The Backs And Doors Are Custom Fitted Spalted Soft Maple With Its Black Lines, Tan and Greenish ColoringThe backs of a custom piece serve a number of functions and they are far from simple pieces of wood. The upper back in this piece provides a mechanism for hanging the clock while it also serves to keep dust out of the clock’s works. The upper back is not, however, visible since it is hidden by the clock dial.

The bottom back is visible, just behind the weights and pendulum that drive the clock. It also serves to keep dust out of the case. However, because the swinging pendulum will draw all eyes to itself and the back, it is important that the back not look like a plain piece of wood, but rather adds to the beauty of the clock. For this clock spalted maple serves that purpose. The random black lines of the early fungus and the tan and greenish color of the wood provides the viewer with an artistic drawing that only nature could render.

Elongated Open Holes, Washer And Screw Allow Seasonal Movement The Backs Are Centered With Gaps On Either Side For Expansion Backs almost always require special treatment to allow for seasonal expansion and contraction. In large pieces I often use ship lapped boards that are spaced one from the other to allow for seasonal movement. Theses backs are not wide enough to accommodate this approach. Instead, after calculating the expected movement, I cut the backs narrow by 1/4” and fastened them with slotted open holes, washer and screws. I cut them narrow because expansion season has only barely begun, and at its peak, the backs will expand to close the gap. If this were peak expansion season I would have cut them to fit and let them shrink to their minimum size. The washer and screws hold the back flat but also lets it move under the washer. I am careful not to tighten too much. Notice that I center the backs so that the gap for expansion is equal on each side.

The hardware and glass are on order and as soon as they arrive I will attach them. Then it is a simple matter of applying finish. For this clock I am going to use Min-Wax Wipe-On Poly Satin Finish.

Leave a Reply

4 Responses to “Back Joinery For A Shaker Wall Clock”


  1. Mark Mazzo says:

    Joe,

    Looking very nice from here! The spalted maple and walnut provide a very nice contrast – should look stunning when it is finished.

    I have a question on the slotted screw hole for the top molding that seems to allow movement from fron to back on the clock…I would not think that you would see much movement in that direction – are you trying to accommodate any movement that there may be the top of the clock?

    –Mark
    The Craftsman’s Path


  2. Joe says:

    Hi Mark,

    Thanks for the kind words. It is appreciated, especially coming from a fellow woodworker and blogger.

    The carcass is dovetailed with the grain running right to left and top to bottom. The problem comes in with the attachment of the trim where the grain runs front to back creating a cross grain situation between the trim and the sides. If I simply glued the trim on, over time the seasonal expansion/contraction of the sides would stress the glue and break it down.

    You might ask how much can that expansion/contraction be. Not much, but not negligible either. If I recall correctly, the sides are about 7 1/2″ wide and are flat sawn. In my part of the country that means about 1/8″ annual change in side width. The trim will change an immeasurably small amount. So that change cycled over a number of years will eventually break down the glue.

    This may seem like overkill, but if you want a piece to last for hundreds of years as it is passed down in your family, then it is a small cost to pay.

    See my previous blog http://www.srww.com/blog/?p=650 for a better or more complete explanation. Hope this answers your question.

    Joe…..


  3. Mark Mazzo says:

    Joe,

    Thanks for the clarification.

    I understand the cross-grain situation that you are referring to. Because you did not use a sliding dovetail cleat to hold the molding on, or maybe just glue it at the front of the case, I thought that there may not be enough movement to worry about.

    You’re right, better safe than sorry. I’m sure that this piece will see may years of faithful service with that attention to detail.

    –Mark
    The Craftsman’s Path


  4. Joe Zeh says:

    Mark,

    It occurred to me after answering your question that there is a role that global warming is likely to play in our furniture making. Global warming is likely real, and while it will bring higher temperatures on average, it is also likely to bring larger temperature and humidity swings with it. That means annual changes in wood movement will be larger than we are expecting today.

    While we didn’t have to worry about this too much if we were an 18th century woodworker hoping our piece would last into the 21st century, it is likely we 21st century woodworkers had better pay close attention to detail if we expect our piece to make it to the 24th century.

    Something to think about.

    Joe….