set rules question

bteigrob · Post by **bteigrob** » Thu Dec 03, 2015 2:37 pm

I just figured out the set rules on sheetcam. So i set some rules like turn off THC and slow to 70% feedrate around corners and what happens is my machine completely stops/starts by the rule and stop/starts by the end of the rule. Anyone have any ideas what setting i need to change in order for my machine to make a continuous smooth transition into the rules?

Post by **Les Newell** » Thu Dec 03, 2015 3:18 pm

Unfortunately this is a problem on some controls. Mach3 for instance hesitates on feed rate changes and THC on/off. I don't know of any fix for the problem.

bteigrob · Post by **bteigrob** » Thu Dec 03, 2015 8:33 pm

I did figure out now if i turn off the THC control option, it does run smoothly. it does slow down and accelerate seamlessly. It's unfortunate that the THC control option does not work. Thanks for the prompt reply though.

robertspark · Post by **robertspark** » Fri Dec 04, 2015 1:28 am

I do have a suggestion....

I presume you are running Mach3, this being the case I can confirm that if you call for any M-codes there will be a pause and hesitation in the motion, this is accepted, normal and just the way it happens, hence setting up an M code to turn THC on / off via two custom macros (M-codes) with script such as
DoOEMButton(123) 'Torch Height Correction "Enable" Toggle On/Off
DoOEMButton(221) 'THC Toggle On/Off
DoOEMButton(222) 'THC Off
DoOEMButton(223) 'THC On

will cause the machine to slow / pause, (whilst the torch continues to fire), execute the THC toggle on/off and then speed up.... obviously causing a divot...

Suggestion... if you are using a bog standard parallel port & driver, or an Ethernet Smooth Stepper you can use and M11Px and M10Px code to turn an output on and off without hesitation..... these are used with laser motion and basically the M11 will turn the port on, and the M10 will turn the port off, the "Px" part defines the port number.... hence M11P1 will turn port one one and M10P1 turn port 1 off (without motion hesitation).

At this point you're probably wondering why the heck you I toggle a relay on and off to control my THC..... simple.... THC will only operate if it recieves the THCOK signal on the assigned pin.... so.... just wire the THCOK signal that comes from your Torch Height Controller via the relay.... hence when the relay is closed.... providing the THC OK signal is recieved.... the Z-axis will move under the dictates of the THCUp and THCDn signals.... and when the M10P2 code is implemented via the post processor it will turn off the THC on corners for instance. (using port 2... as I presume you're probably using port 1 to control the torch fire signal.... may need port 3 if you have an engraver too)

I also use the THC "Enable" toggle via seperate toggle if I want THC at any part in my cut.... so it wont run regardless if I'm cutting small holes or circles.... but will work if I'm doing long cuts and then just toggle the THC On/Off on the radiused corners.

Hope it helps and works

Rob

(I have another tip on z-axis speed via macropump... , but basically the THCUp / THCDN signal will accelerate the torch up and down at the prescribed percentage of the maximum velocity without acceleration (getOEMDRO(25)) .... hence may cause your steppers to stall.... via macropump it is possible to basically monitor the state of the THCUp/THCDn and use a small degree of acceleration to improve the speed of response)... if you are using a proma... forget it... it uses relays to toggle the UP & DN signals and if you're cutting thin plate the THC cant respond quick enough really).

Given the speed of Mach4 via script this has the potential to be much faster than 10Hz (the macropump loop frequency).