mandrels

[hazard]

How often do you guys replace your mandrels/shafts? I have been doing the pen thing for a few weeks now and I am turning out of round at the bushings. It is getting very irritating. Maybe I am overtighting but I try not to. When I put a chisel on the taper or the live center it hums smoothly but when I put the chisel on the center bushing on a slimline the chisel jumps. I am assuming I bent the mandrel shaft.

thanks
Chris

 

[Rmartin]

Yep, what you've got there is a bent mandrel.

Run your lathe with the mandrel only. A little three in one oil and fine sandpaper. Clean up with a paper towel. Take it off and roll it on a peice of glass. Does it wobble? Flex it until the wobble is gone.

Or, you could throw it away and turn one blank at a time without using a mandrel.

Rmartin
I cut corners

 

[wdcav1952]

Chris,

There are also things to watch for with respect to getting a bent mandrel. Pushing too hard on the turning tool will tend to bend a mandrel. Remember the "sharp tools, light touch" mantra. Also, oddly enough, tightening the nut on the end of the mandrel too much can flex an mandrel leading to out of round turning. I went through more mandrels than I care to remember when I started turning pens.

 

[hazard]

2 of my problems have been laid out already. I give it when I am turning. I push harder then I should. I also tighten the nut probably way to much.

Thanks for the input guys
Definite newbie.
Chris

 

[loglugger]

If everything and your blanks are squre, how tight you tighting the nut dosen't make a defference unless you are useing a real soft wood.
Bob

 

[stevers]

If you are pushing that hard you may want to look in to how sharp your tools are. If I pushed that hard, it would spin off the blank in about 10 seconds. If you find you need to straighten a mandrel, look at this.

http://www.woodturner-russ.com/Pen10.html

 

[wdcav1952]

Originally posted by loglugger
<br />If everything and your blanks are squre, how tight you tighting the nut dosen't make a defference unless you are useing a real soft wood.
Bob

Bob, not to be blunt, but you are not exactly right. As you turn, the blank tends to get smaller, [] and there can be slight flex that can lead to out of round turning if the nut is too tight.

 

[hazard]

well I didn't think I was pushing that hard. I sharpen my tools often. I will work on my skills this weekend. I was going to just buy another shaft on Friday when I make yet another visit to woodcraft.

thanks again

 

[loglugger]

William, get out your dail indicator and set it up behind your mandrel in the center, with the blanks on use the center bushing. Turn the lathe by hand for all of the tests, set the mandrel up before without the blank and make sure it is true, then put your blanks on the mandrel and lighty tighten the nut while you are turning the lathe by hand, as you are tighteng the nut at any time it gets out of true, rotate the blanks until it it true and then you can tighten the nut tight and it will stay ture. I have tried this many times and most of the time I put the blanks on the mandrel they needed a bit of turning the blanks to get them true. When they are true I have taken 6 inch channel locks and tighten them down and they will stay true unless they are a soft wood like pine and the bushinge will crush into the wood. Other things that I have found is to make sure the bushings are on past the threads or it may let the bushing throw the mandrel out of round.
Some bushings fit lost on the mandrel with up to 4 thousand play.
As I have said if every thing is true and square then you can tighten the nut and it will stay ture.
I put the blanks on and tighten the nut and bring the tail stock up but not tuching the mandrel
and turn the lathe by hand to make sure it turns true, If it dosen't then rotate the blanks or find out why it is not true, glue on the ends of the bushings or a burr on the tube can do this. This works the best for
me.
This is my opinion on this and I do not recommend to use pliers.
Bob