Aspire PP to wrap Y values around X

[greolt]

"It doesn't matter if the motion is encoded in gcode, sbp code, or hieroglyphics the math is the same"

I use gcode and Mach3 as my controller.

Mach3 has motor tuning parameters for each motor. Steps per unit, Max velocity and acceleration.

These are not set in gcode. They are pre set in the Mach program.

When ever any feedrate is called for in gcode, Mach will not allow a motor to exceed those pre set parameters.

I just assumed this was fairly standard method and Shopbot would be much the same. I guess I was wrong.


Greg

[eaglesplsh]

I updated my own PP with help from Dana's code - works great!

After a bunch of trial and error I found that you don't need to include the MB rate calculations in the "header" section, "feed move" section, or the "new segment" section. This calculation only needs to be done in the "first feed move" section - which is used to create the first M5 command after every Z height change.

Cutting out all the extra calculations could be important to the quality of your final cut and may drastically decrease your cut file size.

Arc cuts aren't implemented in the 4th axis, so anytime you're cutting along a curve you're cutting lots of short vector segments. The control software doesn't seem to like recalculating the feed rate after every 0.005" move - when I tried pocketing out a circle at 5 ips on the 4th axis I got stuttering slow speed moves - even though I have a new Alpha machine running on a 1 yr old computer.

As soon as I trimmed out all the extra calculations my curved movements went back to being smooth and ran at full speed.

[greolt]

Russ

I tried a simple file with Dana's PP and this is just a small section from it,

M5,,-0.3656,0.9500,-54.1241
if 0.9500 > 0 then &AngularFeedRate=(180*0.6)/(3.14159*0.9500)
if &AngularFeedRate > 720 then &AngularFeedRate = 720
VS,,,&AngularFeedRate
M5,,-0.3487,0.9500,-54.4919
if 0.9500 > 0 then &AngularFeedRate=(180*0.6)/(3.14159*0.9500)
if &AngularFeedRate > 720 then &AngularFeedRate = 720
VS,,,&AngularFeedRate
M5,,-0.3318,0.9500,-54.8412
if 0.9500 > 0 then &AngularFeedRate=(180*0.6)/(3.14159*0.9500)
if &AngularFeedRate > 720 then &AngularFeedRate = 720
VS,,,&AngularFeedRate
M5,,-0.3149,0.9500,-55.1719
if 0.9500 > 0 then &AngularFeedRate=(180*0.6)/(3.14159*0.9500)
if &AngularFeedRate > 720 then &AngularFeedRate = 720
VS,,,&AngularFeedRate

It continues like that for the whole code.

Can we take a peek at your new PP?

Greg

[dana_swift]

Russ thanks for the experiment, I will update my PP. I had wondered about whether the speed code was needed after every line or just some of them, and so I did what would amount to a "belt and suspenders" approach. Overkill apparently!

One of the great things about the forum is the collaboration. This PP is just getting better all the time.

Thanks Russ and Greg.

Greg- FYI, SB3 does not have tweaks on motor parameters so the test is necessary. I wish it had real acceleration limit terms in "G's" so I could limit accelerations based on the mass of the load on the table and the torque capabilities of the motors. As it is, its a meaningless "ramp value". So much for all those physics classes eh?

D

[rcnewcomb]

Russ,
Good catch about my post processor not handling subsequent speed changes. I always run my toolpaths in separate files so I didn't catch that in my testing.

[eaglesplsh]

I'm happy to share my 4th Axis PP, which now includes Dana's constant velocity machining code, etc... in case it helps others to improve their own code.

WARNING: DO NOT TRY TO USE THIS PP ON YOUR MACHINE!!!

My PP is loaded with stuff that isn't relevant to your setup. I use it to control: Auto Tool Changer, dust collector on/off, dust collector blast gate open/close, installation/removal of the dust shoe, vacuum hold down on/off, automatic changes to the working coordinate offsets, and some other fun stuff. This code will cause error messages for the rest of you and may attempt to physically run your gantry off the table. Consider yourselves warned!


Most of my custom code is in the header/footer sections of the file. The part that relates to this discussion is:

begin FIRST_FEED_MOVE

"'UPDATE FEED RATE FOR CONSTANT VELOCITY MACHINING IN B-AXIS"
"if [Z] > 0 then &AngularFeedRate=(180*[FC])/(3.14159*[Z])"
"if &AngularFeedRate > 720 then &AngularFeedRate = 720"
"MS ,,,&AngularFeedRate"
"M5 ,[Y],[Z],,[X]"

Thanks to Greg, I added the ROTARY_WRAP_X = "-" at the beginning to match my rotation direction with standard convention.

I use working offsets to temporarily setup the center of my 4th axis location at 0,0,0. You'll find a few places in the PP that include:

"JX %(1) + 4

[eaglesplsh]

Thought I'd add an update to this thread for anyone who's following along...

I tried running a 3D file that was tool pathed in PartWorks 3D and then imported into PartWorks 2D on the indexer... it doesn't look like the constant velocity machining technique discussed above will work in this case. There are many Z moves that happen without calling for "first feed move" treatment.

3D machining is so slow that it probably doesn't make a whole lot of difference, but I thought folks should be aware of the issue anyway.

[rcnewcomb]

Russ,
Can you post photos of some of your work? I'd love to see what others are doing.