Bent Brass Expanding Mandrel

[MadTrapper]

I've got a 5/8" expanding brass mandrel.  It is 5/8" overall with texturing on the call end.  It's machined and a very decent mandrel.  I use it with a Beall Collect chuck.  I've turned several dozen calls with it over the past couple years. 

Yesterday I turned a black walnut call with 4 maple inlays that look like darts, similar to a pool cue base.  I noticed that the darts where showing up at different lengths and couldn't understand what caused that.  It finally dawned on me that perhaps my mandrel was bent.  I pulled the call off and put it on a different mandrel and turned off a little wood and wouldn't you know it, the dart points all lined up perfectly.  I was taking off more wood on one side of the call than the other.

I rolled the mandrel on my bandsaw table and was not able to detect any wobble.  I pushed the lathe tailstock up to the end of the mandrel almost touching the expansion screw and used the tailstock as a reference point.  When I turned on the lathe I was able to barely perceive a slight misalignment at start-up and stop.

Anyone else ever have this happen? 

What do I do with a bent brass mandrel?  (I paid good money for this thing!)

[VECtor Calls]

Not to concern you too much, but it could be an issue of your headstock.  Its worth checking into.

[MadTrapper]

Thanks VECtor Calls.  I guess I assumed that since the other mandrel is running true, that the problem was with the brass mandrel but perhaps not... 

How would one go about checking the headstock?

[LagrueCustomCalls]

Use a dial indicator with a magnetic base. Measure for runout at the headstock. Thousandths there multiply at the end of a mandrel.

My guess is that your mandrel is bent. Unfortunately it is probably scrap.

[MadTrapper]

I've been pondering on this little issue and am left wondering, absent being dropped, what causes a 5/8" dia. brass mandrel to get bent? 

[FDR]

Ever have a tool catch with the blank unsupported by the lathe tailstock? It does not take that much force to bend 5/8 inch diameter brass.

Fred

[VECtor Calls]

1/2" is the biggest I have ever bent.

Any update?  Put any other kind of bar in there to check it out?

[MadTrapper]

Never had a tool catch so not sure I guess what may have caused this...  Oh well, what's done is done.

I am going to need to replace this one so I'm looking for recommendations on a good 5/8" expanding mandrel.  Should I shy away from bass or not?  I'd like to stay with the style of expanding mandrel that does NOT utilize the tailstock and uses only the collet chuck.

Let me hear your recommendations please!

Thank you.

[FDR]

I can recommend the steel mandrels from Wade at Webfoot custom calls. They have a larger screw than the brass mandrels and work just as well. I have both and much prefer the steel ones.

http://www.webfootcustomcalls.com/wfcccart/mandrels

Fred

[Aaron at Wingerts Woodworks]

Not to be insulting by any means, but if your mandrel runs smoothly when rolled on the table I'd be willing to bet you're not putting it in your collet chuck in the right sequence.  As simple and intuitive as it seems, there is absolutely a wrong way to do it. 

Check your steps:
1) Take the mandrel out of the chuck and put it down
2) Take the nut off of the chuck
3) Remove the collet from the nut or the chuck body, wherever it is
4) Insert the collet into the nut, where it should snap in place and support itself
5) Screw the nut onto the chuck body.  I like to run mine down semi-hand-tight for good measure.
6) Back the nut off until you see or feel the collet release a little, but don't remove the nut
7) Insert the mandrel
8) Tighten it down with the Beall spanner wrenches

If you insert the mandrel into the collet and then assemble the collet into the nut, you absolutely positively will get a slight amount of runout.  I cannot explain why, but you will.  I learned this the hard way many years ago and Doug Hess at River Mallard Calls got me straightened out. 

[Wade@WEBFoot]

Is it only at the end or the whole length of the mandrel?  Any run out at the solid portion or only at the petals?

If the mandrel has been over tightened - that can set things off center.  If expanded beyond the yield point the petals can be bent and not return to original position.  AND.... typically - there will be one petal (sometimes two) that bends first - which in turn - can leave things off center at the end when a blank is installed and expanded.  And this can happen if your blank bore is too large (most drill bits go oversize at least a little... and some A LOT) so it can be done inadvertently if you have a drill or setup that goes way oversize.

But without knowing where and how much run out there is - its hard to even guess if anything could be done - but odds are high that if the mandrel or petals are bent - it will take more to straighten it than to buy a new one.

Ive never been a fan of brass mandrels - but I understand why some folks like em... easier on tools when you slip up and hit it, and some like that they expand easier then steel ones - but there in lies the rub...  easier on tools and easier to expand means softer - and softer bends easier and also wears faster.  Of course there are some soft steels out there too...  mandrels made from 12L14 steel are pretty soft too, but tougher than brass yet not as hard nor as tough as say 4140.

Tensile Strengths and hardness (Rockwell B scale):
360 Brass:  58,000 PSI - Hardness 78 Rb
12L14 Steel:  78,300 PSI - Hardness 84 Rb
4140 Steel:  95,000 PSI - Hardness 92 Rb

Of course, you can darn near bend anything... just a matter of the proper application of force...   

Each mandrel I carry has its pluses and minuses... as do all the mandrels out there...  And given normal circumstances and care - they will all last a long time.  Some might have a more steady diet of replacement expanding screws, but a little dab of grease can go a long way in helping curb the appetite :D

Personally I treat expanding mandrels as a consumable - with the pleasant side effect that when cared for, they can last a long time barring any accidents... and some longer lasting than others.

I say pic one that makes sense to you and carry on :D

Aaron is spot on as well.  The reason why this happens is visible the collet nut.  Look inside of the nut - youll see an off center bore - that creates a "lip" on about 1/2 of the nut (yes its visibly off center and yes it really should be there and be like that :D).  That lip is what the groove in the collet clicks into.  Youll also see in front of that lip a tapered smooth surface just inside the end of the nut.  The lip is there for ONE purpose... to pull the collet out when the nut gets backed off.  When you put the collet in the chuck without putting it in the collet nut first - its that lip that is pressing on the front taper of the collet into the chuck.  And since its not concentric to the body of the nut and chuck it gives you lopsided pressure on the collet and the collet doesnt get pressed in the chuck body straight like it should be hence the run out.  When you click the collet into the nut - the tapered surface on the nut is pressing on the tapered front end of the collet (the short little bit of taper at the front of the collet), and that is pushing it into the collet chuck.  That taper on the nut is concentric to the nut and the chuck hence everything goes in nice and straight.  NOT clicking the collet into the nut first, or even the process I have heard some use - of putting the collet in with nothing in it, then the nut, tighten til you hear a "click", back off the nut some and install what ever your holding - will likely do much else other than damamge the nut, the collet, or potentially both as well as the possiblity of abnormal wear in the collet chuck body over time.

Cheers
Wade

[MadTrapper]

Well it would appear that I have other issues going on rather than a bent mandrel.  (Although after looking at Webwood's steel mandrels, I may be buying one of those anyway.  Nice!)

I have an Alisam after market indexing jig screwed on between my Beall collet chuck and my headstock.  Also behind the jig is a plastic washer to assist in removal so things don't get too tight and unable to loosen.  By removing the plastic ring I'm able to tighten the collect chuck onto the headstock a little bit more.  Apparently this little bit makes a difference.  Why one mandrel runs true with the plastic ring on and one doesn't is another of life's many mysteries. 

Anyway I'm going to play with this a bit see how things go.  For now it appears that the problem may be solved.  ???

Thanks for all the insight and help on this.  Much appreciated!

[Wade@WEBFoot]

I would bet the plastic washer is allowing for misalignment.
The way threaded items align on a spindle for example - is the threads provide part of the centering, and the shoulder that the back of the chuck tightens upon is the other alignment.  The threads align radially and the and the back shoulder aligns for parallelism (Im brain farting on the technical term here).  An issue with either the threads or the shoulder (a ding, a chip, etc...) then something will be out of whack.  And with a plastic washer - you can squish it more or less depending on how tight... so depending on how tight it may be in a different position.  Always better to be steel to steel.  A little oil will aid in disasembly... but better to need a wrench to take it of than not... unless its an extremely precision thread and shoulder (which I have yet to see a wood lathe with that).

I bet you drop the plastic and remove any dings or burs or chips etc... and the collet chuck should run true.  Another place a dial indicator will come into play... you can then check TIR (Total Indicator Reading) on the spindle, the chuck, the mandrel, and so on...  then you know if you got it, or at least how far it is out.

Glad you found something to start with though... always better to have found something and have to chase it than to just scratch your head and wonder "what the heck?" and blindly replace things hoping to find the solution.

Wade