Messages

2521

General Mach Discussion / Re: What has gone wrong????

« on: March 13, 2014, 05:08:30 AM »

Hmm, that sounds like a complete different control system?

2522

General Mach Discussion / Re: We're gonna build a CNC Plasma. Is THC needed?

« on: March 13, 2014, 03:15:13 AM »

The break-out-board is optically isolated but the best option i think would be for optical connection from PC to board, I think that is where my RF is getting in possibly.

My machine is only 600x600mm so similar to yours.

Some details here...
http://www.mycncuk.com/forums/plasma-table-machine-building/7004-plasma-table-build-first-question.html

2523

General Mach Discussion / Re: We're gonna build a CNC Plasma. Is THC needed?

« on: March 12, 2014, 05:49:54 PM »

I'm debugging my build now, I have not yet fitted THC but I have fitted a floating Z axis so it can probe the work surface before each cut and set a good height in the code, this part is working really well.

It's main use seems to be for adjusting the height if the work warps or is not flat, most of my stuff is small so flatness is pretty easy.

My main issue is rf interference from the arc to the PC.

2524

General Mach Discussion / Re: What has gone wrong????

« on: March 12, 2014, 10:43:18 AM »

Well, all is still not well.

I had some more play time today, tried some 30A test cuts and it's messing about, stopping cut motion midway, throwing e-stops, losing co-ordination etc.

It will be even worse if i plug the PC into the same extension as the system, I have to run two extension leads back to the wall socket just to get a partial success.

If it was 100% because i have no ground rod then i would stop testing until I take the machine home where I can fit one, but I'm not totally convinced it is that.

The system has a filtered plug fitted and the pc has an in-line filter fitted.

Not sure where to focus my efforts now?

2525

General Mach Discussion / Re: What has gone wrong????

« on: March 08, 2014, 04:18:02 AM »

The terminal I was referring to is a 14mm bolt on the back of the plasma cutter, this is now connected to the table frame, it will go to ground when I get it all home.

I think the big fix was disconnecting the PC case, another idea bought about by internet dredging, definitely not a good idea it seems though.

I will try direct clamping the lead, but I have a sneaking suspicion that because I was rushing these tests due to being near closing time, I may have inadvertently run them at 20A instead, I will redo them more carefully this week.

At least it's running now, that's the main thing.


As for grounding, I did notice that once the first cut had passed over a bed slat it was lightly welded down so surely that would ensure a good connection to the plasma return lead from then onwards?

2526

General Mach Discussion / Re: What has gone wrong????

« on: March 07, 2014, 02:15:04 PM »

Also what type of plasma start does your cutter employ?

This is a 20-50A HF pilot arc torch

When I take the table home, I will definitely have a ground rod, it's easy there.

2527

General Mach Discussion / Re: What has gone wrong????

« on: March 07, 2014, 02:12:58 PM »

i had a chat with the plasma supplier, told them of my woes and the only suggestion they had was to drive an earth rod, connect the terminal on the cutter to that and then connect the CNC table likewise. Unfortunately I couldn't drill a hole through the factory floor so I just connected the terminal to the table frame.

I tried that and managed three pierce tests this time but then locked up again.

Then I disconnected the earth from star point to PC case and it worked! Passed repeated pierce tests, then I run a simple cut-line test of six 70mm lines at reducing speeds, table was still responding so I ran another test pass followed by a more detailed test and it still responded afterwards!

here's the results...

numbers are mm/min at 30A.

i like the result at 4000mm/min, it's very fine and about 0.75mm kerf, this is 1.5mm sheet so very thin.

i gather the point where it closes up at the end is due to deceleration?

anyway, it was getting late so I quickly dialled in 4000mm to my next test in sheetcam and compiled the g-code.


It looked ok, showed up some signs of serious axis wobble but ok. However on turning it over it appears not to be cut very well. ...


Now, I'm not too worried as I did rush the test and the changes to sheetcam so I may have bodged it up. The main thing for this thread is that it's working and surviving extended cuts.

many thanks to all for the helpful suggestions, much appreciated.

2528

General Mach Discussion / Re: What has gone wrong????

« on: March 07, 2014, 09:42:36 AM »

Its random, tried a reboot again, this time no control is regained.

As soon as i triggered the torch, the power led on the bob went out, the y-axis jumps 5mm and that's it, no more action.

Its also holding the motors locked despite being told to disable the drives, this point indicates the fried BOB but I cant risk another BOB until I know what went wrong or it can get expensive quickly.

2529

General Mach Discussion / Re: What has gone wrong????

« on: March 07, 2014, 09:09:04 AM »

I have just tested it again with a different 24v PSU connected to the BOB, this one is a PLC supply so pretty good quality.

It worked ok with the torch off, ran a cut program 10 times in succession and all worked ok.

Connected up the plasma and did a quick test pierce and down it goes again, no movement on the motors.

This now confuses me as it seems the BOB is OK still but i have serious issues elsewhere, trouble is i dont where or how to test them?

Following a reboot, normal control is returned.

The PC showed no signs of a crash, no lock-up or BSOD etc.

Not sure which way to go now but clearly i have issues.

2530

General Mach Discussion / Re: What has gone wrong????

« on: March 07, 2014, 07:44:12 AM »

Here's the current state of wiring...

1 - I have an 11A smps connected to the three motor drives,

2 - a smaller 24v smps connected to the BOB,

3 - The BOB is a cnc4you.co.uk HG07 unit

4 - Another small 24v psu is running the relays for e-stop and limits / torch trigger.

5 - I have used screened cable for all motor leads, this is connected at one end only inside the cabinet to a star ground.

6 - I have connected the Z-axis to the X-axis carriage and then back to the star point.

7 - I have connected the Y-axis gantry to the star point.

8 - The case of the PC is connected to the star point.

9 - All PC leads are fitted with ferrite chokes.

10 - The mains is now filtered at the plug.

11 - The plasma ground lead is clamped to the cutting bed.

12 - The frame of the table (and therefore the cutting bed) is not connected directly to my star point, I am guessing this is catered for by having the cabinet bolted direct?

The whole lot is mounted in a steel cabinet bolted to the machine frame.

Any obvious issues with that?