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Help with lead screw

Discussion in 'General Talk' started by kev20009, Jul 16, 2015.

  1. kev20009

    kev20009 Journeyman
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    Hi guys after having trouble with belts pulling out slipping, changed to lead screw, but having some trouble with these, the screw is lot slower than belt, get it tuned sounds nice, not fast but ok, then after few jogs, lost about 4mm to other side, then I get like jamming and one side pulls more,

    Table size 1200x600 cut, lead screw 2sides of y axis, x running belt ok, only thing not sure of is the lead screw is 12mm 3mm per turn, single thread, and the 2are right hand thread, is this ok or does one need to be left hand thread,

    Thanks guys for any help. Kev
     
  2. Rick 2.0

    Rick 2.0 OpenBuilds Team
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    Right hand is okay for both as long as steppers are spinning the same direction. Sounds like you are trying to spin so fast you may be losing track of steps. A little more system info would be helpful though.... i.e. what steppers, drivers, board, software, movement speeds, etc.
     
  3. kev20009

    kev20009 Journeyman
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    hi rick some info,

    Trapezoidal Spindle - Part Number TR12x3D x1500mm long
    (Ø12mm x 3mm pitch)(x1 revolution = 3mm or 0.1181")

    DIY CNC Kit 5 Axis Breakout Board + 4 x M335 Stepper Driver Board Controller(0.5-3.5A)

    SY57STH76-3008B Nema 23 high torque hybrid stepper motor

    The SY57STH76-3008B stepping motor has a holding torque of 1.89Nm and has a rated current of 2A in series and 4A in Parallel.
    The motor is 1.8 degrees-per-step wired in series

    computer conection is uccnc motion cable

    all other parts on cnc are the same as the ox,

    thanks rick for any help, kev
     
  4. Rick 2.0

    Rick 2.0 OpenBuilds Team
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    So basically you've jumped from a system that was moving 60mm per revolution of the stepper to one that is moving 3mm. That's a factor of 20 and motor speed can't be increased anywhere near that much to compensate without losing steps. While I'm no expert on the subject, I would suggest reducing the speed and increasing step size. Start with whole or 1/2 steps and move at low speed. See if you still have error. If you don't, keep increasing speed until you find where errors begin. Depending on what you are cutting, whole steps may offer a sufficient resolution. With a 3mm lead, you certainly shouldn't need to use anything less than 1/2 steps.
     
    GrayUK and Mark Carew like this.
  5. kev20009

    kev20009 Journeyman
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    hi rick,
    just been trying out, lower speed, most I can go on velocity is 700, motor sounds ruff any more, my main problem is when I try circle its like its stopping, and ive found my wheels different size some not touching extrusion, but if I tighten up then I get the gantry jamming,

    so my thinking is different lead screw, and bearing thanks rick, kev
     
  6. kev20009

    kev20009 Journeyman
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    one ting I would like to ask the guys using belt, on big cnc, is the belts ok. I tried 4 different tapes to stick bottom belt but it would always bubble up in places after about 3 mins jogging,

    just slackend all bottom wheels of and moved centrics to slack but 3 wheels still very tight, so not sure if this is a problem for the belt,

    thanks guys kev
     
  7. Rick 2.0

    Rick 2.0 OpenBuilds Team
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    Sorry but my OX is still a work in progress so I can't offer any personal experience. I have noticed however how poorly the rubber belts stick to the adhesive tape. In testing I have found that putting a coat of Loctite adhesive on the back of rubber and letting it dry and then sticking it to the tape makes a big difference on the amount of grip. The adhesive sticks solidly to the rubber and then the tape sticks nicely to the adhesive. But again as my OX isn't finished, I can't say whether it will work in practice. There is an outdoor version of the same adhesive which may work even better but as I already had the indoor version, I went with it. As far as the tape, the 4910 seems to be the perfect thickness to fit beneath the GT3 belts and hold the bottom belt snugly against the upper one. The 4941 and 4611 tapes are slightly thicker and may work too but I haven't tried them. Be sure and clean the belts thoroughly if you attempt this approach.

    As far as the wheels being too tight, your holes may be too close together. This has been noted elsewhere in the forums. The center to center spacing between the rows should be extrusion depth + 19.8mm. You might check to see if they are too close and if needed, oversize the existing holes a bit to add some slack.
     
  8. kev20009

    kev20009 Journeyman
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    hi rick was looking at this screw would this be a better option, or should I try belts again, thanks kev

    TR16X8D-P2 Multi Start Trapezoidal Right Hand Spindle / Leadscrew
     
  9. Rick 2.0

    Rick 2.0 OpenBuilds Team
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    That will be much better than what you have and should be adequately beefy for a 1500 mm axis length. As for whether it is better than belts though, that all depends on what you intend to cut. For hard to cut materials like aluminum or hardwoods, the screws would be better. For soft materials like foam or balsa, belts are the better option as they offer higher speeds.
     
  10. kev20009

    kev20009 Journeyman
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    hi rick, think that's the screw then, as I would like to cut aluminium some time, but g10 and carbon its mostly will be cutting,

    been all day looking at what is jamming it when I jog the y axis, and found with the weight of 2 nema 23 76mm and big ally block that spindle is going in, looks like the centre of gravity is out on ox plates, and think its tipping gantry forward, so just cut some mdf to try where the gantry is back off middle. and my spindle should be middle then,

    thanks again rick, kev
     

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