Plasma cutter, automation project

[Anonymous Poster]

Jim,
I was wondering if you could give us an update on your plasma cutting automation project. Include some pictures of your whole table if possible.
Thanks for all the information... giving me some ideas here... I would like to see what it all looks like now.

Shari

 

[jimgerken]

I will get some good photos and post them soon. Meantime, here's an update, verbally. Software is the Master5 and is working well. I have now a process figured out to drop an object (like a picture or a leaf or a graphic from wherever) onto the computer scanner, scan it into Adobe Streamline, outline it (clean it up, simplify it a little), output it as a DXF. Master5 takes DXF input from either the above or from Catia 3D modeling software, converts it to G code. The G code is always a little rough, and needs a little polishing, and then it is used again by Master5 to drive the table and torch. Mechanically everything is working well. There is still a need for some kind of active torch heigth control. The issue is if the torch is very close to the workpc the definition is best. But if it is touching it will not start reliably cause air must flow out for it to fire up. The window is about from 0.025" to 0.125". And the table isnt perfectly flat. And the stock warps as its cut. So that is a challenge. Otherwise, it is being productive. I designed some aircraft engine exhaust brackets in Catia and cut out several sets, they turned out well. The materials were 1/8" and 14 gauge stainless. The "customer" was happy, but since he is a good friend, it was yet another "freebie". Also have made a couple of computer sheet metal brackets for another guy, and some cool decorative items from scanned pictures of a German Shepard, the John Deere emblem, a Maple leaf... Its a fun device. Pictures will follow... /forums/images/graemlins/grin.gif

 

[patrickg]

Great stuff! Mind posting a reference to where I could view some G-code. Always curious about "code slinging."

Big strong x-y plotter with "different" pen holder.

I was previously involved in automated code generation of high level languages from specifications and such so your translations and hand coded G-code caught my interest.

Patrick

 

[jimgerken]

Here are some recent projects from the NC plasma cutter. Yes, it's still alive and working well! I have made a BUNCH of stuff from it over the last two years. It has greatly expanded my fabrication capabilities, to the point I had to add a press brake this fall (what a bad problem). Shown are parts for the snowblower project.

 

[jimgerken]

...and this one, which some of you may recognize as an adaptor to the John Deere Quick-Tach front hitch.

 

[sierrabob]

This is a picture of the CNC Plasma system I built about 7 yrs ago. I'm useing my old sign software to create art or drawings and it creates a plot file. I wrote my own soft ware to run the machine itself. It is dos based. I'm useing a Hypertherm Powermax 800 machine with machine interface board. I built my own torch height control by reading the torch voltage, provided by the machine interface board. Also by useing the Powermax system there is no high frequency start voltage so I never had the problems with starting the cutter.

 

[johnbilt]

Jim

Wow - Looks fantastic. Great setup ! Very impressive.

What kind of accuracy do you get with your bearing setup ?? Do you get any errors with the stepper motors, in other words, are the motors you have working to your satisfaction ?

Some stepper motor kits come with much larger motors, but I would think that this is not necessary for a plasma torch. I guess the extra power could be used for a router or such.

Thanks

 

[jimgerken]

Accuracy: Well, the plasma process itself is subject to a bevel that happens depending on the cut travel direction. The bevel is between 3 and 8 degrees. On thinner materials, it all but disappears. When you get to about 1/8 inch, it becomes noticable. Another factor is the cut kerf. The kerf width depends on the height above the material you hold the torch, and the condition of the tip and other consumables. If you virtually drag the tip on the workpc, and your tip is new, it makes only about 0.025" (twenty-five thousandths of an inch) wide kerf. So inside corners are automatically filleted at .025" diameter, if they are drawn as square corners. If the software you use incorporates cutter compenstation, this kerf does not change the part. On my software (Master 5), it is not included so I am adding it with a different pre-processing program. This way, the cut line is fed to the controller card at 0.025" (or whatever you define) offset to the outside, so your finished part meets the original dimensions. On holes, the offset is to the inside of the line, to leave the hole the proper dimensions. There is of course some play in the motor/gear system, but that is much less than half the kerf width. Also, sometimes resonances can be set up by the rate and direction the motors are running, which can cause a slightly "knotchy" edge.
With all the above taken into account, except ignoring the bevel which is an unpredictable annoyance, I figure the accuracy overall to be within 0.020" of the desired final size, end to end of the part dimensions. This is of course way close enough for any welded assembly. Some of the parts this thing cuts out still amaze me and I have used it for over two years and maybe a hundred different parts now. Anything I draw now can have really nice stress-relieving and safety-providing curved edges, and the plasma cutter happily cuts them all perfectly, without question. /forums/images/graemlins/grin.gif
The motors I chose are plenty big enough for the mass they move, and the plasma does not resist motion like a router or mill would. Always remember that the power you need depends on the mass and the speed you want to move it. Tests have shown my system maintains accuracy a speed that is about 5 times as fast as the proper speed for the thinnest material I cut (sorry I cannot remember the exact units right now). So I have a fast speed for testing the layout of the part on the particular pc of metal I have chosen to throw on the table, and also the fast speed to move between cutting operations, but then it slows to a speed appropriate for the material I am cutting. The only time I have any issues with accuracy is if I happen to forget to connect the extra ground clamp to the workpiece. If the workpiece is not grounded seperately of the plasma ground clamp, it "radiates" interference which will sometimes get into the control loop and carry the torch off in a random direction. Thats always fun. /forums/images/graemlins/mad.gif

 

[johnbilt]

Jim

Thank you very much for taking the time for a detailed reply. I'm trying to get a feel for automating my plasma cutter without over engineering the thing. Obviously the expensive linear guide blocks are fancy, but probably unecessary for the hobby fabrication setup. You have presented a very elegant, but simplified design for a gantry table.

The electrical interference may be improved by using a heavy braided copper ground strap. The braided form is more effective at reducing the high frequency noise. Also, covering the control cables with a braided shield, similar to a coaxial cable, may help. The control shield should be grounded at one end only. This provides shielding without allowing a current loop path.

Thanks

John

 

[sierrabob]

I've read all your posts and I was wondering what software you are useing to create your drawings. I was also wondering if Master5 software allows z axis control for torch height control and if it can be used on the fly(while it is running). As I said before I'm useing the machine interface board from my
powermax 800 to control torch height, but I want to build a ox/acetelene system for cutting thicker metals. My current system will cut 3/8" thick but because of the lack of wall straightness I thought I would go with a reg torch. Also in an earlier post you talked about metal warping while cutting. I've included a picture of my machine cutting which shows the water I cut in. I discovered I could in water by accident. But when I realized I could cut in water I set my cutting grate in a 4x8 water tank and brought the water level up to the bottom of the sheet of steel. It really stopped the warping and it really stopped the amount of stuff it put in the air. It made the working enviroment a lot better. I was wondering if you where useing 14.5 degree or 20 degree rack and spur gears?

 

[tomrscott]

Somewhere I had read that there is a risk of getting a build-up of hydrogen trapped underneath your work when you cut in water. The place I was reading had a suggestiion for evacuating the hydrogen, but the trouble is I can't remember what they said or where I read that.

I know that is not much help. I may be able to find it again. I've been scouring so many things lately.

 

[sierrabob]

I've been cutting in water for the last 6 years and have experienced no problems. Although by keeping the water level just below metal I'm probably not setting myself up for this problem. Tommorro I'm going to call the tech support for Hypotherm, they have always been very helpful and can probably answer this question. Thanks for the info!

 

[sierrabob]

You're right! on the last page of my Hypertherm Operators Manual there is a discusion on aluminum cutting and the problem with creating free hydrogen. They also tell you how to build a PVC Aeration Manifold to add oxygen back into the water. I really never cut aluminum so have not incounted this problem. Once again thanks for the info!!!

 

[jimgerken]

Software I use to create almost all my mechanical parts is Catia. It is a 3D solid modeling software with sheetmetal package. The sheetmetal package puts in the material bends and reliefs automatically. There is a one-button flat pattern, and then it will produce a 2D DXF file output of the finished part. Catia is pretty expensive. I am actually using an old "try it" version from a few years ago. Couldnt remember where I got it.
Master5 does not allow Torch Height Control (THC). The same author does offer a slightly more advanced software that does THC. I have not yet upgraded. It hasnt really been all that bad doing the height manually. Lately I have been thinking I will at least motorize the Z rack, and run it from a handheld wired remote, so I can stand back and do it from any side, even when the torch is out in the middle or hard to reach.
Water is a good idea, I want to try that, the air quality could certainly benefit!
My racks are 20 degree, 24 pitch, from memory.

 

[Rgillard]

Jim,

Could ya tell me what stepper motor controller board you are using? Was looking at one there on www.stepperworld.com they have a good deal on the SP-3/HT. any info would be appreciated.

Ronan

 

[jimgerken]

I used a Brewington Tech board. Go here and find the link to Brewington:
http://www.kellyware.com/links/links.shtml
I went to the link but it wasnt much of a site. Try calling or emailing them from the "ordering" link. The board type is a "chopper" which allows the current to be set and the voltage to be WAY over-driven. That is how a person gets performance from steppers. Give them 5-6 times their rated voltage but limit the current. Current limiting can also be done with resistors in-line, large ones which will get hot. But the most efficient solution is to use the chopper driver. The power supply you add to a Brewington chopper is simply a transformer (of about 30-35 volts output). the board does the rectification as part of the circuit (steppers use DC). My board is a three channel unit and cost me about $110 from memory. It has worked in the most hostile environment I can imagine for electronics, from the standpoint of conductive dust and Electromagnetic radiation, stray voltage, etc, for two full years now. I have cut many many parts with it. Hope you can find a way to contact Brewington, they sold me a good product. BTW, NEMA 23 motors sell for about $20 each, all over the internet and on EBAY.
I looked at the Stepperworld stuff, they do at least one "chopper" board (or kit), the MS-1. I think it is only a single channel, and might be in kit form. From everything I read when I did this, the chopper is the way to go, BUT the kit you have your eye on does give great value and it is nice and complete, even some documentation. You will appreciate the "help" the complete kit will give. There were LOADS of unanswered questions for me to dig up when I did this. GOOD LUCK and WELCOME TO THE AUTOMATED WORLD! /forums/images/graemlins/grin.gif

 

[Rgillard]

do you think this project would be achievable using an oxy propane cutting torch rather than a plasma cutter

 

[frederic]

Weird. I posted this twice so far, maybe this third time it will work properly.

Here is a picture of my "in progress" CNC Plasma cutter table thingy.

here you can see a 2mb video of how nicely it slides around too: Sliding CNC trucks

I've chosen to use CNC pro for the software, and I downloaded the free, limited use version just to test my homemade stepper drivers. I built the stepper drivers mostly out of junk Iv'e collected in baby food jars over the years. Transistors from this jar, resistors from that jar, CMOS chips from that jar... heh-heh.

I was going to buy the "Gecko" controllers, but at over $100 each, needing three, that got expensive quickly. Since I recycled parts I had lying around, my cost so far has been zero, for the electronics.

I took a PC104 form factor PC motherboard I had lying around and put DOS on that, it it drives my controller just fine. I have to weld together a little box/case for it, and mount it on the cutter table at the back next to the power supply. The power supply also was a no-cost option, also built of collected parts.

The table is very simple as you can see in the pictures, and no, it's not done. That's jsut as far as I've gotten so far, I've been engrossed in other projects and haven't gotten back to it.

Got four Nema23 180oz unipolar steppers too for a mere $150. Was a price I couldn't argue with.

Anyway, a DIY plasma cutter is not that difficult to make... I'm an amatuer and mine's starting to look okay. And to whomever asked - you are not obliged to mount a plasma cutter gun there - you can also mount dremels, routers, rotozips, a cutting torch, pretty much whatever you like. I intend to make the "Z" axis in such a way that with four allen-head machine screws, I can change the "head" mount, so I can eventually use this thing for many different types of material. Though, my design is gravity based, which is just fine for any type of cutting tool that does not touch the material, such as a plasma cutter or an cutting torch. For a dremel, rotozip or router, my table design is not appropriate. You'd need to make the tracks in such a way that vertical movement is not possible, to prevent the router from getting snagged in the material, and the "truck" to keep going, tilting the router.

There is a yahoo group called "DIY CNC" if you guys are interested, there is a ton of good people there are take this hobby fairly seriously, and share what they know.

Also, I'd be happy to answer emails about making your own, if you like. YOu can post here too, but I don't get to check this forum as often as I like. I have too many projects going, and a newborn.