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Thread: Out of round solution
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1st June 2014, 02:32 PM #1
Out of round solution
I have become more self-critical about my pens and am particularly focused on fit, ie transition bw pen parts and blanks. I've noticed that that on some of the pens, even the latest ones have non-concentric parts, they are out by a smidgeon, but nonetheless they're out. I want to be able to at least get the transition bw the nib and the lower barrel spot on. I have a mandrel saver but i think the hole in it is slightly enlarged and that gave me a bit of run-out, i switched to just the brass nut but there's still a bit of vibration resulting in a less than perfect fit. The mandrel rod is straight, centres line up, i'm now contemplating turning bw centres, what do you think? You can't see any non-concentricity while the lathe is turning but there is a little vibration there.
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1st June 2014, 06:19 PM #2
TBC is the best way to go. I can't remember the last time I used a mandrel.
About half the time I use the blank with bushes between centres, lately though I have been just putting the centres straight into the brass tube, you have to go very steady until you get the corners turned off. But doing it this way, out of round blanks are a thing of the pastBrad.
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1st June 2014, 06:24 PM #3
I should add, that even when I do turn with the bushes to start with, once I get down to within 1mm finished diameter, I take the bushes off and take the final few cuts and sand, with the brass tube between centres.
Brad.
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1st June 2014, 06:44 PM #4
First thing make sure your head stock and tail stock line up and they are no misaligned or you will be oval pens every time. You will need a live centre and a dead centre in to do this. Any mandrel will bend. Before you move the live centre up to the end of the mandrel, rotate the mandrel and see if it rises and falls. If it does move it to the highest position and and then more the live centre in towards it. Adjust the live centre into the end of the mandrel so that it pulls the mandrel down to centre. Don't overtighten it. However, I use an adjustable collet mandrel and not a mandrel saver. Turn the pen down to as close as you can get it to the bushers and then finish off with sandpaper.
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1st June 2014, 11:56 PM #5
You only need a small amount of clearance between the bushes and brass tube, bushes and mandrel, mandrel and mandrel saver hole, or a combination of all, and you will get finished blanks that are not concentric.
I do similar to Ironwood, except I use the mandrel and bushes to turn down to within about 0.5mm of finished diameter, and than put the blank between centres to finish turning and apply the finish. This way you will be guaranteed of a concentric blank.
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2nd June 2014, 02:53 AM #6
Having never even used a mandrel, I can't comment on that part. But there are many things that can cause out of round pens. I noticed I had a few that were just slightly out of round. Turned out, I had some debris in my headstock MT. after it was cleaned out, everything worked much better. And it wasn't much, but it doesn't take much. Now I clean the MT religiously in both the headstock & tailstock.
I will say that I'm a big fan of TBC. I started that way, and have been very happy with the results. Good TBC bushings can be expensive, but so can replacing mandrels. And so far, I haven't worn out any of my bushings. Some may be a bit smaller, but that's ok. I also use the same method as ironwood for final dimensions of the blank.
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2nd June 2014, 07:01 AM #7
All of the above can be true "BUT" it all starts with trueing the ends. If the ends are not 90 degrees to the tube then any blank turned any way will not be concentric. Need to pay attention to this step.
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2nd June 2014, 11:52 AM #8
Appreciate the feedback. Centres line up as mentioned, mandrel is dead straight the vibration is felt at the tailstock end. The mandrel saver which I have used and is a great aid has its hole slightly enlarged (I think) and that gives it some wobble, I have gone back to using the brass nut and the live centre. Have also found that if I run the lathe at high speed, use light cuts that the work is more concentric but not perfect especially at the tailstock end.
I put a blank b/w a dead centre and live centre, there was no vibration or perceptible wobble. I guess I'm going to need to make some bushings for the b/w centre set-up, some form of stepped bushing where part goes flush into the tube. I basically turn slimlines so wasn't keen on going b/w centres as it takes twice as long to turn a pen but for the sake of accuracy I'll have to.
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2nd June 2014, 12:03 PM #9
Try the mandrel with a live centre holding the end in place and see if you still get the wobble. It may be a faulty mandrel saver. First, square off the ends of your blanks after you glue the tubes in using the disc on a bench sander if you have one. Sand down until the tube is exposed at the end. Only other thing I can think of for vibration is the tailstock not being locked down tightly.
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2nd June 2014, 12:14 PM #10
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2nd June 2014, 01:22 PM #11
The mandrel saver must be positioned so that the nose is running on the mandrel proper and not the threaded part of the mandrel.
If it runs on the thread it will not support properly as the thread part is undersizeJim Carroll
One Good Turn Deserves Another. CWS, Vicmarc, Robert Sorby, Woodcut, Tormek, Woodfast
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2nd June 2014, 01:32 PM #12
What if the nose doesn't reach the mandrel, by the time you put the bushings and blanks on I think mine sits on the threads or at least part of it does. The hole in the mandrel saver nose is still bigger in diameter than the mandrel rod, I wonder if there's been some wear on the mandrel saver nose?
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2nd June 2014, 01:42 PM #13SENIOR MEMBER
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2nd June 2014, 02:00 PM #14
You would have had to of made a lot of pens if you have worn the hole in your mandrel saver. I have 2 mandrels which I use. One is very old but not worn, the other is newer and also not worn. The newer one is a perfect fit in the mandrel saver, and the older one is a sloppy fit. It appears that the older one was just made from slightly smaller diameter rod. It could be just a mandrel that is slightly undersize.
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2nd June 2014, 07:52 PM #15
if it has been running on the thread for some time then yes it will be worn and so no help when running on the mandrel proper.
Jim Carroll
One Good Turn Deserves Another. CWS, Vicmarc, Robert Sorby, Woodcut, Tormek, Woodfast
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