More Solid Wood Machining – Curved Mullions

Here’s another, somewhat more complicated solid wood machining project I completed a while back.  In order to get a nice kitchen cabinet job for a contractor I had worked with before, I had to match some curved mullions for several glass panel doors which the client had fallen in love with from a competitor’s catalog.  I planned to order all the doors and drawer fronts for this set of kitchen cabinets from one of my regular suppliers, and they were only too happy to give me a price on the design that my clients had chosen – $350 per door.  For a set of four doors that would be $1,400 above the cost of the door frames and glass.  I figured I could do it myself and save some serious money.

Two of the completed doors.

Two of the completed doors.

I had to start with some basic decisions about how to make the curved strips and how to handle the joinery where the mullions overlap.  I decided that bent laminations would be stronger and easier to machine cleanly than milling the curves out of solid stock.  But the joinery almost had me stumped.  I happened to be looking through a router bit catalog and noticed a router bit set for making the exact same joint with straight stock.  That set would not work with my curved workpieces, but it enlightened me to the concept of using a fancy half-lap joint to get the pieces to mate cleanly, with the profiles matching up in all corners of the completed joint.  I drew the overlapping shapes in my CAD program and zoomed in on the area in question to try to visualize what exactly had to be machined.   It took a while, but I finally figured out that by bisecting the joint vertically and horizontally, I could rout out the top-right and bottom-left quadrants of one piece, and the opposite corners of the other piece.  In fact, by holding one piece upside down during machining, the two halves could be machined exactly the same way, and when the upside down piece was flipped right-side up, the parts would mate.  I had my plan.

Using CAD to figure out what had to be machined.

Using CAD to figure out what had to be machined.

I saved all the narrow scraps of maple that were generated from the rest of the job, and ripped them into strips about 1/16″ thick.  After measuring the door frames, I drew the shapes of the forms that would be needed for the glue-ups, and nested several sets of forms onto a piece of leftover 3/4″ plywood.  The glued strips were clamped into the forms and left for a day or two, then wrapped with stretch-wrap to maintain their shape until all the glue-ups were completed.

Cutting the forms out of 3/4 inch plywood

Cutting the forms out of 3/4 inch plywood

Each curved strip is glued up of 6 laminations

Each curved strip is glued up of 6 laminations

The glued up assemblies were kept in shape with stretch wrap until machining day.

The glued up assemblies were kept in shape with stretch wrap until machining day.

Once the curved shapes were ready for machining, I loaded a scrap piece of melamine on the table and routed out the area where the workpiece would sit.  This allowed me to precisely place one of the male forms on the table  and use the female form with some cam clamps to firmly hold the workpiece in the correct position.  The routed area also created a flat  reference surface for the workpiece to rest on, allowing me to start by  surfacing the tops and bottoms of each strip to create clean surfaces and a uniform thickness.  I then used a profile bit to shape the shoulders of each mullion.  It didn’t matter that the bit also cut away part  of the form.

Some leftover melamine becomes the table fixture.

Some leftover melamine becomes the table fixture.

A workpiece ready for the first surfacing.

A workpiece ready for the first surfacing.

After the top face is cleaned up, the piece is turned over and surfaced to final thickness.

After the top face is cleaned up, the piece is turned over and surfaced to final thickness.

The same setup holds the pieces while a profile bit follows the curve.

The same setup holds the pieces while a profile bit follows the curve.

I machined the half-laps with a 1/16″ diameter straight bit.  I had to order a “long” 1/16″ bit (with a 1/2″ cutting length), and I was sure worried about it breaking when I saw it.  But with such small areas to be machined I was able to use small step-downs, slow feed speeds and ramp settings as gentle as I could get them, and managed to complete all the cuts without breaking any bits.

One half of a half-lap joint.

One half of a half-lap joint.

I thought I’d have to do some hand chiseling in the corners, but to my surprise the overlapping pieces fit together almost perfectly.  They practically snapped into place.

The completed half-laps.

The completed half-laps.

One of the biggest challenges was machining the ends of the mullions to fit the inside profile of the frame.  I drew the profile and used multiple copies of the shape of the router bit to approximate the shape that the ends of the mullions would need.  Then I used the offset and depth of each copy of the router bit shape to create a pass on the router.  It was a little tedious but it worked.  The parts fit together and into the frames so well they hardly needed glue.

Calculating the end cuts using CAD

Calculating the end cuts using CAD

The ends had to be machined to fit the inside profile of the frame.

The ends had to be machined to fit the inside profile of the frame.

Big sigh of relief when the pieces fit perfectly the first time.

Big sigh of relief when the pieces fit perfectly the first time.

Bottom line: this was a successful project.  I started early one morning with the glued-up parts and a vague idea of how to proceed, and ended the day with four custom doors ready for finishing.  Using only scraps, I was able to replicate what my supplier would have charged a high price for, and the customer was thrilled with the result.  Adding up the time spent ripping and gluing, planning, cutting and fitting though, and I came to a realization:  maybe $1,400 wasn’t such a high price after all.

4 comments to More Solid Wood Machining – Curved Mullions

  • Caroline

    Hey David, so you did the exact cabinet doors that I am looking for. Is there any chance you would be able to do this again? We would be very interested to work with you on this if possible. Thanks so much and I look forward to hearing from you.
    -Caroline can8lehigh@hotmail.com

  • Hi Caroline, I would love to do that project again but the bottom line is that it would be very expensive and take a long time. You can get them made more reasonably at one of the major door suppliers like Walzcraft, Decorative Specialties, or Keystone Wood Products. The frames in the pictures came from Walzcraft and I know they were willing to make the mullions as well. Do a quick search on any of those names and “cabinet doors”

    Good luck with your project..
    David B.

  • thomas traun

    finished dinner absorbing this fun just made my 5th mahogany ext dr with mullions, appear to be doing it for the learning not money 🙂

  • Steve

    How did you cut the millions? I’m still not clear on how you did that exactly. Tha ks

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