New Cutter - Now I have Questions!

[storm monkey]

Evening All,

Today I received a new Draper 40A plasma cutter (model 70066) and have been having a play but not everything is going as I'd hoped. I got the cutter on a very chunky 32A supply direct from my consumer unit, with a massive compressor hooked up, all assembled and ready to go. A pull on the trigger produces a strong pilot arc which lasts for about 5 seconds before cutting out, which I assume is what is supposed to happen if you don't start cutting with it. Anyhow, I found some scrap, and set about cutting it into tiny pieces. Generally, it cuts. It flies through the thinner stuff and was getting through about 6mm. but starting to look like quite a scruffy cut. I have not yet managed to get a constant and smooth cutting motion but assume this will help. I've started to find some "quirks" however that I'm not sure about and want to figure out if it's me or the cutter! I know I have a lot to learn but want to make sure the machine is good before I pull my remaining hair out.
Firstly, if I pull the trigger away from material I get a great pilot arc but as I approach the workpiece, it goes out. It's like the arc is trying to transfer from pilot to workpiece earth but doesn't manage it. If I start with the tip on of very close to the work, it arcs up and generally continues cutting however. It this normal? It makes it very hard to start a cut right at the edge of a piece or metal as I seem to need the torch further on to the piece before it will maintain an arc.
Secondly, sometimes whilst moving the torch, the arc just dies. If I go over a gap (e.g. a previous cut line) it also dies. I can understand the gap but not whilst moving the torch along flat metal. It could be the way I'm moving it I guess. I've tried with the torch spacer fitted and dragging the tip on the metal surface. Both are a little iffy on certain cuts, then fine on others. Could it be the metal? All of my test pieces were fairly rusty or previously painted.
Thirdly, Once the arc is lost, it wont re-start unless I release the trigger, wait for the 10s cool down then pull the trigger to start the pilot arc. I can occasionally see tiny sparks at the tip once the arc is lost but it won't re-light. It is making it very difficult to get a decent cut line. I'd assumed the hf meant it would re-light, and it has very occasionally managed it. I've tried giving it the best chance by cutting a freshly cleaned bit of metal but that didn't help.

Any suggestions or advice greatly received.

Phil

 

[john135]

HI check if you have the earth clamp on some clean metal close to where your cutting, drain your compressor incase there's water in the bottom, is there a water trap/filter on the compressor or plasma, check if you have the correct amperage cutting tip and electrode to match amperage of machine. and check that there is no loose connection where earth lead is bolted to the earth clamp.

 

[voipio]

The Parkside PPS 30 B2 plasma cutter comes supplied with a pilot arc torch. The pilot arc electrode (the outer electrode) is connected directly to the terminal that is also connected to the earthing clamp (i.e. the positive terminal), using a Dinse adapter cable.

This differs from the Draper 70066 plasma cutter, in that the Draper's pilot arc electrode has its own separate front panel connection point, which is, presumably, connected to the +ve outlet via a resistor. I have a Parkside PPSK 40 B2 (the internal compressor variant), which comes supplied with a non pilot arc torch, which has to be dragged across an earth clamped workpiece, in order for the arc to strike and a cut to be made. I've since bought a pilot arc torch (non Parkside) and made up a similar Dinse adapter cable to that which comes with the PPS 40 B2. That torch seems to cut fine, on thin (1mm thick) steel and 1/8" thick steel (I haven't tried to find the maximum cut thickness capability using the pilot arc torch, yet). It will make these cuts even without the workpiece being earthed via the clamp, so there must be sufficient heat, and a sufficiently high plasma temperature, for it to work in this fashion.

It might be worth trying to connect the Draper's pilot arc torch lead directly to the +ve output socket, to see if that changes the behaviour. Out of interest, have you tried measuring the resistance on the Draper plasma cutter, between the +ve electrode and the pilot arc terminal, with the cutter switched off, obviously.

 

[storm monkey]

Thanks for the replies.

I've cleaned up the earth connection on a few samples and have a water separator fitted in line with the compressor but will check the tank too and drain that also. The tip is the one that came with it, which i assume is OK as it does cut.

I've been in touch with draper who have confirmed that, once the arc is lost, you need to wait for the shutdown period before re-starting, which is tedious. I will check the resistance as suggested but I suspect, given that the pilot arc dies and won't restart, that there is some control system shutting the pilot off after a short period. Perhaps using the main earth will get around this.

 

[gaz1]

if you damage the tip it cuts awful and ends up blasting molten metal offside

so look at your tip as they do need changing also take apart and look at the internal piece as well if not a fine pin prick then your tip is busted as goes for the internal it should be pointed on both ends or thats what the cut 50 looks like if its worn then its melted down and dosnt matched the other side

also gives awful cuts

 

[Barking Mat]

Check power supply, check air supply, check plasma consumables, i.e. Electrode and shroud or whatever you call it. I have a 'stand off' or whatever it's called gives me 5mm from the cutting surface.

 

[zzr1200]

Have you tried adjusting the air pressure?

I've found on my R Tech P50HF that if the air pressure is to high it blows the plasma arc out or it pulses. I overcome this by adjusting the air pressure (lower) while holding the torch away from the earth/material (ie: don't complete the electrical circuit) until I had a smooth constance plasma stream........this was after changing the torch assembly. You haven't changed torch assembly but your pressure gauge on the plasma unit maybe reading incorrectly....

Worth a try....

 

[jo1010]

That does sound odd - I've got the same 70066 model and it's always maintained it's arc whether on rust or painted metal. Sounds like you have an earthing problem (I always grind a shiny earth on the metal somewhere (as with welding). The only problem I found was the original pathetic piece of bent wire used as a standoff.... Always falling off so I found a stronger 2 prong standoff (Amazon) and that's been brilliant - a lot of problems can be down to incorrect standoff distance.

 

[storm monkey]

Thanks again all. I'll double check the pressure, earth etc. when I next get time to play (probably Saturday now ) and report back. I'll see if I can get photos.