Precision End Trimming

How to Trim Wide Parts Flawlessly

This part of the job is all about preparing the ends of the table top and shelves so they’re perfectly straight and smooth using a router and flush trimming bit. You could cut parts to length with a saw then smooth the cut surfaces with a hand-held belt sander, but you’ll be amazed by the accuracy, speed and results of the router-based technique I’ll show you here.

flush_trim_tableAll flush-trim router bits have a bearing that’s exactly the same diameter as the straight cutters forming the bit. That’s what you can see here in the photo at the left. The router is sitting in a router table with the bit pointing up so you can see what’s going on better. With our table top and shelf, these parts will remain stationary on the bench and the router and bit will slide over them.

As you can see, the cutters can’t trim anything beyond the diameter of the bearing. This unique relationship between bearing and cutter allows flush trim bits to follow specific reference edges while trimming away excess material on neighbouring parts. Specific arrangements of bearings and cutters makes certain variations on the flush trim theme useful for specific applications, and trimming the ends of wide tabletops and shelves is one of them.

The simplest, most economical flush-trim bit has a bearing on the tip, with a 1/2” diameter cutter length that’s 2” or 3” long. This model is perfect for use trimming the ends of the table top and making them perfectly smooth, straight and square. It’s exactly what you need for this table project.

flush-trim_shearStart by grabbing some kind of straight edge that’s long enough to span the width of your table top and shelves. In the mocked up example you see to the right, the straight edge is a piece of 1/2″ plywood. For your table this could be a 4-foot level, a dedicated metal straight edge or even a piece of hardwood that you’ve milled to have a straight shape.

Clamp this straight edge onto the underside of your table top exactly where you want the table top to end. There should be no more than 1/16” of extra wood extending beyond the rough-cut edge you completed earlier. If there’s more than this, use a saw to trim it off so there’s approximately 1/16” of extra.The smoothness of this cut doesn’t matter.

Adjust the height of the flush trim bit in your router so the bearing rests only on your straight edge – not on the wood of the table at all. Put on goggles, ear protection and switch on your router.

Carefully push the router across the table top, letting the bearing guide the cut along the straight edge below. You’ll get a flawless edge that’s smooth and square every time – even though you’re cutting end grain. The only issue might be some splintering of the far edges of the wood as the router bit leaves the workpiece. That’s no problem though. Since you left the table top wider than finished size, these splinters will disappear as you rip cut the table top to final with later. Just make sure you rip cut the edges in two stages. You’ll need to cut off half the excess width off from one edge on the first pass, and the remaining wood on the second pass. Watch the video up next to see how flush trimming works on this project.

Table top ends only need a very small amount of sanding after they’re trimmed like this zwith a router. I have a stationary edge sander for this work, though a carefully wielded sanding block with 120-grit paper wrapped around it can yield excellent results, too. It just takes a little longer. If you opted not to use a router and flush trim bit to smooth the ends of the table top you’ll have at least a few saw marks to remove. Maybe quite a few. An 80-grit belt in a hand-held sander is one option for removing them. Just be sure to clamp your tabletop and shelves to a bench while you’re working. Don’t use anything finer than 80-grit for this work or you’ll get burned edges from the friction. This is especially true if you’re working with burn-prone wood such as maple, oak or ash. Sand with 120- and 180-grit abrasives by hand after you’re done with the machine.

Finish making the top by trimming the edges to final width, but leave the shelf longer and wider than it needs to be for now. You’ll see why soon.

Before going on to the next phase you should have:

  • The ends of the table top and shelf sanded smooth.
  • The table top trimmed to final width, but the shelf left longer and wider than it needs to be. The shelf gets trimmed later.