4axis feed rates in mach3


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    Exclamation 4axis feed rates in mach3

    Newbie alert! Built a 4axis for cutting wings, but struggling with setting up feed rates. All axes work perfectly in direction and speed when operated independently (G01). I have XY set up on my left, and AB set up on my right. My problem is when I operate X and A (both parallel to each other, front to back). When I cut with G01, the feed rate is slower than when I run X or A independently under G01. I suspect that somehow the software thinks the X and A axes are at right angles to each other and is slowing down each axis to get the resultant vector feed rate??? How do I tell the software (mach3) which axes are parallel (and don't need vector compensation for feed rate), and which axes are at right angles (X and Y, A and B) where vector federate compensation is needed.

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    Default Re: 4axis feed rates in mach3

    This video worked for me:



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    Default Re: 4axis feed rates in mach3

    I used that video to set things up, so all pin assignments, motor tuning, soft limits and axis movement directions are good. My issue is specifically with feed rates when using my two horizontal axes (X and A) simultaneously. In G0 they travel at the right speed. In G1 they go slower than expected. I expect this from axes at right angles to each other (when you want a feed rate of 100 resultant, the speed on each axis will be less than 100). However when axes are parallel you need each axis to run at 100 to get a wire speed of 100.....hence the question on how to tell the software the axes are parallel



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    Default Re: 4axis feed rates in mach3

    What program are you using to write your G-code? You might have more luck asking for help specifically with the program you are using to cut wings. I use Desk CNC to write my G-code and the feed rate comes out right.



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    Default Re: 4axis feed rates in mach3

    I use Profili Pro. I don't think it's the Gcode though. Even a basic test shows the feed rate issue. When I jog or G0 the speed is fine. So a Gcode command of G0 X100 A100 gives me 100mm at speed 200mm/min (my motor tuning speed). When I program G1 X100 A100 F200, I get a INDICATED speed of 200, but if I measure the ACTUAL speed of the wire it is actually 140. This just happens to be 200 x Cos45, which is what you would calculate if the axes were at right angles and the resultant was 200. Hence my question about how mach3 calculates the resultant feed rate without knowing the axis angles?? I think they assume the axes are always at 90 degrees to each other, which is mostly true in milling or plasma cutting, but not true in my application. Instead I am almost trying to control two separate two axis machines simultaneously. I appreciate the help - I was hoping there was some setting I may have missed, but the more I test, the more I am convinced it may just be the way the software is designed. There may be a way to fool the machine in Gcode - if only I could put in a formula for Feed rate based on X and A axis movement. But that does not seem possible - or do you have any ideas??



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    Default Re: 4axis feed rates in mach3

    Slave axis.
    If A axe is slaved to X, and B is slaved to Y then you can control only X and Y axis and the other two axis (A,B) are going to do what their master axis are doing.



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    Default Re: 4axis feed rates in mach3

    Thanx Mark, problem is that the root and tip profiles are different, and cannot be cut with slaving. It solves the feedrate problem, but introduces another. From the deathly silence on this subject I suspect that this is just a built in characteristic of the product, and nobody is going to man up and admit it. Since there is no way to configure the relative positions of axes there is also no mathematical way to calculate resultant speed. So speeds are calculated based on all axes being at 90 degrees. It doesn't mean I cannot use the product- it just means I have to "cheat" the feedrate.



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    Default Re: 4axis feed rates in mach3

    I just have cut a tapered foam wing with my 4 axis cnc home made cutter. Root rib profile is almost double size of tip rib profile, and naturally root profile axis of the cutter has to move faster than the tip profile axis of cutter. That is a must, because it is the only way for the wire to finish at the last points of profiles at the same time, ofcourse root and tip profiles has to be drawn with same numbers of nodes (dxf file).



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    Default Re: 4axis feed rates in mach3

    Hi Mark, do you use axis slaving as you suggested? If you did, then I do not understand how you cut a taper because both pairs of axes should exactly duplicate the master axis (A follows X, Z follows Y). I understand that feed rates will differ on each side, based on the profiles to be cut. However, try the following on your machine and tell me what you get. On your two horizontal axes (mine are X and A), set a G1 speed of 120 mm/minute. Program it to run 120mm distance on both axes simultaneously. This should take 1minute. My machine takes 85 seconds - which happens to be 60/sin45 - which is what you expect if the X and A axes were at 90 degrees to each other.....let me know how long yours takes! On the other hand, try this exact same test using only a single axis (say X) and again time the result. Mine gives exactly 1 minute as expected. Again, I would be interested in your result!!



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    Default Re: 4axis feed rates in mach3

    Sorry for confusing answer, ofcourse for tapered wing I do not slave axis, i suggested to you to slave axis because i thought it may solve your problem...
    I will perform the test asap.



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    Default Re: 4axis feed rates in mach3

    I performed the test on my machine and everything is ok, every axis is traveling at exact time and distance (120mm for 1minute at speed 120mm/min)...
    I can show you how my settings look:
    4axis feed rates in mach3-untitled-gif
    4axis feed rates in mach3-untitled1-jpg
    Maybe that is what causing your problem, check it and let me know.



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4axis feed rates in mach3

4axis feed rates in mach3