# 'long' expanding mandrel or collet?



## Chris Burton (Jan 23, 2012)

Does anyone make an expanding mandrel (or collet) that is +2.5" in length (working)? I'm looking for one that I can machine to 0.460", but has a usable, working length of 2.5" (preferably slightly longer).


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## studioso (Jan 23, 2012)

Why not use a pin chuck?


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## Chris Burton (Jan 23, 2012)

studioso said:


> Why not use a pin chuck?



I had to Google 'pin chuck' to find out what it was.  That's new to me, but might work. Does it matter if I'm not using a brass tube, but an acrylic tube that has very thin walls? Any issues with deformation (or anything else)?

thanks,
Chris


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## randyrls (Jan 24, 2012)

Chris Burton said:


> studioso said:
> 
> 
> > Why not use a pin chuck?
> ...



Chris;  I would worry about cracking the acrylic.  You are applying a point stress at the point where the pin contacts the inside of the tube.  

Are both ends of the material open?  Expanding chucks are used in metalworking if both ends of the tube are open.  Arizona Silhouette sells closed end expanding chucks for different pens. http://www.arizonasilhouette.com/Closed_End_Pen_Mandrel.htm


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## Displaced Canadian (Jan 24, 2012)

I made one with a bolt. Filed the head to fit inside the pen, turned some derlin sleeves to go over the bolt and inside the pen, and used some faucet O rings from Lowes. I push the chuck up against the sleeve that sticks out the barrel to tighten and make the O rings expand and contact the tube. First O ring goes up against the head of the bolt, then a sleeve then O ring and on and on.


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## studioso (Jan 24, 2012)

before I started using pin chucks, also for thin wall acrylic sans-tubes, I had the same question. I also assumed that since the pin is on one side hte pen is going to be eccentric.
in practice however it works extremely well. my pin, which I turned myself on a metal lathe are extremely tight. the blank will only mount if if I twist them. so I susprct it will hold even without a pin. and it supports the blank extremely well.
check out this post:
http://www.penturners.org/forum/f56/best-method-holding-kitless-blank-90313/


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