How do I avoid a mandrel nut getting too tight?

[Nickfff]

Hello, I have noticed that after hand tightening the mandrel nut barely snug, I spin and the mandrel thumb screw nut gets very tight on its own-so tight in fact that I need pliers to loosen the nut. This can effect blow outs on the lathe because it locks the barrels. My setup is normal bushings and a washer. I was thinking that may be I need to add some 7mm bushings or maybe that the bushings aren't completely flat on the sides, or the mandrel is bent?

Does anyone have any ideas on why this occurs and reccomendations on how to avoid it?

Thanks in advance for replies,
Nick

 

[hunter-27]

Wish I could help but I've never had that Problem, I do not use a washer, if I need to I use an old 7mm barrel or bushings to fill a gap

 

[airrat]

I have had it somewhat happen when turning harder materials. I check the nut each time I stop the lathe when rounding out a blank. Try sanding the edges off so its not square to begin with.

 

[1080Wayne]

Nick It happens quite frequently if a piece of wood is unbalanced because it was drilled off center . Stop the lathe once the piece is round , loosen the nut and re-tighten . Wayne

 

[Chasper]

Are you using an adjustable legnth mandrel? Is the set screw on the drive end lose enough to allow the shaft to slide in when you tighten the tail stock?

 

[Paul in OKC]

You may need to snug it a little more at first. If you blanks spin on the mandrel when turning, this tightens the nut as well. Otherwise, like said above, stop and loosen the re-adjust after roughing the blanks down a bit.

 

[Rifleman1776]

I have had it happen frequently and never got concerned about it. It does happen without the circumstances listed above, other than the fact I do use washers. My theory is that it happens from inertia when we start the lathe. Not a big deal, doesn't affect anything.

 

[Brewmeister35]

I do exactly like wayne said and loosen the nut after the blank is first nice and round.

 

[Chasper]

Are you using an adjustable legnth mandrel? Is the set screw on the drive end lose enough to allow the shaft to slide in when you tighten the tail stock?

 

[Rudy Vey]

Are you using the large knurled nut that comes with some of the mandrels?? I have changed to a simple nut instead and can in most cases undo the nut by hand. Another way would be to use a spring washer. Or just keep a small wrench by your lathe...

 

[TellicoTurning]

I have this happen frequently too and never thought anything of it, other than it's annoying.. I think like Frank, it's inertia when the lathe starts and when turning harder materials... happens almost every time I do antler. I just keep a pair of channel locks next to the DP, which is right next to the little lathe.. handy when I need them.

 

[Nickfff]

All,
Thanks for the replies.

Here are some answers to the questions raised...
-Yes, I do use an adjustable mandrel
-I tighten the mandrel with on 2 nuts/2 adjustable wrenches-I don't see a set screw
-Rudy-I am not familiar-what is a spring washer and where can you buy them? Sounds like it may help...
-I do need to resolve this as the heightens the likelyhood of chunkoff or melting acrylic.

I am experimenting with less tension between the tail stock mandrel and that seems to help somewhat.

Nick

 

[Rudy Vey]

Originally posted by Nickfff

All,
Thanks for the replies.

Here are some answers to the questions raised...
-Yes, I do use an adjustable mandrel
-I tighten the mandrel with on 2 nuts/2 adjustable wrenches-I don't see a set screw
-Rudy-I am not familiar-what is a spring washer and where can you buy them? Sounds like it may help...
-I do need to resolve this as the heightens the likelyhood of chunkoff or melting acrylic.

I am experimenting with less tension between the tail stock mandrel and that seems to help somewhat.

Nick

I have a link here, the proper name is actually "lock washer"

http://www.thefreedictionary.com/lock+washer

 

[loglugger]

If every thing is squre and the bushings are tight on the mandrel, then I think that the tighter it gets the stronger and strigher the mandrel will be. That doesn't mean to crank it down with a 12" crescent.
Bob

 

[Dario]

Originally posted by loglugger

If every thing is squre and the bushings are tight on the mandrel, then I think that the tighter it gets the stronger and strigher the mandrel will be.

Bob,

You are right but the key word is "everything being square" and "clean" too. Any imperfection or dirt can translate into a bent mandrel as you tighten it and we living in an imperfect world, most of the time, things will not be 100% square and clean. JMHO.

 

[airrat]

Nick again another way to help keep it from tightening up is to use a belt sander to knock off the square edges. I do that to all Acrylic, PR and Corian I do. I have not had a blow out since doing that.

BTW just remembered if you do it this way make SURE to mark the inside of the tubes so you know where your center (center band) is. DAMHIKT