Stabilizing thin boards, with trim, vertically on a router table

Question

I have a 30" long, 1/2" thick piece of plywood. I want to attach a 30" x 1/8" x 1/2" pine strip to one of the long edges. I only have 3/4" pine to cut the strips out of and it's got a bit of a curve, so my plan is to glue it to the edge in its natural curve then trim it flush to the plywood with the router:

The only router I own is a trim router. I could freehand this but with only 1/2" to rest on it's difficult to keep it from wobbling, and also the cuts will have to be cautiously slow.

I have a very no-frills, basic table I made for it. I am more than willing to add features to it since this is a problem I'd like to find a long term solution to (there is a fence too, not shown, that's just some extruded aluminum angles with a wood face, but I actually prefer just clamping wood to the table for fences because I don't have a good fence adjustment solution with a wide position range yet):

I'd be running the board, with trim attached, past the bit like this:

But I'm not sure how to stabilize it (trim not shown in next pic):

How can I do this? The problems I've had while testing:

• Freehand, difficult to keep stable as mentioned above.
• I tried putting the fence in but with the trim sticking out past both the plywood faces, I couldn't figure out how to make that work.
• I also tried just carefully holding it vertically on the table. That was about the same as free hand, a little worse because it's easier to hold the router straight than it is to hold the plywood straight. Holding too high tended to pivot away from the bit, too low into the bit. Plus this was about as slow as doing it freehand.

My goal is to have a way to do this quickly and cleanly, and as perfectly flush as the flush trim bit normally gets it. I want to put the piece on the table, zip it past, and be done. I also want to be able to do this in the future so I don't mind investing time into jig building / table upgrades.

Answer 1

For edge routing, you need a tall router-table fence. Clamped to your router table, this provides a perpendicular surface to guide your boards past the bit. As the linked should point out, the bit gets buried into the fence's surface (ather than trapping the workpiece between the bit and fence which would almost certainly cause a high-speed kickback situation -- dangerous), so the fence can be used to control the depth of the cut. Fingerboards are usually mounted to the table go help press the workpiece against the fence and bit to ensure constant cutting depth.

(As @AloysiusDefenestrate pointed out in the comments, in this case making the fencs with a notch at the bottom edge -- or just setting it on top of a spacer -- would let the trim slide underneath and contact the bit while the panel rides safely on the fence and bearing.)

Oh, a few afterthoughts:

1) If you wanted to freehand this, clamping a 2x4 level with the top of the trim would give you a wider surface to ride on. Less effective if the trim overhangs both sides, unless you cut a notch in that support board's top inner corner.

2) If the right side of the fence is set back a hair from the bit while the left side is level with the bearing, you have essentially created a micro-jointer. (The fence I'm using now lets one side be shimmed out for just that sort of application.)

3) A horizontal router table, such as the ones used for "production" raised-panel work or mortising, would avoid the need to fight gravity.

4) The traditional, solution is to just grab a block plane and take off the excess that way... then, when you're close enough, switch to a sanding block for the last bit (which might be the case with the router too). Hand tools aren't always slower, especially when set-up time is considered!

Thanks to the commenters; their input helped improve this answer.

Answer 2

I think a tall fence, with a gap for trim, is the best solution, but I also had great success with the following experiment.

I wanted to solve the setup problem of aligning the fence with the flush trim bit so I constructed a single point-of-contact fence instead, that uses the guide bearing on the trim bit as the second contact point:

There is a 1/8" spacer under the feather board and fence to let the trim slide through. The big dowel doesn't rotate; I put some paste wax on the contact edge.

Here is a video of it in use:

YouTube

The biggest issue is the very end, after the plywood passes the contact point, is a bit tricky and requires some finesse (this is the sole reason why I think the tall straight fence is the more proper solution). The other issue is since there's no depth control you can't make light passes first, you have no choice but to take the whole thing down at once; I had one piece splinter a bit from a large cutting getting caught up on the way through.

I just chop off the short bits on the end with a flush saw afterwards.

Some construction notes:

• I was able to bolt it into the existing mounting holes for my fence plus one for stabilization. There are tee nuts under the table.
• The 1/8" spacer under the fence is just a piece of MDF cut to the same profile as the top/bottom then with a bit chopped off. It is not glued and can be removed.
• I trimmed the bit of the top/bottom around the dowel after construction to make sure it was flush with the dowel.
• There is a very small bit of flex perpendicular to the support board, it is not enough to have an effect, but it would stabilize it greatly to add a second small board perpendicular to that one. Alternatively, the support board could be oriented perpendicular to the path the piece takes so that any flex is in the plane of travel and doesn't affect the vertical orientation of the piece.

I am going to make a proper tall fence as well, and I am going to cut holes on either side of the bit gap to allow a flat piece of scrap to be temporarily clamped over the gap to help with alignment (rotate fence until bearing hits scrap).

The dowel thing seems to be working well however, and requires zero setup time aside from attaching it to the table.

Answer 3

For this particular situation, I would take your 2x4 or 6? fence and along the bottom notch or rabbet it to have a groove that is tall enough and deep enough to let the lip pass without obvious friction (on the bottom side facing the bit). That way you can have a tall fence to push the board against keeping it straight and still let the lip pass freely to be trimmed.

even better than cutting this on your 'fence', would be to take another 2x4 and attaching it to the face of the fence raised just enough to let the lip pass, this way it can be adjusted, as well as reused.

Kind of like this for the face, leaving a space on the bottom.