Tapping attachment for the mill

How do these tapping attachment work? I can see that they reduce the rpm, but do they also have an adjustable clutch for torque control? Can the direction of the rotation be controled on the fly? How is the tap fed into the work. Is it spring loaded, or do you have to move the quill down progressively to feed it. Does it make any sense to own one of these if you're not doing production.

I would like to reiterate my gratitude for all the wonderful advice that I've being getting.

Albert

If you have a tapping head for the manual mill you can tap holes like crazy. The tapping head usually feeds in that the spindle speed and only turns the tap when you come down with you spindle feed handle on the mill. The tapping head engages at that point and feeds in at your spindle speed. You set a stop on your quill down on the mill so that when you hit the stop, the tap as it is feeding in disengages at the correct depth. At that point, the spindle is still turning and the tap is not. When you bring your quill handle up, it reengages the tap in the reverse direction at about 5 X speed that you had on entry and screws the tap out of the hole lickety split. These little tapping heads are really time savers and money makers if you have a lot of holes to put in . The heads are made for a range of tapping sizes and have collets to fit for that range of taps. The head is also adjustable for torque so that you do not snap the tap off, but will just slip. For the average shop tinkerer, I doubt that it would pay for itself by just putting in a few holes now and then, but if you have money to burn and want the best, go ahead and splurge ! They are great to have. I think my tapping head will handle all the smaller sizes from a # 2 screw to a 1/4 inch. The next larger head may handle anthing from a #10 to a 3/8 inch and so on.

TheMetalDoc

Hold on. When I was taught tapping in a machine shop (years...what I am I saying, decades ago), I was told to turn in 1 revolution and then turn out by 1/4 turn. I've always tapped this way. You mean with this tapping attachment on the mill, I can go straight through to the end? I feel like I've been living in a bubble when it come to tapping. Next you're going to tell me that I can do same thing with my die set


Albert

You can, in a way, on the lathe use a die holder, for short lengths, or start the die and then use the hand holder, let it bump aginst the bed, and turn on the lathe. I tap on the mill, throug holes, by bring the tap down then turn the mill on, need 3 phaze, or you can brake a lot of taps, and be quick on the reverseing switch.

Rotate...a proper tapping head has a clutch, so if it binds in the hole you don't break the tap..it just clutches out till you reverse it a little (it reverses simply by pulling up on the quill) and try again. But if you use good sharp gun taps and good tap lube, this rarely happens in mild steel...it just runs all the way thru in one pass...done it a gazillion times.

Hows about blind holes?

Just specified a part with 8 of them, obviously gun taps don't work as well there.

1/2 inch thick 6061 T6 material, had to be tapped in 0.3 clean at 4-40 thread, 1/2 clean at 6-32.

The price was no diffrent than when the part had through holes, so someone knows something. I had to be pretty careful when I did the prototypes.

Production tapping has always been a mystery to me just on account of the tap breakage issue with the small sizes I am usually involved with.

I never did many blind holes where the threads were required to go all the way down....usually there was enough clearance that I could set a stop for the drill press quill and the tapping head quill would feed until it hit neutral and you could bring it back up. The few that required threads all the way, I would carefully adjust the tapping head clutch so you could bottom a gun tap without breaking it, and then finish the threads with a bottoming tap by hand*. Making my own products, I had the luxury of designing out such handwork usually.

Still, I'm thinking in terms of 10-32 and up sizes...I rarely went below no. 8. It would indeed be a bit more worrisome on no. 4 and no. 6 sizes, esp. in aluminum .5 thick. No. 0 Bilz type tap holders with clutch, would probably be more sensitive to clutch adjustments than a standard Tapmatic head, so might be preferable in that case. Tap lube will be critical also...I'd recommend Acu-lube but there are others.

The ultimate tapper for the smaller sizes is of course made in Germany...called MicroTap. About the size of one of those tiny Servo drill presses, it has electronically programmable torque settings and some other neat features. Suspect it's a bit beyond the home shop budget however...I seem to recall a price tag over $5,000.



www.microtap.de




*Btw, even when tapping by hand, if 1/4 inch or smaller, I don't like having to trust my "hand" to not get "over enthuseastic"...so, even then I often use an overload clutch. I made a T bar that will hold a standard Bilz clutch tap holder and use that. In the no. 8 and 10 sizes I can sometimes just grip the Bilz holder itself without even using the T bar.



[This message has been edited by D. Thomas (edited 03-10-2002).]

If you're tapping a blind hole, just use a good Helical tap that pulls the chip out instead of pushing it thru.
Works great !

My holes have at least 0.1 for incomplete threads etc, so it doesn't require a bottoming tap.
Its really so that the part only needs the fine finish one side. Otherwise both sides need the finish because the assemblers might put it in either way.

Helical taps, eh? Are those the spiral looking ones that look like they would break if you sneezed on them? bet they don't though.
Someone recently posted that turning them backwards out can break them, can they just drive right thru without backing until fully threaded?

I suppose that drilling another size up would also cut the tapping forces, without necessarily reducing strength, which in most cases isn't really an issue anyhow..

J, helical taps are quite strong while cutting but yes, they are very weak in reverse...often not an issue as they don't need much strength to unscrew out of the hole. The problem comes when you bottom one and the sudden torque of unscrewing it. And sometimes a chip is not draw out all the way and it catches on the chip when unscrewing. But I don't have a lot of real world experience with them, they probably work great for many situations.

Another technique for lessing the torque on a tap is to tap first with the next smaller size, and then the size you want, assuming of course you can find the next smaller size in the same threads per inch. For 6-32, for instance, first tap with 5-32 (yes, it exists..but unsure if no. 3-40 exists)

Haven't seen them recently, but taps were also available in progressive sets of three. This is not the same thing as taper, plug, bottoming sets. In this case the diameter increases in 3 steps to finished size for tough jobs.

That's interesting...don't think I've ever seen sets like that advertised....wonder if that's something that's gone the way of the Dodo bird...

Al,

I use a lot of thread forming taps, they can be driven right to the bottom of the hole, then the tapmatic head clutch just disengages if you have the torque set right. No chips to worry about. These taps work great in all soft materials and if you are working harder materials, just make sure to use only sharp taps. A dull tap increases the torque and will cause it to break much easier. I do some materials where I take a new tap every 5 to 10 holes as the tap torque increases to the point where it is on the edge of breaking. Yea.. increase the cost of the part, but taps are usually included in quoting the part in the first place.

TheMetalDoc