thread count / pitch - Churchill

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Bman40

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Nov 26, 2007
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Location
Richmond, BC, Canada.
hi again.

I am thinking about making a Churchill fp, but NOT using the cap 'part' - just turning a cap and threading the inside with a tap to match the thread on the body.

Does anyone have any specs on the thread count / pitch for this (or any other) FP kits?

thanks

Barry
 
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Barry, I can't help you with the thread count, but I don't think you'll find a tap for it. I believe it (like most of the others) uses multi-start threads. I know none of my metric or SAE taps have ever helped me to match any of the capped pens we turn. And, the last time I tried to find multi-start taps, the closest I got was "maybe" (and I say this hestitantly) a company could make one for me.
 
It is a 4 start thread, and the pitch is 0.75 as far aas I can see on my gage.
As far as cutting one on my metal lathe, I haven't a clue.
 
Barry, I wouldn't go down that route, trying to get a matched tap. I recently got a quote for a 3 start matched tap and die. $182 for the tap and $320 for the die!!!!!
What about just using the plastic black threaded part? Remove it from the metal trim and drill the blank to suit the plastic bit.
I am practicing multi start threading on my metal lathe. The external (male) threads are one thing, but the internal threads are an absolute nightmare. No success yet:( I think I'll just buy cheap kits just for the threaded bits from now on.

Good luck
 
Barry

There is another group working on getting multi-start taps and dies. We are wait for a price quote. I know $ 500.00 seems like alot of money but the upside is If you sell enough pens the cost can be covered over time.
 
Ok...so multi-start threads are a pain...

what about 'regular' threads?

Is the issue with regualr threads the number of turns it takes to get the cap on and off? does it really matter?

obviously if I had to spin a cap 12 times to get it off or on, that would be annoying, but do vintage pens feature multi-start?

just musing - and trying to avoid cheap plastic parts / kits.

barry
 
Barry, the issue isn't with the amount of threads or turns to get the cap on/off. The problem with 'regular' threads is that they lock very easily. This is because the amount of mechanical advantage you get with them. Threads are really just round wedges. A wedge with an angle of say 45 deg will be a lot easier to remove than one with say 5 degrees.
I'm sure you have noticed that some threads on pens are just regular, but these are normally only for parts that you rarely need to take apart and are often difficult to undo.
Although the multistart threads look quite fine, they are actually very course. Where a regular thread may have 24 tpi, the ms one while looking similar, will have 3 x 8 tpi.

If you can afford to buy those special taps and dies, then great. But remember that you will only have one size and they will eventually get blunt.

There are some guys on IAP that I'm sure could explain it easier, so I hope I haven't confused the issue[:I]
Good luck
 
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