How Sensitive is Carriage/Arm U-Joint Fit-up to Function?

[Broose]

I have been cruising through the build (fun!) and got to the carriage fit-up. I sanded/filed the plastic carriage platform and arms to fit the u-joints and I had a hard time getting them to just a little bit of friction with no play. I've assembled everything now on the cheapskates and the carriage seems to move smoothly, but there is some degree of friction in the u-joints when I separately move each cheapskate up and down, holding the others in place. How sensitive is the machine to friction in the u-joints? Should I take it apart and file some more or will it work itself in?
Thanks,
-b

[mhackney]

The short answer is "very sensitive". These joints need to be as smooth as butter with very little friction. The symptom if you they aren't is easy to spot - incomplete fill lines in your parts and related issues. I've run my machine now for at least 100 hours and I don't feel any signs of breaking in. Maybe after 1000s of hours it will but I don't think it will in just a few.

Also, add a little dab of white lithium crease to each joint. It won;t affect the plastic and works well.

[Broose]

I was worried that it might be so. Now that I check, with really slow movement there is a bit of stick-slip happening with the joints which I would imagine will cause some heartache like the issues you described. I'm going to pull it back apart and get it right before proceeding. Thanks, and also for the tip on the grease.
-b

[cjdavis618]

I have my slider joints and the plat form joints smooth as glass. The arm ends are not that way because I didn't want slop. The joints themselves can spin with a tap on the platform and slider joints. But the arms are a tight fit. Do they also need to have the joint spin freely in their socket as well?

[mhackney]

Yes, they especially need to be free moving IMO! In fact, if you read my build thread, the incomplete infill was primarily due to stiffness in those joints on one of my axes. I used a sharp excato blade to gently ream out and debur the holes until I got a good fit with no slop but free movement. The entire system of joints needs to be free moving without excess friction or slop.