Making It Plane: How to Flatten a Workbench with a Router

Making It Plane: How to Flatten a Workbench with a Router
Making It Plane: How to Flatten
a Workbench with a Router
est. 1978
by Zach Etheridge
Committed hand tool enthusiasts can flatten a bench
by hand with a jointer plane, but after doing two or three
large benchtops that way myself, I developed a distinct
Tools for Woodworking
urge to find a less laborious method. It was Tage Frid
(it's pronounced "Tay") who showed me a router jig that
could be scaled up to mill even the largest benchtop rapidly and accurately. A couple of versions of the
idea appear in Tage Frid Teaches Woodworking Book 3: Furnituremaking (pages 158 & 164). The design
is typical of Tageʼs approach to woodworking: the concept is
simple and the work itself quite straightforward. All you have
to do is arrange for a router to move in a flat plane just above
your workbench; set your depth of cut to skim the entire surface, and at the end of the exercise the benchtop will be flat.
Nothing to it.
The flattening jig is readily fabricated from solid wood
or plywood. You'll make two side rails roughly 18" longer than
your bench, and you'll make a sled that can ride lengthwise
along the rails while your router slides back and forth within.
Make the rails of 3/4" lumber 6" to 8" wide. Joint one edge of
each piece as carefully as you can, then butt the edges against
each other for a critical look at how close you've gotten them to
straight. I finished mine with my 07 jointer plane to get them
even straighter than my 5-ft. jointer could do. When you're satisfied, rip the opposite edge of each piece parallel.
Make the side walls and bottom rails of the sled in the
same way, taking care to get each component as straight as reasonably possible. Don't waste your time worrying about thousandths of inch, but just do good work.
The router sled
Make the sled with high side walls to resist sagging under load,
and attach strips along the bottom edges to support your router and
stiffen the walls as well. Make a square sub-base for your router so
it will sit stably and securely in the sled. Attach cleats beneath the
ends of the side walls to separate them by the width of your sub-base;
they should hold the sled snugly across the rails on your bench. Nail
stop blocks into each end of the sled to limit the router's travel, so the
bit you use just barely cuts into the side rails. Unlike those pictured,
make the cleats that join the sled walls several inches wider than
the sled (I ran short of scrap plywood) so they'll slide along the rails
without racking and binding. Wax
the top of the rails, the inside of the sled and the face of each cleat to
make all moving parts smooth and slippery.
Checking for twist
Before you start work, get a clear picture of what needs to
be done. The side rails make good straightedges for checking the
benchtopʼs length & width, and together they can be used as oversize
winding sticks to check for twist. Note the edge of the far rail has been blackened with a magic marker
for good contrast, so even the slightest twist will show clearly. If there is twist present, note the high and
low corners, and plan to set up your side rails accordingly: a little higher above the low corners of the
bench, and a little lower at the high corners. This lets you remove as little material as possible while getting the top completely flat.
Leveling the rails
Mount the side rails on the edges of the bench with screws at each corner (plus one in the center on
a long bench). Drill 3/8” holes through the rails to allow for height adjustment, and drive #10 or #12
screws with washers into the bench. Getting the top edges of
the rails into the same plane is unbelievably easy. Drive a nail
into the outside face of each end of each rail. Tie a piece of
strong string to one nail and pull it tight diagonally across the
bench, tying it off to the nail in the far corner. Do the same on
the other diagonal. Since the second string crosses above the
first, it must be shimmed up exactly one string diameter where
it rests on the rails.
Adjust the rails until the two strings just kiss where they
cross in the center of the bench. If you canʼt touch the upper
string without moving the lower one, but the lower one doesnʼt rise at
all when you lift the upper, then you have established nearly perfect
contact — and the edges of your two rails now lie in a perfectly flat
plane. When one of my students taught me this trick I couldnʼt understand why it worked; itʼs just too idiotically simple and far too cheap.
It works, though, with an utterly fabulous degree of precision. If like
me, you're conceptually challenged, just do it without waiting on understanding — results will explain it all more clearly than words.
Getting it done
Put the biggest straight bit you own in your router (mine's 1-3/4" diameter) and set its depth to just
touch the benchtop at its lowest corner (which you determined with the winding sticks way back when).
Start at the far corner of the right end of the bench. Pull the router all the way across, and push it back
along the same path; then move the sled to the left slightly less than the bit diameter and repeat the
process. Routers go left [the subject of another free handout, Routers Go Left!], so make sure thereʼs no
uncut surface to the routerʼs left (not your left) as it travels — thus if your control isnʼt perfect as you
pull the router along, the worst thing that can happen is that the bit will push itself out of contact with
the wood and the router will simply stop moving. Sure beats having it try to rip itself out of your hands
and run off across the bench. Incidentally, this technique also directs almost all the waste straight away
from you, so you can rig up a dust port at the far end of the sled and
capture most of the enormous amount of debris youʼre going to generate. Weʼll not let it go without saying that you are going to wear
eye and hearing protection along with a good dust mask, right?
A No. 80 handled scraper makes very quick work of smoothing
bit marks on the flattened surface to prepare it for finishing. Sand the
edges lightly, wipe off all the dust, and apply several coats of Waterlox or your favorite oil. Now re-mount your vise or vises, trim their
jaws flush with the new surface, and get back to work!
Copyright © 1998 Highland Hardware
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