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New Pm 1030v Lathe

Discussion in 'PRECISION-MATTHEWS' started by shooter123456, Jul 29, 2016.

  1. shooter123456

    shooter123456 United States Active Member Active Member

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    I tried something I hadn't done on the PM1030v yesterday: Metric Threading. Since discovering the 4 jaw had some really bad runout problems, I had 5 TTS holders that were not going to be usable. To save them, I decided to make them into ER20 holders instead and bore the collet taper on the mill to ensure runout is minimized.

    There was only 1 hiccup with the operation. Since it was metric threading and the leadscrew is imperial, I only engaged the thread lever when the chasing dial was on the 1. Second pass and it was off. Maybe something is wonky or I was wrong about being able to use the thread chasing dial, but after the second pass, I left the lever engaged and just turned the lathe off and reversed it for each pass. The thread was an M25x1.5 and material was 4140.

    Here is that holder:
    [​IMG]
     
  2. shooter123456

    shooter123456 United States Active Member Active Member

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    Double Post.
     
  3. shooter123456

    shooter123456 United States Active Member Active Member

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    Triple Post.
     
  4. Bob Korves

    Bob Korves H-M Supporter - Premium Content H-M Supporter-Premium

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    You cannot use the thread dial AT ALL for metric threading on an imperial lead screw, the half nuts must stay constantly engaged. Actually, there is a workaround for that, but will not get into it unless you want it. Is the three jaw accurate enough for what you are doing?
     
  5. shooter123456

    shooter123456 United States Active Member Active Member

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    Thank you for the guidance. I must have mixed it up with something else, and it made sense in my head that even if I engage on the same spot, it will enter the thread in the same place. Apparently, thats not so.

    If the workaround is relatively simple and easy to do, I would love to try it, otherwise, I am content stopping and reversing. It takes a little longer but its not a big deal for me.

    Regarding the 3 jaw, it should be plenty accurate. I indicated off the largest diameter which should be concentric with the shank and using a deadblow, I can get it running within .001" or less. As far as I know, the key part with the collet holder is that the taper is concentric, and as long as the threads are close, it won't cause a problem. The taper will be cut will the tool holder installed in the mill, so hopefully, that will lead to almost no run out.
     
  6. Bob Korves

    Bob Korves H-M Supporter - Premium Content H-M Supporter-Premium

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    The workaround is, that while you must always leave the half nuts engaged the same way while threading metric on an imperial lead screw, you can disengage them if you are able to put them right back where they were originally. That means more than, say, always engaging the half nuts at number 1. The gearing is not repeating correctly when you have the metric change gears in the system. The spindle and the lead screw have an oddball gear ratio that only repeats after many revolutions of the threading dial. So, if you disengage the half nuts, you must re-engage them exactly where you disconnected them, and on the same revolution of the threading dial. Follow along with this... Engage the half nuts and note the reading. It can be on any line or part way between them, but must go back the same way, so remember it exactly. Make your first pass, disconnect the half nuts, retract the tool one turn, and IMMEDIATELY turn off the lathe. In that amount of time, the threading dial will not have turned one complete revolution. With the tool safely out of the work, start the lathe in reverse, and when your spot on the threading dial comes around in reverse, engage the half nuts again. Let the carriage continue under power back to the start of the thread position and turn the lathe off. Leave the half nuts closed this whole time. Advance the tool for the next cut. Start the spindle again in the forward direction to make the next cut. Lather, rinse, repeat. There is no magic here. We are just cheating a bit to get the tool out of the work safely at the end of the cut, and then closing the half nuts again exactly where we disengaged them. If you lose track of the threading dial rotation doing this, you are lost. It works just fine -- if done correctly. Practice on some scrap until you are happy with how it works and have the muscle memory to repeat it for each pass without messing it up.
     
  7. pstemari

    pstemari H-M Supporter - Premium Content H-M Supporter-Premium

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    Note that the procedure isn't much better on a lathe with a metric leadscrew. While all standard inch threads will have an exact count in 16 turns of the leadscrew (== 4" of travel) (and usually much less), the way metric threads are specified is such that you don't get an exact count until you have gone much further and many more turns.

    They do make metric thread chasing dials, but they are much more complicated and you have to wait longer for them to come around to the starting point.

    It's a shame the single point dog clutch on the HLV-H lathes never made its way into general usage. Instant stop, easy reverse, and no threading dial worries.

    Sent from my Pixel XL using Tapatalk
     
  8. Bob Korves

    Bob Korves H-M Supporter - Premium Content H-M Supporter-Premium

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    The relevant part of the video starts at 17:30. This video just came out two days ago, and I just watched it.
     
  9. shooter123456

    shooter123456 United States Active Member Active Member

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    I get what you are saying. The method would allow me to disengage the half nuts to stop the carriage long enough to turn the machine off. Then reverse to the same number, engage the lever again, and back it up. I typically run the lathe slow enough and have enough room that I can have my left hand on the power off button and my right hand on the crossfeed. Once I get to the thread relief, I power off and back up in the same motion. It usually stops within half a turn. I have had a good deal of practice with it the past few days threading these holders.
     

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