Finished making the Milan chain guard

I had to sand and shape some more on the mold; the MDF was showing through in a couple areas, and I know from past experience that no matter how much release wax you try to shove into the MDF it will still adhere to resin.

After sanding more, I resprayed the gray gel-coat on the mold, and also on the mold for the Quest foot-hole covers. Sanding again still revealed some MDF in a few places. I was anxious to make the piece, so I masked off a couple areas with flash tape, and put the piece together.

Used blue flash tape over areas where the MDF showed through the gray gel-coat

It was a very warm day outside when I laid this piece up, slightly cooler in my workshop but it was at least 80 degrees F, so the resin was curing faster than I wanted it to, and I was working fast to get the fabric into the corners fully so there wouldn’t be any bubbles or voids in the end product.

I was so distracted trying to get it all together and in the vacuum bag before resin gelled too much, I didn’t realize until it was all in the vacuum bag that I had forgotten to put the magnets in! It would be too involved to change things now, so I left it to cure.

The next day I removed it from the mold, cut back the edges and cut a notch for the shock absorber, and then cut a strip of CF to lay in over the 3 magnets. Marked off my locations for the magnets, and applied resin, put in the magnets and then the CF strip.

I tried to re-use the bag but I couldn’t get any decent vacuum. I had tried to re-use a bag in the past and it was not successful. I think something about the process weakens the bag material. But it cured up fine. Here’s the interior side of the completed piece. At the far right there is a circular area in the piece; I designed that to allow clearance for that rough metal plate at the end of the chainstay.

The finished piece; the cut out area at the top is where the shock absorber is located.

I added some rubber edging around the outer edges, and will have to add some adhesive to hold that in place. I put that on to keep any rough edges of the CF from rubbing on luggage, and to minimize any squeaks that might occur if this rubs against static parts. The chain guard moves up and down as the rear wheel moves up and down.

I also used some E-6000 to adhere 3 magnets on to the chainstay; I made sure to get the North/South orientation of the magnets correct before putting any magnets in place. You can see red dots on the magnets. These were placed in locations to match the embedded magnets; red marks on the top of the chainstay. The Velcro you can see on the rear wheel housing was the attachment point for the original chain guard.

Neodymium magnets bonded on with E-6000. Red dots on the magnets indicate the correct orientation
so they attract instead of repel the embedded magnets.

I put the Milan up on some crates, removed the rear wheel fairing and set up a video camera on the left side of the rear wheel. You can see the interior side of the guard, as I cycle back and forth on the front chain ring. I also filmed install and removal of the piece; I would estimate it’s about 5 pounds of force to remove the guard.

I went for a 40 mile ride with the new piece installed, and it stayed perfectly in place. I installed my Contour camera into the Milan for the ride, and directed the camera towards the chain guard. Not a lot of ambient light back there, but here is a video from crossing 2 sets of train tracks.

There are blemishes on the surface of the final piece; bubbles where the CF wasn’t fully in contact with the mold. It’s difficult to get the vacuum bag to cover all angles, and the resin fast curing wasn’t helping…. but I’m pleased with how it came out. Here is the new piece next to the part that came with the Milan (and that part was designed for a derailleur).

My chain guard on top, the one at the bottom is the original one; it adhered with Velcro
and the chainstay moved within the center channel. Derailleur was totally exposed at the rear.

Using the flash tape on the mold leaves evidence of the tape on the finished piece, but doesn’t affect it’s functionality.

The shiny areas are where I used flash tape to prevent the piece sticking to troublesome areas of the mold.

The chain guard covers the chain very well, even the area at the front of the chainstay; it works in concert with the cover for the idler wheel, which extends back to the new chain guard.

New chain guard on the left; the CF piece on the right covers the chain and the idler just under the seat.
This is the rear of the chain guard once installed; you can just see some bolts of the chain tensioner through the gap.
I couldn’t cut the piece to create a smaller gap; it needs this much just so I can install the piece; it’s a snug fit
between the chainstay and the body of the velomobile.

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