Re: [Frame] Digest for framebuilders@googlegroups.com - 2 updates in 1 topic

[Chris Kvale]

I always use a bottoming tap after brazing on shift pegs.  Most shift pegs are counterbored at the bottom, but some are threaded all the way down which invites the silver to climb up the threads.  Never use a regular tap as when the point contacts the tube additional turns may pull the shift peg off the tube.

Chris Kvale

Minneapolis, MN

On Tue, Jun 17, 2025 at 3:47 PM <frameb...@googlegroups.com> wrote:

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• Curiosity question to frame builders: How exactly are DT bosses done? - 2 Updates

Curiosity question to frame builders: How exactly are DT bosses done?

Bubba <tape...@gmail.com>: Jun 17 09:41AM -0700 Hello frame builders. I don't check in often, but I'm here with a very specific question about the standard operating procedure around down tube shifter bosses. I think I know the answer but I'm not 100% certain, and I'm not certain if there may be several ways to do it.   The context is this: on another forum a home-mechanic finds they can't get enough friction on their down tube friction shifters. I observe that anecdotally sometimes the D-ring can bottom out on the threads, and a tiny bit shorter D-ring bolt -OR- a washer under the head can shorten the bolt and make it easier to get the friction one wants out of the stack-up.   Another poster chimes in that "STEP 0" is to run a tap through to make sure the threads are all clean.   That is the source of my question about how things are done. I've held shifter bosses in my hand, and they "always" are drilled through, but my observation as a mechanic is that when installed, the act of brazing that on has made the hole blind. In other words, the frame builder does NOT drill the down tube and then align the shifter boss to the hole. The frame builder (I think) marks a spot on the DT and brazes the boss there.   Are ALL down tube shift bosses blind holes? If so, one would need a bottoming tap to chase threads near the bottom. Are SOME down tube shift bosses drilled through? If so, one could use a "normal" tapered M5x0.8mm tap and go all the way through. I think all the bosses I've ever checked as a mechanic would have all been mass produced bikes, and in my experience I think they are all blind holes, but I'm not totally certain. I'm going to spot check a few bikes in my stable, but a broken leg has lowered the priority on that exploration. :-(   thanks for any info Bill Lindsay El Cerrito, CA

Jon Norstog <mutton...@gmail.com>: Jun 17 12:10PM -0700 I've never drilled a hole under a DT shifter boss. That said, most of the bikes I've built use a bar-mounted shifter and a plain cable stop on the DT, and if there is a boss, it just holds an adjustable stop for the bar-cons. My guess is that the problem you cite may be caused by an abundance of bronze/silver in the bottom of the hole. Like all things framebuiilding, mounting braze-ons calls for caution and skill.

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[Duane Draper]

I have noticed on the early Ericksons I have Glenn put a hole in the DT behind the shift bosses. Perhaps for this reason or perhaps another reason. 

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From: frameb...@googlegroups.com <frameb...@googlegroups.com> on behalf of Chris Kvale <chriskva...@gmail.com>
Sent: Tuesday, June 17, 2025 1:53:22 PM
To: frameb...@googlegroups.com <frameb...@googlegroups.com>
Subject: Re: [Frame] Digest for frameb...@googlegroups.com - 2 updates in 1 topic

 

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[Michael F.]

What shifter was the OP trying to get to work ? 

Simplex retrofriction shifters will sometimes have a broken spring inside, and people tend to try and tighten the mounting screw - even though it doesn't do anything to affect the lever slippage. 

Bottoming tap, lil oil, and a small tap handle are the usual SOPs for issues with shifter boss threads. IME it is usually a small amount of paint or flux in there that causes any issues. Unless someone royally screws up and uses the wrong screw and boogers up the threads. 

Good Luck !

MF in SF

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