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  1. #11
    Fwiw..
    On steppers, the max acceleration with 48V DC, 542 drivers, Nema 23 3Nm steppers, 3:1 via HTD 5/15 mm, about 0.8 secs to max speed.
    My table on a moving table VMC is over 200 kg in mass.
    It stops in maybe 1- 2 mm from max speed. Using hw pulsing from a good generator, lately pokeys.

    On 400W ac servos, Nema 23, 3.9 Nm peak, it stops in about 1 mm or less.

    On the lathe, the new saddle assy == 150 kg.
    32 / 4 mm ballscrew, 750W cont ac servos, 10 Nm peak.

    X starts and stops in much less than 1 mm, if I was to use high acceleration - I don´t.
    I use about 20% of max acc. for "normal" use.

    Steppers in the past used to do similar, with much lower top speeds, and much less accuracy.

    My c axis spindle and z axis (lathe) have about 10 kW of power in terms of inertia (I know its not kW technically).
    Ie industrial turning centers (HAAS ST10) of 10 kWh cont. has about the same peak torque (102 Nm at 1200 rpm) as I have (90 Nm) 0-1000 rpm.
    Using a 10" 4-jaw chuck.

    The steppers at 1:3 ran about 600-700 rpm, 200 rpm+ at screw of 5 mm rise.

    The servos run 3000 rpm, but I only use one third or 1000 rpm.
    Very fast accelerations are like hitting the screw mount bearings with a big hammer, 10 kg, literally.
    It wears the bearings out fast.

    My mounts could take 3000 kgf loads, you could stand a truck on them.

    Recap:
    Lathes and mills typically go to max-speed in about 1 mm - 2 mm of travel.
    Steppers are ok for full-out, and servo systems depend on a lot of stuff.

    Anecdote:
    The ac servos go to 3000 rpm in about 20 ms, 0.02 secs. Both 60V 400W and 220V 750 W servos.
    It is likely the lathe servos could do full-peak accelerations, with the saddle, to 3000 rpm, at 0.02 secs or so.

    At 10 Nm direct drive peak, the push force is about 650-700 kgf, 7000 N, near 1900 lbs of force.
    For 150 kg mass on saddle assy, ==> 4.3 kgf.
    43 m s/s acceleration.

    At 1000 rpm x 5 mm, = 5 m/min. /60 = .083 m/sec.
    8.3 cm/sec.
    In 0.02 secs, the travel is 0.166 cm, = 1.6 mm.

  2. #12
    [QUOTE=Clive S;107130]Is there a reason not to use the soft limit as that would stop it[/QUOTE
    No reason. Just need to get a session back in the workshop again !
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

  3. #13
    Clive S's Avatar
    Lives in Marple Stockport, United Kingdom. Last Activity: 10 Hours Ago Forum Superstar, has done so much to help others, they deserve a medal. Has been a member for 9-10 years. Has a total post count of 3,333. Received thanks 618 times, giving thanks to others 78 times. Made a monetary donation to the upkeep of the community. Is a beta tester for Machinists Network features.
    [QUOTE=routercnc;107141]
    Quote Originally Posted by Clive S View Post
    Is there a reason not to use the soft limit as that would stop it[/QUOTE
    No reason. Just need to get a session back in the workshop again !
    I know how you feel
    ..Clive
    The more you know, The better you know, How little you know

  4. #14
    Main reason for not using soft limits seems to be that you can't jog with soft limits on until you have homed the machine. I don't find that a limitation, but it all depends on things like where you home the machine, where you park the spindle when loading/unloading work, work area and rapids speed.

    I've been using my machine this evening, but the cold drove me indoors eventually.

  5. #15
    Aaaah, someone else who has a cold workshop - welcome to the club

  6. #16
    Learn from my mistakes. You will most likely at one point accidentally go further than your limit switches. My CNC crushed them on the very first test because of a dodgy endstop cable. My next CNC will use induction switches that won’t get crushed.

  7. #17
    Yes, they work just as well detecting side-on as face-on. Mounting them side-on allows the moving metal part to slide past the face of the sensor and if it overshoots it will go past and hit the physical end stop, and the sensor is saved. You still have to work out what went wrong, but the sensor is saved.
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

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