How can I encourage my printer to color inside the lines?

Whenever I try to print designs with interlocking parts, such as , I always find that the parts won’t mate – both sides are too big by about 0.25 - 0.5 mm – and I wind up doing a lot of work with an xacto knife to get even one set of parts to connect. Something like cannot be printed at the default size and come out wiggly – the parts fuse. I have to print it larger to get it to work. The printer seems to want to color “outside the lines” a bit.

I had for a while presumed the problem was with the accuracy of my printer itself, but when I went to the Aleph Objects open house the other night, I saw lots of mechanical things that did not appear to have been laboriously shaved down the way I have to do. So I can only presume that I am somehow using it wrong.

I am for the most part printing on the default profiles cura gives me, using HIPS. Do I need a smaller nozzle than the default 0.5mm one? Do I need to use a particular filament? Print on slow settings? Is there an expert “color inside the lines” setting somewhere? Or perhaps this is better asked in the reverse – what do find you have to do to make mechanical parts work?

The best you can do is ensure the e-steps are correct and you’re not over-extruding. Also have to keep in mind the original designer of the part. Their machines may be calibrated differently and often times may not be designing the part completely accurately.

The multiplier or flow rate setting is best ally. I usually adjust down to 94% on my TAZ 5 to ensure good fitment of interlocking parts. Make sure you don’t go too low starving the extruder… or more importantly, reducing layer adhesion higher up in the print.

If you can, design your own test. Make a rod of a set O.D and create a cylinder sleeve with I.D. which is +.5mm. I like to print a quick thumbscrew cap I designed that fits over the M3 or M5 screw caps as a test.

I like the multiplier/flow rate variable because its easy to adjust in the slicer to accommodate for filament issues also (i.e. larger than normal average diameters, fillers and sometimes colors of filament).

Hope that helps.

I have never really asked any of them what they do to get such good prints. :blush: But I know some have customized their Cura profiles to improve part fit issues.

Oh wow – there it is! The Cure profile for eSun HIPS lists a filament diameter of 2.85 mm, when it says right on the reel it’s 3.0. My fit issues have disappeared. Thanks!

Actually, 2.85mm is sort of a default estimate of what is commonly the actual diameter of “3mm” filament. One of the first things to do with any new spool of filament is to measure the filament diameter in several places over a meter or two. I generally check a spot, rotate my micrometer or caliper 90˚ to measure in a different axis, then move on to the next point and repeat the process. After checking at about 4 points (8 measurements), I average all of the results and enter that average for the diameter. I’ll usually check a couple of times throughout the spool to make sure it hasn’t varied much (good quality filament should be pretty uniform). A lot of my 3mm filament has actually been averaging 2.89mm.

The next step is to calibrate your e-steps setting. The e-steps setting basically tells the printer how many steps of the extruder stepper motor it takes to push 1mm of filament into the extruder. You can find a description of the process here. The description is for the Taz, but it works for the Mini (skip step 6, which is Taz-specific). Note that you should have the tension on the extruder idler set properly before proceeding. One thing to note here: you will get more accurate results if you run the test at a speed of 40, rather than the 100 noted in the workflow. 40 more closely approximates an actual print speed. When I ran this, I ended up adjusting my e-steps from the factory default of 833 down to 820.

You should be closer to the right settings after you get the correct diameter and e-steps setting in place. You may find that you are still over-extruding a bit so parts will not fit together. If this is the case, you can try adjusting your flow rate down. I find I need to be around 95% or so to get a good fit.

Note also that parts need to be properly designed to fit. It may seem counter-intuitive, but a 10mm peg will generally not fit into a 10mm hole. You need to design in some clearance. how much clearance depends on what type of fit you want, but designing the hole at 10.02 is probably a pretty good place to start (hoping I haven’t slipped a decimal place here - I’m too tired to remember right now). A good designer should already have done this.

“Calibration” can have many variables to it. The “e-steps” will effect the amount of material extruded. The diameter of the filament will also effect the amount of material extruded.

When size really matters, it’s also good to verify the “x-steps” and “y-steps”. An easy way to check these is to place tape on the build plate along the X axis and mark a fine point. Use the display panel or software to position the nozzle directly over the mark. Now move 100mm. Place a new mark. Accurately measure between the two marks. Repeat to double check. Then do it all again for the Y access.

The Z axis is a bit more tricky but if you can make an exact 100mm tall object - or have something close and know it’s exact height - you can start the extruder at the build plate and move it up the corresponding height. Then slide the object under the nozzle to see if it hits or if it leaves a gap.