Julia, I am impressed with the print quality and the overall design, far ahead of others. That doesn`t mean that it`s OK with 3 loose screws from the factory. Please let me know their purpose (the 3 loose screws).
They say the reason is to prevent binding of the Z screw. But when I didn’t tighten all 4 screws the z screw turns fine so not sure if they know what they did here
I don't know. Fill up the holes? Keep the ballscrew more or less plumb? Zortrax doesn't make the ballscrew, and it comes with four holes. Would you be happier if three holes were empty? Or if they hand-tightened all four instead of only one, even though only one is necessary (not a bad idea, I suppose).
It's quite possible that loosening the screws was something done well into development or even after production was started, based on initial results. It's not often that absolutely everything comes out as planned, especially with a young startup's first product.
The important thing (imo) is that it works well, even if it offends someone's sense of machine aesthetics.
The point here, regarding design, is to avoid possible reliability issues. Obviously the issue here is that the screws come loose, so if the design is such that the XY is supposed to move due to loose screws, it`s not good. The screws need to be tightened down by the factory operator, and I suspect (don't know of course) it is left to the assembly guy to estimate when the screw is "about right". If he uses calibrate torque tools, different story. But this is China, so he might not.....
You have a few potential problems with design, besides that the screws work loose.
If the screws are too loose, there will be vertical free play with associated accuracy problems in Z direction.
There are free holes in the ballscrew nut flange (the holes that the 4 screws go through), so if the screws are loose, the nut will rotate in its free hole till it stops on the screw, again causing accuracy problems.
Calling this “grade A-engineering” is not my choice of words.
Once again,I get what you’re saying, and if I was buying a 90 - or even 20 - thousand dollar machine I’d even agree with you. However, since it’s all of two thousand dollars and has print quality that rivals (and sometimes exceeds) that of 20 grand machines I’m going to disagree. If you want perfection don’t buy a two grand machine. If you want amazing prints at an amazing price, then you need to not have expectations for “perfect” hardware (I use quotes simply because most have no issues with the current design). And as I stated before,I have no doubt that they could have come up with a “perfect” piece of hardware, but we would end up paying more for it for unchanged print quality and only a minor increase in reliability (even this is debatable). I stand by my comment of Grade A engineering
Just checked my machine, it`s a week old. 3 screws were loose, about 0.5 mm clearance under their head. They are free to rotate and wobble around, doing absolutely nothing.
The last screw is tight, can’t rotate it with my fingers anyway. I am less than impressed with this.
All four of mine have nuts just barely threaded on the ends (most likely from factory) and yet I’m getting perfect prints. Why do you have such an issue with a perceived mechanical “problem” when the end result is fine? There are people that have run their printers all day every day from day one for over a year and have not had issues with this.
Julia, I am impressed with the print quality and the overall design, far ahead of others. That doesn`t mean that it`s OK with 3 loose screws from the factory. Please let me know their purpose (the 3 loose screws).
This screws have to be loose a little always for improve Z layers quality. Otherwise the Z stage become overconstrained mechanism. Maybe it is sloppy but it have to be like a this.
Best Regards
Martin
They say the reason is to prevent binding of the Z screw. But when I didn't tighten all 4 screws the z screw turns fine so not sure if they know what they did here
When something is manufactured, it is manufactured to specific tolerances, with high tolerance costing more because more parts are considered failures. Since the z screw only needs to be precise in the z direction, adding tight tolerances in other directions only adds (significant) cost, however not having tight x-y tolerance can lead to wobble. To get around this, they used the loose screws to allow x-y wobble without the platform binding. But this is not needed in every case; you may have ended up with a high tolerance screw. It’s only there to help when a screw is less than ideal.
This screws have to be loose a little always for improve Z layers quality. Otherwise the Z stage become overconstrained mechanism. Maybe it is sloppy but it have to be like a this.
Best Regards
Martin
So how loose should these screws be? Mine where so loose the bed had play in it. UP ans DOWN. So i tighten a bit so the play is gone. Is this ok?
So how loose should these screws be? Mine where so loose the bed had play in it. UP ans DOWN. So i tighten a bit so the play is gone. Is this ok?
Around 1mm+ is ok it do not have to be very precise jus loose 
Best Regards
Martin
Around 1mm+ is ok it do not have to be very precise jus loose :)
Best Regards
Martin
Ok thank you.
On a $200K CNC machine, the ball screws are aligned in a pretty expensive procedure. They are also held in alignment by seasoned iron castings that might weigh a few thousand pounds. Ball screws and nuts are built preloaded (that is, with negative clearance) to eliminate axial play. Therefore if the ball screw is not exactly aligned (or allowed to float) it will bind, or at least wear at an accelerated rate. You are unlikely to get the precision alignment required in a $2000 retail machine - the alignment itself and the structures required to maintain that alignment through shipping, installation, and lifetime are not supported by the price.
This is a Z axis with no machining forces other than gravity, that always moves one direction during operation. Any axial play will always be bottomed in the -Z direction by gravity, unless something else is binding or broken. There is no reason for the screws to be tight. If tightening them fixed something, then something else is likely wrong (perhaps, the linear bearings on the Z axis are dry and sticky).
that always moves one direction during operation.
This used to be true, but now that the software incorporates "Z-lift" is it not possible for backlash/slop to now be an issue?
This used to be true, but now that the software incorporates "Z-lift" is it not possible for backlash/slop to now be an issue?
With this precision is more important than accuracy. As long as the screw rotation is precise and rotates the same on both sides of the hop (and assuming proper lubrication so gravity is enough to pull it back down), then the platform should end up at the same z as before the hop. There is no reason for it to stay up even if there’s a little play.
Backlash is only important if: there are machining forces opposing the direction of approach, or; if the direction of approach reverses. In this machine it seems like the only forces involved are gravity and friction. I don't know if the extrude pressure puts significant force on the build platform but I would guess not.
There could be one source of positioning error though. If the screws are very loose, the nut has rotational play, which could become hysteresis depending on the relative friction between screw and nut, and nut and platform. It would be a small fraction of the pitch of the screw. Screw pitch looks to be around 6 mm, screws about 20 mm from CL, assume 0.2 mm clearance around the screws, that's about .6 deg rotational play, that is about 0.009 mm error (in Z only) - probably too small to be noticed. An inexpensive rolled ball screw is probably going to have local pitch errors that big.