Drilling subframe Bolts

[Nuvo]

Today I finally got the chance to try and remove a sheared sub frame bolt from the chassis leg. I got the sub frame off without too much pain.

The problem I have is drilling the sheared bolt out. I started with a 3mm pilot hole which was working nicely excavating steel chips like it should. I reached a depth of around 10mm and the drill bit was just producing small filings rather than chips.

I'm using cobalt drill bits and cutting compound which is suitable for HT steel. I tried another bit fractionally bigger and I'm getting the same result. I also tried a 6.4mm bit and this resulted in a countersunk pilot hole, it wouldn't drill beyond that.

I only had a 500W B&D drill to hand and I'm wondering if I need something with a bit more power. I used a higher drill speed was for the 3mm drill bit and lower for the 6.4mm. I can't quote RPM figures as the speed is varied by squeezing the trigger.

Can anyone advise me what I need to do in order to get the results I need?

Thanks in advance.

[caterpillar]

you may screw the bolt part IN the leg.... it doesnt matter.... OR use a weldin mashine( mig) and some bigger nuts...weld, and WAIT to the bolt and nut are cold, then unscrew the #¤%@...( use wd40 or likeli)

[rj scotty]

slow speed lots of pressure on the bit

[newsh]

Yes, slow speed lots of pressure or you glaze the steel and it hardens. You could try messing up the surface of the steel with a centre punch to get the drill going again. You have to cut through the hard skin you've made when the drill just spins. Cobalt drills should do it though, it's what I use to drill stainless at work. Are you working on your back under the car? very hard to get adequate pressure.. As Cat says, welding a nut on usually works, the heat from the welding frees the thread up then you can get some plus gas wicked in there.

[Nuvo]

Thanks for the replies so far guys.

Yes, I'm working on my back, not exactly ideal working conditions I know.

I applied a fair amount of pressure and running the drill at a slow speed, erring on the side of caution as the last thing I want is to break a bit in there. Admittedly I did up the revs a little to try and get it cutting again, so I may have work hardened the bolt. I would only drill for around 60 seconds before cleaning the bit and reapplying cutting compound.

I could try punching the surface as you suggest to get thing moving along again.
What about using a carbide tipped drill could I use one of these to break through the skin as an alternative?

The bolt sheared around 10mm inside the hole and stripped the threads too. Sadly I don't have access to welding equipment any way.

Do you think the 500W drill is up to the task or do need to get a more powerful tool?

[S2central.net]

I don't think power is the problem. I have made the mistake in past if using too much speed when drilling.

If you don't have a welder try one of those little heat torches to persuade the ****** out. Pretty horrible job.

[rj scotty]

it could be worse;

Avant rear lower arm to hub bolt, mine shears. It's 100mm + long 12mm diameter.
2 days later the drilling was complete but keeping it centered was a challenge.

you live and learn

[Nuvo]

I found this very informative article which confirms I have most likely work hardened the hole.

[AndyP]

I found this very informative article which confirms I have most likely work hardened the hole.

The subframe bolts shouldn't be stainless steel so I don't this applies. I'd try again with a new cobalt bit and don't to mad with the speed.

[K Simmonds]

Yep, as the other guys say SLOW speed, lot's of pressure is the way to go and cool the bit in light oil frequently, also decent quality drill bits are essential

[Nuvo]

Thanks Andy, I might be okay then.

I tried a using the same cobalt drill bits in a pillar drill on one of the old sub frame bolts and it drilled the holes effortlessly so that verifies that the bits haven't been dulled.

I then tried using the 2.6mm bit in the 500W hand drill and was able to get it to start chipping metal at the lowest possible PRM, I had to apply a considerable amount of pressure to get it working. Which confirms the advice given by the guys above.

Not surprisingly I couldn't get it to drill using the larger 6.4mm bit with loads of pressure applied, I could drill hear the drill labouring under the load.

I just hope I can manage to get this done in the confined space lying on my back.

[Nuvo]

A little progess update.

I got the sheared bolt out in about 30 minutes using an angle drill and then a good quality screw extractor. After feeling particularly pleased with myself I set about drilling out the bolt hole ready for tapping fresh screw threads. Bang! The flippin' tip of the drill snapped off inside the hole. Fortunately I was able to pick out the fragments easily enough.

I'm having a drill guide machined to hopefully prevent this from happening again. I'll report back with my progress.

[Nuvo]

Well the damn thing has kicked my ***, but not without a good fight.

In the end I wasn't able to devise a jig to hold the machined drill and tap guide square to the chassis leg. Sadly I didn't have the required tools or materials to hand to make something suitable. I reluctantly bolted everything back on loosely ready for a calibrated nip up in the morning.

[pasbogdan]

Yes, slow speed lots of pressure or you glaze the steel and it hardens.

Hss in any aplications(lathe,milling,drilling) needs slow speeds and cooling.And pressure is needed for the tool to create and mentain cips/cutting.
Sharp the tools each time you feel it does not cut.Do not force it.Sharpening is the secret.Also use good bits.Does not matter if hss is stamped on them.I once used a bit to remove a broken bolt from a turbine housing(on the milling machine).Sharpened and tryed it several times.Did not worked.Took an old rust bit from comunist 1970 era and drilled all hole

If the bolt has a fiew mm end left outside the longitudinal member use a nut and weld it in the middle.High amp weld to create penetration not only filling material.After weld cools down get a big hamer and give lots of shots in the nut maybe the bolt will separate from chasis and try unscrewing it.

If the bolt is face or under chasis use a guiding nut welded to the chasis to keep you centered at at good angle when drilling.This way you will drill just to insert a tool and create new thread.

Or cut the chasis with bolt and replace the small part that contains the nut.Do not forget about waxing the inside of the longitudinal member.

[UrS4boy]

Can anyone advise me what I need to do in order to get the results I need?

Did no one suggest a screw extractor, aka "easyout" as per this video demonstration?

http://www.youtube.com/watch?v=SMrDYJvY0Ts