[SCzEngrgGroup]

I've always heard Spriral Flute taps were the thing to use for machine tapping, especially on blind holes. Until today, I've always used Spiral Point taps. But, today I decided to try some Spiral Flutes I bought a while back. I was tapping 10-24 holes, using a tapping head. I've done literally hundreds of these over the last few weeks without incident. Sadly, on the VERY first attempt, it went in no more than 1/2", then the tap literally exploded! As I said, I've taps hundreds of holes using the same G-code and same hole size, with no problems. So it's not a coding problem. It just seemed extremely fragile. Do they require a different approach?

Regards,
Ray L.

[MRM RCModels]

What was your torque setting?

[SCzEngrgGroup]

What was your torque setting?

It was set to a reasonable level for the spiral point taps I've been using - haven't broken one of those. Even if the clutch had released, the tap still would've been broken by the time the plunge was done. The problem is the tap seemed to stop tapping while still quite shallow in the hole.

Regards,
Ray L.

[forrey]

I had the same experience as you about 15 years ago, went back to spiral point until about 5 years ago when I switched almost completely to Form taps from 4-40 through to 1/2-13 and have never had any trouble or replaced many. Now these are mainly used in our shop for aluminum, but have also done 1040 and 304.
Forrey.

[SCzEngrgGroup]

I had the same experience as you about 15 years ago, went back to spiral point until about 5 years ago when I switched almost completely to Form taps from 4-40 through to 1/2-13 and have never had any trouble or replaced many. Now these are mainly used in our shop for aluminum, but have also done 1040 and 304.
Forrey.

Yeah, I've got a few of those to try as well. Seems to me they should be the strongest of all, since they typically only one, or no, flutes.....

Regards,
Ray L.

[MichaelHenry]

I had a similar problem with spiral flute taps on a small thread form (#4-40?) in 6061, threading about 0.375-in deep in a blind hole. The tap broke on the 4th or 5th hole by snapping on the shank above the thread teeth. I've since switched to spiral point with extra deep holes (to give the chips a place to go) or to form taps. The tap I broke was good quality from Mari Tool, probably a Morse.

Mike

[zamazz]

We use spiral flute almost exclusively, since almost every hole we tap is blind. I do derate the rpm slightly from recommended, as I had some issues running smaller taps at the speeds recommended by the calculator. I also got a really bad bunch from OSG a couple months ago. They'd last about two holes, tapping very oversized, then snap. I believe they were misground. Usually I get several hundred holes per tap.

[SCzEngrgGroup]

I had a similar problem with spiral flute taps on a small thread form (#4-40?) in 6061, threading about 0.375-in deep in a blind hole. The tap broke on the 4th or 5th hole by snapping on the shank above the thread teeth. I've since switched to spiral point with extra deep holes (to give the chips a place to go) or to form taps. The tap I broke was good quality from Mari Tool, probably a Morse.

Mike

Sounds exactly like my experience. Mine also were from Maritool.

Regards,
Ray L.

[SCzEngrgGroup]

We use spiral flute almost exclusively, since almost every hole we tap is blind. I do derate the rpm slightly from recommended, as I had some issues running smaller taps at the speeds recommended by the calculator. I also got a really bad bunch from OSG a couple months ago. They'd last about two holes, tapping very oversized, then snap. I believe they were misground. Usually I get several hundred holes per tap.

What RPM do you use? I was only running 300 RPM, and had copious lubrication.

Regards,
Ray L.

[rlockwood]

we use plenty of every style of tap and when properly implemented, have roughly equal success with all.. perhaps a bad bunch? do you have a picture of the exact problematic tap?

IMO though, for any CNC tapping in aluminum, you're wasting your time using anything but form taps. Superior in every way, except maybe the initial sizing requirements

[SCzEngrgGroup]

we use plenty of every style of tap and when properly implemented, have roughly equal success with all.. perhaps a bad bunch? do you have a picture of the exact problematic tap?

IMO though, for any CNC tapping in aluminum, you're wasting your time using anything but form taps. Superior in every way, except maybe the initial sizing requirements

That's definitely where I'm headed. Seems to me like the best solution overall, at least in aluminum, and they are the strongest taps as well.

BTW - While Googling around I found an excellent document on tapping: http://www.threadtools.com/Files/Tap...cal%20info.pdf

Regards,
Ray L.

[zamazz]

I typically run 10-32 & 8-32 at 500 rpm, since my code is already written for those speeds. The calculator recommends closer to 1000, iirc. Try hand taping with one of them, that will tell you really quick if you've got a bad tap. They should cut just as easy as a spiral point.

[rlockwood]

a thing of note.. you certainly do not have to tap at the recommended speeds, and it would be impractical to do so on many machining centers.

Its actually quite common to simply tap at 10 ipm, and vary the spindle speed accordingly. It makes for very easy calculations (a 32tpi tap will run at 10ipm/320rpm, etc, much easier to remember than 15.625ipm/500rpm)

I don't quite follow that method, but all of mine do feed at multiples of 10 ipm, as its much easier to verify the proper ratio's than deriving a feedrate based on an arbitrary spindle speed. Also, I like round numbers..

Anyway, that's my pro top-tip of the day, take it or leave it.