View Full Version : How to remove stripped hardened set screws?

Dale Lusby
10-13-2010, 11:45 AM
I recently acquired a very large woodworking jointer and the cutterhead has allen head set screws and 5 of them have been stripped. I've ordered some new ones and while I am waiting for them to arrive I figured I would try to remove the old ones. There isn't a lot of material left on the stripped ones so I figured I would drill a smaller hole deeper into the screw and use this for the remover to grab on to. When I went to drill them the bit wouldn't touch them. Perhaps I should have figured they were hardened but now I'm at a loss as to how I can remove them. Any advice or ideas?

10-13-2010, 11:53 AM
A dental diamond bur can be used to make screwdriver slots. It'll work better in a high speed handpiece.

Do dentists in CA make house calls? :)

Another method (much more tricky one) is to weld extensions to the broken screws. But you need to know exactly what you're doing.

10-13-2010, 12:02 PM
Get a screwdriver bit set that has plenty of sizes and shapes(Hex, splines,torx). Select one that is too big and hammer it in.

The rest you know:)

10-13-2010, 12:17 PM
My first thought is you're drill bit didn't start good because it was on a damaged surface--not flat. I've had this before when trying to remove buggered screws. Start with a proper spotting drill and go in enough to make a good start for your drill point to engage.

Uneven surfaces on small drills can have the effect of snapping a flute edge and then you just RUB. It can sure feel like you're drilling into something unable to be cut! ;)

Dale Lusby
10-13-2010, 12:22 PM
I had thought about the screwdriver as I have a lot of extras to try out. Heck I could grind one to fit if need be. There may be just enough bite to get it out. The diamond bit method will probably be next. Since it's an allen head the base isn't really blemished but mostly the sides. I tried a couple different bits and doubled checked sharpness to make sure it wasn't the bit. Good ideas to start with.

john hobdeclipe
10-13-2010, 12:31 PM
Can you post a pic of the cutterhead, showing the gibs?

I'm thinking that if you have access to the business end of the allen screw...where it pushes on the gib, perhaps you could use a thin cutoff wheel to grind away the end and relieve the pressure on the screw and loosen it.

10-13-2010, 12:38 PM
One other, more traditional, idea is a stub screw-extractor. Those are particularly good for allen head screws because you already have the hole to grab, the problem is your extractor bottoms out before it can.
The Shallow-Grip ones listed here are an example: http://www.mcmaster.com/#screw-extractors/=99c4mv
Or make your own by grinding off the end of the extractor you already tried.

David Powell
10-13-2010, 12:46 PM
and found that the set screws could be drilled only with Dormer brand drills, all the rest failed to make any impression. perhaps you might try some top quality hss drills, and if they dont work then move on to carbide drills, but mind you do not break any carbide ones off !!! Regards David Powell.

10-13-2010, 02:32 PM
I recently drilled out a broken off HSS tap with an Omegadrill bit.


This just one size for illustration, they come in about 5 or 6 different sizes.
It went through the tap like butter. The cutting edges have a negative rake which makes them very tough. Run at about 2000 RPM, dry.

Kind of expensive, but they work.


10-13-2010, 02:42 PM
A left hand cobalt drill bit may sometimes work; either alone or in combination with one of the removal methods noted above.

Are these blind (not through) tapped holes? If so, some of the methods like the Omega drill (generally good) may be a bit harder to use -- you won't be able to punch the bits of remaining set screw through the hole.

10-13-2010, 02:44 PM
I recently drilled out a broken off HSS tap with an Omegadrill bit.

It went through the tap like butter.How much feed pressure is required with carbide drills like the Omegadrill ?


10-13-2010, 03:48 PM
A new or sharpened carbide tipped drill for masonry will drill hard material. A couple of dollars at the hardware store. I might sharpen one left handed and see if it would grab and twist the screw out. If it's deep you'd have to blow the chips out once in a while since the flutes would be backward.

Good luck.

10-13-2010, 03:56 PM
Use a carbide spade drill. They are cheap and tough. They come in a lot of sizes. They will drill hardened tool steel (like taps) so a set screw is nothing.

Dale Lusby
10-13-2010, 08:26 PM
Here are some pictures. It's a 16 inch cutterhead and each set screw is 3/8" x 16 x 1.5". I tried using a mason bit after sharpenig one up and it cuts. Trouble is I don't have an extractor the right size. I would consider drilling it out all the way but at 1.5" long it's hard to tell if I'm going straight enough. Hopefully I can get a good extractor soon that fits and get them loose. As is the machine works and cuts good although once the blades are sharpened it should do great.




10-13-2010, 08:47 PM
For a quick & dirty screw extractor, take a worn out or broken tap a bit over the hole diameter, break/cut off the fluted section, and grind it into a slightly tapered square section. Using your 2 oz. ball peen hammer, tap it into the drilled hole, attach a tap handle and turn the set screw out. Almost takes as much time to tell how I do it, as to do it!


10-13-2010, 09:05 PM
Do you have a welder?

If you do and have a good hand at it here's how I deal with those.

Buy some 1/8" black pipe nipples from the hardware store,say 3" long,cut them in half.

Clamp one half in a pair of vice-grips and position the cut end over the setscrew.

Using a small weld rod (6011-3/32") around 60amp.

Slip the rod down in the pipe.Strike off and keep the rod burning,once the bottom end of the pipe is glowing red kill the arc and hold the nipple steady until it cools.The pipe should be fused to the setscrew.

Once it cools wiggle the vice-grips back and forth gently adding your favorite flavor penatrating oil as you go.They should spin out and leave the threads intact.

Buy some new setscrews and remember Never-sieze is your friend.

Other than that,remove the cutterhead and figure on mounting it up in a milling machine to drill the things out.

john hobdeclipe
10-13-2010, 09:15 PM
Looks like my idea won't work. There doesn't appear to be enough room between the cutterhead and the gib to get anything down in there to cut the screw ends.

Maybe some of the ideas discussed in this thread would help break the screws loose:


Dr Stan
10-13-2010, 09:29 PM
While in the Navy I learned to remove broken/stuck bolts/screws. Several of the techniques have been discussed including left handed drill bits, and extractors.

Another way is to TIG weld a piece (maybe an Allen wrench?) to the stuck screw to use as a handle for a wrench. You can also heat the cutter head as the holes will expand faster than the screw which can help.

BTW, are you trying to remove the screws in place? If possible I would remove the head and mount it in a vertical mill or a drill press either of which will give you better control and precision.

I also remember times when I had to heat the screw or bolt with a torch and drill it while it was still red hot as the bolt had gone through numerous heat/cool cycles as part of the power plant.

One option is ram EDM. Sometimes it is cheaper in the long run to have someone with the proper equipment do the work. Is there a community college or vo-tech nearby with an EDM?

Don Young
10-13-2010, 09:32 PM
A lot of good ideas already. What I generally try in this case is to use a hex (Allen) bit for a socket set. Use an oversized one and grind it smaller with a slight taper and somewhat oversize. After several days of generous soaking in PB Blaster or Kroil, heat everything up good and let it cool. Take the largest punch that wil hit the bottom of the hole and the largest hammer you feel comfortable with. Hit the 'bottom' of the hole several good blows, as hard as you can without breaking something. Then drive the oversize bit in the hole and there is a good chance the screw will come out.

Should this fail the next step would probably be drilling or welding, as others have described.

10-13-2010, 10:27 PM
The way I get stuck fasteners out is heat around the screw, remove heat and hold a candle on the screw allowing the wax to wick into the threads. Then using the technique Don posted remove the fastener while there is still some heat in the part.
I use this on a lot of vintage auto and tractor parts.


People say I'm getting crankier as I get older. That's not it. I just find I enjoy annoying people a lot more now. Especially younger people!!!