Make a pattern using elliptical sticks, and then use a router with flush-cut bit to replicate onto the big stock
I'm in the shop today making parts for this backyard pergola. One of the design elements is an elliptical cut making the sweep in the bottom of these haunches that will hold other parts of the pergola. In this video, I want to show the process I use for creating smooth, consistent, accurate results considering the method uses basic shop tools.
I want to show the process I use for laying out and creating this pattern and then using the pattern to produce consistent, accurate results. Because I'm using a range of lumber sizes for the pergola, starting with 2x12s, going all the way down to 2x4s, I need to make a separate elliptical pattern for each so that the proportions look nice on the width of material.
I started out with the 2x12s in this large pattern, and I'll use the same process to create a slightly smaller ellipse of a different proportion for other 2x10 numbers on the pergola.
01:21: The first thing we need for laying out an elliptical pattern is the major and minor axes of the ellipse, where a circle has one center point and one radius. An ellipse has major and minor axes that give it the elongated shape, and the pattern we're making is for one-fourth of the ellipse which will form the cut on the joists for this pergola.
I have a dimension of 6-1/4 for the minor axis and 10-1/2 inches for the major axis, and those are the two dimensions I need for laying out a pattern for drawing the ellipse.
And when someone asks me how do I draw an ellipse, I say, "Well, with an ellipse stick." Right? To make an ellipse stick, I just need a scrap of wood, preferably somewhat straight, and the length of the stick needs to be a bit greater than the sum of the major and the minor axes. In this case, it'd be about 18 inches. I got a stick that's long enough. I'm just gonna draw a reference line along the stick.
02:27: I need to make three marks on here. One is the major axis, which is 10-1/2 inches. And the other one is the minor axis, which is 6-1/4 inches. Hold 16-1/4, mark 10. Major axis. Minor axis.
To draw this elliptical pattern, I'm just gonna use a mechanical pencil. This is the kind I like, these Paper Mate ones that have a twist-out lead instead of a clicking lead. That way I can set how much the lead extends so that it will draw a good mark but not snap off.
The caliper tells me this pencil is just slightly over 5/16 of an inch. I'll drill a hole at the center mark for a pencil. Redpoint bits are good for this because the center spike holds the drill bit accurately on the mark. Using the drill press assures the hole go straight through the stick.
For the two guide nails, I use a small drill bit to create a straight pilot hole and then drive a nail through. I do a little fussing around up front to get a nice accurate ellipse stick for a more accurate pattern.
04:05: Now, I simply drive a straight hardened nail through each of the guide points. And then the pencil gets inserted through the drawing hole, and because the pencil fits a little bit loose, I'll add a piece of masking tape to snug it up.
The goal is to have the pencil firmly in place and the guide nails to extend further through the stick than the tip of the lead. The process is a same for drawing any ellipse. The only adjustment is in the major and the minor axis distances to change the proportions of the arc.
This is a piece of white melamine MDF. It's extra nice 'cause it's easy to see and use and mark on. This pattern will be used on the 2x10. I'm gonna lay out a nominal 9-1/4 inch width. That'll come in handy later. And the ellipse will be 6-1/4 in. x 10-1/2 in. I don't need to make these marks because they're built into the stick, but I'm drawing them on here for reference.
The pattern piece needs to be big enough so that the two guide points can follow both edges. And because this piece is narrow and the guide nail is gonna slide off the end, I'll just tack the pattern temporarily to another piece of material until the ellipse is drawn.
If you don't have a magnetic tack hammer, you need one.
05:56: If I was using a bigger scrap of MDF, I wouldn't need to tack the second piece on here. And this is the cool part, once the guide stick is made and the template material is laid out with two edges that are long enough, it's just a matter of running the guide nails along the edges to draw the quarter of an ellipse.
That's the nice thing about the mechanical pencil, I can just extend the lead. I draw off the edge of the pattern, scribe it through. And that's all there is to it. I have a perfectly drawn one-fourth of an ellipse with a minor axis of 6-1/4 inches and a major axis of 10-1/2 inches.
I'm using a bandsaw to cut out this pattern, but it can be done just as well with a scroll saw or a jigsaw. I pay very close attention to leave the pencil mark, plus a little bit, that way I can true the pattern up and end up right at the pencil line.
07:17: The more accurate you make this cut, the easier it is to true up the curve. You can see right here I actually took too much of the line, so now I'm gonna have to sand the line away on the whole pattern to keep it accurate. I like to clamp the template in a vise to make fairing this curve easier.
How tight the curve is, determines what shape of a sanding block I use for the fairing process. This is the main reason I like to use 1/4-inch MDF for my patterns. It's easy to shape very accurately quite quickly.
08:08: I use 36 grit for the initial smoothing process, where I take out the saw marks and even up the bumps.
08:26: And I'm sanding heavy on each end and avoiding that center spot, 'cause that's where I cut too close to the mark. Once the curve looks smooth, I'll switch to 80-grit sandpaper.
08:46: And that smoother finish allows me to feel whether the curve is fair or not. I also like to just eyeball along the curve to notice if there's any bumps or dips in there that I don't necessarily feel, but I'm liking that.
The best thing about it is it just took a couple of minutes to make this pattern true and accurate, and now every piece that I route to this pattern will come out identical. One added twist to the final shape I'm looking for is a 15-degree angle that starts at the end of that ellipse. And to keep the drawing process simple, I started out with a square pattern and now I'll add that 15-degree tilt which is a piece of cake.
And if you're not using CA glue in your shop yet, you will be after this. I'm simply spraying this Stick Fast CA activator on the scrap piece of MDF and adding Gorilla Glue's Super Glue to the pattern piece.
10:19: Like I said, if you're not using CA glue in your shop yet, you will after this. The folks that are using it smile when they see how fast and strong that glue is. Now all I need to do is trace a 15-degree line on here, and I have other angle marking tools in the drawer, but I was too lazy to get it out.
10:54: Now that the template's made, all I need to do is add a guide block. I'll mark out 9-1/4 inches on the back side of the template and clamp the guide block accurately on the 9-1/4-inch mark, and we'll add a couple small screws to hold things in place.
11:29: And because a small piece is glued on, I'll add an extra screw for it just in case it gets bumped some more along the way. I'll point out here that I chose to make the pattern in a right-handed format, if you will, so that when I'm routing these pieces and the bit is spinning in a clockwise direction, it's going off the grain.
If you were to do the whole thing backward and the wood grain is running like this, and the router bit's turning this way, it tends to dig in and tear out the wood. By going this way, it makes a very smooth, consistent result and I can just flip the pattern or flip the piece from one end to the other so that I'm always routing with the cutter direction going off the grain of the wood.
12:19: I marked the pattern for its various dimensions for future reference, as I'm working on the different parts of the pergola. Once the pattern is made, using it is a simple quick accurate straightforward process. Simply lay the pattern on the piece and mark out the cuts.
With this particular joist design, I'm just gonna cut this angle on the miter box rather than following the template for that every time. I don't often have that luxury, but because I have it, I'm gonna use it. The haunches I made are short enough pieces where I could rough cut the ellipse on the band saw, but because this 12-foot joist would be difficult to maneuver accurately on the band saw, I'm just gonna use a jigsaw instead.
13:44: Here's a little bit of a pro tip. When I'm cutting with this jigsaw, I'm putting sideways pressure on it in that direction, so if there's any flex in the blade, it tilts it out away from the final mark.
If I'm not paying attention and put sideways pressure this direction, the blade can tilt like this, and although I think I'm leaving myself a strong 16th of an inch to trim off with the router, the blade can angle down far enough and actually cut into the piece. Pay attention to the direction of feed pressure with the jigsaw.
14:16: The final step here is to use a flush trim bit with a top bearing guide to true up the arc. I make sure that the bit is set so that the cutter meets the template but then the bearing has enough surface to ride on. If the bearing is set too shallow, the edge of the bearing will wear off the template and make for an inaccurate cut. If the bit is set too low, then it doesn't cut the top surface of the piece.
This bit has a cutting length that's more than an inch and a half, so I can do this in one pass. With a shorter bit, it could be done in two passes, the first pass with the template and then the second pass with the guide bearing riding on the cut made by the first pass with the router bit.
Hope that makes sense. In some instances, I'll use clamps to secure the pattern, but I prefer to use short brads because I know they're not gonna move.
15:17: A couple of number 18x5/8-inch brads are more than enough to hold this pattern permanently in place with this angle cut perfectly flushed with the saw cut and made with the miter box. This joist ends up being a skinny 9-1/4 inches, so the template hangs over the bottom just a little bit, and for a pergola, that's not gonna be an issue.
You're always better off having the pattern extend beyond the edge of the wood than the other way around. I prefer using a D-handle router for this operation. I wanna make sure that the router is sitting flat on the surface, and then carefully and steadily feed the router in this direction for the smoothest cut.
You need to remember to be extra cautious when working with this setup. There's a lot of exposed router bit here without a guard, and it pays to remember that any part of you that comes in contact with a spinning router bit, you ain't getting back.
16:36: As I do each successive joist, it becomes more of a system, more of a production process. I can duplicate these joists pretty quickly by first cutting the 15-degree angle on the miter box, tracing the template, cutting with a jigsaw, placing and routing to the template, and then easing the edges with a 1/8-inch round over bit.
16:57: And that right there, folks, is how I go about producing smooth, accurate, consistent elliptical profile cuts on the end of these pergola joists.
I was undecided how to wrap up this video, so I guess, while I'm finishing up routing the small shade bars for the pergola, I'll just say thanks for checking out Next Level Carpentry channel on YouTube.
I hope that some of the things you learned watching this video help you take your skills to the next level.
If you like what you see here, I hope you'll subscribe, spread the word around a little bit, and feel free to comment, let me know what you think of some of the methods and techniques.
Thanks for watching.
—Matt Jackson is a master carpenter, remodeler, SketchUp Wiz, YouTuber, and contributing editor to ProTradeCraft. He lives and works in Rapid City, South Dakota.