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GrahamRounce

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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?
 

pcb1962

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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

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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

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just get better qual drill's....this is Dewalt but there are many more manuf's....
F3621559-01.jpg

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.....
 

GrahamRounce

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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!)
 

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