Bandsaw Jigs Session 5 Bandsaw Circle Cutter

If you've ever looked at a project that you want to cut parts for on your bandsaw that requires circles you may have said, eh, I'm not sure I can follow a line well enough to cut a perfect circle on the bandsaw. Well, we are about to cut a perfect circle on the bandsaw 'cause we're gonna use a bandsaw jig. So again, we'll go through how to use it, and then we'll look at how to make it for your saw. Here's the way this thing works, one thing to notice is bandsaw tables have a registration pin here in the edge and what it does is it helps keep the cast iron aligned. Cast iron isn't unlike wood in that sometimes when we cut a slot in it it reacts just a little bit. That pin has to come out in order for our circle cutter jig to go over the top of it. And because we're going over the top any little irregularities there aren't gonna bother us. Way this works is that it's gonna slide onto the bandsaw. I've got carriage bolts going through a strap, that strap as I tighten the carriage bolts is gonna go up against the bottom of the bandsaw table and hold everything in place. There is a dovetailed slider. And that dovetailed slider when I loosen this will oddly enough slide and that allows me to change the radius of the circle that I want to cut. So putting this device onto your bandsaw is pretty straight forward. We're gonna slide it on until a cleat that's mounted on the bottom of the jig, right about here, goes up against the edge of the bandsaw table. The thing that's really important that you have to do is control the alignment front to back. Here's what we want. We have a pivot pin. And in this case, we're gonna use this screw as a pivot pin. We'll talk in a second about the pivot I have at the other end. We need the center point of that screw perfectly aligned with the front of the bandsaw blade. So I'm gonna slide this back and then I'm just gonna have a look down this way. And lock the bandsaw table in place. So all I'm doing now is I'm tightening those wing nuts that you saw on the ends of the carriage bolts. And as the wing nuts tighten they bring that cleat up against the bottom of the bandsaw table to hold everything securely. Jig has made out of MDF which is nice for this 'cause it stays nice and flat. All right, that's nice and secure. That pivot point creates the radius of our circle. We don't need that just yet, I'm gonna slide that out of the way. One of the things I found is that when I'm cutting circles, especially in harder woods, if I simply start cutting, like this, and we'll pivot on that pivot point, the blade has a tendency to kind of stay on the outside of the material before it dives in and starts the cut. So one of the things I've found really helps is to establish a little notch or pocket for the bandsaw blade to start it. So I'm finding the center of my board, or at least the approximate center of my board in this direction. And then the pocket we create. And it looks like I missed that by a mile. That's better. The pocket that I create is gonna look something like this. So I'm gonna go ahead and free hand that into my board. Now we can start using our jig to make circle of magic here. I've got about seven and a half inches of material left there, that tells me how large a circle I could get out of this. Next step, we simply set the pivot point to blade to the radius of circle that we want to produce. Let's do a six inch circle. So I'm gonna set three inches from the blade to the center of that pivot point and then reaching under the table I'll lock that in place. Now we do our circle by putting the pocket so it surrounds the blade. Now, when you do this, don't lean on the board as I'm putting it against the blade. We want to just kiss it against the side of the blade so we don't distort the blades position and then push down and I'm gonna kind of squeeze instead of just push. I don't want to push down and tilt my table out of being perpendicular. So here's what we've done, set the pivot point. The board is now seated on top of that pivot point and all we have to do now is turn on the bandsaw and spin the board, carefully. And as we spin the board we're gonna end up with a circle. Well, we ended up where we started, that's a really good sign. Regarding that alignment between the pivot point and the front of the blade, if you don't get that right this is where you'll find out. Because if you don't have that alignment correct you won't get a circle, the blade'll start to run off track. The other thing that can throw you off in cutting the circle here is two things, if the blade isn't sharp it's gonna be impossible for it to do a good circle. And if you try to feed too fast it's not gonna wanna cut a circle. So like all cutting tool operations, listen to the machine, let it do its thing and you're gonna be okay. And when that comes off. We can see there's our circle. By leaving that pivot point right where it is, we can cut another one and another one and another one and they're all gonna be the same. Now a good question would be, what's the deal with the other pivot point we have? For smaller circles like we cut here I find that that tip of the screw, that's just a sharpened wood screw in there right now as a pivot point, that works just fine. On larger diameter circles the quarter inch dowel gives us a much more substantial anchor point 'cause that's gonna sit in a blind quarter inch hole we've drilled in the bottom of our blank. That procedure we used to cut the circle'll be the same. So for me, when I get out here some place, eight, nine, 10 inches in radius, then I'm gonna start using the quarter inch dowel as a pivot point instead of the tip of a sharpen wood screw. Set up procedure's gonna be the same, center of the dowel aligned with the front of the teeth on the bandsaw blade. That's how that circle cutter works, let's have a look at what parameters you gotta pay attention to to make one of these for your bandsaw. We're gonna do the circle cutting jig next and this is the most complex jig we're gonna do in this class. And the reason for that is I really can't say, make this part this big and this part this big because there are a lot of variations that'll depend on your particular bandsaw. So here's what we're gonna do, gonna start by using the jig that's already made and give you an overview again, of how that goes on the saw, how everything comes together, how it works. Then from there, we'll break it down and start to talk about what you need to do dimensionally with your machine to get a jig goin' in your shop. So let's look again at how this works, components of the jig, here's what we've got. I made this one out of MDF, MDF or melamine would be a good choice for this. And I would stay away from plywoods 'cause they do tend to cup a little bit. And because of the size of our jig if that cups over time, gonna have a problem. So something in the particle board family is more likely to stay flat. On the bottom of the jig we've got a cleat and that's gonna end up under our bandsaw table and it's gonna capture the bandsaw table so that when we tighten the wing nuts we can keep everything in place. Now, as we keep going underneath the jig here, there's another cleat. And this one's job is really simple, it tells us when to stop. This cleat goes up against the edge of the bandsaw table so that as we slide this on it creates a registration point. Last cleat on the bottom. That one has got a threaded insert in it. The threaded insert is accepting this bolt so that as I tighten this it locks the sliding dovetail in place. Those are our components. Now here's what we do for putting this on the bandsaw, it's gonna slide on, like I talked about, that center cleat hits the edge of the bandsaw table. There, that's what tells us when to stop. Then remember that when we sight in our center pin we're aligning that with the bandsaw blade. So as we do that we need to have some travel in this direction, we need to have some wiggle room so that we can make that adjustment. Understanding all of that now, let's talk about how we get one of these for your bandsaw. Got a piece of MDF. And this single slab is gonna become the top part of my circle cutter. We're gonna cut the dovetail slider from this part. So, here's how this works. Make the length of this piece three inches greater than the overall front to back of your bandsaw table. Now, when you do that, be sure that you remember to measure from the front of this fence bar all the way to the back of the table. So it's not just the cast iron table itself, we've gotta incorporate this. The carriage bolt that holds this in place is gonna end up beyond that front rail. So that's step number one, that gives you this dimension. The width dimension just depends on how large a circle you want to make. I'll tell you a weird story, I had a jig like this that I showed in a woodworking magazine many, many years ago. And then when I was teaching at a woodworking show a guy came up to me and said, oh, I'm using your circle cutting jig. We're cutting 48 inch diameter circles on a 14 inch bandsaw. So this jig, identical to what we were doing except that it went way out here. They put an auxiliary leg on it to help support it, but the concept was exactly the same. So you can make this as wide as you need to for your circle needs. In this case what we've got is a board that's 15 inches wide, that's going to let us do circles up to about 26 inches in diameter. In other words, about a 13 inch radius out of our 15 inch wide board. So again, you can change that as you need to for your dimensioning, but 15 inches wide, pretty good starting point. Now we've got this on the bandsaw So we've got this board cut and ready to go. The next thing we need to know is approximately where this board is going to live on the bandsaw when we set it up as a circle cutter. What we're going for here is where dimensionally the slider should end up so that it can line up with the bandsaw blade. Now keep in mind, we're three inches too big. So we've got some travel in this direction to make a final adjustment, but we do want to get this close. So what I would do at this stage of the game is we want to measure so that we have the same amount of material projecting past the table, should be an inch and a half on the back and an inch and a half on the front. And when you're in that position, take a pencil. And from the blade, a pencil whose lead hasn't broken on you. From the blade, we're gonna measure back a half inch and make a mark, measure forward a half inch and make a mark from the front of the blade. What that's gonna do, those two marks are where we're gonna make this cut and that gives us a one inch wide slider. And again, it provides some wiggle room so that when we put this on the saw we have some adjustability. So that's our starting point, get that far in your layout and then we're gonna have a look at our next step. Let's take advantage of being here on the bandsaw and get another mark on here. Remember that underneath here we're gonna have a cleat that's gonna end up up against the edge of the table. So on your bandsaw, the location of this cleat is controlled by the distance from the blade to the edge of the table. Well, a really easy way to make that location happen is right now we're just a little bit away from the blade, that's fine, about an eighth inch off of the blade, and I'm just going to reach underneath and I'm going to put a mark on the bottom of my MDF, I'm just tracing the cast iron so that we get this mark this distance, from that pencil line to there, cleat on that side of the line. We're gonna transfer that all the way the length of the board and eventually that's where that cleat is gonna go to provide that registration spot that tells the jig when to stop. Now, let's revisit this whole dovetail slider business. From here I'm gonna go to the table saw and at the saw what I'm gonna do is I'm gonna angle the saw blade at 45 degrees. And then I'm gonna use these pencil lines to show me where to make these cuts. And I'm gonna take that dovetail slider right out of the center of our material. So I'm going ahead for the table saw and make that happen. Then we'll come back and we'll be pretty close to starting some assembly on this jig. Back at the bench, ready to start some assembly. Let's look at the finished circle cutter, just to see where we're going with this. Next thing we're gonna do is get this cleat on the bottom, which'll lead us to getting holes drilled in this cleat. So remember that this cleat is located, based on that distance from the edge of the table to that position that we marked out on the bottom a step ago, and I've got those lines drawn across my board. Now let's go back and talk about that table saw operation for a second. On my dovetail slider I missed one of my pencil lines a little bit. I don't care, that's fine. 'Cause remember, we've got some wiggle room when this whole thing goes onto the bandsaw. One of the reasons I'm building it this way is so that we don't have to dial this in to bazillionsths of an inch. So if your dovetail slider ends up a little bit too wide or a little bit too narrow, you're still gonna be okay as long as you started with that one inch flat on your layout. If we're a little bit less or a little bit more than one inch on the flat, it's gonna be fine. Now think about what's gonna happen here. We're gonna put this together with our cleat. Now, in my case, this cleat needs to be shorter than the overall width of my jig. And the reason for that is the fence of my bandsaw, the rail for the fence, hangs down a little bit here on the front, or projects up underneath the table here in the front. So if the cleat was full length it would interfere. So this is another thing that you're gonna have to check on this two inch wide cleat how long can it be. If you can make it full width make it full width. But if you need to shorten it up, shorten it up. Now when we put this together, if it ends up too tight we're not gonna be able to slide this. And the solution for too tight is very simple, I'm gonna take a couple of business cards and we're going to use those as shims as we put this together. I'm gonna put one up here and one back here. If for some reason you don't have access to a business card, these are about three thousandths of inch thick. So that's the space that we're creating between the slider and the board so that, of course, when we remove those it'll still be able to slide. All right, here's how this works. My short cleat, it's gonna go on the pencil line, I can see it on my side of the line here. And we're gonna tack that in place using glue and staples. You can alternatively use a brad and then get some screws in there. Bottom line is, we've gotta have some fasteners in there that are holding it until the glue dries. Now, let's pay attention to our gluing operation. I can apply glue out to about there. No glue where the dovetail slider's gonna live. Then I can start about there and go to the end. I've got two layers of three quarter inch MDF so I'm using one and a quarter inch staples. Want to make sure that they don't go all the way through and on the edge of my material I'm checking that all three components are in line with each other. That gives me a registration, a straight line across the edge. Lay it onto my pencil lines. Now the whole shim deal isn't critical yet 'cause I haven't done any fasteners out here. So I'm gonna double check at this point, I want stuff to be snug but if you push too hard it's possible that that slider starts to climb up out of that Valley that it's in because of the taper on it. So just a little bit of lateral pressure, make sure we're snug against those business cards. Then when those come out we still have the ability to slide. And that can come out and stay out for now. Our next thing is we're sliding onto the table like this and that cleat creates our stopping point. So that means that our carriage bolts are up here on this side. Now again, you're gonna have to do a little bit of checking on your machine. what works for me and my bandsaw is five and a quarter inches to the center of the hole for the carriage bolt. Three quarters of an inch in to the center. Same thing on the other end. And I'm gonna get a cleat under here just to keep that from rocking for now, we're not ready to drill all the way through yet. Now here's what we need for a carriage bolt, let's look at our existing. There's gotta be a counterbore for that head to go into so that it's below the surface. I'm using quarter 20 carriage bolts. That means that a 5/8ths Forstner bit will give me a large enough diameter hole for the head of the carriage bolt to seat into. We do the Forstner bit first. So if you do this out of sequence it becomes problematic. If I drill a quarter inch hole when I come back with the Forstner bit it's really hard for the bit to center and make its drill, make its cut. So what we need to do is drill this one first, get that just right, then we'll go back and do the quarter inch hole. If you want to do this on a drill press there's nothing wrong with that. What we need to do, this is a fairly critical step here, we need to get that deep enough that when the head of the carriage bolt goes in there it's gonna seat below the surface. Obviously I'm drilling it by hand and I just double check this by putting the bolt in there upside down. And what I want is for the flat component of the metal to be below the surface of our MDF. On that side, it's just fine. And once you do one and you get it right we can look at the Forstner bit and see, well, okay, there's about a eighth inch of Forstner left above the surface when the depth was correct, I'll drill to that same depth on my other hole. This works great on a onesy twosy basis. If I was counter boring for a dozen carriage bolts we'd be doing it on the drill press. Perfect. Now my next trick is we are gonna drill all the way through. So to do this your best bet is to do the cleat and the body of the jig all at one time. So what I want to do is get the cleat located under the hole, and the deal with that cleat is that if your jig started 22 inches wide then the cleat should be 22 inches long. They're two inches wide. So then I can locate that under the hole position and... Switch to a quarter inch bit. So one of the things that's maybe coming out of this for you is jig building for me is not like building a piece of fine furniture. It's a little bit more loosey goosey, but it gets everything to work and we're constantly going back and forth to the tool to make sure that things are gonna play nice together, but don't sweat measuring stuff out to bazillionsth of an inch, especially a jig like this, it just doesn't demand it. So what I did is I visually centered the cleat under my hole in the surface. We're gonna drill all the way through, that's why my scrap board is underneath. We can use a carriage bolt to hold that in registration. Let me get the junk out of there. That's better Carriage bolt'll pin those together so that then I can come to this end and do the same thing. Now on this end what you might notice is that my cleat is sticking past the body of the jig. Why is that? Well, they started as the same length, but we then took to saw curves side of the body. If you don't like that, mark it, you can cut it off on the miter saw. In this application that doesn't bother me. So same deal, I'm centering visually the counterbore over the cleat. And then drill through both together. Doing it this way everything has to line up because you drilled it all together. This takes care of the alignment cleat, the fastening from the bottom cleat. Next thing we want to have a look at is the cleat on the back here that we put our threaded insert in and the parts that go into the sliding dovetail for our pivot points. Let's start with the work we need to do on the dovetail slider, then we're gonna go onto our final cleat and look at the anchoring, the lock device that we put in there. Got two things going in the dovetail slider. One is simply a screw, the other is a quarter inch dowel. And again, the dealio with this is that on small diameter circles I'll seat them onto that sharpened tip of the screw. On larger diameter circles I'll do a quarter inch counterbore in the back of the blank and seat them onto the quarter inch dowel. Let's talk about that screw first, I started with a one inch long wood screw and then holding it in a pair of vice grips on a grinder I sharpened that tip. Couple of problems with just the tip of the screw, one is that a lot of times that tip is not really well centered on the screw. And so it has a hard time seating on the back of the circle blank. And the other thing is that if I leave it an inch long it's too long. I don't want a quarter inch of screw sticking out, I want about an eighth of an inch of screw sticking out. So do a little grinding on that tip to get it where you want it to be. The quarter inch dowel is easy, we just need a piece of dowel that's about a half inch long or so. Now with that screw what we're gonna do is on your slider working from the back measure and find the center. And then from the end we're gonna come in and a half inch. And in that position drill and countersink just like we normally would if we're driving a screw. And then we can do a little test here and see if I countersinked enough. So here on the face, do I have enough tip sticking out? And I'll show you a little trick here. See how that MDF tends to kind of mushroom up? Let's take the screw back out, come in from the other way, and just barely kiss the counter sink down. And it creates a little well, a little pocket on the top face. And that got rid of all that extra stuff that was sticking up. There's our eighth inch sharpened tip sticking up just the way we want it to. On the opposite end, same deal, on the flat we're gonna measure to the center. Half inch in, there's our point. On my quarter inch drill I've got a piece of tape as a flag for quarter inch depth. And once that's set you'll be able to put the dowel in. Slider is set. Now, our final cleat. Here's what's gonna happen. Got a couple of things going on here, one that you haven't actually seen yet. A threaded insert is gonna go in there. and that threaded insert is gonna receive our locking bolt. And this, you might find this hard to believe, but this is a shop made blocking bolt. Just a carriage bolt, 3/8ths diameter, And I put a wing of wood in here and sandwiched it in place with a nut in a washer so that I can turn this. If you want to go and get a commercially made, studded wing nut for this that's just fine. This let me use stuff that I had laying around the shop. You could go smaller, it doesn't have to be 3/8ths, you could go to a quarter 20 bolt for this, that would be just fine. Now what happens is when I tighten this from the back, of course, the insert is gonna be seated in the cleat. The problem with repetitive use of our cool circle cutter is that especially if we cut circles in the same spot repeatedly the tip of that bolt could start to make a divot there. And then if we want to be just in a little bit different spot, so let's say we cut a bunch of circles at five inches and we leave a dimple. Then we want to go to five and an eighth, it might want to always slide back into that dimple we created at five. So let's prevent dimpling, my million dollar idea, or it's actually a one cent idea, is we're gonna use a penny to spread the load, to distribute the pressure from the tip of that bolt. The penny is much less likely to make a dimple in the back of our slider because its diameter is so big. So we gotta drill two holes here. We have to do a counterbore, three quarters of an inch is what works for a penny. Then we have to drill another hole that's gonna receive our threaded insert. So here's how we go with this. Cleat goes on this side of the jig, gonna flip this over. Now the thing you may notice here is that like my other cleat, this one is actually also too long because we cut those two saw curves out of it, that's okay, that doesn't bother me. What I'm looking for here is I want to see the window here that's created by the dovetail opening. Because when I put my penny in and my threaded insert I want it to be centered on the width of the cleat and on the width of this opening. So I'm going to put my pencil in, hold it straight up and down, and just trace straight up and down, trace. Now like I said, we have two sets of holes to drill. We're gonna do the three-quarter inch, do the bigger one first. Centered on the cleat, centered on the opening. And just like we did with our carriage bolts, like we did with the carriage bolts, do a little drilling, do a little testing. Ooh, that came out great, we want the top of the penny to be even with or slightly below the surface of the MDF. That one's done, now let's not lose that. By let's I mean me. Now for your threaded insert, the size hole you drill is gonna depend on what you're using for a threaded insert, so size that accordingly. Next step then, threaded insert goes in. Now with threaded inserts, if you have a look at this, they've always got these slots across here as though I could take a big screwdriver and just run that in. I don't know about you, if you've used these before, I've never had success with that. What works better for me is use the same size bolt as fits in there and the key is that nut. And the nut'll let us lock against the threaded insert and then we can just use a wrench in order to drive that. MDF being MDF, it's dimpling it up a little bit on the backside. That doesn't bother me because it's the backside, that's why we're driving it from this side. Now I got a watch on the other side that we don't go too far and get up against our counterbore for the penny. Then we can back that out. So sharp crack of the wrist there gets that loose. And that will then receive our locking bolt. Now we're ready to get things together here, which is bring our jig back. There's gonna be one distinct way that this goes together, this ain't it. Gotta go this way. Because our spacing is already locked in place thanks to the center cleat, we can put this on without using the business cards as spacers. And that gets us to the end of our jig building experience with the circle cutter. So let's just get everything, kind of put it together here. All right, penny goes in. Dovetail slider goes in, this is the one that goes with this jig. Lock that in place. And then on the other end, a couple of carriage bolts and our other cleat. That'll end up under there, that's gonna capture it on our bandsaw. Remember, this is going to be built size specific for your particular bandsaw so follow along, pause, rewind, go back and look at parts as you need to so that you can get your circle cutting jig dimensioned to be a perfect fit for your bandsaw. And this is gonna work great in your shop for perfectly cutting those circles.