[NorthridgeFab]

What causes these cut marks on the bottom of the cut? I only have this issue with 3/8 and thicker.

I'm thinking the water table maybe causing the arc to bounce around. But I do not see other people with this issue that have water tables.

[travmc1]

What machine, cut speed, amps, are you using? are you using THC? what is the height of the water? maybe try lowering it and check your tip and electrode.

[travmc1]

Forgot to ask what direction are you cutting in?

[NorthridgeFab]

Powermax 85
85 Amps
New tip/electrode
35-40 ipm
CandCNC THC (Also tried it with thc off)

Water was right at the bottom of the plate. Can't lower it because we need to keep the plate as cool as possible to keep the rings from warping. I'm starting to think it's not just the water, there are shops that cut with the plate submerged and do not get these results.

You know I think I may have had the reverse cut direction clicked in mach! If thats all it was I'm going to feel stupid.

[NorthridgeFab]

Yep it was cutting CCW. I do not understand why sometime SC puts the cut path in different directions. I've always checked the "reverse" box when cutting holes, etc. For this piece I had to check "reverse for the outside cut and un-check it for the holes.

[travmc1]

Thats cool you figured it out. When I looked at the lines on the side of your cut it look like it was going CCW. Good to hear it wasn't somthing major wrong.

[WSS]

Check the drawing for stray nodes or lines. Sometimes a very short line placed just right will make the cam think the part has more than one item, it may not put a path to it depending on your tolerance settings but on import it will see it. AutoCad has a purge feature that will get rid of those nodes and lines, I assume most other cads do too. Try a select all and see if some odd part of the drawing turns pink or whatever your selection color is. Just a thought. I had a ghosting problem recently from a drawing that was drawn on a later version than I had, it would show on selections items that had been deleted previously on my "old" version. Goofy and hard to figure out.

WSS

[NorthridgeFab]

Check the drawing for stray nodes or lines. Sometimes a very short line placed just right will make the cam think the part has more than one item, it may not put a path to it depending on your tolerance settings but on import it will see it. AutoCad has a purge feature that will get rid of those nodes and lines, I assume most other cads do too. Try a select all and see if some odd part of the drawing turns pink or whatever your selection color is. Just a thought. I had a ghosting problem recently from a drawing that was drawn on a later version than I had, it would show on selections items that had been deleted previously on my "old" version. Goofy and hard to figure out.

WSS

Thanks for the info, I will check it out. Currently it's cutting perfect once I got the directions right.

[jimcolt]

Water does have a rather dramatic edge roughening effect. Cutting dry (either a downdraft table...or a water table with water low enough so it does not even splash the plate) will always produce the smoothest cut.

The plasma process (the temperature and the DC power) cause the water, which is H2O (hydrogen and oxygen) to break down through a process called Dissociation....which separates the oxygen and hydrogen molecules. The hydrogen molecules burn rapidly...and tend to deflect the arc, which produces more pronounced lag lines.

Take a look at your "wet" cuts....and compare to the attached cut done on my downdraft table, dry. This is cut with a Powermax at 45 amps...it is 3/8" steel.

Jim Colt

[WSS]

Thanks for the info, I will check it out. Currently it's cutting perfect once I got the directions right.

You mentioned sometimes sheetcam will reverse the path directions. That may be why.

WSS

[carbidecraters]

In my years of laser cutting and plasma cutting I have only seen low air pressure cause breakout on the bottom of a cut.

[xavier2nd]

I don't understand how cutting in CW vs CCW can make a difference??

[WSS]

Read this:

http://www.cnczone.com/forums/hypert...289-bevel.html

Jim has real time experience and kowledge of plasma characteristics.

WSS

[tjb1]

I don't understand how cutting in CW vs CCW can make a difference??

Its due to the air/plasma swirl. The swirl cup spins the air a direction(dont remember which).

[NorthridgeFab]

Ok still having the divots in the cut edge issue, but had cut around 15 sheets of 1/2" that way. Now today still with the edge issue, it has started to not cut completely through the material in spots. It will be cutting fine, then start to just gouge the surface. Like it does when you have your feedrate set too fast, but it's sat at 45ipm like has always been. I've been on the phone with HT about 10 times today. I've checked the entire air system, adjusted the cut pressure, checked the amps to make sure they are not dropping, and other stuff. Nothing has fixed the issue. If I slow down to 35ipm it cuts fine, except for the divots in the edge. Anyone have any ideas whats causing it to not cut completely through the sheet in spots? I'll also take suggestions on what else could be causing the divots, I tried/checked everything everyone suggested with no change.

[jimcolt]

Looking down the thread I see that some advice was offered....but I did not see a response from you in regards to improvements/ or no change in the cuts (such as cutting with the water at a lower level to minimize the "divots in the edge".)

I'm guessing that you are still cutting 1/2" steel at 85 amps (a smoother cut edge will occur using the 65 amp shielded consumables) . You say it is not cutting all the way through....so you have to slow to 35 inches per minute. I know that the 85 amp consumables will cut 1/2" steel at up to 70 ipm....and that 45 is suggested for best cut edge squareness..so if you have to slow down to 35 ipm just to penetrate...then you certainly have something seriously out of whack....check the following:

-Worn, damaged consumables will cause a loss of cut power....and a rough cut edge. Check the nozzle, the shield, the electrode (the manual has a great section on inspecting consumables). If they are in good shape...or even better, are new.....then you may want to change the swirl ring and the retaining cap....either of these can cause air flow issues that will act like a loss of cut power.

-Check the condition of the torch Oring.

-Ensure that you have between 90 and 135 psi at the rear panel air inlet (you will have to plumb in a gauge)...this pressure must be present while the air is flowing at the torch. A drop in inlet pressure will affect cut quality and speed.

-Make sure your air flow is set in auto mode.

-Check the onboard filter assembly......make sure it is not dirty or saturated or partially plugged.

-You could have a damaged torch...or a leaky or restricted torch lead hose.

Jim Colt Hypertherm

Ok still having the divots in the cut edge issue, but had cut around 15 sheets of 1/2" that way. Now today still with the edge issue, it has started to not cut completely through the material in spots. It will be cutting fine, then start to just gouge the surface. Like it does when you have your feedrate set too fast, but it's sat at 45ipm like has always been. I've been on the phone with HT about 10 times today. I've checked the entire air system, adjusted the cut pressure, checked the amps to make sure they are not dropping, and other stuff. Nothing has fixed the issue. If I slow down to 35ipm it cuts fine, except for the divots in the edge. Anyone have any ideas whats causing it to not cut completely through the sheet in spots? I'll also take suggestions on what else could be causing the divots, I tried/checked everything everyone suggested with no change.

[NorthridgeFab]

Looking down the thread I see that some advice was offered....but I did not see a response from you in regards to improvements/ or no change in the cuts (such as cutting with the water at a lower level to minimize the "divots in the edge".)

I'm guessing that you are still cutting 1/2" steel at 85 amps (a smoother cut edge will occur using the 65 amp shielded consumables) . You say it is not cutting all the way through....so you have to slow to 35 inches per minute. I know that the 85 amp consumables will cut 1/2" steel at up to 70 ipm....and that 45 is suggested for best cut edge squareness..so if you have to slow down to 35 ipm just to penetrate...then you certainly have something seriously out of whack....check the following:

-Worn, damaged consumables will cause a loss of cut power....and a rough cut edge. Check the nozzle, the shield, the electrode (the manual has a great section on inspecting consumables). If they are in good shape...or even better, are new.....then you may want to change the swirl ring and the retaining cap....either of these can cause air flow issues that will act like a loss of cut power.

-Check the condition of the torch Oring.

-Ensure that you have between 90 and 135 psi at the rear panel air inlet (you will have to plumb in a gauge)...this pressure must be present while the air is flowing at the torch. A drop in inlet pressure will affect cut quality and speed.

-Make sure your air flow is set in auto mode.

-Check the onboard filter assembly......make sure it is not dirty or saturated or partially plugged.

-You could have a damaged torch...or a leaky or restricted torch lead hose.

Jim Colt Hypertherm

Jim,

I just got busy and forgot to report back. I did lower the water level to about 3.5" below the plate with no change in the divots. I understand 65 amps will give a better edge finish and less taper. I wouldn't think the divots are caused just because I'm cutting at 85 amps.

I have completely replaced every part on the end of the torch. Already have a gauge right at the unit, I have a consistent flow of 105psi.

This literally appeared over night. The day before we were cutting 1/2" no problem other than the divots, next day it started the issue of not cutting completely through.

[Mike 1948]

Ok still having the divots in the cut edge issue, but had cut around 15 sheets of 1/2" that way. Now today still with the edge issue, it has started to not cut completely through the material in spots. It will be cutting fine, then start to just gouge the surface. Like it does when you have your feedrate set too fast, but it's sat at 45ipm like has always been. I've been on the phone with HT about 10 times today. I've checked the entire air system, adjusted the cut pressure, checked the amps to make sure they are not dropping, and other stuff. Nothing has fixed the issue. If I slow down to 35ipm it cuts fine, except for the divots in the edge. Anyone have any ideas whats causing it to not cut completely through the sheet in spots? I'll also take suggestions on what else could be causing the divots, I tried/checked everything everyone suggested with no change.

Could you possibly be losing your "ground" connection somehow? I assume your clamp is on the part. Just thought I'd ask.

Mike

[NorthridgeFab]

Could you possibly be losing your "ground" connection somehow? I assume your clamp is on the part. Just thought I'd ask.

Mike

We've always had the ground clamped to the slats without issues. But I did move the clamp to the plate just to check that as well as check the twist connection at the machine. No change with the cutting issue.

[WSS]

Look into the flow (cfm) at the torch rather than PSI, I had a torch that had some small rubber pieces lodged in it that were causing similar cuts and also had a oil soaked element in the filter housing that was causing this same problem.

Both carbide craters and Jim mentioned low flow of air. Two guys who have seen (almost) every situation imaginable. Start there. It does look like a air related problem somehow. The fact it starts randomly or all of the sudden suggests a gremlin or foreign object moving around or disintegrating and finding it's way to the exhaust ports/swirl ring.

Aren't these little troubles just ducky? I am going through a rash of misfire right now that I cannot track down. When the problem starts I have to hide my four pound hammer LOL.

WSS