Acrylic breaks at end of pen tubes A LOT

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immls

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Not new to penturning I've learned much from here.
Lately the last 1/8" breaks of off my acrylic 7 mm blanks. Usually a sort of U shape. I've tried 2 part epoxy and medium CA no activator. I've pushed the tubes past the opening, applied more adhesive and pushed it back in...both ends!!I've left them sit for days. It always happens when I'm trying to get the pen clip end turned to the correct diameter and it's happened with ET finisher as well as skew on it's side. Am I simply trying too hard to get that small of (lack of word) end return / diameter???? I've blown thru 5 blanks. So now I've come to the experts for wisdom.

Thanks
 
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Tage

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I've found when that happens it is usually faulty glue job, but it looks like you've covered that already. Maybe dry fit of tube in the hole before gluing? Maybe the hole is a bit too large? Just guesses here.
 

ed4copies

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Look at what is left.

Is the material thinner where you are breaking through, than it is on the opposing side of the circle.

Is the end that keeps breaking through also the tailstock end? Are you using a mandrel with both halves on it? 8"+ long?

Picture, from the end of the blank?
 

RKB

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I was having a similar issue. I now add more bushings to lengthen the working area and move my tool rest more to the center of each of the blanks on my mandrel. I think this helps me keep a better cutting angle on each blank. Hope you work it out.
 
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Jim Burr

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As posted last week...Do Not Ever drill through an acrylic blank. As was talked about last week...measure long...drill, and cut. Now you have saved the end of your blank, not pressure fractured it and you can make a pen...like we talked about last week.
 

immls

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Got it thanks

Yes cutting toward tail stock. After first two I spun the cutter head so maybe not. I use the psi blank chuck and have notice a lot of wobble so I did start leaving more meat past the tubes...and I wasn't even here last week to miss that......
Thanks all
 

wyone

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man was there a test I missed? :) I try to always leave some meat at the end of my blanks to make up for.. well mess ups.. the added advantage is I am going to waste that small section anyway, and I can now use it because I saved the width of it. :)
 

sbell111

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I've found when that happens it is usually faulty glue job, but it looks like you've covered that already. Maybe dry fit of tube in the hole before gluing? Maybe the hole is a bit too large? Just guesses here.

Another thing that can cause this issue is a blank the wasn't milled all the way to the tube.
 

bryceprusse

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Make sure that there is no wobble on the lathe. If it is shaking this will cause it to break. Make sure your tool rest is tightened. Also make sure that your tools are sharp and do Not use much pressure. Turn from the center out. What chisel are you using when you are getting close, this can make a difference too. you should be using a sharp skew at this point.
Good Luck
 

Wood Butcher

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Are you using acrylic acetate or Inlace? Are you using a barrel trimmer to square the blank? Are you using a brad point bit to drill the blank? It could be that any of these things, along with the other suggestions, are causing a hairline crack in the blank and when you get it really thin and the tool contacts the crack, kablooy. Fortunately there are ways to reduce the failures of the blank but no matter how good or experienced a turner is there will always be the occasional, you know.
WB
 

redneckmedic

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I've noticed a few consistent variables ...the above mentioned by WB and where did you get the blanks. The first several batches of PR blanks I made had too much MEK in then causing a very fast hardening time thus resulting in a very brittle blank. If its a fairly new design or personal blank, that might be your answer. My best guess... heat is your enemy !
 

Trey

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Don't forget that tightening the nut on the mandrel too tight can also blow out the blank by flexing it slightly when you get it really thin (like toward the end). I have also noticed that if I don't be CERTAIN to take very light cuts toward the end of the job it also has a tendency to crack off in a U shape because the tool will catch.
Just some thoughts from another newby.
 

bobleibo

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Mark
I found that sometimes after milling the ends of the blank and brass tube an extremely small piece of brass debris had found it's way into the end of the tube and was enough to cause the bushing to be pressing too hard on the tube itself thus flexing the blank. It doesn't take much to create a problem.
Always mill the inside of the brass tube before inserting the bushing. I learned the hard way.
Good luck
Bob
 

immls

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Thanks all update

Drilled another blank and noticed the brad point bit wobble. There is a pretty big gap between blank and tube. Hadn't paid much attention in past. It was a mechanical process chuck up and drill. The bit is old so changed to new bit....no cracks. Drilling became so mechanical I just chucked
 

Rockytime

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I've had the same problems. So my question is this. There are, I think, special drill bits for plastics and acrylics (or are they the same thing?) sold by PSI. Wonder if they really work. It would seem the same rules of care would apply but perhaps the drills are a little more efficient. Also wondering if regular drill bits having some slope stoned in the leading edge, the same way it is done for brass or thin metals, to keep the lead edge from being too aggressive. Just kinda thinking aloud.
 

CrimsonKeel

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I always after I glue tubes and mill the ends to the tubes trickle thin CA into the milled part. very often I find that there is a hairline crack or gap from drilling between the blank and the tube. this thin ca fills that crack and helps right there at the ends.
 
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