Join Date: Sep 2007
Location: Baxter, Tennessee
Which side of the mirror are you turning? I use glue blocks on my hand mirrors. I use a square block. I glue it on the good side of the mirror and then I turn the opening for the mirror glass. I sand this side and put a thin layer of finish on.
Then I remove the glue block but leave the waste block on the faceplate. I should tell you at this point that my glue blocks are 3" square. That is because my glass is 4" and the diagonal of the glue block is a hair over that. I very carefully turn down the corners of the glue block until it fits in the opening. This lines everything up pretty accurately. Why do I use a square block? It's easy to get a chisel in the opening to pry the glue block off.
Then just glue the block into the mirror opening. It won't always be perfect so you may have to blend the outside edge since it might be off center a few thousandths.
to answer your first question, no I don't seat the mirror blank on the chuck jaws. I use a 3/4" x3" thick wasteblock. I hold this in 4" jaws on my chuck. After I face it off it's still proud of the chuck. I simply glue the block on using medium CA glue with accelerator. The accelerator makes the glue joint brittle so you can easily break the glue joint with a sharp hammer blow. This is just quicker than a paper joint.
When I teach my classes we use faceplates with the square blocks.