I searched the net for every example of a homemade sander I could find. I also read a lot of reviews for disc sanders from 6" to 15" and learned that a good sander that would stand up to being used in a metal fab shop needed 1) at least a 1 hp motor. 2) A well made platen to mount the sanding disc to 3) all metal frame. 4) A fairly large disc table . When you figure time and materials to build something even close.
Compared to what I pieced together to start with,
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I've had the 12" over a year it's a pleasure to use every time still .
The vise is bolted to a piece of thick table top. It has 2 carriage bolts passing through the bottom so black plastic knobs can be used for fine adjustments. I don't let the vice float when metal working. The only wobbly bits I have are some entry level brad point wood working bits that are used only when accuracy doesn't matter. My most used bit for 3/16" and under is an Irwin single flute Uni-bit with 1/8" deep steps. I use a lot of tapping/cutting oil. For thicker material I have collected, over time, every size Cobalt bit the local hardware store carries, and for larger sizes or metric Mcmaster-Carr has good selections. I spend the extra money to make life easier and so far it's paid off.
Having said that..when I use the Uni-bit on larger than 1/8" I'll flip the piece over and with the bottom knobs loose let the drill center the bit to bring the rest of the hole to size. Just because some days I'm to lazy to change to the correct size regular bit to finish the hole. With care and practice I can still wind up with accurate cuts.
I know, a simple statement, and a long drawn out explanation..
Ron