DIY Kitless Pen Mandrel

[freshmaker]

Hey folks,

I searched this thread and didn't see any other similar topics, so thought I'd post one. I made a mandrel out of delrin (I've only been making pens for 1 year so I'm very new at this). This is my very first attempt at making a tool to enable creating a part for a new pen design. Unfortunately the centre of the mandrel (the rod, turned down to 11mm, and the threads, turned to 13.7 for an M14 die) is just slightly out of alignment, so when mounted in the collet chuck, the piece screwed onto the mandrel is not perfectly in the centre. I find this strange since I turned it in the collet chuck, so how would turning down a part of the rod end up not perfectly centred? When I make a cap, barrel, or section, any holes I drill always seem to be perfectly centred (at least, as best I can do on a wood lathe, I'm sure a metal lathe would add more precision).

Maybe the problem is that the delrin rod needs to be turned down using a metal lathe to be absolutely perfectly round?

I'd be grateful for any advice on how to make a mandrel for a collet chuck on a wood lathe that's perfectly centred!

Thanks for reading.

 

[Displaced Canadian]

I have found that any time you remove something from a collet chuck and put it back in it won't be in the exact place every time and won't be perfectly centered. I have found that having a hole through the piece and using a drill bit as a guide when putting the piece in the collet chuck helps. What are you using the mandrel for? Perhaps there may be a different way to accomplish the same thing.

 

[rherrell]

Delrin is a soft plastic so it "moves" when you turn it, that could be part of the problem.

Also, a piece of Delrin may look round but it's not. What you need to do is turn about 2" down just a little so it's round, then turn it around in the chuck and turn the rest, that way it will be concentric.

Having said all that, a wood lathe is not a precision tool so I'm not surprised you're having difficulty.

I don't usually hijack threads to try and sell something but if you can't get it figured out I can make you a mandrel out of steel that is guaranteed to run true,

 

[darrin1200]

The biggest problem with Delrin, is that it bends under the pressure of the tool. It will also deform ever so slightly. I started with Delrin, then moved to acrylic acetate. While a little better, it still had the same problem and all my stuff was coming out just a bit off. Now I use them for buffing mandrels.
Then I tried aluminum, and it was markedly better. I was still able to use my wood lathe to make them. However, after a half dozen uses or so, the long ones would bend just slightly off center from the tool pressure.
Once I got the metal lathe, I made the mandrels out of brass and it was night and day.

 

[wimkluck]

I turn all the small things between center. It helps but it isn't a metal lathe. I use ebonite or brass.