Ever had an HSS drill just break up during a cut?
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    Default Ever had an HSS drill just break up during a cut?

    This was a new one for me last night. I started running a proven program in the VMC and in the 2nd op (7" deep, 3/4" hole, 400rpm in ETD150) it started getting louder until the machine alarms out on Z axis overload. WTF?

    When I pulled the part from the vise and cleaned it out big fragments of the drill came out, including one whole cutting edge. Here's the thing- it was still sharp. The corner wasn't chipped or burned and the edge still had good form. It was a PTD drill, despite being made in Brazil I've always had good luck with their tools. The drill was about 5" into the cut when this happened.

    So I'm wondering- is it possible I just got a bad drill? If not, I'm at a loss for what happened.

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    My thoughts

    That's a lot of speed for that depth, …..when I go beyond 3 or 4 X D deep I start slowing down.

    How many pecks?

    What's the rate of feed?

    Was there an inclusion in the material.

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    Quote Originally Posted by Limy Sami View Post
    My thoughts

    That's a lot of speed for that depth, …..when I go beyond 3 or 4 X D deep I start slowing down.

    How many pecks?

    What's the rate of feed?

    Was there an inclusion in the material.
    Pecking every .250", I don't remember the feed exactly, I want to say .007-.008"/rev.

    It's a high quality material, so I wouldn't anticipate inclusions but that's not totally out of the realm. I've run this setup probably a dozen times, they all went great until this one.

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    Could have developed a resonance, then since it was under a lot of compression, it just blew up. But normal HSS isn't that brittle so it's a surprising result.

    Regards.

    Mike

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    Quote Originally Posted by Cole2534 View Post
    Pecking every .250", I don't remember the feed exactly, I want to say .007-.008"/rev.

    It's a high quality material, so I wouldn't anticipate inclusions but that's not totally out of the realm. I've run this setup probably a dozen times, they all went great until this one.
    MMM? that's a poser

    MMMM? personally I think that feed's a bit light, my Dormer book says 0.010 - 0.015 '' / rev, and I tend to run at the top end (too many holes in work hardening materials ) but then I run slower which I believe gives a bigger stronger chip that doesn't tend to break up and jam in the flutes etc etc

    MMMMM? the drill got damaged when it wasn't in the machine -or on another job - like dropped - enough to crack it.

    MMMMMMMMMMMM? Shit happens!

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    Quote Originally Posted by Limy Sami View Post
    MMM? that's a poser

    MMMM? personally I think that feed's a bit light, my Dormer book says 0.010 - 0.015 '' / rev, and I tend to run at the top end (too many holes in work hardening materials ) but then I run slower which I believe gives a bigger stronger chip that doesn't tend to break up and jam in the flutes etc etc

    MMMMM? the drill got damaged when it wasn't in the machine -or on another job - like dropped - enough to crack it. Nope, it hasn't left the tool carousel since I bought it.

    MMMMMMMMMMMM? Shit happens!
    Yes, yes it does.

    Bobw's right- if you only have 1 of a tool, it will commit suicide.

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    Well it wouldn't break sitting on the shelf eh ?



    FWIW I bought a big box of used drills at an auction.

    Some just needed sharpening, others a chop saw to the end and then regrind, chipped badly or continued to be shoved into a hole, and smeared.

    But these other ones ....oiy They split up thru the center, leaving 2 long "fangs"
    at least 2" long (1 1/2" dia. drills)

    So yes, it happens.

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    Just several hundred, maybe more. Biggest one to go was a 2" drill just as it was breaking out of the back face of the job at 45 degrees. I never felt a thing honestly.

    Regards Tyrone.

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    Quote Originally Posted by Cole2534 View Post
    Yes, yes it does.

    Bobw's right- if you only have 1 of a tool, it will commit suicide.
    What happens most often to me is the first tool will run 300 parts/drill 1000 inches. Finally the tool gets worn out so you decide to change it. The other tools you got for back up get maybe 20 parts/100 inches even though you ordered them all at the same time, from the same company and they should even be the same lot.

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    Quote Originally Posted by Tyrone Shoelaces View Post
    Just several hundred, maybe more. Biggest one to go was a 2" drill just as it was breaking out of the back face of the job at 45 degrees. I never felt a thing honestly.

    Regards Tyrone.
    Then I'll gladly put this in the 'WTF' pile, it's much smaller than the 'operator error' one. ha

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    Quote Originally Posted by Cole2534 View Post
    Then I'll gladly put this in the 'WTF' pile, it's much smaller than the 'operator error' one. ha
    The 2" drill went very quietly, just like it was a rotten carrot. It went right up by where the flutes begin. No chance of a re-grind either !

    Regards Tyrone.

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    Quote Originally Posted by Cole2534 View Post
    This was a new one for me last night. I started running a proven program in the VMC and in the 2nd op (7" deep, 3/4" hole, 400rpm in ETD150) it started getting louder until the machine alarms out on Z axis overload. WTF?

    When I pulled the part from the vise and cleaned it out big fragments of the drill came out, including one whole cutting edge. Here's the thing- it was still sharp. The corner wasn't chipped or burned and the edge still had good form. It was a PTD drill, despite being made in Brazil I've always had good luck with their tools. The drill was about 5" into the cut when this happened.

    So I'm wondering- is it possible I just got a bad drill? If not, I'm at a loss for what happened.
    This may be out of your wheel house but the drill fracture faces tell a story. Most faces will be smooth and light gray and be a secondary failure. A face that has striations leading to an edge or internal point means a fatigue crack and that the root cause is at that edge or point. Granular faces would say poor heat treat. All faces clean, smooth and bright usually means an instantaneous fracture from overload.

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    Quote Originally Posted by Rickyb View Post
    This may be out of your wheel house but the drill fracture faces tell a story. Most faces will be smooth and light gray and be a secondary failure. A face that has striations leading to an edge or internal point means a fatigue crack and that the root cause is at that edge or point. Granular faces would say poor heat treat. All faces clean, smooth and bright usually means an instantaneous fracture from overload.
    I still have the pieces, I'll investigate after vacation.

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    If you need some help let me know.

    Regards,
    Rick

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    Are you sure it wasn't the "Just one more hole" syndrome. I've been guilty of it from time to time. You know the drill is near the end of it's useful life and should be sharpened. BUT you're pressed for time, and it's still working so you press your luck and try to finish the job. As luck would have it the thing gives up on the second to last hole. Now you have to clean up the mess, dig the chips and remaining drill out of the hole, hope you didn't damage the part, install a new drill, and continue on.

    Been there, done that. Hopefully learned from the experience, but will be retested the next time under the same circumstances. Experience says it only will take a couple minutes to replace the drill, emotion says if I can complete the job with the existing tooling I'll save both time and money. Sometimes you win, but sometimes you loose. When you loose it's a PITA you don't want to repeat. However with a short memory sometimes painful history is repeated.

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    Confirmed feed and speed, .007ipr and 400rpm, .25" pecks with full retract. Drill lip was intact (and found) from one side, still sharp, but couldn't get a pic worth a shit.

    Put in a new drill, same program and had good results (good chip color/formation). One thing I did was turn down the rapid to increase dwell at the top of the cycle to facilitate more coolant spraying on the point.

    However, it squealed a little. What causes squealing sounds in a drill?

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    Quote Originally Posted by Cole2534 View Post
    What causes squealing sounds in a drill?
    Usually chatter from a light load. If it was a material like SS it would work harden and begin fighting you. Needs to get into the cut quicker. I remember reading somewhere that something like 90% of wear on drills happens when entering/rentering the cut.

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    Quote Originally Posted by Hardplates View Post
    Usually chatter from a light load. If it was a material like SS it would work harden and begin fighting you. Needs to get into the cut quicker. I remember reading somewhere that something like 90% of wear on drills happens when entering/rentering the cut.
    Thanks bud! I'll crank the feed and see what she do.

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    I try not to use twist drills larger than 1/2" in a machining or turning center. I have quite a few Allied drills and a few insert drills. The Allied are nice in the mill cause one drill will handle a range of sizes by changing the tip and the inserted drills are nice in the lathe cause you can offset them to make a larger hole and even use them as a boring bar to open up a hole. Good name brand ones can usually be had pretty cheap on ebay. A friend of mine bought 140 new Allied tips for $100 on ebay and gave me 30 something of them. They also tend to leave a better finish than a twist drill since the shank is smaller than the tip you don't get the flutes rubbing and chips caught between them giving you a craptacular finish.

    Also IMO .007" is a decent chip load, it needs to get back into the cut quicker, not necessarily feed harder. I assume the squealing is when it re enters the cut, no? Can always play with the federate over ride until you find the sweet spot and then repost your program accordingly.

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    Quote Originally Posted by Cole2534 View Post
    Thanks bud! I'll crank the feed and see what she do.
    And don't dwell / let it rub, when the drill reaches depth retract immediately, and on re-entry go straight in to the cut.

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