Art Cutting

[tizise]

I run a Thermal Dynamics 300 Ultra-Cut Plasma Cutting System with a Burny controller and Kaliburn iNOVA height controller. I use FastCAM, FastNEST, and Solidworks. But, I've only been doing all this for about six months, and I'm otherwise completely new to the metal fabrication industry.

In an effort to generate further business on the machine, my bosses started putting more emphasis on detailed art cutting. So, we began experimenting with a simple Texans football logo outline drawn in AutoCAD. (Don't ask why my boss likes the Texans. I can't explain it. 'Course, Dallas isn't much better lately.) But, we're having some problems getting rid of the pierce hole left on inside cuts. Because they're simple profile lines to accentuate the bull logo, they are very thin, even in full scale, and the diameter of the pierce hole is often twice that of the kerf on the profile lines (.071" on 1/8" thick mild steel). We've tried reducing our pierce hold down to virtually nothing, and even nothing at all. But, the overly large pierce hole remains. I've noticed that before the pierce hold delay, there is an 'arc-on delay' reading on the Burny. I'm unsure as to whether or not this is the source of the problem, or, if it is, how I might reduce, or remove it.

Any suggestions?

[Torchhead]

Pierce holes will always be wider than the cut kerf. That is one of the reasons you use lead-ins. The concept is to pierce in an area that falls out. Cutting decorative plasma with CAD is a slow and challenging process. In decorative cutting you have to be able to easily import vector clipart (EPS, AI, WMF). High quality vector clipart is available at www.vectorart.com The clipart available in DXF is limited and hard to edit in conventional CAD. The other challenge is dealing with text. Not just sticking in a line of text but being able to wrap it around a circle or along an arc. You need to be able to quickly weld objects in the drawing and fix text so the centers of letters do not fall out.

You have great (and expensive) tools but you can do a lot more, faster, with a copy of CorelDraw X3 and the low cost SheetCAM that allows for plasma specific parameters. Trying to cut and sell dozens or hundreds of the same design puts you in competition with China and Mexico. The real profit in decorative cutting is to do custom and one-off (personalized) designs. That requires you don't spend hours designing or setting it up.

You need to master the drawing/artwork side of the equation. The cutting part is easy.

[tizise]

Oh, the Texans logo was just an experiment. We never intended it for mass production. We just wanted to try and see if we could make an art-type piece come out clean. Obviously, we're going to have to expand from inside contour lines into three-dimensional shapes to avoid that pierce hole showing. Unless you think a pierce ramp might help?

So is it that you prefer SheetCAM to FastCAM because it imports the EPS and AI formats rather than just DXF, IGES, and DWG like FastCAM? The reason I ask is because I'm having trouble finding specs on SheetCAM (i.e. what file types it will import).

Can you suggest any programs good for importing a scanned hand-drawn, or printed image for cutting?

I certainly appreciate all the advice. I'm pretty green in the industry, and I can use all you can give me.

PS
Any suggestions on
...improving small holes for industrial parts?
...getting rid of the small notch that seems inevitable on inside circle cut-outs (even with a lead-in and lead-out)?
...reducing smoke on an above-water table?
...removing the bevel?

[LeeWay]

You can download a free trial of Sheetcam or TNG here.
http://www.sheetcam.com

[Torchhead]

SheetCAM is not a drawing program. It only imports files that are ready to cut (finished artwork) It's import formats are: DXF, HPGL, EMF. It also imports Excellon drill files for PCB drilling but you won't need that! TNG (I think) has added import capability but is still not a drawing program where you can import different files, and in text, weld and trim objects and generally get it cut ready. CAD is great for drawing simple objects. 3D CAD is WAY overkill for 2D plasma cutting and still has limitations for "artsy" type cuts.

Your drawing/CAD program is what has to be able to import the vector clipart. See, the decorative cutting process is more art than pure drafting and the sign folks know what works to do cutouts in vinyl and wood (vinyl cutting is similar in process to plasma). The clipart for signmaking is where their are thousands of designs to choose from. Most sign shops have CorelDraw to generate artwork. You can export from Corel in DXF or HPGL that SheetCAM can "see".

To use lead in's you need to draw in closed objects (like making paperdoll cutouts) and you cannot allow objects to overlap. You then can pierce inside or outside (whichever is the scrap part) and eliminate the pierce devits.

Ramped lead in's won't help. You have to get a complete pierce before you start moving or it may never pierce completely.

Pierce time varies on the thickness of material and even type of metal. It's best to use an ARC OKAY (signal from the plasma) to sense when you have a valid arc so you don't have to continually change the pierce delay manually.

TOM CAUDLE
www.CandCNC.com
Totally Modular CNC Electronics

[Switcher]

tizise,

I would suggest that you have a look at Inkscape for creating your art. I have a plugin on my blog that will output a DXF from Inkscape.

Inkscape is free, so you could have a copy at home to practice with (or gov. jobs ).

I used Inkscape to create approx. half of the dxf files on my blog (the latest files).


.

[tizise]

Thanks for everyone's help.

Small holes and slots seem to be improving. I've been decreasing my speed to about 75%, using path continuous for my lead-outs, and turning off my AVC.

Smoke is still bad, especially when I cut 3/8ths with a 100 amp tip.

Still occasionally getting a one or two degree bevel.

I'm not using SheetCAM because I prefer FastNEST. But, I have been working and practicing with both Inkscape and CorelDRAW Graphics Suite 12.

I think from looking at Torchhead's bulldog cut, that pierce hole we're trying to get rid of is inevitable. I can see the same thing in the image he provided. I guess it's just a matter of making it look good.

[coalstove]

I have been a Corel and Adobe user for a long time and created alot of artwork for not just plasma cutting. Your leads in and out are key, time behind the keyboard has been my best teacher. The best thing since sliced bread is the "delete" button, you can always start over, dissect your artwork piece by piece, remember the old saying, measure twice cut once.

Chip

[Torchhead]

If you build your artwork generically with closed objects using Corel's Bezier curves then they can be used for any type of cutting: Plasma, engraving, routing, vinyl, stencil, etc. With the proper CAM you can add automatic lead-ins/outs and tool offsets. Packages like SheetCAM let you add those things automatically and even which side of the object you want the lead-in and what type of lead-in (arc, tangent, perpendicular). Lengths of lead-ins are done "smart" so that if a lead-in is called to be 1/2" and it will not fit in the area, then it will automatically reduce the length ("don't color outside the lines"). You can redefine any single lead-in and even change where they occur with one mouse click. Not so handly in plasma, but great in doing multi-part routing, is the tab feature that allows you to define a holding tab on the outside shape and choose the width of each tab and the depth of cut over the tab.

By keeping your CDR Corel files native and generic they can be used for other cuts or even illustration without a lot of changes. It can help to close a $$$ deal if you can quickly show a customer a nice shaded isometric drawing of what they are going to get using the actual artwork you will cut from. In custom work it is essential that you get a drawing of the finished design to the customer to sign off on.

We have done a few large custom gate projects with full scenes. Using Corel and ISOCalc (to get the isometric angles/depth) we did up a color/shaded drawing of the entire gate to scale in their entrance. In the end the customer got exactly what they selected and signed off on.

In another case where it was large letters on the side of a building. We took pictures of the building and using CorelDraw to super impose the art over the bitmap of the building to scale, we were able to pick up a $3500.00 job via e-mail. I used the Corel file that was to scale (1:1) to plot out (using our vinyl cutter with a pen) a placement pattern over 20 ft long. We glued it to long pieces of masonite and used it to put on the stone wall and drill mounting holes for each letter. We plotted each letter full sized with hole locations on the back of each letter and had a local shop weld 1/4" aluminum rod pieces in the holes to form studs. The masonite pattern had the same hole patterns so everything matched up perfect. Though out the process we used the same basic CorelDraw file and just added the details on layers.

TOM CAUDLE
www.CandCNC.com