# Pen Tube Size Question



## dow (Feb 8, 2010)

I don't know for sure if this belongs under "advanced pen making" or not, so Curtis, move it if you think it needs to be somewhere else.

Anyway,  I've made several of the one-piece slim pens like in this article by Bob Altig (thanks Bob, for a great article), One-Piece Slimline, but have had some issues that I'd like to find a way to fix.  Specifically, I've made a couple where there was some wood movement, which made the pen hard to twist.  Also, on at least one occasion, I've had a pen split after completion, due to what I believe to be a combination of the blank being turned thin to keep the slimline profile, being a wood that had very straight grain, and possibly a change in relative humidity that allowed the wood to dry out on the inside of the body, which caused the crack.   Both of these problems, I attribute to the wood on the nib end of the pen being unsupported by a brass tube, as none is glued in.  To keep this from happening, I'd like to tube the nib end with a tube that is a slip fit over the standard 7mm tube that slimlines use.  Does anyone know if such a diameter tube is available, and if so, what size it is?  Additionally, I believe that the pen could be more easily extended and retracted by having brass to brass contact between the nib section and the inside of the pen body.

Thanks for your time,

dow


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## mredburn (Feb 8, 2010)

the 7mm tubes i have measure .266 od the ID of an 8mm tube is .285 you would have a 20 thou. difference. A 9/32 tube from K&S Engineering has too small of an ID to fit over the 7mm tube as is. but will slip fit into the 8mm. The 9/32 tube measures.255id and .281 OD. You might be able to glue an inch of 9/32 tube in the nib end, run a 17/64drill bit through it, (.2652) and use a round file or a sanding mandrel on a Foredom/ Dremel set up to finish the fit. However do you have enough material to cover the 9/32 tube? Standard slimlines nibs i have measure .330 so you should have 40 thou. difference. What size are you drilling the hole in the blank?


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## dow (Feb 8, 2010)

mredburn said:


> What size are you drilling the hole in the blank?



Should be pretty close to 7mm.  I use the Colt 5-star pen drill bit to drill the blanks, since they have to be 4-1/2" long.


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## mredburn (Feb 8, 2010)

you would have to drill the blank to 8mm or .307 to take an 8mm tube. It would not leave much in the way of wall thickness. About 12 to 15 thousands at the most unless you made the blank thicker. The 7mm drill if you are turning to match the nib diameter is leaving you about 30 thousands wall thickness with no tube. Would coating the end of the tube with ca help with the crack problem with out a tube? The 9/32 tube would work but would mean a lot of extra effort to do so.


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## SonOfMartin (Feb 8, 2010)

I've made several slimlines that are one-piece using that article.  I feel pretty sure that metal to metal contact of the tubes won't do anything for you from a structural perspective.

However, here is what I would do using the pen you're trying to build.

Lay out the tubes outside of the cut blank (for the 1 piece design).  Put the nib and transmission into the bottom tube and then line it all up to see if you have enough metal in the top tube to firmly grasp the top of the transmission.  That contact area is what turns the pen in/out.

You may need to add length to the top tube if you're creating a longer-than-normal 1 piece slimline.

As far as the splitting is concerned - I drill with a 7mm bit (from Woodcraft) and have turned mine down pretty thin at the nib end and not had a problem.  HOWEVER - I do tend to make my pens a little beefier in the mid section and not slimline profile.

I think your problem with splitting may be from under-drilling the hole "just a touch" and the stress of inserting the nib and the finial cause the stress that cracks the body.


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## KenV (Feb 8, 2010)

Pen State 8mm _pencil_ tube is a reasonably close fit with the 7mm tubes --  They are sold in 10 in lengths in a package of several tubes.  

I use them to fit in the mouth of the 308 shells with the 7 mm tube.  

You still have the challenge of thickness of brass and clearance of the material being used over the tubes.


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## dow (Feb 8, 2010)

mredburn said:


> you would have to drill the blank to 8mm or .307 to take an 8mm tube. It would not leave much in the way of wall thickness. About 12 to 15 thousands at the most unless you made the blank thicker.


That was my concern as well, but I thought it was worth looking into.  I've actually started making the area just above the nib a little beefier, continuing the angle of the nib up for maybe another 1/2-3/4 inches along the blank, and then slowly tapering for the length of the blank, which works to re-inforce the end, but not everybody likes the design.


> The 7mm drill if you are turning to match the nib diameter is leaving you about 30 thousands wall thickness with no tube. Would coating the end of the tube with ca help with the crack problem with out a tube?


I tried that on one, but it's a booger to get the CA spread evenly around the inside of the blank, so I only tried one like that.


> The 9/32 tube would work but would mean a lot of extra effort to do so.


yeah, after reading your earlier response I am thinking the same thing.  What I'm trying to do is to come up with an attractive, unique design that is quick to turn but without the things I don't like about the regular slimline, specifically the way that the center ring on the slimlines that I've made has been just slightly too large ID so that it spins and rattles around with the pen assembled.



SonOfMartin said:


> I've made several slimlines that are one-piece using that article.  I feel pretty sure that metal to metal contact of the tubes won't do anything for you from a structural perspective.
> 
> However, here is what I would do using the pen you're trying to build.
> 
> Lay out the tubes outside of the cut blank (for the 1 piece design).  Put the nib and transmission into the bottom tube and then line it all up to see if you have enough metal in the top tube to firmly grasp the top of the transmission.  That contact area is what turns the pen in/out.


Correct.


> You may need to add length to the top tube if you're creating a longer-than-normal 1 piece slimline.


That makes sense, and I'll consider it should I decide to make a longer pen.



> I think your problem with splitting may be from under-drilling the hole "just a touch" and the stress of inserting the nib and the finial cause the stress that cracks the body.


While this is certainly possible, and is something that I'll measure the next time I drill one,  I don't think it was the cause of the split that i experienced, since until you actually push the mechanism into the upper tube, the whole lower assembly was loose in the pen body. 

In the case of the cracked pen, the pen went together and advanced/retracted smoothly, but when showing it to someone and demonstrating how to remove the mechanism to change the refill, I noticed when i re-inserted the pen into the body, that the end was oval, which is a pretty sure sign that some drying has taken place in the wood.  At the time, I didn't think it was enough out-of-round to make a difference, but then I heard it crack.  An additional concern that I have because of this is that if I break one, knowing that they're pretty thin, then how much more likely is a customer to break one by accident?  It doesn't seem right to sell something that I don't have confidence in, and that's where I am right now.


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## SonOfMartin (Feb 8, 2010)

I think you hit on it - "OVAL" - is it turned round and not out of round?  Look at both ends before assembly - if you're oval shaped on one end and not the other - it's not a drying problem - it's a bent mandrel problem (in my opinion)....worth investigating.


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## dow (Feb 8, 2010)

Nope, it was turned round, as were the other four one-piece slims that I made that day.  Among other things I play Irish flute, and a common issue with flutes made of boxwood is that if they get too dry, they will get out or round and even warp until the moisture content is brought back up to where it needs to be.  I believe this is what happened in that one instance.  It hasn't happened with pens where I turned the nib end heavier, nor has it happened with woods which were cut more cross-grained or which have interlocking grain.  In this instance, the wood was straight grained, and was drilled parallel to the grain.  I believe that what I saw in this case was the natural respone of the wood to change in moisture content, similar to what you see if you turn a bowl too thin while the wood is still green.


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