Made my first cuts today. Cut a 4" square with a 3" circle in the middle out of 16ga steel. I didn't clean it up and it was 98% dross free (pics below).

Here's the problems I can see:

1. There's a bit of taper.
2. The cut is jagged around the radius of the circle.
3. The corners of the square are rounded quite a bit.

Is there a common problem for any of these that I should try to fix first? I'm using Mach3, SheetCam, and I drew the file with AutoCad.

<a href="http://s818.photobucket.com/albums/zz109/tof01/?action=view&current=P1010239.jpg" target="_blank"><img src="http://i818.photobucket.com/albums/zz109/tof01/P1010239.jpg" border="0" alt="Photobucket"></a>

<a href="http://s818.photobucket.com/albums/zz109/tof01/?action=view&current=P1010242.jpg" target="_blank"><img src="http://i818.photobucket.com/albums/zz109/tof01/P1010242.jpg" border="0" alt="Photobucket"></a>

<a href="http://s818.photobucket.com/albums/zz109/tof01/?action=view&current=P1010240.jpg" target="_blank"><img src="http://i818.photobucket.com/albums/zz109/tof01/P1010240.jpg" border="0" alt="Photobucket"></a>

A mild vibration made by both axis moving at the same time can cause those jagged cuts. Decreased your feedrate or check the gantry system if it needs some lubrication.

tof1,
for problem #3 you can loop the corners in sheetcam. What it does is go past the corner and come back in a loop or triangle to hit the next edge. I was watching a video in a post on CNCzone last night that showed a custom machine cut a spiral really fast and accurate! I think it was dnelso who posted it?

Is something mechanical the only thing that can cause the jagged cuts or can it be something with the programming?

I actually checked the loop corners box but didn't see a change on the cutting path. Do you know if there's a setting in sheetcam that I can modify? I was also wondering if you do this, is it bad to cut over the gap of the cut you just made?

tof1,
I am going to tag along here, I am hoping to make my first cuts early next week. I don't have a clue what to expect. I have to say those are some nice pictures. Someone should be able to give you some advice from them.

Good luck!
WSS

The jagged edges most likely are caused by some roughness in the motion...if you put your hand on the torch while it is contouring...and you notice any vibration or roughness..it will show up in the cut. You don't mention what plasma, what consumables and what power level. Are you using arc voltage height control? If the z axis is too tight it can cause oscillation that will produce edge roughness as wel...but usually not as severe as the pics indicate.

To minimize the taper...use the lowest power and the smallest consumable and the lowest speed for the material and thickness you are cutting. If it is a Hypertherm Powermax plasma..the FineCut consumables will dramatically iprove taper.

The rounding of the corners is likely due to drive tuning....it looks like your gains are pretty sluggish (you can see some heat affected shadows where the motion essentially stops)....I'm not sure of the drive tuning methods for your equipment...but you should look into this. For plasma cutting you want maximum acceleration and de-acceleration....tune the gains so to the point where the machine starts to oscilate when exiting a sharp corner (verify with a pen in the torch holder) then back off slightly until the oscilation stops.

Not bad for the first cuts!

Jim Colt

Tof1,
Could you share the design of your machine on CNCZONE? I think the experter at here can brainstorm to help you.

Mongkol

I had the "jaggies" on my first cuts also. After watching the tip of the plasma closely I could see some vibration on movement especially on radial cutting. I added a brace to the top of my Z and that helped tremendously. Another way I have encountered jaggies is in the cut file itself. If a curve is made of a bunch of little lines the cut is going to appear jagged. Having a cut file wherein curves are really curves smooth's these out and cuts very cleanly.

I'm using a Hypertherm Powermax 1000, fine cut consumables, 40A, 150IPM, CandCNC DTHC. I upped my acceleration and "looped" the corners in Sheetcam. I only had time today for one cut and this one has sharp corners but still the jagged edges. The drawing is perfect, only 4 nodes in the circle and 4 in the square. I ran it with my had on the torch and I could feel a little vibrations. I'm surprised it's shows as much as it does in the cut. I'll try slowing the cut speed down to 130IPM and see if it helps with the taper. Still not bad for a second cut in my opinion! Guess I'll have to figure out a way to brace my gantry... Thanks for everyone's help!!

http://i818.photobucket.com/albums/zz109/tof01/P1010245.jpg

http://i818.photobucket.com/albums/zz109/tof01/P1010246.jpg

http://i818.photobucket.com/albums/zz109/tof01/P1010247.jpg

Something I was also wondering is my Z axis tops out at 80IPM how it's set up right now. Would the Z axis not being able to move quickly enough or something to do with a setting on the DTHC have anything to do with the rough edge??

Something I was also wondering is my Z axis tops out at 80IPM how it's set up right now. Would the Z axis not being able to move quickly enough or something to do with a setting on the DTHC have anything to do with the rough edge??

As long as you not getting head "bounce" (visible up and down) then the jaggies are not coming from the Z motion. There are settings in the DTHC that allow you to fine tune the gap voltage (defaulted to 1 volt "span") and the "Tip Saver" (anti-dive) Percentage in the cut profiles. The max response of the DTHC is set by the total loop speed which includes the Z axis speed. You have to normally run the Z at reduced velocity during DTHC operation because there are no accleration curves applied. So if you start with 80 IPM you may be limited to 24 IPM in THC mode. The faster you can move the Z (and still keep resolution reasonable) the better your DTHC will perform. That being said, on flat cuts the 80 IPM is probably not the cause of the ragged edges. The rounded edges are from poor acceleration in the mechanics. The control software will compensate for the inability to accelerate by rounding the corners. While you can loop the corners that won't help you when you are trying to cut detailed cuts with sharp angles you don't have scrap areas to cut on.


I have to agree that the problem looks a look like uneven motion. With MACH , which has constant velocity, and with 4 node circles motion should be smooth as butter. What is your final drive mechanics like? If it's stepper do you have belt reduction? Direct drives to pinon will run with poor acceleration and reduced resolution. Check everything for backlash.
Get the workclamp onto the workpiece and grind off a spot for the clamp to get through the rust. Make sure you air supply is dry.

Heed what Jim says. That 1000 will cut nicely if you pair up the right nozzle with the right current setting and the proper feedrate. I really like the cut quality I get with a 40A tip on material up to about 1/4 ".

Contact me on the CandCNCSupport Forum and I can give you some settings for the Cut Profile for the DTHC to check.

TOM Caudle
www.CandCNC.com

If you are running with belts, can you see if there is a tighter spot at one degree or another in regards to your drive gear? It almost seems like it is rhythmic, maybe the bore is off center causing the belt to get tighter and looser at (almost) consistent intervals. Maybe check to see if anything is stuck in a timing groove (like a drill curly Q or a set screw not set deep enough if it is hubless). Other than that the cuts look good and nice tolerance! The jaggies are bothersome I see. with pitched rails you have to watch for tap holes exiting through the spur side, they can leave a nice bump to wear down if you don't file it or de-burr it somehow. Those are less rhythmic but will appear at the same spot on the table where a drive or pinion will show up anywhere on the table with a regular beat. Try cutting straight cuts about a foot apart with both X and Y and see if it is more pronounced in a certain spot. At least you can narrow down a mechanical issue somewhat.

Good luck!
WSS

Another thought, can you raise and lower the torch from were it is clamped and see if it has more jaggies extended and less jaggies retracted? It may be opposite if it is a single clamp, ie, more jaggies retracted because the weight is now over the top of the clamp point. You get the idea, it could go either way, but the key is if you see a difference.

I've pretty much narrowed the vibration down to my torch holder. I was able to get a much improved edge quality and I will still work on making it better. Now I threw a new sheet of cold rolled steel on the table and I cant get rid of the dross! I'm pretty sure the old rusty steel I was using before was also cold rolled and it cuts virtually dross free. What's the deal??

Smoother edge.
http://i818.photobucket.com/albums/zz109/tof01/P1010249.jpg

Dross free rusty old material and unavoidable dross on the new. I cut these right after each other. :confused:
http://i818.photobucket.com/albums/zz109/tof01/P1010252.jpg

rusty steel always cuts with less dross than clean steel....there's noting for the molten steel to adhere to when there is rust...especially if it is on the bottom surface.

To get rid of dross on clean steel: 1. Make sure your torch to work distance is at the torch manufacturers specification for the material you are cutting...and the consumable you are using. 2. Make sure you pierce at the pierce height and cut at the cut height....if you pierce at cut height you can damage a nozzle on the first pierce. 3. Keep increasing the speed...maybe 5 to 10 ipm at a time and check for dross. Usually.....for beginners with plasma...the problem is with using too much power, too big of a nozzle and cutting too slow. Use the smallest nozzle (I would use the Hypertherm FineCut nozzle) at maybe 35 Amps......and get your speed up in the 120 to 150 ipm range....faster if the dross is still there.....eventually you will find the DFZ (dross free zone......a speed range for the particular process and material that eliminates dross)

Jim

And once you find the magic DFZ you can build a profile in the MP3000 Cut Profiles screen. The upper parameters are for information (Notes) about the feedrates and amp settings and selected nozzle and you can use them to remind you what settings to use for a particular type of material. The lower section is actual settings for the DTHC to use (Preset Volts, etc). Be prepared to do a LOT of entries and testing because even slight variations will bring back the dross. If you start cutting smaller features the feedrates change and guess what......the dross shows up on those cuts. After hundreds of hours of cutting for our decorative cutting business, I found out two things:

1. I could always get a dross free cut if I worked long and hard enough and made detailed notes and never cut anything but larger lines and arcs.

2. I don't have enough patience to do #1

I found that low speed dross is easier to remove with a simple tap with the angled edge of a cheap wood chisel. The time spent cleaning up cuts was less than trying to get perfect clean cuts. As you found, plasma cuts differently on different surface finishes, different thicknesses and different feedrates. Another dirty little secret was I found that having a tank of dilute HCL (Muratic Acid from the Home Center or pool supply) and hanging the cut pieces in the tank for a few hours did miracles and cut finish time by a lot. The acid etches off the rust, black mill scale and loosens the dross to a point a flat drop on concrete leaves you with just running a flap sander quickly over the cut edges before they go to paint or plating. WARNING the acid once it's diluted about 20 or 30 :1 from the muratic state is not too dangerous BUT it will oxidize (instant rust) anything metal in your shop that is exposed to the fumes. I keep my tank outside covered and a large box of Baking Soda handy. The pieces HAVE to be rinsed VERY well right after they come out of the tank and dried IMMEDIATELY.

Lots of other secrets too but Dinner is calling to me!

TOM Caudle
www.CandCNC.com

Interesting. I'm using fine cut consumables with the settings straight out of the manual. Maybe I'll try spraying the back of the material with Pam or the anti spatter spray used for mig welding...

Thanks Tom, would love to hear your other secrets when your back! :)

Is it a no no to lower the amps below 40 with the fine cut consumables?

On 1/16 hot rolled with fine details i have cut my amps back to 25 with fine cut consumables, other wise its to hot and melts out the narrow strip of metal im trying to leave in the drawing... whether or not you are supposed to im not sure...but it doesnt seemed to have hurt anything yet...
The acid works great, i got the idea from Tom also... but i have no place to keep the tanks outside so i gave the practise up... also dont spill it on any cement surface that you are fond of....
I tried the anti spatter spray but gave that up also, in time you will find the sweet spot and the dross will be minimal... if you have a flat steel surface, like a welding table... try hitting the peice flat against it with the dross facing up...wear glasses as the dross comes off like bullets..

EDD

tof1, How about posting a picture of your table?

It's amazing what a volt or two difference will make! Im starting to dial in the settings. It will be nice once I get a collection of them going in Mach and can just choose one for the material I'm cutting. I'm super busy trying to keep up with regular work while working on the plasma. I'll try get some pics up.

I have been working with cnc plasma systems for 30 + years.....and continuously educating users on the need for accurate torch height control- both real time height control during the cut, as well as having an accurate, repeatable pierce height. Torch to work distance is one of the three most imortant factors in achieving an accurate plasma cut part...at a reasonable cost per foot of cut.

The other two factors are accurate motion at the proper velocity.....and of course a good quality plasma system.

Glad to see you are making progress!

Jim Colt

Is it possible to cut 16ga steel with zero taper using fine cut consumables? I thought because it's so thin it would be? Or is it the opposite because it heats up so quickly?

No.....you cannot guarantee "zero" taper with any process (air plasma, high definition plasma, abrasive water jet, laser) on any material.

The Fine cut consumables will get you within level 2 of the iso9013 cut edge quality standards on 16 ga steel if you are maintaining the correct torch to work distance and cutspeed. I expect that the angularity would be relatively uniform and probably in the 5 to 7 degree (from 90 degree) range.

A High Definition plasma torch using oxygen as the plasma gas will do better, a laser will also do better. Some water jets (with the articulating head) will alos do better.

Jim colt

5 to 7 degrees is about what I'm getting so I guess it's as good as it can be. Should I expect more taper on thicker materials? Thanks for the help!

No.....you cannot guarantee "zero" taper with any process (air plasma, high definition plasma, abrasive water jet, laser) on any material.

The Fine cut consumables will get you within level 2 of the iso9013 cut edge quality standards on 16 ga steel if you are maintaining the correct torch to work distance and cutspeed. I expect that the angularity would be relatively uniform and probably in the 5 to 7 degree (from 90 degree) range.

A High Definition plasma torch using oxygen as the plasma gas will do better, a laser will also do better. Some water jets (with the articulating head) will alos do better.

Jim colt


5-7 degrees is a lot. My Powermax45 on 1/4" steel is giving me around 1-2 degree taper sometimes less, unless I do holes.(about .010 taper)

Finecut with lower currents and proper feedrates (and an accurate THC) will give you almost laser quality cuts of 16ga and thinner and leaves you with a small kerf and smaller heat effected zone. I have a customer cutting painted R-Panel (24 ga) with fine cut at 350 IPM and it barely scorches the paint on the edges of the cut!. 16Ga does tend to buckle easier than thicker stuff but it has to do with the stress relief of thinner material (cross sectional area). Finecut actually produces less heat than larger tips but doing lots of detailed cuts in a close area will let heat build up regardless of the nozzle size.

One of the most popular selling items we offer is a custom wallclock cut from 16 ga steel and finished with a copper plate and oxidizing patena. We have the main circular pattern in CorelDraw as a master and just drop in the circular text and the selected pattern in the center. See images.

TOM Caudle
www.CandCNC.com

Bigtoy,

I gues I wasn't real clear about angularity....the thicker you cut with plasma...the smaller the bevel angle will be. It is very common to cut 1/4" with plasma with a 1 or 2 degree bevel...which is hardly noticeable......and it is also common to be able to cut 3/4" or 1" with plasma with a .5 degree bevel.....or even 0. The difficulty is with thinner materials....the bevel number gets higher.....and it does with lasers and waterjets as well!

However....appearance wise....a 7 degree bevel on 16 gauge is hardly noticeable.....if you had a 7 degree bevel on 1/4".....or 1/2"...the part would likely be unacceptable!

Jim colt

Bigtoy,

I gues I wasn't real clear about angularity....the thicker you cut with plasma...the smaller the bevel angle will be. It is very common to cut 1/4" with plasma with a 1 or 2 degree bevel...which is hardly noticeable......and it is also common to be able to cut 3/4" or 1" with plasma with a .5 degree bevel.....or even 0. The difficulty is with thinner materials....the bevel number gets higher.....and it does with lasers and waterjets as well!

However....appearance wise....a 7 degree bevel on 16 gauge is hardly noticeable.....if you had a 7 degree bevel on 1/4".....or 1/2"...the part would likely be unacceptable!

Jim colt

I got it now. I guess I do get good angularity when I cut 16ga.

And once you find the magic DFZ you can build a profile in the MP3000 Cut Profiles screen. The upper parameters are for information (Notes) about the feedrates and amp settings and selected nozzle and you can use them to remind you what settings to use for a particular type of material. The lower section is actual settings for the DTHC to use (Preset Volts, etc). Be prepared to do a LOT of entries and testing because even slight variations will bring back the dross. If you start cutting smaller features the feedrates change and guess what......the dross shows up on those cuts. After hundreds of hours of cutting for our decorative cutting business, I found out two things:

1. I could always get a dross free cut if I worked long and hard enough and made detailed notes and never cut anything but larger lines and arcs.

2. I don't have enough patience to do #1

I found that low speed dross is easier to remove with a simple tap with the angled edge of a cheap wood chisel. The time spent cleaning up cuts was less than trying to get perfect clean cuts. As you found, plasma cuts differently on different surface finishes, different thicknesses and different feedrates. Another dirty little secret was I found that having a tank of dilute HCL (Muratic Acid from the Home Center or pool supply) and hanging the cut pieces in the tank for a few hours did miracles and cut finish time by a lot. The acid etches off the rust, black mill scale and loosens the dross to a point a flat drop on concrete leaves you with just running a flap sander quickly over the cut edges before they go to paint or plating. WARNING the acid once it's diluted about 20 or 30 :1 from the muratic state is not too dangerous BUT it will oxidize (instant rust) anything metal in your shop that is exposed to the fumes. I keep my tank outside covered and a large box of Baking Soda handy. The pieces HAVE to be rinsed VERY well right after they come out of the tank and dried IMMEDIATELY.

Lots of other secrets too but Dinner is calling to me!

TOM Caudle
www.CandCNC.com

What do you need baking soda for? The only thing I dont like about using acid is that it leaves a green haze on parts it seems like. I have never really tryed using it for removing rust before. But do you really dilute it that much? Wouldn't it nutulize the acid? (havn't had a chemestry class in a long time lol) But I have found the best way to remove dross is with a knotted wire wheel cup on a electric grinder. It also leaves a nice finnish as well. But I am going to try building my tumber soon as well and experiment with different medias including the small metal slugs off the table. I also vote for more secrets!

What do you need baking soda for? The only thing I dont like about using acid is that it leaves a green haze on parts it seems like.

Baking soda neutralizes the acid if you spill any concentrate. It happens.

Green Haze? Not on steel. You can pull it out of the tank and all mill scale and rust will be gone. You rinse it very well with running water...then rinse it again! Towel Dry (towels don't last long so use old ones). A heated box in the Winter is a plus. One of the zirconium flap disks (4.5" disk) will clean up the edges and lasts a long time. If you want to plate, the metal has to be shiny clean so the flap sander can be used to take off the layer of grey oxide the acid leaves. For powder coating it just needs to be smooth. Biggest hassle is if you use rusted metal and the rust has pitted the surface, the acid will work in the pits and you have to really work with the flap sander. Textured powdercoat paints ( found a metallic bronze that went on thick and would hide a lot of surface flaws) works best. Glossy paint transmits ANY imperfection.



I have never really tried using it for removing rust before. But do you really dilute it that much?

Muratic in the gallon jugs is cheap but it's nasty stuff. The vapors should not be breathed and splash some on your skin and you will run looking for a water faucet (or the baking soda). Water can either be acid, alkiline or neutral. Adding HCL makes it acid and it stays that way. I have a 300 gallon polytank and I put in about 10 gallons to begin with and just add a gallon every few days. As the water evaporates the PH goes down (more acid). I add water to bring the level back up. I can get a 3 X 3 cutting in the tank and a 4 X 4 diagonally but the top sticks out. I have to turn it every hour.

The stronger the mix the quicker it works. I like it so it works overnight. It will etch the steel over time so leaving it too long will start to make the surface grainy



Wouldn't it nutulize the acid? (havn't had a chemestry class in a long time lol) But I have found the best way to remove dross is with a knotted wire wheel cup on a electric grinder. It also leaves a nice finnish as well. But I am going to try building my tumber soon as well and experiment with different medias including the small metal slugs off the table. I also vote for more secrets!


I tried needle scalers (really loud and slow) , wire brushes (really dangerous) and the hard grinding disks (gouged the metal). Best combo (fastest) was a set of cheap wood chisels and the flap sanders in two grits. I picked wire bristles out of my arms and once out of my head. The acid tank cut our manual cleanup of the pieces a lot. Letting it soak while you cut other jobs makes it a low cost process. I don't live in the city so it won't rust my neighbors car from the fumes!

Sandblasting, unless you are setup with a really big rig, is VERY slow but leaves a completely clean surface ready for paint.

You will find most people want a finished product even if it costs a lot more. I have pricing by the square foot and it varies if it's painted or plated and the thickness of the material. I can throw out a price just by knowing the size. I use the nearest 6 inch increment (UP). I always leave a "gripper" edge (about 1" border) and use the hand spring clamps to clamp the edges to the grid. Without them i have had thin material popup a couple of inches.

Okay here is a quick secret: When you take in a custom job present the customer with a drawing of EXACTLY what they are getting (use your drawing to print AND Cut from). Have them sign off on the "proof" or make any minor changes and check spelling. We used e-mail whenever possible so we had a record of the customer's OK. It saved my grits more than once and it helped me get business. I once did a very profitable job cutting out 24 " tall aluminum letters that ran all the way across the front of a stone faced building. I took digital photos of the building and superimposed the sign on the picture to scale. The owner changed their mind about placement and we had to change the letter size and layout slightly. A LOT easier to do it in the computer than when we got there to drill holes (in stone) and mount the letters. I even had a fullsized pattern printed out on paper and glued to masonite with the drill holes already marked to match the "studs" we had welded on each letter.

Later:

TOM Caudle
www.CandCNC.com

Finecut with lower currents and proper feedrates (and an accurate THC) will give you almost laser quality cuts of 16ga and thinner and leaves you with a small kerf and smaller heat effected zone. I have a customer cutting painted R-Panel (24 ga) with fine cut at 350 IPM and it barely scorches the paint on the edges of the cut!. 16Ga does tend to buckle easier than thicker stuff but it has to do with the stress relief of thinner material (cross sectional area). Finecut actually produces less heat than larger tips but doing lots of detailed cuts in a close area will let heat build up regardless of the nozzle size.

One of the most popular selling items we offer is a custom wallclock cut from 16 ga steel and finished with a copper plate and oxidizing patena. We have the main circular pattern in CorelDraw as a master and just drop in the circular text and the selected pattern in the center. See images.

TOM Caudle
www.CandCNC.com

Do you have to have a bare metal pierce point or can you blow through the paint?

Cheers!
WSS

A torch with a pilot arc will transfer through paint...as long as the plate is getting a good work clamp connection....

All Hypertherm plasma torches use pilot arc starting and have no issues with the arc starting on painted, rusty, or masked materials. Many import torches use scratch start...or a high frequency start that does has to be close to the plate to transfer the arc.....these systems do not work well with painted or rusty plate.

Jim colt

"I have never really tryed using it for removing rust before." I ment so say dross I have only used it for removing rust in the past. But for the wire wheels I have never used the regular loose wire kind only the knotted ones and have never had an issue with the wires flying out like I have heard from so many people. They just kinda wear down real slow over time and leaves a nice clean finnish.

I have more questions on the acid and wat to try this out more. I would I go about self P&Oing steel? soak it in some acid and water then take it out and dip it into baking soda water then dry it off and wipe some wd 40 onto it? alot of the parts I sell need a nice clean finnish and some are welded on by the customer such as tabs and brackets and things. Anybody have any input? Thanks.

anybody on the acid question?

I was having wiring problems with a THC and it was affecting the ARC OK signal. It was turning the torch on and off very quickly which manifested itself like a herk jerky action and with bad looking cuts like this poster has.

I am assuming this poster is using Mach3 and can view what thepins on the parallel port is doing in real time.