Printed Pusa parts don't fit well (too small)

Hi all,

I'm trying to print extra parts for my Prusa i3 to have them as replacements. I'm having an issue which is quite annoying. The overall size of the part is quite what it's supposed to be +/- 0.1 - 0.2 mm. However all the inner holes and cavities are smaller thant they should. For example I've printed a x-carriage (30 mm) the cavities where the M3 nuts are supposed to fit are too small. Not much, but I allways have to end up with a rotatory tool to make everything fit, which is a time-consuming activity.

I've calibrated my printer to the best of my abilities, also the filaments, etc. I'm guessing it is a slicing issue. I'm using now Sli3r. Is there anything in special I should be watching for and I could have missed? or is the Slic3r buggy on that regard?

Any thoughts are welcome. Thanks in advance!

Edited 1 time(s). Last edit at 12/03/2014 09:00AM by Hauser.

To my knowledge it is an standard issue with the slicer, when I design my parts I account for that but on already made files you got two options: either heat up the nut and press it in or scale the part to correct size.

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ggherbaz
To my knowledge it is an standard issue with the slicer, when I design my parts I account for that but on already made files you got two options: either heat up the nut and press it in or scale the part to correct size.

thanks, good to know I was doing it the rigth way. Do you know if it's an issue with all slicer software out there or it's Slic3r specific?? I was about to try Cura to see if it improves things.

Usually a M3 nut is 5.5mm but I draw them at 5.7 for a perfect fit, a M3 hole instead of 3mm I draw them 3.2mm, a 4mm hole will be 4.3, the Lm8uu holes are 15.5 instead of 15mm.

All the slicers have that problem, I use simplify3d and it have it too.

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ggherbaz
All the slicers have that problem, I use simplify3d and it have it too.

that's some useful info. I just wish everyone could take it into account. I will certanly do it if I ever design something worthy of beign shared.

Unfortunately most of the people opt for the heating fit than to find the right size of the holes through experimentation. Both ways are a pain, because you either have post print processes or need to keep on hand a table for right measuring (what I do) .

Slicers are still in infancy, all those bugs will be sorted out with time.

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ggherbaz
Unfortunately most of the people opt for the heating fit than to find the right size of the holes through experimentation. Both ways are a pain, because you either have post print processes or need to keep on hand a table for right measuring (what I do) .

Slicers are still in infancy, all those bugs will be sorted out with time.

I hope so. The thing is that I only have the STL file and I don't know how to modify it (or if it is even possible), so I will have to go for the mechanical post-processing...

If you willing to sacrifice some filament, do a rule of 3 and scale the part to the right percentage, print just one thing and see how it comes out, if my math is not too rusted scale it to 103%. That should cover any hole difference and should not affect the rest of the part too much.

Quote
ggherbaz
If you willing to sacrifice some filament, do a rule of 3 and scale the part to the right percentage, print just one thing and see how it comes out, if my math is not too rusted scale it to 103%. That should cover any hole difference and should not affect the rest of the part too much.

I'll try that and see how it goes, thanks. BTW what are the usual settings for printing the printer's parts? I mean layer hight, infill %, etc...

For those parts I usually print at 0.3 layer height, 20% infill, 3 perimeters 4 solid bottom and 6 solid top. Speed will depend on temperature but 30 to 50mm/sec is what I use. The secret is your first layer, 0.15 first layer and 50% the speed, and level your plate to 0.1 from nozzle.

Models are polygon meshes, so all curves are actually segmented polylines and a polygon always has smaller area than its enclosing circle
http://hydraraptor.blogspot.com/2011/02/polyholes.html


There are more possible reasons, wrote an article about them here.

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