Floating Mandrel

[holmqer]

I prefer to turn pens between centers, but when turning a continuous profile, I was stuck with going back to the standard mandrel and bushings until I made a floating mandrel that gives me the best of both worlds.

I took a roughly 2 3/4" long piece of 1/4" mild steel rod (1018 or 12L14 can't really remember which) and turned it down just a hair from 0.250" to 0.246" so that it would fit just as tight as a good set of 7mm kit between center bushings. Pulling the rod out of a tube with a bushing in the other end makes a nice vacuum breaking pop.

Now with the floating mandrel in the middle and a between center bushing at either end, I can turn a continuous profile and get a very concentric fit for the hardware.

The photos show two bushings and the floating mandrel ready to put together, then ready to turn, then on the lathe.

 

[el_d]

Wow pretty nice set up Eric.

 

[leehljp]

Eric,

That is a great idea. I think an "idea" in general along this line had been mentioned before, but from a different perspective. It never achieved development. You have done it right! Keep us posted on how well it works over several pens. I am sure some here will want to copy this! :good:

I can see this becoming a popular thread quick and I am putting this thread in my little data list of great ideas!

 

[holmqer]

Eric,

That is a great idea. I think an "idea" in general along this line had been mentioned before, but from a different perspective. It never achieved development. You have done it right! Keep us posted on how well it works over several pens. I am sure some here will want to copy this! :good:

I can see this becoming a popular thread quick and I am putting this thread in my little data list of great ideas!

I've turned about a dozen pens using this method so far and found the following.

The fit where the kit hardware mates with the body is as concentric as just turning one blank at a time with between center bushings.

Where I get a big advantage is on the joint between the upper and lower barrel. No matter how careful I was with a standard mandrel, if the two barrels were not lined up fairly closely to how they were turned, you could feel a slight step at some points around the circumference. With this method, that step is either eliminated or drastically reduced. The worst case step I have found with this method is better then the best case I ever achieved with a standard mandrel.

There is some variability in pen tube ID. All the kits I've used are from either AS or CSUSA and the floating mandrel fits in all of them with a fairly snug fit. I made one for JerrySambrook to try out, and he found that it would not fit in any of the kits he got from one of the regular suppliers (I don't remember which one, so won't offer any names at this point.) Those kits appeared to have a slightly larger wall thickness than the kits I have, and thus the floating mandrel would not insert.

I fine tuned the OD of the floating mandrel to fit the tubes I had on hand.

I found that some of the kits I used had either a very tight fit and some were a slightly loose fit. I suspect that this contributed to the "step" mentioned above. Human touch can feel a couple thousanths of an inch step. I suspect that technique may have contributed to the rest of the "step", I may have pressed harder to compensate for hard wood or a slightly dull skew and caused a flex of a thousanths or so.

Just like with between center bushings, clean tubes and chamfering the ID of the ends of the tubes is important to clean insertion. It does not take much to prevent insertion with this tight of a fit.

The ends of the floating mandrel are chamfered to aid in insertion.

 

[Randy_]

The mandrels fron PSI are only 0.243" which suggests their tubes might also have a little smaller ID and possibly would not fit on a 0.246" mandrel.

 

[Rifleman1776]

All the mandrels I have ever purchased, from a variety of sources have been .243". That is why, when doing 7mm pens, I use an adjustable mandrel and only one blank at a time. The mandrel supports the bushings, not the blank.
Nevertheless, this is a fine idea as long as you have the correct match of 'floating' mandrel and tube ID.
However, theoretically, just turning down to the bushings would do the same thing with conventional mandrel use.