Lathe collet chuck

  1. BelgiqueB Member

    Messages:
    156
    Location:
    Belgium
    Messing around trying to make a collet chuck holder for my lathe, i have a flat plate that bolts onto the spindle with the correct taper that came with the lathe. First idea was to make a piece that bolts onto the plate (see sketch below), but i have no accurate way drill the flange holes at the correct spacing, i printed out the pattern on sticky paper and tried transferring it that way onto the part, but it wasn't accurate enough so this attempt ended in disaster :-) .
    Schermafbeelding 2020-09-06 om 20.18.13.png

    I could do away with the flange all together and weld or Tig braze the collet holder directly onto the plate at the red arrow on the drawing. Is this a good idea, the flange itself is cast iron, the collet holder would be mild steel. I would clean up the center hole in the cast iron plate and then machine a protruding part in the collet holder that would fit into the center hole of the plate.

    Once it's all brazed up i could clean up the OD and drill bore,... the center portion of the collet holder making everything concentric.




    Schermafbeelding 2020-09-06 om 20.18.57.png
     
  2. Seadog

    Seadog Forum Supporter

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    6,968
    Location:
    NE London - UK
    You will never get it perfectly aligned, apart from other considerations with the materials. It rather defeats the object of a collet chuck if it's not running true.
     
  3. Brad93

    Brad93 M J B Engineering

    Messages:
    10,375
    Location:
    Essex
    So you’ve got a collet chuck, you have a back plate, but you’ve no way of drilling them holes half through the Flange on the backplate?

    find someone with a mill.
     
    Memmeddu likes this.
  4. BelgiqueB Member

    Messages:
    156
    Location:
    Belgium
    I would weld the part to the back plate and after that i would do the center bore and taper for the collet, that way making it all concentric. I'm just slightly worried about welding/brazing mild steel to cast iron.
     
  5. BelgiqueB Member

    Messages:
    156
    Location:
    Belgium
    I prefer doing stuff myself, even if it makes it a bit harder. It's always a good learning experience. I could draw the part up in fusion including the back plate and probably have it made for under 200 euros at my local cnc machine shop, but where's the fun/learning in that.

    I only have the back plate, the collet holding part i still need to make.
     
  6. pressbrake1

    pressbrake1 Forum Supporter

    Messages:
    2,880
    essex england
    Use geometry to mark out your backplate properly
    Be sure to machine the register on it accurately for a good fit on the collet Chuck
     
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  7. Brad93

    Brad93 M J B Engineering

    Messages:
    10,375
    Location:
    Essex
    Exactly.

    Use chord length to make sure your three holes are bang on the money, they’re 60 degrees apart. A three hole pattern has a constant of 0.86603

    Multiply that by the diameter/PCD and that will give you the chord length. Mark your first hole with a very fine centre dot. Then use a set of dividers to mark your second & third hole. You can then use your dividers to double check the holes from each one.
     
  8. Agroshield Member

    Messages:
    1,365
    His drawing is, I think, slightly confusing. The big round bit is the 'backplate' that already fits the spindle. The smaller piece with the flange in the foreground is the embryo collet chuck.

    ---

    To the OP:

    I might be missing something here, but why do the flange holes need accuracy?

    Read and understand the implications of what Mr Seadog has told you. You cannot use a bolted connection for accurate location.

    Use a register on the part you are making for concentricity (skim the bore in the backplate to ensure its concentricity to your spindle) and then drill the securing holes anyhow whilst the two parts are clamped together. It will only have one way of going back together again out of three possibilities but that does not matter.
     
    eLuSiVeMiTe likes this.
  9. BelgiqueB Member

    Messages:
    156
    Location:
    Belgium
    Realized that there is a 5 taper inside the spindle (very new to lathes :laughing::laughing:) so went a different route after seeing a youtube video were someone made something similar.

    Got an MT5 arbor from ebay and adapted it to take the shaublin collets. All is left now is to make a drawbar for the collets, anyone have some example pictures, doesn't look to be difficult to make one but don't want to overlook something.

    20200914_164733.jpg 20200914_170146.jpg 20200914_170708.jpg 20200914_184108.jpg 20200914_184042.jpg 20200914_184147.jpg
     
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  10. BelgiqueB Member

    Messages:
    156
    Location:
    Belgium
    Finally all came together :-)

    20201004_202038.jpg

    Made a simple drawbar with a delrin tapered plug that locks into the end of the spindle. Had to make the plug so long because the end of the spindle is recessed inside the lathe about 8cm, unfortunately there is a bit of a wobble in the delrin plug / threaded bar when the lathe is running, it has no effect on the collet or workpiece, but I would like to remedy it, any suggestions for a better design?

    20201004_201830.jpg 20201004_201837.jpg

    In action with a 20mm end mill, taking very little cuts on the slowest cross slide speed because I know nothing about milling feeds, depth of cut,... but worked well :laughing:

    20200928_204416.jpg
     
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  11. Brad93

    Brad93 M J B Engineering

    Messages:
    10,375
    Location:
    Essex
    Lead plug maybe?
     
  12. BelgiqueB Member

    Messages:
    156
    Location:
    Belgium
    Not sure if joking or not :-), how do you mean?
     
  13. Brad93

    Brad93 M J B Engineering

    Messages:
    10,375
    Location:
    Essex
    Instead of delrin, melt down a bit of lead, make a suitable conical shaped former, can be thin tin, pour lead into mould. Then turn the lead in the lathe to fit your spindle.

    Lead is very dense but soft so you can pull your collets up with no worry about damaging the spindle. The density should dampen the vibrations better than delrin.
     
    northwest likes this.
  14. Agroshield Member

    Messages:
    1,365
    The taper on the end of the plug is not helping. Make it a close fitting top hat style.

    Alternatively, you could make the top hat very short and integrate the nut into it so the nut is recessed and there is less total overhang from the end of the spindle. Turn down the last 10mm of the threaded rod to thread minor dia. and chamfer the end so the nutbush goes on more easily. You might need to sleeve the outside of the socket you install it with so it centralises in the bore. Think about how you will retrieve it when undoing it.

    A lot of threaded rod comes pre-cambered from the factory. And you will not and should not put enough stretch on it to pull it straight. I suspect the long overhang, the tapered seat of the delrin plug and a bent rod are combining to cause the wobble.

    Most standard collet closers use a draw tube rather than a rod. It is a bit counter-intuitive, but a much smaller dia. threaded rod might assist as you can put more straightening force on it.
     
  15. MBB Forum Supporter

    Messages:
    1,127
    Location:
    northumberland
    How is the chuck fitted on your lathe Do you have a plate that's bolted onto the mandrel?
     
  16. BelgiqueB Member

    Messages:
    156
    Location:
    Belgium
    Makes sense, will have to have a rethink about the drawbar design with this new info! thanks.
     
  17. BelgiqueB Member

    Messages:
    156
    Location:
    Belgium
    The spindle has a MT5 taper in it, I adapted a MT5 drill chuck arbor to accept the W25 collets, pictures in post 9.
     
  18. daedalusminos Member

    Messages:
    1,070
    Location:
    Norwich
    You have too much off-centre mass sticking out the back, and Delrin was a poor choice of material. You have a chamfer, I guess in the hope it would self centre in the spindle, but with Delrin being soft the spindle will just dig in. A top hat design as @Agroshield suggest would be better then perhaps a nut directly behind that and use a box spanner to turn or, if that's too fiddly, weld some hex bar to a disc and turn the top hat into the disc thus keeping everything concentric (you might have to implement some thrust arrangement).
     
  19. MBB Forum Supporter

    Messages:
    1,127
    Location:
    northumberland
    I meant a 3 or 4 jaw chuck, there doesn't seem to be any unless there is a plate that is fitted to the spindle.
     
  20. Brad93

    Brad93 M J B Engineering

    Messages:
    10,375
    Location:
    Essex
    He is using the internal taper on the lathe which is MT5.

    Sounds like he has bored out a MT5 tool to accept collets.
     
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