Build a sled-guided router to shave a little (or a lot) off the top.
Woodworkers have long debated the importance of a dead-flat bench top. Some say a workbench is made to get beat up and doesn’t need to be flat. Others, like me, prefer not to relocate from bench to assembly table during a project; I like to build and assemble all in one spot. I’ve found that having a bench in good working order brings out my best work.
Over the last decade, my bench developed a discernible hump across its length, and a divot near the front vise. Flattening a bench with a jointer plane isn’t difficult, but it is a real workout, and somewhat intimidating for first timers. The sled-guided router is easier to master, and saves sweat for other repairs.
Order of Work
- Remove the vises.
- Scrape away glue and paint.
- Inspect the top.
- Build the jig.
- Attach the rails and rout.
- Repair, reassemble, and refinish.
Clear the deck
To prepare the top for planing, remove the vises and any other hardware. Next, scrape off any lumps that could interfere with your straightedge. If your bench has had a hard life, checking the top with a metal detector can catch hidden screws or nails that would damage a bit.
Inspect the top
Like grinding a chipped plane iron or chisel, the goal when flattening a benchtop is to remove as little material as possible. Before making a diagnosis, use shims to level the base. This eliminates any false-readings that could be caused by an uneven floor. (My Adjust-A-Bench base includes casters, so I raised it on 2×8 beams.)
Using a straightedge and winding sticks, check for low spots or a twist. You’ll use these spots to install the rails and set the bit.
Twist teller. A pair of 4-foot long, 1⁄8"-thick aluminum angles make a reliable set of winding sticks. I attached colored tape for better visibility.
Make the Jig
A simple plywood sled, and a pair of plywood rails transform a plunge router into a trustworthy surfacing tool. Adjust the base to suit your router, but keep the sides at 4-1/2"-wide to prevent the base from bowing.
I paired my 3-1/4 HP router with a 1-1/2" dado and planer bit (see Buyer’s Guide) This bit should be operated at around 16,000 RPM. If your router doesn’t have speed control, use a smaller bit.
Install the rails
Starting at your bench’s lowest corner, install the first rail so that the rabbet sits a hair below the benchtop. To set the rail parallel with the top, I used a digital level. Simply measure the top, then set the rail to the same angle. Next, use the level to determine the front to back angle, and install the second rail as shown.
(Note: If you don’t want to mar you bench with screw holes, you can attach cleats to your bench’s bottom face.)
Ready to rout
Thanks to the prep work, this step goes quickly. To set the cutting depth, position the sled above the lowest spot on your benchtop, and adjust the bit so that it grazes the surface. If the difference between the lowest and highest points is more than 1/8" inch, raise the bit and flatten the bench in two passes.
Listen and watch the bit as you rout. Minor adjustments to your feed rate can make a big difference in the cut quality. Move the sled to your left, as shown. If the bit should catch, the rotation will push the router back onto a previously-routed section, rather than diving into the uncut section.
Use the slot to set the bit. For best results, overlap each pass by 1⁄3 to 1⁄2 the width of the bit. The bench’s till serves as a handy stopping point when shifting the sled.
Post-flattening first aid
While routing the top eliminates stains and minor blemishes, it will reveal damage that’s more than skin deep. To fill small holes and other oddly-shaped divots, mix epoxy with fine wood dust and fill the spots as shown. When the epoxy reaches the rubbery stage, slice away the excess. For bigger divots, try using a patch, or “Dutchman.” Doing more damage seems counterintuitive, but a well-matched patch can make the repair almost invisible.
Finishing Up
The last few steps go quickly, but these details matter, so take the time to get them right. First, clean, lubricate, and reinstall both vises. After installation, use a straightedge to verify that the vises are flush with the top. In some cases, the mounting can be adjusted; if that’s not possible, you may need to pull out a plane. Finally, wipe on a coat or two of your favorite oil/varnish blend to provide some defense against glue and other staining agents. (Don’t use wax. You don’t want your stock to slide off your bench.) After this effort, you’ll want to keep your workbench in tip-top condition. For messy chores, protect your benchtop with rosin paper, or even a Masonite top.
Smooth (and flush) operator. Brush off crust and rust, and then lubricate the rods and threads. When planing the vise, use tape to track your progress. When the blade touches the tape, scrape or sand.
Buyer's Guide
- CMT Dado and Planer Router Bit, 1 1⁄2" D, 5⁄8" CL, 1⁄2" SH — #822349, $31.99
- Veritas Scraping Plane — leevalley.com, $179.00
- WoodRiver Cranked Neck Chisel Plane Set — #151240, $43.99
- Slipit Sliding Compound, pt — #124948, $17.99
