Dead/drive center for Shopsmith?

[terrydowning]

Not using a mandrel with bushing, how do you know when it is the right diameter to fit the pen parts?

I often turn pens without bushing or use undersized bushings.

Use a digital caliper

Measure the hardware
Measure the turning
turn some more off and measure, etc etc. 'til you're done.

This method is more time consuming but is way more accurate as bushings often get worn from contact with chisels and abrasives. Bushings are often out of round from the mfg and pen hardware is often a thousandth or 2 off from the bushing. I know a few thousandths doesn't sound like a lot and most wood workers stay within the 1/32 tolerance realm, but you can feel it once everything is assembled. Pens are not your typical turning and definitely require more accuracy than typical flat work.

[wa2crk]

Just a couple of pics to show the SS components used on a Delta Midi lathe for pen turning. The tailstock is a 60 deg point live center from Sears a long time ago.

Just the basic setup
[ATTACH]19095[/ATTACH]

The pen blank and bushings. No mandrel!!
[ATTACH]19096[/ATTACH]

Ready to turn
[ATTACH]19097[/ATTACH]

Bill V

[fiatben]

I suppose I could go to the pen turning forums and get this answered, but I thought asking here might make this particular thread a little more complete.

I see the two 60° center and understand the friction drive (used a homemade jam chuck for a similar thing just a few days ago.) I see how everything is mounted up, sorta. What I don't see is how you align the brass tube and the bushings (which I understood to be the whole point of the mandrel).

Enlightment??

[wa2crk]

Fiatben;
When a mandrel is used there is some play at the end of the mandrel shaft where it comes into contect with the 60 deg center. The mandrels are always 7mm in diameter but the pen brass tubes can be a larger diameter and the bushings have a step in them that fits into the larger brass tube and the inner diameter of the bushing fits on the 7mm shaft. Because the pen mandrel is usually a fixed length bowing of the mandrel can occur and cause a pen blank to turn out of round. The mandrel can also be a problem when the mandrel nut is tightened causing more flexing of the mandrel shaft.
Penn State Industries has a mandrel saver that is a hollow tailstock center that the mandrel passes through and headstock pressure secures things against the mandrel saver. This adds another problem in that the mandrel saver has clearance to allow the shaft to pass through.
All of these clearances cause some vibration to enter into the system and can produce a less than optimum cut.
I was turning some acrylic blanks for some seam rippers on the mandrel setup and as I moved away from the headstock I started to get some vibration during the cut. I was using a EWT carbide cutter which is extremely sharp.
When I turned some acrylic using the friction drive there was no "buzzing" caused by the vibration.
In short eliminating the bushing to mandrel clearance and the clearance between the mandrel and the mandrel saver and at the same eliminating any possible mandrel flexing makes a much stiffer assembly for turning. The cone centers take up all the slack and things seem to turn much smoother.
Hope this helps. If not type at me some more.
Bill V

[terrydowning]

Bill pretty much summed it all up.
FYI,
When Turning Between Center (TBC) you can not use standard 7 mm Bushing (Slimline, Designer/Euro or any other 7 mm tubed bushings). You can still TBC, you just have to measure more. You can also make your own bushings from aluminum, various plastics, or even wood, just be mindful that they will not last like steel bushings will. I often turn pens with no bushings, undersized bushings, or home made bushings and measure the pen blank against the actual hardware for a given pen. It takes patience and time. I also don't typically do "Production" turning where i have to turn out dozens per day to make inventory.