Disc grinder/sander?

[Pelallito]

Hello,
I am thinking about making a 9" disc grinder/sander for my shop. I am thinking of using 1/2" steel plate and attaching a boss(if I am spelling it right),with a key way cut into it, to it, so that I can attach it to the motor. After attaching it mechanically with bolts and perhaps welding it into place. I plan to turn everything as one unit on my lathe to balance it, get rid of any run out and make it vibration proof.
Can you tell me any reason why this won't work? Any suggestions on making it better would be happily accepted.
The reason for 9" is that I can use normal sandpaper on it. All I have to do is glue it on and trim it in the shape of the disc.
The motor will be reversible, and the disc will have a 1 degree taper on the face. 
Thanks for the help.
Fred

[Bernd]

Sounds good to me Fred. I'd opt for the welding. Never have to worry about screws/bolts loosening on you.

Bernd

[Pelallito]

Bernd,
Thanks for the reply. One of the reasons that I was going to bolt it up first, before welding, was to try to minimize distortion from the heat. Then the bolts would just be along for the ride.
I was thinking of drilling and boring the boss to the correct ID to fit the motor and cut the keyway in it. Find center in the 1/2" material and attach it with bolts. Weld it together. Then make a stub shaft with key way cut in it to spin the disc after centering that shaft. I think that might be more accurate than spinning it by holding the outside of the boss. I could turn it down to size and cut the face without changing my setup..
Regards,
Fred