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Old 12-21-07, 12:38 AM   #1
ParkingMeter
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Keeping BB taps sharp

About to send some of my cutters in to get sharpened and was wondering if any of you guys have used a diamond hone or something similar to touch up the cutting edge on BB taps. I've heard of this as an elbow grease machinist method. A couple of machinists I know also recommended a Dremel with a grinding bit that matches the rake, but I think I'm too clumsy to risk that on a $160 tap . I have a good set of kitchen knives that I'm able to keep nice and sharp with the occasional honing, was wondering if this logic also applied to taps. The facing mills and reamers I'll leave to a tool grinder, I think sharpening those is more tricky.
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Old 12-21-07, 03:12 PM   #2
NoReg
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You can stone the face that is radial (not the threads). You need to keep the stone flat and work the whole face confident that it will eventually erode to the point that the edge is sharp. If you bias towards the edge, you will "dub" it, which means change the rake angle of the edge creating a negative rake. As with all honing you really want to hone while the edge is sharp. If you dull the edge sufficiently it will require regrinding, which can be done by hand or machine, but requires that more material be removed and raises the stakes if you aren't fully confident.
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Old 12-21-07, 07:09 PM   #3
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Originally Posted by Peterpan1 View Post
You can stone the face that is radial (not the threads). You need to keep the stone flat and work the whole face confident that it will eventually erode to the point that the edge is sharp. If you bias towards the edge, you will "dub" it, which means change the rake angle of the edge creating a negative rake. As with all honing you really want to hone while the edge is sharp. If you dull the edge sufficiently it will require regrinding, which can be done by hand or machine, but requires that more material be removed and raises the stakes if you aren't fully confident.
Cool thanks for the reply. My BSC taps are still pretty sharp, not dull enough to need regrinding. When you say stone do you mean a curved hone or just a small, fine whetstone (or something else)? A picture would help. I've seen some diamond knife hones at Excalibur and thought that one matching the rake angle would work. I won't attempt to regrind the taps, too risky, I'll leave that to a tool grinder. Thanks.
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Old 12-21-07, 09:09 PM   #4
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Get them Titanium nitride coated the next time you get it sharpened
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Old 12-21-07, 10:34 PM   #5
NoReg
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Be careful what tool grinder you leave it to, it's getting ugly out there. I guess you are fine if you send them to one of the bike guys.

The surface I am talking about is flat, and you apply a flat stone to it. The other surfaces are the same shape as the BB cups you are going to insert into the BB, You don't touch those.

In case you wreak it, here is how you can make your next one:

http://frets.com/FRETSPages/Machinin...p/19mmtap.html
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Old 12-22-07, 05:11 PM   #6
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I think I know what you're talking about. Still might be a little too tricky for me, I'm no machinist. I've used McKenzie tool grinding in Portland once in the past and they seem to do a good job (they specialize in bike and odd machining tools). They do all the tool grinding work for Andy Newlands (Strawberry Bicycles) who makes HSS mitering cutters. I've looked into TIN coating for my tools; at the rate that I use them, they probably wouldn't need sharpening for several years. Kinda expensive though.
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