STL patterns change size

Greetings,

I'm using Designer 1.187 and I have the stl importer and the pattern editor plugins.

I've created a stl file using the free version of Sketchup that's been upgraded with an stl exporter plugin. I've pulled this file into Carvewright's pattern importer and sliced off a piece exactly the thickness of my board which is .750 thick. I've saved this as a pattern. While in Designer I've created a new project with a board thickness of .750 and plenty of width and length to test my pattern. When I select my just created pattern and place it on my board I notice the X and Y sizes are off in the windows. In other words; I wrote down the X and Y sizes of the slice prior to making it a pattern and they are different than the X and Y sizes now showing in Designer with the pattern highlighted. Also the X and Y's are off by different amounts. To confuse the issue even further, I've found that if I now rotate the selected pattern 90 degrees the X and Y values change again. These values for X and Y are also off by different amounts. To confuse the issue even further I tried to make a cut path from the pattern with no inset value and noticed the numbers changed again! Flipping the cut showed the cut moving on the screen but the numbers in the X and Y boxes in Designer did not change leaving one to wonder just where this thing is actually going to cut? Changing the bit sizes while the inset was at 0.00 also had no effect on the numbers in the X and Y windows even though the cut path clearly changed width on the screen.

I've searched the archives but most size change issues either not related to the stl format and the postings are so old I'm not sure if they apply to my situation.

I can see with the numbers floating all over the place why people seem to have to do so much filling and sanding to do when trying to reassemble their sliced models fresh off the Carvewright.

Is there a solution to get around this? It seems to me like it might be a software problem that should be straight forward to fix with an update?

Brad

The flip cut is only for the cut path and where the bit is going in relationship to the path. It will not change the pattern size as that stays constant.

When you are placing your pattern on the board are you un checking the "fit to board" box at the bottom of the pattern list?

By un checking the red lock on the pattern dimensions you can independently change the width and length.

Yes, I did remove the "fit to board" at the bottom of the pattern list. I realize I can unchain the pattern dimensions. Just to make sure it was a Carvewright problem and not a problem with my patterns created with the STL importer I just created a new project and placed a pattern that comes with the Carvewright basic designer. The pattern is under Basic/Animate Objects/Bulldog 01 in Designer. With the "Scale to fit board" unchecked I selected this pattern and placed it on my board sized: 13 x 5 x 1 and centered it both ways. With the pattern selected take note of the dimensions, it reads Size 3.460 x 2.800. Now click on the rotate by 90CW degree button to rotate the pattern. The size now reads 2.800 x 3.450. We have not done anything but rotate our pattern and we are already off by .01 thousandths of an inch! Try to fix this error by typing in 3.460 in the box that represents our offending size will change it to this number but at the expense of changing the other box to make it now incorrect! I now reverted back to the centered pattern as originally placed on the board. Then I've selected each of the four points of this pattern and attached them to 0 in X and Y. I can still flip the pattern horizontally or vertically with no change to the pattern size but now I am unable to use any of the rotate buttons. This seems to me to mean it's constrained to 0 but not necessarily by a positive or negative number relationship as it should be if 0 is the reference point. I would think the software would be smart enough to allow me to rotate even when constrained to 0 by swapping the x for a y and vice versa but I guess not. The only reason I attempted this rotation after constraining was to try and figure out where the software might be making the mistake. The fact that I can flip it while constrained shows me the software failed to maintain the needed positive 0 and negative 0 directions correctly. What's your take on this?

Howdy,

Since the models are pixel-based, you are always going to see slight dimension variations both when converting from STL to PTN and when rotating a PTN in a layout. This is unavoidable. Much discussion about slight dimension alterations when dealing with pixel-based models on other Forums is common, as well. (For example, the Aspire and ArtCam Forums.)

I don't worry about it because the dimension changes are so tiny, it makes no difference for woodworking anyway. Now, if we were doing precision metal machining or something like that, we wouldn't be using pixel-based models, but rather a much more expensive and different type of software (such as SolidWorks).

This could be the floor feather feature introduced in 1.186. Patterns automatically get an extra boundary of pixels to "floor" the boundary down to the lowest part of the pattern. This was to help clean up the feathers around poor quality patterns. There was some augment about it and the newer Designer Pro allows one to turn the feature off. I am not sure but I think this is what you are seeing.

That could come into play, I suppose. However, if I create a model in Aspire, for instance, then export it as an STL (at a triangulation tolerance of 0.0001), the dimension of the output STL is slightly different than the original model.

I just did a test to see what the difference is on a particular model I had open.

The original model dimensions are:
W 4.5169
H 5.5985

The STL output dimensions are:
W 4.5169 (no change from original)
H 5.6019 ( difference from original +0.0034)

Now, if I simply rotate the original model in Aspire by 90 degrees, the dimensions become:
W 5.6034 (a difference from original of +0.0049)
H 4.5223 (a difference from original of +0.0054)

Now, if I import the STL output of the non-rotated model into the CW STL Importer, the dimensions become:
W 4.483 (a difference from original of -0.0339 or a difference from the STL of -0.0339)
H 5.562 (a difference from original of -0.0365 or a difference from the STL of -0.0339)

The interpretations of the pixels, if you will, can be different from program-to-program and even within a "same" program depending on model orientation. Pixel "rounding" occurs and can vary, as demonstrated above. I am no expert on this at all, but have observed this behavior consistently for all pixel-based models I've personally worked with.

First I want to point out for anyone reading this thread that STL files are not pixel based files and that they are in fact vector based files that also may or may not also contain pixel based information. Second I'd like to point out the Carvewright and Compucarve machines are CNC machines. Most CNC's I'm used to working with were designed around the Cartesian coordinate system and use much of the development data from NIST. (http://www.nist.gov/customcf/get_pdf.cfm?pub_id=821651) I have no idea if Carvewright's software is Cartesian based or if they implemented any of the standards NIST established with U.S.A. taxpayer dollars but I hope so. While I've read many times that the Carvewright patterns are raster files I think someone that helped program the thing needs to weigh in here to set the record straight. My understanding of raster files is they are 2d based. If the Carvewright takes the 2d raster file and then uses colors as a base to generate height information it may be said it is not a true raster system and the output is in fact a 3d based system with no standard other than their own. True? False? I'd really like to know.
I thought when I was purchasing the "STL Importer" add-on I was getting a true "vector" based add on that would allow me to import and manipulate my "vector" based STL files. Since you can create a 3d model without color you would need a way to transform the 3rd dimension into a color value. For example I can draw a 1 inch square with a height of zero and save it as an STL file.(I tested this with STL's exported from several different programs) Since it has a height of zero and no color, how is Carvewright going to deal with it? I tried it to find out. I created a new project board sized 10 x 10 x 1 thinking with nice even numbers Carvewright would have an easier time with the math conversions it does. The importer seems to be working as this 1 x 1 x 0 plain shows up on my screen during import. It looks like the size is correct at 1 inch by 1 inch by 0 inch. I saved it under favorites and clicked on the sea shell in Designer and scrolled to my just created pattern. With the "scale to fit" board unchecked I proceeded to place my new pattern on my 10 x 10 x 1 board. It placed my square on my board and I proceeded to center the pattern both ways on the board. The first sign of trouble was revealed in the "Depth" window at the top, it reads "Depth 1.#QO" and in the "Size" windows it reads "1.016 x 1.016". Clicking in the "Depth" window I changed the number to 0.00 and in the "Size" windows I clicked in the first and changed it to 1.00 and hit enter which also changed the second "Size" box to 1.00 (the size of the model I originally created) Now I tried to rotate the pattern on my board using the "rotate 90 cw" button. FROZE the program and had to perform the "ctrl, alt, delete" to bring up my task manager and finish off the frozen application in order to try it again.
To test the import function further I created a cube 1 inch X 1 inch X 1 inch and saved as an STL file. (I did this with Sketchup, Art Of Illusion and Meshcam) I attempted to import this STL using the STL Importer software from Carvewright. While the windows in the STL Import Wizard under "Scale Factors" and "Working Model Size" show the imported model as a true x1.000, y1.000 and z1.000 inch sizes, further down the pattern making process makes one wonder. I moved the slice plane to 1 inch to represent the full depth of my STL cube. I unchecked the "Carve To Full Depth" and saved it to my "favorites" folder as a pattern. Again using a board size of 10 X 10 X 1 inch as a new project I selected my cube from the pattern list and placed it on my board and centered it both ways. Strange results again! The "Depth" window reads 1.000 as it should but the "Size" windows show my 1" cube now sized 1.016 X 1.016. My cube is no longer a cube and it's grown in two directions. For kicks and giggles I clicked on the "rotate 90 degree cw" button. My new pattern rotates just fine and the sizes remain constant. I click in the "Size" window and change my size to 1" and hit enter. It sizes both windows to 1". Great, my pattern is now 1 x 1 x 1 as originally intended and rotates without changing sizes; as it should.
Clearly the software has some issues and I'm looking forward to an updated version. For now I'll try and document it's limitations so we can navigate around the holes in the road until the road crew can get out there and perform some patching.

Anyone with the newer Designer Pro could test your assumption and if true I'm wondering if a patch is in order for those of us that paid for the STL Importer thinking it would work properly with the basic Designer?