ERCP Buffer Cross with enlarged wheel inset to reduce friction

[NameOfTheDragon]

ERCP Buffer Cross With Enlarged Wheel Inset

This mod enlarges the circular inset on the inside of the buffer cross so that the filament wheel fits completely inside it. The original design has this inset a little smaller than the wheel. I believe the design intent is to prevent filament from falling between the wheel and the cross by pressing the wheel up close. I have found this to be problematic due to the resulting friction between the wheel and the cross, which undermines the point of having the wheel mounted on a bearing. Even with a smooth wheel printed on smooth PEI, I've found that the friction generated is enough to occasionally break filament in the bowden tube or to cause the extruder to grind away the filament and stop feeding. I have even tried applying silicone grease to the outside of the wheel and it still causes printing issues.

Any amount of tension in the filament within the buffer causes increased friction along the entire feed path, as the filament pulls tight against edges and curves. In my opinion, it is critical to eliminate all sources of friction within the buffer.

In this mod, the wheel inset diameter has been increased to 71mm which is just large enough to clear the wheel. The fit is still close and there is not a large enough gap to allow any filament to fall between the wheel and the cross, so this should not be a problem (I have never had this happen in a year of use, even on the older V1.0 design).

The modified cross-arm allows the wheel to spin freely on the bearing and (for me at least) this has significantly reduced printing issues on the unit I've tested.

What's Included

• The buffer cross as a .3MF file (like an STL but better).
• A Fusion 360 CAD model with the modified part, although this is probably of limited use.

[jwhite]

@NameOfTheDragon I merged your changes with my v2 changes (much better for alignment.) Both together is a huge improvement.

I opened this pull request

I will delete my old pull request

[whi-tw]

It feels like this isn't so much a usermod as a fix for the original part - I've been meaning to do the same.

[NameOfTheDragon]

It feels like this isn't so much a usermod as a fix for the original part - I've been meaning to do the same.

I agree, but I have previously tried and failed to persuade Ette of the need for this. So I decided to submit it as a usermod.