Culin & Collela

CNC Router Cuts Time For Creating Curved Millwork From
8000 Hours to 4000 Improving Accuracy Tenfold

By Ray Culin - President, Culin & Collela, Inc.
Mamaroneck, NY

















Culin & Collela produced miles of curved molding and other custom millwork using a personal computer-driven CNC wood router in 4000 hours, approximately half the time it would have taken using traditional methods. The router also improved the accuracy of the work by a factor of ten, helping Culin & Collela deliver curved molding, cabinets, and bookshelves that drew praise from the architect on the project. Creating large curved wood pieces by hand would have meant making a trammel and physically swinging an arc to figure out the radii of curves. Instead, Culin & Collela created shop drawings in its CAD system, then transferred the CAD data to the router's CAM system to create toolpaths for the router. The router then generated the highly accurate fiberboard templates, knife grinding templates, and cauls needed for the project. A caul is a template used for bending that clamps wood into a curved shape.

















Culin & Collela occupies a 12,000 square foot building in Mamaroneck, New York. The company was formed when its president and vice-president, who each had a custom furniture business, met, married and later merged the two businesses. The company employs 23 people and has recently been doing work at the Conyers Farm development outside Greenwich, Connecticut. This is an exclusive enclave of multimillion dollar homes on lots of at least 10 acres.

One of Culin & Collela's recent jobs was the woodwork for a 25,000 square foot house with a curved front wall. Culin & Collela produced the entire interior molding package, which included miles of curved cornice molding, baseboard, and chair rail, as well as wainscot paneling for the curved front wall. Every piece of the molding in the house had a custom profile designed by the architect. In all, the house had at least 150 different molding profiles. Culin & Collela also created the entire kitchen package for the house. This consisted of natural cherry cabinets with curved doors, as well as the wainscot paneling in the breakfast room. Other work for this house included a curved bookcase for the library, a chestnut wainscot wall and chestnut tongue-and-groove ceiling in the family room, and a spiral staircase with wainscot paneling that went up three stories to the children's living area.

Creating curved woodwork using traditional methods presents several challenges. Typically, a template is cut from a piece of fiberboard, either by hand or with a router, and then parts are trimmed flush to the template. The template must accurately depict the radius of the curve. Drawing the radius requires the use of a trammel or beam compass, and building one of these is a big undertaking for larger wood pieces. If a particular piece of wood needs to have a 50-foot radius, for example, someone has to take a 50-foot length of wood and put a point at one end and pencil at other end, then physically swing the arc to get the proper curve.

Curved kitchen cabinets present additional challenges. Not only must the doors be curved, but the box of the cabinet, face frame, styles, and rails must also be curved, and they all require different radii to fit together perfectly. For example, assuming the curve of the cabinet is concave, interior parts such as the box must have one radius while parts farther out such as the door must have a larger radius. The kitchen cabinet doors for the Conyers Farm house had a 45-foot

radius. With this large radius it wasn't obvious that the doors were actually curved. If they had not been curved, the installed cabinets would have had a faceted appearance. To draw the different radii for these cabinets by hand would have required using the 45-foot compass and then adjusting the resulting radius for each cabinet part.

Culin & Collela executives realized that CAD/CAM technology could alleviate some of this work, but when they looked at computer-controlled woodworking machines, they saw prices in the neighborhood of $60,000. That was impossible to justify at the company's current workload. Then the company heard about the Series III PC-driven CNC wood router (Techno, New Hyde Park, New York) which costs less than $16,000 and is designed for production routing and drilling on a wide variety of materials including wood, plastic, MDF, solid surfacing materials and nonferrous metals. Working area for the router is 49 inches by 41 inches and Z-axis height options range from 4.0 inches to 19 inches. Table technical specifications include a rapid travel rate of 200 inches per minute, a Z-axis cutting force of 200 lbs. maximum, 0.0005 inch resolution and repeatability and 0.003 inch absolute accuracy. The system includes the Mastercam® CNC programming system (CNC Software Inc., Tolland, Connecticut) which, although originally designed for metalworking, is ideally suited for woodworking because of its ability to generate the most complex contours with little programming effort. The program features true 3D geometry construction plus IGES, DXF and CADL converters so that geometry can be uploaded from nearly any CAD system.

By using this router, Culin & Collela has greatly simplified the process of producing curved millwork. The router works in conjunction with the company's AutoCAD design software (Autodesk, San Rafael, California). They export AutoCAD files, which contain accurate curve radii for all parts, to Mastercam®, generate CNC programs, and produce templates and finished parts on the router. Production time has been reduced by an average of 50% on the items produced by the router. And, quality has been substantially improved because the computer-generated programs provide far more accuracy than the company was ever able to achieve with manual methods.

Culin & Collela has restricted the use of the router on the Conyers Farm job to making templates and cauls. They did not use it for direct part cutting because they had only a three hp motor on the router at the time. The process they followed started with the creation of shop drawings in the AutoCAD system and submitting them for the architect's approval. Once that was done, a full-time employee worked with the production manager to determine what templates and cauls were required for what operation. That employee then took the appropriate drawings from the CAD system and transferred them to Mastercam® to generate all the toolpaths required to create those templates and cauls. The CAD/CAM work took about 200 hours for this house.

They used the router to make two types of templates: fiberboard templates for use with the shaper and knife grinding templates. Knife grinding templates are used to create the knives that go into the molder head and cut the profile of the molding. Molding knives are only as good as the template, so the CNC router was important in this project to get a high degree of precision. After templates were created, they were taken to the molder or the shaper to cut the actual part. The molder was a Weinig Profimat four-headed molder with automatic head positioning. The shaper was an SAC 10 hp tilting arbor shaper capable of profiling edges of curved pieces and trimming on a curve. The cauls used in this project held strips of solid cherry molding in a curved shape while the glue that held them together dried. The router was used to cut all the ribs and parts for cauls so they had the exact radius needed.

CNC enabled them to produce knife grinding templates in one-third the time needed by hand, or about 20 minutes/knife template vs. one hour by hand. In all, producing the curved millwork for this house took approximately 4000 hours, which Culin & Collela estimates would have been closer to 8000 hours without the CNC router. In addition to the time it saved, the accuracy of the router won Culin & Collela high praise from the architect for the quality of their work.

For basic routing applications, the machine's 0.0005-inch accuracy is more than enough for the job at hand. However, for jobs requiring greater precision – such as inlays and molding cutter templates – such accuracy and play-free motion are essential to producing exceptional work. The router's accuracy comes from its use of anti-backlash ball screws, as opposed to the rack and pinion drive mechanisms used in cheaper systems.

Culin & Collela wouldn't have bid on this contract without the time-saving and cost-saving capability of CNC equipment, nor would they have won it. Their ultimate goal is to increase their use of technology to the point where they download an architect's drawings directly into their computer. This will greatly reduce the effort needed to produce shop drawings, and make the company even more competitive in its bidding.