Laser-cut acetal (POM) chain guard

A few years ago I started playing with a laser cutter in a “maker space”, and the thing that I have had the most luck with was chain guards for my bicycles, to help keep my pants slightly cleaner.  I made one out of mirrored acrylic which looks Very Flashy, but the acrylic is not that durable.

During Covid, I lost access to the maker space, and needed a new chain guard for one off my bikes, so I went and ordered one in 3mm acetal from Sculpteo, and it has worked very well.

I don’t recall if I sent them a PDF or a SVG, but it was one of the two.

Anyhow, my chainring was creaking, some of the chainring bolts were working loose, so this seemed like a good time to take it all apart, tighten things up, and take some pictures.  Obviously the chainring needs some parts to hold it together, and these are shown here.

First, mounted on the bike.  The gap for the crank arm makes life very, very easy, compared to the aluminum ones that usually come with bicycles.  

This is my spare copy (I ordered two, shipping for two was as high as shipping for one).  Notice all the little spacers in the waste section in the center; those will be useful later.

Here is the old one, removed, with screws and washers still in place, and all the spacers in the box below.

To reinstall, use tape to hold the screws and washers in place, then put a pair of spacers (each is 3mm) on the backside.

Here I’ve tilted it the other way so you can see the spacers.

Insert the long skinny screws through the center holes in the chainring bolts, and spin the little nuts on the backside so the screws won’t come out, remove the tape, and crank them down pretty tight (because acetal is tough, unlike acrylic).