I did build a 'cheap' toolkit for eBrompton, here is the writeup
Individual tools.
You can build up a kit of the needed tools, but to get the weight close to the Tern setup (209g) you will need to use a 15mm Titanium wrench, see below.
A 1.5mm allen key is needed for the grub screw that secures the gear inner wire on the chain pusher at the rear of eBrompton. Here a 1.5mm hex bit on something like the angled drive shown below can be used but then so can a standard plain allen key. So why use a hex bit when you can use a real allen key ? In a 1.5mm size the allen key is lighter than a hex bit too, by around 4g.
Most small hex bits weigh about 5g, which is around the weight of a 3mm allen key, so it makes sense, and its more convenient to use proper allen keys in the 1.5mm, 2mm, 2.5mm and 3mm sizes. Then use hex bits for 4mm, 5mm, 6mm and 8mm sizes. For instance even a short 8mm allen key weighs in at a hefty 17g whilst an 8mm hex bit is a mere 9g.
Something like a normal simple screwdriver handle could be good for the hex bits but they tend to be a bit big and heavy. The simple ratchet wrench as supplied with the Brompton kit is almost satisfactory but if you actually try to use it its awkward to impossible to reach some bolts where you really need to use a long allen key in a screwdriver fashion.
Sure a simple ratchet driver can make for quick work and is good and for workshop use. However we are building an embedded tool kit for use when out and about and hopefully we might never use it, so does it really need to be sleek and efficient or is ‘it will do’ good enough ?
I searched around and I found a simple holder for the drive bits, its a cross between a screwdriver type handle and an angled hex drive. It cost £3, weighs 52.7g. See the picture below.
A 3.2mm and 3.5mm spoke key is needed, the lightest I found was on Aliexpress, 24.6g.
Separate rivet extractors tend to be heavy, around 75g. There is a low cost, around £6, multi tool that is similar to the Tern multi tool that has a built in rivet extractor, and cut down this provides a rivet extractor that weighs in at 29g.
Compared to some multi tools most of the above mentioned set of individual tools is very low cost, so we can slash out on the decent 15mm wheel spanner that we need. The ‘substantial’ titanium one I found on Aliexpress costs £16 and it weighs in at 23.6g, it also has the 10mm spanner needed for the mudguard bolts, left on the picture below. An equivalent steel spanner of the same type would weigh around 50g.
We need to add in small open ended 8mm, 10mm and 15mm wrenches. Thin versions can be found very cheap on Aliexpress.
The total weigh of all these individual tools is 201g, just lighter and a lot cheaper than a toolkit based on the Tern tool.
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