Chuck backing plate issues

Discussion in 'Horological Tools' started by karlmansson, Aug 17, 2019.

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  1. karlmansson

    karlmansson Registered User

    Apr 20, 2013
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    Hello!

    I've just recently completed (more or less) a restoration of an old Swiss Habegger DLZTE lathe and I've made my first cuts on it these last few weeks.

    The man who sold me this lathe a while back mentioned that it was very handy that it shared a spindle nose thread with the Blomqvist lathe that is pretty common around Sweden. The Blomqvist is a Swedish copy of the English Boxford lathe and I've since learned that the man who sold me this lathe was misinformed and although they are quite close to each other, the Blomqvist has a 1,5x8TPI thread (as do all the accessories) and the Habegger has a 38x3mm pitch spindle nose thread. This lathe came with a few Blomqvist accessories.


    One being a face plate and the other being a rather nice, by the looks and feel of it rather high quality, Swedish made 155mm four jaw chuck which I'd very much like to use. I have a worn three jaw that came with the lathe a set of W20 collets but for larger, precise work a 4 jaw seems essential.


    My question is how to continue from here. My three jaw doesn't have reversible jaws and is quite a bit smaller than the four jaw so I can't mount a blank in there for making the back plate for the larger chuck. I'm also currently not equipped for cutting a 3mm thread on my lathe (see conversation on change wheels for this lathe). There is a machine shop at my university that has a larger lathe and although I'm not sure how they are set for screwcutting these are my current three options:


    1. The thought occured to me that as the difference in pitch is so small, and that the threads are so few (it's sticking four threads in out of seven now) that I could get a M38x3 tap and run it through the current backplate and use as is. The problem though is that the cylindrical register in the four jaw is 38,6mm where the purpose made three jaw comes in at just a hair over 38. I think I risk a bad registration with a modified and imperfect thread leading up to it. Which leads me to option no 2.


    2. Use brass filler rod and an oxy/acetylene torch to fill in the threads and part of the cylindrical register and then bore and cut the appropriate threads. Could mean distorstions that would then have to be undone with the plate installed in the lathe. The backing plate is cast iron so welding is probably a bad idea.


    3. Making a new backing plate. Probably the best way to go but seeing how hard it has been for me to find cast iron in even so small quantities as to make a straight edge for scraping compounds finding a chunk large enough for this should be near impossible. I would probably have to go with steel. I'm new to this so I don't know if that would be a bad thing.


    I very much appreciate all the help I can get on this! I should mention that I've found nothing online for sale apart from a faceplate and a backing plate for a 102 lathe that had different specifications from mine.


    Best regards

    Karl
     
  2. karlmansson

    karlmansson Registered User

    Apr 20, 2013
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    The chucks in question. The discoloration is dirt. If someone has a good method for getting a stuck back plate off I’m all ears!

    45230E5D-FB0F-4189-9B5F-68E994B4E87F.jpeg 4283EECB-1F23-4CF8-977B-ABCF22264AA3.jpeg 738E5AA5-A413-4557-8306-A5413E8BBA01.jpeg
     
  3. wefalck

    wefalck Registered User

    Mar 29, 2011
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    Several lathe manufacturers in the UK offer back-plates. Perhaps they have something suitable. Schaublin, I think, also offers back-plates.

    The british traders mentioned in another thread offer unmachined cast-iron back-plates of various sizes. You would need to find a way to cut the spindle-thread, the rest can be done on your own lathe.

    I don't think that re-threading the existing back-plate with a tap is a good idea. It may result in too weak load-bearing surfaces.
     
  4. karlmansson

    karlmansson Registered User

    Apr 20, 2013
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    Thank you wefalck!

    Yes, that thought had occured to me as well. On the other hand, as I still have four threads of full engagement I have a feeling it would be secure. The four jaw is heavy though... I want it to be seated snugly.

    I looked through the materials mouses and metal suppliers I could find through links here, through google searches and on ebay and I can't find a back plate blank that is large enough (150mm) from cast iron. I did find large enough plates at RDG Tools but those were finished to dimension for another lathe. It's strange that the 38x3 spindle nose seems to be a rare bird. Maybe power in numbers from Boxford, Myford and Colchester?

    Would it be a problem to make the back plate from steel, to go onto a steel spindle nose?

    Regards
    Karl
     
  5. karlmansson

    karlmansson Registered User

    Apr 20, 2013
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    Alright. I think I may have to take a step back and reconsider this chuck altogether. Going through the Habegger catalogue they don’t list any chuck over 135mm as an accessory. Although the heaviest chuck they list for the W20 spindle weighs in at 6,7kg without the back plate, where mine comes in at a little over 6 WITH the backplate, I think a smaller one might be the way to go.

    For all intents and purposes this spindle can be compared to a Schaublin 102 spindle. The early version that is. What I’ve been able to find for those they’re not recommended for use with anything larger than 120mm.

    Any thoughts on this? I’m thinking that a 125mm flat 4jaw might be the way to go. I’m looking for a precision way to hold work that is larger than my largest collet that is about 25mm. And also ability to hold irregularly shaped work, plus plates for facing.

    All help and input appreciated!

    Regards
    Karl
     
  6. geo.ulrich

    geo.ulrich Registered User

    Apr 10, 2013
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    Karl, To remove back plate reinsert screws, screw in but leave loose and tap screws with a mallet....
     
  7. Jim DuBois

    Jim DuBois Registered User
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    #7 Jim DuBois, Aug 21, 2019
    Last edited: Aug 21, 2019
    I realize this is no help to you in your location, but over here we have a supplier of cast iron disks as well as cast iron rods and the like. I have used the disks for chuck backing plates, with proper machining of course. I have also used the thicker larger disks for bobs on street and tower clocks, and have used some of the larger diameter cast iron rods for weights/bobs on street and tower clocks. I mention it here in case it might be helpful to someone stateside with issues such as you face. McMaster-Carr
     
  8. gmorse

    gmorse Registered User
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    Hi Karl,

    I remember @AJSBSA posted his adjustable chuck mounts some time ago, may be worth a search.

    Regards,

    Graham
     
  9. karlmansson

    karlmansson Registered User

    Apr 20, 2013
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    Thanks, but I’m not sure how that would help. Maybe I’m missing something in the process.

    The bolts are threaded into the chuck proper. Tapping the bolts would just send shocks into the chuck. Do you mean I should have the chuck mounted on the spindle doing this? Because if I don’t hold the backplate somehow, tapping the bolts shouldn’t move the plate.

    Yes, how nice it would be to have a McMaster-Carr in Europe...

    Thanks for the tip Graham! I looked it up and it was for a much smaller machine than mine. Though adjustable backplates exist for machines much larger than my Habegger I’m not equipped to machine such a plate on it. Not even sure how to make one.

    Best regards
    Karl
     
  10. geo.ulrich

    geo.ulrich Registered User

    Apr 10, 2013
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    If you tap the bolts plate should come loose just the inertia should be enough , it should fit well but not that tight. I wouldn't put on spindle and tap. If there is a shoulder inside where backing plate is you could lay it on there and tap down..
     

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