Here is a follow up to my print quality issues… Looks like I have a X axis wobble every 8mm. Shifts left then right. I am not sure if this is related or not, but if I manually move the X axis to home it grinds and stops before hitting the end stop. If I hit the home button, all is ok… Or if I loosen the tension on the belt a little.
Typically, leadscrews for 3D printers are unconstrained at the top; constraining them may cause the z-wobble that you’re experiencing
@Ishaan_Gov it is free floating in the hole. I think I am close to narrowing the problem down though. I got the X axis belt thighter, just short of causing the X axis to grind. The period of the wave is still there; however, the amplitude is greatly reduced.
Is your filament path nice and loose? Any noticeable resistance/binding in your axes when you move them around by hand?
The filament path is pretty much straight up and down. What I am noticing now is about the first 50mm the amplitude of the wave is greatly reduced. Now the print is at 83mm and it looks almost the same as the one I posted…
Is it possible your Z axis smooth rods are not perfectly parallel? If they are a little closer at the top that would allow the x-axis belt to loosen a bit as the print progresses.
@Brad_Dudenhoffer Both ends of the smooth rod are mounted in acrylic with metal collars… And both were a tad bit wiggly… I tightened up the metal collars and will run another print…
every 8mm is gaurenteed your leadscrew. 8mm is one rotation of tr8*8. Free the end of your leadscrews. https://lh3.googleusercontent.com/BF16eP0SrL8-TJgqrFs9Wi1mKBrA0y8jVzsJ5qVAi0M=w908-h681-no Heres a pic of my printer
@adam_paul That is beautiful! The lead screws are in a hole…not sure how to “free” them. The left side has a little wiggle room… the right feels tighter. I am going to take a closer look at the right side.
Edit: a little judicious sanding and it is as free as the other side. Test print to follow
It look like the screw is closer to the rod at the bottom than further up. Can you check/adjust that?
@Whosa_whatsis Originally, it had flex couplers. I replaced them with solid couplers, erroneously thinking that solid was better. But after a lot of research, I was told that they used flex couplers by design. So I went back to flex couplers.
I measured and the tops an bottoms are within 1mm. As close as I can tell anyway. Printing my test piece again… so far so good.
Solid couplers are better if your screws and couplers are both straight. I’ve never liked helical flex couplers because they don’t adequately constrain against forces along their axis or twisting about it. They’re designed to give smooth motion in an axis moving at constant speed, not to provide precision in an axis standing still, which is what our Z axes need. A universal joint would be a better solution, assuming you can buy/build one with sufficiently low slop (they’re also generally built for constant motion rather than static precision). Short of getting motors with integrated screws and just replacing them if they’re not straight (my personal choice), vinyl tube couplers seem to be the most appropriate type that is readily available.
Of course, part of the problem is that your screws and linear guides are the same diameter. Ideally, the linear guides should be significantly wider/stiffer so that any deflection will happen in the screw rather than the guides. Probably not easy to do anything about this with the printer design you’re using, though.
@Whosa_whatsis So you would suggest going back to the solid couplers?
I would try them and see if they reduce the problem. If they don’t, either the couplers or the screws will need to be replaced to get rid of the problem. Switching to tube couplers will give you more good flex than the solid couplers with less bad flex than the helical flex couplers.
@Keith_Applegarth Tops and bottom within 1 mm?
That does not sound good enough. Would it be possible to get them within 0,1 mm? And I have to agree with @Whosa_whatsis that solid couplers are much better for the Z-axis. Not sure they would cause this kind of wobble though. Not restraining your leadscrew at the top is a must, in my experience. Can’t you drill out the hole?
I got that in some really tall support material that only happens with ABS. When I print with PLA it goes away. Only the support material was thin enough to see this effect. The rest of the print was okay until the ABS ripped itself apart.
@Daniel_Jones If you’re only seeing it in ABS prints, it’s probably a temperature-related issue. I’ve seen similar issues due to variable bowing of a platform as it expands/contracts with the heater turning off and on to maintain temperatures.
Could also just be that the PLA feeds cleanly off of the spool while the ABS does not. Not feeding cleanly can result in filament tension intermittently pulling up on the extruder.