Surface plate

hello friends, trying to recreate that famous method of flat surface plates and I was wondering if I could use that porcelain tile that is used for covering floors and walls. I have some left over from my bathroom remodeling and they are 80cm x 80cm. I've heard that ceramics are used as an alternative, would porcelain tiles also be possible? Has anyone thought of this or done it?

Hi Wesley,

Welcome to the forum. Are the porcelain tiles flat? Or do you intend to use the 3 plate method? I know some use plate glass as a cheap surface plate, usually they are made from Cast Iron or granite.

Thor

Really you can only use cast iron because of the way it can be scraped. I'm not sure how other materials would respond. You can grind glass and therefore probably porcelain. Generally tiles of various sorts are gong to be thin and hence flexible so you would want to laminate a few together first.

Another possibility is to find a kitchen fitter and see if they will give you the bits they cut out of granite worktops for the sink. These are still too thin to use as is.

I agree. Kitchen worktops are probably too thin to give you a relaible surface plate. I can measure slight curve in my granite worktop.

See Robin Renzetti's Youtube for lapping a granite surface plate.

Thank you very much for your reply. It's just that I have some very thick porcelain tiles and if I'm not mistaken, the thickness is very similar to the thickness of the granite. I was thinking about it!

Hi Thor, thank you very much for your reply. I was thinking of using the 3 board method. I saw that they are using ceramic and I wondered if I could use porcelain. It has a very similar thickness to the thickness of the granite and I thought I could save money on this step.

A granite surface plate of that sort of size would be at least 4" thick, probably more. Even my 8"x12" is 4" thick.

sorry, I mean the thickness of the granite used in kitchen sink countertops, which, by the way, I've seen used for surface plates. of course, a ribbed bed of flat bars of common steel was used.

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May I just insert a note of semantic clarification here ?

… call it pedantry if you must !

There is [was] [should-be] a distinction between a Surface Plate and a Marking-out Table

On a forum such as this, it is perhaps inevitable that the use of the terms will be ‘fuzzy’ but it doesn’t really help in a discussion like this one.

MichaelG.

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Edit: __ this might be useful:

https://digital.library.unt.edu/ark:/67531/metadc710079/m2/1/high_res_d/650156.pdf

Edited By Michael Gilligan on 23/11/2022 06:21:44

I don't know if I made myself clear, but my question is about the 3 withworth slabs method and whether porcelain tiles could be used in its construction instead of granite. I am aware of the thickness of the tile and that it could warp and lose precision, but I could use a ribbed metal base. I just wanted to hear the opinion of someone with more knowledge.

*withworth 3 plates method

If you do start with three tiles your frame would only be supporting the one at the bottom, what about the one being held above it while they are lapped? What sort of size are you thinking of as the amount of flex on a 200mm plate will be a lot difference to a 450 x 600 plate of the same thickness

Me I just use a tile as it is for marking out on which seems to give me working models which is what I want. It also gets used as a surface plate.

Edited By JasonB on 23/11/2022 08:02:42

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Yes … I know it well [so I guess mine is ‘the opinion of someone with more knowledge’]

And I also know that it would be futile to attempt this with anything that was insufficiently stiff to produce a set of three plates as its end result.

MichaelG.

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Edit: __ I suggest you start your journey here:

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It is available on archive.org 

and I have recommended it on many previous occasions.

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P.S. __ You have two unread ‘personal messages’ from me, Wesley

Edited By Michael Gilligan on 23/11/2022 08:20:04

Allow me please, Wesley, to make an entirely practical suggestion:

If [as I presume] what you really want is a decent ‘marking-out table’ of 800mm square … Just use Whitworth’s logic to check all of your available tiles and find the flatest one. Stone-down any obvious high spots on the best three but, for the sake of your sanity, please stop way short of trying to make a ‘surface plate’ out of a tile.

MichaelG.

Whatever form of table is used, to maintain flatness, it must not be stressed.

At work, an expensive 6' x 4' x 6" granite table was ruined by being left leaning against a wall. It sagged and bowed!

In the Standards and Calibration rooms, the tables were massive cast iron, and carefully levelled, on equally massive cast iron frames.

For The WaterWorks Museum, I made a 18" x 24" table from an off cut from a grave headstone )

The supporting frame was 2 x 2 " angle iron, with the table bedded onto wet plaster on plywood..

Once sited, it was carefully levelled on a purpose made steel bench.

Howard

My experience of tiles is they are not flat, not hard, and not stiff. Not a good place to start.

'Granite' is not all the same.

A bit of float glass is probably better... just use as is for layout and sharpening.

8x12 granite plates are dirt cheap for what you get.

Want to save money? I'd probably investigate restoring a worn out one first before going from scratch.

As an experiment/just for the experience - I would not start with tiles.

An advantage of Granite being hundreds of million of years old is it's effectively time stable - better than cast-iron, and probably much better than tile. Granite can also be cut into much thicker slabs than tile, making it much less likely to flex under load.

I don't know how flat tiles are. Fairly good I expect, because they're made in flattish moulds, and then glazed. The molten glaze would tend to flatten under gravity.

I believe the flattest cheap material available is modern sheet glass. It's made by floating molten glass across a large tank of molten tin, effectively producing a product of constant thickness with an optically smooth surface. The disadvantage is it bends under weight, and I suspect a tile would distort in the same way. However, I use a sheet of glass for marking out and - supported on a stiffish bench - reckon it's good enough for measuring not too heavy objects within my practical limit, i.e. no better than about 0.02mm (1thou). However, the accuracy is low by real surface plate standards, and wouldn't do if I was working within tolerances. Does anybody on the forum work to tolerances?

On a practical note, I worry that tiles being hard and bendy might make Whitworth's method difficult to apply. Whitworth's plates were made from stiff slabs of cast-iron, which is considerably easier to hand-scrape than a ceramic. I fear a set of 3 tiles would bend and move the blue whilst being compared, so confusing the high and low points. And then, the force needed to scrape a tile seems likely to flex it, again confusing the process. Someone needs to try and report back!

Dave

Just a thought!

Are the porcelain tiles glazed or unglazed. Unglazed porcelain is fairly soft - probably too soft even for a marking out table. If they are glazed, the hard glaze layer will be fairly thin and rubbing down high spots will potentially break through.

Porcelain tiles are not soft and seldom glazed. You need diamond drills to drill them and if not snapping a diamond saw to cut them.

Sounds like you are thinking of ceramic tiles Peter and Dave which are more like a glazed porcelain cup or plate.

Typical surface flatness of vitrified porcelain tile is within +/- 0.2% of thivkness 

Edited By JasonB on 23/11/2022 13:10:41

Making a surface plate of any size to a reasonable standard by the 3 plate method is said to be a very longwinded, soul destroying and physically hard thing to do. And that's using cast iron.

Many of the posts above make valuable points about the probable unsuitability of a porcelain tile. eg Peter's question about glaze or no glaze. The "glaze" on porcelain is a layer of glass, and it's just too hard to scrape and too thin to "adjust" it's flatness by abrasive means without going through the layer. And if no glaze the tile is too soft.

Some granite tiles and chopping boards are flat enough to make a marking out surface, take a steel rule to the shop and test. Many "Granite" kitchen worktops are moulded or rolled from a mixture of granite particles in a matrix of synthetic resin plastic or similar, and they won't all be hard, flat or stable.

So, my bottom line would be, If I wanted the experience of trying the 3 plate method I would start with cast Iron. If I wanted a marking out table I might try a kitchen shop. Or go to a glazier for a piece of float glass, and support it on a bed of plaster of paris if the work to be done is heavy. If I wanted a surface plate I would buy one.

Rod