9mm Male Thread for Rollerball Pen

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TonyL

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I have successful made the male threads many times on the section. I even made an aluminum mandrel with female thread to accept the male threads in the section. When I use AA I snap the threads from the main section when attempting to shape the cone (I guess that is called the nib) from which the RB refill will protrude). I have made a section without snapping the male thread from the section using ebonite. Maybe AA is too brittle for me right now? Here is my process:

  • Tool are razor sharp (HSS or new carbide)
  • No hole drilled in the section yet, other than a small 60 degree hole to provide stability to the tailstock end when tuning
  • RPMs 2400 to 2800
  • I have "chucked" the section in collect chuck, the aluminim mandrel and a small spigot like chuck.
  • Thread length is a little more than 3/8ths.

I can make the body and cap with acrylic acetate just fine. Shaping the cone of the section without snapping the threads continues to allude me.
 
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TonyL

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For some reason I can't edit or spellcheck my post (after I added the bullet list). I also meant to add "Thank you.
 

TonyL

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I wonder If for more brittle material. I should use 9 and a 1/2 millimeter threads.
 

Curly

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What is the thread pitch if the 9mm thread you are using? M9x1, M9x.75, M9x.5? The coarser the thread the deeper it cuts, potentially weakening it. AA has a bad reputation for being brittle and hard to play with. Can you try to do it in something else as an experiment to see if the problem persists? Ebonite, Alumilite or even a generic acrylic.
 

Curly

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Then would seem to be the material or maybe the tools you are turning with. Since you are in Georgia you can rule out too cold. ;) I don't think I've ever played with AA so can't offer any tips of experience.
 

darrin1200

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Good be all of the above or just me. Thanks!
Hey Tony

I have made fountain pen sections from AA, with the hole already drilled in the center. I have found that AA has to be shaped with very light cuts. It doesn't take much for a slight catch, and in the AA that can be disastrous. I also have an aluminum mandrel with female threading to hold it. I think what happens, is that because the material is brittle to begin with, a slight catch will cause a severe twisting torque. This tries to turn the section in the mandrel, but it is already tight. The result is a broken section. That's why its not a problem with the ebonite, because it has more give to it. Sometimes I actually need pliers to grip the ebonite section to get it out of the mandrel, because it has tightened up so much.
 

TonyL

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Hey Tony

I have made fountain pen sections from AA, with the hole already drilled in the center. I have found that AA has to be shaped with very light cuts. It doesn't take much for a slight catch, and in the AA that can be disastrous. I also have an aluminum mandrel with female threading to hold it. I think what happens, is that because the material is brittle to begin with, a slight catch will cause a severe twisting torque. This tries to turn the section in the mandrel, but it is already tight. The result is a broken section. That's why its not a problem with the ebonite, because it has more give to it. Sometimes I actually need pliers to grip the ebonite section to get it out of the mandrel, because it has tightened up so much.
I was thinking the same. I just think it is too much torque. Thank you. I may try 10mm male threads, just to see if it helps.
 
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