what causes dross?

[Coffinscreekcustoms]

hello y'all ive been running my table for 2 years now. now its time to tune what i am doing. dross sucks we all know this!
1) speeds to slow down or speed up
2) amps higher or lower
3) air this is an issue i have my air compresser doesnt keep up gets down to the bottom led on my machine then kicks on, is there a way i can turn up my compresser to kick on sooner?
any more tips would help thanks in advance!!

[acourtjester]

HI
Look back at Jim Colt?s posts they have discussed dross very well and that should answer you questions about that most likely under cut quality.
As for your compressor there is a pressure switch that you can adjust (maybe) this will set both the turn on and turn off points for the operation of you compressor. Some are set like to turn off at 120 psi and back on at 80 psi on most this will change both but some can be set each independently. But you will need a compressor that can put out the higher PSI like a 2 stage type if you have a single stage it may not go higher then 120 PSI. Another point is how large is your tank with a small tank you have a shorter reserve and the compressor will cycle often.

[muzza]

Basically 1 and 2 are relevant to each other in that bottom side dross is generally caused by travelling too slow for the set amps so easiest way is to run at book specs or if your table wont run smoothly at these specs reduce the amps and speed proportionately but for optimum cut quality book specs are best.
Top side dross is generally from the torch being too far from the work or too fast
On most cylinder type compressors (rotary screw are different) you should have a pressure valve (pic) which is normally factory set at around 75 to 100 psi to come back on. This switch is electrically live so only make adjustments with the power supply disconected. There should be 2 adjustments, cut in and cut out. Adjust the screw to increase spring tension to make it come on sooner or later.
Murray



Typing reply at the same time

[Coffinscreekcustoms]

ok ill check out the compresser, as far as the speeds and such im running 15ipm faster then the book says, about 50 amps, but my book says somthing in volts? how do i tell what the volts are when i have amps on the dial?
that one really gets me every thing in the book says volts so how would i go about reading my volts at the torch?
thanks y'all

[tnbndr]

that one really gets me every thing in the book says volts so how would i go about reading my volts at the torch?

I don't have a table yet but have seen others run. Your Mach 3 screen should indicate the volts being used at the torch.

[acourtjester]

You can put a multimeter across the pos/neg terminals of the plasma unit and see the voltage this will very with cutting parameters from say 80 volts to 150 volts DC. Hook it up before you use the plasma do not handle the meter while it is testing the volts. This is how the THC finds it info about torch height corrections. You should be ale to download a manual to see what the range will be for cutting parameters this will very with plasma manufactures. Do not do this if you are unsure of what you are doing you could get hurt if you are not carful.

[Coffinscreekcustoms]

ok did some cutting over the weekend. and my burntables mach 3 screen doesnt have the volts read out. any ideas what i can do for a read out of some sort?
thanks jake

[jondbennett]

acourtjester...

I too am interested in the dross issue. You noted that Jim Colt's posts covered it pretty well. I'd love to read them, but I searched for "Jim Colt" and did not find anything.

What search terms should I use?

Thanks.
--
Jon

[jondbennett]

acourtjester...

Sorry to be a pest. I found his user name and can take it from here.
Thanks.
--
Jon

[BTA Plasma]

At 3-4 in per sec per sec acelleration you will always fight dross. Think about it this way, you have 5 times less acelleration than some of the slowest older CNC plasma tables. If you look at config/motor tuning, note you acel number. You need to have at least a number 15 to start to come out of the heavy dross from changing direction and starting a strait line cut. You will never do that with a machine that has a small single motor on a gantry that should have 2 motors and a reduction. To even start making good acelleration with a 300-400oz motor and a 80lb gantry you need a dual drive at a minimum with direct drive and you can run smaller motors from there with reduction. You are running an ultra course 380 steps per with one motor. Your motor is absolutely pushed to its limit and will not benefit from higher acelleration numbers with the setup you currently have.