Drilling thick stainless with step drill
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  1. #1
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    Default Drilling thick stainless with step drill

    So a few weeks ago I was on a job with a plumber and we were only supposed to weld brackets into place but this plumber was to drill at least a 1 1/2" hole through 5/8" thick probably 316 stainless. The guy got half way through with a 1/2" bit and burnt up his brand new drill. He got a 3/8" through hole. I was told to stay out of the plumbers way, but I knew they couldn't handle it. When it got to this point, I asked him how he was going up from the 1/2" hole. He said he was going to use a step drill. Now obviously that is stupid, but I was thinking, is it really possible to do that.

    I ended up pulling my mag drill out and a piece of 1/2" steel flat bar and drilled it out with a 1 3/4" hougen bit.

    Sent from my SM-G960U using Tapatalk

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    That just sounds like a good way to ruin a step drill to me. I would think a step drill should never be used on material thicker than any one step, but for what they are intended to do they are great. A good hole saw blade or two, ideally with good cutting fluid or some form of coolant (and more importantly proper technique) would have gotten the job done if the mag drill had not been available. That is the only way I would have attempted it without the mag drill, and it still would have sucked.

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    Possible? Yes. Sensible: not unless you are on Sentinel islands and your life depends on it.

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    Quote Originally Posted by MattiJ View Post
    Possible? Yes. Sensible: not unless you are on Sentinel islands and your life depends on it.
    Yes it is possible, if you have about 15 step drills.

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    Which is lower cost to purchase. 15 step drills or a mag drill and 1.750 rota-broach?
    All fine if you just happen to own a mag drill already.
    That said the very many hours involved in using a unibit type step drill on this hole just might buy you the better setup.
    Doable, yes for sure. A great idea no, but I've probably done worse when faced with a lack of tools on hand to use.
    I wonder how many Starret hole saws you would eat in this process with a 1/4 guide hole and a hand drill. I think a quite few and also not real fast.

    It may have seemed a real stupid idea but when all you have is a hammer...... Don't be so hard on the plumber who probably has never seen your setup/tools.
    When I have seen such new things all I can think is "I gotta get me one of those".

    I do think it is so great that you stepped in to help even when being told to stay away.
    Bob

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    How is the "Mag" part of said drill, gonna stick to the "stainless" part of the job ?

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    "I ended up pulling my mag drill out and a piece of 1/2" steel flat bar"
    You c-clamp a piece to the part for the drill's mag to grab.

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    Quote Originally Posted by digger doug View Post
    How is the "Mag" part of said drill, gonna stick to the "stainless" part of the job ?

    I've used a mag drill with a clamp more than once--not for all situations but it does work...

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    Quote Originally Posted by Bondo View Post
    When it got to this point, I asked him how he was going up from the 1/2" hole. He said he was going to use a step drill. Now obviously that is stupid, but I was thinking, is it really possible to do that.
    Yes. I've never had to use a step drill in thick stainless but I have in a pinch used one on 1/2" aluminum. A heavy-duty slow speed drill like some of the pro Milwaukee ones and plenty of pipe threading lube would be needed. You can drill from both sides and as long as the stepped hole is not a problem it will work, although it is less than ideal.

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    I’ve used step drills to drill out holes in thick stainless before. It works fine as long as you keep it cool and don’t run it too fast. Keep the SFM low, flood it with coolant and drill away.

    If the max OD of the step drill is the target diameter they work really surprisingly well.

    Obviously the hole will be tapered and stepped if you don’t go full depth in thick metal.

    Two flute Lenox varibits have routinely hogged out 1/2” or thicker stainless for me when I worked as a fitter/turner in a brewery. Still have and use the bits.

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    Quote Originally Posted by Arc-On View Post
    ..... It works fine as long as you keep it cool and don’t run it too fast. Keep the SFM low, flood it with coolant and drill away..
    Keys here in not only coolant but the all important low SFM.
    People with a variable speed hand drill will try to go max speed thinking this makes the hole faster.
    That does not work and they burn up bits and saws like crazy. I've had to spank a few employees here.
    I suspect this was the problem with the 1/2 inch hole.

    Thing is that I did this more RPM and still tend to do it even though I know better so I can't call the kettle black.
    You want to get the hole made now, push the speed and then puck yourself. I should know better but still do it.
    Bob

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    As youtube creator AVE says, “sometimes you have to uses the dick you have got”.

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    Quote Originally Posted by moonlight machine View Post
    Yes it is possible, if you have about 15 step drills.
    Good step drill last certainly longer than 5/8 total thickness even in stainless as long as you use sensible sfm. But 1.5” final diameter would need suitable drill and strong guy.
    Thickest material that I have used step drill was probably 1/2” ordinary structural steel

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    That's why I asked because I only use step drills for electrical and stuff like that. When I found out a plumber was going to drill the whole, I packed the mag drill and a plasma cutter since I thought it was impossible to do. Seems as it is possible, but most likely wasteful.

    Sent from my SM-G960U using Tapatalk

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    Quote Originally Posted by LKeithR View Post
    I've used a mag drill with a clamp more than once--not for all situations but it does work...
    Same here, could even tack weld Mild steel plate to the stainless plate with stainless rod, grind it off when done.

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    Quote Originally Posted by CarbideBob View Post
    Keys here in not only coolant but the all important low SFM.
    People with a variable speed hand drill will try to go max speed thinking this makes the hole faster.
    My dad's old VSR drill had what amounted a throttle limiter on the trigger so no matter how hard you gripped it the drill would only spin so fast. I've not seen those on newer drills but itd sure be handy

    Sent from my SM-G973U using Tapatalk

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    Quote Originally Posted by Cole2534 View Post
    My dad's old VSR drill had what amounted a throttle limiter on the trigger so no matter how hard you gripped it the drill would only spin so fast. I've not seen those on newer drills but itd sure be handy

    Sent from my SM-G973U using Tapatalk
    Not really, it was just a mechanical stop on the trigger.

    What's needed is a true speed control with feedback, so as to govern the speed.

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    I've had to use holesaws in thick stainless with a hand drill before. Wasn't terrible. Slow with a bit of cutting oil.

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    I would worry about work hardening. At some point the pressure available will not be enough if drilling by hand.

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    Drill a center hole for the size of the first step on the step drill. Then use a small drill and make lots of holes to get rid of excess material. Finally run the step drill all the way through. Use water as a flush and lube and you could capture the water with a water vacuum, or a pile of rags.


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