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  1. #1

    cutting Acrylic with New Machine

    After many struggles of my own making, I finally have my 1500x1500 machine up and running. I cut some 3/4 plywood yesterday at a pretty good speed, around 150ipm with no issues and a great looking cut.

    Today I tried cutting 15mm acrylic and had some issues with the machine stalling. I was cutting very conservatively, I thought. 18000rpm, 60ipm, .1" doc. I'd get about halfway through the cut and it would start stalling.

    My drivers are set for 1/8 microstepping and I have 48V PSU.

    Anyone have any ideas why this would be happening?

  2. #2
    Join Date
    Dec 2003
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    1206

    Re: cutting Acrylic with New Machine

    Not enough information.Spindle power?Stepper size?Drive mechanism?Cutter size and rpm?

  3. #3

    Re: cutting Acrylic with New Machine

    Ah, right.

    It runs on 1610 ball screws on all axes with a 2.2KW spindle. The steppers are Leadshine DM856. Motors are NEMA 23 425oz, 3.8 inductance.

    Cutter is 1/4" upspiral running at 18000RPM

  4. #4
    Join Date
    Sep 2012
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    228

    Re: cutting Acrylic with New Machine

    the spindle may be a little week... and the acrylic may be melting on.. causing even more load

  5. #5
    Join Date
    Mar 2003
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    35538

    Re: cutting Acrylic with New Machine

    Is it stalling while cutting, or during rapids?

    There should be practically zero cutting forces with what you're doing. (your RPM is likely way too high, btw).
    Gerry

    UCCNC 2017 Screenset
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    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)

  6. #6

    Re: cutting Acrylic with New Machine

    Yeah, that's what I thought too? It is stalling in the cut. Could the high RPM be melting the acrylic? The finish it's leaving is not great.

  7. #7
    Join Date
    Aug 2018
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    621

    Re: cutting Acrylic with New Machine

    Quote Originally Posted by Frankmali17 View Post
    the spindle may be a little week... and the acrylic may be melting on.. causing even more load
    I was wondering about it melting as well, don't think it has anything to do with the spindle power since I think the steppers are stalling not the spindle.

    Try 140ipm 16000 rpm leave the doc at 0.1 and see if you get better results you have way to low of a chip load for acrylic, if you're machine can't handle 140ipm try 100ipm 12000rpm same doc. Do yourself a favor and start reading up on chiploads and search for recommended ipt and look up some of the feeds and speeds calculator and start playing around with them. You just need to know the correct chiploads for the type of material you are cutting as well as the recommendations from the tool manufacturers. Once you know your machine limitations just try to get in the ballpark for the material and the endmill. For example acrylic recommend chiploads is 0.004-0.015 the speed and feed I gave you gives you 0.0045 and 0.0042, your current feed and speed is giving you a 0.0017 IPT. Alot of people try to slow down the feed rate, but unless you slow down the spindle your usually just going to dull your cutter, with 18000 rpm you would need to be cutting at 150 ipm to have a chipload of 0.0042. All of the information is assuming you are using a 2 flute endmill, if you are using any thing else the chiploads would be different than what I listed.

    Hopefully you can find some of the information I posted useful, if you make the changes and you are still having problems you will need to lower the spindle speed and feed rate while still keeping the proper IPT. You may find that you need to make some changes to your machine, but I would start with playing with your feeds and speeds first.

    Dan

  8. #8

    Re: cutting Acrylic with New Machine

    Thanks so much for the help! I will give these a shot tomorrow.

  9. #9
    Join Date
    May 2005
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    3920

    Re: cutting Acrylic with New Machine

    Something is seriously wrong here if you are stalling at 0.1”depth of cut in acrylic. If the cutter is sharp and you are not welding it into the plastic or plugging the flutes then I’d look into a mechanical issue. But before that take a good look at the cutter.

    The thing is a cutter can easily gum up on plastics due to excessive RPMs in the spindle and slow feed rates (actually the plastic itself can start to heat up too). Due to the high speeds one gets with router spindles you generally want with two flute or single flute cutters. These need to be run at tooth engagements that result in good chip removal and minimizes heating of the plastics. In any event looking at your cutter and the chips you are getting will tell you a lot.

    In any event, assuming that the cutter isn't causing the load, I’d take a close look at your build. It is very easy to have missed something in a build that will result in something coming loose. I’d even try some wood products again to see if your performance there is the same.

  10. #10

    Re: cutting Acrylic with New Machine

    Yeah, I don't get it. I tried plywood today @ 100ipm 18000RPM brand new and sharp .25 2 flute cutter .25" DOC and it stalled? It's like the motors have no torque? Changed it to .125 DOC and it did fine, but this thing should cut at these setting easily. I designed it to cut at at least 200ipm. It only seems to do this on the X axis, but Everything seems OK with the axis. Everything is straight, square and tight.

  11. #11
    Join Date
    Aug 2018
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    621

    Re: cutting Acrylic with New Machine

    Start with the simple stuff, loose wires bad connection, loose bolts and so on like Wizard suggested. I honestly didn't even think about that since you said you had no issues cutting wood. Welcome to the wonderful world of dyi cnc machines, honestly even a new factory built machine will break down on you. Look at the bright side since you built it you can work on it and don't have to pay a tech $150 hr to come out and milk his hourly pay on your dime. I would suggest posting some pictures that might help someone maybe point you in the right direction. Pictures of the machine electronic enclosure and so on, the more information you give the better chance you will have that someone will recognize the problem.

  12. #12

    Re: cutting Acrylic with New Machine

    Thanks for the help. I'll go over it some more and try to find something. Any chance it could be my microstepping at 1/8?

  13. #13
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    Re: cutting Acrylic with New Machine

    Quote Originally Posted by justicedavid65 View Post
    Thanks for the help. I'll go over it some more and try to find something. Any chance it could be my microstepping at 1/8?
    I doubt it, that's really low so it shouldn't do much to the torque. Maybe one of the wires came loose, and the motor isn't running on all the windings. I've seen it happen to someone else and it caused him to lose power and was having a similar issue.

  14. #14

    Re: cutting Acrylic with New Machine

    As usual, the problem is me, not the machine. I had my spindle wired wrong and the bit was spinning CCW instead of CW. Once I changed that it's cutting like a champ. Just cut some maple at .25DOC 18000RPM and 150ipm and it didn't miss a beat. Tore right through it with a beautiful finish!

    Thanks for the help

  15. #15
    Join Date
    May 2005
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    3920

    Re: cutting Acrylic with New Machine

    Quote Originally Posted by justicedavid65 View Post
    Thanks for the help. I'll go over it some more and try to find something. Any chance it could be my microstepping at 1/8?
    Micro stepping is most likely not the problem.

    If it is failing in plywood now something has changed since your startup. Because this is a new build, and the problem cropped up quickly, I’d go back and look at the machine mechanically.

    By the way this is a good reason to write some hand written gcode for maintenance of the machine. You will need nitially wany two sets of programs. One of each axis that runs that axis at its rapid speed back and forth. Another for each axis that runs the axis at the full feed rate speed. In both cases run with the spindle off. Such programs can often help find a binding problem because you can actually hear the change in torque demand. That is the system will labor through moves and you can often hear the problem.

    In any event you indicated above that you think the problem is X axis related. The question then becomes how is the axis drive set up, is it dual leadscrew? How the X is built will define how you go about debugging it to some extent. In any event I’d disassemble the dive enough to verify that the X isn’t mechanically binding. Upon reassembly I’d look real close at your motor to leadscrew connections. A set screw that slips under load can easily lead to a twisted axis.

    By the way it might help to better define what you mean by stalling. Are we talking hitting a brick wall, a slow down to zero movement or some missed steps.

    If there is a sudden stop for instance (hitting a brick wall) there are a number of possibilities. One of these is a ball catching in a bearing someplace in the system. Sometimes these catches are hard to find as the condition goes away once the system is unloaded. Sometimes you can feel the bad bearing while rotating different parts of the machine, sometimes you don’t feel a thing. It’s about finding the right spot. Another possibility is the rotor locking to the stator of the motor. Steeper don’t usually lock up completely but the extra drag will result in failure to drive the load.

    With respect to binding it is easy to have things misaligned in such a way that the binding progressively loads the motor until it fails. With a stepper that might mean seeing the motor suddenly start loosing steps. This usually happens in specific places on an axis. On a servo you might see progressively increasing following error until it faults and you may physically see the axis slow.

    There are potential electrical issues too. For example are all three axises moving when this happens? If so there could be a power supply issue. I might go back to manually developed code and run each axis alone cutting wood. The idea here is to run the axis with a minimal load upon the power supply. Infant mortality is very real in electronics so you can’t dismiss a bad drive or or other component. If it get to this point have a plan to swap components between working axis. Swapping if done with care can isolate out dodgy components and is especially useful if you have no test gear.

    In any event I always start out with the elimination of mechanical problems. It is generally easy and quick on small machines.

  16. #16
    Join Date
    Aug 2018
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    621

    Re: cutting Acrylic with New Machine

    Quote Originally Posted by justicedavid65 View Post
    As usual, the problem is me, not the machine. I had my spindle wired wrong and the bit was spinning CCW instead of CW. Once I changed that it's cutting like a champ. Just cut some maple at .25DOC 18000RPM and 150ipm and it didn't miss a beat. Tore right through it with a beautiful finish!

    Thanks for the help
    Oops

    Glad you got it figured out, still try out the feeds and speeds I gave you and let me know how it works.

    Thanks

  17. #17
    Join Date
    Mar 2003
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    35538

    Re: cutting Acrylic with New Machine

    I had my spindle wired wrong and the bit was spinning CCW instead of CW
    Smoke and burned wood will usually give that away pretty quickly.
    Gerry

    UCCNC 2017 Screenset
    http://www.thecncwoodworker.com/2017.html

    Mach3 2010 Screenset
    http://www.thecncwoodworker.com/2010.html

    JointCAM - CNC Dovetails & Box Joints
    http://www.g-forcecnc.com/jointcam.html

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)

  18. #18
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    Aug 2018
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    Re: cutting Acrylic with New Machine

    Quote Originally Posted by ger21 View Post
    Smoke and burned wood will usually give that away pretty quickly.
    Gerry dumb question but I'm going to ask any way.

    How the hell was he able to do the first cut in wood with out smoking the endmill?

  19. #19

    Re: cutting Acrylic with New Machine

    I was thinking the same thing and the only thing I can think is that I must have inadvertently had it in reverse on the VFD. There is a forward/reverse button and I must had hit it accidentally.

  20. #20
    Join Date
    Mar 2010
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    621

    Re: cutting Acrylic with New Machine

    I did the same thing in a sheet of 6061 with my new spindle... my first thought was, "what piece of crap this spindle is..." my second thought was "what an idiot I am!"

    Adam,
    Gecko G540, Rack and Pinion Drives-X and A axis, 1/2-10 5 Start Acme-Z Axis
    4-THK HSR 25 Linear Slides, KL23H2100-35-4B, Power Supply-KL-600-48 48V

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