Surface table alternative?

[Steve WanParticipant @stevewan33894]

[Steve WanParticipant @stevewan33894]

Hi guys,

Has anyone used a normal small granite/ceramic tiles working as a surface table instead of a cast iron or engineering granite slab? Wonder is it possible using a leftover tile with a smooth surface acting as a reference plane for checking flatness via scraping. Since this job is rarely done, cheaper this way than buying one. Most suitable for Sherline small range of work…

Any comments?

Steve

[SpringbokParticipant @springbok]

Hi Steve

I use a large sheet of plate glass think they call it float glass have had it for years and works a treat
it is about 3/16" thick, came from a large computer (IBM) cabinet.
Bob

[John ShepherdParticipant @johnshepherd38883]

Steve

I saw a similar question on another forum and followed the advice to use an offcut of granite worktop (the bits they cut out for the hob/sink).

Unfortunately the piece I got was far from flat on its finished surface and was useless for the job. I reverted back to using a piece of flat float glass mounted on a board.

Regards

[John CoatesParticipant @johncoates48577]

Steve

I had better luck than JS with my granite worktop piece. Cost me £15 for a piece about 12" x 18" and 3/4" thick. Glued it to an MDF board and one day I will get round to gluing some angle edging onto it to smarten it up

John

[Phil H 1Participant @philh1]

Steve,

I have very successfully used an old ships porthole glass. Its about 1" thick glass and appears to be very flat. My only issue is that its diameter is a bit small so I will be looking for something a touch larger. I was thinking of looking for a bigger piece of glass (nice and thick though) or even looking at an offcut from a piece of granite kitchen worktop.

I hadn't thought about a reasonable sized tile – I will investigate.

These ideas are obviously not as good as a proper surface plate but what accuracy are we trying to achieve? I guess neither of us have a full box of certified slip gauges either?

Phil H

[LambtonParticipant @lambton]

Try your local monumental masons. I was given an off cut of polished marble about 12" x !8" that is very flat. You can easily test for flatness by studying the reflection of a window or fluorescent lights etc. any distortion indicates a lack of flatness. The designers of cars use a similar but more sophisticated technique called "zebra boarding" to detect distortions in body panel curves.

[BaldricParticipant @baldric]

It has been suggested to me that one of the granite type kitchen worktop savers (chopping board) you get in a supermarket for about £15 are ground flat, this has seemd to be true with the one I have.

[John HaineParticipant @johnhaine32865]

6mm float glass is as flat as you can easily get, cheap and easily available. It does get scratched after a while and will need replacing.

[Gordon WParticipant @gordonw]

Depends how big a plate you need. Brake discs are good and cheap. I use the cast iron top plate of an old solid fuel stove, about 8" x 16". Not deadflat but good enough for marking out.

[Russell EberhardtParticipant @russelleberhardt48058]

Posted by John Haine on 10/05/2012 09:35:34:
6mm float glass is as flat as you can easily get, cheap and easily available. It does get scratched after a while and will need replacing.

It also bends quite a bit so, if used on a non-flat surface it will not be flat – sort of defeats the object. Get a peice of glass as thick as possible. Glass merchants sell thick glass for tabletops etc., so you may be able to get an offcut cheaply.

Of course it does depend on the accuracy you require.

Russell.

[David Clark 13Participant @davidclark13]

Hi There

Tesco, Sainsburys and Argos have at times sold chopping boards, medium and small granite trivets very cheaply.

All the ones I have tried seem to be ground flat on one side.

regards David

[Steve GarnettParticipant @stevegarnett62550]

Posted by Eric Clark on 10/05/2012 08:43:48:

You can easily test for flatness by studying the reflection of a window or fluorescent lights etc. any distortion indicates a lack of flatness. The designers of cars use a similar but more sophisticated technique called "zebra boarding" to detect distortions in body panel curves.

I was given some Argos granite place mats as a 'present', and these looked to be ground flat and polished – at least if you used the reflection technique to judge by. Placing one on top of another though revealed that they were anything but! We are talking up to about 3 mm across the width, and it really doesn't show as any form of visual distortion at all…

So to all intents and purposes, these are useless for anything (even being doorstops), including their original function. Being shiny, if you put a plate on them it slides straight off – just what you need in a place mat!

 

Edited By Steve Garnett on 10/05/2012 10:12:06

[Steve WanParticipant @stevewan33894]

Hi all,

Thanks for so many inputs, learnt quite a few things from chopping boards to thick glass panel. My workplace is having some renovation work. At lunch I managed to ' steal' a small ceramic cut off piece. The surface is quite smooth, yet to test the flatness. Will frame it up to raise a little. Hopefully, I could use it to find the high/low spots using engineers' blue paste for scraping the machine bevel runway.

Thanks also to David Clark of MEW forum moderator

Steve

[Sandy MortonParticipant @sandymorton10620]

I have a spare cast iron surface plate which is free to anyone who wishes to collect it. I live on the Isle of Cumbrae which is in the middle of the Clyde estuary.

[Sub MandrelParticipant @submandrel]

I use a bit of granite composite worktop, about 16" x 12", cut off a slab left over from my sister in law's kitchen.

I can't get a 1.5 thou feeler under a straightedge placed across it at any angle.

It is 1 1/2" thick and cutting it off with my angle grinder burnt out the motor! It was fun doing it though…

Even so, i wish I could take advantage of Sandy's kind offer – my brother lives in Galloway so perhaps he could swim round to fetch it one afternoon? Seriously I hadn't heard of Cumbrae, but looking at google maps it seems an amazing place – but that's a big cloud to the North West!

Neil

Edited By Stub Mandrel on 10/05/2012 20:46:53

[Mark P.Participant @markp]

Hi Steve I have a slab of polished granite from a stone masons (lump of grave-stone!) It's 75 mm X 300mm X 500mm I also have a bit of 12mm float glass for tramming my mill. Both bits were free,well only cost me a couple of pints.

Regards Pailo.

[I.M. OUTAHEREParticipant @i-m-outahere]

Hi Steve .

It Depends on how the tile was made as i think they press them so it could be quite flat .

Set it up in front of a decent light source and lay a known good straight edge (Rule or Engineers square ) across the surface you wish to use .

By starting at one end and carefully dragging it across the surface look for any light to appear between the straight edge and the surface of the tile then do it again at 45 degree increments .

If little or no light appears then it will be flat enough for what you will want it to do .

For mounting i found it best to use a thick ply base as it won't distort as much as plain timber and it is pressed flat during manufacture then glue the tile to it with a silicon type sealer (Silastic or similar )as it will take up any differences in expansion rates of the two materials .

Also check to see if it is square because this can be an asset for marking out odd shaped objects particularily sheet metal parts as you can use use the edge of the tile to set a square against , just hold the piece down with some tape so it can't move then set up a datum piont and everything will be at right angles to it or parrallel with  it .

IAN

 

 

Edited By IAN B on 11/05/2012 02:07:44

[Steve WanParticipant @stevewan33894]

Hi all,

Thanks! With all these ideas, I don't need to buy an engineering's surface table afterall. Options are plentyful as long one is creative

Happy machining,

Steve

[Ian S CParticipant @iansc]

Steve, I'v got two old mirrors about 10 mm thick, they are the type that is unframed, but made for hanging on the wall. Quite often I use a bit of plastic coated MDF board, it's quite good for general marking out work (theres a joinery factory about 100meters from home, with a freeby bin at the gate). I do have a cast iron surface plate as well, cost me $NZ15 when the Govt sold the Post Office workshops in Christchurch in the 1980s. Ian S C

[MikeParticipant @mike89748]

For years I have been looking for suitable material for a surface plate and, as I'm far too stingy to buy a proper one, the results using improvised materials have been a bit hit and miss, to say the least. Now, thanks to Eric Clark, I realise that I have two giant examples. Seventeen years ago, when my wife and I started to renovate our Victorian house, we purchased two 4ft x 18in slabs of polished slate from the local monumental mason, to use as hearth stones. These slabs are about 1 1/2in thick, and I've just checked both for flatness. Both are well within limits for all but the most exacting work. Problem solved! Now, where did I put those plans for a full-size locomotive?

[Phil WhitleyParticipant @philwhitley94135]

if you can find genuine "plate" glass from a shop window, or a large glass shelf, this was mechanically ground and polished both sides for absolute clarity and lack of distortion, so it should be near as dammit for most purposes. plate glass is usually 1/4"or more thick. Float glass is made by floating molten glass on a long tank full of molten tin, so that all the imperfections melt out and gravity provides the flatness. the problem is that it is a bit on the thin side and can flex a bit under pressure unless it is adequately supported. I have used a couple of 18" square pieces of plate glass for surface plates for many yyears, with no problems, and a check using the "best straight edge and a light" method remarked on above shows them to be still just about perfect. I use another peice as a lapping plate for carburretor and manifold flanges that have warped. Works a treat!

Phil

[Sub MandrelParticipant @submandrel]

How long has float glass been around? I'm sure I saw the process being explained on Tomorrow's World when I was a kid.

Neil

[StovepipeParticipant @stovepipe]

I seem to remember that Pilkington's invented it in the 1950's. (I stand to be corrected on this)

Dennis

[Gone AwayParticipant @goneaway]

I don't mean to be provocative with this but given the relatively low-cost of small, imported granite surface plates, why do people go to so much effort to find substitutes?

I have one 12" x 9' x 2" which is adequate for everything I do and cost me less than a number of my cutting tools. It's (relatively) light and not only is it way within my needs for flatness, the faces are also parallel. So I can lug it onto the mill table to give me a decent flat surface for alignment checks. It can be a little cramped on some jobs but it's never stopped me doing anything.

I just checked and my local (Canada) supplier isn't listing this one any more – although I know it's still available from other sources. They are selling instead, one that is 18" x 12" x 3" for $40. So I guess the smaller one would be worth around $25 at that rate.

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