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Thread: I wanna tap that !!!

  1. #1
    Join Date
    Aug 2016
    Location
    Appalachian Ohio
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    693

    Default I wanna tap that !!!

    In making my CNC router I'm going to be tapping lots of holes. LOTS of holes.

    (cue up the music from "The Music Man")
    Why sure I've hand tapped holes,
    Certainly mighty proud I say
    I'm always mighty proud to say it.
    I consider that the hours I spend
    With a tap wrench in my hand are golden.
    Help you cultivate horse sense
    And a cool head and a keen eye.
    (cut music)

    But when talking hundreds of holes I begin to think of the desirability of power tapping. One thing makes me hesitate - I have never done power tapping.

    So folks, I need to learn about power tapping. Does one have to use an alignment feature such as a mill, or can one use a hand drill? (I have both, but I am not going to get the 45" by 68" 1" thick Aluminum table onto my mill). If using a hand drill does the risk go up a lot? Do you use the same size drills for drilling the hole prior to machine tapping as one does for hand tapping? Does one need spiral taps? Why spiral taps? Are Chinesium spiral taps as good as USA-ian taps? Any recommendations as to where to buy spiral taps (if needed)? How risky is it - what are the rates of breakage? Any hints on how to avoid failure?

    Help me people...

  2. #2
    Join Date
    Dec 2015
    Location
    Chilliwack, BC, Canada
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    4,909

    Default

    Even a short "thread crest" sized lead in towards the tapping hole can be pretty effective at lining up the tap for a good straight thread. And doing it that way has another advantage. It avoids any potential slight outward bulging of the metal that would tend to concentrate the holding pressure to the area right at the bolt instead of spreading it out for a more stable retention.

    How much of a crest sise lead in? I'd say one diameter would be more than is needed but would certainly line things up really well. Likely half to maybe 2/3 of a bolt diameter would do just lovely.

    Another option that could aid with power tapping with a hand drill is to set up a few taps and grind a short parallel pilot on the very nose of the tap that matches the drill size used for the tapping holes. If you make the drilled holes deep enough so that you can use taper taps there's still lots of lead in even after a short pilot section. Like just a couple of mm's worth.

    If you do both I'm thinking that a half diameter lead in combined with a small smooth non cutting pilot would pretty well ensure really nicely centered threads done using a hand drill on slow high torque range.

    Drill chucks don't hold taps well worth a darn either. So you'll want to grind three evenly spaced flats for the hand drill jaws.

    You still need to do a good job of drilling the holes though. If not in a mill then you're going to need to make up some drilling jigs to ensure straight "square" holes. Jigs with hardened drill bushings. And if you use such jigs and bushings you may as well use the same jigs as tapping jigs with suitable size bushings. At least to start the threads. And then finish them without the jigs.
    Last edited by BCRider; 01-27-2019 at 03:58 PM.

  3. #3
    Join Date
    May 2015
    Location
    Somerset UK
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    1,967

    Default

    My old firm had a couple of these pantograph tapping arms with reversible pneumatic motors on them for the odd times when the CNC's only produced the untapped holes. They are not cheap, but it might be possible to make one.https://www.ebay.co.uk/itm/ARM-950-1...-/152891992177

  4. #4
    Join Date
    Mar 2015
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    Default

    Gun spiral tap in a drill. If the holes are thru hole, makes life much easier. Gun spiral taps I am thinking, draw the chips out as you thread. Get a high quality USA/Japanese tap if HSS.
    Last edited by RB211; 01-27-2019 at 04:18 PM.

  5. #5
    Join Date
    Mar 2003
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    4,331

    Default

    Quote Originally Posted by old mart View Post
    My old firm had a couple of these pantograph tapping arms with reversible pneumatic motors[.]
    -I was going to suggest something like that. If you have that many holes to tap- several hundred, it would appear- it would be worth it to buy a machine like that, fixture everything as needed to be able to use it, buy some high quality, name-brand taps, and use some name-brand, specific-purpose tapping fluid.

    If it were me, I'd probably even do something like swap out for a fresh tap every 50-60 holes, too.

    And once you're done, if you don't need the tapper anymore, sell it off to recoup some of your costs.

    Trying to do it in an unsupported cordless screwgun is just asking to leave a couple dozen broken taps in the assembly, and have half the holes tapped slightly crooked.

    Doc.
    Last edited by Doc Nickel; 01-27-2019 at 04:34 PM.
    Doc's Machine. (Probably not what you expect.)

  6. #6
    Join Date
    Oct 2013
    Location
    Setubal, Portugal
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    Default

    You can use a cordless drill with a guide like a wood router base.
    https://goo.gl/images/v571Ua
    Helder Ferreira
    Setúbal, Portugal

  7. #7
    Join Date
    Aug 2007
    Location
    Leics UK
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    841

    Default

    For M5 and up I just use a cordless drill freehand.
    For M4 it depends a little on the project and material.
    M2 and below I am very careful and usually use the mill as a tapping guide.
    Generally reasonably good quality progressive HSS taps - like these:
    https://www.arceurotrade.co.uk/Catal...ps-Metric-Fine

    Dave

  8. #8
    Join Date
    Aug 2010
    Location
    Victoria BC
    Posts
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    Default

    And of course if you do it with a hand drill, practice first on a piece of scrap.
    "A machinist's (WHAP!) best friend (WHAP! WHAP!) is his hammer. (WHAP!)" - Fred Tanner, foreman, Lunenburg Foundry and Engineering machine shop, circa 1979

  9. #9
    Join Date
    Dec 2016
    Location
    Helsinki, Finland, Europe
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    Default

    Like mentioned many drill chucks don't hold tap worth a hoot. But for aluminium with sharp tap it should work. I use also cordless drill&chuck for steel, works as a overload clutch before breaking the tap. Chinese taps need more torque and almost always slip, whereas sharp free-cutting DC-SWISS doesn't slip.

    Noname chinese taps are too much lottery, some of them work but you better of by buying good brand name taps.
    Gun point aka spiral point for trough holes(or holes with excess depth) and spiral flute for blind holes.
    Last edited by MattiJ; 01-27-2019 at 04:59 PM.

  10. #10
    Join Date
    Oct 2013
    Location
    Setubal, Portugal
    Posts
    522

    Default

    One coat of aluminium tape on the tap shank helps the chuck grip.
    Helder Ferreira
    Setúbal, Portugal

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