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Tap tools
Didn't see this in a search, so perhaps worth a new post. A first frame-related question.
Looking for a recommendation for a specific tap: I need to drill and thread a hole in the bottom bracket to mount a cable guide. Anyone got recommendations on what tools they use for the job? Drill bit size and thread metrics?
Thanks!
-Corey
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Re: Tap tools
IIRC they're M5 8mm or 10mm length.
M5 = 4.2mm drill bit (~halfway between 5/32 and 11/64)
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Re: Tap tools
Thanks for the input! It's not something I'll use often, but always welcome an excuse to buy new tools.
Corey Bennett - Falls Church, VA -
INSTA
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Re: Tap tools
An M5 tap is pretty much essential for any mechanic, the vast majority of sundries & threaded bosses will be M5.
In case you didn't know, the size of the hole to be tapped makes for the amount of thread engagement. The smaller the hole, the more engagement the thread will have, but also the chances of breaking the tap will increase. It depends a lot on the material you are going to drill & tap through.
For an M5 thread on steel, a 4.2mm drill bit ought to give about 80% of thread engagement, which is overkill, and you're very likely to overheat the tap and break it.
An average 70-75% of thread engagement is the best compromise, and a lot easier to work with, since you will have to drill 4.40-4.35mm.
Now, a BB cable guide will get very little stress, so don't need to go mad, but since you're buying the tools just do it right in the first place: get yourself two or three sizes of drill bits per every thread size you're going to work with, and keep those drill bits aside and use them only for drilling holes to be tapped.
For M3x0.50: 2.70 for 60%, 2.62 for 70%
For M4x0.70: 3.55mm for 60%, 3.45mm for 75%
For M5x0.80: 4.45mm for 65%, 4.35mm for 75%
For M6x1.0: 5.30 for 65%, 5.20 for 75%
For M8x1.0: 7.30 for 65%, 7.20 for 75%
"Caron, non ti crucciare:
vuolsi così colà dove si puote
ciò che si vuole, e più non dimandare"
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Re: Tap tools
There are many tap drill charts available for the viewing on line. I generally use a #19 bit for a 5x.8 thread pilot. Andy
Andy Stewart
10%
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Re: Tap tools
This has been my go to tap chart for general purpose stuff for years. The minor diameter should change based on the material and this chart calls that out. You'll have to look elsewhere for a few things like Acme threads or when using form taps but you're probably not going down that road at home.
https://littlemachineshop.com/images...DrillSizes.pdf
This video has a lot of good info about tap selection in it. It's intended for automated tapping but it's largely the same. Just use a good cutting oil when tapping by hand. Rapid Tap is good all around choice and easy to come by.
https://www.haascnc.com/video/tipoft...ruzgooa9k.html
We use a lot of Guhring and OSG taps and drills for production. They're a lot better than the general purpose stuff you'll find at the hardware store, like that tap of Anrdeas that's in two pieces. They aren't that much more expensive either.
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