Can you get a drill bit to drill a drill bit?

[warrenpfo]

The 100 series has 3 bolts with captive nuts on the front cross member that help hold the “bash” plate on. In the process of removing the bolts all 3 sheared off and so yesterday I decided to drill and tap them out.

Its not the easiest of jobs lying on your back drilling up and after I managed to get the first one out successfully I started on the second. I managed to drill the initial pilot hole without a problem but on changing up to the next bit and having got half way through the drill bit snagged and broke. It did fall out and is now stuck up in the whole with now way of me getting it out.

I went on to the third bolt and the same bloody thing happened so I now have two broken bolts with bits of drill bit stuck in them and no way of getting them out. Both bolts are flush so no chance of welding a bolt to them.

Can you get a drill bit that can drill through a drill bit or what are my options.

 

[Jon Wildsmith]

Both bolts are flush so no chance of welding a bolt to them.

Flush or even below flush is exactly the situation where welding is a good solution. You build up a dome of weld on the sheared face of the bolt, then place a nut over that and weld the nut to the dome through the middle of the nut, like a plug or rosette weld. Turn the power up a bit on the welder because you need good penetration on what will be quite a short burst of welding for an M8 bolt. As a bonus all the heat involved in this process usually makes the bolt turn out very easily.

Can you get a drill bit that can drill through a drill bit or what are my options.

There are at least 3 problems with this - getting a hard enough drill, somehow getting it started on a rough surface and somehow not snapping it when it keeps snagging. Others might have more experience and point you at something suitable, I always reach for the welder.

 

[warrenpfo]

Welding is not my strong point BUT to have to weld upside down...i dont even know where to start.

 

[Jon Wildsmith]

Welding is not my strong point BUT to have to weld upside down...i dont even know where to start.

Do some trial runs on say a bolt with a nut right on the end, held in the vice, to simulate what's on the car. Because the welding will be quite short bursts you will already be using the right method for inverted welding so it is mainly a case of not getting burnt by the spatter Clean up the sheared end of the bolt as best you can, doesn't have to be shiny but do degrease it. The area around the bolt is better to be dirty so any overspill of the weld pool is unlikely to get penetration unless you really botch it.

EDIT: Just to add, this really is a very useful thing to get the hang of and worth persevering with till you do because they probably won't be the last sheared bolts you have to deal with

 

[BobMurphy]

Welding would be the best method, but I have occasionally managed to get broken drill bits out this way . . .

The drill bit has spiral flutes, when they break they leave the business end in the hole with a gap on either side (the flutes).

Knock a couple of small nails into the holes formed by the flutes, then grip them side by side in a mole grip.

Try and twist the broken bit out.

Sometimes I have had to use a ground-down 'Obo' nail (hardened steel) and a small hammer to shock the broken bit free.

You can easily lose half a day when this happens

Bob.

 

[warrenpfo]

It’s a real pain. What should have been a simple job of half an hour took most of the afternoon. Ill give your trick a go just incase but the bit is too far up the whole to see the end so it would be by feel.

On a separate note I was told by a friend of mine that the drilling of a pilot hole is what caused the whole problem in the first place and that pilot holes are seen as somewhat dated in technique. It was news to me but just thought I would put it out there.

 

[BobMurphy]

A pilot hole isn't just for centering. A small drill has more pressure at the tip and will cut easier than a large one.

The drill tip is the slowest part of the cutting end as its just rotating 'on the spot'. If you provide a small hole a larger drill will have a much easier time cutting.


Another method of removing a broken drill bit . .

Find a piece of metal rod slightly smaller than the hole (a nail shank is OK). Hacksaw a slot in the end such that the upstanding bits fit the drill flutes.

Tap this into the hole and locate it in the broken drill bit.

Wind the broken bit out (hopefully).

Expect two or three attempts


Or:


Drill two more holes in the siezed bolt such that all three are in line.

Whack a small cold chisel across the holes and form a slot.

Try and wind the broken bolt out that way.



hours of fun to be had !

Bob.

 

[Chris]

Maybe a squirt of Shock and Unlock in there first, to just try and contract the bit a fraction? I know it will affect the hole too but maybe not as much as the bit.

I remember an apocryphal tale about a company the made some incredibly small drill bit and sent it to Rolls Royce as an example of their work. RR drilled a hole down the middle of it and sent it back.

Chris

 

[Graham]

Welding would be the best method, but I have occasionally managed to get broken drill bits out this way . . .

The drill bit has spiral flutes, when they break they leave the business end in the hole with a gap on either side (the flutes).
.

Knock a couple of small nails into the holes formed by the flutes, then grip them side by side in a mole grip.

Try and twist the broken bit out.

Sometimes I have had to use a ground-down 'Obo' nail (hardened steel) and a small hammer to shock the broken bit free.

You can easily lose half a day when this happens

Bob.

.
I have had success with this method by using two masonry nails.
First I ground off the heads so they were essentially headless.
Then gently tap them in, down the flutes.
Then a pair of mole grips, head on, to the end of the "pins" with an adjustable spanned on the head of the mole grip for the turning movement to unscrew the drill bit.

Goodluck

Wear glasses or goggles in case the masonry nail snaps.

Gra,

 

[Chas]

I remember an apocryphal tale about a company the made some incredibly small drill bit and sent it to Rolls Royce as an example of their work. RR drilled a hole down the middle of it and sent it back.Chris

I remember a story similar to that where an American company sent to an English company a needle that would pass through the eye of the smallest needle. The UK company sent it back drilled out with a smaller needle inside.

 

[fridayman]

What are these men doing with needles?

 

[frank rabbets]

That's a good idea Graham. If that does not work an angle grider would cut the nut off the rail including through the drill if you could get in there; or is it inside a box section.
A note on pilot holes. By comparison the pilot drill should be the same diameter as the unfluted cross section of the main drill or smaller. If larger you will just be enlarging an already drilled hole which often leeds to brocken drill bits.

A carbide drill will drill through a hss drill and spring steel but they are amazingly brittle and not suitable for uneven jobs as they will shatter. I've used plenty and they will drill through case hardening like a razor. Wear goggles a high rpm and steady light touch. Off topic now.

Frank

 

[warrenpfo]

Frank its in side box section so not that easy to acccess the nut. Where would one get a carbide drill bit from?

 

[Crispin]

I've drilled out HSS bits by taking a masonry bit with a tungsten-carbide tip and sharpening that up. Upside down might be interesting though as it has to stay cool - the tip is only brazed in so if it overheats then you have a lump of TC stuck in the hole and you'll need something harder than TC

 

[warrenpfo]

I have thought that it may be easer to (A) drill down from the top if I can get in there after removing the bumper but am slightly concerned as I don’t want to weaken the cross member but could always fill the hole on top with some weld or (B) just leave the broke bolts in and move the holes across and re drill the ASFIR plate that uses the whole to hold it in place.

 

[Gary Stockton]

I've got a screwed-up hole in the bottom where an ASFIR plate goes - just drilled out the hole 2mm bigger and re-tapped - it now has an M10 in there instead of an M8.

But that doesn't tell you how to get the original out. How are you going to drill from the top - didn't think you could get in there?

Need to get a magnetic drill I think to help hold it all steady and use it as an upside-down drill-press?

My 2c (Zim) worth

 

[Jon Wildsmith]

To move the holes across you'll have to use long bolts and go right through the cross member because there won't be any handy captive nuts in there ... if doing that, why not try the weld approach first, then even if you end up welding the drill bit to the crossmember you still have your plan B to fall back on

 

[warrenpfo]

I may just do that Jon. Would you have any concerns over weakening the cross member if you went straight through it with long bolts? As that is my only worry but may be unfounded as I don’t thing the cross member is under tension as such.

 

[Jon Wildsmith]

That cross member is obviously there for a reason but I wouldn't have thought it was much of an issue to put a few extra holes in it.

 

[Roger Fairclough]

Can you get at the captive nuts? If yes, try twisting them off, either with a suitable spanner---they are usually square in plan---or something heavier such as Stillson's. Then you can weld in normal nuts.

Do you have access to gas welding kit? If so heat each nut bright red and leave to cool. This usually breaks up the corrosion that locked the screw in the first place. When cold, use a sharp cold chisel to indent a slot into the end of the screw. You may then get them out with a suitable screwdriver.

Roger