I’ve had a Shapeoko XXL for a couple months and have been having problems with cutting circles. They are oblong. Square cutouts are not the same either. I’ve re-squared everything and each axis is snug (eccentric nuts adjusted). I’ve been working on calibrating through grbl but I’ve noticed that the left Y axis is loose.
When I have the machine on the right Y axis is solid - I can’t move it. The Z axis is solid as well. But I can move the left Y axis about 1/4". The belt has good tension (same as right side and Z axis). The pulley is tight on the stepper motor and the eccentric nuts are snug.
I would suggest that while you are at it, you change the set screws for M3 cap screws, it will enable you to tighten the screws more because the hex head is larger and stronger. I have changed all my set screws for cap screw in order to ensure they remain tight.
The alternative to to use two set screws - put a second on on top of the first (there’s almost always enough depth to do this) and it functions like a jam nut.
I would not recommend this because you still have a very small hex that can easily strip before it can hold the shaft properly and putting a second on top will not make it tighter, it will only prevent the one under from loosening more. When I looked at the set screws I had removed, some appear to have a partly broken end (the portion that is against the shaft) and may be the reason they slip on the shaft even if they are tight.
That’s what they’re supposed to look like - it’s a dog end set screw. The tightening depends on the shaft, not the size of the hex. If it’s tight, it’ll stay tight when backed up. As long as it’s not moving on the shaft, it’s tight enough. Replacing with a screw won’t keep it tight. Either way, a little loctite goes a long way.
The size of the head for a set screw is significantly smaller than a cap screw, from memory a 1.5mm vs 3mm for the cap screw. This makes the smaller head more susceptible to stripping and it is impossible to apply the same amount of torque to the head of the set screw compared to a cap screw. Since set screws are made so they do not interfere with other parts/objects when moving I use them in a lot of machinery but in our case, there are no/little possibility of interference. I have had problems like many others here with the set screws breaking stripping, appearing to be fully seated (can’t make them tighter) but still not holding the shaft properly. So why not change for the benefits?
If you are happy with set screws well fine but the cap screws have advantages over the set screws.
Unless you put a nut under the head and tighten it against the pulley, it will still back off eventually. It’s not about “how tight it is” it’s about it not moving after it’s in place. What you’re seeing with the bigger screw is that you can stretch the threads and distort the screw, which puts you at risk of stripping the hole. A jam nut scheme puts that distortion into the thread of the hole in a localized spot, not across the length of the screw, so doesn’t require so much force.
This certainly isn’t something worth arguing about, just trying to point out there are other solutions.
