Broke Torx in Blind Hole
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  1. #1
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    Default Broke Torx in Blind Hole

    Hi all, hope everyone is well! I don't post here very often but read alot and learn.
    I've got two 1/4-20 allen bolts broke off in 303 stainless.
    I drilled a 1/8" hole in the bolts right down the center. I tapped a torx bit in the 1st bolt, back and forth and it came right out.
    The second one would not budge, and I broke the torx off in the hole. The bolt is slightly below the surface so I can not weld a washer / nut on it.
    My next step is to put it into the mill and see if I can cut the bolt out with a 3/16 end mill.
    I'm concerned if the end mill will cut the torx or just ruin the end mill.
    Any suggestions are appreciated.
    Thanks
    olf20 / Bob

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    make up a simple hollow cutter to machine away the head round the broken off key, then you can draw off what the bolt's holding and then just remove the bolt.

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    Is the hole "blind" because there's a screw stuck in it?

    If it was once a through hole, seems the "bolt" was soft enough to drill. You might use a #7 drill to drill most of the bolt (set screw, I assume) out from the other side and run a 1/4-20 tap through again?

    The Torx key is likely going to be pretty hard.

    If it's just semi-tight on the other side, maybe you can borrow an aircraft type right angle drill. Some of those only require about 1.5" clearance.

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    No thru hole. Blind. It is a 8" round 2" thick 303 stainless.
    4 bolt holes drill and tapped. This is on a liquid fertilizer unit
    and the bolts were pretty much ate away. I was lucky to get 3 of the
    4 out. Now I'm trying to figure out how to get the last one out.
    Thanks for the replies!!
    olf20 / Bob

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    Is it possible to just move over and put in another hole in both the housing and cover?

    I expect a little heat with a small oxyacetylene tip will temper the torx bit to where you can drill it out.

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    Usually those bits aren't ridiculously hard though it may have work hardened some when it twisted off. Do you have a cnc? Rigidity and control over feed are key. I've "drilled" out some really hard stuff with small carbide endmills, a super shallow helix and super slow feed rate. I prefer compressed air over coolant or oil.

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    I just had to drill out a broken OSG 6mm forming tap.After I quit sobbing I remembered I had saved a 1/8" three flute carbide em that I had broken the end off.Ground it flat put a little relief on the flute ends and managed to drill-melt(high speed) a hole thru then chipped the pieces out.
    In your situation any carbide drill or center cutting em will go thru the torx end.The problem is if it is loose and starts wiggling around it might break the drill or em.Then just resharp and go at it again.

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    The torx is not loose. I know about the sobbing!! LOL
    I have read that a masonry bit is carbide and with a little sharping it will drill right thru. I have a cnc mill and will set it up in the morning and have at it. We need this done so the farmer (me) can get back in the field. To replace this part is about $1200.
    As far as redrilling the hole, there are 12 evenly spaced holes that connect to barb fittings. I could go on either side of these and put another hole in if I have to.
    Thanks for the replies!!
    olf20 / Bob

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    Just because it is below the surface doesn't mean you can't weld it. Best done with TIG. I assume you mean just below the surface and not 1" down... Hit it with a quick arc and blob of filler and let cool. Repeat until it is up to where you can weld a washer or nut on it (you'll need a nut to grab onto even if you start with a washer) and then back it out. The repeated weld/cool cycles will help it break loose too. 309 or 312 filler would be best given the alloy screw

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    Dremmel sized pneumatic hand diegrinder that take 1/8 bits do 50k rpm, get a pack of diamond or carbide burs and with a squirt bottle full of paint thinner you can slowly cut it out.

    Have a helper squirt the thinner in the hole and blast it with air often to clear it out.

    The thinner also will soak into the threads and help loosen it.

    Sent from my SAMSUNG-SM-G930A using Tapatalk

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    The broken Torx key should be around 52-56 Rc and can be drilled/milled with HSS but whatever cutting tool is used you need to be wary of work hardening the broken bit. Run HSS slower than usual with some dark, sulfur rich cutting oil or use a "peck" type of drilling/milling method and frequently retract the tool to cool it and the work off with compressed air. this will also blow any chips out so you don't re-cut. You mentioned using a masonry drill. I'd also be very wary of generating enough heat that will soften the solder holding the carbide in place. When that happens the carbide will separate from the drill body and you'll then have a broken SHCS, a broken Torx key, and a chunk of carbide to dig out. If I used a Bridgeport I controlled the down feed with the quill stops, advancing only .020 or so with every peck. Yes it's a long PITA method but it reduces the chances of breaking a cutting tool from too much feed when it's near the bottom of the broken key. Hope this made sense and is of some help. Good luck.

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    Since the base metal is stainless and the bolt is not, it may be possible to remove it with acid or a strong base. Someone here may have done that and know what to use.

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    If you have a plasma cutter simply put the torch on the torx bit and give it about a one second blast. It will blow out the bit guaranteed. This works surprisingly well on broken taps too and doesn’t mess up the hole very much if at all.

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    I'm in the Dremel/grind camp. But friction stir welding on to the recessed fastener head would be an interesting approach. Not tried by me, though.

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    Got it done with a 1/8" masonry bit resharpened. Not
    bad at all.
    THANKS FOR ALL THE SUGGESTIONS!
    I learn lots from here.
    olf20 / Bob

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