Masonry bits

[GrahamRounce]

Hi - why are the cutting tips of masonry bits wider than the shaft? Especially with larger holes, it means the bit wiggles all over the place and you can't get a nice parallel-sided hole for eg 10mm cylindrical expansion bolts (my current problem).

I'm thinking of finding a bit whose shaft is 10mm, then grinding down, if possible, the cutting thing to 10mm.

Any comments please?

 

[Phil Pascoe]

I suspect it would bind badly.

 

[pcb1962]

it means the bit wiggles all over the place and you can't get a nice parallel-sided hole

Unless the bit has been badly ground and the web is off-centre then it will go in the direction that force is applied. Try using a bit more pressure and check the runout on your machine chuck.

 

[GrahamRounce]

Thanks. I don't usually have a problem, but this was drilling into a wall about a foot above my head. So it was difficult applying force.
I started off with a small bit, then I think two more successively larger ones before finally going with 10mm.

Imagine my joy, when, after all that sweating, the expansion bolt still wouldn't go in!

 

[clogs]

just get better qual drill's....this is Dewalt but there are many more manuf's....

the standard drill bits have just a plane end, there are some out there with a second but smaller cutting tip.....
my prefer'd choice now.......
u'll also notice the shank has been ground with three sides, no more slipping.....

 

[Phil Pascoe]

I have a set of Hilti bits with solid carbide tips that have a profile similar to that - they're the best I've come across.

 

[GrahamRounce]

Thanks. Could you manage a close-up of the DeWalt bit tip?
Do those and the Hilti ones have a preference for going straight, or will they still rely on the user to hold the drill straight and rigid?
(It's only 8 holes altogether, so I don't want to break the bank!)

 

[artie]