Drilling work hardened stainless
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  1. #1
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    Default Drilling work hardened stainless

    I have some 1" x 1" x 1/8" 304 stainless tube that we drilled 80 holes with a 13/32 drill, there are about 6 holes that my guy didn't press down hard enough with the hand feed drill press causing the bit to rub and not cut causing the material to work harden.

    So I bought some drill bits from MSC, I talked to a tech team guy and he said they should do it, they didnt !!!, so then I bought 2 more that are even better at a cost of 20.00 ea.

    So, before I ruin these, does any one have any ideas to take the work hardening out the steel, would heating it up and then putting it in my fiberglass blankets to cool slowly help.

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    Do you have a mill you can put them in and interpolate them? If not, you could try spot annealing with a little propane torch. I've never done it, but it may work. I hope they at least recommended some cobalt split points.

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    Quote Originally Posted by Portable Welder View Post
    I have some 1" x 1" x 1/8" 304 stainless tube that we drilled 80 holes with a 13/32 drill, there are about 6 holes that my guy didn't press down hard enough with the hand feed drill press causing the bit to rub and not cut causing the material to work harden.

    So I bought some drill bits from MSC, I talked to a tech team guy and he said they should do it, they didnt !!!, so then I bought 2 more that are even better at a cost of 20.00 ea.

    So, before I ruin these, does any one have any ideas to take the work hardening out the steel, would heating it up and then putting it in my fiberglass blankets to cool slowly help.
    .
    .
    use coolant go relatively slow rpm and use cobalt or carbide drill bits. carbide drills are often $100 to $1000. depending on size. when drill is dull stop. thats the biggest thing not to keep going with a dull drill it only makes it worse

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    I've used the info on this site to good effect. Though note that the temps are in celsius

    TLDR heat it to 1050c to 1120c (1922F to 2048F) and quench in oil, which does not harden it.

    http://www-eng.lbl.gov/~shuman/NEXT/...eel%20Tube.pdf

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    Couple of ways

    First Grind a small negative land on the cutting edge of your drill
    It will make the cutting edge much stronger but needs more pressure to drill

    If that does not work take a masonary drill bit Grind it positive Somewhat like a normal drill bit
    You probbable have to regrind or detroy one or 2 but at the end it will work

    Or buy a carbide drill bit

    Peter

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    Honestly i would just regrind the drills i had and add pressure and then turn the drill on, helps to grind them to a more pointy end and 9x out of 10 you can drill straight on through the hard layer with out issue.

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    my guess is you are going way too fast, and not using enough coolant/lube.
    Do you know how to resharpen drill bits?
    I have drilled literally tens of thousands of holes in stainless, and find that if you just resharpen the bit, use a lube, and lots of downfeed pressure, you can power right thru the work hardening easily. I usually drill stainless at 100- 150 rpm, on the bridgeport, and I use CoolTool II because its easy to apply from 4.0z bottles, and is non toxic, even when hot. I use ordinary black oxide jobber bits, nothing fancy.

    The most common problem is people trying to drill with woodworking drill presses, running em at 300, or 500 or even higher speeds.
    low and slow, as the Beastie Boys said.
    Plus, you gotta really yerk on the quill.
    Downfeed pressure.

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    Hey guys, thanks for your tips, my drill press is for steel, I can slow it down one more pulley, I will apply coolant and a lot of pressure.

    I'm also going to heat and cool slowly in blankets.

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    I've had multiple times where I can't drill a stainless item in a drill press with a regular 118 bit switching to a 135 split point fixes the problem and it powers right on through.

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    Drop your speed to half what it should be for steel. Around 175rpm or less, if you have it available. As said, dub the lip of the drill. Put a flat on the cutting edge so the drill has no rake. That makes it a LOT stronger and also provides more surface area to absorb heat. You can probably get away with a cobalt drill if you take this approach. Main thing is go slow and apply a lot of pressure. Stainless work hardens as the drill nears breaking through because the thin section starts to give under it.

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    Default Work hardened 304 stainless

    Quote Originally Posted by Portable Welder View Post
    I have some 1" x 1" x 1/8" 304 stainless tube that we drilled 80 holes with a 13/32 drill, there are about 6 holes that my guy didn't press down hard enough with the hand feed drill press causing the bit to rub and not cut causing the material to work harden.

    So I bought some drill bits from MSC, I talked to a tech team guy and he said they should do it, they didnt !!!, so then I bought 2 more that are even better at a cost of 20.00 ea.

    So, before I ruin these, does any one have any ideas to take the work hardening out the steel, would heating it up and then putting it in my fiberglass blankets to cool slowly help.
    There have been some good suggestions. I was wondering if a slight touch around the top of hole with a die grinder would get through the hard spot. Then as suggested slow down with the drill speed.

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    Yup, as most have said allready, usually I just sharpen the bit and go back in, slow with coolant.

    If you hit a particularly nasty glass like spot, and it’s smoking, squealing and sparking, and resharpening doesn’t work, it’s possible you hit some chromium carbide inclusion (or some other junk, common in cheap stainless).

    A few seconds with a carbide burr in a flex-shaft can break through that and save your drill bits, and your patience!

    If you know you have a bunch of work hardened holes, I’d go ahead and hit them with the flex-shaft and a carbide ball burr ‘bout half the drill dia. or so, if you’ve got that on hand ( or same in the dremel or die grinder, but I much prefer the flax shaft for the dexterity and the foot pedal speed control)

    If you don’t have a carbide burr Small enough to get down in the hole, as implied by your post, “around the top of the hole” , don’t bother, that’s not going to help. Gotta get down in there..

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    I try my hardest to use annular cutters for every hole in stainless. They are just better.

    As far as your current situation, I have always retouched the burnt up drill bits and apply twice the down feed pressure. If you have an air nozzle right on it, and some thick tapping fluid, it helps to keep it lubed and cold.

    As long as you don't have 1/2" of a haz around the hole and it just has slight discoloration or none, your only trying to get through a few thousandths before it will drill fine again.

    When I use hole saws to drill 1/8" plate or such, I use low speed on a hand drill but I full throttle it for 3 seconds and let it cool for 3. Lots of lube and I push as hard as I can. The hole saws last a long time. The trick is making sure the stainless doesn't heat up. I have a 3" Morse hole saw with over 120 holes and it still works great.

    Sent from my 2PS64 using Tapatalk

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    rbent is right-- I never drill stainless with a 118 bit: save those for mild steel or alum.: too much down pressure to go anywhere in that size range for a 118---- hard to feel the cut. Operators have to develop the "feel" for cutting. Its just like milling-- got to be cutting and making a chip because a percentage of the heat goes with the chip and the aforementioned hardening. I like the 135 split points and the close variants. These reduce the pressure required to make the penetration and have greater relief on the backside of the cut which reduced heat.

    Sometimes flipping the part on a overheated area is helpful-- the most work hardened cross section is parallel to the bit's cutting surface. Coming at it from the opposite side makes it a partial contact on the hardest surface and usually goes on through.

    I drill a several hundred holes per week in stainless. You don't really need the super high end bits-- coolant or cutting oil is vital however. Half my holes are in coolant application(mill) the other half is jig on drill press. I like long handle drill presses for stainless as that "feel" is easier. Same for countersinking.

    Going slow means low rpm with proper chip load. I do both 1/2" and 13/32 holes in 304 solid stock 2.125 thick and 1.625 thick. These are with coolant-- I can check my program-- but I thing I'm around 365 rpm and pecking.

    In another non-coolant application, .084 wall stainless tubing(round) oil the bit on first wall and then re-oil for second wall. The first wall is easy-- the second wall in round tube is more difficult because the inside radius mirrors the bit angle so the bottom cut feels different than top surface.

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    What about when the pins are 6mm dia. with 2.5mm holes each end?
    I centred them first so the drill didn't wander...but on reflection I either didn't use enough downward pressure, or should have pecked them...

    Anyway, as others have suggested above, if I turn them, should I be able to drill from the other side? Or should I cut my loss and just start again? I have to make 20 of them

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    If the 2.5mm is a through hole, then flip and try again. But be sure you've given yourself every advantage for success, which includes using a better drill if you can. If you used a standard jobber bit, try a cobalt 135* split point stub length for the second try. And make sure your RPM is suitable.

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    As others have already stated keep it sharp! At times in certain materials I have had to sharpen two or more times per hole on Hss bits to prevent risk of work hardening. The time it takes to resharpen pays for itself over a hard spot in a pricey piece of metal or a loss of hours of labor. It's really surprising what a good grind on HSS will drill through. On bad work hardened spots sometimes it's best to grind (or buy) a spade drill for hard drilling just for the strength aspect to prevent snapping a twist drill in the hole. (BTDT had to dig it out) HSS, cobalt and carbide all work well for them. very short pecks, plenty of cutting LUBE ( plain coolant just doesn't work as well when cutting work hardening metals from my experience)and a good blast of air to clean the hole every peck, it goes faster than it sounds and those work hardened spots get a lot less frightening. good luck.

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    with stainless, sharp bits and coolant, coolant, coolant and more coolant. ive drilled thousands of holes with one good cobalt drill bit, I seem to like these drillco bits. resharpen or touch up as required with a tiny 2" roll loc disc of 240 grit.

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    At my old job we just let it get red hot and pushed the metal out of the way.

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    Never chuck away a chipped carbide end mill.

    You can freehand grind a set of cutting lips and plunge down through the hardened crap, if not all the way through the part.

    Between that and learning to freehand grind drill bits, I saved an awful pile of otherwise useless aircraft parts.


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