The title of this blog should be “Progress In Crafting American Chippendale Mirrors”, or some such thing. But as often happens to me while working on a project, a thought catches my attention and I can’t get rid of it. Over the last few days, while working on this project, it happened that I had to use a commercial fixture and build another fixture; or was it a jig? Woodworkers often confuse the two and use these terms incorrectly, as I have done here – and many times in the past. So I was compelled to do a little research.
It turns out there are many mechanical engineering and fabrication books written that give the definition of, and explains the use of, fixtures and jigs. They are perhaps the most useful source in answering this question. I have a number of woodworking books in my library that also give us some guidance. There is also the dictionary. After reading a number of these sources the difference is still not clear.
However, taking the common elements you can boil the definitions down to the following:
- A jig holds and guides the work piece
- The fixture holds the piece while it is worked on
OK, so what is a tenoning jig? Does it hold the piece while it is worked on? Or does it hold and guide the piece. It is universally called a jig, but it does no more guiding a tenon than it guides a piece I cross cut without its use. I am doing the guiding, or perhaps you can argue it is the table top miter slot that is doing the guiding. But the tenoning jig certainly isn’t. So perhaps the definition should be:
- A jig holds a piece and is movable while working the piece
- A fixture holds a piece and is fixed in place while working the piece
With this definition I can actually determine what I am working with. Now I can clearly say a tenoning jig is indeed a jig, and the Supreme Drill Press Table I wrote about a few weeks back is clearly a fixture. More importantly, I can say the two helpful tools I use in this blog are clearly jigs.
OK, having wasted a lot of time, energy and blog space on that overdone thought I can write about “Progress In Crafting American Chippendale Mirrors”. The picture frames thus far are joined with end grain to end grain joinery; a joint which is notoriously weak and needs reinforcement. There are traditional ways of doing this, one of which is to cut corner slots and use splines. For reasons to be explained later I used a modified version of this joint. To assist me I turned to one of my favorite and most used jigs, the Dubby from In-Line Industries. In the first picture above you can see Left and Right Dubbys set to 45 degrees. I am using them to cut horizontal slices in the corners of the frame. Two opposite slices are cut with each of the two Dubbys producing the slices you see in the picture ant right above. These are the first of two cuts needed to remove triangular shaped pieces.
To make the second cut I needed to build a simple jig. Shown in the picture above left is a vertical board with support stock glued 45 degrees to an edge. The picture frame sits in these supports allowing a properly set fence and blade to cut the corner pieces out. These corner pieces will be replaced with similar roughed out corner pieces with the grain arranged such that there is long grain to long grain joinery. I trace multiples of these corner pieces on a rectangular piece and rough them out using the band saw, leaving just enough along the edges to assure complete coverage. After they are glued in place I use a patterning bit in the table router to trim the edges flat.
In the picture at left you can see the results. From this picture it should obvious the improvement in joinery strength. Imagine picking up the end grain to end grain piece and snapping it with your fingers. No problemo! Now imagine picking up the replacement piece and trying to snap it. Good luck!
Another thing to remember is that a properly glued long grain to long grain joint is stronger than the wood itself. This has been demonstrated in numerous studies and wood working articles. You can demonstrate this in your own shop easily. Glue two pieces edge to edge (1/4” to 3/4” thick). Let the joint cure for 24 hours. Place it in a vice with the joint near the jaws of the vice and hit the protruding piece with a hammer or mallet. You will notice (provided the joint was glued correctly) that the board will split in the grain of the wood, not at the glue line.
So why did I use this modified spline instead of the traditional joint? Because I need to cut 1/4” by 1/4” groves along the top, bottom and sides to accept the scroll work. Doing so would remove a substantial amount of the spline. Further, the resulting joinery when the scroll work is glued in place would be long grain to end grain. Stronger than end grain to end grain but not as strong as long grain to long grain. Does this make a difference? Yes a little, especially if you are expecting your work to last for hundreds of years it does. That said, it’s six of one, half dozen of the other.
In the picture at right is the finished glued up mirrors ready for stain and finish. The strange uneven coloring is a result of using mineral spirits to search for unwanted glue spots before completing the sanding. It will disappear after drying. The mineral spirits also give you a good preview of what the tiger maple will look like when finished. You can see it is quite spectacular. The frame at right in the picture has a cherry picture frame and tiger maple scroll work. The one at left is entirely tiger maple. I love mixing wood types. The cherry will darken over time and the tiger maple will lighten slightly making the contrast even more noticeable.
My wife and I are excited about finishing these mirrors and giving them to our kids for Christmas. A few hundred years from now I hope a descendant will write a blog like An American Chippendale Mirror Makes A Great Gift explaining their origin.