View Full Version : Need Help! Post processor help

05-22-2015, 02:59 AM

I'm having a few issues setting up my post processor in Sheetcam for my floating head.

A bit of background.

Home built plasma table controlled by a Gecko G540 running Mach3. Floating head with a limit switch referenced to Z home.
In Sheetcam I am using the Mach3 plasma THC with scriber and backlash compensation as my post processor as I intend connecting a Proma THC shortly.

I set my switch offset to 12, set marker Z to nil, Ref home to true and slowRadius to true. Nothing else has been changed.

I have set up a tool for cutting 3mm sheet. My pierce height and cut height are both set to 4.8mm. Rapid clearance is set at 45mm and plungs safety clearance is set at 25mm

When I run the post and open it in Mach3, the issues begin.

The G code is as follows:

G00 X72.6171 Y69.4743
G92 Z0.0
G28.1 Z30.00 F6000.0
G92 Z0.0
G00 Z12.00
G92 Z0.0
G92 Z4.8000

I understand the rapids, the resetting of zero and setting switch offset and cutting height. I dont understand G28.1 Z30.00 F6000.0. Once the head has finished it's rapid move, Z wants to go up to find the limit switch. If I manually trigger the switch it will raise by the value of the switch offset and the then the pierce height. If I reverse Z in Mach3, my torch wants to drive into the material

I have also tried running the MP1000 processor with similar results, so it is something I am doing or something I have missed

I have done a lot of research on this site which has helped me greatly with my build, but this time I am stumped.

I would greatly appreciate any advice,


05-22-2015, 10:29 AM
1. The G28.1 Z30.00 F6000 says to do this

G28.1 Z30 says to start a homing move in the direction you have it set in MACH homing and limits. Start the "slowdaown " at 30mm above 0 (here is the kiscker) if you are below 30mm then FIRST move to it THEN staert the slow zone
the F command does nothing on a ref move so is ignored.

To fix it you need to open the POST and go to the function Reference() section

You will find lines similar to the following

function Reference()
firstRef = false
if (refHome) then
post.ModalText(" G28.1 Z")
post.Number(3 * scale, "0.00")
post.ModalText(" G31 Z -100")


The bold line sets the slowdown zone ( in this case above, 3mm) so that will be the place you put a reasonable number BELOW your rapid height. use 12mm

The "post.ModalNumber (" F", refFeed * scale, "0.0###")" can be changed to "--post.ModalNumber (" F", refFeed * scale, "0.0###")" that makes it a comment line instead of a G-Code post line. It won't change the actions but its less confusing reading the g-code

Is your swtich offset REALLY 12mm? Switchoffset is how far it has to backup AFTER the touch off to cancel out the overrun to the swtich after it contacts the material

Home (http://www.CandCNC.net)

05-22-2015, 03:12 PM
I just got this figured out today Under the Config tab of mach3 then homing/limits you can set where you want it to be and this will be" machine cord's " so I set mine at X0 y10 z0 and my g code will read
N386 G0 Z.25
N388 M5
N390 G91 G28 Z0.
N392 G28 X0. Y0. A0.
N394 M30
but my router with go to my machine z0 y 10 x 0

05-22-2015, 04:42 PM
Thanks for the reply Tom,

I'll modify the post later this morning. It's 6.30am here and still on my first coffee.

As I understand it, the switch offset is 12mm. Lowered the head until it tripped the home switch. Zeroed the Z axis in Mach3, then raised the head until it just cleared the material. I will make the switch striker adjustable so I can reduce the distance of travel.

Being my first build, I have tried to be economical while trying to maintain quality which is a bit hard considering the lack of suppliers, exchange rate and the cost of freight to Australia. Once the machine has proved itself, the first item to upgrade will be my THC which will be from CandCNC. Your advice in various posts has greatly helped me to set up my machine.


05-22-2015, 09:13 PM

Modified my post in Sheetcam as recommended by Tom

Also, I had to check Home Neg in Motor Home/Soft Limits in Mach3

And I reduced the Switch Offset to 8mm

Thanks for the help