Screw machine die threading question
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  1. #1
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    Default Screw machine die threading question

    I'm scratching my head at the die action in this video. At 1:24 the die/holder seems to pull off at the end of the threading op but later in sequence you can see what looks like an ordinary split die in a floating holder. Is the spindle reversing that quickly? What am I missing?

    YouTube

    Thanks...

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    Yes, it appears to be a regular die and a reverse to unscrew it. If you look closely, right after the die holder pulls out, the slide reverses motion, and you can see the die holder pull out farther as the slide gets just a little ahead of the unscrewing.

    If you noticed, that machine is crazy fast with the actions (good productivity). It looks like there is a quick reverse when the view of the spindle is reached, a bit later in the video. It is really fast.....

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    It's a button die. The spindle runs left hand for all ops. apart from thread on. You can see the spindle change speed and direction. When you look at the lead cam the last op.(threading) feeds on and off.

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    Thanks. I would love to spend a day or two in a shop that uses those machines.

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    You can get almost that fast a reversal on a manual Hardinge DSM-59 with the usual 3-phase motor. In addition to mechanically variable speed, the machine has two intrinsic motor speeds and is designed to be "plugged" directly from forward into reverse and back again into forward. Takes it like a champ, and does exactly the sort of operations shown in that video, just all hand-lever operated instead of cam operated.

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    Quote Originally Posted by sfriedberg View Post
    You can get almost that fast a reversal on a manual Hardinge DSM-59 with the usual 3-phase motor. In addition to mechanically variable speed, the machine has two intrinsic motor speeds and is designed to be "plugged" directly from forward into reverse and back again into forward. Takes it like a champ, and does exactly the sort of operations shown in that video, just all hand-lever operated instead of cam operated.
    I wish my little Rockwell turret lathe had the Hardinge type of quick speed and reverse setup but it does have a lever operated variable speed control which is fairly convenient and a geometric die head gets the threading jobs done pretty easily.

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    The way it was explained to me, for retract the cam drives out the turret "slightly" faster than newly cut thread's lead, so the die head spring stretches just a bit for the distance it takes to unscrew the die. The idea being to be slightly faster than the screw lead so the spring absorbs the difference, if you tried to make the retract rate equal to lead then the system would be right on the edge of being bound. Not a problem on cnc because the spindle position and threading tool position are always controlled together.

    Since the retract rate and spring are there to let the die unscrew freely then there is no need for a clutch inside the die head, thus it is simpler & cheaper. The same mechanism applies to taps.

    I have a clutched tap holder on my Wade that permits quick removal, but the operator has to reverse the motor and retract the turret to engage the tapholder's clutch so the tap will quit spinning and start to unscrew. When I got the tool it was pretty gummed up, so needed some fiddling to figure out how it worked.

    Tripping die heads are seen on screw machine setups but involve some magic to operate the lever and reset the head.

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    Quote Originally Posted by Greg Menke View Post
    The way it was explained to me, for retract the cam drives out the turret "slightly" faster than newly cut thread's lead, so the die head spring stretches just a bit for the distance it takes to unscrew the die. The idea being to be slightly faster than the screw lead so the spring absorbs the difference, if you tried to make the retract rate equal to lead then the system would be right on the edge of being bound. Not a problem on cnc because the spindle position and threading tool position are always controlled together.

    Since the retract rate and spring are there to let the die unscrew freely then there is no need for a clutch inside the die head, thus it is simpler & cheaper. The same mechanism applies to taps.

    I have a clutched tap holder on my Wade that permits quick removal, but the operator has to reverse the motor and retract the turret to engage the tapholder's clutch so the tap will quit spinning and start to unscrew. When I got the tool it was pretty gummed up, so needed some fiddling to figure out how it worked.

    Tripping die heads are seen on screw machine setups but involve some magic to operate the lever and reset the head.
    Die heads,can be tripped by a pin striking the nose cap or anything else that you can rig up or it can be self opening when the cam stops advancing and the thread already cut pulls the die head body further forward until a detent pin releases the body and the die head opens. This and mixtures of this is the normal course of events.
    To close the die box is by a simple bar, strategically placed,which strikes the closing arm as the turret indexes. Aqua

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