Personally if I'm going to find myself in conflict with someone who's in a two ton metal box, I'd rather be in a two ton metal box (or three ton if possible) myself. I wish I could bike to work, but I wouldn't want to share the road with people who drive like me. Plus the 5000' climb on the way home isn't very motivating.
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Indeed. Thankfully the route I've been taking means avoiding the roads completely; other than an entirely manageable jaunt though the centre of town.
The use of the word "mountain" in your map seem appropriate
Today I awoke feeling horrible by most metrics and decided to give myself the day off; free from attempting to fulfil any obligations to anyone else.
This free mental space to do something for myself with impunity shifted towards thoughts of mating my Polar GPS unit to the Brompton in a more acceptable manner than the current stop-gap.
In short there's no off-the-shelf solution to achieve this, so I've been working on something that uses the Quadlock mount that came with the bike. The chosen solution being to fit a Polar-compatable insert from some other universal mount (that takes interchangeable mounts for different applications) to the Quadlock bracket using a 3D-printed adaptor.
Bits below, L-R: Barfly (IIRC) Polar mount (a bit of a pain to source), 3D-printed adaptor, Quadlock handlebar mount:
The Quadlock mounting bracket has had the actual quadlock interface removed to reduce stack height; while it also appeared that the printed item would be stronger if fitted directly rather than to the QL interface (which would have required some questionably thin wall thicknesses).
The adaptor was relatively straightforward as most parameters were defined by the parts it was intended to join. While I understand 3D printing to a workable extent, I have little experience designing for it and the "finished" outcome below required a non-trivial amount of fettling to get it to this state:
The upper face in the pic was actually the bottom face as-printed. The circumferential channel was only supposed to be a couple of mil thick; however collapsed so had to be cut manually (in this case using a rotary tool and a range of bits with the adaptor spun in a drill press) - hence why it's so wide.
Care has to be taken with this thermoplastic (PLA) as getting it too hot whilst working makes it melt rather than cut; making a mess of everything. In the end I used a mixture of steel burrs and a cylindrical stone with light pressure to prevent things getting too hot.
The central countersunk hole for the retaining bolt was a mess out of the printer - too shallow and offset to one side so that had to be re-cut too. Achieved eventually using a blunt countersink tool in the drill; applying force to one side of the adaptor to get the hole somewhere in the middle. A sharp cutter would have been infinitely preferable; and I found the best approach with the example I had was a series of short, hard plunges into the workpiece to force it to cut without generating a lot of heat.
All through-holes were printed 0.2mm or more undersize and drilled to the correct size for better dimensional control. The upper and outside surfaces were finished with a mixture of coarse and fine valve grinding paste; giving a glossier finish in some areas than expected thanks to the heat generated, I think. A quick wipe over with some boiled linseed oil served to downplay some of the remaining marks.
The finish is far from perfect but a reasonable midpoint between the tattyness from the printer and the additional time it would have taken to have got it significantly better.
The underside of the adaptor (which was the upper face of the print) was left as-printed as it was a lot tidier than the opposite side:
Conveniently as I was getting to the end of the mucky work the necessary fixings came through the door - M4 T-type Nyloc nuts for the (also supplied) M4x12 CSK socket bolts that retain the Polar interface, and 3x6mm steel dowel pins to engage the shallow radial holes in the top of the QL bracket and prevent rotation as the Polar unit is twisted on and off.
One nut pushed in very lightly, another needed winding in on a bolt and all of the pins were a convincing interference fit once pressed into the 3mm holes - I guess the plastic probably deflects a little during drilling, resulting in slightly undersize holes..
Adaptor fitted to the QL bracket with the single M5 CSK bolt - this engages a captive Nyloc nut in the back of the bracket; the hole for which is far larger than it should be and barely prevents the nut spinning. Top marks for design there, then...
Polar interface screwed to the adaptor:
Polar unit fitted and I'm generally very happy with how it's turned out. The interface does flex a bit when assembled causing the gap between it and the adaptor to open up a little; but this is only a minor aesthetic issue.
There was also the case of the missing rubber inserts for the mount to address. I had some 1.25mm thick nitrile sheet in my bits box, so cut some strips to fit inside the mount. The smaller bits superglued to one surface are help locate the strips laterally within the grooves in the inside of the clamp jaws:
Hardly my most aesthetically pleasing work, but they do the job and look fine when fitted
After all that the new assembly was cobbled together onto the bike with no drama. The centre bolt is a bit longer than ideal and projects clear of the nut on the back of the mount by about 5mm. I don't have anything of an appropriate length to replace it with but could cut one down if I can be bothered; or more likely will just keep an eye out for a suitable replacement if I can blag one.. for my future reference the ideal appears to be M5x20mm...
