My reverse chuck technique.

[Bill Wyko]

I have stacks of these round pieces of MDF from cuting out holes in speaker boxes. I always wondered what I could use them for and then it came to me, reverse chucks. They all have a hole dead center from using my router guide so I just opened up the hole to fit my Screw chuck.
http://pic80.picturetrail.com/VOL2109/11908737/24030004/401089037.jpg
After attaching the screw chuck I drilled 4 holes through 2 of the pieces, bolted them together and trued them up to each other.
http://pic80.picturetrail.com/VOL2109/11908737/24030004/401089031.jpg
Then using my parting tool, I turned a hole out of the center, the size I needed for my HF.
http://pic80.picturetrail.com/VOL2109/11908737/24030004/401089033.jpg
Then I took it to the router table and beveled the inner side with a 45* angle.
http://pic80.picturetrail.com/VOL2109/11908737/24030004/401089038.jpg
You will want to use bolts as close to the right length as possible. I had to change these out due to them slightly tapping the motor on my lathe when it was turned on.
http://pic80.picturetrail.com/VOL2109/11908737/24030004/401089043.jpg
In the end I was able to turn the ebony bottom of my HF securely and accurately. I hope this helps with those times that the bottom needs to be smooth. Good luck everyone.
http://pic80.picturetrail.com/VOL2109/11908737/24030004/401089030.jpg

[James Combs]

Excellent version of the classic doughnut chuck Bill. Just a suggestion, make yourself several different clamp plates with different size center holes then you can handle most any size turning. Exactly what I used until I got my vacuum chuck. It is still very usable on porous and tunings with voids. Thanks for posting.

[Bill Wyko]

I have stacks of the rounds so that'll be on the to do list. I have a vacuum chuck as well but this burl had voids all over it. Another expansion on the knowledge front. This should work great on my staved work too.