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Thread: Gantry

  1. #1
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    Gantry

    I'm building a cnc router and just finished the z axis and gantry. The gantry is 3/16 3"x 6" steel with a 1/4" x 7" cold rolled steel for the carriages,

    I was going to use 960oz motors(2 on the x axis),but the gantry is 125 pounds when I add the motorsand router it will be about 150 does anybody know if that would be too heavy for the 960oz motors, the R & P drives have a 2:1 gear reduction.

    How much do most gantries wiegh?



    Thanks,

    Mike

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  2. #2
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    8020 3060 extrusion weighs 7.462 lbs/ft. CRS .25" x 2.5" is 2.1525 lbs/ft. Assuming a 5 ft long gantry you're talking about roughly 60lbs.

    People drive these gantries all the time with 300-400oz motors with no real issues. Considering you're doubling the weight of the gantry but also doubling the torque of the gantry, I can't see you having an issue. Obviously 1200oz or 1600oz motors are also available for not much more money. You just have to be careful about what the torque curves look like.

    You might want to contact the builder from this thread: http://www.cnczone.com/forums/cnc_wo...x8_router.html

    His gantry is just as heavy if not heavier and he could probably give you a review of the package he bought and whether he would do anything differently.



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    My moving table router has a table weighing in close to 300 lbs. The moving Z axis is about 100 lbs with no counter weight, but I will be adding a pneumatic one when I add a 140 lb milling spindle. I can cut at 120 ipm in plywood and 45-60 ipm in aluminum with no issues at all with 960 oz in nema 34 motors and single start acme screws. I expect to be able to double this speed once I finish the upgrade to ball screws.

    What you describe is easily achieved with that size motor. Just remember that these larger motors require a higher power supply voltage for high speeds. I am using 78v power supply on 80v controllers.



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    I believe CarveOne's large build has a 180+lb gantry and he runs with with NEMA23s, so a lot depends on your final drive ratio, and how smooth your linear guides are. Even if you have a lot of weight, if may not necessary need a lot of force to get your gantry moving. Have you tried any calculations to see what size stepper you may need?



  5. #5
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    A 200 oz motor can easily move a 150lb gantry. It just won't be able to accelerate very fast.
    As Ross mentioned, most people use 380 oz motors to move similar sized loads.

    You didn't provide any machine information either. Is it a heavy duty 2x2 machine? Or a lightweight 5x10 machine. Different machines may (and often do) have different requirements.

    Unless you have specific performance goals in mind (top speed and acceleration rate), then nobody can tell you what motors you really need.

    What are you cutting? What spindle are you using?

    People ask which motors to buy every day. I've yet to see anyone that know what they want the machine to be capable of.

    Gerry

    Mach3 2010 Screenset
    http://home.comcast.net/~cncwoodworker/2010.html

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)


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    Quote Originally Posted by louieatienza View Post
    I believe CarveOne's large build has a 180+lb gantry and he runs with with NEMA23s, so a lot depends on your final drive ratio, and how smooth your linear guides are. Even if you have a lot of weight, if may not necessary need a lot of force to get your gantry moving. Have you tried any calculations to see what size stepper you may need?
    Mine is mostly steel and some aluminum construction. The gantry weighs 185-190 pounds last time I had it apart enough to weigh the individual parts of it. This includes everything that normally rides on the gantry carriages.

    The gantry is driven with two Keling 495 oz-in NEMA23 step motors, Gecko G203V drivers, Keling 72 vdc 20 amp PSU, and CNCRP r&p drives. I limit the cutting feed rate to 250 ipm at 30 accel rate because the mass of the gantry shakes the machine enough to be worrisome that the pulleys on the 1/4" motor shafts may slip (or worse, snap a motor shaft). The machine can rapid at 1,400 ipm. With NEMA34 motors that have 3/8" or 1/2" shafts I would be more comfortable cutting at higher speeds. With a heavier duty framework I wouldn't hesitate to ramp it up even more. In its current state it is doing very well for my hobby needs though.

    The key to these numbers is the 72vdc PSU and the 3:1 ratio r&p drives. Run this machine with 48vdc and the motors won't develop full torque and rpm.

    CarveOne
    http://www.carveonecncwoodcraft.com


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