Help! I cut a tube

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Angela S

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Jun 26, 2019
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I made a segmented blank for the Cosmopolitan kit from penn state. After glueing in my tubes, I had a significant amount of the blank on one side. So, I marked and went to trim it off. Apparently, I am crappy at marking and I hit the tube. I was hand sawing so I didn’t go very far through the tube. It is about a millimeter of the tube is missing on a small section. I am not sure what to do. Suggestion would be appreciated.
 
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jttheclockman

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A photo would help. Some times the kit is not all that critical with overall measurements and you can get away with taking some extra off and not have it effect the mechanism. I am not familar with that kit so can not say if this is the case. You can do a number of things. When you say a small portion I assume you nicked some of the tube on an angle and cut free. If so the problem will be when you square the end up, the entire tube will be cut away to make it flat. If you did not cut the other end yet and have excess left you can drill the tube out completely with the same 3/8" bit you used. Then start over. Now you run the risk of breaking any segmentation and have to redo that. The other option is to really look at the blank and ask is it worth saving or use it as a learning experience. The final option is to make some sort of oops band and cut more of the tube off and glue on the oops band and now add a small piece of tubing They do not have to be connected because the tube is there to support the components. Maybe others will have a better idea but as I said a photo would help.
 

Angela S

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Seattle
A photo would help. Some times the kit is not all that critical with overall measurements and you can get away with taking some extra off and not have it effect the mechanism. I am not familar with that kit so can not say if this is the case. You can do a number of things. When you say a small portion I assume you nicked some of the tube on an angle and cut free. If so the problem will be when you square the end up, the entire tube will be cut away to make it flat. If you did not cut the other end yet and have excess left you can drill the tube out completely with the same 3/8" bit you used. Then start over. Now you run the risk of breaking any segmentation and have to redo that. The other option is to really look at the blank and ask is it worth saving or use it as a learning experience. The final option is to make some sort of oops band and cut more of the tube off and glue on the oops band and now add a small piece of tubing They do not have to be connected because the tube is there to support the components. Maybe others will have a better idea but as I said a photo would help.

Here is a photo
77272EDE-84C8-4FA1-949C-BC0611032BBB.jpeg
 

Sly Dog

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It doesn’t look too bad to me, but I probably would not complete that cut and risk cutting even more of the tube. I don’t know how you square up the ends of your blanks, Angela, but I sand (as opposed to using a barrel trimmer). I think I would sneak up on the tube, sand or trim it square, and turn it. Like Lin and John wrote, shortening the tube by a mm or so probably won’t effect the function, but I also don’t have experience with the Cosmo. Good luck!

Russ
 

magpens

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It is no problem if your brass tube is only 1mm too short. . Your picture is very helful, BTW.

I have made several Cosmopolitans (quite a nice kit) ... the tube/barrel length is not critical. . It can be a little short (or it can even be a little "too" long).

I am holding a recently made Cosmopolitan pen as I write this.

As Russ said, do not proceed with the cut you have started. Make another cut closer to the same end of the wood. And make sure his new cut is past the end of the brass tube.
Everything you do must be done very carefully and take your time doing it .... and also, check what you are doing frequently.

After the new cut, I think that you should round the blank ... but don't take it down to the correct diameter ... just get it round.

Next, trim the rounded blank to length .... this is where you want to be extra careful. . I assume that you use a disc sander or a vertical belt sander to trim.
My suggested method might work with a barrel trimmer but you will have to be extra careful ... and do it slowly.

I think you should trim it down to the originally intended length first. . Make sure that the end of the blank is trimmed square to the axis of the blank.
This squareness is important even with this preliminary trimming.

Next .... and this is the critical part .... very gradually trim further to get rid of the "bad" part that I see in the picture. . You will now be taking off the approximate 1mm long "bad" part. . Do this very carefully ... just a little bit at a time .... inspecting each little bit of progress as you go ... keeping the trimmed end as accurately square to the blank axis as you possibly can at every stage in the process.

When you have removed the "bad" part, your blank will be approximately 1mm shorter than the original plan was.
But with the Cosmopolitan that will be OK. If it is only 1 mm or even 2 mm I am sure it will be OK. The Cosmopolitan design is very forgiving with regard to the overall blank length.

The reason is this .... the critical length is related to the length of the refill and the refill is contained within a metal "tube" which is internal to the brass tube. . So even though your brass tube is a little short ( 1 mm or so), the internal metal tube still maintains its original length.

The internal metal tube has two parts ... the lower part is permanently attached to the intermediate nib piece, onto which the actual nib screws.
That lower part has (at its top end) an internal thread at the opposite end to the nib end.

The twist mechanism (which I call the second part of the internal tube) screws into the top end of the lower part.

The top end of the twist mechanism slides into, and is gripped by the top (or finial) piece of the pen hardware. That friction grip extends over quite a few millimeters.

So with your slightly (1 mm) short outer brass tube/barrel, the top end of the twist mechanism will push up into the finial end just a little (1 mm) further than normal. . I am quite sure this will not present any problem, other than making the friction fit just a little bit tighter. . There is room for this.

I am quite confident that everything will work out OK.

If you want to put your mind at ease by convincing yourself, just set the brass tube/barrel aside for a minute and assemble the other parts of the pen kit without the barrel. . You will see just how far down you can push the finial end ... but be careful doing that because you will have to disassemble after you are convinced that all will be OK. . As you push down the finial (top end), measure the "free space" between the nib end and the finial where the barrel will eventually fit. . I am quite sure that you will convince yourself that a shortened barrel can be easily accommodated without compromising the operation of the finished pen. . Don't press the top finial piece down too far because you do have to disassemble ... but you might want to make a note of how short the barrel could actually be, just in case you want to take advantage of this "feature" and deliberately make a short version sometime in the future. . (Notice that I said "deliberately" .... no future cutting "mistakes" will be allowed !!!)

Good luck ... and please ask further questions if you have any. . I will watch. . And, please let us know how it turns out ... finished photo will be nice.
 
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jttheclockman

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From the photo I would suggest just clean up the rough edges in the tube with a file and sand down the edges . I would not use a barrel trimmer. I would sand them down which is a better method anyway and you are good to go. Do not worry if there is a chip missing. As long as there is no rough edges and it is smooth the components will slip in. They grab much further down the tube than just the first mm. Good luck.
 

penicillin

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Feb 27, 2019
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I trim on the bandsaw,carefully taking only a couple of mm's on each pass. I quit when I get within 2 or 3 mm from the tube.
I am pleased that @Angela S found the answer she needed.

I like to trim off the excess after I have drilled the blank. I get square pieces with holes that I make into beads for my young nieces to play with. (Note: Choking hazard for infants!!)

I use an engineer's depth gauge to measure the tube glued inside the blank. Slide the ruler along the inside of the hole until it touches the tube. Pull it out, and the ruler shows you how deep the tube is. Place the depth gauge on the outside of the blank and make a mark at the end of the ruler. Sometimes I slide the pencil with the gauge to make a crosscut line, and sometimes I pick up a 4 inch square and draw the line using the mark. Use your bandsaw or small handsaw to cut slightly proud of the line ... duh!! (P.S. Save the ends to make bracelet beads for the young ones! If the trim is wide, then I may cut off several smaller pieces for beads.)

Mine is an old vintage Lufkin 510 depth gauge, but you can find new ones everywhere. Pay $90 for a Starrett if you wish, or $10 for a no-name model. It doesn't matter how accurate it is, because you use it only to transfer the depth of the tube from the inside to the outside.

Here is a basic one that I found:
https://www.amazon.com/Stainless-Steel-Engineers-Metric-Imperial/dp/B07B9VH493

Here is a set that might be useful to woodturners, and it includes a depth gauge:
https://www.harborfreight.com/6-piece-technical-measuring-set-94447.html
I bought one recently, so I just opened it. These are the cheapest-made, stamped metal tools I have ever seen, but the depth gauge will work for pens as I described above. Frankly, the depth gauge looks identical to the one on Amazon above for less money, and you get calipers and other "tools" with it. I bought it for the three calipers, which are awful, but should (barely) do what I need for turning. Someday I will buy better quality calipers if these prove worthwhile.
 
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