How to Bend a Board - Kerf Cut

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oh hey what's up working hard or hardly


hardly working today we just did a

dining room of crown molding and we're

waiting for the caulking to dry before

we can paint it so we're going to give

that a couple of hours but I thought you

know what the heck let's go outside and

show you guys how to kerf a board if you

don't know what that is let's go outside

and check it out so here's our little

setup for kerfing a board what we use is

a sharpie speed square and this little

setup that you see right here so this is

a pretty simple process and I'll explain

to you

kerfing a board is for trim carpenters

basically what it is is we're going to

make a series of cuts all along the back

of this 1 by 6 MDF this is 3/4 inch

thick by 5 and a half and we're going to

make a series of cuts that are 3/4 of an

inch from one another and what that's

going to do is that's going to allow

this MDF to get a really good bin to it

so we can curve it around an arched wall

this is just an example today we're not

doing anything like this at this house

but we've got some time to kill so

here's how I do it what you want to do

is get your circular saw calibrated this

is a rigid and the fence on this from

this fence to the blade is an inch and a

half but that's too big for the kerf I

need it to be 3/4 so this little divot

right here where this goes in that's the

run of the blade that's exactly where

the blade cuts so you can follow those

lines but what I'm going to do is I'm

going to get on that with just an using

the 7 here you can use any number I just

don't like to use the end of the tape


I feel that this is more accurate so

right on that seven and then I'll go

over three quarters and I'll make a line

right there it just needs to be three

quarters from that line you can see

right there

so what that's going to do that's going

to allow me to line up that sharpie line

with the next cut and that line doesn't

have to be pretty obviously you can see

it's not perfectly straight I just it's

just a little line so you can know where

to make the next cut so before I make

the first cut on this piece of MDF what

you got to do with your circus circular

saw is set the depth and I'll come

around here to show you how I do that

there's this little blade guard you want

to lift that up and you can see that's

going to cut straight through the piece

we don't want that we want to go about

half way through with that depth on that

blade so I'm just going to eyeball it

and call it about half way right there

you see how that looks from this side

and that looks pretty good actually

right there

so I'll lock the saw down I'll make sure

that that's locked in place now my saw

is calibrated and I'm ready to make the

first pass of the circular saw so here's

what I'm going to do when I get started

I'm going to take this speed square in

my left hand with the fence of the speed

square away from me that way I can grab

onto it and slide it out like an

adjustable fence and this circular saw

the fence on the left side of the

circular saw is going to ride against

that so what I'll do is I'll get that

sharpie line lined up with the edge of

the material and then I will make the

first pass

so with that first cut now it's just a

repetition of lining up the Sharpie line

with the previous cut and I'll do that

the whole way down

and I can already feel the flexing over

here but it won't be until I get the

full board curved that we'll be able to

actually bend it if I try to bend it

right now it would just snap right here

at the weakest link right here where

it's as a whole board this is the

weakest link so I just thought I'd

mention that but this side over here is

really flexible

and you can see this part that I already

did thats hanging off I don't want to

bounce it around too much but it's

really bendy right now alright so that's

it this is the kerf that we did and you

can see just how flexible it is and we

will break this board I'm going to push

it to its limits but before I break it

and push it to its limit if we wanted to

get some more Bend out of it what we

could do is we could set the depth of

these cuts a little bit deeper but you

don't want to go too deep because you

could end up breaking the board that

right there is a good amount to keep the

wood strong and together or in this case

the MDF so MDF if you ever worked with

it you know already that it's a it's

already flexible before you do this but

I've got a piece it's the same exact

size over here and I'll show you what it

looks like with the kerf verses without

the curve so here's without I'll set

this one down and I'll try to bend this

it bends alright and we're going to push

this to its limit but it bends pretty

good but it's going to break now watch

how much I can get this thing bit

pretty cool it bends a lot more but it's

always going to break at that weakest

link whatever it was the the weakest

link was right there at that cut maybe

it was a little bit skinnier than the

other ones but we've still got this

piece you can see how it keeps breaking

you can see how you could get that so it

keeps breaking you can see yeah

so yeah in all seriousness that was

pretty funny but in all seriousness this

is a really cool method to get around

curved walls and incurved architectural

drywall and it really works we've used

it before

now if the wall is too curved you're

going to need to go to the the rubber

you know the flexible millwork route

yeah it's a really cool method we use it

we've used it on baseboard before where

we take the same method and we just

score the back of the baseboard before

you get to the top so you don't see it

in that top profile and it works great

so anyways hope you learned something

from this video about kerfing it's a

really cool method and I will see you

all next time