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What to adjust so Ultimaker can start printing wholes for M3/M4 (now holes are too small)

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Well I noticed that lots of projects using precise wholes like for M3/M4 nuts...

Unfortunately after adjustments my UM can't print precisely, not sure what I'm doing wrong...

When it's coming to any wholes which should fit on rods, or anything else to 0.2mm I can't print it as it will be always in wrong size... Drives me crazy as now it prints really nice but useless as any object, model isn't precise...

Any ideas ?? Hard for me to believe that UM can't print precisely enough for pretty common nuts like M3/M4....


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Hi Carmamir,

It is common for the holes to be a little smaller than expected because the plastic (PLA or ABS) shrinks a little as it cools. You can try to account for this in your models by making the holes a little bigger than you need, but it's almost impossible to accurately estimate just how much they will shrink. When I make holes for a M3 screw I typically make them at 3.2mm diameter. That usually still leaves the holes fairly small so that the bolts bite in (and form threads in plastic). You can also drill the holes out to the proper size after printing, which I think is what most people do.

Another common problem is oval shaped holes. If your holes are not perfectly round then it's usually a problem with the short belts not being tight enough. Make sure that the short belts between the motors and the rods are as tight as you can make them.




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Due to the physics of extruding plastic in a circular path and the properties of the melted plastic, the extruding material will "pull" toward the center of the holes while printing. This is unfortunately normal and expected. You will find the effect is greatest on small holes and diminishes as holes get larger. To print a 2mm hole, it might be necessary to size the modeled hole at 2.75mm or even 3mm before slicing. On 30mm hole, your model may be 30.25 or less to get the desired result. Trial and error is the key to success. When I have a hole that is critical, I make test prints that duplicate the intended print settings and even the surrounding geometry of the part. I can generally make one test print, measure the print, make an offset in the model and print precisely (repeatable and within a reasonable tolerance) the size hole I want on the finished part. Lately, the guesstimate used to make a test print tends to be right on and needs no further adjustment. If in doubt, err on the small side and open undersized holes by drilling if necessary.



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How accurate do you need? You should be able to get errors under (1% +.5mm) for X and Y directions and much more accurate in Z direction. Also the errors are consistent so you can simply print a part, then adjust all the errors into the CAD and then print much more accurately the second time within about .1mm. I don't think you can get better than about .1mm accuracy.

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