Dross and Letter Cutting Help

[Charlie6017]

Hello, I have a rack and pinion DIY plasma cutter, Im using a Lotos LTP5500D plasma cutter. Im cutting at 110ipm and I just lowered my amps down to 28. Im using 16 gauge steel. Cutting at .06 inches and using a proma thc. See the pictures below. The manual says to cut at 110ipm at 30amps. I keep getting dross on the bottom. The top is coming out perfect. I am also having issues with small letters. Any advice would be great. Thanks.

[robertspark]

what axis acceleration are you running for X and Y?

what CV distance tolerance are you running (general config tab, RHS if running Mach3.... if not, what software are you running)?

[Charlie6017]

axis accel is 29. See photo of CV Control. I have never adjusted anything on that.

[acourtjester]

That is lot of dross and you need to use longer lead ins and outs to remove some of the divots see attached. Also attached is an image of my cuts using Hypertherm fine cut nozzle and 200 IPM with 45 amps. Your nozzle may be to big and this is causing the dross too. What is the air pressure you are using. Not sure as to the wavy cuts but it may be your THC is bobbing up/down to fast correcting the cut height.

pierce.JPG (148.25 KiB) Viewed 1785 times

pierce.JPG (148.25 KiB) Viewed 1785 times

[Charlie6017]

Thanks alot. I am using the 1mm tips. I dont know if they have fine tips for this plasma cutter. I will have to look around. It is the IPT60 torch. The air pressure is at 90psi. Thanks for the info. I will do some more testing.

[robertspark]

which way is your cut direction?

clockwise outside offset, counterclockwise for a hole (inside offset)

your acceleration is quite low... but so is your feedrate so both should be alright together. the CV number is very large so the machine is unlikely to slow down much for changes in direction which means that the over riding corner rounding would be governed by acceleration alone and not the CV distance tolerance.

have you done some linear cuts to determine the optimal feedrate for the metal thickness you are cutting ?

plus have you tried to determine what the optimum pierce interval is for the material you are cutting? (a series of dimples / pierces with increasing dwell from 0 sec, 0.05 sec, 0.1 sec, 0.15; 0.2; 0.25 up to about say 0.6?

it is recommended that the first pierce is a double one so say 0.2 sec to get the airflow going... then start the sequence in a line

[xnaron]

I have a similar setup with a herocut hc6000 and proma sd. I have similar dross with 16 gauge (and others). I have tried different speeds and amps and air between 55 and 70 psi. I have tried the 1.1 and 1mm tips (the ones that were included). My plasma cutter says do not exceed 70 psi on the front where the air pressure gauge is. You can checkout my thread viewtopic.php?f=4&t=30670 maybe some info in there will help? You are lucky you got a cut chart with your Lotus . The Herocut does not have one.

[adbuch]

Here is an interesting thread about preventing dross. He sprays the back side of the metal sheet with weld anti-spatter spray. His parts look nice and clean on both sides.
David

viewtopic.php?f=85&t=29703

[_jay_]

I have the same problem with dross on the back, and i know it's coming from my cheap plasma cutter. I should add air pressure to flush it more but it'll cut off the flame. So atm running with around 30 PSI untill i caa afford a brand name plasma cutter.

[Charlie6017]

which way is your cut direction? Cut direction is counterclockwise for outside offset and I am not sure for inside. I will have to check.

clockwise outside offset, counterclockwise for a hole (inside offset)

your acceleration is quite low... but so is your feedrate so both should be alright together. the CV number is very large so the machine is unlikely to slow down much for changes in direction which means that the over riding corner rounding would be governed by acceleration alone and not the CV distance tolerance. What CV number is optimal?

have you done some linear cuts to determine the optimal feedrate for the metal thickness you are cutting ? I have done linear cuts in the past but I have made some changes so I will try and do more tonight when I get home.

plus have you tried to determine what the optimum pierce interval is for the material you are cutting? (a series of dimples / pierces with increasing dwell from 0 sec, 0.05 sec, 0.1 sec, 0.15; 0.2; 0.25 up to about say 0.6? I have not. I will also try this tonight. Thanks

it is recommended that the first pierce is a double one so say 0.2 sec to get the airflow going... then start the sequence in a line

[robertspark]

https://www.google.com/url?sa=t&source= ... NyPrgXm0HC

cut direction page 3/6 + other tips

I have some test drawings for setup testing that I think are useful to plasma, I am trying to figure out how to program a simple user interface, I think I may try to setup them up in sheetcam as a plugin..... totally different topic...

CV... depends on your setup...
https://www.google.com/url?sa=t&source= ... ef9mRIyb8V

[robertspark]

CV cannot be dynamically changed in mach3 (it can in some newer alternatives)

I would set it at a minimum of the kerf width, and as an optimum setting.... probably 1.5 to 2x kerf width.

too small and you will get undercutting on the inside corners and a minor dogbone shape with more bottom dross. too big and your acceleration will control the corner radius... so at 29"/s/s accel and higher feedrates then you'll get more rounding on the corners... at 100ipm ... this won't be very great 0.04451704996" radius

however...

at 200ipm 0.38314176245" radius

at 300ipm 0.86206896552 radius

at 400ipm 1.53256704981 radius

[xnaron]

Here is an interesting thread about preventing dross. He sprays the back side of the metal sheet with weld anti-spatter spray. His parts look nice and clean on both sides.
David

viewtopic.php?f=85&t=29703

I like that idea. The only concern I have is whether this spray would contaminate my cutting fluid in my water table. I am running greencut. I am not sure if that would be an issue or not.

[PlasmaGuy8]

I had the same problem with the LPT 5500. No matter what I did it had a lot of dross. I finally bit the bullet and got a Hypertherm 45 xd with fine cut tips AT 45 amps 95-100 psi Running the Proma 150 THC. I found by lowering the water in my table almost 2 inches I get very little dross. The higher the water the more dross.
Still tweaking it into shape but numbers and letters look good, as long as they are 3/4" or taller.
I will say I'm not loving the Proma...I think that's going to have to be my next upgrade.

[adbuch]

Thanks for the update! The 45xp is a nice machine.
David