Tapping

[kenlambert]

what is a good tap for hand taping hard steel without breaking easily?
I am taping a 10/32 thread in grade 8 bolts

[Karl_T]

I'm partial to OSG spiral point taps. There are certainly other high quality taps.

Get a two flute in that size.

Karl

[HuFlungDung]

The tap has to stay sharp. Grade 8 is tough going for any HSS tooling, so don't expect the tap to last for long.

But having said that, I would get a premium quality ground thread tap, rather than using lesser quality 'cut thread taps' such as one might find in cheap tap and die sets. Ground thread taps are hardened before the machining is done, so the stress risers created by the teeth are non-existent in the hardening stage. This gives you a tougher tap body.

Inspect the tool frequently. Avoid reversals in mid-cut as much as possible, because this is most often when the tap will be damaged, as the chip that is still attached to the hole will scrub the edge of the tooth flute, in the unsupported direction. Once even a single tooth is chipped, that tap is practically useless, unless you have the wherewithall to resharpen it.

[Geof]

Because you are using grade 8 bolts you may be able to cheat a little and use a larger than normal tap drill size. Possibly go for a 60% thread rather than around 75% which is where most tap drill tables aim for. To compensate for the reduced thread depth use a deeper than standard thread engagement for the 10-32 bolt going into the thread to get back a bit of the strength you have given up.

[mxtras]

I almost prefer three flute taps because they seem to cut smoother but I think the two flute suggestion has a lot of merit as the flute strength would be greater, right?

I also agree with using the slightly larger tap drill.

Scott

[kenlambert]

Ok thanks for the replies. I have some expensive taps and some craftman taps ,The craftsman seem to be wor out halfway down and the expensive seem to break very easy.

[Ken_Shea]

Ken,
Is there any possibility of annealing the bolt, tapping and then hardning. Depending on what critical use these me be of service in this may not be an option.

Ken

[kenlambert]

I could go to grade 5 if that would be a big difference on tapping.

[Ken_Shea]

Yes

[Geof]

Ok thanks for the replies. I have some expensive taps and some craftman taps ,The craftsman seem to be wor out halfway down and the expensive seem to break very easy.

This is merely a manifestation of Murphy's Law.

[DareBee]

I doubt that the tap is the issue, it is probably the Hand tapping itself. I would only do this tapping using a tapping block or better yet fixture it in a machine (lathe, mill, drill) and tap it by running the spindle by hand. rigidity is the key to tap life.
Or I would just toss it in my EDM tapper ;-)

[kenlambert]

I use a hand tapping machine that keeps everything lined up ,the kind MSC sells.