Need tips on making a base for float glass

[Ian Kim]

Hi, I bought some float glass to use as a lapping table and I need to make a base for it. The first thing most people have to deal with in this type of material is probably deflection so I need a stiff substrate with a preferably tacky surface (but not sticky) to grip the glass. I'm thinking of using a product that can be poured in liquid form and will solidify with the desired characteristics. This will be easier than hand truing a surface as you can fit the glass while the product is still liquid.

I'd really appreciate any suggested product but I need to clarify a key quality it has to have. That quality is the ability to distribute even pressure across the glass so that the surface will remain true. In the absence of this quality the glass would deflect on the product, tranferring a depression that would defeat the whole purpose. The dried product should also have only enough tack to hold the glass as too much would probably effect the dimensional stability of the shape. I'd like to use something that would be effective in thin layers (under 2") but this is just a preference and not as critical as the above mentioned points.

To establish a starting point, maybe a body filler would do the trick. To be honest I'm not sure if there's any product that would be suitable but in the case you know something that I don't, please feel free to point me in the right direction, thanks.

[Ian Kim]

Had a thought and if I make an impression of the glass into the substance then I really don't need any tack since the glass is fitted into its own shape. Maybe that will help narrow the search. I want the glass to be removable so the "filler" shouldn't stick to the glass after it's been "molded", thanks.

[sean m. titmas]

Im working on the same thing for my shop next week and plan to do the following;

cut a piece of MDF about 1" larger than the float glass on all sides,

scarify the surface with 30 grit belt sander to give it some "tooth",

apply silicone with a 1/4" notched trowel over the entire surface,

bed the glass in the silicone by using a slight side to side, back-n-forth motion to eliminate any air bubbles,

allow silicone to cure for at least 48 hours,

since the MDF is slick i might need some grip tape or similar product on the bottom side so that the base will grip the wood surface of the bench during use.

[Mike Henderson]

You don't say how thick your glass is. I have a piece that's 3/8" thick and about 14"x12" and it doesn't deflect that I can detect. I just put four plastic feet on it.

If you have a thin piece of glass I'd glue it to 3/4" MDF. MDF is flat, especially in a small piece. Use another piece of MDF on top when you clamp it up.

Mike

[I don't use that glass any more. I bought some DMT diamond plates and use those for lapping and flattening my water stones.]

[Cliff Rohrabacher]

My diamond glass lapping station is a plywood box large enough to take the 4" by 24" plate glass slabs.

Don't worry yourself about deflection and irregularities and what not.
It's a lapping station. I used to hand lap little pieces of steel to tolerances of flatness that we had to measure to Light Bands (angstroms) of flatness and I did it using plain old fashioned lapping compound on a hunk of cast iron that had been around since before I was born into which some seemingly careless machinist had randomly carved a series of grooves.
And I'd never done it before.

And that was my objection: "But I've never done this before" I protested thinking my inexperience would be an issue - especially given the precision required. "No worries " came the reply "The Janitor can do a better job than the best machinist in the place." They assured me. They were right.


The movement of your work across the microscopic irregularities will normalize out. It happens naturally. Unless you are one of those people who absolutely positively HAS to make each stroke exactly like the last one over and over again. If you are: Then learn to add a touch of randomness to the process.

[Ian Kim]

sean: I recently had a bottle of silicone blow in my hand and it was a nightmare to get off. That little incident tends to steer me away from ever using it again, but I'll mull it over :).

Mike Henderson: The piece is 1/2"x6 1/2"x32". With enough pressure I can detect deflection and seeing as I'm lapping a jointer plane (22") I'd like it fully supported. I understand that extreme flatness isn't neccessary on a plane but I have a set amount I'm willing to work within. Thanks for the tip on mdf, I'll see what I can do with it.

Cliff: I think you're referring to the "automated generation of gages". That's something I'd definitely like to try out in the future but from what I understand of it the method requires 3 pieces as only 2 will tend to make a convex-concave shape. This is off-topic from what I'm currently trying to do, but seeing as it relates to a previous research topic I'd love to hear a bit more on your lapping technique (you can pm me if you like). Mearsurements of angstroms are probably more than accurate enough for me.

Note: My request to Cliff is completely off-topic and really has nothing to do with the project at hand. I'm still interested in hearing your solutions to the "plate base" problem, thanks.

Forgot to mention, I'm using sandpaper attached to the plate, not compound.