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How often do you run into oddball thread sizes?

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  • #91
    Originally posted by demerrill View Post
    Not particularly applicable to small threads typically cut with taps/dies. But for threads large enough to be single pointed on a lathe, it is noted that a wide range of pitches can be cut with the range of gearing combinations possible on many lathes. For short thread lengths a 'close enough' combination may be found. An example for a typical 12x36 lathe: http://www.truetex.com/grizzly-12x36-pitch.htm

    David Merrill
    I've seen where a lot of lathes use a 120/127 tooth gear set. But it happens that my own older asian lathe uses the 86/91 gearing that the chart in your link refers to. Saved and printed and much thanks for the link. It'll make it a lot easier to do those oddball threads and to get back to making that custom screw for the Crackshot.
    Chilliwack BC, Canada

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    • #92
      Earlier, someone mentioned banjo threads. The banjo hold down threads on most vintage banjos are #8 X 26 TPI. Taps and dies for those are not generally available anywhere, except probably on special order. If I can ever find a set, I'd certain ly buy them unless the price is way too high.

      No one knows why the banjo makers started using that particular thread, but they did and it's caused a lot of trouble.

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      • #93
        Finding that size of screw would certainly be hard. But a few years back I found that KBC had a page of listings for oddball size taps and dies. I'll bet MSC has something similar. You might check with those suppliers.
        Chilliwack BC, Canada

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        • #94
          I recently made a special tool post for the museum's Smart & Brown model A lathe. The intention was to be able to swap tool posts in seconds, so all the parts had to be made, including the central quick clamping thread. It was 10tpi acme twin start, and the lathe only went to 8tpi. As the head output and the gearbox input shafts ran at the same speeds, I just bought a couple of gear blanks of 36 and 72 teeth and machined them up to double the leadscrew speed. Setting 10tpi gave me the required 5tpi pitch. Of course when the thread was completed with the standard acme thread depth of 0.5 X the pitch, (0.050"), the screw would not even look at the female thread. Still, it's easy to pick up such a large thread, it took about 0.008" more depth of cut to get the parts to screw together.
          The S & B now uses a 125/127 gear to do the more common metric threads.
          Last edited by old mart; 12-01-2017, 01:27 PM.

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          • #95
            I run into weird threads all the time as I restore the older guns, If a tap or die is not available I will make a tap and then use it to make the die if the thread count is known. It works for metric as well. But it depends on the value of the gun as some are not worth the time. European shotguns are the worst due to non standard threads and tiny screw slots.

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            • #96
              Have you tries looking at BA threads for that 3/16 or 10 gauge screw maybe its a 1 or 2 BA https://www.royalsignals.org.uk/articles/threads.htm

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              • #97
                Originally posted by wierdscience View Post
                How often?Well this week I encountered -

                1-3/8"-6 left hand
                M7 x .85
                M9 x 1.75 left hand
                .275 x 32
                and M15 x 1
                are you sure the .275 was not slightly undersize 9/32 https://www.carbideanddiamondtooling...er.Plug.Bottom

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                • #98
                  Some years ago at work we had an interesting situation due to literal mis-translation in a contract. The company had contracted a German firm to build a pair of pusher furnaces (we make powdered metal, including carbide). The contract stated that they preferred "English" threads, but would be OK with metric sizes of piping on the process chemical sleds. (eg large flanged pipes) In a way it makes sense (and this was 1986 after all, somewhat early in the company's history).

                  Years later the vacuum pump burned up on the "cold" (quench) end of the one furnace. We translated the motor tag with Google and found an equivalent modern unit. No go. After pulling out hair out for two days it turns out the Germans had interpreted the contract very literally: They used BSPP for the threaded piping!

                  The lathe saved the day, making the proper adapters to NPT out of the scrap bin.

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                  • #99
                    I run into truly odd sizes once or twice a year because I do maintenance and repair on some very old equipment, and sometimes very specialized stuff. Other times I get jobs that make you wonder how to unbolt it. For example the screwdown nuts on a rolling mill from 1900. Turns out those were 4-7/16 dia X 4 TPI, (sharp vee thread, early American...) so we ended up making a wrench out of some scrap 3/4 plate.

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                    • Originally posted by nickel-city-fab View Post
                      Some years ago at work we had an interesting situation due to literal mis-translation in a contract. The company had contracted a German firm to build a pair of pusher furnaces (we make powdered metal, including carbide). The contract stated that they preferred "English" threads, but would be OK with metric sizes of piping on the process chemical sleds. (eg large flanged pipes) In a way it makes sense (and this was 1986 after all, somewhat early in the company's history).

                      Years later the vacuum pump burned up on the "cold" (quench) end of the one furnace. We translated the motor tag with Google and found an equivalent modern unit. No go. After pulling out hair out for two days it turns out the Germans had interpreted the contract very literally: They used BSPP for the threaded piping!

                      The lathe saved the day, making the proper adapters to NPT out of the scrap bin.
                      And ”Metric” alternative to NPT is BSPP. Used pretty much everywhere exept north america.

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                      • Originally posted by MattiJ View Post

                        And ”Metric” alternative to NPT is BSPP. Used pretty much everywhere exept north america.
                        Er, bspp uses whitworth threads, if I understand your meaning correctly. Nothing to do with metric.

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                        • Originally posted by nickel-city-fab View Post

                          Er, bspp uses whitworth threads, if I understand your meaning correctly. Nothing to do with metric.
                          Yeah but.. commonly used in every metric country including Germany. Most common standard for things like water pipe fittings, pneumatic fittings (and some hydraulics).

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                          • Just this week.
                            I have a Rockwell combo sander /grinder with the 12" disk and the 4x48 belt that was making a lot of noise. Turned out the upper drum shaft lost three of the four jam nuts. The shaft is 15mm but the thread is 24 TPI. Making new nuts on the lathe was a fun project. Click image for larger version

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                            • Maybe we should start including fraction metric threads, just to piss the French off "That needs a 15/16cm x 3/4mm thread"
                              .

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                              • Originally posted by Mcgyver View Post
                                Maybe we should start including fraction metric threads, just to piss the French off "That needs a 15/16cm x 3/4mm thread"
                                They dont need your help when Swiss already use 1.6666mm pitch in schaublin collets

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