1. #1
    Hi all,
    looking for ideas regarding x axis travel methods.

    for my y axis I have two steel plates on the outside of my chassis...
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    On these I have built two carriages that run smoothly and will be driven by toothed belt on each end.

    once the gantry is bolted to the carriages, I need to make some sort of transport for the z axis to ride on but not sure of the most cost effective way to do it. Stuff like HiWin track is way over budget.

    any ideas on a good choice?

  2. #2
    Dave that base frame is way to weak and when you get a gantry on then the inertia will rock that frame like a Jelly. Needs plenty more bracing.

    Regards the X axis (Which I call Y axis) then just use the same method for Y & Z axis.? No point making the other Axis better than the X axis has the machines only has good has it's weakist link.

    For a plasma machine then these rail methods will be fine has you only really need positional accuracy not ridgidity like a router/mill does,

  3. #3
    You certainly want to add some diagonals to that frame. If it's staying in the same place then bolting it to the wall is an easy (though not ideal) way to constrain it.

    Suggestion.. design the rest of the machine before you continue making it.
    Old router build log here. New router build log here. Lathe build log here.
    Electric motorbike project here.

  4. #4
    Lol, thanks all, my fault that I didn't mention the frame supports are temporary, and are being used for construction at this stage only.

    when I take it home to the workshop, I intend mounting one end of it to the unused end of my workbench which is welded steel frame and bolted to the wall and floor. I have to do this as space is stupidly tight which is why I'm not making a bigger CNC.

    the front legs will be on the floor and can be braced and bolted down as needed.

    Once I have a rough idea of the job, I like to design as I build, if it don't work then lesson learnt, change it, weld a bit on, cut a bit off and move on :)

    as said, a carriage made on the lines of one of my carriages will work I think, will need an extra bearing or two but I think it will work.

    am I correct in my assumptions that reduction gearing is a good idea on the stepper drives? I was working on 3:1 for each axis but I'm not 100% convinced yet. My motors are 3Nm 4.2A Nema 23's.

    dave

  5. #5
    Quote Originally Posted by Davek0974 View Post
    am I correct in my assumptions that reduction gearing is a good idea on the stepper drives? I was working on 3:1 for each axis but I'm not 100% convinced yet. My motors are 3Nm 4.2A Nema 23's.
    Well that depends what you attach them to.? . . . . You mention timing belts so if this means your using them has the linear drive rather than say Ballscrews or R&P then you'll definatley need some gearing.! . . . . .Not because of lack of power but to increase resolution.?
    Problem with timing belts is the pulley diameter determines the Pitch, now I've built several machines that use timing belts for linear drive and 18-20T is about has low has you want to go. If you go lower then the amount of teeth engaged is lower and you get premature wear etc.

    Now the diameter for HTD 5mm pitch 20T pulley is approx 30mm so the amount traveld (pitch) for 1 revolution is 30*pi so 30*3.141=94mm.!!!
    This is massive pitch and not practicle so you'll need at least 3:1 for plasma and more if router. I used 5:1 on last machine I made.
    The other problem with timing belts with no gearing is the speed is so high that to go slow means the motors have to turn very slow and this can make them run very rough.
    Typical steppers will give approx 1000rpm of usable speed so with 94mm pitch you'd get 94mtrs/min rapid speeds which is stupidly fast.
    Now say you just want to cut at say 5mtrs/min which is still quite fast feed rate for cutting even with plasma the motors will only be spinning at 53 RPM so say you want cut at more realistic cutting speed of 2.5mtr/min for thicker material then your down at 26rpm which is slow and so going any lower really makes the motors unhappy.

    The principle is very similair for R&P and often 3:1 is enough.

    Ballscrews mostly don't need any gearing if correct pitch is choosen.

    One other thing I've found it's often not much cheaper if any using belts than buying ballscrews from china.!!

  6. #6
    Quote Originally Posted by JAZZCNC View Post
    Now the diameter for HTD 5mm pitch 20T pulley is approx 30mm so the amount traveld (pitch) for 1 revolution is 30*pi so 30*3.141=94mm.!!!
    It doesn't change the point you're making, but that's a rather roundabout way to get the circumference! To find the distance traveled per revolution just multiply the pitch by the number of teeth - i.e. 5*20=100mm. Save the pi for other occasions.
    Old router build log here. New router build log here. Lathe build log here.
    Electric motorbike project here.

  7. #7
    Brilliant, thanks for that.

    i have the pulleys to do 3:1 on both axes. I'm using T5 20t pulleys on the motor and final belt drive so the overall reduction is 3:1

    maybe ball screws on the mk2 build, this stuff is addictive :)

    will be be using micro stepping as recommended by mach 3 manual.

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