Crackhead-Proofing My Bike

In hope of keeping my bike seat out of some crackhead’s streetcorner sale, I have applied polycaprolactone (AKA Shapelock plastic or PCL) to the vulnerable hex-head bolts. I covered the top bolt on the seat (pictured), the seat post bolt, and the headstock bolt. It is impossible to remove by hand but can be removed in a few seconds with [redacted]! Then all you need is a bucket of hot water to reapply it.

Just last week, my neighbor Laurie had her bike seat stolen by loosening of the bike seat bolt :-(

If there is no update to this post, you know the PCL has done it’s job!

Coreyfro got a huge quantity of “CAPA 6800” at Tri-ISO and Noisebridgers split it up. I got 2 kg at $18/kg. I’ve made a couple things so far, over the door coat hangers that I use often, a headphone holder (Trebor’s idea, I expounded on it) that is awesome, a little plastic shield for a wire that goes through my window sill…

Great fun!


  1. Julie Bright says:

    I was wondering how one could prevent a missing seat. Once my bike is in better condition, I plan on riding around Berkeley/Oakland, but I don’t want it ripped apart by vultures!

  2. Lee Sonko says:

    I have read about putting a ball bearing into the hex bolt hole and securing it with CA-glue (AKA crazy glue, super glue). The idea is that you can use acetone to remove the CA-glue. I tried it today on a test bolt and it was kinda messy. I hope my solution is better.

  3. I use plumber’s putty and a ball bearing, which has a reasonable balance between being a pain in the ass to remove and being removable/serviceable. The plumbers putty stays pliable enough to remove if you have time to be meticulous, which is too much for the typical crackhead.

  4. Lee Sonko says:

    David, very interesting! I’ve got some museum wax, that is similar. My neighbor is going to try museum wax and a ball bearing!

  5. Lee Sonko says:

    Julie, give me a call when it’s time to secure your bike!

  6. trebor says:

    very nice! i use a heat gun to do my PCL work. a friend with a machine shop made me a custom nozzle for fine work, which has been a huge help. in any case the heat gun means i could more permanently attach things to my bike – with an option to easily remove it later (rather then dunk my bike in hot water). i would imagine a hair dryer would work well also.

    also i am reminded of the sugru lego hack:

    which might work with PCL and say a bike light. :)


  7. Fro says:

    To strengthen the capa, stretch and fold it in on itself a couple times. This aligns all the polymers, adding strength. Think of it like pattern welding a samurai sword.

  8. lee says:

    Weee! The Sugru-lego hack is fun! Thanks!

    I think that the friction-fit of Lego probably isn’t a good match for the vibration of a bike. Of course, if PCL can be made long and thin, formed into a spring that could hold something in place like so:

  9. I am so glad that this type of thing is not remotely a concern of mine anymore :) Nobody swipes bike seats here — nice.

  10. Lee Sonko says:

    They don’t need bikes in Seattle. Everyone skips to their destinations singing Zip-a-dee-doo-dah!

  11. Jesse says:

    All you’ve got to do to remove shape lock plastic is to heat it up to 160 degrees Farenheit.

  12. lee says:

    That is true Jesse. But how do you expect the crackhead-thief will do this in the field? First they have to realize this fact, probably by careful molecular analysis of the material; most plastics melt at 500+ degrees F. Then they have to heat the material up by maybe holding a lighter up to it for 5 minutes (PCL doesn’t conduct heat very well). Or if they brought their blowtorch, they’re good to go. Usually crack-head thieves don’t carry a blowtorch so I still feel pretty good about this method.

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