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  • Selecting number on chasing dial

    My lathe is not American made therefore a plate is attached to the front of the lathe to assist in selecting the proper number on the threading dial when threading using TPI. Image of the plate is included with this post.

    As an example, if I wanted to cut threads at 18 TPI then looking at the chart I could engage the half-nut on the numbers 2,4,6, or 8. However, if I wanted to cut threads that were 4 TPI or say 16 TPI there are no associated numbers, rather, diagonal lines.

    I don't know what to do. The lathe will cut 16 TPI or 4 TPI but since it has no numbers on the instructional plate associated with the threading dial I am at a loss. Surely there are others who may not have the same lathe but do have similar instructional plates. How do you cut a 16 TPI or 4 TPI using this chart?

    Additionally, the far left plate has a column shown as "T" and directly under the "T" is a "0". I don't know the significance of the "T" or "0" and hopefully you can answer this riddle as well. The area of the plate showing dial numbers has a "T" and beneath that "16". How is this information to be use?

    Help would be greatly appreciated.

    Harold

    For those having fought for it, Freedom has a flavor the protected will never know.
    Freedom is only one generation away from extinction.

  • #2
    What type of lathe is it? What TPI is on the lead screw? I would be tempted to say that you can engage those threads at any line, numbered or not, because they are probably multiples of the lead screw pitch. Test it out by engaging the half nuts on a line and making a fine cut. Then back the tool off and make some more passes at different lines without the tool against the work. You should be able to tell pretty quickly if it is following the thread or not.
    Stuart de Haro

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    • #3
      Yep. What hornluv said.

      Comment


      • #4
        Hi guys,

        I can't help but wonder why they would even make a chart like that since, for example, 20 TPI uses any line or any number indicated by "1 - 8" in the scale column. Why would they not do all number threads that way since they went to the trouble of clearly instructing the user that 20 TPI can use any line or number. They seem to be specific when any line or number can be used.

        Do you guys have any idea what the "T" column is for and the "0" under the "T"? Surely it has meaning or they would not have gone to the trouble of labeling the plate in such a way.

        Harold
        For those having fought for it, Freedom has a flavor the protected will never know.
        Freedom is only one generation away from extinction.

        Comment


        • #5
          Hello,

          I asked something similar a while ago and I don't have a plate like that on my machine. Below is a link to thread that I started. There are some complete explanations of the use of a threading dial.

          http://bbs.homeshopmachinist.net/showthread.php?t=33230


          Regards,

          Brian
          There are only 10 types of people in the world: Those who understand binary and those who don't.

          Comment


          • #6
            I just got a Lathemaster 9x30 that has similar markings. I was also wondering at the diagonal line versus the 1-8. I just figured it was one more thing that is obvious to someone who has been around lathes before.
            I have much to learn to even make simple parts.
            Thanks for asking the question.
            Great pic by the way.

            Comment


            • #7
              Originally posted by Rif
              Hello,

              I asked something similar a while ago and I don't have a plate like that on my machine. Below is a link to thread that I started. There are some complete explanations of the use of a threading dial.

              http://bbs.homeshopmachinist.net/showthread.php?t=33230


              Regards,

              Brian
              AHA!
              I read that thread before I had my lathe so I really had no frame of reference. Now reading back over it I THINK that the 1-8 means I can engage on any line. The diagonal line means that I can engage anywhere without even using the dial.
              Maybe

              Comment


              • #8
                Originally posted by Berniep
                AHA!
                I read that thread before I had my lathe so I really had no frame of reference. Now reading back over it I THINK that the 1-8 means I can engage on any line. The diagonal line means that I can engage anywhere without even using the dial.
                Maybe
                How does that work? How can you engage anywhere without using a dial? If you notice in my picture, that would mean I could cut more than several different threads without using the dial. If that's correct then that would be sweet!

                I didn't completely answer the first question. The lathe is a PM1236. I do not know the TPI on the lead screw. I am not currently at home so I will try to find that out this evening.

                Harold
                Last edited by hwingo; 03-26-2009, 01:10 PM.
                For those having fought for it, Freedom has a flavor the protected will never know.
                Freedom is only one generation away from extinction.

                Comment


                • #9
                  Originally posted by hwingo
                  How does that work? How can you engage anywhere without using a dial?
                  If those threads are multiples of the lead screw pitch, then it would be impossible to make a mistake in engagement (assuming you fully engage the half nuts). You could engage between lines on the dial and you'd still get the correct thread. That is as opposed to the threads marked 1-8, which would have to be engaged on the line.
                  Stuart de Haro

                  Comment


                  • #10
                    Originally posted by hornluv
                    What type of lathe is it? What TPI is on the lead screw? I would be tempted to say that you can engage those threads at any line, numbered or not, because they are probably multiples of the lead screw pitch. Test it out by engaging the half nuts on a line and making a fine cut. Then back the tool off and make some more passes at different lines without the tool against the work. You should be able to tell pretty quickly if it is following the thread or not.
                    The lead screw has a TPI of 8. Hope this helps.

                    Harold
                    For those having fought for it, Freedom has a flavor the protected will never know.
                    Freedom is only one generation away from extinction.

                    Comment


                    • #11
                      More later

                      Harold.

                      I have the answers for you - I think.

                      I would appreciate a pic of your threading dial as well as a count of the number of teeth on the thread-dial "gear" that engages the lead-screw.

                      My guess is that the chaser-dial is divided into 8 parts - or 4 large and 4 "half" parts and that the chaser gear has 16 teeth.

                      I'd also guess that the lathe saddle will traverse 2" on the lathe bed for each revolution of the threading dial (when engaged with the lead-screw).

                      As regards your pic:


                      The "slash" diagonal line means that you can engage at any point on the dial.

                      "16" is the number of the teeth in the chaser gear that needs to be engaged with the lead-screw.

                      "0" means that no/zero teeth are required - just disengage the chaser gear as it is performing no useful purpose - or just leave it engaged and ignore it.

                      Don't worry - this will just "come out of the blue" as a "Light-bulb moment" (aka - colloquially - as a "head-banging" or "Oh $hit yeah" moment - we all have them).

                      Don't feel bad about it as you may be surprised at just how many people do not understand the reason and logic behind "thread-dialing" - but its all that simple that many cannot accept that it is so easy.

                      I will come back to this when I have the pics and info from you.

                      Comment


                      • #12
                        Thread dials come in two flavors............ "2 inch" and "4 inch". The dials typically have half the lines numbered, and half plain.

                        With an 8 tpi screw, a 2 inch will have 16 teeth, a 4 inch 32. Inches is related to how many inches travel is equal to one turn of the dial

                        There are usually 8 lines for a 4 inch dial. so each line is a half inch.

                        On a 2 inch dial, there are usually 4 lines

                        The usual deal is for the 4 turn, that on even threads, any line can be used. because any even number repeats on the half inch (or sooner, but that doesn't matter).

                        For odd threads, they repeat on the inch, so you use only the numbered lines.

                        For half threads (4 1/2 tpi, etc), they take 2 inches to repeat, so you can close on any even number.

                        For quarter threads, they repeat in 4 inches, so you always use the same number.

                        Those folks seem to have numbered ALL the lines, so they need a fancy table to instruct you. better they had left every other one blank.

                        Since they want you to use 8 (same number) for every half thread, presumably the gear has 16 teeth.....

                        Usually, with 4 lines, even: any line, odd: numbered lines, half: same number. But they don't follow that quite, and they have more lines than is typical, or really needed.

                        if the teeth is 32, then you should be able to follow the above, but changing it....... It would then be even, any number. Odd, even numbers. halfs, 4 or 8, and quarters, 8 only.

                        if the tooth count is 16, seems it should be evens: even numbers, odds: 4/8, halfs: 8 only.

                        Dunno about theirs.... it doesn't seem to quite add up. They have odd AND evens 4/8 , but SOME evens with any even number. I'd need to do some calculation to understand what their issue is, and I don't feel like it!
                        Last edited by J Tiers; 03-26-2009, 11:55 PM.
                        1601

                        Keep eye on ball.
                        Hashim Khan

                        Comment


                        • #13
                          Good Evening Tiffie,

                          Attached is an image per your request. Tooth count is 16 and as close as I can figure, the lead screw is 8 TPI. If helpful, the dial diameter is 1.250".

                          Harold


                          For those having fought for it, Freedom has a flavor the protected will never know.
                          Freedom is only one generation away from extinction.

                          Comment


                          • #14
                            Here it is

                            OK - thanks Harold.

                            One of the problems with this sort of thread or stuff is that the "teller" (me?) in communicating with the "tellee" (you?) is that the teller gets bogged down in telling the tellee what the teller knows - or thinks he knows - and while he (teller) may have the best of intention, the "message" misses the intended mark (helping the tellee) get the information he needs in a form in which the tellee can use it.

                            Its a lot like authors who write almost for themselves or their peers (or those that they like to have the tellee regarded as a peer) - and the reader is almost disregarded or ignored.

                            I will try to avoid that situation but in the event that it happens - please do let me know in such a way that I "get the message" and in turn make sure you (tellee) gets the message from me to your satisfaction.

                            In short - just tell me to get back on track - or more to the point - to stop *ucking (you?) around.

                            OK - so here we go.

                            The aim is to get the half-nuts engaged (ie to "drop in") such that the point of the screwing tool is aligned to the thread that was cut previously (this refers to the second and subsequent "cuts" of the thread).

                            This is done by using the threading dial. Your threading dial has 16 teeth and they should be engaged with the lathe lead-screw. There are 8 major divisions on your threading dial of which 4 are "major" and numbered (1, 3, 5 and 7) with "half" or "minor" divisions (not numbered).


                            So, if the lead-screw is stopped (ie stop the lathe spindle), the half-nuts disengaged and the carriage moved along the lathe bed (to or away from the head-stock or tail-stock) the threading gear and the dial (which is attached to it) will move 1 tooth for each successive thread. As there are 16 "gear teeth", each engaging a thread, it follows that one rotation of the gear and the dial to which it is connected will be equal to 16 threads on the lead-screw.

                            Those 16 threads at 1/8" pitch equal 16 x 1/8" = 2" travel of the carriage relative to the lead-screw and the lathe bed.

                            Or put another way, each of the 8 marked divisions on the threading dial will equal 2 turns or pitches of the lead-screw = 2 x 1/8" = 1/4"

                            4 turns of the lead-screw will equal 1/4 of the 16 teeth on the gear and so will rotate the threading dial 1/4 of a turn and will equal 4 x 1/8" pitch = 1/2" travel of the carriage.

                            8 turns of the lead-screw will equal 1/2 of the 16 teeth on the gear and so will rotate the threading dial 1/2 of a turn and will equal 8 x 1/8" pitch = 1" travel of the carriage.

                            16 turns of the lead-screw will equal all of the 16 teeth on the gear and so will rotate the threading dial 1 turn and will equal 16 x 1/8" pitch = 2" travel of the carriage.

                            Provided the chasing dial gear remains in mesh with the lead-screw, the relationship between the positions of the lead-screw and the position of the carriage will not alter - whether the lathe spindle and the lead-screw are rotating or not.

                            The requirement is to get the first cut of the thread done by starting the lathe spindle - bottom or lowest speed - which in turn will drive the lead-screw. If the threading dial gear is engaged with the lead-screw, and the half-nuts are NOT (yet) engaged, you will see the threading dial rotating.

                            Now, wait for the threading dial to come to the index mark at "1" (which we will use as a start point), engage the half-nuts. When this happens, the threading dial will stop rotating as there is now no relative movement between the lead-screw and the carriage but the carriage will now be driven along the lathe bed toward the head-stock by the engaged half-nuts which are in turn being "pushed along" by the rotating lead-screw.

                            When the carriage gets nearer the head-stock, disengage the half-nuts and the carriage will stop moving even though the lathe spindle and lead-screw keep rotating. Also, as soon as the half-nuts are disengaged, the threading dial will re-commence rotating as well.

                            The half-nuts will only engage with the lead-screw when they are in line with the "groove" of the thread on the lead-screw - that is to say, every 1/8" - which is the pitch of the lead-screw.

                            The next requirement is to keep successive cuts also in line with the previous cuts. That requires that the pitch of the thread being cut must be a multiple of the pitch of the lead-screw at the point at which the half-nuts are engaged.

                            So, if you were cutting 8 threads per inch (tpi) the lead-screw and the work pitches are identical and so the half-nuts can be engaged anytime the "groove" in the lead-screw is opposite the mating parts of the half-nuts - in short anywhere at all.

                            There are full threads of even numbers of work tpi at every 1/2" - ie 2, 4, 6, 8, 10, 12, 14, 15, 18, 20 ..... 30, 32, 34, 36 ........... 40 .... 48 .... 64 etc. (1/4 turn of) the threading dial, so any even number of threads per inch will align with the lead-screw at every 4/16 = 1/4 turn of the threading dial.

                            There are full threads of odd numbers of work tpi at every 1" - ie 1, 3, 5, 7, 9, 11, 13, 15 ...... etc. (half a turn of) the threading dial, so any odd number of threads per inch will align with the lead-screw at every 8/16 = 1/2 turn of the threading dial.

                            There are full threads of "half" numbers of work tpi at every 2" - ie 1 1/2, 1 1/2, 3 1/2, 5 1/2 ...... etc. (a full turn of) the threading dial, so any "1/2" number of threads per inch will align with the lead-screw at every 16/16 = 1 turn of the threading dial.

                            There are full threads of "1/4" numbers of work tpi at every 4" - ie 1 1/4, 1 1/4, 3 1/4, 5 1/4 ...... etc. (2 full turns of) the threading dial, so any "1/4" number of threads per inch will align with the lead-screw at every 32/16 = 2 turns of the threading dial and is thus out of scope/range of your threading dial. You will need to keep your half-nuts engaged for the entire screw-cutting job.

                            I suggest that you get a selection of bolts or screws of varying pitched or threads per inch (tpi), put them in your lathe, set your quick-change gear-box tosuit the number of threads, put a screwing (or any pointed) tool in your tool-post, set the threading dial to "1", engage the half-nuts, rotate the lathe spindle by hand - slowly - and watch the carriage move along the lathe bed. Stop and align the pointed tool to be in line with the bolt/screw thread groove, but not touching (use the top/compound slide). Now start pulling the spindle over by hand and watch the pointed tool to see if it stays in line with the thread groove.

                            Now try it out with other thread pitches and use the threading dial to tell you when/where to engage the half-nuts.

                            It will take a bit of time, concentration and effort - as well as some frustration - but it WILL "come" and it will be so satisfying that you will be so pleased that you have "got it" that the reward and satisfaction will be well worth the effort.

                            I hope this helps - but come back if you need more help.



                            Comment


                            • #15
                              There is an obvious solution to all of this confusion. Its called a Single Tooth Dog Clutch Reversing Lead Screw. Eliminates the need for the Chasing Dial all together and the reverse tumbler gear in the leadscrew gear train. Or simply engage on the same number all the time.
                              Forty plus years and I still have ten toes, ten fingers and both eyes. I must be doing something right.

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