I just snapped my twentieth o-ring trying to install them. I’ve been successful ~4 times. I’m using the recommended o-rings straight from McMaster-Carr. I put a lot of force on the large gear, pushing it down, but I’m thinking this must not be the trick. I’m open to any suggestions.
It is very important that you use the nut tool to lock the actuator while you are inserting the O-rings. The nut tool will also try to go at an angle as you push the band in: using a spare finger to keep it at right angles to the actuator body and firmly in the hole can help. You also need to push evenly both sides at once. With the old band tool there could be problems if the cap was not used. This was not so clear in previous versions of the instructions, but for v7.0.0beta2 onwards we hope it is clear, and the new band tool means that the cap is an integral part.
The O-ring is stretched quite a lot in the actuators It should still be well within the maximum elongation overall, but if you have not got it evenly set in the four times that it goes up and down inside the actuator then one of the parts may break. There is too much friction across the base of the foot and across the top of the band tool for the O-ring to move and even itself out.
Band breaks should be rare, if you break more than one in a row something is not right.
Hm, that’s troubling because I’ve certainly been trying to arrange the o-ring evenly and use the nut tool to lock the actuator.
Maybe I need clarification on the position of the actuator. It seems to me that if the actuator lifts up from the base, then the hooks get further away -hence the nut tool. I’ve been trying to keep the actuator flush with the base -should I be pushing it down past the base? That would seem to bring the hooks closer to the o-rings.
For now, I’m going to try reprinting the band tool. The clearance of the cap to accept the two arms was very tight, requiring a lot of hammering to get the arms into the cap and even then the proportions did not match the image of the tool in the assembly instructions. I don’t know why this would cause the issues I’ve been facing, but I don’t know what else to try.
You are right to be trying to keep the actuator flat at the base - in the position that it was printed.
The band tool arms not fitting the base well might be an indicator of general printing issues again. You cannot see inside the actuators, but obviously if the columns have bits sticking out they could catch and snap bands. You did have some printing issues before, I think? If you have still got the main body that had printing problems in the legs then you could break out the inner actuator columns from that and see whether there is anything obviously wrong.
Have you got access to a different printer? Or someone who can print a test for you? The separate_z_actuator.stl for the upright microscope is a shorter print for an actuator to test on.
Have you tried stretching the O rings with your hands before installing?
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I had some printing issues before with the struts, but I got those resolved. I opened up one of the troublesome prints to see how the hooks and actuator look on the inside. I couldn’t find any obvious signs of a misprint.
The O-ring hooks over the two ‘arms’ on the sides of the actuator column. In the photographs they both look quite rough, particularly the left-hand side. Harder to tell on the picture of Y than on X.
I see a lot of print problems in this image. Your overhangs are poor, there is a lot of resonance and layer defects. This guide helped me a lot fixing some of those defects. Welcome! | Ellis’ Print Tuning Guide
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Aha! It turns out it was an issue with the band tool arms not fitting the cap well. Cutting open the base allowed me to see what was going wrong: the long arms of the tool were not flexing laterally. When I re-printed that tool as a single piece, the arms could flex laterally and the o-rings stopped snapping.
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I am glad that you have a solution!
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