Tapping questions

Unlikely that the 3M oil had anything to do with breaking the tap. This is an arguable point because there are other fluids recommended for tapping aluminum such as penetrating oil (Liquid Wrench). Next time make sure the chips aren't remaining in the flutes when you "back up" as this would tend to indicate a lube problem.

IMO, and assuming above is not the problem, there is a good chance you leaned on the tap wrench. This is usu. more of a problem with smaller taps, such as 6-32 and smaller. Tapping is safer when you use some sort of an alignment guide to hold things straight.

Bob Swinney

Unless it was a gun tap, yes.

No. You would have been better off using a bit of WD-40 as a cutting fluid, or better yet some cutting oil.

Yes.

Definitely yes, there are no decent taps or dies sold at home desperate.

Jim

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I'd have to have seen the way that you were actually handling the tap to say what went wrong. The biggest problem often is just leaning on a tap and that usually happens as you are turning it in and not feeling any real hard stress. I've also seen taps just break because and that is often because the tap was stressed earlier and the skin started to fracture. Eventually, the tap then breaks all the way through. If the tap wasn't "freezing up" in the hole or picking up an aluminum coating on the cutting teeth, it really shouldn't break. If you are getting thaqt coating, you're using the wrong lubricant on the hole. Power tapping is often done by better machines and that is a single turn into the work and then removal although taps designed for such work are usually used.

-- Bob May Losing weight is easy! If you ever want to lose weight, eat and drink less. Works every time it is tried!

I use high-grade industrial taps, many in the spiral-flute type for blind holes. They are incredible, and will tap the entire hole, up to at least 5 x the diameter, without backing up.

In some cases, you have to not only back up to break the chip, but pull the tap all the way out every three or four advances and brush the chips out of the flutes.

Proper tapping fluid (I use Alumtap) seems to help immensely in aluminum. Any old oil works fine on steel and brass, but aluminum can be more tricky. Especially soft aluminum like extrusion that is not heat treated afterwards.

You might want to look in thread FORMING taps. They don't cut, the reform the material into a thread. You start with a bigger hole.

Jon

Small holes in aluminum are difficult. Some alloys are gummy when cut (extrusions typically so), and a #10 size is sooo easy to snap off.

Easiest solution is just to start with a slightly larger drill. I usually go up 1 or 2 in the numbered sizes, perhaps 0.005". The "recommended" drill is a compromise that assumes, among other things, that you are tapping steel, not aluminum. You lose a little of the thread crests, but you don't break taps. Given that you're using alumimum to start with, I wouldn't expect the slightly lower strength to be a problem.

Sounds like a dull carbon steel tap - too brittle. Use new HSS tap and AL fliud and baby it.

Not in order of your inquiry, but:

Countersinking the holes to the thread diameter helps a lot. The tap has less starting pressure the first thread or two, and tends to start straighter. Your screws will also start better.

Spiral point taps are best for through holes. They push the chips ahead of the tap and you don't need to back up to break the chips.

Sossner & Brubaker are a couple of excellent tap manufacturers, but you probably need to visit an industrial supply house to find them.

Also purchase "ground" high speed steel taps. (Vs cut and carbon steel)

Lubricant is desirable, as mentioned in other posts. I like to spray some WD-40 into a small container, then brush it onto the tap and into the hole.

For technique, the tap wants to run true to the hole. Being a cutting tool, they will tap crooked if not straight. Of course, being crooked, all of the cutting forces occur on only one side of the tap and breakage occurs.

If tapping by hand, try to keep even pressure on both sides of the tap wrench. If using a standard wrench, put back in tool box and invest in a tap wrench.

Good luck!

Once you get more experience under your belt, you will get better at it. The correct quality tap and technique is the key, as others have noted. For this job you described, I personally would use a quality gun tap in a battery drill with WD-40 on it, and drill them right through, throwing the drill in reverse before the tap bottoms out. Practice this on scrap after you have mastered the hand tapping, and you can impress your friends. The trick to this is that the drill must be RIGIDLY held up against the chest with both hands so that it can not twist in your grip or kick around as it does it's work. Make like it's attached to your sternum. I had a relatively inexperienced maintenance trainee doing this after his third hand tapping assignment, and he was thrilled to be able to accomplish it. He was using a

1/4-20 tap in 1/8" angle iron and did about 20 holes without incident, once he knew how. There is also a commercial power tool called a tapgun made for this purpose. It automatically reverses direction when you pull back on the tool, similar to a tapping head.

Good tapping, RJ

Now *that* trick was taught to me by my first boss, the man who first put a tap in my hands! The countersink really does help the tap to start on axis for some reason and should be done on *all* tapped holes, when possible.

Here you are probably thinking of so-called "gun" taps. Spiral flute taps do tend to eject the chips backwards out the hole. But those (gun taps) really are my favorite.

Also Greenfield Tap and Die, AKA "GTD."

Here the mantra is, "cheap tools steel will *not* save money." You are spot on with this.

WD works for aluminum, for steel I like either sulfurized cutting oil or lard oil.

And if you start a tap crooked, it will cut crooked and eventually leaves the hole off to the side - and tries to cut into material on its own. Which invevitably causes the break.

Yet another trick of the trade for very small taps (below no. 10) is to realize that the weight of the tap wrench *alone* will snap one a small tap. The solution: take appropriately sized electronics knobs and make bushings to fit the tap into the knob. One has to fix up setscrews at 90 degrees to hold the flats on the tap, but once done this gives an almost unbreakable tap. As long as the knob is sized to the tap, one has to be really working at it to apply enough force to snap one. The torque applied is very even and has none of the on-again-off again nature when using a T-handle tap wrench.

For 0-80 up to 4-40 I like to use half inch diameter knobs, from 6-32 and 8-32 they are about 5/8 or so, and the 10-32 has one also, but it will not tap fresh, it's only good for cleaning things up.

Jim

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Hey Roy,

If it was me, I'd just get a VS reversible drill motor, and chuck the tap in it and run it straight on thru the 1/4" aluminum if you have room. One guy makes the holes, the second guy does the tapping. I'd get a can of RapidTap For Aluminum and place a couple of drops on the tap just before starting.

Take care.

Brian Laws>A neighbor asked me to help him tap some threads yesterday. We were

I agree with using spiral point taps-especially in through holes. The chip is pushed out the bottom of the hole and doesn't seem to cause any binding. I haven't broke a tap in a long time.

Gary Repesh

Sounds as you were doing thru holes. If a hand tap is used, it will align itself to the hole nicely, provided one does not get ham-handed. #25 is correct. Assuming the holes were thru, you just run the tap until threads are cut, then back out and do the next hole. AlumaTap, A-9, an all-purpose CUTTING oil, kerosene, diesel works, even WD-40, but NOT 3M, 3in1, Castrol

10-30, or anything such.

OSG, Sossner, Brubaker, Balax, Greenfield, Cleveland, Regal Beloit, Titex, Emuge.

If a tap looks like it has a shitty, dull, chrome job, not worth the first look, let alone a second. I don't frequent, or even rarely, stores like Homey Deluded, but that is not where I would go looking for cutting tools.

michael

It really helps if you can use a drill press to drill the holes and then start the tap using the drill press to be sure you are starting it straight. There are various ways to do this, sometimes I just leave the drill in the drill press and use the drill as a reference as to where the back end of the tap should be.

If you can't use a drill press, then use a short piece of 2 by 4 and drill a hole thru it on a drill press so you know it is perpendicular to the surface. Use this to make sure your drilled holes are straight and use it when starting the tap too.

Dan

One of the handiest tools in the shop, is the deburring tool. Most makers have the countersink tip available. I use the Royal Roto Drive deburring and chamfering tool. I have one on the drill press and one on the mill

* Works dandy for cleaning up the hole prior to tapping and takes just a second or two. Ive gotten several of them used from the bins at Reliable Tools..

Gunner

That rifle hanging on the wall of the working-class flat or labourer's cottage is the symbol of democracy. It is our job to see that it stays there. - George Orwell

Hi guy's, posted a pic of a tap guide that I made & use often. Not my idea, saw it in a magazine a few years ago. It consists of a ground steel rod about 8 mm (5/16") diameter (from a discarded printer, kerbside recycling) & a steel body with a reamed hole to suit. It has a small cross hole to let air in/out. A small (1/4") chuck is screwed on to the body. The knurled aluminium rings are a recent addition to give a bit more purchase. In use, a bench drill or mill is used to keep the tap square with the work. (Tapping is done by hand.) My chuck is a keyless, from some old, probably hand powered drill. To keep the chuck from loosening, I tap using the ring on the body & back out using the ring on the chuck. Can also be used in the lathe, un-powered by hand, & also running the lathe slowly & holding the tap chuck to stop it rotating, if the tap starts to load up, just let go & it will spin harmlessly 'til you turn off the lathe. Hope this comes in handy for someone.

Cheer's, Iam Sutherland. (Oz)

Thanks to everybody who answered my question.

I've been looking around a bit and see that taps are rated with an "H-Limit" number. What's that all about?

When the maximum pitch diameter is over basic pitch diameter by an even multiple of .0005 inch, the taps are marked "H" or "L" respectively.....

See page 893 of Machinery's Handbook, 25th edition.

A 1/4 depth of tapped hole in aluminum should be effortless for a

10-24 tap. Use a spiral point tool steel tap, insert it into a battery powered electric drill, and tap away. Super fast, easier on the tap than a tap wrench, and it allows you to focus on keeping the tap aligned with the hole instead of turning a tap handle. Tap magic makes aluminum tapping fluid. I use pipe threading oil. Or, if you have any, the best tapping fluid for Aluminum I've ever used is liquid rosin flux used in electronic soldering. Messy to clean up, but a fabulous aluminum tapping fluid.

Brownnsharp

IIRC a tap made to exactly the size of the thread, will cut slightly undersize. So taps are usually made slightly oversized. An H3 tap is oversize by

3/10000 inch. At least that is what I remember.

Dan