Tapping machine?

I've never had my hands on one of these, so how does it work out when to go backwards to break the chip?
Also, are they senstive enough for 10BA and smaller?
The book, "Steam Trains in your Garden" calls for a lot of 10BA holes :-(
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wrote:

I bought a 2MT tapping head to go on the drill press when I had a large number of holes to drill in some aluminium rat-wheel hubs I was manufacturing for SWMBO. It doesn't know when to go forwards or backwards, but has a differential gearbox that drives the tap clockwise if you press down and anti-clockwise if you retract the spindle. There's about a quarter an inch of 'neutral' in the middle of the range.
So when using it, one presses down lightly until the tap is at the desired depth and then retract the spindle, doing so at such a rate that the tap is moving up and down at it's desired rate any you aren't trying to push it though the work or lift the work off the table with it.
The one I got has an adjustable clutch, and it's alleged to be good down to M1.4, which is just smaller than 10BA.
You need to use spiral point; spiral flute or form taps unless it's very thin stock, so that the chips don't clog the flutes. Spiral flute taps are suicidally delicate and wouldn't go down to 10BA, but I've had good results (over a hundred holes per tap) with M6 and M4 form taps in aluminium, FCMS and silver steel.
--

Mark Rand
RTFM

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On Thu, 20 Nov 2014 20:38:29 -0000, "gareth"

If you are speaking of a tapping head, the kind that you fit to the spindle of a mill for example, then they don't automatically reverse to break the chip. When ever the the head is tapping a hole and you pull it up it then reverses. With the proper taps, spiral point is one, the tap doesn't need to be withdrawn to break the chip. The chip just flows ahead of the tap. If you are using a 4 flute hand tap then you would need to retract the head whenever you thought you should. But hand taps really aren't made for power tapping. There are two basic styles of tapping heads. One is the Tapmatic style. These have a friction clutch and dog clutches inside. You can set the friction clutch to transmit the amount of torque desired. The dog clutches are for forward and reverse. The other style of tapping head, Procunier and Ettco come to mind, have conical friction clutches inside. The harder you press down the more torque is transmitted. Inside the Procunier is a planetary gear system that drives the female half of the clutches in opposite direction. Both clutches are constantly turning. The Ettco head uses a different method for driving the reverse clutch and the reversing gears are outside of the clutches, and the tapping head has a bulge in the side to accomodate the reversing gears. Each tapping head style comes in various sizes, you use a bigger head with bigger taps. In my shop I use Tapmatic, Procunier, and Ettco heads. The Procunier brand tapping heads are my favorite to use. They do require a little more skill to operate than a Tapmatic but once you learn the "feel" of operating them you can tap very small holes without breaking taps. For #10 BA the size 1 Procunier is what you want. I had one job where I needed to tap about 70 holes with a 00-96 tap. I tapped all the holes without breaking any taps. Procunier heads are also great for installing Heli-Coil screw thread inserts. Eric
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