Spiral aluminum Z coupler question

I'm looking at how the spiral aluminum shaft coupler would work on these reprap based printer (printbot for example). The spiral Z coupler can be pushed down or pulled up a bit, and most of the assembly photos I saw don't have anything to prevent the shaft from moving in the axial direction (i.e up and down if the coupler is for Z axis).

Is it because the force required to push these coupler down or up is larger than the weight of what being carried by the Z axis?

Thanks

-Thanh

I have used them from the beginning and never had a problem - all layers as they should be.

Thanks for the feedback Waitaki. I guessed it must be working well for many since I see many people use them. I'm still puzzled as why it works without introducing lashes. I'm holding one in my hand and by pushing the two ends of the coupler together, it can shrink as much as 1.2mm. So I'm wondering why it's not shrinking or bouncing during its operation without a fixed end.

Thanks

There is no reason for them to expand/contract. The X carriage weight remains constant throughout the print so the couplers remain constant.

I wondered about this too when I was sorting out my Z couplers. I think in the end the Z-motors move small enough and smoothly enough that they don't introduce any bounce or rotational issues to the X axis when you combine in what waitaki said about the weight of the X carriage. Any energy from side to side movement of the heavy extruder should be absorbed by the Z-axis rods and shouldn't translate into "slop" in the threaded rods. If the Z-motors were doing a lot of "thrashing" movements I would think this "springy" play in the couplers would be a problem vertically, but I don't think that's the case.

I converted my friend from the plastic printed ones to the machined aluminum ones and his print quality improved. There's a reason why professionals use real couplers instead of tubing and other undergraduate level workarounds for zero budget work, and it's not just to spend money. They're designed for coupling motors to shafts.

They are designed to couple motors to shafts supported by a thrust bearing. They are not intended to take varying axial load and maintain their length to with a few tens of microns. Being a form of stiff spring I would be surprised if they do not change in length when the extruder moves from one end of the axis to the other.

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Well, the answer is in the print.

waitaki Wrote:
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> There is no reason for them to expand/contract.
> The X carriage weight remains constant throughout
> the print so the couplers remain constant.


The weight of the X carriage is not the same when the extruder is moving one end to another. If it moves all the way to one end, the nearest end has more weight than the other, and that would make the coupler on that end shorter than the other end.

I don't know how much weight it would take to compress the spiral coupler. I guess it's easy to find out with a scale. I was wondering in the original post that it could be that the weight of the X axis and the extruder is too small to compress this spiral coupler. Maybe it's the case here that explains why everyone sees better result with them and don't have problem.

Well, F=kx, so it takes minimal amount of force to compress the spring a minimal amount, and a lot of force to compress it a lot. How much, depends on the k, which is the spring constant. The effect is linear.