Kerf size???

[Team Sundown's Charles]

Hey guys i'm playing with kerf port design. But i'm clueless on how big the kerf needs be, compared to the size of the port. The port i'm using is 2.5 x 37.5. Should the kerf be the the same size as the port width or half the port width? Here is the design so everyone can see how i'm tring to get the kerf.

[skittlesRgood]

fritosaregood is the man to talk to about kerfs.

[Team Sundown's Charles]

Thanks man I'll PM hims to see if he'll help me out

[fritosaregood]

my rule is when i have a single side kerf i like to keep it close too, but not bigger than the port width. If i have 2 flares i cut it in half.

but its not absolutely necessary to have them that big. my last few boxes have been all 3" kerfs, and sometimes i go smaller do to size restrictions.

for yours i would do a 2.5" radius kerf on just one side. Its already gonna be a little tough doing one that small and 37.5 inches long

and also, just my preference but i would make to top and port all out of one piece with 3 bends in it. outside flare, 90degree bend, and inside flare. not sure if you just forgot to put the inside flare or what, but you should really use it if your gonna flare one end.

then just add a second baffle above or below the top of the kerf piece.

I always add the second baffle on top for better strength, since your kerf will need to to have to be in the inside of the side pieces, youll just have another piece on top that covers the side piece ends and the kerf pieces top. if that makes sense

and for making the inside flare, make your boards total length about 3 inches longer than you need, that way you have something to hold onto when you do the inside kerf, and then just take a circular saw to it one its done dryed to get rid of it.

you cant kerf the piece with a few jigs outside of the box and then put it in and hope you built your jigs straight and it all lines up good, or you can bend it while your attaching it to the rest of the box. but if you bend it when your putting it in the box your will still need to do the inside flare first so you can cut the lip off that is used to help you bend it.

I hope most of this makes sense, but its kind of hard to describe without a visual reference for me to help show.

[MXmike800]

Uhhh you lost me. Lol I'm curious how deep you go on a 3/4 mdf and how far of a spread between cuts? I'm sure its different between port sizes but let's say your 2.5" radius.

Thanks.

[EricR]

I've heard to cut 5/8" deep in 3/4" and 1/2" apart

[MXmike800]

What radius is that?

[Team Sundown's Charles]

Yea I understand ...thanks for the info

[fritosaregood]

Uhhh you lost me. Lol I'm curious how deep you go on a 3/4 mdf and how far of a spread between cuts? I'm sure its different between port sizes but let's say your 2.5" radius.

Thanks.

I've heard to cut 5/8" deep in 3/4" and 1/2" apart

there is some math behind it

If your using 3/4 inch mdf on say a 3 inch radius kerf.

your outside radius will be 3inchs and the inside radius will be 2.25 inches

so you take 1/4 the circumference of the 3inch radius part and subtract 1/4 the circumference of the 2.25 inch radius kerf

the distance you get will the the distance of wood you need removed. to find how many cuts that is you divide that by your saw blades thickness i think most are 1/8".

so by that logic, every 90 degree bend in 3/4" mdf will have the same amount of cuts. the only thing that changes is the spacing. to find the spacing you just divided it out evenly. and add 2 cuts on each end( so if you were looking at an actual circle you have a cut at 0 and 90 degrees and then however many cuts in between them

as for depth. i just test and test the blade depth before i do a kerf each time. i just use a piece of scrap and get it deep enough where its easy to bend, but not so deep that it rips apart if i try to move it

so for the math

3" radius circle_ circumference is 18.85"_ 1/4 circum is 4.71"

2.25" radius circle_ circum is 14.137"_ 1/4 circum is 3.534"

so the amount of wood you need to remove is 4.71-3.534 = 1.176

so you number of cuts is -- 1.176 / (1/8) = 9.4 so 10 cuts

you have that you need 10 cuts now for a 3/4 board, plus the 2 cuts on the end. so 12 cuts for 3/4 inch wood.