Question on pen blank preparation

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jimr

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I hope I can ask this without getting to long and boring. Now that I have really got into pen turning I am noticing a problem that is bugging me. On several pens when I turn them down to finish diameters the wood thickness is not uniform around the entire brass tube. I think this is because when I use the barrel trimmer the surface of the cut on the end is not perfectly perpendicular to the length of the barrel. For me it is almost impossible to get the hole drilled perfectly parallel with the sides of the blank which makes it impossible to trim the blank ends perfectly perpendicular with the barrel. This results in the blank not being perfectly perpendicular with the barrel trimmer when I use the drill press to trim the ends. This results in the bushings not fitting perfectly against the trimmed blank when they are loaded onto the mandrel.

So far I have confused myself with this dissertation so if anyone can follow what I have described I would appreciate any comments, observations, recommendations or whatever.
thanks a lot
 
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RussFairfield

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Trimming the ends of a pen blank so it is square with the INSIDE of the brass tube is not difficult with the tight tool. You didn't say HOW you were trimming the ends of the blanks. From your description, I am assuming that you are using something other than a dedicated barrel trimmer. The long pilot on the end of these tools references the cutting tool to the inside of the tube,, and not the outside of the blank. The result is an end that is as square as you are going to get. Different pilot diameters are available for different tube diameters. There are also jigs available for doing the same thing with a disc sander.

I know there are folks who are drilling and trimming pen blanks without referencing the trimming device to the inside of the brass tube. This requires a degree of accuracy in sizing the wood, drilling the hole, and gluing in the tube that I have never been able reach, and choose not to try.
 

dw

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Jim,

I'm no expert, but I had exactly the same problem. I don't think it's the barrel trimmer. As long as the trimmer fits the brass tube closely, there's no way that the barrel trimmer can leave the end of the barrel less than perfectly square with the tube. That's the theory, anyway...and it's held up pretty good for me.

The problem, in my case at least, was that my lathe (or the mandrel) wasn't spinning true. These mandrels get bent pretty easy. I was ever so careful with it. but after reading RussF's webpage, I put my mandrel in the headstock and ran it without any wood on it, and without bringing up the tailstock. There must have been at least an eighth inch "runout!" I tried truing it but to little effect.

In any case, the way I solved the problem was to remove the morris taper from the mandrel and chuck the shaft into a self-centering four jaw scroll chuck(PSI--$79.00 with three sets of jaws!). You can use a collet chuck if you have one . Then I pushed the shaft into the chuck and into the headstock so that only enough shaft protruded to turn one barrel. I also brought up the tailstock and tightened it just so that the live center and the mandrel turned together. Not only did the shaft run true but I've not had a single out of round barrel since. Watch your knuckles, however!

Hope this helps...it can be frustrating.

DWFII
 

timdaleiden

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I hope I can help with this. If your drilled holes are not perfectly perpendicular with the outside of the blank, it really shouldn't matter too much. It sounds like you use a pen mill to square, and this should make a perfect 90 degree angle to you tube.

There are few things that can cause eccentricity in your wood thickness. A bent mandrel is often to blame. If the knurled nut is too tight it can bend the mandrel. If the tailstock is pressed too tight this can bend the mandrel. Your mandrel may just be untrue all by itself.

You can easily test for this. Get your lathe going, and hold a pencil on your tool rest, and touch it against the bushings. Turn off lathe and see if there is a mark on only one side.

One other cause is relying too heavily upon sand paper when nearing the end of your turning. Your tools will make perfect cuts, but sand paper is not supported except by your hand, and so does not necessarily take off an even level of wood.

There may be other things that can cause this, but these are common causes. If this doesn't help, keep asking. Some one will get you through it.
 

Daniel

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One other cause of out of round barrels I have ran into, Tools not being sharp enough. the duller the tool the more force you use to get it to cut. push to hard adn you are bending the mandrel. I can only repeat what was mentioned before about trimming the blanks. Please add how you are trimming them.
 
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