Internal threading with a metal lathe

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RicardoPG

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Dec 7, 2024
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Oporto, Portugal
Hello everyone!

I recently started pen turning with a metal lathe and wanted to ask if anyone exclusively uses their lathe for making all of the threads, such as those inside the caps and barrels (for the section), or if most people prefer using taps and dies.

While I find that taps and dies might be the more straightforward option, they can limit the dimensions and thread types available. However, I'm struggling to find tools small enough to bore the inside of a cap or section and to thread it, especially since I want to use carbide bits. I've discovered that HSS (high-speed steel) tends to not work well - it wears areally fast - with the ebonite I'm turning.

I've come across small tools like Thinbit inserts, but unfortunately, I believe they are only sold in the US, and I am located in Europe.

What are your thoughts on using only the lathe for threading?
 
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Personally, I will recommend using taps and dies.
Making multi-start threads that are recommended at least for the cap - barrel thread will be very hard without taps and dies, especially the internal tapped threads. That is unless you're a very experienced machinist and have a capable manual lathe or otherwise use CNC. standard multi-start Metric ISO threads should work just fine.
 
You can get tools like this. Solid carbide.
 

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Hi, @hooked and @rherrell,
Thank you so much for your feedback and recommendations. I have searched for Micro100 and found a Lithuanian supplier that carries them. Since I am inside the EU, I will probably purchase from them. I also found a brand called Simtek that sells solid carbide tools for small parts turning in the EU, and I will also check them.
 
Personally, I will recommend using taps and dies.
Making multi-start threads that are recommended at least for the cap - barrel thread will be very hard without taps and dies, especially the internal tapped threads. That is unless you're a very experienced machinist and have a capable manual lathe or otherwise use CNC. standard multi-start Metric ISO threads should work just fine.
Thank you, Amihai, for your reply and advice!

Honestly, I am not a very experienced machinist (I am a beginner, really, so I'm nowhere near that), but I have a metal lathe capable of cutting threads.

Having a capable lathe, I was considering learning to cut multi-start threads with it. When you mention that it will be very hard, do you say it because of the thread cutting process itself or because of having to thread to a shoulder, both internally and externally, without a relief cut? I was thinking of doing this by threading away from the shoulder, with a right-hand tool upside down.
Nevertheless, wanting to use metric threads, I know I will face a problem with my lathe for cutting triple-starting threads, as it doesn't cut metric pitches divisible by 3 (like 2.4mm, making a triple 0.8mm thread). I will likely end up using double threads with a pitch of 0.75mm (1.50mm/2), as making a triple 0.5mm thread would probably be too thin.
 
I am a beginner too, but I will say - the hobbyist community is big on triple start threads, but if you go into a fountain pen store and look at the pens from big brands, you will find that many of them have a double start thread. Use your phone flashlight on them and see. As far as how strong that makes the thread and which one would be better for a beginner to make I am not sure. But maybe if doing custom double start threads would be easier for you, then maybe get a fountain pen that has double start threads and copy that.
 
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