8 tries and still not there yet

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brownsfn2

brownsfn2

Member
Joined
Jun 23, 2011
Messages
1,574
Location
Plain City, OH
So I thought I finally had two good casts with PR and carbon fiber. As you can see from the picture below there are small cracks at the ends. I was hoping someone might know what caused them. When I first assembled the pen they were not there. Days later these "cracks" appeared.

My process for this one was to first use epoxy to glue on the Carbon Fiber. around 1/2 later I cut the carbon fiber to within 1/16" of the tube. Then I mix the PR with about 7 drops mekp per once. Then into the Pressure Pot for overnight for 50 PSI. It is tacky when I take it out of the pot in the morning because my basement is cold. So I put it in my hot garage for a few hours. Then I square the ends with my mill and turn it. Press in the parts with my pen press. Days later I got the cracks on the end.

So I think it might be the PR shrinking and pulling away but I am really not sure. Any guesses?

IMG_4723 (864x1280).jpg
 
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It looks like stress cracks from the assembly process to me. Barry Gross has a video on turning acrylic pens. In it, he says that the acrylic is easily cracked when stress is applied. Therefore, he uses a chamfering tool on his tubes before assembling acrylic pens. This reduces the pressure. I bought a chamfering tool from Ariz. Silhouette, which is now owned by Barry. Most of my pens have been wood so far, but I know that after chamfering, assembly is much easier, whether wood or acrylic.

I hope this helps.
 
Barry Gross has a video on turning acrylic pens. In it, he says that the acrylic is easily cracked when stress is applied. Therefore, he uses a chamfering tool on his tubes before assembling acrylic pens. This reduces the pressure
Click to expand...

+1
I have had one PR crack, but it happened while being pressed. I make sure and chamfer the ends of all the tubes before pressing now. On another note, I recently changed over to the "Clear Casting Resin" from Douglas and Sturgess (Douglas and Sturgess: Clear Casting Resin, 1 Gallon ) and it seems to dry and harden better than the "Casting Craft" brand.
Dan
 
After taking it apart I noticed that the tube inside could have been cleaner from glue and resin. This might be it. Strange thought that I did not notice the day I assembled it but only days later. Hmmm... We I will just need to give it a try again. I did order like a dozen sets of Jr Gent tubes from Exotics to try. I guess if I can't get it right in 12 tries I will sell my pressure pot and air compressor. :)

Thanks guys!
 
The one thing I do know about is your mix ratio. To much MEKP will make the PR brittle. Most use 3-4 drops per oz.
 
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+1...check your mix and think about alumalite (sorry about the spelling). More forgiving on casting. Watch the heat on trimming barrels...can't hurt:redface:
 
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