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Modify post processing script to move spindle start, sync coordinate axes and not go "home" at the end

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Message 1 of 4
jeff7RZ4Q
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Modify post processing script to move spindle start, sync coordinate axes and not go "home" at the end

I am using the very open source 3018 pro cnc that can be found in many places for under $200, which doesn't seem to have a machine in the fusion library.  And I use the generic grbl (although testing the haas generic also produces the same result) which produces the following 3 features that I would like to change.

 

1) the very first thing the machine does is start the spindle.  This is even before starting to move to the proper location for the first operation.  I find this to be dangerous because if the machine is left in a state where moving will hit something, instead of just the bit being damaged, the stock could be damaged too.  a better option to me is to change the spindle start to right before the first feed for a cut. 

 

2) the coordinated axes are different - there is the machine home position (using candle grbl program) and then the "home" position that fusion creates somehow.  In my case, the start reference point for the stock (a premade enclosure I am just making cutouts and drill holes in) is x-68 and y+120 away from where the home on the part is.  this means that after the final milling operation, the head moves all the way to a "neutral corner" and the spindle is still on again, although in this case the motion is more annoying than dangerous.  making the machine and reference coordinate systems the same would just move the spindle right where it started from.

 

3) the last command is to go "home", which for tooled cnc machines, etc, this is the norm, but for these generic very open source 3018 walmart machines, there are no tool holders, and it can just stop at any point and be done, so it doesn't need the additional travel of going to home then back to a start point. 

 

maybe i am asking too much, but changing the spindle start seems like a prudent option, the other two are a matter of preference.

 

my current method is to make the changes by hand editing the gcode, but being able to customize the post processor would be nice, in that if I forget to make the changes, it might be an unexpected operation that catching me off guard.

 

i looked for any of these options in the setup for the cam operations, but it doesn't look like any of these options exist - most likely since the 3018 machine is not in the fusion library.

 

any hints as to how to make some changes would be appreciated.

 

thanks

 

3 REPLIES 3
Message 2 of 4

Use this post.

1) you can go in there and re-arrange the spindle start command to be after the Safety Z move if you really want, but I would discourage this. 

2) "making the machine and reference coordinate systems the same " all comes from how you set the WCS in your program and if you are 0'ing the G54 on your machine, or running off of absolutes from the home position (G53)

3) This post allows for that. In your post window, set the x and y position to be 0. 

Please click "Accept Solution" if what I wrote solved your issue!
Message 3 of 4

Thanks for the reply and the code

 I will give it a try and see how it works

 

thanks

Message 4 of 4
jeff7RZ4Q
in reply to: jeff7RZ4Q

Hi,

 

imported this to use as the post processor, and the first thing that happened was that line 338 spit an error because the 3018 spindle is only rated to 3000rpm, while the code expects >8000 rpm.  setting that line to <1000 rpm as the spindle speed condition allowed the code to generate properly.

 

the behavior is different - the spindle rises before turning on, so that is pretty nice, but still moves with the spindle running.  not sure how common that is with cnc machines, as the first move is typically a significant move and why have the spindle run then? 

 

for example, here is the generated code:

G0 Z9
M9
T3 M6
S2000 M3 G4 P1
G54
M9
G0 X54.734 Y62.707

Z4

Z2

G1 Z0.3 F100

 

why couldn't it be:

G0 Z9
M9
T3 M6
S2000 G4 P1
G54
M9
G0 X54.734 Y62.707

Z4

Z2

M3

G1 Z0.3 F100

 

This makes the spindle move to the first position and the spindle starts right before starting the feed?  Z0.3 should still be above the work surface, giving a decent amount of time to spin up fully - mine spins up (to 2-3000rpm) probably in less than a second.

 

The first spindle rise is good though, and it should be enough to keep me getting into too much trouble.

 

The home command at the end is still going to have to be removed by hand.  In these 3018 machines, clamping the stock onto the platform is usually done with some of the clamp on top of the stock - which makes any big motions (like to a machine reference far away) pretty dangerous in that the spindle and bit can hit the clamping assembly. 

 

My use is mainly batch processes or testing, which isn't too hard to work with to remove the few lines of code.

 

thanks

 

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