dynamic breaking ,metric threading
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  1. #1
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    I have been cutting metric threads on an 83 ee, the half nuts must remain engaged because the 8tpi leadscrew is constantly going out of time with the gearing when in the metric mode. The problem is when the leadscrew reverse trip dog returns the spindle control lever to neutral the spindle does not stop as fast as I think it should. The dynamic breaking is working, if the red button is pushed the spindle will coast to a stop. Is there a way to increase the dynamic break? /

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    Not having a modular drive itself but only the schematic I'd suggest looking at the dynamic brake contactor. This guy should be on when neither the forward or reverse contactor is on, and shorts the armature across the 2 4.8 ohm wire coil resistors. If this guy is energizing check to see if there's conduction through the resistors - if there's an open on them then you'd see the same problem.

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    This is not an answer to your dynamic breaking question, but is a technique I usually use when threading metric. Go ahead and disengage the carriage feed at the end of the thread (as you would when threading English); then back the cross feed out and stop the spindle quickly (do not let the spindle turn longer than it takes to back out). Then reverse the spindle and re-engage the carriage feed at the same thread dial point. You are still in the proper timing with the gearing. I find that this technique works better than stopping the spindle without disengaging the feed (which usually breaks my carbide threading insert).

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    Thanks for the help! This is a great site!

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    Hardinge solved this problem with the HLV-H "quick release" feature on the cross slide, which does not require disengagement of the half-nut.

    I have heard more than one machinist state that the perfect toolroom lathe would be a Monarch 10EE with a Hardinge HLV-H quick-release.

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    I agree. The HLV series of lathe is really nice to chase threads with the auto spindle shut off and quick release compound feature. Otherwise the monarch 10EE is a better machine. I have one of each now and only use the Hardinge to thread. The monarch is my preferred lathe for everthing else!!!

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    Perhaps Metal Lathe Accessories' Quick Retracting Toolpost could be adapted to the 10EE to provide the equivalent of the Hardinge HLV-H "quick release" feature on the Monarch?

    http://www.statecollegecentral.com/m...he/MLA16D.html

    Comments?


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    My 42 MG lathe has instant reverse; when the stop is engaged or the lever is thrown (off/forward/reverse) it will reverse the cut (the motor reverses direction). Just back it off slightly simultaneously. The EE is designed to take it, even though it seems like abuse for such a fine piece of machinery. I know that this was done in production shops. It is a bit noisy...

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    Sounds like the combination of "instant reverse" and the MLA Quick Retracting Toolpost would be ideal.

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    My 51 plain jane mfg lathe with motor generator will reverse instantly at threading speeds. It works really well using taps and dies. The module drive in my other lathe doesnt have this responce. I noticed that the MG uses field control after 600 rpm and the module drive uses field control after 1200 rpm, maybe braking is not as good because of the much higher spindle speeds the module drive has.

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    "I noticed that the MG uses field control after 600 rpm and the module drive uses field control after 1200 rpm, maybe braking is not as good because of the much higher spindle speeds the module drive has."

    Correct.

    The "base speed" of the M-G's drive motor is about 690 rpm.

    That of the tube drive models is perhaps 1725 rpm, give or take (probably take).

    So, the point at which the respective drive's transition from full (shunt) field with variable armature to full armature with variable (shunt) field is indeed quite different.

    And, that affects the dynamics of ... er ... the dynamic brake.

    I wonder if an "instant reverse" modification is possible on a tube drive machine.

    I was observing some very interesting threading yesterday ... a SHARP (an HLV-H clone) lathe using the "quick release" and the instant reverse features made this M14-1.25 threading job in some very difficult material seem like child's play.

    Too bad the operator dialed-in 1.35 mm instead of the required 1.25mm pitch.

    The 1.35mm pitch threads were perfection, however.

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    <<
    That of the tube drive models is perhaps 1725 rpm, give or take (probably take).
    >>

    Hmm, the motor data plate says 1150, but we're driving it at 245 instead of 230 so we're likely getting 1200 and a bit before field crossover starts.

    The best threading system I ever saw was a pneumatic retractor on a big-ass oil field lathe we were cutting AWS thread on pre-hardened 4130 collars. The thread tool was (if I recall rightly) a 3/8 HSS bar with a chipbreaker groove ground into the top and some relief in the face. The cut was about .100 deep on a taper and the retractor sounded like a rifle shot when it pulled the tool, but the end of the thread was pretty dang square. The chips coming off looked like blue finger nails and were moving fast - I think we wore a hole in a welding screen someone put up one day to keep the chips from landing on him.

    I wish the 10EE had as positive a stop. Might keep me from busting about half the inserts I manage to break.

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    "the motor data plate says 1150"

    So does my 5 HP GE motor.

    Still, 690 rpm (3 HP Ward-Leonard drive) vs. 1150 rpm (5 HP tube drive) is quite a difference.

    But, so also is 3 HP vs. 5 HP.

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    I found that the Howard D method works well threading into a blind hole. Over all the machine works really well cutting metric threads.
    On dynamic braking- The 51 motor generator lathe will come to a complete stop from 2500 rpm in about 2seconds.
    The 83 module controlled lathe will come to a complete stop from 2500 rpm in about 4 seconds.

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    Here is another approach you might want to consider thats been around for a century or so. Instead of trying to stop so quickly go the other way and stop it slower with more control. Move the trip dogs back out of the way and use your speed knob to slow down and stop the spindle. an indicator is helpful in doing this. In any event you want to make sure your tool is completely out of the cut before the spindle stops or you might break a tool. You can make a few sample runs(tool backed out)to get the hang of it.
    Just a thought,take it for what its worth.

    drof34

    [This message has been edited by drof34 (edited 07-05-2003).]

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    Drof35, you have a good point, it is the carbide threading inserts that make high speed threading necessary.
    I have rediscovered that I can grind high speed thread cutters and work at slower speeds with great results.
    On the dynamic braking i will check out the 5hp motor on the module drive machine, make sure that the brushes make full contact and stone the commutator.

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    "On the dynamic braking i will check out the 5hp motor on the module drive machine, make sure that the brushes make full contact and stone the commutator."

    If the commutator is uniformly blackened and is not grooved, then there is probably no problem with the commutator.

    Patches of dark black indicate possible flashover points, or other faults, and the need for service more involved than stoning.

    Definitely check the brushes.


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