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  • #46
    Originally posted by mardtrp
    You DO NOT have to set the compound slide to that stupid angle AT ALL.

    Now some on this forum will say that you do, I'll say Bu!!$#it to that stupid totally outdated theory, so will lots of others, who don't use that outdated confusing stupid crud.
    There's another thread running here where going ballistic is more appropriate .

    It comes down to choice - either way you have to turn a crank to get the job done. Doesn't matter to me which crank it is.

    Comment


    • #47
      I have tried all ways to thread, by the book, not by the book and winging it.
      I don't think there is a right and wrong to thread but more a way that works for you.
      What you have to remember though is nothing is new in engineering except materials and electronics.
      What was written in textbooks years ago is still repeated parrot fashion today.

      As an apprentice you were taught one way, usually from the same 3 or 4 set textbooks and whoa betide anyone who decided to try any other method. As most set exercises were markable exercises you HAD to stick to the book to pass and there was no time to try other methods.

      The only way to find out is to try other methods, in the homeshop / self employed situation NOTHING is written in stone.

      I must admit it does make sense to set the top slide over when doing course threads to reduce the cutting forces.

      I make a lot of short worm with an 8tpi thread left hand on them.
      I use a carbide tip ground to the correct Acme profile and swing to top slide over to 14 degrees, just less than half the 29 degrees Acme angle from the perpendicular. Been doing these for years and it get a beautiful finish on the flanks due to the material, high tensile, and pure cutting oil.

      It was only recently I realised that because these worms were left handed I was feeding on the trailing flank and not the leading flank.
      A big no no in terms of text book screwcutting but again something that has worked for me.

      I have had another idea today to improve / alternate design / knacker up the swing threading tool but I'd not like to comment on this until I do some more testing. After rushing out to Wilko's at 10 minutes to 6 on Christmas eve to get Gert chrissy box and spending £4.25 in the process I reckon I can get me passport stamped and shoot into the workshop tomorrow, watch this space !!

      .
      .

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



      Comment


      • #48
        Originally posted by mardtrp
        You DO NOT have to set the compound slide to that stupid angle AT ALL.

        Now some on this forum will say that you do, I'll say Bu!!$#it to that stupid totally outdated theory, so will lots of others, who don't use that outdated confusing stupid crud.

        If you just use the infeed to add to the cut, it works, and exceptionally well.
        You just watched a video made by somebody who actually "does it for a living" and did you see him stuffin' around setting a compound slide to some stupid angle, no you don't, so it does work.

        Now I got to ask the 'naysayers', how does a CNC do the thread cutting, well it just plunges straight in, none of this set over crud.

        Don't believe that it will work for you when your threading, well go right ahead and try it, you'll wonder why you have never used it previously, and now you wont get all confused and bugger it up any more.

        Mark
        Oh dear!

        Comment


        • #49
          John, I too experiment to hell and back and found what I sure as hell don't want to do again and what will work most the time. I have to agree that what may not work for me does for someone else and that's why I always try to present the other side of the argument.

          I have had some OMG incidents while threading and have learned to be very careful and plunge threading above a certain pitch was one of them. BUT, if someone can get a real good looking thread plunging a 10 tpi or coarser then go for it but I can't.

          As to a CNC cutting a thread, the program advances the tool to only cut on the leading side of the thread as far as I understand it as I have been told. It don't care how it does it because I don't use a CNC.
          It's only ink and paper

          Comment


          • #50
            Carl,

            I don't advocate one way over another, I much prefer to suggest that people find what suits them best.

            Just because I can do this on a decent sized rigid lathe doesn't mean that a newcomer can do it on a 7 x 12 lathe. It depends on many variables.

            Most CNC lathes I have come across have variables where the infeed angle can be altered for different threads, no good having a 29 degree angle written in stone if you are cutting a 55 thread or an acme.
            It can also be canceled if needed for plunge cutting.

            .
            .

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



            Comment


            • #51
              Originally posted by Carld
              BUT, if someone can get a real good looking thread plunging a 10 tpi or coarser then go for it but I can't.
              On reflection I should qualify what I said in my earlier post with the fact that I never cut any threads above 1.5mm pitch, coarser pitches do not occur in my normal work. The only "large" coarse threads I have ever cut were done on a big DSG or Holbrook over 20 years ago & I have no memory of what techniques I used.
              I certainly take your point about the excessive tool load when attempting plunge feeding such a heavy cut.

              regards

              Brian

              Comment


              • #52
                Peter,

                Mmm, knurling; now that I think about it, maybe I should set the compound slide over to the angle of the flanks of the knurling wheel, and infeed it that way.

                Once I've calculated the right diameter of the work to be a whole number of knurled teeth, that is...

                (Running for cover)

                Ian
                All of the gear, no idea...

                Comment


                • #53
                  Originally posted by pistonskirt
                  On reflection I should qualify what I said in my earlier post with the fact that I never cut any threads above 1.5mm pitch, coarser pitches do not occur in my normal work. The only "large" coarse threads I have ever cut were done on a big DSG or Holbrook over 20 years ago & I have no memory of what techniques I used.
                  I certainly take your point about the excessive tool load when attempting plunge feeding such a heavy cut.

                  regards

                  Brian
                  I usually have the compound parallel with the lathe axis, and when cutting large threads may put a shift of a few thou on the compound between cuts. Rough & ready and 'seat of the pants' so there's always the risk of making a b*lls of the job but it does make for an easier cut and yet allows simple control of cutting depth via DRO or cross feed dial.
                  It wouldn't be too hard to draw up a scale for axis feed vs cross feed to get whatever your chosen infeed angle might be.

                  Tim

                  Comment


                  • #54
                    Originally posted by Ian B
                    Peter,

                    Mmm, knurling; now that I think about it, maybe I should set the compound slide over to the angle of the flanks of the knurling wheel, and infeed it that way.

                    Once I've calculated the right diameter of the work to be a whole number of knurled teeth, that is...

                    (Running for cover)

                    Ian
                    How about a swing knurling tool so you can go back for a second cut without loosing pitch ? ?

                    .
                    .

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



                    Comment


                    • #55
                      Originally posted by Timleech
                      I usually have the compound parallel with the lathe axis, and when cutting large threads may put a shift of a few thou on the compound between cuts. Rough & ready and 'seat of the pants' so there's always the risk of making a b*lls of the job but it does make for an easier cut and yet allows simple control of cutting depth via DRO or cross feed dial.
                      It wouldn't be too hard to draw up a scale for axis feed vs cross feed to get whatever your chosen infeed angle might be.

                      Tim
                      Which would indeed seem to achieve a similar cutting flank bias as with the half included angle compound feed method, as you say it just requires care not to advance the compound too far.

                      On every other lathe I have owned or used I would always have the compound "parked" parallel with the bed axis, however my present "daily use" lathe is an S&B 1024VSL on which the compound slide assembly is so long that one would be forever clouting the tailstock drill chuck with it, so it usualy sits at 45 degrees for whipping on a quick chamfer.

                      regards

                      Brian

                      Comment


                      • #56
                        My compound just lives a 29° for 60° threading so it is out of the way of the tailstock or the crossfeed handwheel. Makes threading a non-event, as all I do is set the gearbox for the proper pitch and drop the threading tool onto the QCTP. The compound has a gib lock, which stays locked for turning and facing for rigidity reasons, and unlocked for threading.

                        Tim's method is interresting, but complicates the issue as it's basically the same as setting the compound to 29°, but adds to the confusion with the need for a chart or guess work to end up with the correct thread form.

                        Threading is not as difficult as some seem to make it out to be!

                        Threading, parting, knurling, and using a DTI seem to be huge stumbling blocks for home shops. Just takes a little practice, that's all!

                        Comment


                        • #57
                          My compound stays "parked" in the 2nd drawer down in the lathe stand.

                          Makes my little lathe think it's much bigger. Way less chatter, takes (relatively) huge cuts and there's no comparison in the parting off performance.

                          It only comes out t'drawer when absolutely necessary for tapers or threads.

                          OK, now back to our regularly scheduled thread content.
                          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


                          • #58
                            Originally posted by Glenn Wegman
                            My compound just lives a 29° for 60° threading so it is out of the way of the tailstock or the crossfeed handwheel. Makes threading a non-event, as all I do is set the gearbox for the proper pitch and drop the threading tool onto the QCTP. The compound has a gib lock, which stays locked for turning and facing for rigidity reasons, and unlocked for threading.

                            Tim's method is interresting, but complicates the issue as it's basically the same as setting the compound to 29°, but adds to the confusion with the need for a chart or guess work to end up with the correct thread form.

                            Threading is not as difficult as some seem to make it out to be!

                            Threading, parting, knurling, and using a DTI seem to be huge stumbling blocks for home shops. Just takes a little practice, that's all!
                            It makes no difference to the thread form, unless you c*ck it up, because the last couple of cuts will just be shavings with direct infeed (they will be if I do it, anyway!), the thread form is determined my the tool form.

                            Tim

                            Comment


                            • #59
                              Tim,

                              Agreed, but the possibility exists of cutting too wide in relation to the depth with the compound for someone just learning or that struggles with thread cutting already.

                              The point is, if you are going to use the compound, why not just use 29°? Makes it easier to keep track of thread depth withut having to guess.

                              I always sharpen up the tool and plunge the last .001" or .002" as well to clean up the threads. Makes a nice finish.
                              Last edited by Glenn Wegman; 12-26-2009, 09:53 AM.

                              Comment


                              • #60
                                That's the problem with most lathes and the main reason why I decided to store the topslide on the small TOS until needed and instead opt for rigidity in the shape of a big packing block with a cutaway made to miss the tailstock.



                                In it's lifetime it has probably been fitted about 10 times for the odd taper. Chamfering is done by a ground tool in one of the QCTP holders which is ground to do both internal and external chamfers at the same setting, handy for the quick deburr.



                                Looking at this picture makes me realise I need to start looking for a new tool, not muck life left in this old girl but it has been in use for about 20 years .

                                .
                                .

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



                                Comment

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