DXF Stepping

[john@mindsightdesign.com]

Hey folks, I have another newbie problem. I am trying to import a DXF into Part Wizard from one of several programs. I am trying to eliminate the number of steps in the imported DXF.

The shape is an ellipse. I am exporting from an old program called Vellum, also Rhino. When I draw the parts in Rhino, and export as AI (adobe illustrator, the parts come into PW as a spline, no visible faceting. One problem is my scale is not 1:1. All the units are set in Rhino for the export, but when imported into PW, it's not to scale, I can't figure it out!

This job is running out of time, many have helped with my vacuum questions, but now I am trying to make my spoil board and need some suggestions for this DXF problem. Any suggestions?

John S.

[kerrazy]

John,
send me the dxf version and I will try and make it work for you. I should be able to have it turned around for you today.

dale

dale.kerr@sympatico.ca (mailto:dale.kerr@sympatico.ca)

[john@mindsightdesign.com]

Dale-
This is what I did:
I drew the shapes in Vellum (only do it because it has good printer control), imported to Rhino as IGES, exported from there as an AI (adobe illustrator) file.

I opened the file in AI to see if the scale was off from the Rhino export and it was still 1:1. I then resaved as a native AI and when imported to PW, it was still not to scale. This all seemed to work for the eliminating of facets, but it doesn't solve my inability to import DXF's properly.

How do you do it, do you have Rhino? I think it is in the export from Rhino. I think that if I send you a DXF, it will be stepped. I tried all DXF export methods within Rhino and either it imported in pieces or stepped.

John S.

[kfitzgerald@graphicmetalsinc.com]

John,

I export dxf files all the time directly from Rhino to Part Wizard. I have found that the AutoCAD r12 flavor works the best.

Don't understand what you mean by "stepped". It will come into Part Wizard as individual lines (is this what you are calling "facets"), but this is not a problem at all.

As far as the scale problem goes, I think you are somehow creating this by all your conversions. I have never had a problem creating dxf's with Rhino and importing into PW. Having said that, you can easily correct the size in PW by selecting the ellipse, going to transform, and typing the correct size (if you know it).

Regards,

Kevin Fitz-Gerald
Project Manager

Graphic Metals, Inc.
P.O. Box 31
715 East Perry Street
Bryan, OH 43506
Voice 419-636-5757
Fax 419-636-6404

kfitzgerald@graphicmetalsinc.com (mailto:kfitzgerald@graphicmetalsinc.com)

CNC laser cutting up to 14 ga steel
CNC routing wood and plastic

[graphicmetals]

John,

I drew a 4" x 8" ellipse in Rhino and exported both a dxf and an ai file. I imported both into Part Wizard and the dxf imported at the correct scale, while the ai file imported at the wrong scale.

I don't see the advantage you are trying to gain from the ai format. I will email you the PW file.

-Kevin

[john@mindsightdesign.com]

Well, at least from what I see on my screen, if you zoom in on the dxf import from within PW, select, ungroup and reselect the entire ellipse - then zoom in on an edge of the ellipse. You will see that the ellipse is created from straight line segments. The AI file will show one continuous curve with handles on it.

I don't know if the cutting software just interpolates the curves back into straight lines or uses the curves, but I have received CNC wood, laser/water cut metals, and plastics and vinyl letters from guys that didn't understand that this was happening with the DXFs. They usually end up re-doing the job unless they catch it early. Now that I have a Bot, I am running into the same problems, but I don't want to just run a file as they would. These guys also have an arsenal of CAM packages and programmers with many years experience. I normally just give an IGES and the problem is solved. With vinyl cutters, I give an AI file.

Perhaps the number of line segments in the ellipse will will run fine, but I just have to believe that a more simple and pure curve will run more smoothly. Anyone care to correct me? I will be more than happy to run a shape that is broken up into 1000 straight lines if that is how the Bot sees it.

john@mindsightdesign.com (mailto:john@mindsightdesign.com)

[gerald_d]

The Shopbot code only accepts straight lines or circles - you have to chop up curves into one of these two codes

[kfitzgerald@graphicmetalsinc.com]

OK John, I stand corrected. I am happy to report that the AI format does in fact produce a cleaner cut than DXF. I'm happy because this is going to help us make a better product.

What I did was to cut a side-by-side comparison of two identical ellipses; one with a DXF file, the other with an AI file. The results are clear. The DXF cut is composed of many visible straight line segments. The AI cut has no visible straight line segments. It appears to be a smooth arc.

In adition, the AI cut part was 87.5% faster than the DXF; 21 seconds compared to 24 seconds. All feeds and plunges were identical.

Well done John! You are on to something here. Now, back to one of your original problems. The AI imported at some crazy scale, but knowing the ellipse should be 8" long, I simply changed the length to 8" using the transform tool. Took seconds to accomplish.

I appreciate you bringing up this topic. The AI format may even make our vinyl cutting guy happy.

Regards,

Kevin Fitz-Gerald
Project Manager

Graphic Metals, Inc.
P.O. Box 31
715 East Perry Street
Bryan, OH 43506
Voice 419-636-5757
Fax 419-636-6404

kfitzgerald@graphicmetalsinc.com (mailto:kfitzgerald@graphicmetalsinc.com)

CNC laser cutting up to 14 ga steel
CNC routing wood and plastic

[gerald_d]

Regarding resolutions of ellipses and curves, you may have missed my interjection that the ShopBot will only cut straight lines and circle arcs - it cannot cut smooth curves or ellipses. (This is true for most CNC machines, and not only ShopBot). Have a look at the .sbp file and you will see if the commands were for straight lines (M commands) or circle arcs (C commands). The length of the file (no. of commands) tells you how many segments the ellipse was chopped into by your software.

Just for confusion, if I draw a 20x14 ellipse in ACAD LT2000 and take it to Vector, Vector will chop it up into about 130 straight line segments. If I draw the same ellipse directly in Vector, it asks me if I want circle arc segments (default) or straight lines. With arc segments it chops into 40 pieces, with straight lines it chops into 1500 tiny pieces! Of course the circle arc segments are the smoothest curve and least number of lines of code.

[graphicmetals]

Hi Gerald,

No, I didn't miss your statement about the straight lines and circle arcs. True, and well worth noting. I was aware of this, hence my statement in my first post that the geometry coming in as individual straight lines (via DXF) is not a problem.

However, as I stated above, "...The results are clear. The DXF cut is composed of many visible straight line segments. The AI cut has no visible straight line segments. It appears to be a smooth arc."

The key words here being "visible" and "appears". The cut based on the AI file is still composed of individual straight line segments (and circle arcs), but that is not how it appears. And as we know, appearance is everything when it comes to CNC machining.

I would encourage others to repeat my "experiment" in comparing DXF to AI. I'm sure this is nothing new to most folks on this board, but it is a pleasant revelation to me.

-Kevin

[kerrazy]

Kevin,
I too have had a similar situation. I had the challenge of creating pocketed circles to hold medallions. When I first cut the item, which I thought was a pretty decent circle, it ran the lines so I had a poly sided circle, rather than a true circle. I ended up putting in millions of nodes to reduce the sides. This seemed to work fine. Than I was trying a demo version of ArtCam Pro, and it has a place to adjust allowances, that PartsWizard does not. I set the allowance to .0004 and the circles were great DXF, or AI files. I found this to be the solution, and maybe there is other software out there that will allow the user to adjust allowances?
Dale

[gerald_d]

Kevin, I go along with Dale in that one must check that your software is set up correctly. Yes, there are some programs where you cannot change the resolution/allowances (we find this all the time when we work in millimeters and the programmer was thinking only inches). Your experiment wouldn't encourage me to stray away from PW to see if AI does it better - rather, I would try to find a way in PW to make it better.

Connecting the "problem" to a dxf file is not correct. A dxf file can be produced by many programs, set "coarse" or "rough" and it can give you exactly what you want. If you open a dxf with notepad, you can see that it is simply a table of coordinates and the line types that connect them - a very similar structure to the ShopBot .sbp file. The rough steps are not caused because it is in .dxf format.

Sometimes, when we get the millimeter/inch problem we scale up/down 25 times and then a fixed resolution gets into the right proportion that the programmer had in mind.

[gerald_d]

Oops, I meant "smooth" or "rough

[jsheldrake@pollyspies.com]

I have a newbe problem. I can not inport DXF from autocad. I have 2000 and have tried by saving in 12, 13 and 14 still no luck. I can bring in DXF files from correl draw.

Help Jimmy

[gerald_d]

Try closing the file on AutoCad first. When AutoCad has a file open, it blocks all other applications from using that file.

[graphicmetals]

Can't import into what program?

[kaaboom_99]

I had a similar problem with Corel 10 in that the .dxf files I exported would not convert with the SB converter unless I exported as an Autocad ver.10
Try saving your file as an earlier ver of Autocad if you can.

[SPOT ON! (Unregistered Guest)]

just go out and spend the money on enroute by
amiable technologies
and dont stuff around converting files when
you can use one program to do it all!
TIME IS MONEY