Surface table alternative?

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

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

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

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

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

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.

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.

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.

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.

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

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

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

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.

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

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.

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

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

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

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?