Hello Guest it is July 12, 2020, 12:19:46 AM

Author Topic: THC moves on the Z axis...  (Read 6796 times)

0 Members and 1 Guest are viewing this topic.

Re: THC moves on the Z axis...
« Reply #10 on: February 13, 2016, 07:57:19 AM »
Have you tried a z axis test script?

Say your travel is 5" (125mm)

set the z at 10mm from the bottom of travel, zeroing the z axis, and give it the following gcode (best done in excel by dragging cells down and then copying and pasting to text file and then saving as a *.tap file)

G00 Z100
G00 Z0
G00 Z100
G00 Z0
etc.

Then change it to
G01 Z100 F3000  (or something of your choosing)
G01 Z0
G01 Z100
etc

Then change it to:
G00 X100 Y100 Z100 (make sure you obviously have the travel distance, and all axis were zero'd at the start)
G00 X0 Y0 Y0
G00 X100 Y100 Z100
etc

This last one will test your power supply by moving all three axis at the same time as well as how well your drives cope....

You obviously want to make sure your machine is setup in its normal cut mode (i.e. torch on torch holder etc.... so the effects of shunting an axis about are correct).

Rob

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

Offline Davek0974

*
  •  2,597 2,597
    • View Profile
    • DD Metal Products Ltd
Re: THC moves on the Z axis...
« Reply #11 on: February 13, 2016, 08:05:07 AM »
Going out  to try it now.....
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives.
Plasma table, Mach3 V062, Step motors, C&CNC THC.
Re: THC moves on the Z axis...
« Reply #12 on: February 13, 2016, 08:20:59 AM »
Oh..forgot to say.. I sort of  give it a motion of say 1000 lines  (500 one way or the other).

If nothing trips out or stalls (my drives fault for a few different reasons and give an error output which I have linked to my estop) then I know I'm good to go.

Its quicker that using the MDI, one line at a time (you can use "teach" too.... but excel is quicker for me [drag, copy paste, save etc]

I'd do G02 / G03 as well .... when I feel confident doing MDI circles [one day get my head around doing them] .... after that there is not much else you could throw at a plasma cutter is there given the cutting force should be zero.   (bit different on a mill with different feedrates and tools and materials being cut etc).
Rob

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

Offline Davek0974

*
  •  2,597 2,597
    • View Profile
    • DD Metal Products Ltd
Re: THC moves on the Z axis...
« Reply #13 on: February 13, 2016, 08:58:12 AM »
Well I gave it 100 repeats of each test, I only used a travel 0f 55mm on Z as it trips at 65.

At 3000mm/min in motor tuning, it passed 100%, I started out at Z1 with a feeler gauge on a test plate and after each series it was back at Z1 perfectly.

I tried 4000 in tuning but it was not happy and stalled after two repeats.

So using the 75% of stall setting rule I put it back at 3000.

I did try a couple of simple test cuts and it ran fine, no skips in the G28.1 anyway, also left the THC rate where it was before so that is effectively doubled now I guess and still seems happy, or at least I could not see any sign of see-sawing on the Z axis in the cut.

Did not try G02/3 as not enough knowledge there yet :)

Now need some jobs to run.

Does not explain why a different screw made any difference though, the only other change was that the nut is now brass and not delrin, don't know yet if thats good or bad though.
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives.
Plasma table, Mach3 V062, Step motors, C&CNC THC.
Re: THC moves on the Z axis...
« Reply #14 on: February 13, 2016, 09:56:22 AM »
delrin coefficient of friction ~0.33
http://www2.dupont.com/Plastics/en_US/assets/downloads/design/DELDGe.pdf (page 33)

brass on steel (no lubrication 0.35.... add lubrication 0.19)

not sure what you would lubricate delrin with.

given it is a polymer, it obviously has creep and also some elasticity + a higher coefficient of expansion etc....

there is brass and then there is brass too.... phosphor bronze is a very "slippery" material.... then there is sintered bronze (I suspect oilite goes into this category... but not sure how good it would be at making "bronze nuts"...)

In short it will probably be better than delrin for slippiness .... but may not last as long before showing backlash (where as the delrin will probably mask this)


I have been looking using one of these for my new Z although probably the delrin nut and not the brass one.
http://www.engineeringtoolbox.com/friction-coefficients-d_778.html


If anyone has any experience with either I'd be interested to know a comparison in use / longevity.
Rob

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

Offline Davek0974

*
  •  2,597 2,597
    • View Profile
    • DD Metal Products Ltd
Re: THC moves on the Z axis...
« Reply #15 on: February 13, 2016, 10:16:11 AM »
luckily backlash is irrelevant as gravity will keep that in check for a plasma.

How long it lasts is anybodies guess :)
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives.
Plasma table, Mach3 V062, Step motors, C&CNC THC.
Re: THC moves on the Z axis...
« Reply #16 on: February 13, 2016, 10:32:17 AM »
I don't know about backlash being irrelevant, as acceleration is very high under THC up and dn control, but the degree of slop may be small.

One of those time will tell moments as it probably will have little effect until wear becomes a big issue... Talking 1mm sort of movement not hairs thickness stuff (m8 nut + studding backlash)

How much travel does your z have endstop to endstop?

I've got about 135mm (5.3"), can't make my mind up if I need more with my redesign (175mm / 7")

Plan on putting a 4th axis below my table... Underslung ... So I can take the slats out and cut tube below ( about 1" to 4").  I have converted a 6" rotary table, but in hindsight... At 90:1 reduction ratio... It may not have been a good idea....  As getting 3m/min cutting speed will be hard (0.75 rev / sec on 1" 1.5mm thick stuff)... Anyone got suggestions on z axis travel or a good idea for a plasma 4th axis?
Rob

Albert Einstein ― “If you can't explain it to a six year old, you don't understand it yourself.”
Re: THC moves on the Z axis...
« Reply #18 on: February 13, 2016, 10:40:32 AM »
Aghhh, thanks!
Rob

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

Offline Davek0974

*
  •  2,597 2,597
    • View Profile
    • DD Metal Products Ltd
Re: THC moves on the Z axis...
« Reply #19 on: February 13, 2016, 10:53:56 AM »
I have a total of 70mm Z travel, I wanted to keep it tight to help prevent wobble etc as it is usually cutting at near full extension.

A 4th axis or tube cutting was not a design consideration so adding one would be hard.

Yes I may have overstated the irrelevant part of backlash but with about 1.7kg on it, the z would have to get very stiff i think before it stopped responding to small moves due to backlash.
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives.
Plasma table, Mach3 V062, Step motors, C&CNC THC.