router/jig gurus: mortising curved stretchers

[jp]

Hi all,

Working on a pretty standard Arts/Crsfts rocker. Using QS ash.

As you'd expect the back consists of curved upper and lower stretchers with vertical slats mortised into the bottom of the top stretcher and into top of the bottom stretcher.

Still with me?

Anyway, I want to route these mortises. Have any of you built a router fence that allows you to follow the curve of a chair back stretchers?

Naturally i don't want the mortises themselves to be curved. My thought was I could avoid this by keeping them short in length, and by using a fence that, instead of consisting of the cutoff piece from the stretcher, is instead a flat piece of stock with two points (think the bottom of a capital "W") maintaining contact with the side of the stretcher.

Theoretically, if the inside radius of the stretchers is the same, and true, it seems to me like it would work.

But before ruining stock and/or fingers, I thought i'd check in here.

Am i heading in the right direction here? Anyone dealt with this challenge before?

thanks!

[Ken Massingale]

How wide are the stretchers? Can you route the mortises before cutting the curves in them?
ken

[Tom Miller]

You could avoid the problem altogether by using a round tenon. There are techniques for making round tenons on the ends of square stock, or you could use a floating tenon (aka dowel).

Just trying to think outside the ol' bun.

I have cobbled up a curved fence for my router table before, too. (I was making Thomas the Tank curved train tracks.)

Regards,
Tom

[jp]

response

How wide are the stretchers? Can you route the mortises before cutting the curves in them?
ken

Thanks Ken,

MY bad. First off, i should have called these RAILS.

OK, so the rails are cut from 8/4 stock. They end up around an inch thick. The challenge is that the mortises, though sq., are laid out to follow the curve of the back rails, so whether you mortise first, or cut the rails from the sqare stock first, i still need a way to giude the plunge router aloing the curve of the face of the rail. make sense?

check out this image (courtesy PM): http://media.popularmechanics.com/images/3077_17.jpg

In this case the woodworker is using a drill press to rough out the mortises, then he'll clean up with chisel. I don't have drill press, and love the ease and quality of plunge routered mortises.

[JR]

Thinking out loud here...

It would seem like you'd want to keep the stretcher fixed in position and move the (plunge) router, as opposed to running the stretcher through a router table setup of some sort.

I guess this is what your W with flat bottom does? So you can use a router edge guide against the W flat bottom, moving the W to the various mortise positions.

If that's what it does, it sounds good. The challenge would be to get the top and bottom matching mortises to line up well. Maybe you could put a mark on the the center point of the W to indicate center of mortise. Then have a constraining setup on the face of the W - think of a router dado jig that allows the router room to roam up until the limits of the dado width and length.

You'd line up the center mark on the mortise loction and clamp down the jig. Plunge the router in and move it back and forth to the limits of the stops. Release the jig and reposition to the next mortise location. If your centering marks are consistently applied to the top and bottom stretchers everything should line up reasonably well.

I think.

JR

[JR]

Seeing the drill press jig made me think a little more out loud (I'm talking to myself now!). How about this setup?

The green part is the jig, the brown is the rail. The jig is fixed now and the rail moves from position to position, and is then clamped down (to the jig? I dunno.)

Anyway the edge guide rides on the flat portion of the jig. Stops on the edge guide constrain the router movement to the length of the desired mortise.

JR

[LarryG]

You're on the right track.

Or, if you prefer, what JR said. (EDIT: In his first post. I'm not sure that second one is what you need.) There are endless variations on how you could do this, but they all come down to the same basic thing: you need something against which to guide the router, with stops to limit the travel.

I would probably do this by making a jig with an opening the size of the desired mortise bit + clearance for a guide bushing. I'd install four to six (in two rows or two or three) short locator blocks on the bottom side, into which the curved workpiece would fit. One row of locator blocks would follow the inside radius, the other the outside radius. Slide the workpiece between the two rows of blocks until the mortise window on the top side aligns with the desired mortise location, clamp it down, and make the cut with a plunge router.

[jp]

Or, if you prefer, what JR said. (EDIT: In his first post. I'm not sure that second one is what you need.) There are endless variations on how you could do this, but they all come down to the same basic thing: you need something against which to guide the router, with stops to limit the travel.

I would probably do this by making a jig with an opening the size of the desired mortise bit + clearance for a guide bushing. I'd install four to six (in two rows or two or three) short locator blocks on the bottom side, into which the curved workpiece would fit. One row of locator blocks would follow the inside radius, the other the outside radius. Slide the workpiece between the two rows of blocks until the mortise window on the top side aligns with the desired mortise location, clamp it down, and make the cut with a plunge router.

You guys make me feel like a maniac. I was just gonna freehand to the layout lines once i had the edge guide piece figured out. I was planning on a guide for just one side of the rail, but LarryG's idea sounds better. On the other hand, if the edge guide is only referencing one side of the rail wouldn't i be dealing with fewer imperfections than if it was referencing both? (Once i bandsaw the curves it's the belt sander for fairing.)

My plan was to clamp together both rails such that i can fair the curves as if they were one. then, when i use this inside curve for reference, any imperfections will be matched on both pieces.

Now that i think about it though it makes more sense to use the outside of the rail, then there's less likelihood of the fence getting stuck.

[atgcpaul]

My teacher (Russ Filbeck) makes a lot of ladderback chairs
using steam bent or bent lamination techniques. Here's
some of his work. http://www.palomar.edu/woodworking/html/CFT155_156.html

I thought for sure he'd use a router and a template but nope.
All hand cut mortises and tenons. He says it's imperative
to do all the mortising after making your curves because
the bend is not always predictable. It took him just a few
minutes to chop out a mortise for one of his slats. With
some practice you can get there pretty quickly.

If you're taking thicker stock and just bandsawing it to a
curve, then you could do as was suggested earlier and cut
them out beforehand. Making a slot mortising jig like you'd
do for loose tenons.

How are you going to make your tenons? Is the slat
the tenon with no shoulder?

[LarryG]

Any of these will work.

When I composed yesterday's reply, it was at the short end of the day and I had one foot out the door. I looked at JR's sketch (in his second post) and drew a blank. Now, on second look, I get it. That'll work fine.

atgcpaul's comment about a "slot mortising jig like you'd do for loose tenons" is exactly what I was trying to describe.

And actually, that's what JR's proposed jig is, too. The only difference is whether the router bit is positioned by an edge guide, sliding along a fence, or a guide bushing, moving back and forth in a slot.

[JimD]

We sit at 4 chairs with slats like this most nights at our kitchen table. My back rails are straight and flat, however, following plans from Woodsmith. I made a plywood template for the back lets, the complicated part, so I could make all 8 legs the same. It contains 1/2 inch wide slots for a 1/2 guide bushing on my PC 690 series plunge router. I used a 1/4 solid carbide upcut spiral bit. It took a little while to make the jig but it saved time overall. I made a jig to allow me to easily cut each of the 1/2 wide cutouts in the main jig (the same way except 5/8 guide bushing and 1/2 inch router bit).

Jim