Centering lathe faceplate on a disc.

[dbhost]

I am building a disc sander accessory for my lathe. At least I hope I am. I have a 12" + a hair disc cut from 3/4" plywood, and a Penn State 1x8 tpi 3" faceplate to install to. I am wondering what is the best way to insure the disc and faceplate are centered against each other such that the disc doesn't wobble.

I was thinking of using a pencil compass set at 1.5" from the center pin hole from the circle cutting jig to outline where the 3" should be, draw crossed lines at 90 deg from each other to index the screw holes, and run it together that way, chuck it up, and run it sanding until it is perfectly round at 12" even...

I ordered a dedicated faceplate for this purpose. I wanted to be able to chuck it up, slide / clamp the table into position, hook up the dust hose and have a good go at it...

[Black wallnut]

That sounds to me like it would work.

[Bill in Buena Park]

Dave, I agree with Mark - should work. Another way would be after following your process to mount the faceplate, connect to headstock, brace a pencil against the tool rest and BY HAND rotate the faceplate to mark a circle toward the outer edge of the disk, then further trim/sand off any out of round areas before you remount and finish your process with the final sanding, which should be minimal.

[LCHIEN]

I would use a centering square to draw as many as four lines (two is sufficient but four gives you great confidence when they all meet int he center) on your disk.
AN attachment like this


on a adjustable square's rule


can do it but a search on Google for centering square will find a lot of other models. The one I showed will have a reach to get to the center of your disk.

Once you have marked several radial lines you can measure 1.5" out on all of them to indicate the outer circumference of your mount. Place it in place then mount accordingly.

[dbhost]

Loring,

Those look nice, but not in my tool arsenal. Sounds like it would work on the same principle as the pencil compass. I have had one of those things since Kindergarten...

I would use a centering square to draw as many as four lines (two is sufficient but four gives you great confidence when they all meet int he center) on your disk.
AN attachment like this


on a adjustable square's rule


can do it but a search on Google for centering square will find a lot of other models. The one I showed will have a reach to get to the center of your disk.

Once you have marked several radial lines you can measure 1.5" out on all of them to indicate the outer circumference of your mount. Place it in place then mount accordingly.

[LCHIEN]

Dave, you probably already have the rule from your adjustable square.

I have a starrett. But the one I use the most (because its not stored in a case) is the HF one. Its the only remaining parts from a combination square kit (right angle, protractor, and centering head) - i tossed the combinatin head and protractor because they were so bad. Still, I think I was only out about $8 and the centering head is great. I looked quickly and the only head- only parts are from Mitutoyo, Starrett and others and run about $30-40, too bad they are so expensive,

Here's the kit - only $7 and toss the other parts.

http://www.harborfreight.com/12-inch-combination-square-set-92471.html

If its off its easy to fix. $6.99 and 25 % off coupon....!!!

[RAV2]

You can do the same thing with a framing square (I'm sure this is in your 'toolbox'):

http://www.woodworkingwithajo.com/finding-the-center/

[gerti]

Am I missing something? You mount the faceplate roughly centered, start up the lathe and turn the edge. Now the faceplate is perfectly centered.

[LCHIEN]

Am I missing something? You mount the faceplate roughly centered, start up the lathe and turn the edge. Now the faceplate is perfectly centered.

that's the other way I thought of.

[Bill in Buena Park]

Am I missing something? You mount the faceplate roughly centered, start up the lathe and turn the edge. Now the faceplate is perfectly centered.

The plywood might not turn well which is why I think he planned to sand it into round.