Threading the old way on my lathe. How to do it?

piscov

piscov

Active User
Registered
Hi all,
I am doing some threading with my lathe ( not using taps or dies). The material I am threading is Ebonite and acrylic in order to produce a fountain pen. I will be doing the inner and outer threads in fountain pens barrels, sections and caps . Diameters will range from 6 to 15 mm.



My question is:

If, for instance, I want to make a thread to do a junction in a barrel with external diameter of 14mm, what should be the inside diameter to use on the cap so that screwing is correct and tight?
The threads will have around 0,5 mm deep and 30 32 or 36 TPI.

Is there any formula that relates the Inner diameter with external diameter of a threaded junction?

Thanks in advance and best regards

Vasco
 
The info you seek is available in the thread charts of Machinery's Handbook and other reference books. If you want to create your own custom thread, the formula and relationships you'll need can be found here.

Tom
 
I would stick with standard threads rather than trying to figure out custom threads unless you _really_ have to. If you can get hold of a machinery handbook, they have extensive tables of standard SAE and metric threads. If you don't have a copy, you could probably find one at your local library, and photocopy the pertinent pages.
 
Because of variables,like the plastic springing,or relaxing,etc.,and several other things,the best thing to do is just cut the threads and "sneak up" on the right diameter until you get the fit you want. I have used thread charts before,and ended up with loose tolerances.

Keep track of your settings if you are making several perms. After you get the fit you want, use those same depth settings every time.
 
If you're into vintage pen stuff, you'll find some nasty things - like 3-start threads, for example. I have a substantial collection of pens and parts, and so far I've chickened out on the possibility of making replacement caps, etc.
 
Thank you all for the info!


@Frank

Yep, Vintage pens is my thing. I have bougth a lathe to fix my pens. I collect from 1880 to 1960 fountain pens.

Yes you are right... The threads between cap and barrel have always 3 or 4 starts. All the others have 1-start. and on top of that there are some inner threads that have 3- 4 mm diameter.

Today I have started to build a pen. I will do all the parts except the Nib and feed. I will post this project as I go along.

I would love to see some pictures of your pens and parts. Send me a PM if you can.

Best regards

Vasco
 
Ah.. well, there goes the idea of using standard threads ;)

If the material is tap-able, you might consider making your own taps. Maybe you have steadier nerves than me, but cutting a small diameter, fine pitch, triple start, internal thread sounds... daunting to me. At the very least make some go/no-go gauges for testing fit. If you can get a copy of the Machinery Handbook, it will be your best friend through this.

Please do post more of your progress, it sounds like a great project. My girlfriend and I turned up some wooden pens last year. It was a fun and interesting project, but the mechanical components were purchased. What you are doing is a whole level beyond that.
 
DMS said:
Ah.. well, there goes the idea of using standard threads ;)

If the material is tap-able, you might consider making your own taps. Maybe you have steadier nerves than me, but cutting a small diameter, fine pitch, triple start, internal thread sounds... daunting to me. At the very least make some go/no-go gauges for testing fit. If you can get a copy of the Machinery Handbook, it will be your best friend through this.

Please do post more of your progress, it sounds like a great project. My girlfriend and I turned up some wooden pens last year. It was a fun and interesting project, but the mechanical components were purchased. What you are doing is a whole level beyond that.
Click to expand...

Thank you DMS. I will post my first project as I go along.
 
When I wanted to make a 10 start thread for a flintlock Ferguson rifle breech,I made a little indexing plate with 10 accurately spaced holes drilled around it. The steel I was threading was set screwed into a hole in the center of the flanged plate. I would cut a thread and index the little plate with a dowel pin,and cut the next thread. The threads spiraled at about a 45º angle around the threaded shaft. These rifles had their 10 start threaded shafts going up through the breech of the gun at 90º to the bore. The threaded shafts were connected to the brass trigger guard below. A half turn of the guard would lower the plug just below the bore. You could reload these advanced(and very expensive) rifles laying down. You had to stand up to load the normal muzzle loaders at that time. Plus,oversize bullets were used that bit completely into the rifling. They were used on us in the Rev. War. Thankfully,only a limited number were made. I'd love to have seen how they made those breeches with 18th.C. equipment!!!
 
You must log in or register to reply here.
Back
Top