Folks: I just broke a standard Dewalt pilot point drill bit (1/8 " dia) while drilling through a 416 stainless knife bolster. The bolster is only 3/8" thick, but is already epoxied to the knife side (hole was pre-drilled into the knife, so it binded inside the bolster.)

Have done my best to drill it out, using other bits (smaller and of same diameter) and even a cobalt bit, at low and high speeds, but am getting nowhere.

Would anyone have a trick up their sleeves to remove it? Thanks much!!

Can you drill from the oposite direction, and punch it out?

To drill out HSS taps I use a solid carbide spade drill. This is not done by hand, but in a machine.

First thing is to clear any chips that may be stuck in the hole, they are not helping your efforts.

If you have a Dremel you can grind it out. Try to work just the center, and remove in pieces. Diamond bits will do a better job at that size.

Good luck, and take your time.

If you have a milling machine you can drill out the broken bit with a center cutting solid carbide endmill. Works on broken taps too.

thanks much.  I did try drilling from the other direction and hit the same "wall."  Then I tried a dremel tool with diamond coated head, no luck.

In disgust, and out of impatience, I ended up doing what I didn't want to do: ripping the xxxxxx thing apart.  So this question is now overcome by events.  But thanks for the pointers. 

The short & easy answer is "EDM." The long answer is to chalk the loss up to tuition in the school of hard knocks. Drill bits don't drill throuhg other drill bits. You need EDM for that...

I have used carbide tipped concrete bits to remove broken bits. The inexpensive ones work just fine for this.

epoxy isn't that big of a deal usually you can figure a way to pop it off and then be able to work on it without the knife causing problems. Riveting is another matter...

We drill every thing and fit up before epoxy.
Drilling one bolster at a time. If you break through before twistinge bit off.
You can use a smaller sized bit in reverse at a very slow speed and back the broken bit out----sometimes.
416 work hardens real fast. Have a fresh bit and cutting oil before you start.
It is best not to predrill and ream on 416. The work hardening can be a problem of several metals.

Hope that helps

chuck

anywhere near White Lake,NY? bring it around,will burn it out . i do drills ,taps,and the famous e-z outs on a regular basis. Just burned a tap out of a very expensive mold for a local mold builder. He had close to 80 hrs of work in it when he broke a new tap in the last hole . Came in the door near tears,left 20 mins later a happy camper.
Lee from NYS land of taxes

One trick I have found on small broken bits and bolts is to use an annular cutter and drill around it. It wasn't the solution here, but it can save a lot of grief in cirumstances where there is a through hole. Without the through hole the annular cutter creates a tube that has to be broken off to remove. Then the space has to be filled before redrilling, of course. I sure wish I had an EDM.

My quick fix for this kind of thing. I use about a 6" piece of flat bar. Drill a same size hole
Inna FB heliarc or mig thru the hole. Tap with hammer usually comes out.
Ken.

Can you take it to a machine shop and get them to punch it out on a hole puncher? Because it is 1/8 drill in 3/8 it might be a stretch. I work with 316 stainless and it is soft in comprassion to carbon steel. However I,m not formillaler with 416 stainless, do you mean 316 stainless? If you drill from the other side why can,t you punch out the drill with a small centre punch? Or best of all, take it to a lazer cutter shop and get them it cut it out, it will be done perfect but you will have to pay. My last answer is let it rust away in there and then drill it out, a drop of acid will speed up the process, it is stainless so it will be ok. I wouldn,t put any heat near it.
In a fabrication workshop, If you break a tapp or drill, no one wants to know you, it is a real hard one to fix. But it can be fixed. Just be pataiant with it, cause its not an "easy fix". You just have to find an engennging solution to it. An would be a shame to damage a project for lack of a solution.

Mick

And i forgot, you can take it to a machine shop and get it machined out on a mill.
Mick

You could water anneal the end of the drill bit. Bring the bit up to a dull red with a torch, air cool until the red is gone and cool with water right away. This should soften the broken bit enough to facilitate drilling it out.

Easy with the right tools. While tapping a part in the lathe I snapped a 4mm spiral flute tap off in a piece of O-1. Ground the top flat, then drilled it out with a 1/8" solid carbide 2 flute drill that we make in house. I was left with three small sections of the flutes that fell out of the hole - sweet.