Plunge safety clearence

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Powerglide
Posts: 4
Joined: Wed Jul 15, 2020 12:44 pm

Plunge safety clearence

Post by Powerglide » Wed Jul 15, 2020 3:41 pm

Good morning all,

I have a home made plasma table, with Bob DB25, THC Proma, Ohmic Sensor, And Mach3.

I have a Little Problem with the height detection!

In Sheetcam I enter 20 mm in "Plunge safety clearence"

and in reality, I have 3mm.
Which corresponds to my drilling height.

That is to say that my materials did not detect that if the torch passes under Z3mm ....
So the Sheetcam adjustment does not affect this height!
and when I change my drilling height, the detection height also changes!

I use the Pro post: "Mach3 plasma THC with scriber and backlash compensation.scpost"

It is really complicated when I have deformation on the sheet

User avatar
Les Newell
Site Admin
Posts: 2576
Joined: Thu May 11, 2006 8:12 pm

Re: Plunge safety clearence

Post by Les Newell » Wed Jul 15, 2020 4:13 pm

Plunge safety clearance is not used for plasma. For milling/routing it is used to control how the tool rapids down to the cut. When moving from traverse height to cut height it will rapid down to this distance above the cut. It will then move the rest of the way at feed rate.

Do you need the backlash compensation? If not I would recommedn using the 'Mach3 THC with scriber' post.

I'm not really clear what problem you are having. Could you explain a bit further.

Powerglide
Posts: 4
Joined: Wed Jul 15, 2020 12:44 pm

Re: Plunge safety clearence

Post by Powerglide » Wed Jul 15, 2020 5:39 pm

I would like to understand how a post processor works!
Indeed, I would like to improve the operation in my homemade plasma CNC, on the probing sequence.
Currently my probing is carried out as follows.
The very first probing the torch gently descends to 200mm / min until it touches the sheet, the ohmic sensor detects the sheet (Z = 0), the torch goes back to 3 mm, ignition torch for drilling, descent to 1.5mm from the sheet metal and then off we go for cutting.
The following descents are done in the same way except for one detail.
The torch descends at 1600mm / min (initial speed of Z), up to 3mm from the sheet, and only at this precise moment, the torch goes into slow speed (200mm / min) to palpate.
The first concern is that the probing sensor is only taken into account at slow speed.

My concern is that if my torch is found above a deformation of the sheet more than 3mm high, my torch comes into contact with the sheet without knowing it, and the probing is blocked because at the time of taking into account of the sensor, it is already ON, and therefore generates an error.

My wish would be that the probe sensor is active from the start of the descent of the torch, whether at high or low speed, that if the sensor touches the sheet at high speed, and although it goes up and then down again in low speed, for clean probing. (Like a homing switch)
Like this sequence
G31 Z-100 F1500
G92 Z0
G0 Z10
G31 Z-100 F200
G92 Z0
G00 Z3



Example of Gcode Ihave with "Mach3 plasma THC with scriber and backlash compensation.scpost"

N0010 (Filename: carré test 50x50rond30.tap)
N0020 (Post processor: Mach3 plasma THC with scriber and backlash compensation.scpost)
N0030 (Date: 15/07/2020)
N0040 G21 (Units: Metric)
N0050 F1
N0060 G53 G90 G40
N0070 (Part: carré test 50x50rond30)
N0080 (Operation: Décalage extérieur, 0, T1: Plasma, 0,8 mm Fente de coupe)
N0090 G00 X25.0000 Y12.4000
N0100 G31 Z -100 F100.0
N0110 G92 Z0.0
N0120 G00 Z0.0000
N0130 G92 Z0.0
N0140 G00 Z3
N0150 M03
N0160 G04 P0.5
N0170 G01 Z1.5000
N0180 Y10.4000 F2000.0
....
N0460 X25.8623 Y12.4295
N0470 M05
N0480 G04 P3
N0490 G00 Z50.0000
N0500 X52.4000 Y0.0000
N0510 Z3 Why Z3?
N0520 G31 Z -100 F100.0
N0530 G92 Z0.0
N0540 G00 Z0.0000
N0550 G92 Z0.0
N0560 G00 Z3
N0570 M03
N0580 G04 P0.5
N0590 G01 Z1.5000
N0600 X50.4000 F2000.0
.....
N0750 X49.6283
N0760 Y-2.4000
N0770 M05
N0780 G04 P3
N0790 G00 Z50.0000
N0800 X0.0000 Y0.0000
N0810 M05 M30




Thank you for any improvement

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Les Newell
Site Admin
Posts: 2576
Joined: Thu May 11, 2006 8:12 pm

Re: Plunge safety clearence

Post by Les Newell » Thu Jul 16, 2020 11:09 am

That 3mm is your pierce height. Edit your post. Around line 221 you should have this code:
if(offZ and firstRef == false) then
Change it to:
if(offZ and firstRef == false and endZ ~= pierceHeight) then

This will block the move to pierce height.

Powerglide
Posts: 4
Joined: Wed Jul 15, 2020 12:44 pm

Re: Plunge safety clearence

Post by Powerglide » Mon Jul 20, 2020 8:12 pm

Ok I will try!

Thanks you

Powerglide
Posts: 4
Joined: Wed Jul 15, 2020 12:44 pm

Re: Plunge safety clearence

Post by Powerglide » Mon Jul 20, 2020 8:17 pm

Ok!
But if I want a double touch
first touch at normal speed
up 10mm
second touch at 100mm/min

for all the pierces.

thank you

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