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  1. #11
    ivars211

    I'm not knowledgeable enough on the electronics side to recommend anything but this is a popular digital driver for background reading:
    AM882 Digital microstepping driver with stall detect

    On the mechanical side I would second the twin ballscrew what you are calling the "Y" axis. I used to cut aluminium on a single ballscrew machine with a gantry of around 650mm. You could see the legs of the gantry moving back and forth since the gantry restraint was only in the centre. This effected the cut accuracy which if aluminium is your main material then it will not be sufficient. It is more money, so you can build single now if you like but be prepared to upgrade and build in the holes etc for a twin ballscrew so it is easy to upgrade.

    On the "X" axis plate (to which the Z supported rail is bolted to) this needs to be re-arranged at the bottom where it interfaces with the horziontal small plate which connects to the bearing carraige. You have managed to 'trap' the "X" axis plate between the upper and lower bearings which you will have to cut slightly undersize and then shim out etc. Better to grow the "X" axis plate down a bit, and cut back the small plate, then bolt horizontally. Using oversize holes you can tighten these bolts up once everything is set and know that the bearing load is where you want it. Hope this makes sense.

    The gantry crossrails are a bit on the small side with 2off 50mm box sections, and no connection between them. I think this will cut OK but surface finish is very sensitive to vibration and I would personally beef up the rails considerably if aluminium is your main cutting material.

    Oh, and welcome to the club . . .
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

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  3. #12
    Quote Originally Posted by ivars211 View Post
    It might be stupid question, but what do you mean with "digital drives"?
    I think you convinced me, so I am going to redesign it for twin ballscrew drive then.
    Any advice where to buy timing belt and pulleys?
    No not Stupid question at all.! . . . Digital drives are newer breed of drive that use advanced alogrithams and techniques for working which results in better smoother performance. Older drives used anolgue technolgy and where restricted or lacked advanced features for dealing with issues like Resonance.
    Digital drives are much better for this resonance handling alone and the better drives often allow fine tuning thru software if problems do arise but in general they just give smoother running motors and often allow higher speeds.

    I use my local bearing supplier but these guys seem ok Timing Pulleys and they will machine them for you at a cost.!

    You want HTD 5mm pitch and 15mm. Don't go to small on the pulleys but at same time don't go to large, I use between 18-20T depending if I apply a ratio or not. 2:1 I would use 18/36T.
    Last edited by JAZZCNC; 15-04-2014 at 09:41 PM.

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  5. #13
    OK, cheers. I have to re-think quite a lot now. I will post my new design after I have finished.
    I cannot tell how thankful I am for all your inputs!

  6. #14
    Quote Originally Posted by ivars211 View Post
    OK, cheers. I have to re-think quite a lot now. I will post my new design after I have finished.
    I cannot tell how thankful I am for all your inputs!
    Just a mute point when talking about X and Y axis most people on here refer to the X axis as the longer axis (generally) quite often with two screws and the gantry as the Y axis, if you keep to that it will stop a lot of confusion when asking questions. Oh welcome by the way looking forward to see your build log. ..Clive

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  8. #15
    Ok, I will keep that in mind. The question I am having, if perhaps I am going to buy one pair of profiled linear rails (DFH15), which axis would mostly benefit from them? If I am not wrong it should be Y - 700mm (allowing Z to move).

  9. #16
    Quote Originally Posted by ivars211 View Post
    Ok, I will keep that in mind. The question I am having, if perhaps I am going to buy one pair of profiled linear rails (DFH15), which axis would mostly benefit from them? If I am not wrong it should be Y - 700mm (allowing Z to move).
    No all or None is the only way really.

    If you must Then Z axis is actually the most important area on the machine because it carry's the sharp bit and if that moves or flexs then doesn't matter how well built the rest is the machine will give rubbish and inaccurate parts.!!.. . . . . . . It's very common for people to under build the Z axis only to instantly regret when the chips start flying, it's also often the most upgraded part of any DIY machine.!

  10. #17
    Thanks. The thing is, I cannot really afford going all profile. I wish... someday.

    EDIT: I cannot find any information about these DFH15 profiled linear rails Chai is offering me, maybe someone knows?
    Last edited by ivars211; 16-04-2014 at 03:15 PM.

  11. #18
    Quote Originally Posted by ivars211 View Post
    EDIT: I cannot find any information about these DFH15 profiled linear rails Chai is offering me, maybe someone knows?
    Try PDF Linear technology company Ltd. They are actually Taiwanese bearings imported into china. Seems the taiwanese make most of the linear bearings.

    I tell you thru experience of using plenty that they are perfectly fine and worth every penny thou the small difference in price between 15mm and 20mm makes the 20mm the better option due to bearing size providing better footprint and giving more clearence for ballscrew on Z axis.

    If you want to see a picture of them let me know I have some 20mm here.!

  12. #19
    Yes, having some pictures would help. What do you mean by 2:1 ratio, does that mean that pulley diameter(or circumference) that's attached to motor is 2 times the ones attached to x axis?

  13. #20
    Quote Originally Posted by ivars211 View Post
    Yes, having some pictures would help. What do you mean by 2:1 ratio, does that mean that pulley diameter(or circumference) that's attached to motor is 2 times the ones attached to x axis?
    Ok I'll take pic for you tomorrow.

    The ratio works other way around. The driver is always expressed before the driven. So in this case the motor turns 2 revolutions while the screw turns 1 revolution.
    Or put another way the motor moves twice the distance the screw does. So with a 10mm pitch screw 1 revolution of the motor will equal only 5mm movement not 10mm or put another way only half turn of the screw. This gives the same resolution as 5mm pitch at 1:1 ratio but with the added affect of increasing torque but at the cost of speed. Now because the Pitch is higher the same speed is achieved as 5mm pitch at 1:1.

    This won't affect you because your not using long screws but the other benifit of using higher pitch screw with a ratio applied is that screw speed is reduced for the same speed as lower pitch screw at 1:1 ratio so reduces chance of whip on long screws. But again at the cost of speed compared to same screw at 1:1 ratio.

    Look here for a simple explination of ratios etc. Gears Index Page

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