China and will be a lot less expensive.


Unless the market has changed remarkably in the past couple of years that is one expensive plate for what you will likely need.   Like I said above I got a small rectangular granite block for well under $50, this was about the same size as what you have here.


> Anyone know if this type of surface plate is adequate for model engineering?
> http://www.ebay.com/itm/202036207677



It probably is.   

On the other hand it is cast-iron which can age and stress relieve over the years.    This means that it can warp slightly needing to be scrapped in again.  Thus if you really want tp buy this plate I'd suggest buying three so that you can use the three plate technique to keep them flat.    This can be as much an advantage for cast-iron plates as a disadvantage, because you can always return them to pristine  flatness, with a scrapper, if you have a set of plates.

There are a couple of realities that tome with surface pates in general.   #1 is that the are heavy which makes me wonder about shipping costs for this plate.    #2 you need to size the plate based on your needs and usage.   A 12 inch plate might be a bit small.

Speaking of usages, once you have a plate unexpected usages pop into existence.   for example in the wood working world (WWW hahaha) they are often used in conjunction with very fine grades sand paper to sharpen various types of blades and cutters.    Similarly they can be used in lapping operations to flatten matting surfaces and clean up tooling marks.   So just don't think of them as a solution to marking out.    Also a cast-iron table like this can function as an assembly table for delicate mechanical works.   The ability to clamp to it or use magnets allows for a lot of versatility.


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## Rudy (Oct 6, 2017)

Thank you very much guys, for very educating posts.. I'm learning more now than ever.
Know what? Think I will go get me a piece of thick glas. Use it until I get my own ideas about the needs I really have.


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## bazmak (Oct 6, 2017)

I have a natural aversion to to a glass plate. Glass is not accurately flat
and is danger to breakage.If you can get a sink cutout of any stone
worktop material it would be better.And ground very precise for some
reason


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## Rudy (Oct 6, 2017)

bazmak, I noticed that. I simply had problems believing bench plates are flat. Glossy ok, but the flatness? I kind of think it would be dependent upon the very machine the plate was grinded. However, I'm believing her, not knowing.


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## Hopper (Oct 6, 2017)

Bit of thick plate glass scrounged from the tip has served me well for many years.


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## DJP (Oct 6, 2017)

I saw a Youtube demo of a glass plate being used to tram a mill. You can get 360 degree sweep of a dial indicator attached to the quill and no parallels or slots to traverse. I haven't tried it yet but for my level of accuracy it may be sufficient.

So double duty for a small flat surface plate.


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## Sansspaceship (Oct 6, 2017)

bazmak said:


> I have a natural aversion to to a glass plate. Glass is not accurately flat
> and is danger to breakage.If you can get a sink cutout of any stone
> worktop material it would be better.And ground very precise for some
> reason



+1 on not using glass, but comes down to what accuracy you want. I will occasionally need to do an out side job that I need to check for parallism; not crazy accuracy where you have to worry about things like temperature control etc, but enough that I want a good starting point. 

I think if you wanted enough accuracy say for lapping, and u used a piece
 of glass u would be for forever chasing your tail, with normal run of the mill plate glass.  That said I have not tried it, as always used a flat plate.... so I could be wrong and happy to be put back in my box, by someone who has done it. :hDe:

Also another use is bluing, this is ideally where u want a metal flat plate 
as for this task I consider them better than granite but probably the only + side in my opinion.

Cheers,
.adrian


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## Sansspaceship (Oct 6, 2017)

DJP said:


> I saw a Youtube demo of a glass plate being used to tram a mill. You can get 360 degree sweep of a dial indicator attached to the quill and no parallels or slots to traverse. I haven't tried it yet but for my level of accuracy it may be sufficient.
> 
> So double duty for a small flat surface plate.



Haven't seen the video but suspect it may be an inspection optical flat - that will be flat!

But get your cheque book out. 

Edit - found some references on line, and apparently quite common for  people to tram with a normal sheet of plate glass....


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## nautilus29 (Oct 7, 2017)

Has anyone tried a piece of granite or marble flooring?  I've been tempted to buy a couple of pieces to see how flat they are.  They are around $2.5 for a 12"X12" square around ¼ to &#8540; thick.  I thought maybe they'd make a good  sanding plate or small scribe table if they are flat.


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## Wizard69 (Oct 7, 2017)

nautilus29 said:


> Has anyone tried a piece of granite or marble flooring?  I've been tempted to buy a couple of pieces to see how flat they are.  They are around $2.5 for a 12"X12" square around ¼ to &#8540; thick.  I thought maybe they'd make a good  sanding plate or small scribe table if they are flat.



I can't say that I've tired such but the problem you will have with any materials as it gets thin is flexing.   Also flatness out of the box varies widely unlike counter top remnants that are normally polished to pretty good flatness.


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## bazmak (Oct 7, 2017)

A granite countertop is normally 30/40mm thick which is ideal and CHEAP
The cutout for the sink is usually the ideal size and almost throwaway price
I cut off a couple of pieces for model engine bases,and as wizard say is 
very accurately ground flat where glass is not.Dont know if they still use the mercury float methaod for plate glass. If you note that thick granite of say 100mm is very expensive and accurate. Between cast iron and granite i 
dont know which is considered best


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## Cogsy (Oct 8, 2017)

I expect (but don't know for sure) the optical glass from a quality (expensive) scanner would be as flat or flatter than a kitchen counter top. However, I just use a granite chopping board that I purchased damaged for a whole $5 - someone had dropped it and broken a chunk out of one corner. It's flat enough for what I do but I'd hesitate to call it a 'surface plate'.


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## bazmak (Oct 8, 2017)

Depends on what you call a surface plate. Its perfect for marking out
with a height gauge etc but dont know how accurate for scraping etc
Good enough for most engineers.As for a piece of 3mm scanner glass
being better ,i dont think so,glass actually bends over its own weight
I was very interested in the mount palomar telescope and making the mirror
Cast in glass and weighing many tons it took 2 weeks to let cool down or normallise. Look at the problems with the Hubble telescope. But its out of 
our league. There is flat,optical flat and VERY OPTICAL FLAT


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## Wizard69 (Oct 8, 2017)

OXTOOL recently ran a series on YouTube related to making lapping plates using the three plate method.   While the plates are somewhat small in diameter the idea may be useful to a model engineer as a lapping plate often has the same tolerances as a surface plate.   The nice part is he approached the issue from the standpoint of somebody with very limited tooling or machinery.    The cast-iron disks came from one of the big online suppliers.

The point here is that making your own is a real possibility.   By doing so you can choose whatever material you would like to use.   I'm still of the opinion that buying makes sense as good enough for our needs means spending someplace between $30 & $50 for a granite surface plates.    Something that will last forever in a home shop.


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## DJP (Oct 8, 2017)

I have also heard of tramming mill by using the rotor for front brakes of a car. A new rotor for sure and I happen to have a couple from a car that was recently sold. Beats glass for durability and still provides 360 degree swing of a dial gauge.

I like practical solutions for my home machine shop as with old worn machines it will never be an high accuracy operation.


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## bazmak (Oct 8, 2017)

I used my 9" faceplate from the lathe for tramming.Amongst other things


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## Cogsy (Oct 8, 2017)

I didn't think about my brake disk. Good old ebay got me a brand new one for about $35 delivered and it gives me a nice big 360 degree swing for tramming. I forget what flatness I measured it at when I got it (by taking tram readings then rotating the disk and repeating), but it was good enough that I didn't mark it for future orientation.

I agree the glass will flex a lot on its own. It needs to be backed by something reasonable flat as well, but it's not flexible enough to conform to the underlying shape of an object. So placed on top of a granite block would be as close to perfect as I could expect to get in my shed. If I remember I'll try and take some measurements at some point.


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## bazmak (Oct 9, 2017)

Your defeating the object of the excercise.If you need to put flat granite under glass why bother


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## Herbiev (Oct 9, 2017)

We have a company here that make headstones. Their bin is full of good offcuts


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## Cogsy (Oct 10, 2017)

Baz - it doesn't have to be flat granite, just flat-ish to support the flat glass so it doesn't flex.

Herbie - that sounds like a very good idea. I might just head off to the mason works near the cemetery next time I'm out that way.


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## Rudy (Feb 7, 2018)

Many good alternatives to make a surface plate here. Anyway, this is what I ended up with. A big slab og granite. After searching the net for plates no suppliers could send such a heavy (56kg) item within reasonable costs. This one however, is coming from Chronos Ltd Engineering Tools in the UK and shipping cost to Norway was £48 (+VAT). And this is the whole point. The price of the plate is also reasonable at $66 +VAT.
I guess this will serve me even long after I have gone. Just carve my name to it and put it upright. Talk about investment beyond life! (I actually might like that thought &#128522;.
I opted for a plate with known flatness since Im very interested in high accuracy. Im already stressing my machines accuracy capabilities. Having confidence in the measurements is there for something I find valuable. This stone is 40x40x10 cm and comes with a map showing max deviation of 2,2um. That is probably good for any model engineering. Chronos also have a 45x45cm at about the same price, but it was out of stock so I got this one.
Credit to Chronos for having a very reasonable and fast shipping method nobody else bothered to arrange for.

Rudy


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## Ghosty (Feb 7, 2018)

Hi All,
I used to have a 18" square X 1" thick ground glass plate, It got "lost" in one of my moves, I had it for almost 30 years, I ended up going to the kitchen build/supply place and got a 400mm x 400mm x 20mm marble tile, only cost $40, and is polished on both sides

Cheers
Andrew


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