Grinding/drilling out exhaust bolts

[pepperami]

Not long ago I had a nice shiny aftermarket exhaust put on my bike.

I’m trying to rescue the old pipes as a backup/spare.
The bolts that hold the silencer onto the downpipe protrude from the silencer.
Even though I was super careful when I tried to separate the down pipes from the silencer, the nuts sheared.
I used penetrating oil left for a couple of days and used heat when trying to turn the nuts.
They still sheared.

So now I have two broken studs that need to come out.
I started off by trying to pilot drill a small hole in each.
Ordinary drill bits had little to no effect
After getting through 3 bits , I have made some headway.

I’ve been keeping my drill bit cool with frequent dipping in water.

How can I soften the stud metal.
Is it a case of prolonged heat on the studs?

I was thinking of using an old bit and a dash of grinding paste, what do you think on mighty BCF?
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I am the sum total of my own existence, what went before makes me who I am now!

[stinkwheel]

Stainless or mild steel?

Stainless, you're screwed, it's hard and will just get harder. Mild steel should be able to be annealed by heating to just below red heat for a while.

Lubricate and cool the bit. I've used antifreeze for this before, or dribbled a shaken up mix of water/oil onto the drilling site. Even WD40.

Sometimes there is just a hardened surface your bit is skating on and you can break through it a bit with a punch to allow the bit to bite again.

Try a masonry bit. Tungsten carbide is super hard and should chew through pretty much anything. Brittle though.

You can get tungsten carbide drill steel drilling bits. £££ though.

EDIT: A tungsten carbide centree drill isn't a bad investment. I keep meaning to get one. Harder to break and less prone to wandering. Drill the centre with that then chew in with the normal bit. Rinse and repeat.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[pepperami]

[Riejufixing]

[stinkwheel]

[pepperami]

[kramdra]

www.shop-apt.co.uk/carbide-burrs-ball-nosed-cylinder-type-c/carbide-burr-6mm-diameter-16mm-head-length-double-cut-ball-nose-cylinder.html

Small carbide drills are not that expensive but they are brittle, but burrs can take some abuse, even if a cordless is far, far too slow.

[stinkwheel]

[pepperami]

Thank you for your wisdom
____________________
I am the sum total of my own existence, what went before makes me who I am now!

[mentalboy]

Are you trying to rescue both the silencers and the downpipes or just the downpipes?

It took a re-read for me to realise that you're talking about the bolt that pinches the silencer onto the pipe. The original bolts will be stainless and if you've already cooked them with repeated drilling attempts then, as Stink has already explained, you are going to have a joyous time drilling further.

If it were me and I were trying to save the silencer, I'd grind off the old pinch bolt set up and buy some loose jubilee clip style bands to do the job instead. But I would consider the visibility aspect, so in time old fashion, what bike are we talking about?
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Make mine a Corona.

[stirlinggaz]

hi,
i havnt read all the replies, so apologies if its been mentioned before.
decent quality cobalt drill bits.
when all else fails i dig out my set of cobalt drill bits (think there dewalt)
i start off slowly with plenty of cutting oil or even 3 in 1 oil.
keep it cool & just work your way up the sizes till its hollow enough to pick out or been shocked so much it actually turns.
Once its out i clean threads up & run a tap down it.
never had to resort to carbide bits...yet.

cheers,
GAZ

[pepperami]

[martin734]

I have noticed one of the problems many people have when drilling metal is that they use too high a drill speed. For a 1-5mm drill you should drill at a max of 3000 rpm and for 6-10mm a max drill speed of 1000 rpm. Remember, the faster you drill the hotter your drill bit will get and as it gets hotter it will get softer and blunter.
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Current bike: ST1100 "Big Red"

[Riejufixing]

[kramdra]

[martin734]

[Pete.]

I drilled out all 8 broken studs on a Bandit cylinder head. If you're drilling stainless you want to keep the speed down and drill with quite a lot of pressure. The lower speed will stop the drill tip from cooking and the heavy weight will avoid work-hardening the stud. If it stops cutting, stop immediately and sharpen the drill.
____________________
a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[kramdra]

No, lower value for stainless, higher value for aluminium. Suggest you look at some of the manufacturers technical spec rather than some pdf written by a school teacher for classroom use, and anyway the ideal numbers you'll find in references are irrelevant if other conditions are not met. The main one, as I said, is the feed rate. The best way to judge this is the resulting chip, if the chip and feed are wrong, you will ruin the bit at any speed.

www.vikingdrill.com/viking-Drill-FeedandSpeed.php

As I said above, stainless hardens as it is worked. It does not harden if it is cut, hard stainless is avoidable.

And I disagree, those are rubbish guides. THIS is a proper guide, tho I admit the numbers are somewhat less than the generally accepted SFM in other references.
www.presto-tools.co.uk/file.php?filename=PrestoCounsellor2016.pdf

[pepperami]

Well back to the job in hand.
Taking Mr Stinky’s advice/wisdom, I did some heating/quenching on the bolt stubs, getting them up to a bright orange before quenching.
The studs were a bit softer I think, but they still put up a fight against a drill bit.
Progress was being made but very slowly.
After a rummage through my junk tools and bits & pieces I found the worlds smallest tungsten carbide burr.

Three studs down and one to go
Still a lot of work to do but slowly getting there.
Once the last stud is drilled out, I will need to slightly enlarge the holes and cut a new thread to match some new bolts.
____________________
I am the sum total of my own existence, what went before makes me who I am now!

[mentalboy]

[pepperami]

Well thanks to the wonderful little tungsten carbide burr, I now have got through all four bolts.

The next step is widening the holes !.
One thing at a time, but after I have the holes the right size, I will need to cut threads to match some new bolts.

If cutting new threads is as hard as drilling out the old bolts, I’m in for a motherfugger of a bitch of a job.
The things we do to save a few quid .
____________________
I am the sum total of my own existence, what went before makes me who I am now!

[kramdra]

If you drill it ok, decent chips and no rubbing, any sharp drill and tap should have no problem. If not, a cobalt drill plus one of these

www.ebay.co.uk/itm/M6-x-1-0-HSS-E-6H-SPIRAL-FLUTE-RED-RING-M-C-TAP-DIN371-TM15300600-EUROPA-TOOL/271815438092

I could use one of these myself, ordered. Decent tools have saved me a lot of time.

[stinkwheel]

Taps are usually super-hard. Harder than drill bits which need to retain a certain amount of flex. It's why they snap so easily. Lots of lube, go slow don't force it and remember to back-off frequently.

Drillng once you have a pilot hole is usually straightforwards because you don't have that "skin" of really hardened material for the bit tip to skate about on. Move up drill size in stages, then you're curling off less material at once, generating less heat and mechanical stress.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[kramdra]

A relatively small hole and drilling in stages will ruin your bits and your hole, chip the corners off, rub and harden. If the chips stop flowing, stop and resharpen, or change bit, dont keep going.
Holes below 10, use a 2.5 or 3mm pilot then final size. You want 4-6mm diameter increase per stage.

[pepperami]

Tungsten carbide burrs rule even small ones!
A combination of drill bits and burrs means all four holes are now ready for a new thread.
The holes are a mildly lose 6mm/HSS6 and there is plenty of metal to cut a new thread into.
The four bolts will be holding the silencer onto the down pipes, but the silencer is also held in place by hanging onto the passenger foot peg via another bolt like most modern bikes.
They are sort of load bearing as the original silencer is fffking heavy.

The world is my oyster when it comes to choosing bolts and threads because I will buy bolts & taps at the same time to ensure I buy the right taps for the bolts I put on the counter.

Mr Stinky : I seek your wisdom again, any pointers?
____________________
I am the sum total of my own existence, what went before makes me who I am now!