Question on fit between brass tube and pen components

[Stephen]

What is the desired fit dimensions (interference fit) between the I/D of brass tubes and the O/D of pen components to prevent the tube expanding and cracking the wood when assembling pens?
I am aware the type of wood and the degree of dryness is a factor to consider. I normally measure the two mating parts and if the interference fit exceeds 0.004" I will reduce by sanding the I/D of the tube. I use red Locktite as an insurance.
Like to know what others do to prevent stressing the wood after assembly.
Thanks for sharing your experience.

 

[magpens]

I ream out the brass tube using a straight-sided adjustable reamer (see picture) until the interference is less than 0.001" (estimated ... you get a feel for it) and then use epoxy.

 

[Stephen]

Thanks Mal,
I now think my 0.04" has been my problem.
The epoxy will surely be better than Locktite.
Thanks again for the information.

 

[Sylvanite]

When I'm worried about such damage to the pen barrel, I pre-expand the tubes. That is, I press the end fittings into the bare brass tube, knock them out again, and then glue the tube into the blank and turn it. That way, when I press the parts together in final assembly, the tube doesn't expand (or not very much). A dab of red loctite on the inside of the tube secures everything in place.

I hope that helps,
Eric

 

[magpens]

When I'm worried about such damage to the pen barrel, I pre-expand the tubes. That is, I press the end fittings into the bare brass tube, knock them out again, and then glue the tube into the blank and turn it. That way, when I press the parts together in final assembly, the tube doesn't expand (or not very much). A dab of red loctite on the inside of the tube secures everything in place.

I hope that helps,
Eric

That's a very good idea. I might have trouble remembering to do it before gluing tube in :redface: !

 

[Stephen]

When I'm worried about such damage to the pen barrel, I pre-expand the tubes. That is, I press the end fittings into the bare brass tube, knock them out again, and then glue the tube into the blank and turn it. That way, when I press the parts together in final assembly, the tube doesn't expand (or not very much). A dab of red loctite on the inside of the tube secures everything in place.

I hope that helps,
Eric

Hi Eric,
Many Thanks.
Great idea! Why didn't I think of this? Perhaps my thinking process goes to sleep knowing IAP is there when I need help. This is why I love IAP where sharing of information widens our knowledge in an ever unending learning curve.
Thanks again..
Stephen

 

[Sabaharr]

Short of expanding the tube you really should chamfer the entrance of the tube with a beveled reamer. Just 2 light rounds by hand is enough to smooth the edge and should remove any burrs you may have. Another useful thing to do is press the ends of the tube into flat dental wax to block the tube entrance when gluing. Just a thin invisible layer of glue or epoxy can shrink the diameter of the opening enough to expand the tube when the components are pressed in the you get the dreaded TINK sound and it back to the drawing board. The wax presses out with a dowel or your center punch set so its not a hindrance at all. I have even forgotten it in and when I pushed it on the mandrel it popped out. I also use it when casting resin. I push it in just far enough to clear the plugs in the mold so there is no air trapped that can escape and leave that dreaded bubble slipping out the end of the tube that you don't discover until the resin is gelled. Wax and a deburring tool will solve lots of your problems.

 

[csr67]

Short of expanding the tube you really should chamfer the entrance of the tube with a beveled reamer. Just 2 light rounds by hand is enough to smooth the edge and should remove any burrs you may have. Another useful thing to do is press the ends of the tube into flat dental wax to block the tube entrance when gluing. Just a thin invisible layer of glue or epoxy can shrink the diameter of the opening enough to expand the tube when the components are pressed in the you get the dreaded TINK sound and it back to the drawing board. The wax presses out with a dowel or your center punch set so its not a hindrance at all. I have even forgotten it in and when I pushed it on the mandrel it popped out. I also use it when casting resin. I push it in just far enough to clear the plugs in the mold so there is no air trapped that can escape and leave that dreaded bubble slipping out the end of the tube that you don't discover until the resin is gelled. Wax and a deburring tool will solve lots of your problems.

Both great ideas. Since I started using dental base wax to plug the tubes prior to glue-up and a simple reamer to chamfer each tube end, my issues with blank cracking went wayyyyyyy down.