Enlargening hole with flat wood bit?

[fenzi]

I've got a 22mm hole through a door for a bolt which needs replacing with one which is 25mm wide. Can I use a 25mm flat wood bit accurately to make it bigger to accommodate this or is there a better way? My concern is that the drill bit will wander as there is nothing for it to bite into.

Thanks

 

[Diyisfun]

You wont be able to use a bigger drill, as you say

 

[big-all]

square off the hole a bit
glue in a block to fit the the hole and start again when dry
or in this instance just use the sharp chisel to enlarge the hole to a square the correct size assuming a faceplate that will allow this

 

[Jasonb]

Drill a hole with your 25mm bit is a scrap of wood, clamp it centrally over the 22mm hole and drill away. The hole in the scrap will guid the bit so it won't wander or snatch.

Works with holesaws as well

Jason

 

[crank39]

Drill a hole with your 25mm bit is a scrap of wood, clamp it centrally over the 22mm hole and drill away. The hole in the scrap will guid the bit so it won't wander or snatch.

Works with holesaws as well

Jason

But you'd have to use an auger bit for the clamped bitof wood to hold it centrally, if you use a flat bit then once the flat part goes through the clamped bit of wood your left with a 1/4" shank waving about like a sausage in a bucket

 

[foxhole]

You could use a 'Mad Bit Multi-Angle Drill Bit' needs no centering.

 

[Jasonb]

But you'd have to use an auger bit for the clamped bitof wood to hold it centrally, if you use a flat bit then once the flat part goes through the clamped bit of wood your left with a 1/4" shank waving about like a sausage in a bucket

Once the flat bit has started to enlarge the hole the two edges of theflat will be guided by this.

Given that you should drill from both sides with a flat bit that means you only need 22mm (assume half a 44mm door) depth from each side and a flat bit is usually about 40mm long so almost half would still be in the scrap

Jason

 

[ladylola]

Failing all else use a gouge or a 1/4" chisel and pare away the 1.5mm or so from the hole, it'll be covered by the furnature anyway.

 

[ColJack]

you can get holesaws that "stack".. one inside the other..

if you buy an arbour that the drill dit goes all th way through ( ie not a hex shank one ) then you can take out the drill bit and fit it to a 22mm blade, then slot the whole thing onto the pilot bit of a 25mm holesaw and arbour..

 

[Harbourwoodwork]

all your fears are well founded I stopped using flat bits in the late 1970s and changed over to augers what type of hardware is this bolt ?

 

[Deleted member 174758]

Of course, if you don't want you use JasonB's excellent suggestion there is a type of bit made specifically for the task - the traditional Forstner bit. With those you need to turn the drill backwards a couple of revolutions to whilst pressing down to generate a "track" for the bit to follow before drilling the hole. True Forstner bits, as opposed to the cheap solid body ubbish palmed off as Forstners, are designed to be guided by their rims - unlike every other bit you'll ever use which either require a centre point to goide them (brad points, flat/spade bits, etc) or have a threaded nose to pull them ionto the work (augers, etc). Personally I'd use JasonB's suggestion

 

[foxhole]

all your fears are well founded I stopped using flat bits in the late 1970s and changed over to augers what type of hardware is this bolt ?

Two year old post.