When to replace a tap?
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  1. #1
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    Default When to replace a tap?

    Ok, so I just broke a tap in a blind hole. Before tapping the hole was blown clean and greased up afterwards, tap did not look worn. Just bad luck.
    What's the best common practice? I am considering logging how many holes I tap and then throw the tap away at a given number of cycles irrespective of its apparent condition. It was a "high end" Carmon M6 tap (chips up).

    If I reduce the feed drastically, would it work to drill it out with the 5.1mm TC carbide drill ot will I just break the drillbit? I see that milling is recommended, but that means a bit of work setting up and programming. I'd rather break a small drill than a more expensive end mill.

    Thanks. Still a rookie on my second year of CNC machining..

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    Before it breaks.

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    If I ever figure out the secret to never breaking taps I'll let you know.

    As far as getting them out. You don't need to kill an endmill. Just keep
    your old ones. Busted off teeth, Dull.. Doesn't matter.

    I wouldn't go in with the tap drill, I usually just go just big enough
    to eat the web of the tap out. I'd probably go with a 3/16, or a
    4mm if you have it. Feed a few tenths a rev, I usually keep the
    surface speed low.

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    Quote Originally Posted by Schjell View Post
    Ok, so I just broke a tap in a blind hole. Before tapping the hole was blown clean and greased up afterwards, tap did not look worn. Just bad luck.
    What's the best common practice? I am considering logging how many holes I tap and then throw the tap away at a given number of cycles irrespective of its apparent condition. It was a "high end" Carmon M6 tap (chips up).

    If I reduce the feed drastically, would it work to drill it out with the 5.1mm TC carbide drill ot will I just break the drillbit? I see that milling is recommended, but that means a bit of work setting up and programming. I'd rather break a small drill than a more expensive end mill.

    Thanks. Still a rookie on my second year of CNC machining..
    Are you gaging the holes after machining ?
    Can you look at a load meter on the control ? Set a stop point ?

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    You definitely need carbide to get that tap out. I usually just mill it out to the tap drill size spinning at a lower RPM and about .0005 ramp. It won't sound happy but it will come out. Might use a couple mills though.

    Another shop I do a lot of business with will take the piece to the Bridgeport and plunge it out with a ball endmill. No sharp corners to break off like you have on a flat or rad mill. I haven't tried it yet as I never seem to have a "bad" ball mill to sacrifice at the time. Always have junk flats or rads though.

    As for changing them out, its a head scratcher. The way I see it, tapping doesn't make me a lot of money, especially something small like 6-32. Our stuff is all one off injection molds so there is no do overs. I'll toss a 6-32 after 8-12 holes in P20 and 400 series stainless. Larger taps will obviously last longer. We don't tap in the machines either. We have a FlexArm pneumatic tapper. With that you can feel when a larger taps is getting dull as it won't tap as deep. As for the small stuff, the feel isn't quite there but you can catch a tap going bad once you break enough of them

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    Thanks for the tip. I've got a newer Haas where I see the spindle and axis loads. Will Google myself to how to program a max allowable load. I think it's good fun to finish the parts in the lathe, but that being said it's no prob to handtap M6 holes with a handheld drill at low speed and plenty of grease. Less risk I think.

    I ended up drilling out the tap with my carbide tapping drill. The drill tip broke, but it got the hole cleared, so I'm happy enough. Will try milling next time.

    Thanks for all tips!

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    What material
    I use roll taps when I can
    Gun taps when I can't
    Even in blind holes

    Dont break a lot of taps
    But I work mostly in aluminum

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    Quote Originally Posted by gustafson View Post
    What material
    I use roll taps when I can
    Gun taps when I can't
    Even in blind holes

    Dont break a lot of taps
    But I work mostly in aluminum
    Apologies, it was 316 stainless.

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    Quote Originally Posted by Schjell View Post

    would it work to drill it out with the 5.1mm TC carbide drill
    Never, ever use your tap drill to remove a broken tap or a broken anything. You'll just destroy it.

    EDIT: I see you already did that. Oh well, at least now you know!

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    Quote Originally Posted by RCS Machine View Post
    You definitely need carbide to get that tap out. I usually just mill it out to the tap drill size spinning at a lower RPM and about .0005 ramp. It won't sound happy but it will come out. Might use a couple mills though.

    Another shop I do a lot of business with will take the piece to the Bridgeport and plunge it out with a ball endmill. No sharp corners to break off like you have on a flat or rad mill. I haven't tried it yet as I never seem to have a "bad" ball mill to sacrifice at the time. Always have junk flats or rads though.

    As for changing them out, its a head scratcher. The way I see it, tapping doesn't make me a lot of money, especially something small like 6-32. Our stuff is all one off injection molds so there is no do overs. I'll toss a 6-32 after 8-12 holes in P20 and 400 series stainless. Larger taps will obviously last longer. We don't tap in the machines either. We have a FlexArm pneumatic tapper. With that you can feel when a larger taps is getting dull as it won't tap as deep. As for the small stuff, the feel isn't quite there but you can catch a tap going bad once you break enough of them
    +1 to everything said, I do molds as well. You typically feel it and your last thought before you break a tap is "Hmm this feels tight." You make zero money on tapping but it can cost a boat load to get a broken tap out.

    Also the load meter on a VMC will tell you sweet FA.

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    Usually it all starts out with a crooked tap then it just gets worse. Have you ever noticed the same tap taps one hole better then a different one it’s because you weren’t straight.
    And try to buy top line taps cheap taps just suck
    Don


    Sent from my iPhone using Tapatalk Pro

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    Not so much on small taps, but on larger ones (3/8 or so), if it squeaks the last few turns going in, or clicks when it reverse it's time for a new one.

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    I think you could try with the old one, in case it fails you will have already tried it and you will only have to use a new one.
    At IGC we also use 5.1mm TC carbide in some of our machines.

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    Quote Originally Posted by Schjell View Post
    Apologies, it was 316 stainless.
    Well, then you can be forgiven for breaking taps................

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    Drill out tap with carbide tipped masonry bit. Cheap drill bit. Cut off shank to make it stubby, even green wheel grind to make it cut in reverse with hand feed and a drill press. Or learn to TIG weld the fekkers out.
    I keep tool life on all production tapping operations. I do not look at the tool but once in a while. Swap and chuck.

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    Quote Originally Posted by Milland View Post
    Before it breaks.
    two holes before it breaks!

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