Chucking on finished surfaces

[Maplehead]

Hi All

My guitar volume/tone knobs have many steps they go through in the making of them. I try to avoid steps which put completed surfaces in the chuck but it doesn’t always work out that way. So, do you have any tips on how to chuck material, (in this case in my lathe 4 jaw chuck), without getting the jaw marks on the job?
Note: the two knobs in the pic have been sanded with 400 grit. Most of the knicks are out of them.

 

[Wreck™Wreck]

Soft top jaws if the chuck has 2 piece jaws, if not make a fixture in a soft material.

Had to face the ends of clear acrylic tubes so I made a PVC split collar, this is a 3-Jaw but will work in a 4-Jaw. For brass make an aluminum collar.

 

[Technical Ted]

A lot depends on hold securely you have to hold the pieces, like are you going to polish or drill the part?

Since it's a 4 jaw and you can indicate things in you can put something in between the chuck jaw and part i.e. aluminum shim stock, pieces of paper/cardboard, hard rubber or soft plastic, small blocks/strips of wood, whatever. Collets work well for this if you have a set.

Ted

 

[Dan_S]

Because your parts are so small in my opinion, your best option is probably the most expensive one, and that is a collet chuck. Next would be vaious types of fixtures for the 4 jaw. The last would be brass or copper jaw covers, but they would be a pain on parts this small

 

[Technical Ted]

Here's something I've done in the past to hold small parts that would most likely help you. It's a poor man's collet. A picture is worth 1000 words. Just make one of these up out of a softer material and it should hold the part securley and not mark it up. It works great in a 3 jaw chuck too.

Good luck,
Ted

 

[Asm109]

Can you bore the hole first and then mount the part on a self locking stub mandrel?

To make the mandrel, chuck up a piece of stock larger than the hole.
Turn to a diameter that is a slight slip fit.
Leave stub in chuck.
With a file cut a flat on the side of the mandrel. Put a small diameter pin on the flat and measure the diameter of the stub + pin.
File until the distance is about .003 SMALLER than the ID of your knob.
Place the pin on the flat, slide your part over the pin and give the part a turn clockwise.
The pin will roll slightly and lock the part in place.
Now do the OD turning and shaping.
A quick ccw turn and the part will release.

 

[Maplehead]

Hi All
Thanks for the replies.
I have to try that mandrel idea. Sounds cool.
For now though I cut a piece of aluminum flashing I have and I made a “collett” out of it like in the pic. It worked perfectly. Thanks again.