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Cutting 11.5 tpi on a Craftex B227l lathe

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  • Cutting 11.5 tpi on a Craftex B227l lathe

    Have a craftex B227L lathe and need to cut a 11.5 tpi internal thread for a pipe fitting. The lathe can cut 8, 9, 10,11, 12, 13, 14, 16... but no 11/2 threads. Does anyone know if I can achieve this through the change gears I have? I have tried to work it out myself and used a few on-line change gear calculation tools, but have come up empty. The closest i can come is 11.27 tpi- and the thread jams after 4 turns of the fitting.

    Pictures of the lathe gear combinations are in another thread in this forum:

    I am working at home in my garage so do not have the luxury of hobbing my own gears.
    Saskatchewan, Canada

  • #2
    There are simpler methods of cutting gears than hobbing. One of the simplest methods can be seen here:

    That method requires a little bit in the way of fixturing/tooling but it's all pretty simple. The accuracy you achieve is sort of proportional to the care and effort you put into making and setting up the fixture. If you took a lot of time with it I think you could make gears more than accurate enough for your need here.


    • #3
      You don't say what gears you have with the machine, also be nice to know what pitch the leadscrew is

      Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.


      • #4
        What Sir John said. I was going to say, use more Teflon tape, but that would not be a nice way to welcome a new member, especially on his very first post. Welcome to the forum. Bob.


        • #5
          Most pipe threads are tapered so cutting internal pipe threads is not easy even if you had the correct pitch. A pipe tap can do it but good large pipe taps are expensive. I have used an existing fitting to machine a bushing to be installed in the host part. It is easier to install a 1/2 of a short nipple and then a coupling if that would work.
          Byron Boucher
          Burnet, TX


          • #6
            As you have tried it id go with welding a socket in as mr Boucher has suggested
            Welcome to the forum btw, its the only intelligent conversation i get some days, talking to myself doesn't count as intelligent anymore lol
            Last edited by boslab; 01-06-2014, 06:23 PM.


            • #7
              11.5 is a straight pipe pitch, the threads on garden hoses are an example. Oddly, this is one thing Atlas lathes are handy for, 11.5 is "native" to them.


              • #8
                Welcome littleirv.
                Don't let them get you down, they are a gnarly bunch of knowledgeable folk.

                The lead screw pitch is '7' guys.
                We've been through this before, although quite a while ago.
                Here. Post #11.

                My Dad always said, "If you want people to do things for you on the farm, you have to buy a machine they can sit on that does most of the work."


                • #9
                  I did an analysis of my B227L gears and came up with the following for 11.5 turns per inch:

                  A = 65 Tooth
                  B = 70
                  C = 105
                  D = 40

                  Formula to get this:
                  E = B/A = 1.077
                  F = C/D = 2.625
                  G = E/F = .410

                  Turns/inch = G * 28 = 11.487 turns/ inch

                  This formula works for all standard gears
                  example 10 turns/inch = 80 70 98 40 or 80 40 70 50
                  E = B/A = 70/80 = .875 40/80 = .5
                  F = C/D = 98/40 = 2.45 70/50 = 1.4
                  G = .875/2.45 = .35714 .5/1.4 = .35714
                  .35714 * 28 = 10

                  Not sure how the formula works but it works for all the standard listed in the manual.
                  I assume the factor 28 would change with different lead screws.

                  I found the 11.49 by trial and error. There may be a closer one but I would need a program to compute all the possible gear combinations.

                  Hope this helps


                  • #10
                    11-1/2 is the thread pitch for 1",1-1/4" & 2" NPT threads which are tapered 0.75" per Foot. There y also be straight versions of these but NPT is tapered.
                    Byron Boucher
                    Burnet, TX


                    • #11
                      The lead screw is 7tpi. (got it from here: )
                      Change gears are: 30, 35, 40, 45, 50, 55, 60, 63, 65,70, 80, 98, 100, 105, 120, 125
                      The usual arrangement is 4 gears (A, B-C, D) - pictured at the left of the plate on the picture below.


                      The size of gears that I can mate up is limited-e.g., If I try a 40, 45-60, 120 arrangement, I can not mate the 40 and 45 gear-the swing arm on the intermediate shaft does not swing far enough up to mesh the gears. Same problem if the gears in the C and D positions are too large.

                      The closest I came-that would fit-was 8, 40-70, 63 by trial and error, mostly error. Thx for the factor of 28-I assume it is lead screw tpi * reduction b/w the head stock and the drive (A) for the gear train. I was further off than I thought.

                      I am looking for the proper fit as this is for a 1.5" NPT hose coupling for a 2500psi/62gpm hydraulic pump. Don't want steel filings in the hydraulic fluid, and don't want the fitting to let go when the lines are under pressure lifting round bales. (Can't use too much teflon tape or my brothers will think I'm just jury-rigging this thing together and I'll lose my street cred.)

                      Thx George 4657
                      Last edited by littleirv; 01-07-2014, 12:52 PM.
                      Saskatchewan, Canada


                      • #12
                        Cutting tapered internal pipe threads is a pain. Not only do you have to worry about the pitch but you've also got to consider the taper. If this fitting is for a tank or cylinder why not just do as suggested and buy a coupling, split it in two and weld it on. We do this all the time. You can get the fittings in STD (Sched 40), XS (Sched 80) and XXS (Sched 160) designations--one of the latter two will give you lots of wall thickness to work with. With all the oil and gas stuff happening in Saskabush now it shouldn't be hard to find what you need. Where in the flatlands are you?
                        Just one project too many--that's what finally got him...


                        • #13
                          Thank-you gentlemen. Next time, teflon tape.
                          Last edited by littleirv; 01-07-2014, 12:54 PM.
                          Saskatchewan, Canada


                          • #14
                            I did run all the combinations using Excel. I filtered out only the results that were within 0.1% of the desired value.

                            I came up with the following four combinations that yield exactly 11.5 TPI:

                            A 125 // B 98 // C 105 // D 55
                            A 105 // B 98 // C 125 // D 55
                            A 125 // B 55 // C 105 // D 98
                            A 105 // B 55 // C 125 // D 98

                            They are essentially four different ways of arranging the same four gears. I am reasonably certain that they are the only combinations of the given set of gears that will come within 0.1% of 11.5 TPI.

                            I do not have that lathe so I have no way to determine if any of these combinations will be physically possible.

                            I am going to make a complete table of all such combinations of that gear set that come within the same percentage of any 1/4, 1/2, 3/4 or integral TPI value on that lathe and post it somewhere. If anybody wants me to send a copy please PM me.
                            Paul A.
                            SE Texas

                            Make it fit.
                            You can't win and there IS a penalty for trying!


                            • #15
                              I tell ya maybe not what you want to hear but NPT taps are money well spent. Good ones over 1” are speedy but the $40 China ones hold up well in the bigger sizes. I fought that taper inside threading thing and it sucks. Not fun fighting taper attachment and compound inside a little hole praying you don’t run past the last pass and need to set the whole thing up again.

                              BTW what the heck kind of round bail contraption uses a 1-½” pressure line? I used to have a 64 ton wrecker with 2 pumps the size of 35 gallon drums and it only had 1-¼” main pressure lines on it.
                              Anybody that thinks they know it all doesn’t even know enough to understand they know nothing!