BAD CUTS - What's going on?

[signtist]

When I cut out some simple letters, it's cutting weird shapes. Jogs in the curves. Not showing on the drawing. I'm cutting from VCarve pro or Aspire. This has never happened before.

[chodges]

I'm not sure if you are having the same problem we were, but your symptoms are the same ...

Turn your control box ON and see if you can move either side of your gantry even the slightest bit by hand. Then try to move your spindle/router mounting plate by hand.

If you can move any of these, then turn your control box OFF and remove your motors. Check the set screws that hold the gears on the motor shafts. Ours had worked loose, and were causing the same slop (unwanted jogs in curved shapes) that you are describing. When we re-tightened the set screws (there are TWO per gear - one over the shaft key, and another about 1/4th a revolution away from the shaft key), our problem disappeared.

Hope this helps!

[signtist]

No everythings tight....it's in the cut path.

[beacon14]

Are you sure the angle of the bit you used for cutting matches the angle of the bit used in the toolpath?

[signtist]

On a 15" O .....it looks like a potatoe with lumps, some "Lumps are 1" or so out.
The center of a 15" 8 is not a nice oval, its a wierd potatoe shape. Yet the drawing tool path looks fine.
Something is major wrong!

[Brady Watson]

John,
You might want to check your pinions if you are running anything other than a PRS Alpha with keyed gears. The grub screws on ALL other tools are notorious for loosening when you least expect it & should be loc-tite coated prior to cranking them down to the point of bending the hex wrench (no kidding! - this is why SB gives you 3 hex key wrenches when you buy a 4X4 or larger tool!)

Don't be fooled - you should pull each X and the Y motors off and inspect them off of the machine to be absolutely sure. A quick glance while they are on the machine will not verify this.

Just for the heck of it, throw some scrap on the table and go into SB3 and run the CC command (be sure to set cutter dia in VC 1st) and cut out a 12" circle at 2 or 3 IPS. If it comes out oblate, then you know the pinions need attention or one of the X motors has a 'lazy' driver - OR your unit values are off (verify via VU command). If it comes out perfect, then you have a software problem, which in my opinion, is a rare instance.

-B

[myxpykalix]

If your "lumps" are 1" out from your toolpath you might check your vectors to make sure everything is connected, that might be a possibility? This has happened to me in partwizard in the past.

[signtist]

I've got the PRT Alpha 4'x8'. I'm having the computer checked out right now. Seems fine. I'll check the paths to make sure the paths are closed.
This seems to happen with files from customers, not my created files.
Any other suggestions?

[signtist]

Jimmy, I think I just figured it out. I tried using an EPS file instead of a DXF. It works great-nice and smooth.
Thank you so much..........

[Brady Watson]

John,
Are you doing a DXF conversion via SB3 or are you using PartWorks or similar CAD/CAM program?

-B

[signtist]

Brady, I just take the customers file into CorelDraw and export as a DXF file to VCarve or Aspire. This has worked fine for the last year and a half since I got the Bot.
I don't understand "conversion"
The EPS seems to work fine.

[chodges]

We are using Corel Draw v12, and we have experienced some of the same issues with exporting to .DXF files. My guess is that there are issues with the way Corel "converts" a file originated in another format to .DXF format vs. the way PartWorks interprets the .DXF file.

When we bring the exported .DXF files into AutoCad, they are not "clean" - vector segments are not always properly joined, and sometimes there are phantom lines that don't appear in the original drawing. We have also noticed that curved shapes are made up of short straight line segments (splines) - not true arcs.

When computers use spline functions to interpolate (smooth) a set of straight line segment nodes to approximate a true arc, they are limited by the roughness constraints imposed by the interpolation algorythms. The result is a shape that closely approximates a true curvilinear arc, but which is really just a piecewise polynomial (parametric) curve interpretation called "curve fitting" which is based on points along straight lines.

This strategy always introduces a bit of error, and I suspect that PartWorks' strategy may be just different enough from Corel's to cause your toolpaths to be less than wonderful.

.EPS files generated from Corel Draw work MUCH better for us too - probably because the spline functions used by Corel to create .EPS files are closer matched to those used by PartWorks for reading them.

[gerryv]

I came across this about a year ago after reading some positive discussions. I've never tried it but it might be worth a look. I've no connection. - Gerry

http://www.candcnc.com/DXFToolDetails.htm

[Gary Campbell]

Charlie...
Right on the money! We cut for local sign companies. They design in Corel 12. We get much better vectors from them using .eps than .dxf. This has worked better than them sending their ver 12 files to our ver X3.
Gary

[signtist]

QUESTION - Why did the DXF files work for my first year and a half of owning the ShopBot, then all of a sudden it starts acting up?
EPS files are now the preferred method.

[erik_f]

you may be getting older versions or newer versions of the DXF format...from auto cad 14, or 12, or what ever...you get the idea.

[dray]

John. It may be a setting in sb3. If you have upgraded to a new version of sb3 this may be the culprit.

[signtist]

I just install Aspire a few weeks ago, but I have not upgraded anything else.

[chodges]

John;

If any aspect of the "mix" has changed, that might have introduced the difference you see between "then" and "now."

For example, if you previously used files originated in one version of Corel Draw and now you are using files originated in another version, it's possible that Corel Corporation might have changed the .DXF Export code in Corel Draw as part of the newer version. Any such change has the potential to be more compatible with some software and less compatible with others.

Unfortunately, there are no industry standard chunks of code that everyone can use in their programs to ensure perfect compatibility. Instead, each software company must "re-invent the wheel" to come up with their own code for deriving "foreign" (not natively generated by the program) file formats.

Discrepancies are inevitable because of this. Not that any one software company does this necessarily better than another, but that they all approach the same problem using differing strategies to some degree.

[dray]

Charlie is right. This constantly happens to me with software.

Back when software/hardware Technical support was done in the USA and not India, the tech's would always ask what was the last thing you installed before the problem started.