Blanks not to my liking

[Woodchipper]

I assembled four kits today to deliver to the craft mall. I was disappointed that some of the wood blanks were not completely round. The first group was a perfect as I could want. These were slimline kits and the components were measured with calipers that went plus or minus one thousandth. I have turned on the long mandrel for years and never had this problem, turning two at a time. Considering only turning one at a time and positioning the blank close to the headstock. Or make the plunge for the shorter mandrel as carried by several suppliers. Considering this one: https://www.woodcraft.com/products/woodriver-professional-pen-turning-mandrel. Your thoughts?

 

[keithlong]

The way I turn slimline pens is with turn between center bushings. You can turn both blanks with these bushings and a short piece of a mandrel. The mandrel rod is a 1/4 inch round, so I bought a piece of drill rod and cut the length that I needed. To determine that length you need to take 2 slimline tubes and then lay the bushings flush to the ends of the tubes and measure the distance between the 2 bushings. It is faster this way because you can see both blanks as you turn. Place a regular bushing on the rod between the 2 blanks. The TBC bushings lock both blanks in place and you turn them without a full length mandrel. I have turned hundreds of pens this way with no issues and no vibrations. Hope this helps.

 

[jttheclockman]

Of all the pens I turned and from the very start I never had two blanks on the mandrel at the same time and never will. Lining up blanks is a joke. You can do it it even not side by side.

 

[montmill]

I'm fighting eliptical shapes also. The end closest to the head stock is fine, the end toward the tailstock is out of round. Obviously something is not running true. Tailstock itself, moris taper messed up, dirt or something in the morris taper, live center out of round? Problem solving. Try shortening up your mandrel by turning only one blank and see if you can figure out where the problem is-head stock, tail stock? Process of elemination. Scientific method, eliminate variables. Good luck.

 

[Woodchipper]

Thanks to all. Lots to consider.

 

[hewunch]

I no longer use a mandrel, but when I did, I would get close to size and loosen the nut and spin the blank. Then tighten the nut and knock off the high spots. I would do this a total of 3 or 4 times and found I was closer to round.

 

[ed4copies]

I'm fighting eliptical shapes also. The end closest to the head stock is fine, the end toward the tailstock is out of round. Obviously something is not running true. Tailstock itself, moris taper messed up, dirt or something in the morris taper, live center out of round? Problem solving. Try shortening up your mandrel by turning only one blank and see if you can figure out where the problem is-head stock, tail stock? Process of elemination. Scientific method, eliminate variables. Good luck.

While this answer is not perfect, it will likely greatly improve your results:

Do NOT lock your tailstock in place until you have turned on the lathe and allow it to spin to "center" the mandrel on the tailstock point.
This way, you are not locking it "slightly off center" to creat an ellipse.

When it is centered, you will get a circle!
(Answer courtesy of years of listening to Dick Sing)
Ed
Hans posted while I was typing--similar solution

 

[KenB259]

When I very first tried penturning, it was a slimline and I had both barrels on the mandrel at the same time. I didn't like the amount of flexing I wad getting so from that point on, I turn one barrel at a time.

 

[Mortalis]

Between centers, no bushings, go light on the cuts until you get familiar with the technique. I hold the blank with one hand and tighten the quill until the blank turns. Then see if you can stop the live center in the tailstock by lightly grasping it as it turns. If you can, then tighten the quill a bit more. Keep doing that until you cannot stop the live center (usually takes a couple times no more). You will most likely need to retighten the quill on the tail stock from time to time (go back to beginning technique). It's no big deal. Just done crank down on it.
Obviously you will need to gage the ends with some measuring device. Measure the assembly pieces and then turn till you get same measure. Sand till smooth. Round over the end edges a bit.

 

[jttheclockman]

While this answer is not perfect, it will likely greatly improve your results:

Do NOT lock your tailstock in place until you have turned on the lathe and allow it to spin to "center" the mandrel on the tailstock point.
This way, you are not locking it "slightly off center" to creat an ellipse.

When it is centered, you will get a circle!
(Answer courtesy of years of listening to Dick Sing)
Ed
Hans posted while I was typing--similar solution

If this were the case then the end is not 60 degree or the center point is not 60 degree. The center point needs to fit the end of mandrel at any time because if it does not then spinning lathe will push it off center anyway. Now does the center point wear? yes it does so may need new one or the mandrel has waddled out a larger hole. Hans did not say what you are saying. he mentions the old adage of spinning the blank a couple times as you get closer to finish size to help with off center spots. That was my understanding. This has been talked about many times here because of maybe out of round bushings too.

 

[egnald]

I went through several different iterations of mandrels until arriving at the combination of tooling that I use today. I find that I rarely get anything that is out of round with it.

For the mandrel I use an "Adjustable Pen Mandrel" that I got from PSI, but instead of the "threaded, brass knob type" mandrel rod that came with it, I use a piece of "D" Drill Rod.

The "D" Drill Rod is specified as 0.246-inches +/- 0.0005 inches typical and is a very good replacement for most standard 0.247-inch "A" mandrel shafts. However, if the sizing bushings have through holes that are on the small side of the tolerance and fit too tight on the "D" Drill Rod, I step down to a "C" Drill Rod which has a slightly smaller diameter of 0.242-inches +/-0.0005 inches.

For the tailstock end, I use a "Hold Fast Mandrel Saver" by TMIProducts which replaces the simple through hole in a typical mandrel saver with a small centering collet. This not only applies pressure against the components on the mandrel shaft but also closes the collet down on the shaft to center it more precisely in the tailstock than what can be achieved with the typical through-hole mandrel saver design.

So, I wind up with a good, precision, straight mandrel shaft that is the shortest possible (no spacer bushings) which is precisely centered by collets on both headstock and tailstock ends. I think that TBC might be the only thing that is better.

Unfortunately TMIProducts discontinued their mandrel saver this year (2025), but the precision and performance of the Woodpeckers Ultra-Shear Pen Mandrel System or the Axminster Compression Pen Mandrel System should be comparable.

Dave