Mach 3 Antidive / THC Min Speed HELP!

[robertenigl]

Hello all, I'm pretty new here and pretty new to plasma cnc as well, I'm A wheelchair user who is trying to start making Adaptive equipment for a new non profit I'm trying to start... Long story short (not really), I bought a new table that i thought was a good price, little did i know the person who makes them, didn't include a Thc that could work with sheet-cam path rules and i couldn't visually see what the torch was doing at all.. Promo THC SD, I have had nothing but problems getting good cuts from this unit... i bought a new promo THC 150 and completely rebuilt and rewired my control box. every thing works well and the system is working a lot better than before. The issue i'm having is with anti dive in corners, I'm not even sure I'm in the right area(cant find any setting for it in config for antidive), but I believe the THC Min Speed option is what i should be adjusting. After failing to get Macros to turn THC on and off to work without causing Pause in the cut (causing dings), i then started to explore mach 3 anti dive features.(which i can only find THC min speed). I have made path rules in sheetcam that slows corner cuts to 70% and tested that it works properly without the torch on. But when i turn on the THC min Speed( at any speed 1%-99%),it doesn't seam to disable the THC in the areas where sheet cam says it has been slowed down. I can watch z height change in slow mo video i took right in the corners where it is diving. i even made a large area test where it was slowed for 4-5 secounds of cutting on both sides and it still is moving thc up and down doing exactly what it shouldn't be doing

some things ive noticed ..I do notice that when i go to setting Alt6 tab, i see enable thc tog blinking. i also see antidive%feedrate selected ( im assuming anti dive and THC min speed are the same because when i change this it also changes the other.) also noticed that in diagnostics tab output 6 is blinking red at same pace ad enable THC tog. output 6 isnot enabled and no pins are assigned to it (not sure if these are related) I'm assuming i don't have Mach 3 configured correctly to tell the Anti dive to work properly. Any help you guys can offer would be greatly appreciated

[acourtjester]

Ok this is my take and I could be wrong. I do not think the Proma THC has a anti-dive function. I have a Price THC and it does have one, there is a separate input to the BOB board for a anti-dive signal. I have not used it yet and I think there is a macro that is needed to turn the THC on/off at the correct times to achieve the function.
You may see if you can contact msimpson99 a member here the gave me some info about anti-dive operations. Also East German has a Price THC but not sure if he still uses Mach 3.

[Rodw]

Its hard for any external THC to deal with antidive becasue they do not know the cut velocity you set. Any sheetcam rules in gcode are only going to be an approximation. Its best done in the motion controller becasue it knows the commanded feed rate and the current velocity. So the motion controller sets an output to disable the THC when the current velocity falls to say 90% of the feed rate. An external THC has to guess the feedrate from the step pulses if it receives them . But if the external THC does not have some kind of input to allow disabling THC, it can't be done.

In Linuxcnc, this is trivial to achieve. My first corner lock component was about 10 lines of code. The Linuxcnc Plasmac plasma controller supports corner lock and also the Proma 150 and other up/down style THC's.

I also thought CandCNC was promoting true antidive in their Linuxcnc based Command CNC system as significant improvement over Mach3 becasue they ran a component similar to the one I wrote that told their external THC to disable THC action when velocity fell. I've never used Mach or any external THC's but I think that was telling me that its not really possible to run true antidive in Mach or CandCNC would have been doing it.

[robertspark]

Hard sellin linuxcnc, without helping ...

What motion controller are you using?
Smooth stepper, parallel port.... One of the million Chinese ones...

The ding (divot) when turning thc on/off is because most macros in mach3 are non synchronous (same as linuxcnc) only m11/M10 are synchronous. This means that the machine slows down (actually it stops ... But very quickly accelerates back up) when any other M-codes are issed (linuxcnc and mach4 use g63/g64 as synchronous macros)

M10/M11 is built into the motion controller.... It has it within its firmware or it does not.... You cannot add it... Hence I asked which motion controller do you have?

If you have an older version of Windows which is 32 bit and use the parallel port then you get I think up to ten (it may be 5 I forget) M11/M10 macros available M11.1; M11.2 etc .... But with mach3 you can only use two parallel ports (as far as I am aware)....

M11/M10 is the "laser" output.... It's a high speed on and off signal to fire a laser in a pulse. It requires M3 to be active before M11/M10 (M11 is on and M10 is off.... Some other CNC software it is the other way around). It also requires motion (G1, G2 or G3) on the same or next line for it to work...

With the proma 150 you are limited what you can do as it only has a few parameters within it (I owned one bought second hand as the previous owner did not like it.... And I have long since sold it onwards). It also only has three outputs and 1 input (voltage)

The proma provides an arcok signal which is calculated by a parameter within it to determine when the voltage drops below a level it gives an arcok signal because it takes this as an arc transferred signal.

If you have a plasma cutter that provides arcok or arc transferred I would recommend using that instead of the proma as it will be more accurate. You can do what I did which is lower the voltage to about 150 or 140 volts which was above my cutting voltage at the time of about 95v with an old hypertherm powermax 350 which did not have an arc transfer signal.

The setpoint voltage on the proma 150 is a bit course in my opinion at plus / minus 1 volt minimum around the setpoint which is set via the (2 volt) hysteresis setting inside of it

With regards to mach3 antidive, this is an internal function within Mach 3 that will ignore the thc down signal when the actual feedrate drops below the set / desired feedrate..... This will only occur when the machine is accelerating or decelerating .... If you set the feedrate at 70% of the book then that is the set feedrate.... The machine will be looking for this to drop below the set percentage below this number before ignoring the thcdn signal..... So you are best to set the feedrate at the book number and set the thc antidive percentage in mach3 high (say 80/90 or even 95 percent....) In my opinion.

Unless your machine has high acceleration then it will work as intended

If you are cutting small circles and arcs then you are best to turn off the thc input and lower your feedrate to about 60% which is what is recommended to minimise bevel. How you do this without a divot in mach3 is always a tricky one with the proma 150. I did it with a high speed no/NC digital switch similar to a relay but without the switch bounce and state delay of being between on and off, this allowed me to disable the thc DN signal from the proma ((you could use a Reed relay with a small resistor (large value) on the output to act as a bias to ground too)

Mach3 is all about compromise and understanding what it's limitations are, and deciding what the workarounds are.

The hard sell (I get no commission or discounts from anyone nor have I ever and could not really be bothered what you use )
I no longer use mach3 or or proma. I now use uccnc which has many macros designed specifically for plasma and to deal with all of these issues. It is being regularly developed and maintained. And I spend very little time under the bonnet other than my fiddling with screensets and trying to get my lathe to work with it (they don't support turning / lathe but I like the software and hardware)
I have Mesa hardware but see linuxcnc as spending even more time under the bonnet than I do at present dabbling (and another load of languages to learn). YMMV.
I cannot see linuxcnc impring my cut quality any more than it is using uccnc with either the minithc THC or the neuron Lite (why have both... Well I do now and I don't need the low resale cost selling either (or the Mesa 7i76e + thc)

It's sometimes easy to loose sight of the problem. And seek perfection forgetting that plasma cutting is a bit of a hammer and cold chisel when compared to laser or milling something..... But it beats nibbling, grinding, jigsawing or filing something to shape again YMMV

I can also mig / Tig any imperfections and grind if needed plus I'm just a hobby user dabbling and doing one offs for myself

Good luck

[Rodw]

Hard sellin linuxcnc, without helping ...

I did not think I was but rather explaining how velocity anti dive worked if implemented properly and why it is executed better on the platform I use. I don't get divots when disabling the THC as Linuxcnc can turn signals on and off synchronised with motion but I never bother with that becasue the cut quality is maintained by the anti dive.

Mach3 is all about compromise and understanding what it's limitations are, and deciding what the workarounds are.

Which is exactly the opposite of what LinuxcncCNC is. There is no compromise or understanding of the limitations required.

[robertspark]

Which is exactly the opposite of what LinuxcncCNC is. There is no compromise or understanding of the limitations required.

I disagree, but each to their own opinion.

The limitations are the programming knowledge required and time needed invested to get it to do exactly what you want.

How many programming languages and syntaxes do you need to know. Not when you load the disc.... When it doesn't do what you want it to and need it to do something else.

Again YMMV and none of this helps the op with his original question and request for help with that problem.