tapping threads

I use mine to tap. But I have a 3 ph motor and VFD. With the belts at the lowest speed and the VFD at 5 Hz, my spindle turns 30 rpm - plenty slow enough to tap. I also have a foot switch that can reverse. So I run the tap forward a little, reverse to break the chip, forward again, etc. without ever moving my hands. Really slick.

Bob

If you mean the photo just above the "L-Shaped Table Extension" header, that looks like a hand-operated tap wrench -- just photographed up close enough so you don't see the T-bar handle -- and perhaps the ratchet as well.

As has already been mentioned in a previous followup, using the drill press (or a milling machine) can help assure that the tap is started square -- and even concentric with the hole if the hole is drilled in the same setup.

One trick which I have used in the past was to blip the switch on and off quickly, and bring the tap down while it is still rotating. This gets it started cleanly, after which I would loosen the drill chuck and continue with a tap wrench. (Ideally, for a through hole, you want a "gun" tap -- a spiral-point tap which chases the chips ahead of the tap, instead of requiring you to stop and reverse frequently.

I now -- whenever I have three or more holes to tap -- remove the chuck and replace it with a tapping head. I have two by TapMatic, in different sizes.

The benefits of these (and there are other brands, TapMatic just happens to be what I have come across at an affordable price used) are:

1) The smaller size has an adjustable torque limiting clutch, so you can set it so it just won't slip with a new tap. When it starts slipping again, it is time to replace that tap *before* it breaks off in the workpiece. 2) The larger size does not have that (not really needed with the power of my drill press -- it will slip before the taps break), but it *does* have and adjustable end-float, so you can set it up for tapping shallow blind holes. 3) When the tap head reaches a stop (normally a pre-set drill-press spindle stop), the rotating tap pulls down another short distance (determined by the end-float) and then disengages a dog clutch allowing the tap to stop turning, while the drill press continues to turn. 4) Once you reach this point, you start to back the drill press spindle up, and a set of gears in the tapping head will reverse the rotation of the tap -- and speed it up at the same time, to back it out of the workpiece quickly.

For these, you certainly need a tap designed for machine tapping -- either the "gun tap" mentioned before, or a spiral flute tap, which will pull the chips back out of the hole.

Absolutely do *not* use carbon steel taps for machine tapping. They are too brittle, and are not made in the right forms anyway. Pay the extra for a good HSS gun tap and you will be very pleased with the results.

Another choice, and a good one with the right materials, is the "thread-forming" (or "roll") tap. It doesn't cut, so it doesn't produce chips. You need the hole a bit larger, because it causes the material to flow under pressure from in the grooves to form the crest of the thread. Obviously, this is hardly useful in hardened steel -- or in brittle things like cast iron, but for mild steel, brass, aluminum, and many plastics, it works quite well -- and produces stronger threads. It does take significantly more torque than the thread-cutting styles do.

Obviously, there are some situations where the workpieces can't be brought to the drill press, and here you are stuck using a hand tap wrench -- though I have used a reversible variable-speed electric drill motor on taps of sufficient size -- though you have to be careful to not apply side force, or you will break the tap. I consider 1/4-20 to be a reasonable size for this, and a 10-32 to be doable with care. Below that, I opt for hand over the electric drill.

Enjoy, DoN.

P.S. Referring to your mentioned web page -- not all of the 4x6 bandsaws have motors which overheat like that. I got my 4x6 bandsaw from MSC -- and even after long cuts I can lay my hand on the motor with no discomfort. I suspect that they replaced the motor -- or specified a better motor -- from the start.

There are also tapping heads available. You put one end in the morse taper and the tap in the other. It has gears and clutches inside that let the tap feed at the right speed then when you raise the spindle the tapper will reverse and back the tap out. I can't even think about how many holes I tapped when I worked on the drill line in a shop. For any kind of production they are essential. They are expensive, I have tried to get one at an auction and I am always outbid by a large amount.

Scp

How bad do you want one? Ive about 4 of them. Ive a couple that are elderly but still do work but need some tlc.

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

I realized that just after I posted. But the question is just as valid. I

Tapping heads sound really cool, but out of my price range. I like the idea of getting the tap started in the drill press, so I think what I will try is just chuck the tap and disengage the belts so the spindle can turn a little easier. I had been wondering if I'm a big chicken, but after reading the responses, I'll definitely go with my gut which tells me not to put this under power, at least not with the equipment I have. Hopefully I can get enough leverage to cut enough threads that it stays aligned when I switch to the manual tap handle.

Thanks for the responses!

- Owen -

Hey Gunner,

I'd be happy to show an elderly tapping head some tlc. How much do you want for one of your old ones?

Eide

Let me dig em out and see what I have. Im pretty sure one is #2 Morse and the other is 1/2" shank. I think one is missing the left handed collet bolt. Ill let ya know this weekend as Im on my way to LA for the next 4 days.

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

Tapping by power is something better done by those that have already experienced the many broken taps that happen before they learn the technique. Then there is the TapMatic and other devices like that which contain a friction drive and a backout gear. They are used by driving the tap into the work and then releasing the down handle and the device reverses the tap and pulls it out of the work. I'll note that unless you want to do a lot of tapping, they are a bit expensive. Also note that the tap handles have a sloped hole in the top of the handle? That hole can be used with a cone point in the drillpress to drive the tap into the hole while you turn it with the handle of the tap, making it easier to keep the tap going in properly into the hole.

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

Once you have belt removed, try turning the pulley by hand. It also helps to keep enough down pressure on the drill press handle to avoid tearing out the first few threads.

More leverage can be obtained by taking a rod of correct dia. and putting into holes where chuck key goes. (or even chuck key).

For benefit of all safety enthusiasts, it is a NO! NO! to ever leave the chuck key in a chuck. But you do remove the belt first, right?

I

Thanks, look forward to hearing from you.

Eide

My email is: nickAToldbranchDOTcom

I tap manualy using my drill press and Bridgeport with the aid of the the tool handles I constructed for them as shown in the following:

Once I align the work piece under the spindle it is: center drilled, tap drilled, chamfered with a countersink, and tapped.

HTH Rick Renner

Here's what works for me:

T

[ ... ]

Interesting approach. I presume that the handles are carefully designed to be just short enough to miss the column. Well balanced, too, I hope -- or things could get rather exciting if someone hit the switch while it was mounted. :-)

Enjoy, DoN.

You presume correctly. At a few rev's per minute intended speed, I didn't but much effort in balancing. As far as idiot proofing, I wasn't concerned much about that either since, to my mind, there's really no such thing as an idiot proof device. If you make one, let me know how it performs at a couple of thousand rpm :-)

Rick Renner

Don't bother trying!

They'll just breed smarter idiots!

Refinish King

PS

Paint job in the booth, I walked out 15 minutes before, an employee walks in with me to look for hazing/dieback and touches the car while asking: "Is it still wet?"

Actually, the key to power tapping is to NEVER use hand taps. They are not made to deal with continuous chips, which will stack up in the flutes and often lead to a broken tap. One exception is when tapping very thin material, where the chip doesn't get big enough to fill the flute.

Be certain you select a tap that is made for power tapping, either a gun tap, or a spiral fluted tap. As long as you keep the chip in motion, it won't bind in the flutes of the tap and then in the hole. You can even tap blind holes with gun taps so long as the hole has enough depth past the end of the thread. I've tapped holes like that for years. There's not really a better tap for power tapping than a gun tap, so that's the tap of choice for me, even blind holes. Spiral fluted taps seem to be somewhat more fragile in my experience.

Power tapping on a drill press, mill, or lathe, is best done with an instant reverse. You usually have that automatically if you have three phase. Drill presses could be the exception, I suppose. I almost never use a drill press, preferring to use my mill instead, where I have greater control over precision. You can tap a 1/4-20 hole in so little time that you'll wonder why you haven't done them that way all your life. Unless I am tapping precision (inspected) holes, I almost never mount either of my tapping heads.

Tapping by this method does require a little skill, but pretty much all of us have the required level to master it quickly. One caveat. If you have a chuck that runs out a great deal, you may end up with terribly oversized threads where they start. It's a good idea to have a chuck that runs reasonably true. Lubricate well before tapping, and use an air hose with a needle tip to remove the chips from the tapped holes if they're blind. You'll be surprised to see a couple pieces of what look like wire that are wound together, the one chip from each flute of the tap. Very cool!

Harold

Harold, over the years, I have trained a lot of new entry level machinist graduates from the local community college program who enter our workforce. You know, gotta "Get that chip in 'em", before turning them over to the other departments. They work with me in the shop to settle in and give them some exposure to the repair side of things. I believe this causes them to respect the machines a little more, and to not abuse them. This also gives them exposure across the plant in order to see all operations at work. Since they are trained by the college in hand tapping, one of my favorite things is when the need arises to tap a hole through a part. You should see the puzzled looks when I place the part into the Bridgeport and chuck up a tap. They usually take a step back as I apply power, and the looks on their faces is priceless when I switch to reverse and it soaks in that they have been doing all that hand tapping in school! One thing I have consistently noticed is that after power tapping a hole on the BP, most bolts go in really tight, or not at all. The same tap can be removed from the machine and run through the previously tapped hole by hand, and the bolt will glide right through. The same effect is not observed when using a tap head. Have you experienced this?

RJ

Yes. The cat's behind for this sort of thing is the two flute gun tap. Drives the chip forward.

Unless it's a drill press that is. In which case I would suggest that a Procunier tapping head is the absolute best way to go. I once tapped about two hundred 0-80 holes in niobium that way. Did not break a single tap.

Jim

================================================== please reply to: JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com ==================================================

snip----

Yep, it's my tapping head of choice, too. There's no better way to power tap than with a tapping head, if for no other reason, they usually reverse at a much higher speed than when tapping, and the reaction is almost instantaneous. The ability to closely control the depth of the thread is certainly another great advantage. By the way, that's an enviable record for tapping with an 0-80!

Harold

Well, I did cheat a bit. I only used each tap for 20 or so holes. I also rigged up a drip tube to run lard oil onto the tap while I was working.

Jim

================================================== please reply to: JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com ==================================================