Hello, I just started making my first custom all metal pen from scratch. I am at the point where I need to create a thread where the top and bottom barrels screw together. I was planning to make the thread M9x0.75, for no good reason other than it seemed about right. I was wondering if there is a common thread size used or does it vary from pen to pen. The red arrow in the attached image is pointing to the threaded part I am referring to.
Thread size?
- Thread starter jaynev
- Start date
Signed-In Members Don't See This Ad
Signed-In Members Don't See This Ad
rixstix
Member
I went from using m9x0.75 to 3/8"UNEF (32tpi) which is extremely close to m9.5x0.8
duncsuss
Member
For a ballpoint (or rollerball) pen, M9 x 0.75 is okay. The only reason I went from that to 3/8"-32 is because I make fountain pens. They require a 1/4" internal bore to receive the ink cartridge (or cartridge/converter) and there's not much wall thickness left.
Your diagram doesn't look like a fountain pen nib section, so you wouldn't have to drill it out to 1/4". And you are going to be using metal, which is much stronger than the materials I use for pens. Draw the cross section of the part with dimensions of the non-optional feature - the center hole size - and work up from there: add the wall thickness you feel comfortable with, and that gives you the smallest value of minor diameter for the threads. The minor diameter of M9 x 0.75 is 8.25mm (9 minus 0.75), you can probably go smaller than that, perhaps M8 x 0.5 (you can use finer threads on metal than on plastics).
Your diagram doesn't look like a fountain pen nib section, so you wouldn't have to drill it out to 1/4". And you are going to be using metal, which is much stronger than the materials I use for pens. Draw the cross section of the part with dimensions of the non-optional feature - the center hole size - and work up from there: add the wall thickness you feel comfortable with, and that gives you the smallest value of minor diameter for the threads. The minor diameter of M9 x 0.75 is 8.25mm (9 minus 0.75), you can probably go smaller than that, perhaps M8 x 0.5 (you can use finer threads on metal than on plastics).
My brain thinks in metric so metric sizes come naturally. Anything imperial I need to mentally convert to metric before I can picture the physical size in my mind. Sounds like choosing M9x0.75 will work for my pen. Duncan, you are correct, it is not a fountain pen. It is designed to take a Parker G2 refill. This pen will be quite chunky at 12mm diameter. Hopefully it doesn't end up being too heavy as there will be plenty of wall thickness left after it is hollowed out.
Now to practice threading on some scrap before attempting to thread the pen.
Now to practice threading on some scrap before attempting to thread the pen.
duncsuss
Member
The through hole for the tip of the refill should be a smidge over 2.5mm. I've found that some off-brands get hung up and don't retract properly when the hole is a "perfect fit".
There has to be a step inside the "nib section" to act as a stop for the spring. Square is best, but I've found that a regular 118 degree drill bit works okay, I don't remember the size drill bit I used, it has to accommodate the spring in compression (which is fatter than when the spring is relaxed) and perhaps the wider part of the refill, depending on how much of the refill you want to sink into the nose cone.
Typically, a die will not cut a full thread all the way to the step-up. Some people cut a groove at the step-up to remove the partial threads, I prefer to cut a relief around the inside of the rim of the barrel. It's out of sight, and it reduced the number of broken nib sections I had to make over again.
duncsuss
Member
Oooh - just realized, you might be make a pen that doesn't retract. In that case, you wouldn't need a spring around the narrow part of the refill. Perhaps a small spring at the back end of the barrel to give a little cushioning, it can make the feel of the writing a little nicer. (Most rollerball kits have a spring behind the refill.)
It also takes up the slack, otherwise you have to drill the barrel to exact depth - and the tip of the refill will stick out different amounts if there's any variation in the length of the refills.
It also takes up the slack, otherwise you have to drill the barrel to exact depth - and the tip of the refill will stick out different amounts if there's any variation in the length of the refills.