Breaking Taps like a .... BOSS!

Brian Avila

Brian Avila

Joined
Jan 2, 2011
Messages
1,286
So I broke every single tap that I owned today trying to tap threads in my liners.

I was curious if you guys have any suggestions. I went slow, I used tap fluid, I was straight and everything seemed to go ok and then snap...

I didn't have any problems with the 2-56 taps. But when I went to the 3-48 it was something else.

I just want to make sure.... #47 drill hole to tap a 3-48 screw?

-Brian-
 
According my Starrett chart #47 is correct. Below is a link where you can download a Starrett wall chart.

http://www.starrett.com/catalogs

I have not done a lot of tapping, but I was breaking a lot of taps (2-56), just working with stainless. I bought a hand tapping fixture from Hawkins Knife Supply for $40 and it helped a lot. This will have to do for me until I can justify spending $300 - $400 for used tapmatic.

Below is the link to where I bought the hand tapping fixture.

http://www.hawkinsknifemakingsupplies.com/11.shtml
 
Are they hand taps or spiral flute or spiral point? Is the the hss or carbon? What type of material are you tapping? Do you know the hardness?
 
Is the hand tap marked hss? If not, it's likely carbon. Can you explain what you did after drilling the hole? Did you tap with any cutting tapping fluid? Did you use a guide or just tried to go in squarely? Did you just tap all the way unit il it broke or did you reverse the tap?
 
Brian, what material are you tapping? I know for titanium liners, it's not uncommon to go one drill size larger before tapping to prevent breakage of the tap.
 
I purchased it as hss from Enco. I drilled the hole. Debured it. Used tapping fluid, tap magic, used my hand tap handle. It was straight but seemed to be really really tight. I have tapped a lot of holes by hand and didn't really have problems till this one.
 
I didn't know about going one size bigger on Ti. I am using Ti liners. Why go bigger because of Ti? So try a #46 instated of the #47. I didn't have problems with the #50 for the 2-56 holes.
 
It's merely a compromise, since the Ti is still plenty strong enough to hold on to screws with a slightly bigger hole, but it decreases the chance of breaking the tap. Just something to try, I'm sure there are plenty of people that have success with the "normal" sized hole, but tutorials from knifemakers much more experienced than me recommend going one size up.
 
Looks like you could move to a #45 drill, which at .082" is 4 thou larger than a #47, at .078". The #47 yields a 76% theoretical percentage of thread engaged. The #45 yields a 66% theoretical percentage of thread, still well above the 60% of thread needed for acceptable strength.

If you are tapping titanium, I found that moving to a slightly larger bit can really help. The TI is harder for the tap to cut, and requiring more torque, is hard on those little taps.

My best results have come with using a Tapmatic (wish I had one) or, with using my hand tapper and some good tapping lube. I watch the tap in the light, you can see smaller taps torque a bit in addition to the feedback you get through the tapping fixture. If the tap is twisting more than just a tiny bit, I back off the pressure. It's easy after a minute to observe how the tap is cutting, and develop a rhythm with cut/back out, cut/back out.

If you don't have a hand tapper, it's easy enough to make one. Also, Tap Magic may not cut the mustard. Moly dee lube is better. I got some alternate advanced tapping lube from (IIRC) Chuck at AKS that works well, too.

Also, how thick is the material?
 
Mainly because it's a little bigger yet, but still plenty big enough. 0.071" is a little thick, starts resisting more.
 
If you have, or ever see for sale, a broken or otherwise expendable small drill press, you can make a great hand tapper out of one. Just take the motor off, remove the spindle pulley, and put a crank/arm in its place. Chuck a tap in the 3-jaw chuck, and away you go. The best type of drill press to use is one that has a spring return feedlever, reverse the spring and you have automatic light down pressure to start the cut. Works better than the commercial hand tappers you can buy...
 
I've broken enough taps in my life to know that hand tapping 0-80 and 2-56 threads was not going to be an option when I started making folders. I picked up a used Tapmatic 30x on Ebay for $125. I had to buy an appropriate collet for it which was about $23 from Enco and I have not had a broken tap in 50+ holes in Ti. Huge time savings also! I've been running it in my mill but I'm now on the lookout for another drill press that I will dedicate to the Tapmatic.

Most tap drill recommendations are for 70% threads but they are all just recommendations. You can adjust the minor diameter to suit the material and the need.

Bob
 
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