CNC controller

Discussion in 'CNC machining projects' started by ddmckee54, Sep 12, 2019.

  1. ddmckee54

    ddmckee54 Silver

    What are you guys using for a controller on your CNC's?

    The last CNC machine I built ran off TurboCNC so I'm looking to step up to something that's using technology that's at least in this century.

    I'm in the process of designing/building a CNC router and I'm not sure which way to go. I'm currently designing around a 48"x24"x6" working volume and planning on using NEMA 23 steppers for the X, Y and Z axis. I'm not planning on, and don't need to run this at blinding speeds, I figure that rapid travels in the 125"-150" per minute range are more than enough. I'll be cutting mainly wood and plastic with MAYBE some non-ferrous metals thrown in at greatly reduce feed-rates and DOC. The spindle will either be a Bosch Colt compact router, that I already have, or a Chinese spindle in about the 1KW range.

    I have looked at the following:
    Mach 3/4
    Flashcut
    LinuxCNC - I don't have a Linux machine but I'm including it because somebody would say I need to use it.
    Acorn Centroid
    TinyG
    Arduino GRBL

    I know each one has advantages and disadvantages. What are you guys' using and why?

    Don
     
    Last edited: Sep 12, 2019
  2. Jammer

    Jammer Silver Banner Member

    Mach 3 works for me and it was what I could afford at the time.
     
  3. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Don, are you a member of any of the CNC Router forums or blogs at the manufacturers sites? If you search it you'll get plenty of hits. -Might get the latest skinny.

    Best,
    Kelly
     
  4. DavidF

    DavidF Administrator Staff Member Banner Member

    I'm running mach 3. But have been thinking of switching to linux...
     
  5. ddmckee54

    ddmckee54 Silver

    Kelly:

    Yeah, I'm a member there, just haven't been active for a long time.

    Part of the problem is that there are many camps and each camp has it's own followers, sometimes rabidly so. I'm trying to find out some of the whys' in "Why did you do it that way? I can afford to do it right this time, I just don't want to have to do it right multiple times.

    As far as I can tell, the big three: Flashcut, Mach 3, and LinuxCNC, all do pretty much the same thing to varying degrees of accuracy and smoothness. I can pretty much guarantee that what I will be doing will NOT push the software to the point that it I would notice it out-performing the others.

    With the possible exception of Acorn, I think all the others that I have listed will require some type of interpreting software to spoon-feed the g-code to the stepper controllers, still researching that.

    Don
     
  6. Gippeto

    Gippeto Silver

    My little machine came with and runs Arduino GRBL...as will the one I'm building. Dads machines (router and Taig mill) are running Mach 3...I've started learning a little Mach to better decide whether to switch them over to GRBL. GRBL and UGS are open source, well developed and do everything I need at this point, and IMO, they are super easy to use...I've got it setup via bluetooth on a tablet which is super convenient.

    Al
     
  7. ddmckee54

    ddmckee54 Silver

    Gippeto:

    It's my understanding that GRBL doesn't do smooth arcs, but rather divides the arc up into a gazillion short - but straight lines. Is this the case, and if so has this been an issue? What are you using your machine for?

    I have always liked the idea of using an Arduino, one of my 3D printer is running on an Arduino. The reason that I was leaning away from them was my understanding of how arcs and curves are dealt with by their associated software.

    This is one of the reasons that I started this thread, to talk to people that use the various controllers/systems and ask what they like and do not like about that system.

    Don
     
  8. Gippeto

    Gippeto Silver

    I mostly use it for foam patterns as it's pretty light duty. GRBL may well divide the arcs up, but I have not noticed any issues related to it. Most of my parts have more than one arc or curve.

    Al
     

    Attached Files:

  9. 509Maker

    509Maker Copper

    I have used Mach, uccnc, LinuxCNC and GRBL ( with Bcnc ). All work very well. With Nema 23 motors on all axis I would recommend picking up a Gecko G540 and giving all options a go, to see what you like. For mach / uccnc I have always used the uc300eth ethernet board. Linuxcnc the Mesa 7I92H ethernet board. With grbl I just designed my own G540 plug and play usb controller. It is open source "Here" feel free to make one. With the projects I tend to tackle on my routers I have never reached a bottle neck with grbl or noticed any quality issues arising from how grbl process g-code.
     
  10. Guster

    Guster Silver

    I'm planning to run a RichAuto A11 DSP on my current build. Uses a pendant style DSP with a fully featured breakout board that supports a wide variety of configurations. This is quite a common component in midrange commercial CNC router machines which Fusion360 has post processing support for. It removes the need for running a dedicated PC for CNC control thought it is a little harder to use compared to say Mach3 or Linux CNC alternatives. It also comes in other flavours for CNC plasma cutting or multi-axis milling. As well as other variants with touch screens that support running interactive g-code processing.
     
  11. garyhlucas

    garyhlucas Silver

    I just finished cutting most of the frame parts for a 24” x 48” x6” CNC router for the high school FIRST robotics team. Very special design. Overhead bridge design pulls the X axis rails in so it fits through a standard school door. So it has a very rigid 8020 aluminum cross braced frame and 8” casters. The frame design allows passing a full 4’ x 8’ sheet through.

    It is also intended primarily for metal cutting. There is a full coolant pan under the table, a built in vacuum, air compressor and vertical slide doors on all sides with sound proofing. It has a large electrical cabinet and an industrial PLC in addition to what will likely be an Acorn CNC controller.
     
  12. master53yoda

    master53yoda Silver

    I have had fairly good luck with Arduino running GRBL the older version was 3 axes only because it was based on a Arduino uno and limited ram When the mega2560 came out the ram and control point issues were no longer there. the new GRBL 1.01 is supposed to handle 5 axes plus spindle, cooling, door interface etc. I have used the older version to run a long-arm quilting machine for my wife. I'm waiting for ramp6 kit a and intend on building a 3Dprinter when it gets here supposedly next week. eBay show it arriving in the states earlier this week.

    Art b
     
  13. ddmckee54

    ddmckee54 Silver

    Thanks for the replies everybody.

    For better or worse I finally pulled the trigger and ordered some motion hardware. I've ordered, and received a DDCS v3.4 standalone 4 axis controller. I've got Nema 23 270 oz-in 3A stepper motors, M542T 4.2A stepper drivers, and a power supply for the drivers, that I believe is 36VDC @ 9.8A, on order that are due to arrive any day now. I ordered a 3 axis motors/drivers/power supply kit, and a single axis motor/driver kit. I couldn't find a 4 axis kit with the motor/driver combination that I wanted, so I went with a 3 axis kit, + 1. I'll need to get another 36V power supply, the 9.8A power supply that I've got ordered isn't going to handle four 3A motors. What can I say, it came with the 3 axis kit and that kit was a decent price.

    Right now I'm waffling over whether go with lead screws or belt drives. Belt drives would give me faster travel speeds, but I'm not building something that would require high speed travel. I'd like to use lead screws, but I'm worried about the screws whipping during rapid travels, especially on my X axis. I'm planning on 1200mm of usable workspace on that axis so I'd be looking for a minimum length of 1500mm lead-screws, maybe more. I did find a couple of reasonably priced 3/8-12 x 6' leadscrews. I think 3/8" would be about the minimum diameter leadscrew I'd go with for that length. A bearing at both ends should help to minimize the whipping of the leadscrew.

    Don
     
  14. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    There's a mind numbing amount of linear rail/lead screw/motion control stuff out there. Not really sure what you mean by lead screw whipping. Wouldn't you always have both ends of your lead screw anchored and preloaded in bearings?

    I've bought from this seller.

    http://www.ebaystores.com/imsrv

    and...

    https://openbuildspartstore.com/

    Best,
    Kelly
     
    Last edited: May 4, 2020
    master53yoda likes this.
  15. master53yoda

    master53yoda Silver

    Don
    on my electronic gearbox Im working on for my 36" lathe I went to stand alone driver and just tapped into the points needed where the DRV8825 Stepper drivers would have plugged on the Arduino CNC interface board. that way I still had all the connection points for end switches etc. and if I later decide to CNC my lathe I'm all ready half way there.

    On your belt or leadscrew question when I did the 10 ft longarm I used belts but on the long axes when changing direction I had to slow down the acceleration to compensate for belt stretch. It had to do with the mass of the sewing machine setting on the table that was being moved. In your instance will there be an inertia issue when changing directions if so a belt may not work at 6 ft.
    how fast will that lead screw be moving on a 3d printer. If your driving a fair amount of weight like on a lathe crass slide 3/8th is really light, my lathe uses a 3/4 the earlier models had 5/8 with wipe issues. and that is on a 36" lathe.

    A
     
  16. ddmckee54

    ddmckee54 Silver

    Kelly:

    By whipping I mean that the lead screw is not remaining straight when rotating at higher speeds. This would be especially evident if the machine was close to the motor end of the lead screw, with the other end of the lead screw unsupported, and was making a rapid travel movement. The end of the lead screw would tend to whip around in a generally circular path. It can also happen if the lead screw is too small of a diameter and the length between the supports is too great, the lead screw starts acting like a jump rope. Regarding anchoring both ends of the lead screw, from what I've seen the answer is not all the time, it all depends on the length and diameter of the lead screw. I hadn't planned on a lower bearing for my Z axis lead screw, that axis will only move 150mm so it will be fairly short,and the z axis movement will be relatively slow. Even though it's short that lead screw, and all the weight of the Z axis, will hang from a pair of bearings supporting the lead screw. The motor bearings will not have to take any of the axial load from the lead screw.

    The Y axis will move 600mm so that will definitely have bearings on both ends of the screw. Again the motor bearings should not see the axial load of the lead-screw. Same with the X axis if I use lead screws there, no axial load will be transmitted to the motor bearings. Most motor bearings really hate axial loads.

    Master53yoda:

    This will be a gantry style machine with 2 X axis motors/lead screws, one on each side of the gantry. The X axis motors/lead screws will have to drive the gantry. The gantry contains everything for the Y and Z axis, and the spindle motor - which is a Bosch Colt compact router at this time. If I decide to go with a belt drive, I'd use a steel reinforced belt to minimize stretching. Even though a steel belt takes more power to drive, I'd think a pair of Nema 23 motors at 270 oz-in should handle the load. If not I can still upsize the X axis motors to 300 oz-in and not overload my stepper drivers, but it WOULD be pushing their limits.

    Don
     
    Last edited: May 4, 2020
  17. Guster

    Guster Silver

    Leadscrew whipping is where a long length of unsupported leadscrew develops a a harmonic oscillation that can become an eccentric motion at higher rotational speeds if it is not retained well. Often accentuated on the compressed side and may only show during acceleration or change in direction. Worst case think of a long thing piece of steel held in a drill and whipping around. The harmonics can cause binding in the leadscrew nut and the gantry to judder under motion. Causing premature wear and machining artifacts like "ringing". While good retention and preload minimises the effect, leadscrew diameter choice has the largest impact on leadscrew whip. Keeping in mind that effective material diameter on a leadscrew is much less that its overall diameter. Leadscrew cost also increases significantly with its diameter making it more of a difficult decision for budget builds.

    I would go no smaller than 1/2" over 1.5m given the gantry weight and cutting loads involved.

    Another great option when using belts is 'belt on belt' drive. Little more complex to build but removes many of the issues with traditional belt drive. Relies on using belts that mate perfectly and the static belt being securely adhered and held to the frame. Quite a few people using this now and lots of designs and pictures for ideas.
    [​IMG]
     
  18. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Certainly dependent on unsupported length to but the above seems to be both the cause and solution to the problem to me. Can't imagine it being an issue on your short Z. How long of an unsupported length are you talking on x or y?

    Never built a lead screw actuator that wasn't isolated from the motor with a coupler and bearings; usually preloaded back to back angular contact ball bearings but sometimes thrust bearings too.

    My machine is rack and pinion drive on both X & Y with dual Y rack & steppers. Only Z is lead screw. I didn't build it, I bought it........I have enough to learn becoming a proficient practitioner. ;)

    Best,
    Kelly
     
  19. garyhlucas

    garyhlucas Silver

    Kelly,
    Finally got a CNC router up and running? What are you using for CAM software? I use CamBam which I find is very easy to use and a good deal at $149. 40 sessions free before you need to buy it. Excellent support forum too.
     
  20. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    It's mechanically together but not quite up and running. I'll have to start a new thread so as not to hijack Mac's thread here.

    Best,
    Kelly
     

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