Possible bug with CAM gcode output.

[Anonymous]

Hello fellow Fusion Cam fans,

I have been using fusion 360 for a while now and am starting to get used to it. I love the Fact that It is an all in one software, from sketch to 3d design to cam and then Gcode. I have a small CNC Mill that I machine mainly soft plastics, glassfiber sheets and wood. I used to use freecad and a programm called CAMBAM to do my designs and make the Gcode. I have been doing it like this for a few years now and everything worked fine, It was just a long process.

Recently I have designed a part in Fusion 360, a new hoover fiting for the mill. Through the CAM tab in fusion made the requred toolpaths and outputed the gcode using the "mach3mill.cps" postprocessor. I ran some simulations before and it all seemed fine.

Now comes the problem....

The Cam tab has 4 process's, 3 cut fine but on the 4th it starts to drift on the y axis.

1. A slot around the outer edge.(2mm endmill)

2. 4 Holes for magnets.(6mm endmill)

3. 2 large holes. (6mm endmill)

4. The outer shape. (6mm endmill and Here's the problem)

It appears to drift upwards on the y axis by about 1mm on each pass around the outer edge. I have ruled out backlash and am 99% sure that its not missing steps. (If it is missing steps its doing it in exactly the same places, Everytime I run the code and only on the last toolpath.... VERY unlikey) It is as if it happens gradually over the course of one time around, There is at no point a recognizable "step". What I dont understand is why it can cut everything else fine but not the outside cut, In my opinion it has to be a software/ gcode problem.

I have also tried a few different things like:

- Plunge into matirial and ramp into material

- With and without lead-in and lead-out.

- Changing the cutting feed rate.

.... But the result was the same everytime.

I must admit that fusion can do alot more than what I understand sometimes, maybe I have missed something but I am currently at a loss and don't know what else I could try.???? Any help would be Greatly appreciated!

Here is a link to the model im trying to cut: http://a360.co/2dtOIje

... And I have attached some pictures to show the result after cutting (I didn't let it run until the end as i could see it wasn't correct)

Luke

[daniel_lyall]

@Anonymous I would not rule anything out of hand to you know for certain it is not the problem.

I have seen this problem many times I have even had it.

for me it was 3 things wrong size stepper, electrical fault and the accluration to low on the X axis putting the Y axis out.

Mach 3 works on time off flight X, Y and Z need to get to a point in time at the same time if one of the 3 are held up for some reason it is going to be out on one axis if it happens again in the same run it snowballs to it is way off.

you said you rebuilt it years ago and it has been running fine for years, then bang problems. have you checked everything since then, a just tight what ever nut bolt, what ever if you have a slight jam up it will slip and it will be out.

a little bit off RF or EMF can make it go bad it can be random as hell.

you need to rule out everything it does not take long if you go at it one thing at a time.

the cut is melting at one point that may jam it (or even rack the Y axis),  so it could be holding A axis back if it loses a step or 3 it is going to be wrong for the rest of the cut a axis will have lost time, and it will just get worse as the cut goes on.

and use plastic O flute cutters for plastics that have a low melting point, they chuck the chips straight up. you cut plastics like stainless steel get the heat out with the chips

@HughesTooling I find useing Radius to be way better than I and J, the test files I run at services time are done with V carve pro and they show up any problem there is they use I and J,

doing the same thing with fusion useing R those problem don't show up.

[Anonymous]

Ok.... Now I really am stumped???

I have just inspected the machine to see if i could find any faults... nothing. No noticable backlash, everything is tight and all the conections look fine.

So I thought to myself what if I change the orientation of the model in the "Setup" under fusion 360 cam tab. I changed it so the Y axis is aligned with one of the sides and then outputed the Gcode with no further changes. I then did a cut  above the stock in the air and was expecting to see the Y axis to be off by about 10mm as before..... but it wasn't.

I then put in a endmill and cut the part, it all went fine. The problem is now that i dont understand why ??? How would just changing the model orientation affect this.

I have attached the code i just run which cut fine and also a picture to show how it was mounted on the machine, In my first post their is a photo of who it was mounted originaly.

@RandyKopf @xander.luciano On this run I lowered the spindle speed to 8000 and uped the feedrate to 1000, The result was much better. bigger chips and much less melting. Thanks!!!

[RandyKopf]

Dang so yeah maybe there was something in how that last toolpath originally got defined. The results are much better. You certainly knew the machine was capable. It almost acts like a separate origin or something was in effect but the important thing is it's working now. Typically in 3Axis work each tool path just inherits the WCS and tool orientation and you don't need to touch them. Though the software allows for those values to be changed espectially for multiaxis work. Glad you got it going!!!

[daniel_lyall]

@Anonymous it show that there is a problem with X or Y.

as a test what you should do is run a 3D toolpath of something that has in the range of 100,000 moves in the X and Y have the long axis in Y then run it again with the long axis in X have it so you have a straight edge on one side of the cut then you can eyeball it when it is running and if it starts to drift you can stop the run.

what you have run into is a problem Mach3 has.