Thread: Float glass lapping plate

Hi, you probably could just use it as is, Bunnings sell glass for patio and pool fences at a very reasonable price. This is what I use to lap in critical parts for race engines, and in the wood shop

If it is 5mm that is the thickness of most glass shelves in shops. You could make a tray from MDF or wood for it to sit in if you are worried about breakage

There is an alternative; marble suppliers usually have offcuts from sink cut-outs etc that they would otherwise have to pay to dispose of so they are usually happy for people to help themselves out of their scrap piles. The polished marble is flat enough for sharpening and honing purposes; the difference in flatness between float glass and polished marble is less than you can measure or feel. Hold a piece up to the light and look at the reflection; if it reflects straight lines in all planes it's flat enough.

For final honing using a polishing compound thick MDF or accurately planed hardwood is the go; and neither of those could be considered as flat as either glass or marble.

HI yoboseyo

I use a piece of 8 mm toughened glass bought from the local tip shop for $2 - mate says I should have bargained them down to $1 ! But it sure beats Bunnings prices.

I do not see a lot of advantage in laminating glass. But if you are worried about the risk of breaking the glass then you might consider sticking it with el cheapo plumbers silicon to a piece of acrylic or polycarbonate sheet or even to a piece of MDF or plywood.


Cheers

Graeme

I use a piece of 6mm glass to flatten my wet stones with carborundum powder of different grits works very well and fast you would have to be pretty rough with it to damage it I use the other side with sanding sheet spray glued to it to flatten the top and bottom of boxes.
Regards Rod.

I was thinking that because it's flat, but also flexible, it would be better to laminate multiple pieces than laying it on something not as flat like MDF. Sound like a lot of people use thinner glass, because TBH I don't know where people who say "just get a piece of 1/2" float glass" actually get it from

I just dropped into a local glazier and asked.
They seem to keep offcuts and salvaged windows - I think he just gave me a piece a bit smaller than a4.

Russ

It takes a fair bit of pressure to flex a piece of 6mm glass I just put mine on the flat bench top and go for it you would have to have something under it to get and deflection and then I feel you would have to put a lot of force into it.
Regards Rod.

Originally Posted by Chief Tiff

There is an alternative; marble suppliers usually have offcuts from sink cut-outs etc that they would otherwise have to pay to dispose of so they are usually happy for people to help themselves out of their scrap piles. The polished marble is flat enough for sharpening and honing purposes; the difference in flatness between float glass and polished marble is less than you can measure or feel. Hold a piece up to the light and look at the reflection; if it reflects straight lines in all planes it's flat enough.

For final honing using a polishing compound thick MDF or accurately planed hardwood is the go; and neither of those could be considered as flat as either glass or marble.

Thanks Guys, this thread came at a very good time. I have one of those sink cutouts from one of those composite granite countertops that was about to be dumped. I will put it to good use now.
Rgds,
Crocy.

I got a load of black granite stove hearth offcuts before.
I was hoping they would be dead flat, but all of them were noticeably convex on the polished surfaces, and slightly concave on the undersides.
Not near good enough for checking anything, as there would be a 1mm error butting a 4" square against an accurate block.
The test I do is push the square against the block all over the plate, and use a good lamp behind to see any errors.
Tom

Originally Posted by Tom trees

I got a load of black granite stove hearth offcuts before.
I was hoping they would be dead flat, but all of them were noticeably convex on the polished surfaces, and slightly concave on the undersides.
Not near good enough for checking anything, as there would be a 1mm error butting a 4" square against an accurate block.
The test I do is push the square against the block all over the plate, and use a good lamp behind to see any errors.
Tom

I have found this too, at least with my kitchen bench, which is 40mm.

That's why I'm interested in procuring a piece of floatglass, even if it's at cost. Not so much to flatten things, because there's always the question "how flat do you need things to be?" which I have no good answer for, but just to have a reference for flatness. Then, I can put my straight edge against it and find out how flat that is.

I needed a piece of flat glass for a sort of Scary Sharp process.

I went to a shop that made glass enclosures for showers. I explained what I needed. The owner asked me to give him a few minutes. He brought out a piece of hardened float glass about 3/8 (9mm) thick. He had cut it with a water jet and rounded over all 8 edges and four corners. I remember giving him twenty dollars but I don't remember if he asked or I just gave.

What I do is use 3M #77 spray adhesive to hold wet or dry sandpaper on the glass. Then use the sand paper wet. Mineral Spirits easily helps in removing the sandpaper. During the sharpening process I put the glass in a shallow baking tin. (Teflon coated so it doesn't rust.)

Try a square against another square or square thing while you're at it.
You'd be really surprised what errors can accumulate over four inches, which might be unnoticable with a straightedge.
I found when making a surface plate (bodge job) with some unknown lab countertop material
I had to get it to somewhere between 0.05 and 0.10 mm for it not to show light using the square and block.
Tom