Continuing on from last weeks post about the design of this mirror/shelf, this week I thought I’d share my process for building this piece.
The first main task was to glue up the bent laminated frame, which also required making a bending form. The form is made from three layers of 18 mm thick mdf stacked and screwed together.
I made the jig using a router to cut the shape out the first piece of mdf, and from there used a pattern bit to cut the same shape on the subsequent layers. I cut the initial shape out of the mdf creating a 14mm space between the inside and outside forms. The frame itself is 14 mm thick, made up of 7 layers of 2 mm thick pieces of wood. My thought was that I would glue the laminates up by sandwiching them between the two forms, and that’s exactly how I glued up the first frame that I made.
As I mentioned last week I started to make this form based on a design that included a series of staggered shelves, which you can see drawn on the form above. Through the process of drawing that design full scale I realized that it felt way too big, so I decided to modify and simplify the design, but since the overall frame only changed in length, I was still able to use this bending form. I simply reduced the multiple shelves down to one and shifted it’s location closer to the glass mirror.
The problem with using an inside and outside form, especially for an extreme bend like the U-shape bend I have here, is that if there is any deviation in the thickness of the plies, meaning if each piece isn’t exactly 2 mm thick, then you will end up with gaps in the final glue-up. Working out of my current shop, which is a shared space, I’m sort of stuck with the tools available to me, and right now there is only one planer for thicknessing parts. To mill material down to 2 mm thick, I have to use double stick tape to hold the laminates onto a piece of ply when sending them through the planer. That’s the only way to thickness really thin material on this machine which otherwise will just destroy stock that is super thin. A smaller benchtop planer would be great and would probably produce better results, or even a thickness sander, but for now this is the simplest approach available. While it works, there are sometimes slight inconsistencies in the final thickness of the stock, so using an inside and outside form for bending hasn’t resulted in the best glue-up.
After doing a bit of research I came across a process used by Michael Fortune in Fine Woodworking magazine. He used an inner form, lots and lots of clamps, and multiple layers of thin mdf plies and cauls to distribute the clamping pressure. I’ve used a similar process in the past, but usually more of a quick and dirty setup. This time I tried to really do a proper job of prepping all the parts including the cauls, and this second glue-up went much better. There are still a few areas for improvement, but overall I had much more control when it came to closing stubborn gaps. The big downside is the number of clamps, and the amount of time spent trying to all the components together smoothly. One plus to bent laminations using inside and outside forms is the simplicity of the whole thing; two forms, and a few big clamps.
Anyway this is how things looked using the Michael Fortune method.
After letting the glue dry over the weekend, I pulled the frame off of the form, and proceeded with the next phase of work. Here’s the frame out of the form, after joining one edge on the jointer; nice and flat.
To cut this piece to width I setup a tall fence on the table saw and very carefully rotated the frame through the cut. You can see that process in the video here.
I realize this cut may look creepy to some folks, but the tall fence adds a lot of stability to the whole process, and going slow I’ve been able to perform this kind of rotating cut on the table saw many times without any issues.
With the frame cut to width, I moved on to cutting the groove for the mirror glass itself. The glass sits in a groove that is inset from the back edge of the frame by about 12 mm. That distance allows room for a mdf backer board that I use for hanging the mirror. There are lot of different ways to go about cutting a groove for the mirror glass, but I opted for a setup that allowed me to cut a groove while pivoting the router around the exact center of the glass. The tricky area that this method allowed me to cut really cleanly was the transition point between the mirror glass and the frame. Since the round glass plate is only half covered by the frame, the groove needs to taperer to nothing as the glass exits the frame. This method allowed me to make that kind of cut really easily. And since I already had my bending form with all the necessary centers drawn on the surface, it was easy to simply attach a series of blocks marked with the exact center of the mirror glass, giving me a reference surface from which to locate and pivot the router. It all looks complicated, but was actually really simple, and makes for a pretty fool-proof cut.
Here the router setup with a side cutting bit, and my super simple circle cutting attachment; just some thin ply screwed to the base, with a hole drilled at the correct radius.
Here is the router and circle attachment fixed in place with a nail in the center pivot point.
And the groove after cutting. You can see where the groove starts and slowly tapers in.
After cutting the groove I reset the router with a new bit and adjusted the distance on my circle cutting attachment, and cut a rebate for the mdf panel.
At this point the groove for the glass is mostly exposed as a result of the cut for the mdf back, nevertheless I found that last little bit of groove actually does a pretty good job of holding the glass securely. And combined with the mdf backer that gets screwed to the frame and fixed to the glass with a few pieces of double stick tape, the whole assembly is pretty rock solid.
I used the same circle cutting attachment to cut the mdf panel itself.
The bottom of the mdf backer panel has a 45 degree cut to accommodate a French cleat for hanging the mirror on the wall. So I followed that 45 degree cut through onto the frame itself.
At this point the work on the frame is almost done, but I’ll save the final details including the joinery work and carving of the shelf for next week. Thanks for following along.
