Thicker Walls

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TonyL

TonyL

Member
Joined
Mar 9, 2014
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Location
Georgia
Hey Folks:

Never thought I would find myself posting here, but I have become fascinated with making threads. Attempted my first kitless yesterday and flew a little too close to the sun. My wife is also wondering where all of the cooking spray has went :-).

I used a 12mm (body) and 9mm (section) taps and dies. I thought if I used 13mm (body) and 9mm (section) or 12mm and 8mm it would produce a thicker body wall. I bought a bunch of sizes from Victor and another bunch of tools from Neil Butterfied (what an o/s human being). I am surprised that he still answers the phone when he sees my number come up. :-)

I'm was a very good in algebra, geometry and calc (40 years ago), but want to ask the more gifted and experienced minds, what they think.

PS. I made my own plugs and mandrels for support; and I did use the diameter less pitch equation for "starting" diameter. I didn't crack one thread while making them (I did use enough Pam to grease the state of Texas and my hands have never been so soft) . Then I cracked one when screw the finial thing to the top of the cap.

I also made reliefs on all of the male threads.

I don't like thin walls (especially after spending 4+ hours on a pen).

Thank you all very much. This was a lot of fun. And despite cracking the cap, I didn't feel compelled to the start throwing the other parts around the shop. I did shed some tears though.:biggrin: My wife thought I was watching Brian's Song again.
 
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Congratulations Tony! It's good to know someone paid attention. Don't know why you cracked the cap while attaching the finial? Maybe threads too long? If we had a photo might be more helpful. The fun is when you can look things over, and figure out what went wrong. Or right! Keep going!
 
Thank you. I did what was recommended in a few articles and YT's. I am not blaming them. I just wanted to know if my thought (above) would produce a thicker wall. I am going to try the 12 and 8 and see if the wall is thicker. Thank you.
 
Awesome Tony! I think you forgot to attach pictures... :tongue: Sounds like you we close to perfect for a first attempt.

I haven't experimented too much with thread sizes, I'm comfortable with a 13mm body/cap combined with 10mm section/body. Not sure if I'd be able to squeeze a 13/11, feels like that's an important junction in the pen and I don't want it to be weak. What's a "thin wall" for you?
 
Thank you. 13/10 is like to produce what I am calling a thin wall and produce the same as the 12/9 pair. The wall may be perfect. I was just wondering if anyone has tried a 4 mm difference and produced a thicker wall. Thank you again.
 
A rollerball refill will need a roughly 6.5mm hole to go through the section, an ink converter about 8mm. So a 12/8 combination should work for a rollerball but might be too tight for a fountain pen.


TonyL said:
Thank you. I did what was recommended in a few articles and YT's. I am not blaming them. I just wanted to know if my thought (above) would produce a thicker wall. I am going to try the 12 and 8 and see if the wall is thicker. Thank you.
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What pitch of thread were you using? A 12 x 1mm leave less material than a 12 x .75mm for example.

How about some pictures for educational purposes?
 
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Here is a good place to learn about threads and dimensions. It's set up for inch but can convert to metric. With some iterations, you can match metric threads and then convert back to inches to measure on your lathe and match drill bits. I've been successful with 9mm x 0.75 section threads and 11mm x 0.75 cap threads in metal and acrylic.

http://theoreticalmachinist.com/Threads_UnifiedImperial.aspx


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What pitch of thread were you using? A 12 x 1mm leave less material than a 12 x .75mm for example.

How about some pictures for educational purposes?
Click to expand...

Must pull out of my shop trash, but i will.

12 by .75
 
Tony,

Typically a 13mm thread on the body and a 10mm thread to accept the section is plenty of clearance. If you like a thicker wall, have at it. It's whatever you want!

I didn't notice if you mentioned the material you were using or not. You will need to take that into account too. Some are more brittle than others.

In my opinion, 9mm section to body threads is cutting it close to being large enough for a fountain pen section, though I have done it.

The main thing is be careful when you cut a thread relief on the tenon behind the threads. If you are not careful and cut a little too deep it will weaken the piece and it will be very susceptible to breaking. This goes for body to cap threads and section to body threads (or anywhere really).

A suggestion would be to cut a relief in the female part that will be accepting the male part. For example - make a relief at the beginning of the cap threads so when you get close to the back of the body threads, they won't be engaged.
 
Acrylics are a little more brittle than alumilite. They require a more deft touch. Some people suggest practicing on alumilite or delrin.
 
My normal formula:

- section to barrel = M9 x 0.75 single start, I make the hole into the barrel (which receives the ink cartridge/converter) 8.25mm; I use the same threading for the finial that holds the clip onto the cap;

- cap to barrel = either M12 x 0.8 (drill with 11.2mm or 11.25mm, whichever I can find) or M13 x 0.8 (drill with 31/64ths since I don't have a 12.2mm drill bit).

I've never had a cap break when screwing in the cap finial. Are you certain your material was solid to begin with? I've occasionally had acrylic acetate blanks with air bubbles and cracks (especially the "chunks of colour" type of blank.)
 
Thank you Lewis and Duncan. I wanted to use-up/practice on some AA blanks that I found to translucent for my tastes. I am not really sure of much at this point; I am learning by trial and a error. So far, I haven't done so bad other than starting out with rod that was too thin for male threads. I turned the rod to the die diameter less the pitch; I did not know that that formula only applies to female threads. Another member corrected me. Thanks again. I will send some pics.
 
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One other thing - tapping threads creates significant outward forces on the walls of the hole that you are tapping.

When I'm making the barrel, I thread the outside first, then screw on a "collar" that I made from a piece of Delrin to prevent it from blowing apart when I tap the inside threads.

When I'm making the cap, I try to clamp around the area I'm tapping by sliding the piece into the collet chuck I use. Anything that holds the piece tightly can help.
 
I guess with more brittle materials courser and longer thread lengths are more suitable?
 
TonyL said:
I guess with more brittle materials courser and longer thread lengths are more suitable?
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My personal opinion: life is too short to work with unsuitable materials. I won't use polyester resin, I won't use inlace acrylester, and I won't use "alternate casein" because when I have tried them, the threads I cut simply crumbled away.

Materials that I've found work nicely with taps & dies: acrylic acetate, alumilite, cellulose acetate, Cebloplast, galalith (casein), celluloid, ebonite (hard rubber). I'm sure there are more, and I'm sure that some of the materials I've had trouble with would be perfectly fine if I were single-point threading on a metal lathe (but I'm not :rolleyes:)
 
Thank you for the list; I will consult it when selecting materials.

What do you think I this statement; is it true? I guess with more brittle materials courser and longer thread lengths are more suitable?
 
In answer to your question, Tony ... not sure if longer threading is too relevant, but coarser threads (greater pitch, like 1 mm) are certainly more durable. . However, greater pitch also means greater thread depth so you have to allow for that in your thickness.

Most common threading uses roughly 60 degree threads, I think ... standard taps and dies ... the thread cross-sectional shape resembles an equilateral triangle.

You can get around some of the problems with the 60-degree type of threading by going to threads which have a flat top and flat bottom (there is a name for this cross-section but I can't think of it). . I think you have to cut your own using a metal-working lathe because I don't know of any taps/dies that do this. . I believe jalbert, one of the IAP members who commonly posts pictures of his work, uses this type of threading a lot. . I would think that this type of threading might be better for the more brittle materials, but I have never used it because it requires a lot more work and care .
 
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Mal is correct, coarser threads (fewer threads per inch, or more millimeters per thread) are more durable -- but that comes at the cost of both thread depth and, by definition, the amount of material you have to remove to create the threads. Removing more material is more difficult -- and if the material is uncooperative to begin with, cutting deep threads can be a real problem.

It's actually easier to cut very fine threads in brittle material, because you are not attempting to remove much of it. What you get is not as durable though.

(The square-ish-profile threads that jalbert specialises in, using his metal lathe and the cutters he made himself, have the advantage of durability and less material removed. I don't know of any way to do it without a metal lathe.)
 
Thank you both. When I said length, I was referring to the length. I am still learning the terminology. Thanks adain
 
Threading

Tony:

For more information and understanding of threading I suggest you might want to go on-line (Wikipedia Screw threads).

This will give you good information of the threads specs. Which is the same info that is showing in my Machinery's handbook 14th addition that I use when in school machine shop class. By the way I still use it often.

My threading on pen's is the same of what Duncan is telling you about.

Cheers


Charlie
 
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[QUOTE
(The square-ish-profile threads that jalbert specialises in, using his metal lathe and the cutters he made himself, have the advantage of durability and less material removed. I don't know of any way to do it without a metal lathe.)[/QUOTE

I don't think I've ever compared the strength of my threads to traditional 60 degree threads. I typically don't cut very deeply though—significantly less than what was mathematically dictated by 60 degree thread cutting methodology.
 
Dan, thanks for that info ... good to know ! . "Acme" is the name I could not think of when I wrote post #21 above.
 
Hah! I never thought about the ACME threads. I am close to $400 in taps/dies/holders and drills and that was buying the cheap single start ones. I am enjoy learning how to do it though. Money well spent; especially when there are folks like you guys to bounce things off of. I fell "in love" with the guy from Niels Niche - such a nice man (Neil Butterfield). I just sent him 2 nice pens in appreciation for his advice, patience ( I was calling him 4+ times a day), and quality products that he sells. I spent about $200 on his stuff, but it is excellent.
 
Tony, the thing about Acme threads is it is probably better to cut them on a lathe. . I did not know that you can get taps/dies for them until Danny mentioned it. . But if you buy them, you are stuck with that depth and pitch. . If you design and make your own then you can tailor the Acme threads to your particular need or want. . In the case of our pens, you can make the depth quite shallow to suit your pen wall thickness. . I don't know for sure, but I would think it is harder to buy ideally suitable tap/die in Acme.
 
TonyL said:
Thx. You mean cut them on a metal lathe?
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You thought tap and dies were expensive, time to get a metal lathe and all the associated tooling. It does help having a small metal lathe with the kitleas pens where you can turn to very precise dimensions. Important for the tendons and front section.


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TonyL said:
Thx. You mean cut them on a metal lathe?
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Yes, Tony. . That's what I mean and jalbert has developed his own tools and techniques for doing that.

Amazing, eh? ... like, cutting a fraction of a millimeter at a time until it's right, and both pieces accurately mate together just like a "normal" nut and bolt.
 
You thought tap and dies were expensive, time to get a metal lathe and all the associated tooling. It does help having a small metal lathe with the kitleas pens where you can turn to very precise dimensions. Important for the tendons and front section.
Click to expand...


I was preparing for that two years ago. I was going to order the PM after researching the ones that LMS sells, Taig, Sieg etc (can't remember the others) . I thought it was going to be plug and play. I understand that metals lathe need to be tweeked, and properly using one requires learning a new skills (machining). Maybe, I will get the urge again someday.


Thanks Dan and Mal.
 
Many colleges offer a basic machinist class in there continuing education programs. Also, if there is a nearby makerspace, they will also have training and equipment to try.

Most lathes can be used without tweaking. Mods are done to maximize precision that aren't really necessary for pen work.


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Tony,

If you do go for a metal lathe, I do not recommend the Taig for pen making, partly because of the offboard motor ... and the exposed belt ... and also because of the non-standard design which severely restricts your choice of accessories. . The Hi-Torque lathe from LMS is a good choice, IMO. . The smallest lathe that Grizzly sells is basically a Sieg (name on internal parts only) and not bad for the price. . Of course, the PM lathe is probably the premium lathe. . Whatever else, make sure you have variable speed down to extremely slow (v. useful for applying CA).
 
Thank you very much. My shop is now at capacity with still new, completely boxed tools to be installed. If I get a metal lathe, I have to knock down the walls to adjoining room (gym). I am good for now. Thank you!
 
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