How to do EXACT Kerf Bending

this looks like a solid piece of plywood but think again today i'm going to show you how curve bending works and i'm going to give you all the mathematical tools that you need to make perfect bends every single time enjoy hi guys my name is isak and this is one time builds today i'm going to be explaining the geometry and mathematics behind curve bending which is a technique in uh that you would use to bend mostly plywood uh with round shapes i used this recently to make a lump bending a piece of plywood into a complete ellipse but today i'm going to talk about the geometry and mathematics and to explain you and show you how this works i'm going to be using a ruler straight ruler a caliper a piece of plywood and a pen and i will also be recording some drawings in the ipad and i'm going to try to make this into one single take at least for the explanation part then i will show you how this looks once it's bent so let's get on with it so curved bending is a technique in which you will take straight this piece of plywood and then you will be cutting some grooves in one side of the plywood and this allows you to bend the plywood around the area where you actually cut the grooves now how this works precisely is fairly straightforward and for this we need to consider a couple of things so first we're going to talk about the thickness of the plywood so how thick the plywood is going to be in my case i'm going to be using this piece of plywood which is a 12 millimeter plywood so i'm going to write this down so my plywood is going to be 12 millimeters now um there are a couple more interesting things that we need to uh realize one is that a full circle it's a whole 360 degrees right and therefore if i cut it in four each of these quadrants is going to be about 90 degrees right there is one more piece of information which is critical which is the diameter sorry the perimeter of the circle so the uh the distance that you would travel if you would walk along the line that forms the circle that can be calculated with a formula that is 2 times pi times r and r will be the diameter the the the radius of the circle so the distance between the center and the other side so this will give you the perimeter right now these are the basics that we need to consider now curve bending is a fairly straightforward technique so you have a piece of plywood that is of a certain thickness right so some certain thickness and if you would want to bend this piece of plywood between this location and this location at a certain angle which could be whatever angle you want right then basically if you would look at a full circle what happens is that in the outer perimeter of the bending the distance or the perimeter will be longer than in the inside so basically what we will need to do is calculate how much difference in that distance there is so um let's take a very simple example uh let's say that i want to bend a piece of plywood at the 90 degree angle so this will be so i'm going to bend this piece of plywood at a 90 degree angle so that's the first thing that we're going to do 90 degree angle the second thing that we need to decide is what the radius of the bend is going to be so basically this distance how big do i want this distance to be in this case i'm just going to pick a random distance let's say um let's say seven centimeters right so the distance or the radius of the bend is going to be 7 centimeters or 70 millimeters now because i'm using a 12 millimeter plywood which is basically the thickness of my plywood this means that the inner radius let's call it r small is going to be 70 minus 12 millimeters and that is basically 58 so 58 millimeters is gonna be the inside radius okay so um so far so good now what i need to know is that this the difference in distance between the outer perimeter and the inside perimeter so the outer perimeter i'm going to call it large d and the inside i'm going to call it small d now large d it's fairly straightforward this is one-fourth right so oops let me write this with a proper number remember that one-quarter one-quarter of the circle is basically one-fourth of the entire of the entire circle so we're going to do 90 degrees which is exactly one-fourth so it's one-fourth of the entire formula for the perimeter so 1 4 of 2 times pi times big r big r is the radius of the outside of my plywood so this is my large t and my small d is 1 4 of 2 times pi times the small r so fairly straightforward now if i make these calculations it comes to large d will be and i'm going to be using a calculator to make sure i don't mess up so large b will be zero times 25 times three times fourteen times two and times the large radius which will be 70 millimeters so that would be 109 comma 9 millimeters now small d is going to be 0.25 times 2 times 3.14 times the small r which is 58 millimeters so that's 91 comma one millimeters so now i have the difference between these two numbers which comes to 18.84 so this would be the difference of d minus d equals 1884 millimeters this is the key amount that i need to substract from my inside now let's get back to the curve bending technique so i have a piece of plywood and i'm going to be cutting groups right so we decided we said that this is how you actually make the curve bending technique now the question is now how many how many grooves do i need to cut so that i can bend at the angle that i want with the radius that i want and this is where this distance d where the difference between these two distances becomes critical so i have a distance here which is large d and a distance here that i need to cut down to small d so basically i need to get rid of all these material in my wood now obviously if i would get rid of this material only only at the very end so on this side there will be no bending will just break so that doesn't work what i need to do is i need to take this distance and distribute it through my piece of plywood so again i'm going to draw a piece of plywood this is large d and now i have a distance here which for us and for my particular case is 18.84 millimeters and this needs to be distributed along this distance so i have the large d which is uh which is 109.9 millimeters 110 millimeters and i need to cut out 18.8 millimeters now one more thing that we didn't discuss is how am i going to cut these grooves and i'm going to be using a circular saw right a hand saw and i know that my saw has a thickness so my blade has a thickness of about one millimeter so when i cut the groove i know that the space left in the wood is roughly one millimeter so if i need to cut out 18.89 84 millimeter so let's say 19. so we're going to approximate this with 19 millimeters so if i need to cut 19 millimeters out of wood and i know that every cat will remove one millimeter that leaves me with roughly 19 cuts that i need to distribute along this distance so i will need to make 19 of these cuts along this distance now because i want the cut to be completely round this means that this need to be distributed equally throughout my plywood so now the last bit is i have a hundred my large d is 109 so let's say 110 for approximation 110 millimeters and i need to cut 19 grooves into that distance so if i want to calculate what is the distance between each of these groups i just need to divide 110 divided 19. so 110 divided 19 which basically gives me 5.8 millimeters so this is 5.8 millimeters so this is basically this is all the information that i need at this point right so when i have my plywood i have a piece of plywood here i'm going to be marking a few things i'm going to be marking the start of the bending point the end of the bending point and i know that the distance between these two points is going to be roughly 110 millimeters and then i need to space 19 cuts in this direction and the spacing between these cuts is going to be 5.8 millimeters so i'm going to start measuring 5.8 millimeters from every single cut and space them out through the wood this is going to allow me to cut all my 19 all my knight in groups and this will finally give me a piece of wood where the outer perimeter is going to be 110 millimeters and the inner perimeter is going to be my small d which was 91.1 millimeters this is going to be 91.1 millimeters and the reason i know this is because by removing or by carving 19 grooves of roughly one millimeter thickness i'm gonna removing a total of almost 19 millimeters of material which is the distance between the outer perimeter and the inner perimeter so once i have done this the only thing i need to do is just bend the plywood to make sure and check that indeed it bends at exactly 90 degrees with a radius of um i think we set the radius to 7 centimeters from the outside now this is all the math that we have to do so now i know that i need to mark these are the key measurements i have 110 millimeters which is the bending point every groove 5.8 millimeters and 19 groups in total so the only thing left is actually cathode and show you how this actually works let's get on with it okay so um i took my piece of plywood with the markings that i did and i cut the 19 grooves um in the space that is going to be the [Music] the rounded part of the of the of the piece there is one key aspect which is how deep you need to set up your blade and um i don't have an exact answer to this but um i think that the key would be to leave at least in plywood the last hardwood layer intact so that you can bend it and if you want to have more flexibility on bending you can also make the uh the intact side a bit humid to achieve the bending now i've cut all 19 grooves so the question is does this bend to my desired specifications which is seven centimeters of diameter and 90 degree angle so let's find out i'm gonna just you know apply some force until i can't apply anymore so i can apply a bit more but not a lot more so you can see this is exactly 19 degrees um and now the question is whether this is the right angle and i think i'm gonna do that i'm gonna show you that on the ipad so that's about 90 degrees i'm going to trace the line both outside inside now the question is whether this is seven centimeters in diameter so i think this is about you know here and this should be around here or less so the question is how much is this distance and the answer is exactly seven centimeters i'm very pleased so this distance according to my ruler it's exactly seven centimeters see if i can show you this so the distance it's exactly whoops the caliper so that's that distance is exactly 7 centimeters so there you go that's it that's how you um the curve bending is rather straightforward just a few formulas and then you can get the bending right your specifications i hope that you found this useful i certainly would have found something like this useful before i did my first branding but now i know how to do this and i hope you do too uh thanks for watching and uh yeah see you next time cheers so i was done with the video but i find the bending of plywood so satisfying that i thought i thought i'm just going to show you one more time it's just fantastic look at this look at this it's great it's the shapes that you can make with this it's just it's just amazing and this is an extremely robust material once you put what you apply wood to the inside of the groups this will basically stay solid uh basically forever so how great is that and this is with a very simple uh hand tool no um no table saw nothing like this a very simple a handheld tool to get these groups and look at that perfect curve fantastic thanks

Channel: One Time Builds

Views: 91,148

Keywords: plywood, kerf, kerf bending, carpentry, math, wood, makers, firniture

Id: auLHu3s8B1c

Length: 17min 53sec (1073 seconds)

Published: Thu Nov 05 2020