Edge molding for plywood

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Forum topic by MrRon posted 03-01-2016 05:27 PM 571 views 0 times favorited 5 replies Add to Favorites Watch
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3891 posts in 2664 days

03-01-2016 05:27 PM

I’m in the process of building a shelf system. I am using 3/4” (.712” actual) plywood from Lowes ($42/sheet). The sheets don’t lay flat. That causes a problem when trying to apply a solid wood edge. I used a 1/4” rabbeting bit centered on the plywood edge, but due to the unflatness , the rabbet is not centered in some areas and centered on others. I used hold downs on either side of my table mounted router bit, but the rabbet is still not centered. Since the outside veneer is so thin, I can’t risk planing or sanding the edge for a flush surface. Maybe I could use a trim router and a flush trim bit. Any ideas? The edge trim strips were already milled down to .712” wide previous to installing.

5 replies so far

View CB_Cohick's profile


448 posts in 672 days

#1 posted 03-01-2016 07:51 PM

How about doing some edge banding instead of moulding?

-- Chris - Would work, but I'm too busy reading about woodwork.

View clin's profile


485 posts in 417 days

#2 posted 03-01-2016 08:20 PM

Since plywood won’t necessarily be flat, as you have found out, it’s hard to do this. While I would use iron on edge banding, you could make your approach work fine by over sizing the molding so it is wider then the shelf thickness everywhere. Then just trim it flush with a router using a bit with guide bearing.

-- Clin

View brtech's profile


882 posts in 2343 days

#3 posted 03-01-2016 08:27 PM

You started with an assumption that you should mill the edge to the thickness of the plywood, and things went downhill from there. Don’t do that: start with the edge piece bigger than the plywood and edge trim after you have it attached.

I would throw the edge pieces away and start again.

OTOH, if the plywood wasn’t flat when you milled the rabbet, how are you going to flatten it out later? Imagine you cut the rabbet on a curved board, and then straighten the board. Ignoring the edges, you couldn’t get the edge into the rabbet because it will “stretch” unevenly.

Consider making the edge a lot bigger than the plywood; maybe 1.5” finished. If the rabbet is not uniformly the same height from the top of the plywood throughout, consider clamping it down flat to your bench, hanging off the end a bit, and using a router with an edge guide to make the top of the rabbet the same distance from the top of the plywood for the entire length. It won’t be a uniform width when you are done, but the top edge will be parallel to the flattened ply.

Then cut a new edge say 1 9/16” high, and put the tongue in so the edge stands 1/16” proud of the top. Assemble the piece with the plywood clamped down flat and use a generous amount of glue on the entire edge of the ply and good pressure holding the edge to the plywood. Wait 24 hours before unclamping the ply to the bench. I’ll bet that ply will stay flat after it comes out of the clamps.

Then use a trim bit in the router to make the edge flush with the top of the ply.

View JBrow's profile


748 posts in 341 days

#4 posted 03-01-2016 09:35 PM


Starting from scratch and working to obtain a solid wood edge that is flush on both side of the plywood, clin’s approach would be my approach – use a router with a flush trim bit and slightly wider glued on edges so that the edges end up proud of the plywood face on both faces. I would add to clin’s comments by suggesting the flush trim operation be performed at the router table. Feather boards would keep the stock against the fence and a tall auxiliary fence would be installed for support. Balancing a handheld router on ¾” wide material is very difficult.

Unfortunately, if the edge is already glued to the plywood, the flush trim bit will only remove the lip standing proud of the plywood on the top. However the plywood lip on the bottom edge cannot be flushed up without ruining the plywood. The edge must stand proud of the plywood all along the length and on both faces for the flush trim option to be viable.

I like brtech’s idea to enlarge the front edge of the shelf from ¾” to 1-1/2”. As weight is applied to the shelf, it can sag in the middle, especially if the shelf is wide or more than 3’ long. Therefore I like to add a little more structure along the front edge. However, I would approach the joinery a little differently. My approach would be the cut a 3/8” deep x 3/4+” + 1/16” wide rabbet in the 1-1/2” edging material along one edge. Then glue and clamp the rabbet to the plywood edge – no tongue and groove. A dry run before spreading glue is a good idea, since there are two joint lines that must be tight. After glued in place, a flush trim bit is used to flush up the edge to the plywood face by removing the 1/16” lip from the 1-1/2” stock. This operation could probably be done freehand or at the router table.

View MrRon's profile


3891 posts in 2664 days

#5 posted 03-04-2016 06:24 PM

I solved the problem by narrowing the width of the tongue on the trim strip. I was then able to center the trim strips to the plywood edge. i then applied glue and used a pin nailer to hold the strips in place. The pins don’t even show

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