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Pens off center -- need help!

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Forum topic by jayman7 posted 12-27-2009 04:52 PM 1637 views 0 times favorited 5 replies Add to Favorites Watch
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jayman7

218 posts in 2966 days


12-27-2009 04:52 PM

Topic tags/keywords: pens lathe mandrel bushing

I’ve been having a great time turning pens with my new PSI lathe. I’m slowly learning about the world of turning. Only problem is the pens aren’t exactly centered. Part of the wood is flush at one part of the bushing, but 180 degrees around the other side of the pen, the wood protrudes away from the bushing. I checked the headstock and tailstock and they line up perfectly. I tried a slimline bushing and fountain pen bushing and they both have the same problem, so it has to be the mandrel. This problem happens predominantly at the center bushing and not at the end bushings. But I’m not tightening the knurled nut or pushing the live center in too much either; I’m using light pressure.

Anyone have any ideas? Maybe I need a new mandrel?

I’ve been using this mandrel from Woodcraft:
http://www.woodcraft.com/Product/2003759/2325/2-MT-Mandrel.aspx

Maybe this mandrel doesn’t have that problem. What does it mean by “self-centering?” How does that work?
http://www.woodcraft.com/Product/2001608/10989/Professinal-Pen-Turning-Mandrel-2-MT.aspx

Thanks!!


5 replies so far

View flyingoak's profile

flyingoak

68 posts in 2569 days


#1 posted 12-27-2009 04:59 PM

I have had a similar problem. usually this is caused by the tube not being completely centered in the blank. if it is angled much at all it will spin off center leave a gap at the hardware.

you might just want to check this…. it could be something else but when mine do that i have not drilled in the tube straight

-- where is the duct tape.....

View LONGHAIR's profile

LONGHAIR

94 posts in 3275 days


#2 posted 12-27-2009 05:03 PM

It sounds to me like your mandrel is bent in the middle. So when you turn the wood to “round” and it spins true, the mandrel is not centered. Try spinning the mandrel with out anything on it. If it is indeed bent, you may be able to straighten it.

View JerrySats's profile

JerrySats

237 posts in 3071 days


#3 posted 12-27-2009 05:12 PM

Sounds like a bent mandrel to me too . If you can’t get the bend out when you get close to the finished size rotate the pen blank itself half a turn .

Don’t apply to much pressure on the mandrel with the tailstock , just enough to hold it . Same goes for the nut in the mandrel . These can both cause the mandrel to bend .

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jayman7

218 posts in 2966 days


#4 posted 12-27-2009 05:32 PM

Thanks for the suggestions. I will check to see if there’s a bow and try to get it straightened out. If not, I will try Jerry’s idea of rotating the blanks which sounds like a great idea.

View JTTHECLOCKMAN's profile

JTTHECLOCKMAN

176 posts in 2610 days


#5 posted 12-27-2009 05:55 PM

A couple things were mentioned and I agree with most of them. The one I don’t agree with is the drilling the tube off center. This does not matter unless there is not enough material left on the thin side for the kit. Two things that are needed and that is flat ends and a round blank when completed. You will get the round blank because that is what a lathe does. It will always find center so if drilled off center it does not matter. Now if the ends are not trued before putting against the bushings than that is your reason for off centered blanks. You need to true the ends with either a barrel trimmer with the correct sleeve or a disc sander with the tube, not the blank, 90 degrees to the disc.

If you are not putting much pressure on the securing nut and not applying excessive force when turning than a couple things maybe the problem. One is a bent mandrel rod. Take it out and roll it on a true flat surface and you will tell right away. Fix is to replace rod or get a better mandrel. The one you show with the adjustable rod is the way to go but I do not like the 2 nuts sytem because that requires wrenches that you can’t find when you need them. I like the setscrew type and uses an allen key. I think PSI carries them. I know CSUSA has them. You want to keep the spacing as short as possible between the head stock and tailstock and especially if doing kits that have only one blank this is a big help.

Next problem can be the live center you are using. You want to use a 60 degree live center and not the stock one when using a mandrel. It will not center in the hole on the end on the rod properly so this can cause a wobble that is hard to detect but is there. The next thing can be a worn morse taper on the mandrel or the rod hole is not centered. It happens even in the best tools. Quality control is not what it used to be. The last thing is are the head stock and tail stock dead on??? That is something you have to check before turning.

Now with all that said there is a way to get perfect round blanks and you don’t use a mandrel. It is called turning between centers and uses special bushings only thus elliminating the mandrel and the problems it can cause. If you want to learn about this you need to join the best turning site on the net and that is the IAP penturning site. There is a fella there that sells the bushings.

One other thing, if the fit is close and not too bad then the rotaing of the blank on the mandrel maybe enough for you. The key here is to get close to final sizing and then loosen the nut and spin the blank and make sure the bushings do not spin or else you defeat the purpose. Rotate the blank about 90 degrees and tighten nut and now finish turning and sanding. Good luck and sorry for being longwinded.

-- John T.

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