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Author Topic: THC moves on the Z axis...  (Read 7029 times)

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BR549

• 6,932
Re: THC moves on the Z axis...
« Reply #30 on: February 13, 2016, 12:20:22 PM »
The pierce divot is ONLY an issue cutting open lines where you cannot use a leadin (;-). With a closed shape and a leadin who cares about a divot ? it falls out anyway (;-)

robertspark

• 596
Re: THC moves on the Z axis...
« Reply #31 on: February 13, 2016, 12:32:28 PM »
Dave, what stepper drives are you using?

At the moment you are using 10ustep resolution...

500 steps per mm... 1u step = 0.002mm

Suggestion to try (if you are up for an experiment and its easy for you to try...)

Change you z axis usteps to 4

This will give you 200 steps /mm (0.005mm per step)

If you can still command 3000mm/s/s acceleration before stalling

Using the above acceleration formula

(3000 / 200 x 60 ) / 3000 (if that is what you want for you rapid velocity), means your target THC % or rapid speed will be 30%

That way you get THC rapid % range (30%)... And Z axis rapid motion speed 3000mm/min

I'll work out the time difference later dropping from say 3mm pierce height to 1.5mm cut height... But the difference should be very small

What is your retract height before touch off (25mm?)
Rob

Albert Einstein ― “If you can't explain it to a six year old, you don't understand it yourself.”

Davek0974

• 2,597
Re: THC moves on the Z axis...
« Reply #32 on: February 13, 2016, 01:51:09 PM »
Using CNC4YOU's digital stepper drives on this one, yes all axes are set to 10micro-steps.

I can easily change the Z as very accessible.

I take it steps per would be 200 then?? ((500/10) x 4)

Yes Z retract is 25mm, Z slow limit for G28.1 is 8mm
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives.
Plasma table, Mach3 V062, Step motors, C&CNC THC.

robertspark

• 596
Re: THC moves on the Z axis...
« Reply #33 on: February 13, 2016, 02:15:49 PM »
Yup, 200 steps at 4usteps.

4mm pitch / 200 full steps / 4 usteps = 0.005mm/step

1/0.005 = 200 steps per mm.

Make sure its all off electrically before flicking dip switches.

First try it at 3000mm/s/s acceleration...then try increasing it to see if the stall point has gone up (or down).

If down, your fallback is just to go back to what you had.

Nothing lost but a bit of playing around time.

You can then try to find your THC up / dn sweetspot.

Try thcspeed at 30% if Ok try at 40%, if fail, try 35% if Ok, try 37%, if Ok try 39%......sort of split the difference ( must have a name for it ), then split again etc.

You at least know the maximum setting and can adjust down to prevent overshoot (if you end up with that)
Rob

Albert Einstein ― “If you can't explain it to a six year old, you don't understand it yourself.”

Davek0974

• 2,597
Re: THC moves on the Z axis...
« Reply #34 on: February 13, 2016, 02:26:27 PM »

First try it at 3000mm/s/s acceleration...then try increasing it to see if the stall point has gone up (or down).

What speed though?
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives.
Plasma table, Mach3 V062, Step motors, C&CNC THC.

BR549

• 6,932
Re: THC moves on the Z axis...
« Reply #35 on: February 13, 2016, 02:28:42 PM »
That is an interesting thought and worth testing BUT normally you are up against the Physical limits of the motor not teh electronics that drive it.

You can normally adjust teh feedrate of teh screw itself to a point where you can easily outrun the THC responce rate. It will be somewhere around .5 - 1"motion per rev of the motor

(;-) TP

robertspark

• 596
Re: THC moves on the Z axis...
« Reply #36 on: February 13, 2016, 02:55:00 PM »
Well it works for you at 3000mm/min... And you are happy with that?.... Start with that (I.e just change the ustep dip switch, plus z axis steps per mm from 500 to 200 and see how it runs... Then increase your acceleration (and see what you get shunting the z using the keyboard THCUp and THCDn buttons you've setup.

If 1500mm/min is what you had before changing the leadscrew and you know what divot you ended up with that... Then that is your ultimate cannot go worse than that point.

Terry had an interesting point about the THCOK before motion.... Especially on thin stuff and high amps as some of the hyperthem cut tables have zero or near zero for pierce delay....hence not sure if you can decend to cut height on the move (never tried it.... Still waiting for my new machine to arrive)
Rob

Albert Einstein ― “If you can't explain it to a six year old, you don't understand it yourself.”

Davek0974

• 2,597
Re: THC moves on the Z axis...
« Reply #37 on: February 14, 2016, 04:39:24 AM »
Interesting, flipping to 4micro-step gave some odd results.

200steps per, 3000speed, 5000acc = G00 moves pass, G01 F3000 fail

200steps per, 3000speed, 4500acc = G00 moves pass, G01 F3000 fail

200steps per, 2500speed, 3000acc = G00 moves pass, G01 F3000 pass, THCrate at 25% pass

Not sure really what its telling me, it seems stable at the final settings so i've left it there for now.

Not sure why G00 worked but G01 failed??

I hammered the THC inputs and it returned home every time so no lost steps there at THC rate 30% it did lose a few steps.

The motor seems to whine a bit more at 4micro steps.
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives.
Plasma table, Mach3 V062, Step motors, C&CNC THC.

robertspark

• 596
Re: THC moves on the Z axis...
« Reply #38 on: February 14, 2016, 08:08:10 AM »
Well, that has confused me if g00 passes and g01 fails.

Interesting you got the acceleration higher up to 5000mm/s/s
Rob

Albert Einstein ― “If you can't explain it to a six year old, you don't understand it yourself.”