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help understanding whats going on in cuts

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lockeyone
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help understanding whats going on in cuts

Postby lockeyone » Sat Jan 07, 2017 11:14 pm

First post, reading site since early December.
Got my plasma going for first time today, totally new to plasma cutting. Cutting cam plate file as my learning file. My first issue I would like some help. Is the first inside cut it triggers plasma but shuts off and machine continues to do circle, 2nd inside cut it cuts it all and outside is fine. If I change the first cut to other inside does the same thing, triggers plasma then shuts off but machine continues its inner cut. Only the first cut. Any ideas? Using Mach Plasma Post in SheetCam.
The zip file should have short video of this along with post file. Video shot from a friend with iPhone. I thought the video is crappy, maybe it was how he sent it to me but you'll get the idea.
If I didn't attach the right file or something let me know.
cam plate.jpg
Attachments
cam plate.dxf
dxf file
(8.29 KiB) Downloaded 20 times
cam plate (2).zip
quick video and sheetcam file
(380.25 KiB) Downloaded 23 times
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beefy
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Re: help understanding whats going on in cuts

Postby beefy » Sun Jan 08, 2017 12:39 am

Don't know if this is a Mach3 timing issue.

Some time ago, in my pursuit of achieving perfect hole centre marking, I heard that Mach3 may "pause" slightly longer on the very first pierce.
>> IF << this has anything to do with this problem it could cause a flameout. A solution to this was to do a dummy pierce on a scrap section of the plate before the main cut commenced.

Your selected tool says it's for 18 gauge steel which is only about 1mm yet you are using 45 amp consumables (according to your tool) instead of Finecut nozzles. So the slightest delay could cause a flameout. Does the first pierce point "hole" look any bigger than the subsequent ones. With thin steel the torch must pierce and start moving quickly so that the pierce hole doesn't blow out too much and cause a flameout.

One thing I'd try is set your Plunge Rate to the fastest your Z axis can do. You need to move from pierce height to cut height ASAP. Can your Z axis move faster than 60 ipm.

Does the Torch On LED stay lit when the torch goes out, i.e. is the torch having a flameout or is it being told to turn off by Mach3.

Keith.
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ovrrdrive
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Re: help understanding whats going on in cuts

Postby ovrrdrive » Sun Jan 08, 2017 8:31 am

Until you get it figured out you could always just add an extra pierce off to the side of your piece to blow the first delay on... I've seen discussions on this before but I wouldn't know where to start searching for it.

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Re: help understanding whats going on in cuts

Postby lockeyone » Sun Jan 08, 2017 9:15 am

I thought of the sacrificial first pierce but figure I would at least try and figure this out. I did also try the 28 gauge tool set with same issue. Material is sheet metal from an appliance. I collected some of this for this learning curve. At the moment my Z will not move any faster and will eventually add THC. XY can do 500ipm but Z is too slow for me but will work with it while I get my head around what the heck I am doing. I will watch for green light later today on that first pierce.
I went through this learning curve when I bought my used BobCad 5050 back in 2003. Took time and experience to finally get it to where I was knocking stuff out in no time. To this day I am still doing trial/error stuff just testing new ways. But if I need something cut now I know exactly how to do it quickly. I do this stuff as a hobby and it is what gets my head away from my real job.
Plasma, well my head hurts sometimes :-)
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Re: help understanding whats going on in cuts

Postby acourtjester » Sun Jan 08, 2017 10:28 am

Parts of the G-code are controlled by the tool set and others are by the operation section of SheetCam. Your cut height shown is 0.020" that is low Book specs are 0.060" for both 45 amp and fine cut nozzles.
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lockeyone
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Re: help understanding whats going on in cuts

Postby lockeyone » Sun Jan 08, 2017 10:31 am

I will look. This is the kind of stuff that I am looking for to help me understand process. I will make some changes. My goal yesterday was really to get torch to fire. But of coarse I had to try a file. Let the learning continue.
I guess I am still stumped as to why first one does this but not other two.
Thanks
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Re: help understanding whats going on in cuts

Postby lockeyone » Sun Jan 08, 2017 12:26 pm

I went out and did a couple of tests. Raised torch height a hair, same thing. Then I duplicated part so I would have two to cut. Only the first pierce/cut on first part did this do it, second part all was cut. Even turned amps down to see if that changed anything but no. Yellow light flashed through first cut even though it wasn't cutting. I looked at my consumables and don't have any fine cutting ones. Will pick some up this week.
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Re: help understanding whats going on in cuts

Postby beefy » Sun Jan 08, 2017 1:59 pm

Just a sidenote on troubleshooting.

Many people treat the plasma setup as somewhat of a black box and don't bother to learn gcode. I advice not to be that way because it really helps you out when you can just glance at the gcode and see something obviously wrong, or if the problem lies elsewhere.

Up to this point it's looking more like that first pierce in Mach adding extra delay. Things like this is why I've converted to UCCNC.

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Re: help understanding whats going on in cuts

Postby tcaudle » Sun Jan 08, 2017 3:56 pm

The problem is not a problem if yoou have a THC that uses an arc ok. That waits until there is a valid arc before it starts moving. The pierce delay, the plunge rate and the heights all play a role It takes the plasma longer to fire the torch if purge air is not on (that is not a function of the software). The pierce cycle is longer.as well. On really thin metal everything has to be faster to keep the torch from itself losing arc current and snorking out.

Its for this reason on pecking with the plasma for hole centers we have code in the POST that raises the torch and fires a short burst in the air to start purge air so the short cycle of the ON/OFF for the hole peck will work.

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Re: help understanding whats going on in cuts

Postby lockeyone » Sun Jan 08, 2017 10:55 pm

Its for this reason on pecking with the plasma for hole centers we have code in the POST that raises the torch and fires a short burst in the air to start purge air so the short cycle of the ON/OFF for the hole peck will work.

As I was playing with machine today I was thinking this same thing. I will try and see if I can get this to work first. Since I have been using Mach1,2,3 since sometime in the 90's I am beginning to think it is time to move to another control software. I have always had some issues with Mach but always worked around them in one form or another. Thinking some of the other programs may have made those issues go away.
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Re: help understanding whats going on in cuts

Postby beefy » Mon Jan 09, 2017 2:19 am

tcaudle wrote:The problem is not a problem if yoou have a THC that uses an arc ok. That waits until there is a valid arc before it starts moving. The pierce delay, the plunge rate and the heights all play a role It takes the plasma longer to fire the torch if purge air is not on (that is not a function of the software). The pierce cycle is longer.as well. On really thin metal everything has to be faster to keep the torch from itself losing arc current and snorking out.

Its for this reason on pecking with the plasma for hole centers we have code in the POST that raises the torch and fires a short burst in the air to start purge air so the short cycle of the ON/OFF for the hole peck will work.


Tom,

I'm not understanding the connection with the ops problem here.

The Arc OK is like a feedback mechanism telling Mach to start motion ONCE the arc is established. However long it takes to turn on the torch shouldn't be relevant. All that matters is once the arc is on the axis immediately start motion. Isn't the issue how long the torch remains stationary once the arc is established, not how long it takes for the arc to turn on. For the op he doesn't want his torch to wait for an Arc OK signal, he just wants motion ASAP after Torch ON, especially on this thin steel and 45A nozzles. For that matter the op may be better trying this cut without THC enabled so that Arc OK is not necessary for motion. This way the axis will immediately start motion after M3 and doesn't need to "hang around" waiting for an Arc OK signal. If there's room for a longer leadin the op could even insert the gcode in the leadin to enable THC. This will give the fastest possible motion start after M3/Torch On signal then have THC control before the main cut is entered.

I found Mach3 response to closed loop control via the Arc OK signal to be "crap" for want of a better word. That's why for my hole centre marking I made a custom microcontroller board that took control away from Mach3 and controlled the Torch On and Arc OK signal directly. After doing that I got great consistency in my hole marking and could get much smaller "centre punch" marks from the plasma torch whether the torch air flow was on or off.

Keith
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Re: help understanding whats going on in cuts

Postby lockeyone » Mon Jan 09, 2017 9:07 am

In my situation no THC as of yet. I am just trying to get the basics working (understanding whats going on) before adding THC. So for now the program just tells torch to fire, 0 second delay and start machine movement. I think my issue is just Mach3 just has a delay on that first cut while winding up to run program. My router was never an issue.
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Re: help understanding whats going on in cuts

Postby SONIC » Mon Jan 09, 2017 9:36 am

A few thoughts:
Is your appliance metal painted? How's your ground?

Try doing just one piece (say a 1/4" hole) on the scrap of the sheet before you run the part.

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Re: help understanding whats going on in cuts

Postby WyoGreen » Mon Jan 09, 2017 7:06 pm

I think what's happening is the air is not flowing on the first pierce, there is a slight delay because of this, so the pierce is blowing a hole thru the thin metal, the hole gets bigger quicker in thin metal, causing the plasma cutter itself to shut off the arc. On the 2nd cut the air is still flowing, so the torch starts moving slightly quicker before the hole gets too big.

This is why I always recommend that you learn on thicker metal. It makes things work a little easier for you. Once you've learned the basics on the thicker stuff, then you go to the thinner stuff. I like to start out on 10 gauge, it's not all that expensive or hard to handle.
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Re: help understanding whats going on in cuts

Postby beefy » Tue Jan 10, 2017 1:07 am

WyoGreen wrote:I think what's happening is the air is not flowing on the first pierce, there is a slight delay because of this, so the pierce is blowing a hole thru the thin metal, the hole gets bigger quicker in thin metal, causing the plasma cutter itself to shut off the arc. On the 2nd cut the air is still flowing, so the torch starts moving slightly quicker before the hole gets too big.


Wyogreen,

not sure if we're on the same page with our reasoning, but I'll put things in detail. You may be saying the same thing as the following.

Whether the air is flowing or not, with a typical Hypertherm torch that uses the internal blowback electrode, the airflow must stop to allow the arc to strike again.

When no air is flowing, the internal electrode is pressed up against the inside of the nozzle, ready to be pushed back by air pressure and strike a pilot arc. When the plasma cutter gets the Torch On signal, it energises its' air solenoid, and air pressure pushes the electrode away from the nozzle thereby drawing a pilot arc which ignites the main arc. THAT is the faster one, not the slower one.

2nd scenario, post cut air flow ON, and plasma cutter receives the Torch On signal. The air solenoid must de-energise to stop the air flow, then the electrode moves under spring pressure and re-contacts the inside of the nozzle. Then the solenoid energises again and same as above, the electrode is pushed back under air pressure, and the pilot arc is created, etc, etc.

So as you can see the the arc is actually established quicker with the first one (no air flowing).

If THC is enabled in Mach3 (whether there's a THC or not makes no difference) then Mach requires the Arc OK signal before motion is allowed. If Mach3 has good reaction time to Arc OK then it won't matter how long it took for the arc to establish. All that matters is how long it takes Mach3 to give motion commands once Arc OK is received.

It THC is disabled then Mach3 does not require the Arc OK signal to start motion. If there are gcode motion commands after M3 they will be executed immediately whether the torch lit or not. So bearing that in mind and remembering that with no air flowing the arc is established FASTER / EARLIER then the first pierce could be happening for a tiny bit longer before motion starts. That then begs the question: is the extra arc time enough to cause a blown out hole and a loss of arc, OR does Mach truly delay longer in the first M3 in a gcode file ????????????????????????? I don't know but I have heard some say it does. I could hook up my logic analyser and see the time different between M3 output and the first XY step pulse, but sorry I'm not that motivated to find out LOL. Too many other missions to accomplish and Mach3 is becoming a memory now.

Jim,
if you're listening in and anything I've said is not right on the ball, please correct me.

Keith.
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Re: help understanding whats going on in cuts

Postby WyoGreen » Tue Jan 10, 2017 12:45 pm

Hey Beefy, I think we're saying the same thing. I kinda remembered a discussion a while back, I think on drill/peck either on here or the CandCNC site, that seemed like it might fit this problem. You obviously have a much better memory than I do, thanks for saying what I meant. ;)

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