Here's a tough job I just completed. I have a very nice Moore pen that had bad barrel threads. To top it off it is a two piece section of a type I was not familiar with. For your reference here is how I did it:

First I had to get the sections apart and removed from the barrel. The sections were very tight together and tight into the barrel as well. As I did not know how the parts were joined I had to be very careful. Soaking for 2 days in water did not work. Luckily I have a similar Moore pen that I am also restoring at this time and it came apart fairly easily with heat from a alcohol lamp. I could see from the other pen that both section parts had right hand threads. Now that I knew for certain how to proceed it finally came apart with applied heat.

Second: The bad threads were on the visulated part and had to be turned off on my 7x10 mini lathe. I turned off just enough so I could affix replacement threads and at the same time preserve the existing inner threads. I had to sacrifice about .100" length of the section which was cracked but I still had enough inner threads to accept the nib end section. (see pics) My first choice was to find the same type and size threads out of my scrap drawer. I was lucky to find a barrel of the exact same color and thread size. I bored the ID to the proper size but as I was cutting to length it shattered. Now my only choice was to make my own threads from an extra black plastic barrel. I turned the ID and OD to the proper dimensions. Easy so far!

Third: The threads needed are 36 tpi quadruple lead. I have machined many threads during my career as a machinist/toolmaker but never quad or even triple lead. I have done double lead with special chasers which is not near the same as single point threading. I wasn't even sure I could do it on my 7x10. I checked on the internet for help and found that it could be done with the right gear changes and procedure. I found a very cool site with a downloadable gearing caluclator for mini lathes. His name is Paul Bussieres and his email is koak005@hotmail.com. You could try a internet search for gearsvb6 or mini lathe gearing calculator and probably find it. Now following the somewhat conflicting methods I had come up with I thought I needed to gear for 9tpi. 36/4=9 right? wrong! Tried it, been there, doesn't work! What works is gearing for 12tpi. You put the compound tool rest parallel to the part - feed cutting tool in .017, engage the dial on a even number and make the first cut. Stop the machine, back out the cutter and leaving the lead screw engaged reverse the machine. Go to a point somewhere beyond the part and stop the machine. Feed cutter in to the same setting, advance the compound rest .028" and make the second cut. Follow this proceedure for all four threads and all should be well.

Fourth: Cut the threaded part to the proper length and reassemble. Depending on your machining skills this will give you a professional repair nearly impossible to detect except to the most expert eye. Best of all I have saved a very nice Moore pen from the parts bin or worse.

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My sincere congratulations on an impressive and -as I can see - excellent job done !

A tricky repair, and it shows what great things can be done in pen restoration with the aid of a lathe.


That is incorrect. 36 tpi quadruple-lead threads are indeed composed of four 9tpi threads, as your arithmetic proves. If you gear instead for 12tpi and advance the compound 1/36" (~.028") for each thread after the first (which is the correct advance for 36tpi, of course), the fourth thread will re-cut the first thread (likely imprecisely, resulting in an irregularity every three threads as seen here), as each 12tpi lead's threads are 1/12" apart by definition, and three advances of 1/36" is 3/36" or 1/12", resulting in a triple-lead 36tpi thread rather than a quad-lead 36tpi thread.

--Daniel

Incorrect or not it is what worked. I tried the 9tpi gearing set-up with the .028" advance. I ended up with a huge gap after the third cut. It is possible there was gear slippage or backlash or who knows. After all the machine cost under $400.00. I will try the set-up again first chance I get.

It's not a function of the price of the machine or any limitation attributable thereto. There should be a huge gap after the third cut; that's where the fourth cut goes. It's a quadruple-lead thread.

--Daniel

That's so cute. I had 4 cuts with the huge gap in between the third and fourth. Tough Crowd!

Oh, sorry -- I thought you meant you cut just three threads and then saw there was a gap left. Which gears did you use in which positions?

--Daniel

For the 9 pti gearing I used A-#55, B-#35, C-#60, D-#50. This configuration did not work for me unless I made an error in the actual machining. The 12tpi gearing which did work I used A-#55, B-#45, C-#75, D-#65. This produced very nice looking threads that screws nicely into the cap. It's always possible I made an error somewhere along the line but the threads I ended up with seem to be right. If you have an explanation please let me know, Stan

I'll check my gear tables and get back to you, but if you examine the threads that you cut at 12tpi, do you see three starts or four?

--Daniel

A beautiful job.
I too suspect that you've got a triple start thread or the pitch given by the calculation is wrong. When playing with my Chinese made/UK badged 12x20 lathe I came to the conclusion that whoever had set out the gear ratios in the manual had:
a) No idea what they were doing.
b) Never actually tried to see if the suggested gear would actually fit.
c) Couldn't tell RH from LH threads - half the metric ratios use 5 gears and give LH threads, meaning there's no room for a reversing idler.
d) Couldn't do maths.
Apart from that, all was well.
I've had to re-calculate all the ratios myself, and found that half the imperial ratios they specified were wrong with pitches randomly above or below what they specified. I was not impressed. The final thing that didn't impress me was the way they didn't supply all the gears referred to in the manual, while giving multiples of odd sizes.

Regards

Richard.

The gear train you set up for 9tpi is incorrect; it will produce ~8.48tpi threads, which will have an extra gap of about 0.008" using your threading procedure. The train for 12tpi is also incorrect; it will produce ~11.35tpi threads.

The correct train for 9tpi is A=80, D=45. D must be in the back position (gear on shaft first, then spacer on top, then screw) so it is coplanar with A. B/C should be set up with any gear in the B (back) position to act as an idler (the single gear should engage with both A and D), so you'll need to use another gear at C to act as a spacer to position B properly on its shaft so it is coplanar with A and D.

Here is the formula I derived for the threading calculation:

For four-gear trains: tpi = (B/A) * (D/C) * 16
For two-gear trains: tpi = (D/A) * 16

--Daniel

Lots of food for thought here and thanks for your response. Right or wrong I am happy with the results. 1. There is 4 leads - I counted 'em. 2. It screws in nicely. 3. it looks great. I have a nice "keeper" pen for my own use. It is now reasembled and filled with ink. It writes lika a dream so it was all worth it. I have gained a lot of knowledge for future reference. Thanks again!