Help Needed With Kitless Threading

[ABinBoston]

Maybe someone can help me with some measurements. I have been practicing with some taps and dies, but the external threads are either not deep enough, or very tight when screwing a cap to a barrel.

 

I am using acrylic blanks, pretty sure it is Alumilite.

 

When using dies, what is the best diameter to turn a pen barrel or tenon for the following threads.

 

12x.8 triple start

13x.8 triple start

14x.8 triple start

 

When using taps, what is the best size hole to drill for the same threads?

 

I am using the following

 

12.8 - an 11.2 bit

13.8 - a 12.2 bit

14x8 - a 13.2 bit

 

Thanks!!

[Oruc Gazi Kutluer]

These are correct numbers. Unfortunately most drill bits do not give the correct drilling sizes.. I am boring the hole I drilled to the correct size to get the most precise diameter..

[ABinBoston]

Thanks!

 

What about the diameters to use dies for external threads?

 

For example, what's the best diameter for a a 12x.8 thread? I tried 12mm, but the threads did not seem deep enough??? I tried 12.2 or so and it fit tightly to the cap?

 

 

 

These are correct numbers. Unfortunately most drill bits do not give the correct drilling sizes.. I am boring the hole I drilled to the correct size to get the most precise diameter..

[richardandtracy]

I suspect the limit would be 60% thread engagement, if the nominal thread engagement diameter remains the same, then the diameters will be as calculated below:

External diameter = Nominal Diameter - ((100 - percentage thread engagement)/200) * pitch

Internal thread bore diameter = Nominal Diameter - pitch + ((100-percentage thread engagement)/200) * pitch

 

12 x 0.8 triple start External thread, 60% engagement: 11.84mm min dia

12 x 0.8 triple start Internal thread,60% engagement: 11.36mm max bore diameter.

Similarly for the larger diameters:

13mm: 12.84/12.36

14mm: 13.84/13.36.

 

Can I suggest you try this on a trial piece so that you can check whether it works, first.

Much less than 60% thread engagement & the thread will start getting a bit weak when using plastics. With metal threads the limit could be down to 50% engagement.

 

Hope this helps a little,

 

Richard.

[darrin1200]

For a 12mm, I normally use an 11.2mm hole and an 11.9mm tenon.

 

Is your die adjustable. Some of the better ones come with a small screww in the side to tweak the fit.

[ABinBoston]

Thanks. I will experiment with the measurements you guys provided.

[More4dan]

This site has been invaluable in my kitless adventure. http://theoreticalmachinist.com/Threads_UnifiedImperial.aspx

 

You have to convert the dimensions to inches for the input but you can display the output in metric. Change the pitch entered in tpi until it calculates the right metric pitch. The class 1A would be used for the male thread and 1B for the female. You can even select the number of starts. It will calculate minimum and maximum dimensions for the hole and the tendon.

 

When selecting the class 1A use the major diameter for the tendon. Select 1B and the minor diameter for the hole. Select something in the range.

 

Class 2A and 2B would be for tighter tolerances and more engagement. Class 3 is the tightest and not necessary for pens. Experiment on scrap.

 

I use this calculator to make my own feed taps for the odd fountain pen nib feeders on my metal lathe.

It even gives me the depth of cut for the threads.

 

It also helps when deciding which threads to use for sections and body to cap threads by stacking up the dimensions you can see how much wall thickness is left between stacked threads.

 

 

Danny

Edited April 26, 2017 by More4dan

[ABinBoston]

Danny - thanks. I see how that calculator can be helpful!!

 

AB

[ABinBoston]

Thanks!

 

I'll try some of these diameters and bores

 

AB

 

 

 

I suspect the limit would be 60% thread engagement, if the nominal thread engagement diameter remains the same, then the diameters will be as calculated below:

External diameter = Nominal Diameter - ((100 - percentage thread engagement)/200) * pitch

Internal thread bore diameter = Nominal Diameter - pitch + ((100-percentage thread engagement)/200) * pitch

 

12 x 0.8 triple start External thread, 60% engagement: 11.84mm min dia

12 x 0.8 triple start Internal thread,60% engagement: 11.36mm max bore diameter.

Similarly for the larger diameters:

13mm: 12.84/12.36

14mm: 13.84/13.36.

 

Can I suggest you try this on a trial piece so that you can check whether it works, first.

Much less than 60% thread engagement & the thread will start getting a bit weak when using plastics. With metal threads the limit could be down to 50% engagement.

 

Hope this helps a little,

 

Richard.

[LeonardS]

@AbinBoston, Can you tell me where you got your triple start taps?? I am looking for a M14 like the one you have.

[Inspector]

The IAP (International Pen Turners) had a group by recently and their order is in. You could join and get ahold of the organizer and let him know you would like one if someone decides they would like to cancel or sell their tap later.

 

You can buy them new from Beaufort Ink but because they are not an off the shelf item are pricy little critters.

http://www.beaufortink.co.uk/index.html

 

There is a Facebook group Custom Pen Makers (Kitless) and occasionally someone sells theirs if they moved up to a metal lathe or are getting out of pen making. In fact there was a post on the 3rd of someone doing just that.

https://www.facebook.com/groups/963060603830389/

 

Pete