# Matching Cap to Body Width



## EatenAppleCrafts (May 19, 2021)

Hello all, I have been making kitless/custom pens for about six months.  I use a standard wood lathe.  I normally use a triple lead m12x.8 for the Cap to body threads, and m9x.75 for the section to body threads.  The issue is I cannot seem to make a pen where the cap and body have reliably the same width at all three points on the triple lead threads.  I thought it was some sort of out of round error, but I completely re-aligned my lathe and am having the same issues.    For my process, I do the threads first and turn each part on a brass mandrel.  Any thoughts?  Here is an example of the alignment I am attempting.  Thank you.


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## Pierre--- (May 19, 2021)

Your brass mandrels could be out of round, or more likely not holding the pen as it should.
Anyway, you could try shaping the outside (I mean the part near the threads) when your blank is just threaded, without taking it off whatever mandrel you use, so you are sure threads and rim are aligned. Then put the part you shaped in a spring chuck, and turn the other end. 
If I understand well, this kind of brass mandrel are OK for sanding, not much more.


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## duncsuss (May 19, 2021)

How tight are your mandrels in the bore of the cap and barrel? Any slop at all will give you problems - to the point that if you have not run a groove the length of the mandrel, it should be impossible to put the workpiece onto it (due to the air pressure building up ahead of the "piston".)

It's also really important that the ends of the work pieces are truly square to the drilled bore inside them (not necessarily to the outside of the blank which is going to be turned away), and the face against which the end of the workpiece butts is square to the mandrel rod.


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## EatenAppleCrafts (May 19, 2021)

Pierre--- said:


> Your brass mandrels could be out of round, or more likely not holding the pen as it should.
> Anyway, you could try shaping the outside (I mean the part near the threads) when your blank is just threaded, without taking it off whatever mandrel you use, so you are sure threads and rim are aligned. Then put the part you shaped in a spring chuck, and turn the other end.
> If I understand well, this kind of brass mandrel are OK for sanding, not much more.


So are you saying to essentially do a turn between centers, tbc, with a dead center in the threaded portion, Rather than using the mandrels with a solidifying live center at the other end?


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## EatenAppleCrafts (May 19, 2021)

duncsuss said:


> How tight are your mandrels in the bore of the cap and barrel? Any slop at all will give you problems - to the point that if you have not run a groove the length of the mandrel, it should be impossible to put the workpiece onto it (due to the air pressure building up ahead of the "piston".)
> 
> It's also really important that the ends of the work pieces are truly square to the drilled bore inside them (not necessarily to the outside of the blank which is going to be turned away), and the face against which the end of the workpiece butts is square to the mandrel rod.


I honestly never even thought about air pressure, that’s a really interesting point. I’ll make sure the square from now on into a groove.  I was thinking from outside in, and maybe need to adjust how I plan.


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## Pierre--- (May 20, 2021)

EatenAppleCrafts said:


> So are you saying to essentially do a turn between centers, tbc, with a dead center in the threaded portion, Rather than using the mandrels with a solidifying live center at the other end?


Not really. I 'll try to be clearer: you put your blank not between centers, but in whatever mandrel you like, long jaws, ER or any other. Then, *without taking the blank out of the mandrel*, you drill, thread and shape the outside section near the threads,  so you are sure everything is concentric, threads and outside surface. Then reverse, holding what you just turned in an ER32 to shape the outside other end.


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## PatrickR (May 20, 2021)

My solution would be to leave material on the ends (with center points) and turn the assembled parts as one. then finish the ends on the mandrel or in a collet. i have done this with double closed ends before.


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## Displaced Canadian (May 21, 2021)

I do them separate close to size, put them on a mandrel together and make a final pass with the pen put together as one piece.


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## EatenAppleCrafts (May 21, 2021)

Displaced Canadian said:


> I do them separate close to size, put them on a mandrel together and make a final pass with the pen put together as one piece.


Interesting, I think I'm just going to have to spend some time in the garage experimenting on my process, thank you for the option.


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## peytonstreet (Dec 15, 2021)

If you are having a problem with concentricity, make sure you are not doing your threading/drilling work with the piece extending too far from the mandrel.....


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## EatenAppleCrafts (Dec 15, 2021)

peytonstreet said:


> If you are having a problem with concentricity, make sure you are not doing your threading/drilling work with the piece extending too far from the mandrel.....


Thank you PeytonStreet, I've started to do all drilling/threading first, then shaping once the center has been established on the worked-on end.  It isn't perfect yet, but it's getting there.  I notice most of my issues come with not doing the small stuff, like turning on centers first, or running the lathe prior to pushing in the live center to find the true center while spinning, etc.


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## darrin1200 (Dec 16, 2021)

I would check your mandrel, mounted on the lathe. I found that on mine, there were very minor variances (maybe .001), at each point in the chain. Lathe mount, chuck, collet, mandrel. These accumulated to give the mandrel tip a few thou wobble. It only takes a very small amount to give a variation for each of the thread starts.
Check with a dial indicator. If you can’t get it out, leave the cap slightly larger than the barrel as a design feature. The difference will be harder to detect.

The offset aside, your pen looks excellent.


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## JamesC (Jun 24, 2022)

EatenAppleCrafts said:


> Thank you PeytonStreet, I've started to do all drilling/threading first, then shaping once the center has been established on the worked-on end.  It isn't perfect yet, but it's getting there.  I notice most of my issues come with not doing the small stuff, like turning on centers first, or running the lathe prior to pushing in the live center to find the true center while spinning, etc.


Been working on this problem myself. My best improvement has come from doing as much work as possible without moving the piece. I use a collett chuck and have learned to mark the chuck and the blank if I need to move it for any reason. Also learning to keep things as clean as possible. My success turning on a mandrel has not been great. I have not turned the assembly together but have one in the works I’m going to try it on. Probably just the final sanding though.


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## JamesC (Aug 18, 2022)

EatenAppleCrafts said:


> Hello all, I have been making kitless/custom pens for about six months.  I use a standard wood lathe.  I normally use a triple lead m12x.8 for the Cap to body threads, and m9x.75 for the section to body threads.  The issue is I cannot seem to make a pen where the cap and body have reliably the same width at all three points on the triple lead threads.  I thought it was some sort of out of round error, but I completely re-aligned my lathe and am having the same issues.    For my process, I do the threads first and turn each part on a brass mandrel.  Any thoughts?  Here is an example of the alignment I am attempting.  Thank you.


Looks great! How are you cutting the flutes in the barrel?
Jim


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