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FelixPQ
02-13-2012, 09:37 AM
Hi,

I made a few STL patterns, simple parts actually and each time I put one on a board with "scale to fit board" on or off, the dimensions are incorrect, not by much but still off. Most of the time I wouldn't care but sometime I would like to be as exact as possible with this machine.


Anyone as noticed that? Can I use the manual size box without adverse effect (though it shouldn't be necessary)?


Just a note, the STL importer reporst the exact design dimensions as far as I can see, it seems to happen when the stl model is converted to a pattern.


Thanks,
Felix

Alan Malmstrom
02-13-2012, 01:04 PM
I don't know about STL importer but raster patterns I know. If you have white space around a raster pattern when it is imported the software then automatically crops your image to the edges of the darker pixels. And this effects the size that you have set it up to be. It's a little bit of a hastle to get the right size pattern but it is possible. I don't know about STL import though because I have never used it. Sometimes I draw a box in Designer and change the size to what I want and then just eyeball it while I resize the pattern.

Alan

Digitalwoodshop
02-13-2012, 01:06 PM
If your Real World Board is too small then it will ASK YOU on the LCD... Scale to FIT? Watch for this....

I would make a STL Scale Factor Pattern or Guide Board... This takes into consideration the calibration of your machine that has a direct relationship to what the Digital turns into when cutting the Actual Board... Remember the Pulses of Rotation need to be setup as a Scale Factor of Rotation to Inches of Board... Dealt with this all the time in my Analog Gun Fire Control Computer Days..... Rotation of a Shaft to Yards of Distance...

The down and DIRTY way to take out this digital scale factor error for YOU is to cut a test board..... I did with a few bits, here I did one with the 3/8 Bit that LHR sells. My test board in clear pine works well to get me close quicker. The Wood will Swell with Humidity and Shrink when dry... But it is close.... I then find the required dimension on the board and look at the readings on the designer mpc for that slot. This takes the BIT DIAMETER Out of the Calculation... You may simply be seeing the Center of the BIT as the Designer Measurement and the REAL WORLD BOARD is cut with a THICKER BIT.... So your size is off by the thickness of the Bit.... 1/2 the diameter for each side...

I have 4 machines and the same test board cut on one machine is different for the the other so I label the boards with the machine...l

Good Luck....

AL

eelamb
02-13-2012, 04:51 PM
FelixPQ, yes I have seen this. An example is I import an STL file, it is 6.727 wide. When I place the pattern on a board in designer it shows up as 6.750, and when I look at the same pattern in PE it is 6.734.
If you change the size in PE (Pattern Editor), the pattern on the board in designer does not match the size you set in PE. This must be a recalculation due to the 1/16" bit, depth, and 7 deg. angle of the bit. At least that is my feeling.

mtylerfl
02-13-2012, 06:23 PM
There may be other factors involved, but the primary reason the dimensions differ slightly from the original STL vs. the PTN is due to mathmatical rounding in the software itself. This occurs when using any pixel-based conversion method, regardless whether it is Designer or some other software. An STL is converted to a pixel-based PTN in Designer and that's why you see the small discrepencies. No pixel-based conversion can deal with fractional pixels, so they are rounded to the nearest "whole pixel" up or down. Plus, depending on the software used and how it is programmed, the rounding factor may vary. Not really a problem, though - I've not had any serious issues when creating "fit-critical" projects - your parts should still fit together just fine.

FelixPQ
02-14-2012, 04:44 AM
mtylerfl,

I can understand that if an STL file is converted to pixels it will most likely be off by a little amount. I wasn't sure about that. Is it the same with vector files like DXF, AI and or other vectors made inside designer, are they converted to pixels as well?

Thanks,
Felix

mtylerfl
02-14-2012, 07:53 AM
mtylerfl,

I can understand that if an STL file is converted to pixels it will most likely be off by a little amount. I wasn't sure about that. Is it the same with vector files like DXF, AI and or other vectors made inside designer, are they converted to pixels as well?

Thanks,
Felix

That's a good question, Felix. An imported DXF remains a vector and I don't recall seeing any dimension changes of those after importing. But remember, you must create "correct" DXF files to begin with...2D only...no 3D DXF's.

FelixPQ
02-15-2012, 05:10 AM
That's a good question, Felix. An imported DXF remains a vector and I don't recall seeing any dimension changes of those after importing. But remember, you must create "correct" DXF files to begin with...2D only...no 3D DXF's.

That's what I thought but wanted to make sure. It's really unfortunate that we can't use any form of 3d vectors, it would such a time saver...

Thanks,
Felix