solid carbide twist drills

I have lot of mild steel drilling to do and thought I would buy solid carbide drill bits with the idea they would drill more holes before needing sharpening, but they quickly chipped the cutting edges and became ineffective. what am I doing wong ?

thanks

Georges

Give us some idea of the drill dia and what speed you are running it at. You must bear in mind that carbide tools need to be run at speeds roughly 4x normal for H.S.S. i.e. 6mm drill needs to run at about 2000/2500rpm. Running them at a slow speed will likley cause them to chip as although very hard they tend to be brittle.

Hi Dusty, thanks for your reply, I have three sixes 5mm 10mm and 13mm , I have only used the 5 and 10mm the 13mm is still new . I used them in 12v cordless hand drill black and decker, the speed I dont know but it feels a lot slower than the standard corded mains drill. It sounds from your reply that this may be the probelm

The handheld drill is your biggest problem, the Carbide drills are brittle so any slight wandering will damage them. They are really only suited to drilling or milling machines where the work is rigidly held below the drill bit. 12V drill will run them at about 1200-1400rpm.

I would suggest you buy good quality HSS drill bits which will last well, take this part for example all holes drilled through the 1" thick metal with the same bit that was not new and it still cuts fine afterwards without sharpening.

Edited By JasonB on 20/09/2012 08:31:21

Edited By JasonB on 20/09/2012 08:32:25

I second what JasonB says ( just to confuse things..) solid carbide.. does not like flexing. it does not even like a miss alingned "center pop"..try 0.3 mm drills at 36,000 rpm if you don't believe me..( 10 /1000" etched centers)....funny still drill moderately well when broken .. just not to depth..

seriously if using hand drill you have been lucky ( or very skillful) to have any success with carbide ..and cordless..ROLLS EYS...WOW..

with hand drill then ...HSS and if metal thin enough consider center drill .. other wise pillar drill ..

Oh Did I mention saftey specs?

... and using a cutting oil will make a big difference too.

Hi all, thanks for the terrific feedback, its answered my question nicely, clearlly carbide drills are for specialised use, again many thanks

Not intending to argue but to ask...

How do carbide (tipped) drills for cement manage to avoid chipping? Many are used in hammer mode that would seem to add further insult.

Could these drills be used to drill metal? Re-griding of the carbide required?

Dunc,

First, if you look at these masonry drills, even new ones, the included angle of the cutting edge is somewhere around 90 degrees or more, so will be much stronger than the edge of a metal cutting tool. Second - and this is a little more specualtive on my part - tungsten carbide tools are not pure WC, they are WC powder in a metal matrix; variations in the amount, composition and structure of the matrix will give a trade off between hardness and toughness, and I guess masonry bits tend to the latter. Third, even if blunted, the hammer action relies on battering the brick or whatever into powder and then scooping it out; I doubt if real sharpness is an essential for this.

They would be fairly poor at cutting metal without serious re-grinding; I'm sure they would scrape their way through, but it wouldn't be pretty. If you want to try, I suggest cast iron might be good, it quite likes a negative rake.

They are pretty good for getting through ceramic tiles - but don't forget to switch off the hammer action! Also, make a nick in the glaze to stop the point skidding around uncontrollably, or use a bit of masking tape for the same purpose.

David

Edited By David Littlewood on 23/09/2012 17:14:47