External threading question

[Chewy]

Look at eBay and Amazon. The ones on eBay here and in the UK come from China. 2-3 weeks. Amazon here in the states, I can have a tap and die for around $25 in about 5 days. Faster If i order overnight from McMaster Carr, but I would need to float a loan. The die alone is $72 US.
Me, I would order one each from China. Then go ahead and try to thread the one I have. If it screws up, I would fall back on making one from brass.

 

[o0norton0o]

So, here's the resolution. I had no trouble cutting the short nub of the jet holders down to the correct size to be threaded. I used a die in a manual die holder and easily threaded a few of the parts that I had cut down,..... Unfortunately, the threads were just slightly angled and those parts were ruined as far as finished parts go because they need to be dead straight when assembled. Those ruined parts allowed me to keep experimenting... and researching to improve my technique.

I realized that I needed to keep the die perfectly straight. For such a short nub the best way would be to use a die holder in the lathe tail stock and turn the lathe by hand as was suggested here early on in the thread, so I bought a cheap Chinese die holder. The first thing I noticed was the die holder's 30mm fixture was actually 29.84mm and the die I had was 29.98mm. So job #1 was chucking the die holder in the lathe and turning it out to 30mm. The holder cut like butter with insert tooling and I got a good fit between the die and the holder, and I was on my way to the next step.

I still could not find a die without the lead in taper on both sides of the die, so I ordered 2 cheap hexagonal dies from amazon which I was going to remove the tapered portion on one side and then use it as a follow up die to complete the last little bit of threading that the tapered die could not reach. I had a few ruined parts to practice on, but I had to cut down the cheap die to remove the taper to do the process I had devised.

I chucked the die in the lathe and it was immediately obvious that it was very hard to cut, so I gave up on cutting it down and switched to grinding it down. I mounted the die on a workmate with angled trim head screws in the relief holes and built a small damn around the die to fill with water. I used the hand grinder to grind away the tapered lead in to the full depth threaded section. It was tedious work and I was showering my back yard with a rooster tail of sparks while the rain did it's job if keeping me from burning up the neighborhood, but I got it very close to perfect, then I ran the surface flat on the horizontal belt sander to blend the tiny undulations together... It worked like a charm.

I took the ruined jet holders and used the cut down die to try to see If I could finish the cut I made on them and it worked perfectly. The taper on the hex die that I cut down was actually less than the round 30mm die's taper, so I used the hex die with the taper side first and got a little closer to the shoulder then flipped it over and got virtually all the way up to the shoulder with the cut down side. That adds a full thread to a very short stub that needs all the threads it can get to hold on to the bowl of the carburetor..

So I am waiting for delivery of some more jet holders to modify. I feel confident that I've learned enough and practiced enough to make the parts that I struggled with on my first run. It cost me $30 in ruined parts to learn about tailstock die holders and making straight threads, but I've spent a small fortune in screwed up first attempts in just about every thing I've ever undertaken.

Here's 6 of the brass parts that thread onto the jet holders that I have yet to finish making, along side the original parts that I copied.



Thanks everyone for the help and advise.

 

[mksj]

Most round dies have a lead in on only one side, when needing a thread up to a shoulder I flip the die and carefully advance the die back and forth until threaded up to a shoulder. Works most of the time, but you can also break the die thread teeth in particular with the cheaper dies. You could also cut a small relief groove for the last thread next to the shoulder. Alternative which I have done is make a thread chaser type of cutter say with some O1 steel cut some round relief grooves and then tap it in the center, then use it to cut the last few threads to the shoulder. Wouldn't need to heat treat for brass, other materials I heat treat. I have also made custom taps. The two attached articles are more specific to taps.

 

[Chewy]

There is always a learning curve on special one of a kind items. Don't count the modified tools unless you will never ever use it again. Sounds like you will only have one modified die that will cut up to a shoulder. I have lost count of things that I modified or invented that I decided to do over with more changes or a different way of machining. It is and always will be a learning experience every time you go into the shop. The parts look good in the picture and it sounds like you are well on your way to getting what you wanted.