@BobC2951
Before you read the novel I wrote below, can I suggest that if you've already got a setup that is working for you, then there's no reason to change it. I know that a lot of turners--many that are well-known and well-respected--use mandrels with great success. The only reason I found my way to TBC was that I was not happy with my finished pens. If that's you as well, then read on and continue to ask the fine folks on this forum for their expertise, from which I too have greatly benefitted.
I tried the PSI TBC setup, and I had the same issues (mainly non-concentricity) that I did with a mandrel. Anecdotally, I've seen very mixed reviews from people on this forum. Many have had the same experience as me. Others have found the setup works. On the other hand, I've never heard of anyone giving true TBC a chance and then going back.
True TBC is just a dead center and a 60-degree cone center to hold the work and a set of calipers to measure with. Bushings are optional.
- Once I've prepared the blank (drilled, glued, squared), I simply put it between the dead center and the cone center, snug it up (not too tight or you can stretch the tube and crack the blank), and get to turning.
- I use the calipers to take the actual diameter of the mating kit parts, and then measure as I turn.
- I go just past the diameter so that I can build up my CA finish to the exact diameter. As I'm turning, I'm looking for the very slightest bit of travel when I measure with the calipers. I go until I can get the calipers over the blank without forcing them, and then a tiny bit further.
- It helps me to have two sets of calipers. I use one for the mating part on each end of the barrel. Even for kits like slimlines that ideally have the same diameter for all mating parts, I've found there's slight variations depending on kit quality. I may even add a third set so I can get all the measurements for a double-barrel pen at once.
- Bushings:
- I've stopped using bushings entirely for single-barrel pens.
- If I have the bushings for a double-barrel kit, I'll use them on my mandrel to get the blank down to a little over size, moreso in order to see the grain and decide which end will be the nib rather than as a time saver. Once the blanks are down approximate size, I'll switch to TBC and finish the barrels individually.
- You can buy specialized TBC bushings for a lot of kits, and you can make them as well. A lot of people make bushings from delryn (spelling?) because it's relatively inexpensive, it turns easily, and CA doesn't stick to it. Ultimately, you're going to want to use calipers to get the best fit, so for me, buying/making TBC bushings is not worth the time/money investment.
- CA glue: Although I often forget, I do try to take my dead center and 60-degree center off the lathe and soak the tips in acetone to remove any CA. CA buildup is really the last place left in my process where I can introduce non-concentricity.
One final note: My switch to TBC was motivated largely by issues with non-concentricity. There are many potential causes for non-concentricity, but IMO the biggest are issues with:
- Headstock-tailstock alignment
- Sanding technique
- Workholding (bent mandrel, slight defects in the mandrel, worn bushings, etc.)
- Inaccurate blank squaring.
Lathes can generally be adjusted/calibrated for #1. I solved #2 with practice and advice from folks on this forum. #3 was by far the worst offender, and TBC eliminated probably 90% of the non-concentricity I was experiencing. The second biggest culprit was #4. I switched from manual squaring with a pen mill and hand drill. I now use Rick Herrel's
offset sanding jig (scroll about a third of the way down), and haven't looked back. I know others have had great success with jigs for a disc sander.