Section threads.

[BerneseMtDogEatsArco]

Hi FPN!

 

I have a quick question: What's up with the different thread sizes, twists, thickness and number (for the cap-to-section threads)? I've seen a lot of variation, and am wondering if anyone could advise me on a safe thread type/size/number for a pen I'm trying to design.

 

Coarse vs fine (number of threads per axial interval)?

Number of threads total?

 

This is for a celluloid nitrate pen.

 

Ideally, the pen would have an excellent seal, since it's an eyedropper, and also, I'm placing the threads in FRONT of the section, as with the old safety pens, so I would like as small of a longitudinal length as possible taken up by the threads. On the old safety pens, I see they sometimes have larger but less numerous thread widths (width of each thread). Is this good? I know that the safeties had to seal in the free flowing ink. Or, was this just a manufacturing/material limitation?

 

I have seen some modern pens (such as the Classic Pens) with these wide, less numerous threads as well.

 

OH! And one more thing: if I have a friction-fit nib and feed, how often is it OK to pull out? I imagine that on tope of the risk of messing up something, I would also slowly sand down the fit and make the nib/feed too loose within the collar?

 

I really appreciate your help!

 

Best,

Michael

Edited August 2, 2009 by BerneseMtDogEatsArco

[Tsujigiri]

One problem I can forsee with threads at the tip is cleaning ink out. Not sure about why many threads are needed, though. It may be that manufacturers have gotten more accurate with better technology.

[BerneseMtDogEatsArco]

One problem I can forsee with threads at the tip is cleaning ink out. Not sure about why many threads are needed, though. It may be that manufacturers have gotten more accurate with better technology.

 

Thanks, Tsujigiri! I've been looking at pen after pen for threading, and venture that the manufacturers determine thread parameters in a highly scientific method based upon the complex MASH Process. Young children are employed as chief designers for this endeavor.

[dfurlano]

Not exactly sure what information you are looking for but threads are usually made to fit a design. A pens size, weight, and material have more to do with type of threads used. I do know one pen maker that uses a very unique thread design and that has become his signature. Some don't even use threads for caps but a bayonet style. Also in my opinion you do not want to create the seal with the threads but with a liner in the cap or a silicon grease on the section threads into the body.

 

Dan

Edited August 2, 2009 by dfurlano

[Artie]

Most of the pens I know of have an inner cap that fits tightly against the top of the section to create a seal. You want the threads to tighten against the inner cap before the tines on the nib get smashed against the top of the cap.

 

PS any threading should work as long as it holds the cap on the pen and stops tightening before the nib travels to the top of the cap. Also if the friction fit between the feed and the section get loose, and you don't want to get another feed, you can paint a thin coat of lacquer on the inside of the section to make it smaller. You could not paint a coat on the feed if it is hard rubber but you could on the section or collar if it is celluloid.

Edited August 2, 2009 by Artie

[sexauerw]

My preference is for medium threads such that it takes about two turns to put the cap on or take it off. With coarse threads you tend to get less turns and a greater likelihood that the cap will come off in your pocket. Fine threads are too easy to cross-thread. And more than two turns to operate are unnecessary and too annoying.

[fountainbel]

I've succesfully used 8TPI, 3 leads on some of my pens ( thread profile being 8x3= 24 TPI)

On other pens I've used a double bayonet enclosure.

A few demonstrator pens with threaded cap/barrel fixation were posted on this forum a few days ago.

You can see the threads clearly on the pictures

Enclosure- over 4 mm thread length - occurs in approximately 1.25 turns

Francis

 

Edited for enclosure figures correction, sorry!

Edited August 2, 2009 by fountainbel

[BerneseMtDogEatsArco]

Thank you, all! I'm leaning towards a regular double thread, or a thicker single thread.

 

fountainbel, I really like your pen designs! The portholes you have used for the ink viewer is something I've not seen before, and I look forward to seeing more of your work as time goes on!

[Ruaidhri]

Bear in mind that you will need more depth for a single coarse thread (one of the main reasons for multi-start threads).

 

Cheers,

Ruaidhrí