Trimming a Houseful of Windows — Production
As the owner of a custom mill shop that works exclusively for
Baud Builders in Narragansett, R.I., I'm always on the lookout
for ways to deliver the highest quality woodwork as expediently
On the new-house project shown in this article, for instance, I
took on trim installation for 58 windows. Although the house
had both double-hung and casement windows, they were all
getting the same trim treatment — making it the perfect
opportunity to use a measuring and cutting system I've
developed over the years.
You might look at the fabrication work involved here and
wonder, "Why bother? Why not just buy the material and turn a
pair of carpenters loose for a couple of weeks?"
The reason is that there are advantages to my method that you
won't get with conventional site carpentry. Most important is
the quality of the installation: The parts fit together quickly
and accurately, with no joints opening up down the road.
Also, we can get to work on the trim even before the
wallboard-and-plaster phase starts. Site installation takes a
few days, rather than weeks. And even if you're not fitted out
with a millwork shop, most of the tools and techniques I
describe are totally transferable to the job site.
The design for the trim includ-ed nominal 1-inch-by-4-inch
square-butted side casings, a 1-inch-by-6-inch head casing with
a 3/8-inch parting bead along its inner edge, and a 5/4 sill
with a 1-inch-by-4-inch apron (see Figure 1).
1. Window trim kits ship to the
site in three pieces: the jamb extensions with sill, side
casings, and parting bead attached; the head casing; and the
Pine extension jambs were supplied with the window order and
were 5/8 inch thick.
I drew the components at full scale and included a
3/16-inch-deep relief plough on the back of the casing material
to accommodate irregularities in the skim-coat plaster walls.
The trim was to be painted, so we specified the stock in
poplar. We ordered the material custom-milled from a local
molding supplier and had it delivered to the shop.
At the job site, I measured each window, noting the interior
distance between the head and sill and between the side jambs,
and assigned each a number that denoted size and type; this job
had five casement sizes, numbered 1 through 5, and five
double-hung sizes, numbered 6 through 10. Then I labeled each
window with a piece of masking tape stuck to the glass.
I recorded each window's number, type, jamb interior width and
height dimensions, quantity, and any special considerations
such as proximity to a corner or another window or door unit.
And — as always — I took digital photos of details,
including all combination configurations; these would give me a
reliable visual reference back at the shop (Figure 2).
Figure 2.Digital photography provides a foolproof
record of special site conditions. This printout has been
marked up for concise shop reference.
Next, I had to determine a standard width for the extension
jambs. I first gauged the distance from the window jambs to the
face of the wall studs by scribing a scrap of wood. I ended up
with a series of lines that averaged 2 7/16 inches. I added
9/16 inch for the thickness of the gypsum board and plaster
skim coat, which resulted in a final "standard" jamb extension
width of 3 inches.
Each window trim package had nine individual pieces —
extensions, head, bead, stool, and casings. With 58 windows,
that meant I had a total of 522 pieces to process.
Since one of my primary concerns is efficiency, from this point
on I made no further use of a tape measure, other than to
transfer the site measurements to a master layout stick.
Cutting to the Layout Stick
On this job, my layout stick was a length of 1-by about 2
inches wide and slightly longer than my longest trim dimension
(Figure 3). I clamped it to an auxiliary bed on my chop saw
with a stop block under the clamp.
Figure 3.Here, the author's layout stick is
clamped to an auxiliary fence on his chop saw (top). Colored
lettering matches the layout stick to the white offset stick,
which provides the lengthening dimensions for reveals, stock
thickness, and overhangs (center). With a stop block clamped at
the appropriate layout mark, the author can cut side extension
jambs two at a time (above).
When I use a layout stick, I don't set the end flush with the
saw blade. That's because there are several offsets to take
into consideration: the reveal between the window jamb and the
extension jamb; the reveal between the extension jambs and the
casing; the overhang of the parting bead beyond the side
casings; the stool horns that extend beyond the apron; and the
thickness of the side extension jambs, which rest on top of the
To keep track of these differences, I make a pair of "offset
sticks," one for the casements and one for the double-hung
windows. These hold the marks for the various offsets.
I cut a small reference kerf on the correct side of each offset
line to avoid error, aligning it with a kerf cut into the
auxiliary bed of the miter saw.
I hold the offset stick against the bed, with the saw kerf
properly aligned, then slide the layout stick till it bumps the
offset stick. I clamp the layout stick to the fence, then place
the stop block on the correct line for whatever component I'm
Color-coding provides a quick way to sort and keep track of all
the parts during assembly and installation.
For example, here I used a red marker to label the casement
head and apron layout marks, and a green marker to label what I
call the legs, or side components. I used blue and black
markers to label the comparable double-hung marks.
Every component receives a label.
As I cut each component, I lay out the pieces side by side,
facedown on a worktable. Once I'm done cutting, I label the
identical pieces with the appropriately colored marker; I do
this all at once, across their backs.
Ganging Material Is More
Breaking the whole process down into the smallest repetitive
steps, rather than treating a single component to two or three
operations one piece at a time, is key to saving time and
This is the order of my cutting operations:
• Rip the jamb stock slightly on the heavy side and
gang-feed it on edge through my planer to take it to a uniform
finished width of 3 inches.
• Cut extension head jambs to length
(I cut several extra pieces to serve as spreaders during jamb
• Rout a 3/8-inch-wide groove in the head jambs to receive
the parting bead (Figure 4).
• Cut extension side jambs to length.
• Cut stool stock to length.
• Cut head casings to length.
• Cut aprons to length.
• Cut parting bead.
Note that I don't cut my side casings to length yet. I wait
until I've assembled the extension jambs, sill, and parting
bead to double-check the exact dimension.
Figure 4.A routed groove in the extension jamb
head will receive the 3/8-inch-wide parting bead, making a
strong, self-aligning connection between the two
For this particular project, I first assembled the extension
jamb sets (Figure 5).
Figure 5.Three-piece extension jamb sets are laid
out on the table for assembly, six at a time (A). Polyurethane
hot-melt adhesive provides a strong 30-second bond between
parts, allowing accurate and secure alignment (B). Trim-head
screws add strength to the glued joint (C). Completed jamb sets
are stacked to one side, awaiting the next assembly step
Holding the pieces down against the worktable to align the
edges and square up the joint, I glued the sides to the head
with a couple of spots of Titebond HiPurformer (Franklin
polyurethane hot-melt adhesive has a 30-second set time and a
bond strength of 1,360 psi after 24 hours.
I also drove a couple of 2-inch trim-head screws in at each end
for good measure.
Routing Bullnose Profile
Next, I milled the bullnose profiles on the sill and parting
bead with table-mounted routers. I own enough routers to
dedicate individual tools for each bit. Since the routers have
custom polycarbonate bases attached, I can simply drop them
into a matching recess in the tabletop. When I'm done with one
bit operation, I switch routers.
Rounding the end grain on a piece of trim tends to break the
grain out, so I always profile the ends first, then the edges.
A zero-clearance fence reduces grain blowout, and a good
exhaust port prevents chip buildup between the cutter and stock
(Figure 6). Chips interfere with the cutting action and cause
Figure 6.The author's shop-made router fence has a
built-in dust port to reduce chip buildup (top). A hold-down is
screwed to the fence to control the stock feed, while front and
rear stops on the end-milling sled help prevent grain tear-out
(center). After rounding all the ends, the author sends the
long edges through the router table. This sequence wipes out
any minor tear-out that may have occurred during end-milling.
Dual feather boards ensure absolute stability
To make the fence, I began by carefully pushing it straight
across the running bit, freehand. Then I glued it to a square
of 3/4-inch MDF that I'd drilled with a clearance hole for the
bit. Finally, I hot-melt-glued the MDF to the router base. The
MDF base allows me to use a stock sled made from the same
material to guide the workpiece across the cutter during end