Triple Start Tips

[freshmaker]

Hi folks!

I see a lot of posts about the importance of triple start vs single when making custom fountain pens, but haven't been able to find any on best practices for using triple start tap & dies. So I wanted to pose a question: what techniques do you use to ensure your triple start threads actually work (the pen caps properly) every time?

Please allow me to explain why I went searching in the first place. I made a pen today, and after using a die to thread the tenon on my barrel, the three "entry points" where the threads start are wafer thin (for obvious reasons, nothing new here). I used a carbide tool to shorten the tenon by 0.5mm to get a really clean surface so that the grip section sits nicely flush against the barrel's tenon when screwed in. My main question is what to do with the thinnest part of the threads at the edge of the tenon? Sometimes a few mm of one of the threads will break off because they're so thin. Sometimes I'll break off a few mm from each thread as well to try and result in thicker threads as starting points. In both of these cases, I find the cap can cross thread onto the barrel because the three threads are starting at uneven spaces, not perfectly equidistant from each other. This drives me NUTS. If my section is wide enough that the cap has almost zero play (wobble) when going on, then even in this scenario cross threading isn't likely. But on the pen I made today, there IS play (which is preferable IMO to avoid almost creating a vacuum that risks pulling out ink from the nib when uncapping too fast), and half the time I cap the pen it gets stuck and I have to back off to align the threads before tightening again.

I would love to hear what methods you like to use with triple start threads! And feel free to tell me I'm crazy - I'm not an expert here by any stretch.

Happy pen making

 

[hooked]

I'm not entirely sure that I understand correctly. I'll try to give you a couple of ideas. It might help a bit if you provided some details, such as the size of the tap/die you are working with and the tool you are using to cut the threads.

First, ensure that you are sizing your tenon properly. It almost sounds as if you have a wobble that your tenon might be mis-sized, but it's hard to tell.

I would also radius the outside edge of your tenon at about 45 degrees for 1-2 mm. This will give the fragile end a smoother start at the threads and allow the threads to start a millimeter or two from the edge. I believe this also allows them to engage more effectively.

Ensure that you polish your tenon before threading. Ensure you use plenty of lubrication when cutting threads. Go slow and back out a bit every few turns to clean out the debris.

 

[freshmaker]

Thanks for the reply @hooked!

Here's a picture of the threads at the edge of the barrel tenon I'm referring to:

Your third paragraph might be the key to what I'm doing wrong. If I make a 1-2mm 45° angle cut at the end of the tenon, I won't have this thinning thread issue. The reason I haven't done this is because I want the "valley" of the tenon threads to be roughly the same level as the section. Here's what I mean (the gap is me intentionally unscrewing the section to make it easier to see how they line up):

- Barrel tenon is 13.95mm (cut w/ 14mm die)
- Section is 13.05mm at its thickest (where it meets the barrel when screwed in)

Maybe what you're saying is that the solution is to angle the barrel tenon @ 45° down to 13mm, which will allow it to still line up with the section and be right at the lowest point of the threads (the valley).

Thanks so much! And thanks for the other tips

 

[hooked]

Yes, I think if you take a tool to that edge and give it a 45-degree angle, your edge will not be as sharp. It will give the thread a better start. It won't chip either.

Additionally, you may want to chamfer the inner edge of your cap slightly to improve the fit. That may help with your sticking cap. You can also place the relief you built behind the threads into your cap if you encounter problems with putting it behind the threads.

Good luck!