Cutter settings - back dross

[JamieL]

I've got a cheapo Cut50 with pilot arc which I've to date mostly used for dismantling stuff, at which it's great!

Fitting it to a CNC table, really struggling to find any settings that'll give a clean cut. The controller has floating head and does a probe and so sets cut height accurately, I don't think that's the issue.

No matter what amperage, speed or air pressure, there's always around 1mm of back-end dross when cutting 3mm steel (bit less on 1.5mm sheet). Pictures below are underside of cut.
The top and sides are beautiful, clean cut through the metal but spoiled by the scabby mess on the back face.


I've gone from 20A right up to 50A and air from 25 to 65psi. Air pressure seems to make little difference and I've changed consumables and even tried two different torches.

Cut speeds from 800mm/min (won't penetrate) down to 300mm/min (penetrates well but over 30A just gets too hot). Best results seem to be slower and less amperage.

Where I'm stuck is knowing what makes it better or worse and so I feel like I'm going round in circles. Any ideas?

 

[Erie Fred]

Get a 4" wide masonry chisel, and grind it sharp.
Slide it along the sheet to shear off the slag.
How hard is it to remove when using this method ?
Report back here with the results.

 

[roofman]

Ime sure those cut 50,s don't cut too well floating over the work, just like my parkside cutter the tips cut much better getting dragged touching the work..Looks like the hot end of yours is curling under the steel which tells me its to high and should be touching...

 

[8ob]

I've got a cheapo Cut50 with pilot arc which I've to date mostly used for dismantling stuff, at which it's great!

Fitting it to a CNC table, really struggling to find any settings that'll give a clean cut. The controller has floating head and does a probe and so sets cut height accurately, I don't think that's the issue.

No matter what amperage, speed or air pressure, there's always around 1mm of back-end dross when cutting 3mm steel (bit less on 1.5mm sheet). Pictures below are underside of cut.
The top and sides are beautiful, clean cut through the metal but spoiled by the scabby mess on the back face.

View attachment 409456
I've gone from 20A right up to 50A and air from 25 to 65psi. Air pressure seems to make little difference and I've changed consumables and even tried two different torches.

Cut speeds from 800mm/min (won't penetrate) down to 300mm/min (penetrates well but over 30A just gets too hot). Best results seem to be slower and less amperage.

Where I'm stuck is knowing what makes it better or worse and so I feel like I'm going round in circles. Any ideas?

Have you had a play with different tip/nozzle sizes?

Bob

 

[zzr1200]

This might worth reading....

Upgrading my R-Tech HF50 Plasma Cutter, to its full potential.....possibly....

I've owned my plasma cutter for several years now, but never really been happy with the quality of the cuts in material above 13mm (steel), and never achieved the 18mm clean cut/24mm severance, plus the tips always seemed to burn out quickly. I needed to stock up on consumables again but...

www.mig-welding.co.uk

 

[tigdlo]

Your cut speed is too slow, I would expect at least 2000mm/min for 3mm at 50amps.

65psi is low too unless the manual says otherwise, set it to the max the plasma allows.

Do you have a time delay to allow it to pierce first? If so how long and what is the pierce height? What is the cut height? Does it fully penetrate before it starts to move? Could you post a photo of the plate you cut out of.

 

[JamieL]

Your cut speed is too slow, I would expect at least 2000mm/min for 3mm at 50amps.

65psi is low too unless the manual says otherwise, set it to the max the plasma allows.

Do you have a time delay to allow it to pierce first? If so how long and what is the pierce height? What is the cut height? Does it fully penetrate before it starts to move? Could you post a photo of the plate you cut out of.

Pierce height 2.5mm, cut 1mm. Delay of 0.25 sec between.

It pierces cleanly, as you can see. Cut rates marked on the picture.

 

[tigdlo]

I would increase the pierce and cut height by 0.5mm to test. 3mm pierce, 1.5mm cut. Ensure the air is clean dry and at check the pressure when running, where is your pressure gauge?

Check the pierce and cut height is accurate by adding a line in your g code to stop it just before it pierces then measuring it with a feeler gauge or anything the correct thickness. The steps or software scaling could be off for the z axis, or the offset for the height switch in the floating head.

Check the consumables, they could have been damaged, check the earth too but as it's piercing well I doubt it's that.

Cut speeds from 800mm/min (won't penetrate) down to 300mm/min (penetrates well but over 30A just gets too hot). Best results seem to be slower and less amperage.

Heat input takes time, cut faster and it won't get as hot.

You are getting plenty of top dross too, cutting too fast can cause this, but I'm confident this isn't your issue, low cut height and low air pressure could cause this.

 

[JamieL]

Thanks for all the advice and tips. I raised the cutting height slightly (as per @tigdlo ) which helped, raising pressure much over 70psi just made more top-face dross.

I made a new test cut of just a 50mm line, what I can see there is that the last 5-6mm is clean and watching it carefully you can see that the dross builds up after the cut has passed. I've tried faster but it then just doesn't cut all the way through.

So I'm thinking that my torch / consumables combo isn't happy and doesn't make a good airflow or swirl pattern.

Any suggestions for budget "proper" torches? There's clearly a world of difference between a £12 Chinese no-name torch and a £6-900 maintstream branded one but my budget doesn't stretch that far! Anything decent in the £50-100 range?

 

[JamieL]

Seems to be sorted now, thanks for the advice. I got some new tips and nozzles which were better made and a smaller dia (1.1 vs 1.3).

Much finer plasma jet leading to some clean cuts at much higher speeds. These were 35 and 45 A at 800mm/s, 65psi.
Back:
front:

Bit more finessing of settings but I can see the end in sight at last!