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  1. #11
    Thanks for the info guys.
    The power supply build looks a lot less scary than I expected, and I will defiantly consider this when I get around to buying electronics.

    Regarding drivers I plan on just using 1 motor to drive both Y axis screws, so will go with the cheaper drivers.
    Does anyone have any thoughts on how well a single 3Nm motor will move a 40Kg gantry, assuming im using 1610 screws and ~70V PSU?

    Other than noise, are there any other major benefits of digital drivers over analogue drivers?

    At the moment I am finalising the mechanical side of the design, particularly the stepper motor brackets and connection to the ball screw.
    The plan is to use 16mm HTD belts on all axis.
    To connect the two Y axis ball screws I will go with the setup jazzcnc sugests here
    http://www.mycncuk.com/threads/4513-3-Axis-CNC-router

    I just need to get a custom end machining on the ball screws so I can fit 2 pulleys on the drive end. All 3 X and Y axis screws are the same length, so will just get the same extra long end machining on all for simplicity.

  2. #12
    My thought is ditch the 1610 for a 2010 with BK15/BF15 you can spin it 30% faster before it whips (Ballscrews become skipping ropes at a certain speed the thicker it is the quicker you can spin it)

    Also if going the single motor, dual ballscrew route cnc4you do a 4nm nema 23 not sure how good it is but worth investigating.

    Also the prices of Hiwin's from cnc4you is very good, the rail is clone but the carriages originals I intend to buy mine from there for my upgrade.
    http://www.mycncuk.com/threads/10880...60cm-work-area My first CNC build WIP 120cm*80cm

    If you didn't buy it from China the company you bought it from did ;)

  3. #13
    1610 screws are a good choice for X & Y with 1605 on Z. With a cutting area of 600x600 you could use just one screw for the Y put up the centre. Get the end machining to suit the machine it makes no difference to the supplier.

    I would not buy any electronics until you have the frame built. Re the Spindle in post #1 The water cooled ones are very quiet and generally cost about 210 inc. the VFD that drives it.

    Good luck with the build.
    ..Clive
    The more you know, The better you know, How little you know

  4. #14
    Quote Originally Posted by Desertboy View Post
    My thought is ditch the 1610 for a 2010 with BK15/BF15 you can spin it 30% faster before it whips (Ballscrews become skipping ropes at a certain speed the thicker it is the quicker you can spin it)
    Nope bad idea with nema 23 motor.!! The inertia of the larger diameter screw and ballnut means more load on motors and less speed before torque falls away.
    However there is one way to use 20mm screws while keeping same speed and lower whip. Use 2020 and gear 2:1 this increases torque and halfs the screw speed while keeping same speed as 10mm pitch.

    DIYCNC:

    There's massive difference between Analog and digital drives. Night & Day difference don't buy Analog drives you will regret it.

    Watch or should say listen to these to see difference. Same machine same Motors only change was drives.

    Analog https://www.youtube.com/watch?v=WnuLnKtqDX0
    Digital. https://www.youtube.com/watch?v=K2-Aub2fetw&t=4s
    Last edited by JAZZCNC; 24-01-2018 at 10:09 PM.

  5. #15
    The critical speed for these 16mm screws (assuming a 13mm min diameter) is over 2700rpm, thats a whopping 27m/min. I think 16mm will be OK.

    Thanks for the stepper driver advice JAZZCNC.

    How do you guys attach linear rails to a steel frame. Do you just drill and tap straight into the 3mm wall?
    An M5 screw has 0.8mm pitch, so will be over 3 full threads in the steel, which is the rule of thumb iv come across a few times.

  6. #16
    Quote Originally Posted by diycnc View Post
    The critical speed for these 16mm screws (assuming a 13mm min diameter) is over 2700rpm, thats a whopping 27m/min. I think 16mm will be OK.
    Don't get caught with the Critical speed trap doesn't often work out that way. So many variables come into play to screw the job up.

    Let me put it this way you wouldn't find me using 16mm screws much over 1600mm on any machine I build and even then they would have fixed end BK bearings on both ends to help support.

    Yep M5 screws are ok in 3mm box provided you don't swing on them with breaker bar. Make sure you loctite them.
    Last edited by JAZZCNC; 25-01-2018 at 09:51 PM.

  7. #17
    Quote Originally Posted by diycnc View Post
    The critical speed for these 16mm screws (assuming a 13mm min diameter) is over 2700rpm, thats a whopping 27m/min. I think 16mm will be OK.
    I am using 1605 screws driven directly with NEMA23 motors and get more than enough speed with that solution. My X and Y has 9m/min and Z has 7m/min. Stalling speed is about 11m/m on all three. My machine is though a moving table type, which I think is better for DIY because it is easier to make and more rigid than a similar one with moving gantry would be.

    Here is a short video, running all axes at 10m/min.



    I am using analogue drivers, DQ542MA and it may be better with digital drivers, but the biggest difference in speed is made by the PSU which is based on toroidal transformer. The second difference is the external motion controller I am using (UC300ETH).

    Speed wise I don't think Arduino would be an issue actually. I am running a 3D printer with Arduino and that 3D printer has even more speed than my CNC, currently has 15m/min on X and Y and 5m/min on Z but the Z is driven with simple dual 8mm threaded rods with 1.25mm pitch. Though I am using A4988 drivers, I am pretty sure that I could drive my CNC with the same Arduino but with the drivers from my CNC if I wanted to. Pulsing is generally not the problem, the problem is the drivers and the power supply. To get the speed I have in my printer I changed the delivered 12V PSU to a 24V PSU and that made a HUGE difference. Of course, if I'd run the CNC with the Arduino board (GT2560) I would not be able to use UCCNC or Mach3, but in theory it should not be an issue.

  8. #18
    Quote Originally Posted by Desertboy View Post
    Also if going the single motor, dual ballscrew route cnc4you do a 4nm nema 23 not sure how good it is but worth investigating.
    I have only ever used these motors along with their "digital" DSP drives - the pair make a great combination.

  9. #19
    Quote Originally Posted by diycnc View Post
    Whats so great about A882 drivers, Iv seen a number of people recommend them.
    Leadshine are a brand name already that is proven these last years for top quality and reliability. Or you could buy a copy of a copy and cross your fingers it will work properly.
    project 1 , 2, Dust Shoe ...

  10. #20
    Thanks for the advice. I will defiantly use fixed supports on both ends of the ball screw. it will add no extra cost, and as JAZZCNC suggests will improve rigidity.

    I have been working through some of the final details of the design. major changes since last time are i have added the motors belts and pulleys.

    Y axis motor is attached to the gantry end plate (which is now 15mm thick, 10mm just look to flimsy!) with 4 50mm long spacers. 1:1 drive to the screw is achieved with two 15 tooth htd 5 pulleys and 15mm wide belt. Can anyone suggest if this is enough teeth on the pulley, or point me towards the datasheets and formulas to work it out. i assume there is a max load per tooth to keep below.
    Click image for larger version. 

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    X axis motors is attached the base frame with a long 5mm thick steel plate (I think i need to added a stiffener to this, looks very long and floppy at the moment!). The motor hangs down quite far to avoid the piece of extrusion connecting the bottom of the gantry end plates. I tried removing this extrusion, and replaced it with two small plates to connect the ball nut to the end plates, but a little FEA showed this was a very bad idea! The long end plates twist allot!!
    1:1 drive to screw again with 15 tooth pulleys. I can increase to bigger pulleys here if needed.
    Larger taper lock pulleys and 15mm wide belt are used to connect the two screws. I will size the pulleys later to suit the available belt length and tensioner adjustment. Belt tensioner will just be couple of bearing on bolt in a slot, no need for anything complicated here.
    Click image for larger version. 

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    Next thing to do is add all nuts and bolts to the model to make sure nothing clashes!

    I also managed to pick up a used kress 1050 for little over 100. Would rather have one of the Chinese water cooled ones that everyone else uses, but at 300+ they are pricey. If i dont like the Kress i can always sell it on and probably get back all my money anyways.

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