I've been using an old sliding cabinet glass door as the surface to sand things (usually handle scales) dead flat. I bought a porcelain tile from the store which gives me a little more area to work on. I remember reading that the method of making glass tends to ensure they are pretty flat. Does anybody have knowledge of how flat the tile would be in comparison? My Google-fu on this was weak so figured somebody here would know? Thanks!
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Dead flat: glass versus tile
- Thread starter milkbaby
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My *guess* would be the glass is a little more flat then the ceramic. I've put down enough tile over the years to know they're not that consistent in flatness or thickness.
A granite surface block can be had pretty cheap - have you considered that for an option? As far as I know, that's the only thing out there that's really dead flat. I picked mine (12'' X 18'' X 3'') up from Production Tool Supply in Michigan for around $38, IIRC.
A granite surface block can be had pretty cheap - have you considered that for an option? As far as I know, that's the only thing out there that's really dead flat. I picked mine (12'' X 18'' X 3'') up from Production Tool Supply in Michigan for around $38, IIRC.
Got my granite from a construction site that cut out a section for the sink. They were gonna toss it in the dumpster! Its big, but a great, free score.
I would use the glass, but consider investing in the granite surface place.
One thing to note is - what is flatness?
From a geometric tolerancing and practical to knifemaking it means that a given surface is flat within some specified tolerance and unrelated to any other feature. Here's a simple pic to describe - https://goo.gl/images/shJLce
In other words you generally want handle scales flat within .001 across the whole surface of 4-5 " handle length, any more than .001 deviation and you see a gap.
I would suspect the porcelain tile has bumps and valleys across its surface.
One thing to note is - what is flatness?
From a geometric tolerancing and practical to knifemaking it means that a given surface is flat within some specified tolerance and unrelated to any other feature. Here's a simple pic to describe - https://goo.gl/images/shJLce
In other words you generally want handle scales flat within .001 across the whole surface of 4-5 " handle length, any more than .001 deviation and you see a gap.
I would suspect the porcelain tile has bumps and valleys across its surface.
Knife making rookie. Long time window industry worker.
Architectural glass is made by pouring molten glass into a giant vat of molten tin. The glass floats on the tin like grease on water. The end of the vat furthest from the glass furnace is cool enough for the glass to solidify, but the tin remains liquid. So sheet glass with a very high degree of flatness rolls continuously off that end of the vat. Amazing process to see.
A couple of points;
-how flat is "flat"? I don't have specs on how flat architectural glass really is; the objective is to produce a product with no or minimal visible ripples. For sharpening woodworking tools, I'd say plate glass is plenty flat enough. But I wouldn't suggest that a machinist/toolmaker would be satisfied with glass as a substitute for a proper granite surface plate that might have a 0.0001" tolerance.
-the glass has to be thick enough to be rigid. You can get glass (or sheet metal, for another example) that is very flat, but is not capable of supporting its own weight without flexing. That's at least part of the reason real surface plates are as thick as they are. Inherent flatness is beside the point if the material is so thin that it conforms to the surface you lay it on. Just guessing, I would think that 3/8" would do pretty well for a 2ft by 2ft piece of glass. 1/2" would be better.
-avoid tempered (heat treated) safety glass. Heat treated sheet glass like what is used in windows inevitably gets ripples in it from the heat treatment process. It isn't a desirable feature in window glass, but if tempered glass is necessary, ripples are considered normal. Now, I'll point out that the deviation in flatness required to cause a visible ripple is very small, but in any case annealed glass will be flatter than tempered.
-I don't know what flatness standard granite countertops are made to either. I have a sink cutout in my basement, and it is flat enough to suit any woodworking / tool sharpening need that I have had. But again, it probably is no comparison to what Starrett would sell you.
So, just how flat do you need it to be, and how tight is your budget?
If getting something as flat enough that you can't find defects with a quality straightedge and a feeler gauge is good enough, then you can probably take your straightedge and feeler gauge to a counter shop or a glass shop and get what you need cheap.
If you want something really FLAT, then you can get an actual made to the purpose surface plate for a couple of hundred dollars or less, depending upon whether there is a local source where you can pick it up (even a small one is pretty heavy. so freight charges could be a factor)
Architectural glass is made by pouring molten glass into a giant vat of molten tin. The glass floats on the tin like grease on water. The end of the vat furthest from the glass furnace is cool enough for the glass to solidify, but the tin remains liquid. So sheet glass with a very high degree of flatness rolls continuously off that end of the vat. Amazing process to see.
A couple of points;
-how flat is "flat"? I don't have specs on how flat architectural glass really is; the objective is to produce a product with no or minimal visible ripples. For sharpening woodworking tools, I'd say plate glass is plenty flat enough. But I wouldn't suggest that a machinist/toolmaker would be satisfied with glass as a substitute for a proper granite surface plate that might have a 0.0001" tolerance.
-the glass has to be thick enough to be rigid. You can get glass (or sheet metal, for another example) that is very flat, but is not capable of supporting its own weight without flexing. That's at least part of the reason real surface plates are as thick as they are. Inherent flatness is beside the point if the material is so thin that it conforms to the surface you lay it on. Just guessing, I would think that 3/8" would do pretty well for a 2ft by 2ft piece of glass. 1/2" would be better.
-avoid tempered (heat treated) safety glass. Heat treated sheet glass like what is used in windows inevitably gets ripples in it from the heat treatment process. It isn't a desirable feature in window glass, but if tempered glass is necessary, ripples are considered normal. Now, I'll point out that the deviation in flatness required to cause a visible ripple is very small, but in any case annealed glass will be flatter than tempered.
-I don't know what flatness standard granite countertops are made to either. I have a sink cutout in my basement, and it is flat enough to suit any woodworking / tool sharpening need that I have had. But again, it probably is no comparison to what Starrett would sell you.
So, just how flat do you need it to be, and how tight is your budget?
If getting something as flat enough that you can't find defects with a quality straightedge and a feeler gauge is good enough, then you can probably take your straightedge and feeler gauge to a counter shop or a glass shop and get what you need cheap.
If you want something really FLAT, then you can get an actual made to the purpose surface plate for a couple of hundred dollars or less, depending upon whether there is a local source where you can pick it up (even a small one is pretty heavy. so freight charges could be a factor)
Last edited:
Horsewright
Knifemaker / Craftsman / Service Provider
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I have on a 6x48 grinder a ceramic tile to act as glass platen similar to what I have on 2x72. We spent about an hour at a large tile store with the help of the owner's son, with a straight edge looking for a flat tile. It became a challenge to him and we literally tested probably a hundred tiles before finding one that was flat according to the straight edge. I bought that one tile and its still in use years later floated on the platen of the 6x48.
We have a very large surface plate in the office where my wife does her leather tooling.
Forget what we paid for it but it was spendy but certified as crazy flat. Also crazy heavy. Had to build an extra stout work bench for it. Don't need the flatness so much as the mass in this application. I too would go with granite, glass and then the tile.
We have a very large surface plate in the office where my wife does her leather tooling.
Forget what we paid for it but it was spendy but certified as crazy flat. Also crazy heavy. Had to build an extra stout work bench for it. Don't need the flatness so much as the mass in this application. I too would go with granite, glass and then the tile.
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i have read that the $7.99 real granite tiles sold at home depot are very flat because they are sawed out, unless you are making submarine parts a real granite surface plate is not required. this is open to interpretation but i think the glass and tile would be more prone to not as flat.
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I have granite and glass. I prefer glass because I spray glue my sandpaper to it for flattening scales. I’ve had a brand new razor blade score the granite but the glass cleans right up with a fresh razor and a little acetone.