Out of round blanks

[Woodchipper]

Have turned a bunch of Slimline pens and have had good luck with roundness (if there is such a word) but got ready to deliver two pens to the craft mall. Had some areas that were proud of the components. I was browsing the forum and noted that some do the final turning with a 60 degree live center and a 60 degree center in the headstock; have both. Will disassemble then and try that. Your ideas, experience, sympathies are most welcome.

 

[KenB259]

I always do the final sizing between centers, just as you described. Checking size often with calipers or my micrometer.

 

[Woodchipper]

I always do the final sizing between centers, just as you described. Checking size often with calipers or my micrometer.

Good to know. "Often" is the key, IMO. Thanks.

 

[thewishman]

When getting close to the final dimensions I stop the lathe and twist the bushings in opposite directions about 30 degrees. Repeat when sanding through the first grit. That helps to ensure the barrels will be as round as possible.

 

[Woodchipper]

Getting away from bushings or only for part of the turning.
PM sent.

 

[leehljp]

Many many people have had problems with mandrels and proud areas. The causes are several -
1. just a hint of dull tool, almost imperceptible - causes one to apply a bit more pressure to finish the turning. This causes minuscule flex in the mandrel and the results as you had.
2. An ever so slight bent mandrel can do the same.
3. Some people are not aware until later on - but many wood lathes come with a very pointed live center, i.e. non-60° live center. The pointed live center (non 60° live center) will ball up inside the small dimple/cup on the end of the mandrel. (Standard Mandrels require ad 60° live center to properly mate with the small dimple in the end of the mandrel.) This too causes what you experienced.
4. And then there is the pulling the tail stock up too tight which can introduce flex and a spot that is proud.

That is part of the reason I quit using mandrels years ago.

 

[Woodchipper]

Hank, thanks for the list. I do use the long mandrel from Woodcraft and try not to tighten the tailstock/quill too tight.
Question to Hank: What do you use now?

 

[NGLJ]

I now only turn between 60 deg centers to minimize out of round. Like most, I started out using a typical mandrel, progressed to using a mandrel saver, progressed to using turn between centers mandrel system, and eventually turn between centers using bushing adapters, and occasionally without bushing adapters. My original mandrel was used to make a polishing buffer with 2 wheels for plastics and ebonite. One wheel for applying blue buffing compound, and one for polishing. Since we need "perfectly" round blanks for custom pen making, I have got into the habit of turning all blanks to round between 60 deg centers, even for using with kits. It makes for accurate drilling using a collet chuck, and a square blank is going to get turned round anyway at some point. I no longer use my pen jaws for drilling on the lathe. Despite owning a centering vise for lathe drilling, I was never fond of using it. Of course, each to his own!

 

[Woodchipper]

NGLJ, I have a 1/4 inch mandrel for gluing a turning custom fishing rod grips. Seems to be a hard steel so I need to see if it will flex over the length. Might see how I can adapt that. Thanks for the idea.

 

[leehljp]

Hank, thanks for the list. I do use the long mandrel from Woodcraft and try not to tighten the tailstock/quill too tight.
Question to Hank: What do you use now?

I use a 60° live center and a 60° drive center for all, and have since 2008 - when I stopped using a mandrel. Even Mandrel savers were not yet invented back then. My idea for the TBC came from John Goodin and Frank? aka Rifleman. I had problems with CA lifting off of oily ebony wood when I snapped the bushings off the blank. John and Frank mentioned something they both heard or saw somewhere else in which the blank was finished turning and finished between centers. I called it "mandreless" for a few months but as others caught on, they called it TBC. About 3 years later, PSI and a couple of other companies began coming out with different versions of TBC or mandrel savers. The "mandrel saver" idea came from the fact that several of us learned that we were getting much better accuracy with the TBC than with mandrels. Then as we each analyzed the problems we all came up with the different ways mandrels introduced problems. Since some did not want to let go of the mandrel, and companies were seeing a falling off of mandrel sales, I can only guess that the came up with the name "Mandrel saver" as a replacement of pure TBC. The sliding mandrels in mandrel savers cut out some of the flex of the mandrel and increased accuracy.

I use bushings on the blank between centers to get it close to size - maybe 1/2 mm from final size, and then remove the bushings and finish getting to size with a very sharp scraper. If finishing with CA or GlueBoost, I usually take it .005 below the size of the nib end, center band or clip end and build up with CA to size. I do not use bushings after getting the blank to near size. I measure and measure and measure again with calipers. I think I have 5 sets of calipers.

 

[randyrls]

With Mandrels, if the ends of the blank are not exactly square to the tube, tightening the mandrel nut can pull / bend the mandrel out of straight. The head stock and tail stock need to be clean with no junk inside the tapers. To verify the mandrel is running straight, insert it into head stock bring up the tool rest very close but not touching the mandrel end. Rotate the lathe by hand and see if the distance changes.

You likely know all this......

 

[bugradx2]

Similar to others, I stopped using a mandrel and went to Turn Between Centers and haven't had an issue with the blank turned out of round since.

 

[greggm]

A long time ago, I stopped using the tail stock live center to tighten the mandrel. I got a mandrel saver that slides over the mandrel shaft and up against the bushings. That eliminates the potential for bending/flexing the shaft. I haven't had an issue with out of round blanks.