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  1. #1
    RobertS1 is offline Junior Member
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    Hello all,

    I have a need to tap really small threads (2-56) on 5 precision locations in aluminum at approx .2 deep. Any advice, techniques, etc? Do I roll tap? Cut with minimal percentage of thread? I need some help here.

    I would like to do these in my CNC mill, which does have rigid tapping.

    Thanks,

    Robert

  2. #2
    Dave K is offline Diamond
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    Hands down, I would roll tap. With no flutes in a roll tap, it's the strongest tap you will find. I actually roll tap that same size in some 1018 parts, and I get about 250 holes per tap.

  3. #3
    PBMW is offline Titanium
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    I second that....
    Roll form taps are the way to go
    Jim

  4. #4
    richardny is offline Hot Rolled
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    roll form tap is great, but you need a big hole and is this what the print calls for? If it isn't, I would not substitute it

    I would not expect any problems doing normal tapping just because it is a small tap

    we use average quality taps and still have no problems because all factors are so closely controlled

  5. #5
    Dave K is offline Diamond
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    roll form tap is great, but you need a big hole
    Whether you roll form, or use a cutting tap, the difference between the 2 drill sizes is .008 in this case. That's hardly a "big hole".

    No disrespect, I know what your saying. But when the tapping is all done, the major and minor will be the same if everything goes good. So, the final product is the same. This is not really a deviation from the print. You will actually have a stronger thread, and I can't imagine anyone wanting the weaker of the two.

  6. #6
    RobertS1 is offline Junior Member
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    First of all, thanks everyone for the advice!

    The print does not specify, so if roll will get me more holes I'll try that. Does anyone have a good roll tap type/make to use? I will also need speed/feed for such taps.

    thanks again,

    Robert

  7. #7
    CDiPrecision is offline Cast Iron
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    .008 is not alot,. but it is a large percentage of a 2-56 drill hole....I would not go that large in aluminum..the threads may pull out too easy..follow the chart for normal tap size hole, use a good tap, and oil(no coolant)..2-56 isnt small...00-80 is small,lol...

    are they thru holes?? if not , use a good spiral tap, and make sure you dont hit the bottom of the hole with the tap(the only thing that will break your tap)..

  8. #8
    gar
    gar is offline Stainless
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    060527-1351 EST USA

    RobertS1:

    Try this site http://www.osgtool.com/ . They make good tools and provide drill sizes for their form taps.

    As Dave K said you will generally have a stronger thread with a form tapped hole than with a cut thread, and you have no chips.

    Often times we use a hole slightly larger than the one specified by OSG for their form tap. Less strain on the tap.

    .

  9. #9
    Dave K is offline Diamond
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    OSG makes a good roll forming tap. Also, Greenfield tap & die company, Vega, and I'm sure there's more. Anyone who makes a quality cutting tap, will make a good roll tap also.

    When roll forming threads, the drill size is more critical than it is on a cutting tap. I wouldn't deviate from drill and tap charts very much at all when dealing with roll forming.

  10. #10
    mjk
    mjk is offline Stainless
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    Do a test on simular material with the differant hole size suggestions prior to running the production pc.

  11. #11
    Ox's Avatar
    Ox
    Ox is offline Diamond
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    Often times we use a hole slightly larger than the one specified by OSG for their form tap. Less strain on the tap.

    I almost always use a SMALLER drill than spec'd. In LC Free Machining steels and alum I will push it right up to 100% full threads with a form tap. A big hole in form tapping will yield you a "double thread" ~~~ sorta.

    Never tapped that small'a hole tho.

    Think Snow Eh!
    Ox

  12. #12
    Jackmo is offline Hot Rolled
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    I have used roll taps for many years in alum as well as other materials including ss I have found the hole size recomended by the mfg. is very close to right most of the time but I also check the hole after tapping to see what % of thrd. only to make sure it matches the print if there is a callout.
    I use coated taps even in alum I find they gall a lot less. Machinery's Handbook has most of the info you should need. Hope your spindle is tight as well as positioning of the table these taps are a lot stronger but they are on the small side, not 00-80 but still smaller then most common taps.
    I use coolant without any trouble.

  13. #13
    SeymourDumore is online now Diamond
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    Big time vote for rollform taps.
    See a previous thread about my dilemma with 1/4-28 helicoil threads that had to be rollformed because the existing hole was .015 OS. These threads were also gaged for min. dia. as well as many others in similar size I've done such as 2mm, 1.5mm etc. in 303 stainless.
    By far the strongest thread produced by the strongest tap geometry.

  14. #14
    CDiPrecision is offline Cast Iron
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    As long as the threads check out with a thread gauge, rollform is ok..I just dont see the need....2-56 in alum is an easy job, now if it were 440 SS or 316, or Ti then it would be a diffrent story...

  15. #15
    SeymourDumore is online now Diamond
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    CDiprecision

    I remove a tons of broken taps for others.
    I'm betting 3:1 for Al vs. everything else for tap removal. Prolly because most thinks " hey, it's only AL ". 20:1 is the average for broken taps in blind holes, 50:50 for taps broken due to packed chips vs. spirals. I personally had absolutely piss poor experience with evacuating spiral taps. Slow spirals are OK, but they do not bring the chips out.
    As for the threads checking out on a gage, threadformers should be the same as the regular ones as long as the pre-drilled hole is within the recommended limits.

  16. #16
    CDiPrecision is offline Cast Iron
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    I know what u are saying, just my experience has been diffrent...I have tapped tens of thousands of holes in Al, with very few troubles...6-32 being the biggest pain in the ass size....I have had excellent luck with Spirals too, mostly STI size taps..

    Now, one reason I may have had less troubles is I use a tapping arm..not CNC machine for tapping(Do a search on my name to see my distaste for that,lol)..CNC tapping is a waste of spindle time and hard on the machine...

    Im sure most guys that crunch taps in AL are hitting the bottom of the drilled hole....Instant snaperoo,lol..

  17. #17
    Gd2noYou is offline Plastic
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    cdi....i sent you a private message.

  18. #18
    Dave K is offline Diamond
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    CNC tapping is a waste of spindle time and hard on the machine...

    Im sure most guys that crunch taps in AL are hitting the bottom of the drilled hole....Instant snaperoo,lol..
    I respectfully dis-agree. First, if the tapping is done in the cnc, then the operator is free to go hit cycle start on another cnc. Much better use of his time than to be tied to one machine just to tap holes. I know the cycle time is decreased by taking the tapping out, but I think the benefit of running 2 jobs vs. 1, far outweighs the extra time to tap a hole.

    Also, snapping taps in aluminum is, like you say, a sure way to break a tap. But binding chips can also break them. With rigid tapping, there is no excuse for hitting the bottom anyway. If you drill 1/2 inch deep, your tap must be shorter than 1/2 inch. Pretty simple.

  19. #19
    Solar71 is offline Titanium
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    Taping in a cnc is a waste of time and the machine ????

    uhhh... No...

    It takes my mill a few seconds to make threads...
    And how is rigid tapping hard on a machine ?

  20. #20
    Jackmo is offline Hot Rolled
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    Spindle reversing could be bad for some spindles but I think today's spindles are ok.

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