Thread Cutting on WW Lathe

Discussion in 'Horological Tools' started by Neuron, May 30, 2011.

  1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.
  1. Neuron

    Neuron Registered User

    Nov 4, 2010
    557
    2
    0
    Neurologist
    SF East Bay
    Country Flag:
    Region Flag:
    On EBay there was a recent auction for a thread cutting accessory for use on Levin lathes (open headstock design) which presumably could be modified to work with an ww style lathe. The gadget consists of a gear holding plate that attaches to the HS end of the bed and a bushing gear that attaches to the rear of the HS spindle and engages the gear train of the gear plate (this is the equivalent of the gear box of a regular machinist's lathe). So far so good, But instead of using a lead screw or "thread chaser" along the bed, this gear train apparently connects via a shaft to a nubbin protruding from the top slide of the slide rest.

    My question is, how does this shaft advance the slide rest along the bed? Does the "nubbin" connect to and turn the slide rest lead screw? Do you use the motor to spin the HS spindle when cutting threads, or do you use a hand crank attached to the spindle? Does anyone know where information on the use od this sort of ww threading attachmnt can be found?

    BTW, I bid on the auction, but it ended without the "reserve" being met, said reserve being more than $900! :eek:

    Nick
     
  2. wefalck

    wefalck Registered User

    Mar 29, 2011
    494
    34
    28
    Male
    Geochemist (Consultant)
    Paris
    Country Flag:
    Somewhere I have pictures of the Levin threadcutting-attachment ... anyway, it bolts to the end of the bed and connects to the topslide-screw via a splined shaft.

    I had and used for many years a similar antique Lorch, Schmidt & Co. No. 7 lathe with the (very rare) threadcutting-attachment: http://www.wefalck.eu/mm/tools/ww/wwlathe.html

    273.jpg

    Compared to the ordinary WW-crossslides, the topslide-screw extends about 1 cm beyond the topslide-ways, allowing the dog-clutch to be secured on it with a couple of set-screws (not an ideal arrangement).

    274.jpg

    There is only one banjo-arm, but a reversing arrangement.

    275.jpg

    With a couple of additional, custom-made, changewheels I can cut threads with 0,05 to 6,50 mm pitch or 10 to 100 tpi.
    In theory one can cut threads under power, but for all but the slightest cuts (0,05 mm) the torque transmitted by the usual round belts on watchmakers lathes is too low. So I fitted a ball-handle crank to the drawtube. I is secured with a tapered pin.

    276.jpg

    The dog-clutch in conjunction with a throw-out bar allows to cut threads under power. The bar was missing from my equipment and I rebuild it after the rather blurred images available. However, I only use power for the last smoothing cut.
    In the past many precision bench lathe manufacturers offered such threadcutting-attachments for their lathes: http://www.lathes.co.uk
    NB Levin equipment seems to attract always high prices and the reserve you mentioned is quite in line with what I saw in the past for such attachments.

    wefalck
     
  3. Neuron

    Neuron Registered User

    Nov 4, 2010
    557
    2
    0
    Neurologist
    SF East Bay
    Country Flag:
    Region Flag:
    Thanks wefalck!

    That Lorch jig seem to work just like the Levin in the auction. I've got two Levin lathes, one with the BB HS and one with the cone-bearing B HS, along with the Levin triple slide rest, whose "nubbin" is in reality an extension of the top slide lead screw. When the threading jig's shaft is connected to it, the shaft makes the top slide advance to cut the threads on the workpiece. This is a very different system from the thread chasing lead screw used on most machinist lathes and some ww lathes.

    Since it often takes multiple passes to fully cut threads, I wondered how this would be achieved with this system. When I cut threads on my "regular" lathe I use the dial on the lead screw to diengage and engage
    the slide advance (stopping and restarting at 3, 6, 9, or 12 on the dial). Since no such dial is used on these types of thread cutting jigs, I assume that you just back off the tool fom the work, leave the gearing engaged, and reverse the slide to the starting point, advance the tool closer to the workpiece and cut again. Since the geaing has nevr been "disengaged" you should still be in register for the subsequent deeper thread cuts.

    I think I understand the process now. I can also apreciate how driving the spindle with a hand crank could work better than advancing under motor power.

    I can't undertand why these jigs should command such high prices...

    Thusfar I've been able to make do with a small but good set of watchmaker taps and dies, but I'd like to be able to cut threads on my ww style lathes.:mad:
     
  4. StephanG

    StephanG Registered User

    Jun 24, 2007
    916
    1
    16
    Australia
    Country Flag:
    The dial you describe is the " Chasing " dial.
    The numbers are not so important as it is a position indicator.
    The places you can engage for a particular job depend on the relationship between the threads per inch of the lead screw compared to the threads per inch you are cutting.
    I don't remember exactly how it works but to keep things simple I usually use the same spot for each cut.
    If you are cutting metric threads on an imperial lathe or the other way around then you can not disengage the half nuts or you loose the relationship.
    I have seen those attachments and did wonder at the cost.
    Would be usefull for cutting tapered threads but at those prices I think I would be having a go at making my own.
     
  5. Smudgy

    Smudgy Registered User

    May 20, 2003
    2,845
    18
    38
    Country Flag:
    Region Flag:
    I have a Marshall with a thread cutting attachment. It has a back gear setup built into the headstock, so it can thread under power. You can't disengage and reset these. What you need to do is stop the machine, back the cutter out, then reverse the motor to get back to the beginning of the cut. Run the lathe forward (by hand or under power) to remove lash before re-engaging the cutter. Short threads are easy to do by hand. The longer ones I use power until close to the end, then finish by hand.
     
  6. wefalck

    wefalck Registered User

    Mar 29, 2011
    494
    34
    28
    Male
    Geochemist (Consultant)
    Paris
    Country Flag:
    Exactly. The whole process is a bit of a pain, actually. Forward hand-cranking is ok, but running the slide back under power would be nice. However, loosening the belt after each cut is equally tedious.

    In this way one is also cutting the thread in full depth, which puts a lot of strain on the machine for coarser threads. I got a Wolf, Jahn & Co. three-slide slide-rest, which I plan to adapt for threadcutting. In this way one can set the third slide a slight angle so that the tool is not fed-in perpendicular to the workpiece axis. This means that the tool is essentially cutting on one flank only, which requires less power and puts less strain on the machine.

    On standard threads I normally cut just above the required size and take off the rest with a die. The die acts as gauge and ensures that the thread is shaped correctly, even if I did not grind the tool perfectly.

    The biggest part machined today was the replacement worm for the table drive of my Wolf, Jahn & Co. horological miller (http://www.wefalck.eu/mm/tools/wja/wjamiller.html)

    299.jpg

    The picture also shows the knock-out bar in action.

    wefalck
     
  7. StephanG

    StephanG Registered User

    Jun 24, 2007
    916
    1
    16
    Australia
    Country Flag:
    Nice job on the worm. Your idea of feeding the tool in at an angle is a good one and oft used in the trade.
    You usually use an angle that matches the angle of the thread you are cutting.
     
  8. Neuron

    Neuron Registered User

    Nov 4, 2010
    557
    2
    0
    Neurologist
    SF East Bay
    Country Flag:
    Region Flag:
    StephanG,

    Thanks for your comments re the thread chasing dial, which I've used for threading screws on my regular machine lathe, which employs a gear driven lead screw and what is called a "half nut" that you can engage and disengage at will. The dial is divided into 12ths on my lathe (and most others). The purpose of this dial is to allow the machinist to disengage and re-engage the half nut so that succesive passes of the cutting tool allow threads to be cut in register.

    The Levin tool I have been describing doesn't use this half-nut to engage/disengage/re-engage the slide advance screw. Instead, the slide advance screw is constantly engaged, so that after th first pass you need to reverse the spindle to bring the slide/tool back to the beginning and then reverse spindle rotation to take a deeper cut after bringing the tool closer to the centerline of the workpiece.

    I now understand this, though I wasn't clear on the concept earlier.:)

    Nick
     
  9. Thomas Hammond

    Thomas Hammond Registered User
    NAWCC Member

    Apr 17, 2010
    37
    5
    8
    Some may not be aware that the Levin & Levin book "Practical Benchwork for Horologists" contains plans and instructions for making and using a thread-cutting attachment to fit typical WW or 10 mm lathes. In the 8th (final?) edition, the plans are on pages 72 to 79.
     
  10. wefalck

    wefalck Registered User

    Mar 29, 2011
    494
    34
    28
    Male
    Geochemist (Consultant)
    Paris
    Country Flag:
    True. A very good description.

    wefalck
     
  11. juanca

    juanca New Member

    May 12, 2019
    3
    0
    1
    Male
    Country Flag:
    ha tengo un trono paresido con el tren de enranajes pero me faltan los enranajes me puede desir las medidas i paso que usa

    himajenes del movil 130.jpg IMG-20190418-WA0003.jpg
     
  12. juanca

    juanca New Member

    May 12, 2019
    3
    0
    1
    Male
    Country Flag:
    [QUOTE = "juanca, post: 1284330, miembro: 89394"] no tengo un trono en el mismo momento, sino que me faltan los enranajes.

    View attachment 535190
     
  13. wefalck

    wefalck Registered User

    Mar 29, 2011
    494
    34
    28
    Male
    Geochemist (Consultant)
    Paris
    Country Flag:
    You will have to determine the module of your existing gears. Then you may be able to find a supplier that has spur gears that can be adapted to your set-up.

    Tendrá que determinar el módulo de sus engranajes existentes. Entonces podrá encontrar un proveedor que tenga engranajes rectos que se puedan adaptar a su configuración.
     
  14. motormaker

    motormaker Registered User

    Apr 5, 2010
    101
    11
    18
    Tucson, AZ
  15. motormaker

    motormaker Registered User

    Apr 5, 2010
    101
    11
    18
    Tucson, AZ
    Here is the final setup on my thread cutting attachment. It works beautifully if you set the approach angle to be 30 degrees. The sliding "U" joint is now installed in these photos. One photo shows cutting a tool steel tap and one threading brass.

    20190106_182311-picsay.jpg 20190106_182349-picsay.jpg 20190106_184805-picsay.jpg 20181209_132339-picsay.jpg
     
  16. motormaker

    motormaker Registered User

    Apr 5, 2010
    101
    11
    18
    Tucson, AZ
    Here are a few examples of threading. The first pic is 3/8" diameter brass bar stock. The second is 1/8" O-1 and 1/8" brass rod both with 30 threads per centimeter (approximately 80 tpi). The steel will become a tap for the threaded brass screws. The third pic is additional 80 tpi examples.

    20181205_180750-picsay.jpg 20190610_235951threading.jpg 20190610_235927threading.jpg
     
  17. wefalck

    wefalck Registered User

    Mar 29, 2011
    494
    34
    28
    Male
    Geochemist (Consultant)
    Paris
    Country Flag:
    How did you connect the universal joint to the top-slide spindle ? On my Lorch, Schmidt & Co. lathe the cross-slide has an extra-long cross-slide spindle, so that that the joint can be attached with a grub-screw, but normally the spindle does not protrude beyond the slide. I don't linke the grub-screw arrangement, but that is how it was done then.
     
  18. motormaker

    motormaker Registered User

    Apr 5, 2010
    101
    11
    18
    Tucson, AZ
    The three way cross slide I used on my Levin is a Marshall brand and has an extended tip on the slide threaded shaft. Several brands were made with this extension. If your three way (necessary) slide does not have this extra long tip, you can disassemble the slide and silver solder on a short extension. The "U" joint connects with a very small set screw. One of these days I will replace this with a larger screw for quick release so I can use the lathe as a lathe more quickly.
     
  19. wefalck

    wefalck Registered User

    Mar 29, 2011
    494
    34
    28
    Male
    Geochemist (Consultant)
    Paris
    Country Flag:
    Traditionally, the WW thread-cutting lathes were sold only with a two-way cross-slide. In fact, Lorch, Schmidt & Co. never made a three-way slide. A three-way slide has advantages, of course, but is not an absolute necessity. I have got a Wolf, Jahn & Co. three-way slide on which I will adapt the longitudinal spindle one day for screw-cutting ...
     
  20. motormaker

    motormaker Registered User

    Apr 5, 2010
    101
    11
    18
    Tucson, AZ
    As one who has tried thread cutting both with a 2 and 3 way slide, I am telling you that the 3 way is by far the better setup. By cutting only one side of the thread, you can avoid deflecting the metal being threaded and can cut threads without requiring tailstock support. Metals cut so smoothly when doing the job with a 3 way slide.
     
  21. juanca

    juanca New Member

    May 12, 2019
    3
    0
    1
    Male
    Country Flag:
  22. kevin h

    kevin h Registered User

    Apr 9, 2015
    408
    151
    43
    Male
    cambridge md
    Country Flag:
    I really think a good set of tap&dies may be cheaper and more effective , I can understand using a lathe if you are doing production work , but that is rarely the case in watchmaking
     
  23. motormaker

    motormaker Registered User

    Apr 5, 2010
    101
    11
    18
    Tucson, AZ
    For one offs to replace oddball screws I prefer one of my many screw plates. For my uses (production work on custom spring powered motors) I prefer the lathe setup. Taps and dies are cheaper but I can make virtually any size that I might want with the lathe - including matching taps. For the custom building that I do, the power and freedom to make any size of specialty threaded parts is very desirable.
     
    kevin h likes this.

Share This Page