713Maker part. 7075 aluminum.
No way, wax string all the way! The belts are tensioned to around 200hz. Don’t think zippy ties would hold.
In a few days I’ll get to test it out.
The theory is the bearings will keep any bend in the threaded rod from translating to the bed. The bearings ride on the magnets, and the other two magnets are closer together to keep the plates straight. As long as the rod is lubed properly, they don’t really spin out of place enough to cause issues.
I really hope this Belted Z axis works because those are a lot of parts. Sexy as hell but…a lot of parts.
Did you manufacture these parts yourself? If so, on an mpcnc or lowrider?
How do you measure the frequency?
specdroid app on my phone.
That is beautiful, and should work at least as well as the current one that is part of the corners of the Primo. But what I am looking for is one with a spring in it, so that when the belt stretches a little bit, it will still have the same tension on the belt. With screw adjustments, you have to keep checking and adjusting them for every little bit of stretch. You could use the amount of spring-stretch as a gauge to see how much tension is on the belt, no more twanging it to test tension. I could even imagine putting a slide potentiometer on that spring to have a system that reports if the belt has stretched too much and needs replacing, like how my tire valves now report to my car if the tire pressure is too low.
You don’t want it to stretch though. The tension is a way to keep it rigid. Adding a spring would keep the tension, but sacrifice position.
The ringing on prints would be all over the place with a spring.
I think a spring might not be terrible if all these conditions are met:
- Only one side of the belt has a spring, the other side is rigidly attached
- The preload on the spring is high enough that it always comfortably exceeds the force from acceleration
- Creep or temperature expansion or whatever causes the belt to change length is large enough to justify the spring
Imagine a clamp with a spring on one side:
When accelerating to the right, the clamp presses rigidly on the orange object and everything is fine.
When accelerating to the left, the spring could compress, but if the preload on the spring is high enough, it will be held firmly against the left jaw and it will not be much worse than if it were rigid.
If the orange block has a high temperature coefficient or if it is subject to creep, this is potentially better than a tight fit on both sides which can become loose. The preload on the spring will stay consistent.
Now this is all theory and one thing that is a factor is that in a real system the belt is also a spring. Using a preload on one side will probably cut the overall stiffness in half. The clamp model implies ‘infinite’ stiffness but when it is not infinite then it does matter if you have one jaw or two.
On the MPCNC Burly at least one end of each belt should have an extremely short zip tie to have decent stiffness. The other end may also be short but it is not the end of the world if it is a bit elastic. With enough preload the belt can “push” as well as pull, and only one side need be rigid. But two sides rigid is better.