Can anyone help me? I'm trying to drill a 3mm hole through/across the shaft of an m8 bolt and it just won't have it. The 1mm drill goes through (then snaps!) but not the 3mm. A pilot hole tends to make things worse. I'm using good drill bits that've never failed to go through anything but I'm getting peed off now Want them to use as swivel joints for my clutch and accelerator pedals.

3mm through m8 dosen't leave much solid material --- less than 2 mm each side.

Try locking 2 nuts on and drill through the flat of one nut

You can buy jigs for doing this -- can't remember who sells them

Should be right enough eh? They're not pulling a lot of weight. I'll go and try the nut thing now I think.

clevis pins?

Frost Auto Restoration do the Jig for bolts -- 17 quid

Don't seem to have the one for nuts.

They have the one for nuts as well part number T204 --- 21 quid.

I've got going but its like trying to drill diamonds or summat. I don't get it. I really like the clevis pin idea though. A couple of them'd do the trick nae messing cheers conrod.

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've got going but its like trying to drill diamonds or summat.

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Hmm. I did file a bit of a flat on but the ends are that rounded triangular shape that you mention. I've tried 3 so far and I've tried across the head just as another area but no way they're not having it.

Another thing with self tapping bolts is that usually the heads have a flange (like a built in washer)

Nope not got that. I can't understand it. I drilled right down the centre of a different bolt yesterday with the same bit but these ones just seem to be monsters. I'll have to rethink I think.

Any stampings/markings on the bolt head??

Hi,
If you make a pilot hole too close to the size of the final hole then you will just knacker your larger drill as it knocks the cutting edge off it towards the outside edge. 3mm doesn't need a pilot hole IMO.

Have you tried using drilling lubricant? I think I got mine at Halfords - comes in a spray can and is dirty brown in colour. This helps although I usually only use it for larger holes in thick material.

Finally, are you using appropriate speed and pressure on the drill? I don't know what RPM you should be using but it is possible to use too much pressure AND too little pressure. Smaller bits like higher speeds and less pressure but don't let it overheat. I usually know I've got it right when I get long curly bits of metal coming off.

Sorry if some of my suggestions are a bit basic but, like you, I'm a bit surprised you are having problems.

One last thing - I have had a situation where I was cutting through a water pump shaft where I could cut most of the way through no problem but there was a harder "core" within the shaft which was hard as hell. It was like normal steel outer around a hard tool steel inner shaft. You don't get bolts like that do you?

HTH,
Craig.

Are you using a pillar drill and holding the bolt in a clamp or vice?

Another tip (again basic, but worth a mention) is to "peck" drill - i.e. drill a little way, then back off to allow the swarf to clear the drill bit and hole before drilling a bit further. This becomes more inportant the deeper the hole. It could be why you're getting part way through and snapping drill bits.

Yep its in a pillar drill and vice, markings on head are 8.8 and a couple of letters and yes I quite regularly get that solid core thing. I'm going to try a different batch of bolts, get one from B&Q or summat and give that a try. Wonder if I've blunted the bit now keep zizzing away at it.