X Idler Bearing and X V-wheels

[Big Man Black T-Shirt(Patrick)]

I have two issues I want to ask about.

1)  While adjusting the X belt I noticed that the belt is very loose on the idler bearing after I run the carriage in one direction and then stop, I can easily slide the belt up and down on the bearing, with almost no pressure from my finger. When I run the carriage in the other direction and then stop, the belt requires a lot more pressure from my finger to slide it up or down. I suspect that means my belt is way too loose but I wanted to ask you guys first.


2)  After letting the CNC sit overnight, this morning I moved the X carriage by hand, with no power applied. I noticed that it seemed to lurch slightly every 3 inches or so. I suspect that one or more of the V-wheels has a flat spot on it. Has anyone here experienced this? If so, should I just try to find the offending wheel(s), loosen them, and hope the rubber comes back to round again?

Thanks!

[Derek the Admin]

Yes, the belt is too loose. It will tighten more as you get close to the idler because it's wrapping more around the bearing because of the relative position of the belt anchor on the x plate.

Just loosen the eccentrics and let the wheels rest. Polycarbonate like other materials can experience "creep" where it deforms when a certain amount of pressure is applied. You are just over that threshold right now. It will return to proper circularity in a couple hours or overnight depending on how tight they were.

[Big Man Black T-Shirt(Patrick)]

After I loosen the eccentrics and let the wheels rest overnight, would a good way to adjust the eccentrics be to turn all 3 of them until the wheels on the bottom start spinning freely, and then snug the eccentrics back up until the bottom wheels start to grab?

[Derek the Admin]

Somewhere in the assembly instructions we talk about a little method to kind of adjust by the seat of your pants. I don't have an exact page for you to reference for you at the moment, but basically what you want to do is tighten the wheels enough so you can turn the wheel and move the plate just by turning the wheel, but loose enough that when you put a little pressure on the plate resisting the movement that the wheel just free spins.

[Big Man Black T-Shirt(Patrick)]

Very good, I just loosened all 3 and then snugged them down as you said and I believe I now have a good balance of snug but not too snug. They were quite a lot tighter when I started!

Thanks!

[Derek the Admin]

No problem! That's what the forum is all about.