Matching Cap to Body Width

Signed-In Members Don't See This Ad
Joined
Aug 20, 2019
Messages
42
Location
Los Angeles, CA
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.

B5A0E2B1-52EB-4C5A-8A62-82D2A83342B3.JPG
 
Signed-In Members Don't See This Ad

Pierre---

Member
Joined
Jun 10, 2012
Messages
316
Location
France
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.
 

duncsuss

Member
Joined
Jun 29, 2012
Messages
1,738
Location
Wilmington, MA
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.
 
Joined
Aug 20, 2019
Messages
42
Location
Los Angeles, CA
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?
 
Joined
Aug 20, 2019
Messages
42
Location
Los Angeles, CA
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.
 

Pierre---

Member
Joined
Jun 10, 2012
Messages
316
Location
France
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.
 
Top Bottom