Heat treated 17-4 PH snapping taps

[eject_21]

By the looks of things I'm going to be tapping this stuff for a while. Several sizes from 4-40 to 1/4-20. I'm using a swing arm style "tapmatic" air powered tapping rig, and Emuge. I can do 6 holes (4-40). I'm starting all 6 holes, changing the tap and then finishing all 6 holes. If I try to tap a hole to depth, it's hit or miss. I have plenty of depth to work with, and my minor dia's are right on. Opening up the minor a couple grand helped, but still kicking my butt. I cant afford to keep breaking taps in shoe-box size parts.Any help would be greatly appreciated. TiALN coated taps.

[dandy]

Get yourself a greenfield screw thread manual. You say the minor diameters are right on. How many diameters of engagement do you have? Example 1/4- 20 the recommended hole size for 1-1/2 to 3 diameters of engagement the hole size should be .210 to .204. If you are using a standard no 7 drill this could be a huge problem. Also how hard is the heat treatment.

[HuFlungDung]

What kind of flute geometry are you using? I find spiral fluted taps to be weak overall. Also, the extreme positive geometry of the spiral flute tap weakens the tooth form even more.

Its the tips of the tap teeth that are the weakest and first to give up, and its those same dull tips that bind up and jam the tool in the thread being cut.

For really tough going, I would probably grind a serial tap. Remove the tops of the teeth all the way up the tap in such a manner as to retain some relief. (I use a Darex tap sharpening attachment, with eccentric cam motion). This roughing tap should wind in quite readily. Then chase the thread with your finishing tap.

BTW, I have never done this as proof of concept, but it sounds good, don't it?

[kalmah]

Originally Posted by eject_21 By the looks of things I'm going to be tapping this stuff for a while. Several sizes from 4-40 to 1/4-20. I'm using a swing arm style "tapmatic" air powered tapping rig, and Emuge. I can do 6 holes (4-40). I'm starting all 6 holes, changing the tap and then finishing all 6 holes. If I try to tap a hole to depth, it's hit or miss. I have plenty of depth to work with, and my minor dia's are right on. Opening up the minor a couple grand helped, but still kicking my butt. I cant afford to keep breaking taps in shoe-box size parts.Any help would be greatly appreciated. TiALN coated taps.

The best solution for your problem is the thread whirling tool. It's like a thread mill but there is only two profile.
You can thread a lot of material with a great tool life duration. If the tool breaks, it's not a problem, your parts isn't broken.

I've an great exemple with Hastelloy alloy.
With HSS taps M4, the tool life duration is 4 holes. With thread whirling tool the tool life duration is more than 200 holes.

If you want more information, send me a private message.

[dxxx]

tough stuff,need to keep fresh and sharp tap in spindle,also we used a special tapping compound. i think it is called "hardcut",it red and pours like cold honey.also drill out hole to the limit.if blind hole you may have to tap by hand at bottom.use plenty of cutting fluid.if you are limited on taps,make setup to sharpen taps.

doug