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  • Question about attached Threading Chart

    Hey guys,

    I have a question which I am certain that someone can answer. Take a look at the below image. This is an image of the chart on a lathe which tells what numbers to pick on the chasing dial when threading. On the far left side is the column " T ". Also the " T " is a middle column. Under the " T " is the number 16. What does the " T " represent (what is this saying to me) and what is the significance of the number 16 in both columns?

    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
    that number refers to the "threads" (thread pitch of the lead screw on the machine) meaning that the turning screw that the half nuts lock onto has 16 threads per inch. then you can close the half-nuts on the numbers shown for the particular thread you are cutting. i am not sure what the upper blocks with the zeros are unless that particular machine will not cut those threads.
    a little more particulars on the machine might let us discover more specifically.

    Comment


    • #3
      I think its for the threading dial indicator.

      Some of the sino lathes have a gear train in the threading dial indicator.

      So the basic range is the 0 setting ,and if you add the 16T gear to the train , you get the extra scaling factor.

      Rob

      Comment


      • #4
        The part at the top tells you that you can engage the half-nuts at any mark on the chasing dial (scale) for those threads-per-inch. Some marks might not be numbered on some lathes.

        The part at the bottom tells you you can only engage the half-nuts at those specific numbers on the chasing dial for those threads-per-inch. You can't engage at the marks not numbered.

        For example: You can engage at any number for 40 TPI, but only at 2, 4, 6, and 8 for 10 TPI.

        I'm not sure about the 1-8, though. I'd guess it means any numbered mark, but not the ones not numbered.

        It would be easy enough to check this out with a piece of scrap round bar. You only need to go deep enough to see if the path of the tool is correct on passes with different points of engagement on the chasing dial.
        Last edited by winchman; 11-23-2013, 09:50 AM.
        Any products mentioned in my posts have been endorsed by their manufacturer.

        Comment


        • #5
          I suspect the dial IS numbered 1-8, and there are NO non-numbered marks.

          But it isn't totally standard, because some even tpi show only some good numbers. Usually, ALL even numbers can use any mark, odd numbers just numbered marks, half threads just odd numbered marks, and quarter threads (if supported) must use same mark.

          if you numbered the dial 1-8 instead of having 1-4 and 4 non-numbered marks, "odd" numbers could be the same as standard "non-numbered", then you would have 2,4,6,8 left similar to "1,2,3,4" on standard dial. Then "4" and "8" would be like the standard "even" numbers, and "2" or,"6" would be like standard "odd" numbers.

          I'm not sure this totally corresponds to that. Some even numbers take any mark, others a subset. And 5, 6, 7, 9, 11, 13, 15 can take either the 4 or 8 marks.

          10tpi , an even number, can take only 2,4,6,8, but 12tpi, also even, can take any mark. But if there were say 6 tpi on leadscrew, then 6 and 12 would be similar. And the multiples of 8 would not be "close anywhere" numbers as shown at top.

          It seems that either there are some mistakes on the table, OR the person making it up didn't quite "get it" and limited the choices more than required, OR that there is something else going on that I have not spotted yet.
          Last edited by J Tiers; 11-23-2013, 10:08 AM.
          CNC machines only go through the motions.

          Ideas expressed may be mine, or from anyone else in the universe.
          Not responsible for clerical errors. Or those made by lay people either.
          Number formats and units may be chosen at random depending on what day it is.
          I reserve the right to use a number system with any integer base without prior notice.
          Generalizations are understood to be "often" true, but not true in every case.

          Comment


          • #6
            Can you provide some information on the lathe. It likely has an 8TPI leadscrew which accounts for engaging the half nuts at any point for multiples of 8. The 16 probably is the tooth count for the threading indicator gear and scale is the number to engage the half nuts on for the various thread counts.

            If using transposing gears for metric threading, different tooth count gears would be required for different thread pitches.
            Jim H.

            Comment


            • #7
              Originally posted by JCHannum View Post
              Can you provide some information on the lathe. It likely has an 8TPI leadscrew which accounts for engaging the half nuts at any point for multiples of 8. The 16 probably is the tooth count for the threading indicator gear and scale is the number to engage the half nuts on for the various thread counts.

              If using transposing gears for metric threading, different tooth count gears would be required for different thread pitches.
              Yes, I will send more information. I need just a little time to gather the information but it will be sent.

              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


              • #8
                Originally posted by JCHannum View Post
                Can you provide some information on the lathe. It likely has an 8TPI leadscrew which accounts for engaging the half nuts at any point for multiples of 8. The 16 probably is the tooth count for the threading indicator gear and scale is the number to engage the half nuts on for the various thread counts.

                If using transposing gears for metric threading, different tooth count gears would be required for different thread pitches.


                The lathe is a PM1236. The lead screw measures, to the best of my ability, 8TPI. I do believe the chase gear has 16 teeth.

                The chase dial is numbered 1,3,5, and 7. There are lines between the numbers so ostensibly the lines represent 2,4,6,8 respectively.

                I had once received a message that stated the following:

                Lathes differ in how the dial is set up. Many of the machines I have run will read: even threads any line, odd threads any number. Now you can be pretty safe in threading by going back to the SAME spot each time. In fact you can thread without a dial, just leave the half-nuts engaged. At the end of each cut, crank the tool out of the cut and reverse the lathe. Now, re-engage the threads being cut using the cross feed, advance the compound .001” and go forward with the next cut …… and so on.

                Apparently the statement “even threads any line” and “odd threads any number” does not apply with this lathe if you go by the table on the lathe. The numbers 3,5, and 7 are not listed on the chart.

                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


                • #9
                  If you're a member you can get an updated manual here: http://www.hobby-machinist.com/showt...l=1#post110916

                  Comment


                  • #10
                    The usual tooth count for an 8TPI leadscrew is 32. The 16 tooth count on the PM lathe may be the cause for the odd numbering method used on the dial. I can't quite get my head around why exactly.

                    The threads that are designated as 1-8 are multiples of 4, and can engage on any number. I doubt that you can engage the half nuts on a non-number, making the top block unnecessary, those threads could have been included in the main body of the chart.

                    The message you posted is correct for the usual thread dial numbered 1-4 with hash marks in between, but the odd and even numbers are shifted when every position is numbered.
                    Jim H.

                    Comment


                    • #11
                      16 tooth gears work the same as 32 tooth.... because there are the same number of turns per mark.

                      The differences are that:

                      * there are only 4 marks, two of which are numbered.

                      * You can't do 1/4 threads on the dial

                      Otherwise it works the same, multiples of leadscrew can be engaged anywhere, even numbers on any mark, odd numbers on numbers only, and 1/2 threads on the same mark (equal to odd numbered marks).
                      CNC machines only go through the motions.

                      Ideas expressed may be mine, or from anyone else in the universe.
                      Not responsible for clerical errors. Or those made by lay people either.
                      Number formats and units may be chosen at random depending on what day it is.
                      I reserve the right to use a number system with any integer base without prior notice.
                      Generalizations are understood to be "often" true, but not true in every case.

                      Comment


                      • #12
                        The top of the chart, where T=0, indicates that the feed can be engaged at any time without using the thread dial for threads that are whole multiples of 8. The part that shows 4 TPI is an error, as you can split a 4 TPI thread with an 8 TPI leadscrew.

                        The Bottom of the chart, where T=16, is for a 16 tooth gear on the dial. It shows for threads that have 1/2, you must use only 8. This just means you must let the dial go all the way around, you can use any number as long as you always engage on the same one. That is because for 1/2 threads you must go 2" to have a whole number of threads on both the feedscrew and work. You can not split either the work or leadscrew threads.

                        For whole number threads, you only need to go 1" to get whole threads on both the leadscrew and work, so the dial only needs to go half way around. This is shown as 4-8 but you can use any two numbers which are halfway around from each number. The '8' for 19TPI is an error unless the 19TPI is not exact but only approximate, it should be 4-8.

                        For even number threads, you only need 1/2" or 1/4 of the way around the dial. This is shown as 2-4-6-8 but you could use 1-3-5-7 just as well. 4TPI and 6TPI are errors and should be shown as 2-4-6-8.

                        For threads that are divisible by 4, you only need 1/4" or 1/8 of the way around the dial. This is shown as 1-8 and means any numbers can be used. 4TPI should be included here.

                        It is not unusual to find errors in threading and other tables and that can make them hard to understand. This table is unlike some others as some assume '1' as the starting point and this table assumes '8' but it is all just whether you use no dial, all the way around, half way around, 1/4 way around, or 1/8 way around. Of course if you miss the first possible point you can use any later one.
                        Last edited by Don Young; 11-23-2013, 11:44 PM.
                        Don Young

                        Comment


                        • #13
                          Sorry, i can not add to the confusion or help any, but have to comment that... Gezz... you even make an image of a thread chart look good

                          Best of luck... if all else fails, you could always drop Matt (PM owner) an email or call him, im sure he will help you out, hes a good guy.
                          ~ What was once an Opinion, became a Fact, to be later proven Wrong ~
                          http://site.thisisjusthowidoit.com
                          https://www.youtube.com/user/thisisjusthowidoit

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                          • #14
                            Originally posted by iMisspell View Post
                            Sorry, i can not add to the confusion or help any, but have to comment that... Gezz... you even make an image of a thread chart look good ...............
                            Thanks! Regardless of intended subjects, I always try my best to produce acceptable images. I think I do my best with Industrial and Landscape images. A world-celebrated-image-critic recently view several of my Industrial images and remarked, "It difficult to imagine these sorts of images fitting into the ‘artistic’ category, but I think you’ve pretty much managed it"! Needless to say, this coming from a world-acclaimed-critic (in writing) elevated my spirits for the day.

                            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

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