How to Modify a Tap?

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tonydi

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I finally broken down and bought a B&S spring loaded tap guide. Much to my surprise when I went to use it on a 8-32 spiral flute tap I discovered that the tap had a "flat" top, not a pointed one like I thought. Looking through my other small taps (6-32 through 1/4") they're all like that (man, I coulda sworn....).

I presume these taps are hardened so I thought maybe I could grind a point on the top using my bench grinder but that doesn't seem very precise. I don't think I can drill a dimple in them either.

But would something like a tiny (1/8"?) carbide end mill make a dimple in this material?

Oh, I'm concentrating on the tap itself for these small ones because I made some small tap handles like Joe Pi recently featured (here) so using the tap guide on a conventional tap handle that has the dimple in the top won't work.

All suggestions appreciated!
 
I would think more like a small carbide center drill and put a real center in the end.
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What brand taps are these? I never saw taps that did not have a center on both ends to hold it for grinding?
 
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I would turn a small bushing about twice the length of the square section and a internal diameter slightly less than the distance across the diagonal of the square section and press it on the tap. Aluminum or brass would be the material of choice.
 
I'd use a "poor man's lathe" ... Chuck the tap, threaded end inward, into an electric drill. Spin it in the drill (medium speed) while holding it diagonally against the grinding wheel.
 
@Flyinfool The spiral flute taps are OSG, so not exactly cheap Chinese junk. Here's a pic of the 1/4-20 OSG along side a conventional 8-32 tap made by Vermont-American that's probably 30 yrs old. Why a center drill and not something like a small carbide ball end mill?

taps.jpg


@RJSakowski That was my first thought since it's something I already have material and capability to do. But I kept coming back to the fact that it's 4 little pieces (each tap has a slightly different dimension) I'd have to keep track of and deal with when I wanted to use the tap guide.

@hman Ahhh, I got it! The "cone" tip on the B&S tap guide is really tiny, though, about .075". So I'd need to take quite a bit of material off the taps to make a point small enough to fit in a manner to assure it couldn't slip out.
 
OK. I guess I missed how large a tap you were wanting to modify ... though you did mention small taps in your initial post. Anyway, on to "poor man's lathe #2" ... chuck the tap into the drill motor as before. While spinning it, use a Dremel with a small mounted stone or a dental burr to form some kind of a dimple in the center. If it's not deep enough for your tap guide, it might be useful to guide a carbide center drill or end mill.

Alternatively, you might want to make a "deep cone" adapter for your tap guide - something like 1/2" diameter, with a conical depression cut with a large countersink bit. The large cone would span the end of the tap and either center on the corners or the conical bevel of the square shank.
 
Those taps to have the remains of the conical end. You just need to make a bigger cone for your alignment guide.
OR go with a point on the guide and drill a center in the taps.
 
Flyinfool said:
Those taps to have the remains of the conical end. You just need to make a bigger cone for your alignment guide.
OR go with a point on the guide and drill a center in the taps.
Click to expand...

Gotcha. So carbide tooling should be able to drill into these taps but I'm still curious as to your suggestion about a center drill vs ball end mill. Looks like I can get a .125" carbide ball end mill for a lot less than a center drill. What's the disadvantage of going the cheaper route?
 
@Cadillac Yeah, I have a set of those but as I mentioned in an earlier post, I've made some "Joe Pi" small tap handles (see this link) that I prefer to use. A) these make it easier to get a feel with these small taps and B) I gain a lot of Z axis space on both my mini lathe and mini mill by not using the more conventional t-handles.
 
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