Chainring guard

Use case: I use a regular (not narrow-wide) chainring in the middle position of a triple crankset; a poor man's 1x drivetrain.

I currently use a front derailleur as a measure of chain retention, but I still get rubbing when in either extreme.

I'd get a narrow-wide chainring, but they are expensive or not available in the tooth count I want (40-46T) & BCD combination (96 mm).

This chainring guard replaces the largest & smallest chainrings to keep the chain from derailing off the middle ring.

This wasnot designed for preventing chain derailment off the largest ring (essentially a high limit screw replacement).

I have STLs for my own use in 96 & 64 mm BCDs (4-bolt) as a well as a test STL in 110 mm BCD (5-bolt).

Has countersinks for standard M8 x 0.75 chainring bolts.

Customization

The SLDPRT file is parametric to an extent, but there are certainly many combinations that will fail to render.

Here are the parameters I currently have:

• TotDia: diameter enclosing the outermost part of the teeth. The smallest diameter that will fully enclose your chainring.
• BCD: bolt circle diameter
• CrankDia: outer diameter of the interface between your crankarm & the chainring itself. Needed to ensure a good fit. Assumed to be circular (you can probably get a very close fit on most chainrings).
• ArmWidth: width of the crankarm where it meets the chainring. For aesthetic reasons.
• GuardWidth: thickness of the guard itself.
• BoltCount: number of bolts (4 or 5 in 99% of cases). CAD file is untested for other BoltCounts.