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Improving or adding tolerance/precision

vulcan500rider

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Joined
Nov 28, 2007
Messages
558
Location
Regina, SK
Hi, all!

Back for more advice, I'm afraid. So I've been experimenting. had a hell of a time with PETG blobs and strings, but sorted it out (most of the time). I also calibrated everything I could figure out how to--I used a calibration cube to get the x/y/z to proper steps, I calibrated my extruder, as well. I've even built a dry box to try to ensure moisture isn't an issue, and successfully printed bolts and nuts that fit well together for the build.

However, what I just can't seem to get to work is having my various flat pieces fit well together. I'm trying to do something akin to stained glass, so I build everything in CAD and then extrude the parts that I want to print for each colour (so just the frame for black, then pieces 1 and 4 in green, 2 and 3 in red or whathaveyou). I get all of that into Cura, slice it up, and take it to the printer.

I've tried printing everything exactly as it is extruded, but it just doesn't fit. The interior pieces are larger than they should be to fit the frame. Fine. So I try scaling those pieces down by a percent; the smaller ones are still too big, mostly, and the larger pieces fit, but if there are any remotely complex angles, they fit improperly because the shrinking changes the angles...

Ideally, I would love to be able to avoid rescaling, and instead take off 1mm around all edges, but I have not idea how to get Cura to do that. I guess I could try to build in an extra boundary in CAD and then not extrude it, but that seems like a hell of a lot of work.

Has anyone made something like this work?

Thanks!
 

lowfat

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Feb 12, 2007
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Grande Prairie, AB
You should look in to doing a tolerance test to see what your printer is capable of. On my Prusa, if I want a 3mm hole, I design the model to be 3.4mm. So if you need multiple parts to fit very snug, you'll need to know exactly how much you'll need to modify the edges of the parts by.

Also calibrate linear advance if you haven't.
 
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lcdguy

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Folding Team
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Mar 17, 2007
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An undisclosed location
when I need to design close fitting parts i try to make the dimensions all divisible by the nozzle diameter with no remainder if possible.
 

danmitch1

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Dec 15, 2007
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1,880
I find leaving a .25 mm gap in your design works perfectly.. at least on my printer.. seems close to what lowfat has actually.. as a hole would be .25mm on both sides giving me a total of .5mm.. Or another good way is for example.. design a 10mm part, if your physical print comes to 11mm, change the digital model to 9mm.
 

vulcan500rider

Well-known member
Joined
Nov 28, 2007
Messages
558
Location
Regina, SK
Thanks for the advice, as always!

I have found a few tolerance tests that I can try out. So, do you then take that information and scale accordingly in your slicer when you print, or are you building that tolerance directly into your CAD models, prior to slicing? And, if possible, try to make dimensions multiples of the nozzle diameter--again, in CAD, I presume?

Also, thanks for the tip on linear calibration, lowfat. I had never even heard of it before. Is that something that you did through a firmware update, or a different process? Are there any guides you found useful? I took a quick look, and it seems that some have had issues getting it to work on the V2, and some are saying they got it working with some sort of config change, but it went above my head.
 
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