Printing Servo Horn 25T
Hello Forum,
I've been struggling to print a custom servo horn for a 25T spur using PETG in my Prusa XL. Attached is a screenshot in which I've circled the problematic part in turquoise (this is not the servo horn I am trying to print, I am just pointing out the hole/teeth):
Either the hole is entirely too big (the printer skips the teeth), or the hole is too small (the teeth overlap/fuse). I've gotten tips on slowing the print speed and testing/calibrating the filament rate. I've tried the former with no success, and I am about to try the filament calibration.
Besides these two tips, are there any more suggestions for how to print a servo horn with properly sized teeth? Would buying a 0.2 mm nozzle solve this issue?
Thank you
You don't give dimensions but I suspect you are attempting to print features finer than you can extrude.
The smallest feature possible is one extrusion width wide - by default your XL might have a 0.6mm nozzle or a 0.4mm - the default extrusion of a 0.4mm nozzle is 0.45mm wide. A crude minimal gear tooth would be two minimum feature wide - 0.9mm and you have about 40 of them giving a circumference of 36mm and therefore a minimum printable hole diameter diameter of roughly 11.5mm I suspect your server shaft is smaller. Whilst you could, in theory, print finer with a finer nozzle you are not going to get a decent grip.
Instead I suggest printing a shaped, say hexagonal hole that friction fits and then packing the assembly with a setting filler or resin making an insert that grips both parts.
Cheerio,
RE: Printing Servo Horn 25T
I've been printing quite a few servohorns lately. When I'm in a project I dedicate my MK3.9S to printing these items. Not only servo horns but also gears and other connectors. I pop in the 0.25mm nozzle and design the gear to fit. It usually takes a few iterations to get the perfect fit - shrinkage do vary by filament - but I have yet to not get there.
If I wanted to use my XL, I would do the same. 0.25mm nozzles. You need this to get the details. If I had one smaller than 0.25 I would use it. The resolution increases the smaller nozzle you use. It's logic and physics.
Good luck.
RE: Printing Servo Horn 25T
If it helps, I printed a servowheel for a Waveshare servo simply using their .step CAD model. Whether the spline was recreated faithfully is matter for debate but the fit was perfect.
I used 0.4 mm PETG IIRC. 0.25 mm doesn't exactly improve strength, you might need to increase temperature over defaults for strength.
RE: Printing Servo Horn 25T
What servo gear wheel size? I am trying to print a horn for a 25T wheel. Waveshare has a few different servos. What settings did you use to get the results that you did, with 0.4 mm PETG for the XL?
Thank you
RE: Printing Servo Horn 25T
I have never used my XL with nozzles other than the default. If I ordered the 0.25 nozzles in this link, then would I be able to simply plug-n-play (assuming I change the Slicer settings, of course)? Meaning, is changing nozzles on the XL simply a matter of unscrewing and re-screwing, or do other parts need to be ordered/replaced as well?
Thank you
RE: Printing Servo Horn 25T
What servo gear wheel size? I am trying to print a horn for a 25T wheel. Waveshare has a few different servos. What settings did you use to get the results that you did, with 0.4 mm PETG for the XL?
Thank you
I use Core One but they should be equivalent. Unfortunately, I didn't keep the print, it was just an experiment.
The servo in question is ST3215-HS. I used this step file, loaded it in FreeCAD and exported the wheel (note, it has two - one with spline and a smooth one that acts as a bearing).
If it doesn't fit, just scale the whole print - it won't need more than a few percent.
I used this material but there is nothing special about it. "Generic PETG" temperature probably adjusted to 255°C (as this is the recommended high end)
RE: Printing Servo Horn 25T
I did two test prints in 0.4 mm (5 min job). The second one was at 103 % and a very tight fit. 104% or 105 % would probably be optimal.
Under magnification, the spline appears just as a slightly wavy inner wall. But when I attach it to the shaft, it clearly locks in and after first removal, it's nicely shaped.
I'd say it's pretty usable within PETG expectations - probably even better than the stock plastic ones that are often too flexible.
BTW, this is el-cheapo PETG and "almost dry".
RE: Printing Servo Horn 25T
Depending on the XL you have. If only one tool, all you need to do is replace the previous nozzle with the new one. Same if you have a 2 or 5 tool version. But here you might neeed to do a tool calibration after changing nozzle to tell the printer how the position of the new nozzle is in relation to all the other nozzles.
I guess if you not are going to use the multi-tool function for the print you don't really need to do this, since the probing and such is done with the same head you're printing with.