Hi there, need to drill out some bolts but whenever i try and do this my drill bits never seem upto the job, and advice as to which set to look out for i normally go for hss bits but they just dont seem to last! any suggestions? Many thanks in advance, Greg

Buy good quality such as dormer or presto.

Cobalt are harder and will handle higher temps better but are more expensive.

Use the correct speed and a cutting lubricant, rule of thumb for speed is that you should just about be able to see the individual flutes.

Davie

Cobalt but dear

Last set of 12 cobalt bits I bought was about £30. They do last if you look after them though.

i like the bosch(?) Bullet ones. i got a 10mm one years ago, drills through 5mm steel plate in seconds.
not sure if they're really suited to drilling bolts out though, due to the shape of the tip, but worth a look anyway

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Originally posted by MakeEverything
Last set of 12 cobalt bits I bought was about £30. They do last if you look after them though.

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try using some wd40 it will keep the bit cooler so should last longer

If you can find them C1150 drills are good for drilling bolts, they only have a short flute so don't bent at all, and are really hard. like this https://www.bolt.com.au/32mm-hss-c1150-sheet-metal-drill-p-81476.html

Normal hss stuff isn't that great, def need decent brands or cobalt.

A mate works for Irwin, and nabbed a set of their drills. Absolutely brilliant, but not cheap. I guess like so many things quality costs. Or make friends in the right places

It also depends on the bolts you want to drill out, If you can flatten the top and centre punch 8.8 you will probably have no problem but a jagged top will push the drill to one side no matter what it is made of and harder drills are almost always more brittle. If you are drilling 10.9 or 12.9 you will break anything occasionally.

i only use dorma now as cheep ones are a false economy. i have got some rather nifty cutting gunk that you dip the drill bit into before you start drilling. easily doubles the life of the drill bit and stops it getting hot.

The fact that they are HSS doesn't mean that they have been heat treated properly as you will find with all cheapo bits.
As well as the Dormer, presto ones I have found the DeWalt 'Extreme 2' series to be good value for money.

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Originally posted by RickRick
If you can find them C1150 drills are good for drilling bolts, they only have a short flute so don't bent at all, and are really hard. like this https://www.bolt.com.au/32mm-hss-c1150-sheet-metal-drill-p-81476.html

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Another vote for cobolt bits and cutting fluid. If the bolts have sheared it may be possible to weld a nut onto the shank, the heat often helps to shift them

Thanks for replies guys looks like ill be spending some money then!

I have tried welding a nut on but it just keeps shearing, oh and incase anyones interested its bolts on a mini subframe that im having trouble with Thanks again