Restoration & Preservation Enterprises removed and rebuilt 765 windows on Chicago’s
Marquette Building, a National Landmark designed in 1895 by Holabird & Roche.
Photo by J. Crocker. 

Anon-descript industrial complex in Kankakee, IL, houses one of the high-tech secrets in window rebuilding: Restoration & Preservation Enterprises. Among top-flight architects handling high-profile renovation projects, however, word has spread, making principal Ray Drazen and his staff of 14 woodworkers and seven installers, the go-to-guys for restoring windows to state-of-the-art energy efficiency on high-profile properties around the U.S.

Architects and contractors praise R&P for historically precise craftsmanship executed with high-tech support. Drazen and his team are celebrated for gifted traditional wood window finishing, glazing and historic hardware rejuvenation.

 R&P restored 205 windows in the landmark Sears
Chicago Homan Square project, handling interior
and exterior aspects.

Among the globally recognized structures for which R&P Enterprises’ work has won acclaim are the Marquette Building and the Glessner House, fabled Chicago-school National Landmarks. Each required careful restoration of a variety of windows. R&P also handles significant projects with smaller numbers of windows: the historic Lodge at Colonial Williamsburg, VA; a 19th century Evanston, IL, mansion for the Consul General of Japan; vintage window restorations at Purdue, Cornell, and Northwestern Universities; and Washington, DC’s prestigious Bowen Building, with a 60-window 1920’s beaux-arts limestone facade.

“Windows are part of the original fabric of the building,” says Drazen, whose 24,000-square-foot plant includes SCMI CNC moulders and router, Northtech planer, Kern laser engraver, its own tool cutter, and plenty of computing horsepower to drive the demanding projects. Also on hand: a climate-controlled inventory of northern white sugar pine, Honduran mahogany, maple and red oak, some of it pattern grade.

Drazen says his clients take either a “conservation” or “restoration” approach, the former reusing original glass, the latter allowing for widening the channel in the window sash to hold more energy-efficient Thermopane-style double glazing.


Caliper measures or scans of moulding profiles create
nested files (bottom) for window parts (before/after at
top). R&P transforms AutoCAD, AlphaCam and Xylog
and other files for nested cuts on its SCMI CNC router.
Thin slices of original brick frame are scanned, then
transformed to files for machining cutting tools inhouse
to cut components on a SCMI 6-head CNC moulder
and 5-axis router.
“Landmark projects are interested in the exterior integrity of the building,” Drazen notes. “The site lines have to remain the same.” When sashes on such historic buildings are routed to widen the channel for the thicker double glazing, “I have to route inward, toward the interiors,” says Drazen. CNCs can produce solid wood “stops” to hold the glass panes in place, which Drazen says is superior to glazing putty for some jobs. As much original wood is retained as possible to preserve the historic integrity of the buildings.

“We are milling only what is necessary,” says Drazen, showing an antique pine double-hung window on which he has added mahogany strips to improve weather resistance. With digitally driven tools, “I can recreate it or replicate it exactly,” he says.
Drazen learned the wood trade at a furniture factory. He has also worked doing retail commercial interiors, eventually moving to restoring architectural millwork.

One key challenge in the projects is simple logistics: keeping track of hundreds of windows, each uniquely sized, even in cases like the 280-window Robert Vance Federal Building in Atlanta, the 765-window Marquette Building, or the 810-windows for a neoclassic 19th century Cook County, IL, government center.

When these structures were built, says Drazen, on-site window fabrication mills tailored windows to each opening. As buildings have settled, openings vary even more.

So window rebuilds are mostly one-offs, replaced typically in these steps: windows, consisting of two or more sashes, are carefully labeled using a placement number system established beforehand with architects, owners or general contractors to ensure proper communication and tracking of every sash and window component. Windows are then removed from the opening. A custom-milled cleat is installed to accept a 3/8-inch Plexiglass panel.

“That lets our workers repair the frames without intruding on the building occupants after the sashes are removed,” says Drazen. Hardware is removed and restored, often including chains and counterweights that balance older windows. Frame sashes are lined with bronze tracks, so sashes move freely. Work on site and at R&P happens simultaneously so sashes can be reinstalled within two to three weeks of removal.

Wood components are hand stripped; brick wood frames stripped, painted and recaulked, with damaged wood components from windows, sashes and frames replicated, using SCM equipment: a 6-head Superset class CNC moulder and Record 110 AL Prisma pods-and-rail 5 axis CNC router with ride-along tool changer.

Digitally driven CNC wood components for windows, frames and doors are machined on
a 6-head SCMI Superset CNC moulder (left) and Northtech dual helix NT 610 EL, which
planes both sides in one pass. Wood from each is near fully sanded on delivery.

A minimum of three custom knives and two CNC router bits are needed for every project. “We have needed over 12 sets of knives for some projects due to moulding variations from floor to floor,” says Drazen.


A factory video shows the SCM CNC
router at work
The ability to grind our own knives not only produces a better end product because we can sharpen periodically over the course of a run, but it allows us a quicker turn around time on our product. The more we can do or rather the more self sufficient we are aids us in the controlling the end product and lead times.”

Read related article: Making Wood Cutting Tools In House

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