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Thread: Tapping with a screwdriver

  1. #1
    mklotz mklotz's Avatar
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    Tapping with a screwdriver

    I've never tapped anything under power. No matter how much you laud tapping heads, there's just no way I'm going to trust one to tap 0-80 into a model engine part I've spent eight hours making.

    But never say no. I had the task of tapping a bunch of non-critical 6-32 holes in some 2" plastic pipe. It occurred to me that this would be the ideal job to try my hand at power tapping. An electric drill is way too fast but an electric screwdriver might just be the ticket. It's slow and stops pretty much instantaneously when you release the trigger plus it's easy to reverse to back the tap out. 6-32 is the weakest common inferial thread but plastic is a pretty forgiving medium so it's worth a try.

    I made a simple chuck to interface the tap to the screwdriver...


    Most taps from #6 downwards have the same size shank so by drilling a #28 (0.1405) hole, the chuck will serve for most small taps. The body is a piece of 1/4" steel hex and the tap is held in place by 6-32 setscrews which bear on the square end of the shank.

    It worked very well. I'll consider power tapping again if the stock is soft and the part non-critical. For stuff with a big time investment, I'll stick with guided hand-tapping.
    Last edited by mklotz; 07-08-2017 at 05:16 PM.
    ---
    Regards, Marv


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    Marv,
    Nice adaptation for taping in plastic. I do take extra care when taping with 6-32 taps because of its cross section weakness. A real bummer. Thanks for the posting.
    Regards, Paul

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    Marv, I like your solution
    I generally try to buy my taps in a 3 tap set with taper(starting), plug, and bottoming taps.
    I am a firm believer in lots of coolant/ lubrication when taping, but there are times when you absolutely cannot use any solvent or petroleum based lubricants. When the taps are small like the 0-80 2-56 4-40 6-32 and up I keep bar of Ivory soap to rub the tap in the soap may not be much good for any other industrial use around a shop but it works well for taping almost as good a beeswax for sawing aluminum
    I also often cheat and thread at 60% instead of 75% for the smaller taps
    I used to work with a guy who had made a friction clutch/chuck for his modified Yankee screwdriver . He could tap a dozen 6-32 holes to anyone else's in service panels. But then again I'm the type of guy who will grab a 3/4" impact to tap 1"6 holes and use a 50 hp Cincinnati mill when threading 4" 12 thread holes in 6" thick plate.
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    mklotz mklotz's Avatar
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    Reducing the depth of thread is certainly a good way to make tapping easier and reduce the chance of breakage. I covered this subject at length in one of my hints...

    Calculating tap drill size
    ---
    Regards, Marv


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    Quote Originally Posted by mklotz View Post
    I've never tapped anything under power. No matter how much you laud tapping heads, there's just no way I'm going to trust one to tap 0-80 into a model engine part I've spent eight hours making.

    But never say no. I had the task of tapping a bunch of non-critical 6-32 holes in some 2" plastic pipe. It occurred to me that this would be the ideal job to try my hand at power tapping. An electric drill is way too fast but an electric screwdriver might just be the ticket. It's slow and stops pretty much instantaneously when you release the trigger plus it's easy to reverse to back the tap out. 6-32 is the weakest common inferial thread but plastic is a pretty forgiving medium so it's worth a try.

    I made a simple chuck to interface the tap to the screwdriver...



    Most taps from #6 downwards have the same size shank so by drilling a #28 (0.1405) hole, the chuck will serve for most small taps. The body is a piece of 1/4" steel hex and the tap is held in place by 6-32 setscrews which bear on the square end of the shank.

    It worked very well. I'll consider power tapping again if the stock is soft and the part non-critical. For stuff with a big time investment, I'll stick with guided hand-tapping.
    nice!

    I've been playing around with different styles of taps for a while and I'm starting to build up sets of spiral point, spiral thread and roll form taps for each size. Each is really good at a particular type of tapping (although arguably spiral thread can replace spiral point) and the roll form taps are simply amazing at tapping non-ferrous materials under power. If you haven't tried a spiral thread tap on a blind hole, boy that's a treat

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    Thanks mklotz! We've added your Power Tapping Chuck to our Tapping and Threading category,
    as well as to your builder page: mklotz's Homemade Tools. Your receipt:




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    wizard69's Tools
    Nice adaptation to the electric screw driver. Such an idea might get me to buy one of those who lecturing screw drivers.

    As for the 6-32 problem, just don't use 6-32 screws. Go up a size, go metric or something else.

    As for power tapping when I first saw a guy in a shop using a drill motor to tap some 3/8" holes in steel I thought he was nuts. After trying it out myself I'm pretty convinced that done properly it leads to fewer broken taps not more. For one thing you can concentrate on keeping the tap square and letting the drill do the twisting. Mind you these are through holes used in fabrication type work and the taps are designed for power tapping. When I was doing a lot of panel work, I powered tapped almost all of the 10-32 holes I did, the time savings are huge. The only real requirement is that you variable speed drill have good speed control.

    These days there are a number of drill/tap combos available. Haven't tried them but the idea of drilling and tapping with one tool is very appealing. See are meant for electrical panel work thus thin gage metal.

    I certainly don't recommend power taping for the very small taps but it is useful for larger.

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    Rule #1-If your an industrialist, power tap. If your a hobbyist, tap by hand. Why twist the dragons tail! Rule #2- Avoid strong coffee when tapping anything under 1/4" dia.


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