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  • Cutting bottle cap threads?

    At the risk of starting another debate, I have an amateur machining question.

    I haven't cut a thread yet on my lathe but would like to make an aluminum cap to fit an 8 oz. polyethylene bottle. (It's a squeeze type fueling bottle for my small r/c model aircraft.)

    As supplied, everything is very durable, being made out of poly-e, poly-p and brass, excepting the screw-on cap which is a brittle plastic. I've dropped both of mine and the caps are cracked. What would be the best method of duplicating the caps in aluminum? The threads are somewhat blunt in form so I guess a small boring bar with a shop-ground form tool would be needed? How do I measure and calculate the pitch of the existing thread and how do I transfer those pitch numbers to my lathe. It's a small (8x16) Sieg lathe but did come with a bewildering array of gears that can be exchanged to change feed speeds.

    A gentle nudge from you wise veterans would be humbly appreciated.
    Milton

    "Accuracy is the sum total of your compensating mistakes."

    "The thing I hate about an argument is that it always interrupts a discussion." G. K. Chesterton

  • #2
    The soda bottle I've got here looks to be about 8 TPI.
    Todd

    Comment


    • #3
      The size of the cap/neck are in two numbers the first number refers to the cap diameter in millimeters. Second number is the height and thread configruration of the closoure cap such as 15/415, 22/400 don't know if this will help you out any but check thier selection out here http://www.usplastic.com/catalog/default.asp
      Also you can go to the glass packing insitute or the society of the plastic industry and they will have some more info on thier web sites.
      Glen
      Been there, probably broke it, doing that!
      I am not a lawyer, and never played one on TV!
      All the usual and standard disclaimers apply. Do not try this at home, use only as directed, No warranties express or implied, for the intended use or the suggested uses, Wear safety glasses, closed course, professionals only

      Comment


      • #4
        There have been many articles and threads on threading. It is a bit difficult to explain at one sitting on a forum. I would suggest getting a basic lathe text such as How To Run a Lathe by South Bend or, the much better Atlas Manual of Lathe Operation. Neither is a waste of money, and will provide much information on the use of any lathe. I recommend them to anyone who has a lathe.

        You will have to directly measure the threads to determine the pitch and derive the change gear set up to accomodate it. Measure the center distance between two or more threads and convert that to a number per inch.

        A form ground tool on a boring bar will be used to cut the threads. It will be a fast thread, and cutting it on a blind bore will be exciting. You might consider practicing first on an open tube to get the thread right, and maybe making a two part cap with the end soldered on.
        Jim H.

        Comment


        • #5
          I hope this does not unnecessarily complicate the answer but many bottle cap threads have multiple starts. Many milk jugs, for example, that I have seen have a three start thread. This does not make the project impossible but it may may make it more difficult.

          Comment


          • #6
            Randolph is right and I forgot to mention that most of the threads are only one or two complete ones at the most. And since they are molded on the bottles they do not conform to the standard thread inch or metric. It is one hell of a starting threading project. good luck It will take a few trys before you hit the right combo.
            Glen
            Been there, probably broke it, doing that!
            I am not a lawyer, and never played one on TV!
            All the usual and standard disclaimers apply. Do not try this at home, use only as directed, No warranties express or implied, for the intended use or the suggested uses, Wear safety glasses, closed course, professionals only

            Comment


            • #7
              Bottle threads

              There is a standard for Pill Bottle type round threads. Sandivik and others list cutters for them. I tried to grind my own without very good results. Foregoing appearance it is really not necessary for the male-female forms to match. A Pointed type V thread captures the round profile quite adequately for most cap closure applications. Have been looking at the threads on Plastic bleach bottles they look to be somewhat of a modified Butress form. Hope this helps.
              Byron Boucher
              Burnet, TX

              Comment


              • #8
                Ouch, as in many things, sounds like it's far more complex than it looks! Discretion sometimes being the better part of valor, I think I better retreat and find myself another 1st time threading project.

                Might be easier to make a small furnace, make up a mold from the original bottle cap and cast it out of aluminum. Overkill maybe, huh.

                ps: Thanks for the link and the RTFB advise. I do need to study up on basic threading techniques.
                Milton

                "Accuracy is the sum total of your compensating mistakes."

                "The thing I hate about an argument is that it always interrupts a discussion." G. K. Chesterton

                Comment


                • #9
                  You could just turn an aluminum "cup" into which you epoxy the bottle cap. That'll protect it, and you don't need to bother with the threads.
                  Todd

                  Comment


                  • #10
                    (Whacking self in the head) Now that's an elegant solution! Or, I could machine the "cup," partially fill it with JB Weld, stuff the bottle in it, wait 24 hrs. and unscrew it. JB weld won't bond to polyethylene so it should come off pretty easily.

                    Thanks!
                    Milton

                    "Accuracy is the sum total of your compensating mistakes."

                    "The thing I hate about an argument is that it always interrupts a discussion." G. K. Chesterton

                    Comment


                    • #11
                      Another Idea

                      Starting with a solid rubber stopper which is a larger diameter than the soda bottle neck, drill it half way though using a diameter smaller than the threads on the soda bottle. Then "screw" the rubber stopper on the botle and there should be enough "play" in the hole you drilled to thread onto the bottle and create a seal. Add a smaller hole for the dispensing of the liquid.

                      Bill
                      Bill

                      Being ROAD KILL on the Information Super Highway and Electronically Challenged really SUCKS!!

                      Every problem can be solved through the proper application of explosives, duct tape, teflon, WD-40, or any combo of the aforementioned items.

                      Comment


                      • #12
                        ****y,
                        Don't give up on this threading project.

                        I'ts a fast thread so thread a tube of suitable thickness a few inches long, or start with a solid rod and bore/thread the inside.

                        Part off several discs so you can have several caps. Now make some tops with a shoulder to fit the ID of the cap and solder them on. sand and brush to make pretty. Drill the top to screw in a barb and attach your hose (or whatever)

                        Don't forget to machine a grove in between the soldered on top and the threads for an "O" ring gasket.

                        Comment


                        • #13
                          Bottle cap threads

                          Hello ****eybird,

                          I might as well put my $.02 in this thread.

                          I have a friend that made an aluminum cap to fit a 2 liter drink bottle. He did have to make a boring tool with a shape to fit the thread profile.

                          For your application you could use a wad of clay to get the impression of the thread. This can be use to count the number per inch as well as the form of the tool needed.

                          Also you could take a cap and split it and do the measuring this way. Fit your threading tool to it.

                          Doable, but time consuming.

                          Hey I use a lot of time making stuff. I like to know that I can do it.

                          I'm the plant manager at my home shop. So not a problem with how long it takes.

                          Good luck on this project.

                          skeeter

                          Comment


                          • #14
                            Thanks skeeter, didn't think of the clay trick.

                            "I'm the plant manager at my home shop" Sounds like a start for a good signature line to go at the end of your posts!
                            Milton

                            "Accuracy is the sum total of your compensating mistakes."

                            "The thing I hate about an argument is that it always interrupts a discussion." G. K. Chesterton

                            Comment


                            • #15
                              Cutting bottle cap threads?

                              Originally posted by JCHannum
                              There have been many articles and threads on threading. It is a bit difficult to explain at one sitting on a forum. I would suggest getting a basic lathe text such as How To Run a Lathe by South Bend or, the much better Atlas Manual of Lathe Operation. Neither is a waste of money, and will provide much information on the use of any lathe. I recommend them to anyone who has a lathe.

                              You will have to directly measure the threads to determine the pitch and derive the change gear set up to accomodate it. Measure the center distance between two or more threads and convert that to a number per inch.

                              A form ground tool on a boring bar will be used to cut the threads. It will be a fast thread, and cutting it on a blind bore will be exciting. You might consider practicing first on an open tube to get the thread right, and maybe making a two part cap with the end soldered on.
                              JC is absolutely correct!!! Blind hole threading on a fast spiral can give you ulcers, but there is an easy fix. If you had a big lathe with a clutch it would be a piece of cake, but since you have one with just off and on don't dispair. You can engage the threading lever and turn the spindle by hand, being careful not to crash into the bottom. I have done this and it works just fine on soft materials like aluminum and delrin. You may need to make a hand wheel to go on the rear end of your spindle to make it easier to work with. My Clausing has one and it is useful for a lot of things.

                              good luck,
                              Jim (KB4IVH)

                              Only fools abuse their tools.

                              Comment

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