lol- agree! My sister broke a dish once, my nephew said "Uncle David will fix it!" I think there are too many cheque repair men out there, I prefer to do it for myself...
A couple of tips on cutting threads on a lathe. Use .750 divided by pitch, example.750 divided by 20 = .0375, this gives you some idea how much to feed the compound. But don't go all the way on compound, when you get close to end number, start checking with ring gage or nut. Turn the major .005 undersize ie. 1" 1.000 make it .995 to start. that way it won't drag when you go to fit thread ring gage or nut. Take first p*** as scratch cut .005, use compound set at 29-30deg. check the scratch cut with pitch gage, to make sure you have gearing set correct.Use cutting oil, take your time with compound cuts .002 then some spring cuts with out advancing compound. When you get near finish take a 3 corner file and file the thread to remove burrs before you check with ring gage. blow off or wire brush before you try your gage or three wires. three wire are tricky till you get more familiar with using them. only use file when clean, don't try to file with oil on thread. Use a nut as gage if that is all you have. If you are just starting , slow the rpm down and make some practice parts. Until you get some experience don't try to thread anything smaller than 1/4". To make an internal thread without a gage, you make an external thread, then measure over it with the wires. Then use it as a gage to make your internal thread. But use bolts or nuts as gages unless it goes thru the insopecion department. Then you need calibrated go and no- gages, either thread ring gage(nut) or plug gage (bolt). The machinery handbook has a wealth of info. It gives you all the info on minor dia. for internal threads, acme, stub acme, UNC (co****) UNF (fine) UNR radius root etc,etc,etc. Now available in larger print an also on CD. Hope this helps. Ago
Here's a tip I use for those making internal threads. If you do things by the book, you'll have to turn the point of the threading tool towards the operator, and work the controls backwards from regular thread cutting. But if you start inside the part, reverse the threading screw so it cuts AWAY from the chuck and thread on the opposite side, you can actually see the threads you're cutting and the controls work in a more conventional fashion. That way if you get in a panic situation or the tool breaks, backing the tool out works just as it does on external threads. Not much worse than chipping the tool, then turning the controls the wrong way to find you actually are digging into the part instead of out of the cut.
There are micrometers called "thread mics". They have a very narrow blade that can fit into the threads, but the way I was taught to measure threads is by using the "pin method". Too long to explain here, but look it up in a Machinery Handbook" for a real description.
Very, very good advice. If you are just repairing a part and only need it to have threads, there is nothing at all wrong with just cutting until the nut fits. It's fast and effective. But if you are making something for someone who either didn't supply a nut, or it has to fit something you have never even seen, then you need to measure over wires. There are commercially-made wires that come in a set and vary in size depending on the threads per inch. Then you use the math formula supplied with the wires or look it up in the Machinery's Handbook, which you will need to find the pitch diameter anyway. The wires, plus a micrometer are used to measure the pitch diameter, which is the standard threads are made to. There is such a huge variance in tolerances between manufacturers of cheap nuts and bolts that our shop has actually had brand new nuts that won't thread on to brand new bolts from different manufacturers, so using a nut you got off the shelf to make a part for a customer is risky and a good way to make a "boomerang". You know, you send it out and a week later it comes back, usually in the hands of an unhappy customer...
A lathe like any other job you need the ap***ude for it plus the desire to do it. Even with that I have had people that could not stand the chuck rotating, makes them dizzy. Cutting threads some times scares some people when you are running the machine fast and you coming up on the chuck or a shoulder on the part.
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