Multi Pitch Threads?

[SerialCoder]

Hi all,

I'm not a machinist or even an engineer but i've gotten involved in a project where I am reproducing a vintage pen. I need to tap the threads where the barrel and the cap screw together and found that it has 4 starting points for the beginning and end of the thread. I'm not sure what this is called or how to do it. The pen that I am creating is going to be cast in sterling silver and I was hoping to re-tap/die the threads like the original. are there companies that make this sort of tool? Should I just tap it to something standard?

I appreciate your help.

SerialCoder

 

[BillPSU]

If you want to make the cap identical to the orginal you have two basic choices. You can make/order a tap and pay the price or single point thread the cap on a lathe. The male thread on the pen body will also have to be made.

I'd recommend you find an old machinist which is real proud of doing exceptional quality work. Have him make your parts on a good quality engine lathe. If you are going to make several/many of these vintage pens then spend the money on the tooling.

My thoughts,
Bill

 

[SerialCoder]

Thanks,

I'll be doing at least 10 of these so it looks like i'll be going the tooling route. So there are companies that can make / match a particular thread then?

Thanks for your input.

Dave

 

[griffengm]

SerialCoder,
Yes, there are people who can do this. It is not that rare. The formed multiple thread on a plastic pill bottle or a screw top tin are very similar.
Multi pitch threads are somewhat different however. These have two different pitches at different areas along the length of the screw. I've seen them used in bone screws to increase the pull with which two pieces of bone can be pulled together(At least that's what the podiatrist said).
Most any competent tool maker should be able to do this.
Griffy

 

[ornerynorsk]

I believe that you're referring to a multiple lead thread. Multiple pitch, or variable pitch as it is properly called, is much more expensive to produce in a tap and die. Multiple lead taps are easily made by most good tool grinding shops, but be prepared to pay.

 

[SerialCoder]

You are right. That is what I meant. I had a conversation with one of our enginereers at work and he called it a multi-lead when he looked at it. I guess Ill Start looking for a tool shop. Thanks!

 

[cliffy]

I have had these guys make many special taps for me over the years: they're excellent!

http://www.ocmfg.com/western.htm

 

[EngJW]

Also called multi-start threads. There is a little bit about them in Machinery's Handbook under Acme threads. I came across them years ago as part of a clutch in a chain hoist. There was no design information. All we could do was measure the parts and reverse engineer it. It worked only because we could also make the mating part.

 

[unclesyd]

Checkout this website came across it while looking for another type tap.

http://www.e-taps.com/