Help with thread size of Braze on bosses
 

Hi,
I am running into a problem trying to pre-fit the Domenic's I just bought...It seems as though the right shifter boss was not tapped all the way and the shift screw will not insert far enough to tighten the lever.
Does anyone happen to know the tap size needed to tap out the threads? :foo:
Information much appreciated...I don't trust my old eyes to read my gauge correctly.
Thanks, Ben

Shifter bosses are usually 5 x 0.75mm.

Reynolds,
Many thanks, Ben

I cited that size off the top of my head, but checked it and it's actually 5 x 0.8mm :o

OK, thanks for the clarification.
Ben

You will need a finishing type of tap since you will need threads nearly to the bottom of the hole.

Most lever bosses are 5mm x 0.8mm but some Shimano bosses are 4.5mm x 0.75mm:

N.B. you will need a "bottoming tap" rather than a typical "plug tap" if you need to fully chase the threads on your lever boss.

http://www.os2.dhs.org/~john/lever-bosses.jpg

Why not just measure the screw?

thread pitch gage

https://tse2.mm.bing.net/th?id=OIP.W...vwHaHa&pid=Api

http://i.ebayimg.com/images/i/121046...-1/s-l1000.jpg

True.

(Not to confuse things, but I'll add that some early Huret bosses are 5mm x 1.0mm.)

Especially important. You don't want to find out what happens if you don't.

[MENTION=367427]xiaoman1[/MENTION], it's not that the boss wasn't tapped all the way, it's likely there's just some gunk in it. I'd try swabbing it out before sticking a tap in there. If you clean it out and the screw still won't go in far enough, make sure you aren't bottoming the screw against the frame tube first. If that's all good, then there's probably some flux or braze in the thread, and a bottom tap will clean that out.

Or a ruler and arithmetic (and you don't want that!).

Its how real machine shops do it , but this is people writing from the computer at work , not in machine shops.

I did not have a gauge but have some taps and thought I could get some information here so I could finish up...anyhow thanks for the reply.
Best, Ben

5x.8 is pretty typical , that's what I use in the bike shop.,
(not a bottoming type, as most common use is in chasing paint out of threads..)

[QUOTE=JohnDThompson;20273838]Most lever bosses are 5mm x 0.8mm but some Shimano bosses are 4.5mm x 0.75mm:

N.B. you will need a "bottoming tap" rather than a typical "plug tap" if you need to fully chase the threads on your lever boss.



I knew I missed something thanks. thumb:
Best, Ben

[QUOTE=JohnDThompson;20273838]Most lever bosses are 5mm x 0.8mm but some Shimano bosses are 4.5mm x 0.75mm:

N.B. you will need a "bottoming tap" rather than a typical "plug tap" if you need to fully chase the threads on your lever boss.

Thanks for the information..did not know about the need for the bottoming tap...I got it done.
http://i66.tinypic.com/2rxcr2v.png
Best, Ben

Durn, other times y'all caution people against buying BB wrenches and such that will be only used once. Now you want someone to buy thread gauges?

Bike shops may, and a professional machinist will ...

I use them often enough that I bought a set of taps.

I've had some for 54 years and probably only used them a dozen times. I can count the threads and measure with calipers to figure pitch. Or I try a bolt or nut of a known size to compare.

But it is gratifying to know that I'm up there with the "professional" machinists since I own several sets of them.

I'm also not certain that bottoming taps are necessary. I'd check with Andrew or one of the others in the frame builders forum, but drilling a hole in the tube for a normal tap shouldn't be an issue. Just don't mess up the existing threads.

Why do two jobs when you can do one?

If you have a belt sander or a bench grinder, it's not hard to convert a plug tap into a bottoming tap: just grind off the taper.

If you do your own car work they will be used much more. Thread gauges aren't applicable to just bikes.

Important to remember to quench it frequently to prevent the hardening from being ruined.