Tap and drill recomendations

[Boucher]

I need to tap some small holes ( 4-40) in 416 stainless and 12L15 What taps and drills would you recommend. Quality is more important than cost. I have zero experience below 10-32. I am open to any suggestions and guidance would be appreciated.

[tattoomike68]

Use a roll tap, they dont bust near as easy but do cost more. follow the manufactures tap drill size its not the same as a cut tap.

316ss is not near as bad as 304ss.


call the pros and ask them for a second opinion.
http://www.balax.com/index.html


good luck

[Carm]

If they're through holes, use a gun tap.
Unless there are engineered specs, drill 60%.
Cobalt drills seem to stand up to repeated holes. I like screw length. C'sink the hole one thread deep before tapping.
Remember SS work hardens, so get'r done with some cutting juice and steady feed.

[ckalley]

I think you will find that the 12L15 will tap very easily with the standard tap drill size. Most any good quality HSS plug tap will work fine.

For the 416, go with Carm's suggestions. I'd suggest a TIN coated Cobalt HSS gun (spiral point) tap for thru holes or a spiral flute tap for blind holes.

I would also suggest using a hand tapping fixture so you apply the force srtaight in and out. You can't have side loads, especially with the small taps. (Don't ask me how I know).

Good Luck
Craig

[Paul Alciatore]

I've never used the roll taps so I can't talk about them. If you use a conventional tap:

1. Get a high quality tap, preferably a ground thread type. Some will tell you that carbon steel taps are sufficient, but I have always had better luck with High Speed Steel (HSS) ones.

2. Get a "taper" style tap. It is good for completing through holes and for starting blind holes. If they are blind holes, then get the complete set: taper, plug, and bottom taps and use them in that order. You may get away with just the taper and plug taps in some holes if the threads do not have to go all the way to the bottom.

3. Use the correct tap drill or a bit larger. 75% thread is usually recommended, but in steel you can probably go to 60% as Carm suggested. This makes it easier to cut and helps prevent breaking the tap.

4. Use a tapping guide of some sort. I have several steel blocks with holes drilled to clear the various tap ODs and I use them to start the taps to ensuer they are square. I also have a tap handle with a 1/4" extension on the rear and a 1/2" sleeve that fits in my drill press chuck. The 1/4" extension fits in the hole in the sleeve and it is turned by hand, not under power. This is another way to keep the tap square. I used mine earlier tonight to do a 1-72 hole in steel with no problems. And there are other devices to help the taps start square but the two described can be made in your shop in a short time and for little cost. Do use one such device.

5. Use a good cutting fluid. I like Tap-Magic for tapping but there are other good ones. In a pinch just use oil, but do use something.

6. Back the tap out when you start to feel additional resistance and clean the chips out of the flutes. Add more cutting fluid and start again. Don't force it.

7. Tap wrenches have Tee handles for a reason. The torque must be applied evenly from both sides to prevent any tendency to twist sideways and break the tap. Apply even pressure on both arms or the tap wrence while turning the tap. This applies both when cutting and when removing the tap.

[Circlip]

And if you hear a squeek when tapping, get a new tap straight away.

Regards Ian.