584,861 active members*
5,138 visitors online*
Register for free
Login
Results 1 to 13 of 13
  1. #1
    Join Date
    Aug 2009
    Posts
    2

    Cutting off head of hardened steel bolt?

    We use hardened steel hex bolts, hardness C38-45, shaft diameter 3/8, head diameter 9/16, head length 3/8, to fasten large and expensive climbing holds to a plywood wall, with a nut behind the wall. Some nuts cannot be reached, the bolt sticks in the nut, and the nut may spin behind the wall. Rather than sacrifice the holds that are stuck, we would like to remove the head of the bolt, so the hold may simply slide off the bolt shaft (the bolt is a bit recessed into a roughly 10/16 hole in the climbing hold). We tried a 9/16 carbide extraction bit, but 15 minutes of drilling only removed at most half the head. Is there a better method? A cutting wheel with aluminum oxide quickly cuts the bolts (albeit with many sparks), but for large holds a cutting wheel cannot reach behind the hold to cut the shaft. Is there a burr or drill bit with aluminum oxide (or any other equipment) that we could use to buzz off the head, by inserting the device into the opening in the hold containing the bolt? I'm not sure this is the correct forum for this query, so let me know if it should be posted elsewhere.

  2. #2
    Join Date
    Dec 2004
    Posts
    1865
    Quote Originally Posted by shiffrin View Post
    We use hardened steel hex bolts, hardness C38-45, shaft diameter 3/8, head diameter 9/16, head length 3/8, to fasten large and expensive climbing holds to a plywood wall, with a nut behind the wall. Some nuts cannot be reached, the bolt sticks in the nut, and the nut may spin behind the wall. Rather than sacrifice the holds that are stuck, we would like to remove the head of the bolt, so the hold may simply slide off the bolt shaft (the bolt is a bit recessed into a roughly 10/16 hole in the climbing hold). We tried a 9/16 carbide extraction bit, but 15 minutes of drilling only removed at most half the head. Is there a better method? A cutting wheel with aluminum oxide quickly cuts the bolts (albeit with many sparks), but for large holds a cutting wheel cannot reach behind the hold to cut the shaft. Is there a burr or drill bit with aluminum oxide (or any other equipment) that we could use to buzz off the head, by inserting the device into the opening in the hold containing the bolt? I'm not sure this is the correct forum for this query, so let me know if it should be posted elsewhere.
    If you can get behind the handhold with a hacksaw, I think that they make some "grit" blades that should cut the bolt.

    Mike
    Warning: DIY CNC may cause extreme hair loss due to you pulling your hair out.

  3. #3
    Join Date
    Aug 2009
    Posts
    2
    Unfortunately, we cannot reach the bolt shaft with any tools that fit between the climbing hold and the wall. Thus we need to 'buzz off' or 'drill off' the bolt head from the front opening.

  4. #4
    Join Date
    Sep 2007
    Posts
    11
    Is there a way that you could cool off the head of the bolts using liquid Nitrogen to get them brittle enough that you could break them off with a chisel and hammer?
    !!! Caution using the liquid Nitrogen !!!

    Only other idea is to get out the cutting tourch and protect what you do not want burned and cut the bolt heads off if you can reach them this way... of coarse have water and a fire extingwisher available...

  5. #5
    Join Date
    May 2007
    Posts
    781
    First off I am wondering how the bolts are tightened if the nuts cannot be reached.
    Seems like a bad design.

    I assume the drill is not cutting because the bolt is turning.

    If so take a socket and weld a handle on to the side so you can hold the bolt head while drilling down thru the socket.
    Would be best if you had somone with a lathe bore out the socket and put a drill bushing in it to guide the drill.
    For a 3/8 bolt I would only use a 3/8 drill with this system, no reason to make more chips then needed.
    A good cobalt drill bit should work and be less likly to brake.

  6. #6
    Join Date
    May 2008
    Posts
    85
    You're right not to use the head size. That's almost 4 times the material to remove. I'd go a touch bigger to account for off-centre drillling, say 7/16 for a 3/8 bolt. It may help to centre drill the bolt with a 1/8 bit first or even to use a solid carbide centre drill for the job.

    Quote Originally Posted by Andre' B View Post
    First off I am wondering how the bolts are tightened if the nuts cannot be reached.
    Seems like a bad design.

    I assume the drill is not cutting because the bolt is turning.

    If so take a socket and weld a handle on to the side so you can hold the bolt head while drilling down thru the socket.
    Would be best if you had somone with a lathe bore out the socket and put a drill bushing in it to guide the drill.
    For a 3/8 bolt I would only use a 3/8 drill with this system, no reason to make more chips then needed.
    A good cobalt drill bit should work and be less likly to brake.

  7. #7
    Join Date
    May 2008
    Posts
    85
    Another thought is to use studs in the future. You should be able to buy decent studs that have a female allen key depression in them. This way both the stud and the nut can be held from the outside.

  8. #8
    Join Date
    May 2008
    Posts
    152
    JB-weld (or other tough glue) an impact socket with a retention ball hole to the bolt head.

    Get an impact driver with the retention ball in tact and line it up with the hole in the socket. You should not be able to separate the socket and the driver easily with the ball engaged in the hole.

    Pull on the driver while spinning CCW. You can probably generate enough friction to grab the nut on the back side.

    back on the ground, you'll be able to hammer (or burn and hammer) the bolt back out of the socket for re-use. If it works, buy a bunch of the sockets and glue them all at once.

  9. #9
    Join Date
    Jun 2008
    Posts
    130
    You could use riv-nuts in the wood - if they have them with enough grip length - so that the nut part is more secure. They install from the accessible side, too.

    Jim
    No time to do it right, plenty of time to do it twice.

  10. #10
    Join Date
    Mar 2006
    Posts
    489
    How about just grinding the heads off with a regular hand held grinder? Yeah, lots of sparks, but it would be done quickly. (watch the heat buildup though...)

    Paul

  11. #11
    Join Date
    Jul 2009
    Posts
    12
    I am not an expert on drilling out hardened steel bolts, but I do have a few suggestions that are a little more exotic than the usual advice.

    Don't know if this will work in your situation, but it works to drill a hole in a hardened motor shaft or a hack saw blade. Try using a rod the same size as the drill bit or the back end of the drill bit or a bit you have already wrecked, etc. Put it in the drill and pretend you are trying to drill as fast as possible. This is to spot anneal the bolt. Then use the real bit. But first let it cool before applying the drill bit (lest you wreck its temper) or applying cutting fluid (lest you quench it). This beats ruining the temper on the bolt and the drill bit at the same time. And keep the real bit cool and lubed. Spot anealing might not go deep enough, unless you repeat the process (using a rod with a cone tip that matches the drill bit/hole). Or
    http://home.comcast.net/~jaswensen/m...annealing.html

    You need a bit that is harder than the steel you are drilling. Carbide, diamond, titanium, cobalt, abrasives, etc.

    There are a couple tips here about using masonry bits in hard steel:

    http://www.practicalmachinist.com/vb...-96842p20.html

    You need some sort of cutting fluid. Unfortunately, that can be a problem at that angle. You will have cutting fluid everywhere but where you wnat it.

    Drilling concrete with masonry bits, I have ruined multiple bits in one hole but adding a little water one drill does many holes. A little reminder of the importance of cooling when drilling hard stuff. So spray water in the hole. Given your vertical orientation, you might try a water based gel such as K-Y jelly - works drilling teeth. Cuts down on flying chips, too (just drilled a u-bolt plate). It has to boil the water before it can wreck the bit - provided the water is in the right place.

    Whatever you use for a cutting fluid, the drill bit is pumping it out of the hole so you want to replace it frequently. Also, carbide doesn't like intermittent lubrication (thermal shock leads to chipping). It doesn't like hand drilling much either. If you have one of those drill press stands used to convert a hand held drill into a drill press, try rotating it 180 around the column so it can steady the drill. Since this is a climbing wall, supporting the weight of the drill/drill press should be no problem at all (belay on). You might even bolt the base to the wall. Not exactly a uni-mill or mag drill press but might help if you find you are chipping carbide.

    You might also use progressivly larger drill bits. Reduces the amount of metal you are trying to remove at one time. Also, you don't technically need to drill out either the bolt flange or the core - the only metal you actually need to remove is a hollow cylinder about the size of the bolt diameter -i.e. a coring drill.

    If you don't have enough pressure, you will generate more heat than chips. A piece of 1" webbing between two climbing attachment points and behind your shoulders may help.

    Another option is to take a sawzall to the plywood, then remove your bolt the old fashioned way, and cut a new piece to cover the hole and give your climbing wall some detail. Or tack weld another bolt head on and use a slide hammer to extract the bolt, climing anchor, and nut through the plywood.

    Someone else has a similar problem:
    http://www.lets-do-diy.com/Forum.aspx?g=posts&m=779

    Of course, this being CNCzone, no response would be complete without suggesting you hammer a piece of PVC pipe over the bolt head, fill it with deionized water, and mcgyver an EDM hole popper and post the video on youtube. :-)


    http://bbs.homeshopmachinist.net/arc...p/t-30515.html
    http://www.britishblades.com/forums/...ad.php?t=81795

  12. #12
    Join Date
    May 2008
    Posts
    85
    Another thought, is there any way you can use a magnetic base drill? That way you could get nice even pressure that is dead square to the head of the bolt. They also have a nice low rpm so you won't destroy drill bits. You can usually rent them. You may need to temporarily attach a steel plate to the wall but it might be worth it.

    It strikes me that the more time you spend setting this up, the easier the job will be.

  13. #13
    Join Date
    Jul 2004
    Posts
    127

    a couple of ideas

    Drilling out a hardened bolt is a PITA- especially if its mounted high on a wall and the nut in the back may be spinning. Yes it can be done, but I'd try it as a last resort. Annealing the bolt would help with the drilling, but the heat is likely to damage the climbing hold if not done very carefully/patiently.


    The very first thing that I'd try is to try to get the nut in the back to catch into the plywood. Two ideas come to mind:
    -unscrewing the bolt while putting tension on the the climbing hold (or possibly the bolt)
    -drilling a ~1/4" hole in the plywood directly above the bolt and squirting in epoxy so that it can hopefully dribble down, hit the nut, and bond to the plywood.

    Not sure exactly what the climbing holds are made of, but if they are the standard resin kind, you can probably take a sawzall to the side of it and cut the bolt off. you may have to cut through a bit of the hold in order to do this- not sure how big of a deal it is to sacrifice the the .1" slide that's closest to the wall.

    Other obvious options is to either cut a hole 2" or so in diameter above the hold and try to get a wrench in back of there, or just cut out a replace a section of plywood as whitis suggested. I am not sure what is involved certification/inspection wise after cutting out a section of plywood, but that is likely to be a fastest method.

    Hope this helps,

    Matt

Similar Threads

  1. Are Ballscrews Hardened Steel or not????
    By Hellbringer in forum Benchtop Machines
    Replies: 9
    Last Post: 02-26-2008, 07:15 AM
  2. cutting 10mm hardened steel shaft?
    By andy_ck87028 in forum Mechanical Calculations/Engineering Design
    Replies: 5
    Last Post: 06-25-2007, 02:12 AM
  3. Machining Hardened Steel Shaft
    By jimbobbus3 in forum MetalWork Discussion
    Replies: 15
    Last Post: 11-10-2006, 04:41 AM
  4. Cutting Hardened Steel
    By Smackre in forum Waterjet General Topics
    Replies: 0
    Last Post: 02-08-2006, 08:12 PM
  5. Drilling hardened steel shaft
    By Zephrant in forum Uncategorised MetalWorking Machines
    Replies: 12
    Last Post: 06-13-2003, 09:42 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •