I have an x2d and although the lead screws are housed in a bearing in the base of the machine, the top end is not it’s just loose moving around under a plastic cap. Should it be housed in a bearing or a bush at the top end. Could this be causing banding and bed adhesion problems
This actually is good engineering. The XY position is completely determined by the two linear rods behind the lead screws. When the lead screw had a bearing at the top, the mechanics would be overdetermined and could potentially bind. If a leadscrew is ever so slightly bent, it has a chance to compensate by tiny wobbling instead of binding.
Hi Alex.
Thank you for your reply. I’m not sure slight wobbling is good for precision, surely any movement would be reflected in the model such as banding or irregular layer lines?
Regards
Jeff
Yeah, it doesnt sound intuitive, but not having the lead screws bound at the top isolates the heat bed which reduces banding and increases precision.
The leadscrews are purely used to actuate the stage, it’s the linear rails that keep the bed moving perfectly in a single axis.
If the leadscrews were fixed on both ends, there would inevitably be a potential for binding if the screws weren’t perfectly parallel to the linear rails. Could they be? Sure, but it would require a significantly more high precision design, more difficult and costly mnaufacture, and then the potential for the linear rails and screws to go out of parallel for customers.
I promise this is the best design choice.
Yes, this really sounds counter-intuitive. But if a lead screw isn’t perfectly straight, it is better to let the free end move instead of forcing it into moving the rest of the printer or even bind.
And they never are perfectly straight. So if you add a bearing at the top, you have to decide were in the printer you want to add flexibility to allow the motion.
You can manufacture mechanical parts only to a certain tolerance. You can improve tolerances to incredible values, but cost explodes quickly. And you can never achieve perfect precision.
So in a cost sensitive product like our printers, you have to live with the imprecision and instead take measures to reduce the impact.
One of those measures from mechanical engineering 101 is not to overdetermine assemblies.
We are talking here about tolerances in the range of 1/100 to 1/1000 of a mm.
Ok thanks again Alex for your assistance