Two broken taps

Preventing two more broken taps

I tap #4-40 threads tap drilled #43 in 1018 with a reversing tapping head at 800 - 1000 rpm all day using some old sulphurized cutting oil I've had for years and I've power tapped #4-40s with a 3 phase Bridgeport, you have to be careful but it can be done. I don't know about the Irwin taps as I've not seen them but it sounds like a tap you would buy at the local hardware and just as a rule, run away from that isle. Go to a local industrial supplier, KBC, Traverse, Shars, etc., even the cheap Chinese tools they sell are better. The steel is likely better, the heat treating is better and the threads are ground better, you will save money in the end. The other suggestion I'd make is that if it's a through hole, use a spiral point tap, they are MUCH stronger and you don't have to back them up every turn to break the chips. Did I mention that they are MUCH stronger. If the hole is not a through hole, drill it about a third of the tapped length deeper so there is somewhere for the chips to go, these taps push the chips ahead of the tap. Finally, if the thread is engaged more than 3 - 4 diameters, in this case .3 - .4 inches, you will break almost any bolt before you strip a 50% thread so you can drill oversize and if you're using a machine screw or a grade 5, all you need is 2 - 2 1/2 diameters. This application shouldn't require it but if you're tapping stainless, some of the higher strength steels or titanium, go oversize. Just as an additional point for tapping, if your tapping steels in general, use a black oxided tap and the bright uncouted taps for aluminum, the black oxide coating is supposed to retain an oil film to prvent buildup on the face of the cutting edge and the bright finish is smoother ata microscopic level preventing the aluminum from sticking
 
autonoz said:
Not sure what you mean by this.
Click to expand...

You can chuck a spring-loaded center in the mill. The point of the center engages the hole in the end of your tap wrench. This keeps the tap aligned, as you hand thread.

http://kontraptionist.tumblr.com/post/523437498/using-a-spring-loaded-tap-guide-in-the-mill-a-tap

The guide is available commercially, but for many of us, it was our first lathe project.

http://www.projectsinmetal.com/free-project-plan-spring-center-metal-lathe-mill/

spring tap follower.JPG
 
If the top end of the t-handle tap wrench is flat and smooth, remove the t-handle, chuck it in your lathe and use a center drill to put a center hole in the end. That way you can use a lathe dead center in the tail stock to align the tap and wrench straight when starting the thread. I turned a 60° point on a piece of round stock and chuck it in the mill drill chuck to align the tap and holder on the work in the mill vise.

Some taps have a center hole drilled in the end or are ground to a 60° point for the same purpose if used in the straight type of tap wrench. If that is not clear, let me know, and I'll take some pictures of mine.

I just bought a DuBro t-style tap holder for my smaller taps. It does not have the center in the tool for alignment, so I will be adding one.

Chuck
 
You can use a dead (or live) center in the quill if you do not want to make the spring loaded center. Just be very gentle with the down force as not really any is needed to center the tap. The other downside is it is kind of a 3 arm operation to turn the tap and control the quill, but its a lot straighter than I can hand tap.

I second Irwin now sucking. Shars has always worked for me or Mcmaster Carr.
 
WOW, good discussion. Been tapping holes forever and still pick up on a few good points.

My 2 cents worth;

Tapping oil I use and supplied my not machinist employees with is "RAPID TAP" for feris media and the "RAPID TAP" green can for aluminum. Great stuff and if it made those guys stop breaking taps it has to be good!

Next, watch the steel the tap is made from. HS usually good sturdy tap for horsey hands. CS, carbon steel, cut really well when brand new but dull quickly and are very brittle. They cost 1/3 to 1/2 as much as a HS tap but after 6-8 holes they are pretty much done. Price difference alone should be a give away. Most of my CS taps are oddball gunsmith sizes and the price of a tap is figured into most every tapping job. So I keep my set full and thank everyone for their generosity.

Most of our tapping at work was in 3/8" or less material. We all used variable speed drills and two flute gun taps with lots of fluid. You must get the feel to start a straight hole and start slow, hold firm and zip-in and out like magic. If we were to have tapped by hand the labor units would be so high as to mandate the use if self tapping or zip screws and the finished product would have looked like well--****! Our tap sizes were #8, #10, and 1/4" the majority of the time.

As for a tap center for lathe or mill I made several. Some with springs some not. The one I usually grab to use is a 1/4" fixed only about an inch and a half long, with a ground 60 deg end. So much space is taken up by the tap handle that short is cool. Not a real big deal on the lathe as the tailstock slides away but the crank, crank, crank on the mill gets tedious and makes me want to forget using the center but then I usually screw something up and curse myself for the rest of the day. And my mill is a Bridgeport so room is usually not a problem.

As far as tapping heads go I was talked into getting one by a friend who is a knife maker. He uses these little tiny torx head screws to hold his folders together and drills and taps a whole bunch. I am not sure on size but I think a #3 or #2 and does them all with a tapping head at 1K rpm. He claims he does not break taps anymore. Making knives he taps some pretty wild stuff at times. Now I have 3 tapping heads because they do such a fine job. Actually I only need 2 for "0" to 1/2" but the big one is big so the middle one is just handy to have.

Popular tap brands around here are Greenfield, Ace, and Hanson. Irwin is usually left for the week ender or carpenter tools. MSC is a really neat place. I wonder how they provide their service for what they charge but Grainger follows the same business model and both are great.

I do agree with going 1 or even 2 sizes over on drill size as it makes a huge difference in the torque required to tap the hole. As one of my mentors told me "A 50% thread will hold anything you have and any depth of thread over diameter of fastener is wasted because you have already exceeded the breaking strength of the stud". Good points.

Tap guides. I made a simple set for #4 to 1/2" out of 1" cold rolled. Milled a flat the length of the side, 1", to make a flat spot for engraving. Polished it a might and engraved the size on the side and end. Then a piece of pine was ordered up and a tray was fabricated and varnised to keep them in order. (And looking cool, of course) Ever notice, orderly, neat things get used. Crap in a box remains, crap in a box.

Good tip on the soda in the hole, you can bet I will try that one. :tiphat:

Aren't you glad I didn't give you the 50 cent version!!!

Now, go make some SWARF! It is good for the mind.
 
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WAwoodman.

thanks for the links. I've used my drill press taking advantage of the verticle slop in the wspindle but this is a much better solution and it's a rainy day here and this is a rainy day project.

Joe
 
To remove broken taps from holes,try grinding a used center drill.smaller than the tap.
Grind a flat from the inner diameter to the 60 degree.almost like a spade point.
Run the spindle of the mill/lathe in reverse and let the conical section of the center drill locate on the flutes of the broken tap,
and unwind.
It works most of the time.
John L
Spain
 
WOW! Great information here. If I can not succeed with this type of support I'm a rock. Thanks for all the tips.
 
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