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I hate to tap. I've broken more taps than I'd like to admit. So with this in mind here's my question. How does a tapping head work?
Do you use tapping fluid and back the tap out every turn or so to clear the threads? I've only broken one so far ... 3/8" in the bottom of my Jeep when I was putting new shocks in. Spent several days trying to break/twist the end out, and finally ended up ordering a tap extractor with the little fingers that reach up into the flutes. Sucker came out in less than a minute.
SPEEDRE - check out the following thread...
Vince's BP CNC conversion
part way down there is this video
http://www.flyingcritters.com/video/Tap.wmv
and more discussion... I am interested in getting one of these as well.
Thanks I watched it, the sound did'nt work so I'm not sure what I saw. I take it that they have a sensitive clutch system and if one uses cnc a special code utility for them, correct. But by hand they use the quill pessure and feed for frwd and bkwd.
Speedre - I think you are correct. Be sure to read the messages following the posting of the video. He talks a bit about how the tapping head works and mentions the need to know the reversing rate in order to get the correct feed rates on forward and reverse. He got his from Ebay pretty cheap I think but I sure have yet to find one that is "cheap" on Ebay.
Speed, some of it is getting GOOD taps to begin with, 1/4-20 is a popular size to break, the 4 flute break a LOT easier than the 2 flute do, same thing in larger sizes, 3 flute in a 1/2-13 is a lot stronger than a 4 flute.
One thing you can do hand tapping is take a block and tap a hole thru it, hold this block against the part with just the very sharp tip of the tap sticking out, run the tap from the block into the part, the block guides the tap and advances it properly, sort of a small leadscrew tapper, that will allow you to tap 4-40 in 4140 28-32 rockwell without breaking them.
If you are making parts for yourself and you have plenty of thread length it is ok to cheat a bit on tap drill size too, I used to go .005" or so larger on H-13 and it helps a great deal avoiding tap breakage.
The other basics are to make sure you pull equally on the two handles of the tap wrench, it will become second nature after awile. I have seen more guys break them talking while they tap, often holding the part in one hand and the tap wrench in the other...rather than the guys that put the part in the vise and concentrate on the task at hand :-).
For a lot of parts run on cnc even we used to just start the tap say 1 dia. deep, and hand tap to depth while the next part was running, this was in A-2, D-2, 4140ht, M4, H13 other tool and die steels, beats the heck out of having to bribe the EDM guys to burn a broken tap out for you :-).
Save your dull 1/8" solid carbide centercutting endmills too, if you run 1 about 1000 rpm, and feed it in .0001" per rev with coolant you can often go right down the middle of a tap and get it out of there, sometimes it takes 2 endmills, they don't have to be "nice" ones because they sure won't be when your done with that :-).
Bill
Speedre,
Do some research on form taps. They generate the thread by pressure forming, not cutting. They are stronger and last longer.
Wayne Hill
I solved most of my breakage problems for machine and hand tapping by using reverse spiral machine taps. Two flute
They pull the chip back rather that choke up between the flutes.
I also tap a lot of holes in stainless using a tapping head mounted in a portable drill by holding the rod that stops the body from turning.
Your question how tapping heads work, they have a clutch and gear train in the body.
When pushed they rotate clockwise and when backed off or pulled they reverse.
One of the most useful tools in my shop.
The More I Learn The Less I Seem To Know
Thanks guys. Great info and sound suggestions. I break mostly #8's and #10's. I think I'll try thread formers and a tap guide block.
The Tapmatic cnc heads are nice, I bought one for a cnc I ran at one job, I set it up to run a bunch of 4-40 in some 4140-ht to test it out, as I recall I was tapping at 1000rpm or more, I did about 20 holes just to prove it out, the head was of the type where the spindle does not have to reverse, when Z reversed directions the head would coast a few revs..then reverse, you could hear the tap cutting zzzzzzzzzzzzpppp, :-)...worked slick, Thats the only I know that you can HEAR a 4-40 cut and not break it hehe.
Tapping is an aquired skill for sure, some get very very good at it, and some of us just get by :-)
I'v never really liked form taps, but that opinion was formed 20 years ago when they first came out, and buffered by the fact that I used to get stuck burning out taps, it is not hard to burn out even a 4-40 fluted tap, but try to burn out a form tap sometime :-)
Do yourself a favor too, Start looking in pawn shops and ebay and get you some starrett tap wrenches, they are truly nice, and a sloppy crappy tap wrench will help you break a tap.
Bill
I like the forming taps. They're stronger threads, break fewer of them. (in fact, I never have broken a forming tap) No chips from tapping to get caught when backing out. The only draw back I've found is that the material must be ductile enough. Can't use them on cast iron or graphite for example. Besides I live less than 2 miles from the Balax shop where they are produced in the booming metropolis of North Lake, WI just 3 miles west of the other megelopolis of Merton, WI
DZASTR
I have about (4) 5 gallon buckets of Balax M11x1.75 taps that we have used in the last 4 years at my present job, They have been used to tap the head stud holes for GM I4 and I5 engines in Colorado's, Canyons, and now H3's.
They swore they were going to go to form taps 2 years ago but the engineering dept chickened out, each tap does 375 parts at 12 holes per part...if we kick life to 390 about 10% of the time the tap breaks. Thats 4500 holes per tap, material is A356T6 coolant is Richcut 516+ with thru spindle coolant at 800-1000psi, this is rigid tapped.
Bill
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