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Drilling downtube for internal wiring

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Drilling downtube for internal wiring

Old 10-03-23, 06:22 PM
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Drilling downtube for internal wiring

Hello all,

I hope this is an appropriate place to ask. I have a 1978 Trek 510 that has had some extra brazing done after the fact. The original frame had a stop brazed onto the downtube for the shifter clamp to bear against. Now it additionally has downtube shifter bosses added, so I won't be using a band clamp around the downtube for anything.

I would like to add a hole for internal wiring for generator head and taillights (as seen on Specialized Expedition, Miata 1000 and others). I know that thes holes are often reinforced, even though they are (hopefully) located in a lower stress spot on the tube (depending on how deep the butts go).

I had the hare-brained scheme of drilling a small hole (and tapping it as well) right through the downtube braze-on, since it's not serving any purpose any more. I had hope it would act as a little bit of reinforcement for the tube, so I wouldn't be needlessly weakening the frame.

I know that I'm the one who will eventually be riding it, so all liability falls on me, but would you think this is an adequate frame reinforcement for a small (M4 or maybe smaller) tapped hole in the downtube?

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Old 10-04-23, 07:49 AM
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When I did this, I went through the lug. I don't know if it's perspective, but the lug on your bike looks a bit small. I feel like the stop is in the wrong place for a generator wire.
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Old 10-04-23, 05:28 PM
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If you wish to drill through that shifter stop for wiring, go for it, it’s a perfect reinforcement, just not in an aesthetically pleasing location.

Were it me, I would drill through the underside of the lower head lug at about 7-o’clock. Have several bikes done like this including some I built myself, here’s a pic of my custom ‘83 Mariposa so drilled.

Mark Beaver
Tamarack Cycles
Halifax, NS
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