I need a drill bit! (for cutting metal)

[308mate]

• Mods, dont move this to home and garden, B&Q dont have what I need, Ive checked.**

I need a drill bit for drilling glav'ed mild steel ( I think?). 9.5mm hole is needed, 5mm pilot hole already driller.

HSS bits have just been burning out.

Got 130 holes to drill by tomorrow but noone has a 9.5mm cobalt bit.

Im in salisbury, Wilts.

Any ideas?

[garycat]

Is there a Toolstation near you?

http://www.toolstation.com/shop/Power+Tool+Accesso...

You should be using a cooling agent if you are burning out cobalt drills

[madbadger]

Are you sure it's mild steel? Galv wont make a difference.

As above use a coolant and fairly slow drill speed and you should be fine.

[Vidal Baboon]

As above- spot of oil

[Mexico.]

http://www.bizrate.co.uk/powertools/drill-bit-type...

OR

[308mate]

Not tried cobalt drills yet, only HSS.

Slower drill speed helped with the HSS bits but they still burnt out.

Not in a position to use a cooling solution I dont think. Unless its a very simple process?

[Spacekadet]

Sorry, i can't help you with sourcing bits but are you using tap/drill fluid?
It will extend the life of your bit by a fair amount. It's very simple to use, just keep the bit coated with it

[madbadger]

Is it a thick sheet you are drilling? Still don't think you should have such a problem with mild steel. I have drilled high strength (800Mpa) steel and staniless with an HSS bit.

Coolant you just squirt on. in comes in a dropping bottle like bike chain oil or you can get some types in a spray can.

[308mate]

madbadger said:

Is it a thick sheet you are drilling? Still don't think you should have such a problem with mild steel. I have drilled high strength (800Mpa) steel and staniless with an HSS bit.

Coolant you just squirt on. in comes in a dropping bottle like bike chain oil or you can get some types in a spray can.

Its about 3-4mm thick. High revs toasts the bit, low revs and lots of force cuts the steel but toasts the drill (smoke out of the back, casing hot!).

Got a cobalt bit on the way and some small gear oil for coolant. Will that be alright?

[madbadger]

Thats reasonably thick. Galvanised stuff I'm used to is normally a bit thinner.

You should be fine with the cobalt drill. Don't use too much force, keep the speed low and use plenty of coolant. You will get through in the end. Might take a little while to do 130 holes, but if you try to speed up the job thats when you will have problems.

[WorAl]

Any oil is better than none, just keep on dripping it on as you work, keep revs low. HSS bits through 4mm plate should be no problem....dont use too much pressure, thats when your drill will give up as will burn out the clutch.

[madbadger]

WorAl said:

Any oil is better than none, just keep on dripping it on as you work, keep revs low. HSS bits through 4mm plate should be no problem....dont use too much pressure, thats when your drill will give up as will burn out the clutch.

Just double checked with one of our operators.

No point in using Cobalt bits HSS will do the job fine.

Most likely problem you are having is going too fast with too much force. His rule of thumb is 250rpm for 1" hole and he recommended 350rpm to start. If it is going fine increase to up to 500 rpm.

Also don't bother with a pilot hole - unless the location is critical. The drill bit is designed to cut so will work better without a pilot.

Drip on the coolant. Don't go nuts with it.

[GreenV8S]

308mate said:

HSS bits have just been burning out.

If they are getting too hot then they will lose their hardening and be blunted very quickly.

You need to keep dribbling coolant over them to keep them cool, water will do if you don't have anything else available. If you can't do that then put oil in the hole and stop to let it cool down as soon as it starts smoking.

[308mate]

madbadger said:

WorAl said:

Any oil is better than none, just keep on dripping it on as you work, keep revs low. HSS bits through 4mm plate should be no problem....dont use too much pressure, thats when your drill will give up as will burn out the clutch.

Just double checked with one of our operators.

No point in using Cobalt bits HSS will do the job fine.

Most likely problem you are having is going too fast with too much force. His rule of thumb is 250rpm for 1" hole and he recommended 350rpm to start. If it is going fine increase to up to 500 rpm.

Also don't bother with a pilot hole - unless the location is critical. The drill bit is designed to cut so will work better without a pilot.

Drip on the coolant. Don't go nuts with it.

Good tips, thanks chaps.

Problem is, the pilot is already there. Theyre actually holes that are the wrong size, so Im drilling them out. I think that might be causing some of the problem.

The other part is that the Black and Decker is not exactly a precision bit of kit in terms of the clutch or setting the RPM.

Ill employ as much of your advice as I can and see how I go.

[HRG]

Do NOT use ordinary oil, the bit will slide instead of cutting then heat up and burn out. You actually want the bit to dig into the parent material.

[GreenV8S]

HRG said:

Do NOT use ordinary oil, the bit will slide instead of cutting then heat up and burn out. You actually want the bit to dig into the parent material.

I disagree - the lubricating properties work in your favour by reducing friction between the tool and the workpiece and do not stop the tool from cutting. Oil/water emulsion is the most commonly used cooling fluid. Oil on its own is too expensive to use at any significant volume, but just keeping it oiled gives you a smoke alarm when it starts to overheat. A water or water/oil emulsion cooling stream would be even better since it prevents the overheat in the first place.

I would say the existing holes will make your job much easier. The core of the drill has a harder time than the fluted cutters and by giving it a pilot hole you stop it wandering and give the bit a much easier job. It's good practice to start small and work up if you have a large hole to drill.