What caused this?
- Thread starter booney0717
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reiddog1
Member
Could be a couple of reasons. Bent mandrel or head and tailstock not aligned properly come to mind. If you are a mandrel user, be careful not to overtighten the tailstock. Also, check for tight fit of your bushings. Some peeps turn between centers without bushings to avoid mandrel and bushing issues. Hope this helps.
Dave
Dave
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76winger
Member
Bent mandrel is the first thing that comes to mind if you keep your tool firmly planted on the rest and don't use the bushings as a guide for your turning tool (which would be done if using one of the many carbide tip scrapers). Pushing too hard on the tip of the mandrel with the center of the tailstock could cause it to bow the mandrel and cause this problem as well.
If using a skew and riding the bushings and moving onto the material when cutting those final passes (to avoid the result you got), then the truness of the bushings would be in question.
If using a skew and riding the bushings and moving onto the material when cutting those final passes (to avoid the result you got), then the truness of the bushings would be in question.
booney0717
Member
Just went down and looked the mandrel is bent. Thanks
tommax
Member
I switched to a mandrel saver after bending a couple, now I can't over tighten...
#2MT Pen Mandrel Saver at Penn State Industries
Tom
#2MT Pen Mandrel Saver at Penn State Industries
Tom
its_virgil
Member
Oh yes you can! Too much pressure on the bushing, whether with the brass nut or the mandrel saver can cause the tubes to bow. Too much pressure onto the end of the mandrel will cause the mandrel to bow. Too much pressure with both and the problems are compounded.
Do a good turn daily!
Don
Do a good turn daily!
Don
Dan Hintz
Member
You found your problem, but I did one recently that looked similar... a quick inspection showed it was the hole through the bushing that was cut off-center. I should probably throw that away before I accidentally use it again.
Chrisjan
Member
I went through this ritual a couple of times... Get a dead center for your headstock (left), a revolving center for you tailstock (you had to have one already?) and turn between the centers...
You can still use the mandrel to sand after you've turned and applied the finish. Just remember, if you chisel catches and doesn't blow up the blank chances are pretty good that the mandrel is bent - two mandrel rods are the same price as a dead center...
There are people (I use to) who wants to see the two blanks lined up to envision the shape; I made a coupler to use between the two blanks while turning between centers and it works like a charm - obviously is has to be well made otherwise you are back to the same problem.
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Hendu3270
Member
Definitely not saying this is wrong, but I'm having a hard time visualizing how the tubes would bow if you overtighten with the mandrel saver. I use it as well and have not experienced this. I have, like Dan indicated, seen the bushings with the hole not centered. I have a set of Majestic bushings that are like that and you can get it all set up to turn and see one bearing has a slight wobble look to it while running. Once my center comes in I'm planning to give it a go between centers as well.:wink:
Edit: Thinking about it a little more, It is pretty easy to overtighten if using the brass nut and are a beginning turner. The mandrel saver could probably be overtightened as well, but it seems you'd really have to be hacked off at your mandrel, and tighten the snot out of it to get any bowing.
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mywoodshopca
Member
What I normally do is rotate the blank on the bushings a few times before finish. When I have it rough size, I rotate it and double check for roundness, then sometimes once more before starting to sand. This gets rid of any potential out of round.
its_virgil
Member
What is the difference between tightening the brass nut against the right bushing and squeezing the bushings toward each other possibly causing the tube to bow, buldge or distort and tightening the mandrel saver against the right hand bushing and squeezing the bushings toward each other possibly causing the tube to bow, buldge or distort?? Distortion may not take place until most of the wood is removed...or it may not happen at all. But, it can happen. And yes, it will take a lot of cranking. The mandrel saver does eliminate the mandrel bowing problems associated with cranking the live center against the mandrel's end.
A pen barrel can go out of round while sanding. Grain alignment can be different on opposite sides of the blank causing one side to sand away quicker than the opposite side thus making the once round barrel now out of round.
There are several variables that can produce out of round pen barrels. I had several "bent" mandrels but as soon as I purchased a Beall collet chuck and started using it to hold my mandrels they all mysteriously became straight.:biggrin::biggrin:
Do a good turn daily!
Don
A pen barrel can go out of round while sanding. Grain alignment can be different on opposite sides of the blank causing one side to sand away quicker than the opposite side thus making the once round barrel now out of round.
There are several variables that can produce out of round pen barrels. I had several "bent" mandrels but as soon as I purchased a Beall collet chuck and started using it to hold my mandrels they all mysteriously became straight.:biggrin::biggrin:
Do a good turn daily!
Don
booney0717
Member
Thanks to all for all the good feed back. For now with finances being as low as they are i'm just going to have to go buy a new mandrel but as soon as i can get them i'm going to start turning between centers. I have read everyones posts and all had good points. Defently got alot of good from this one. Thanks again.
Hendu3270
Member
Absolutely nothing at all. I took your first post incorrectly. I thought you were saying the mandrel saver will bow the mandrel. You stated it could bow/damage the tubes, and tailstock overtightening can bow the mandrel, which is correct. :good:
Stay safe Don! Looks like you'll gonna get some mean weather tomorrow and it gets down here on Sunday.
Happy Friday everyone!!
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