Dominoed Cabinet Door

WOOD WORKING BY DESIGN

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IMAGE 1
Seen above is the first of two (or more?) shop wall cabinets I am crafting for my most frequently used hand tools.

Introduction

Plywood is a great building productl for woodworking projects. But personally, I hate seeing plywood edges in finished projects be they shelves, cabinets or whatever. That said, anyone who has ever tried to join plywood sections and hide the edges faces the same dilemma: How do you hide those ugly edges and not spend a month in the process? Good question.

Background

I have needed to build two wall cabinets for tools in my new shop and wanted them to span the entire width of the walls between my north-facing windows. The fixed half of these cabinets is fastened very securely to the wall studs. The planned cabinet doors will pivot on full-length piano hinges on the left side of each cabinet. One of these fixed cabinets will hold all of my carving gouges and the other will store all of my hand chisels.

Both fixed-halves of the cabinets have been completed and are in place. The project I am going to detail involves the crafting of the doors for these cabinets. While building simple doors would have been quick and easy, they would have also been a wasted opportunity to create storage stace within them.

Plan B

I'm calling this project Plan B and I want to share it with you. Whether it works or not we will both find out soon enough. So just what is this Plan B?

Plan B is going to utilize the functionality of two Festools - the Domino, the Track Saw and my table saw, to build a box-shaped cabinet door (like the one on the left in the image above) for one of my shop wall cabinets. The door I am planning will have ample depth to store tools in. The 11/16" plywood (advertised as 3/4". Right!) door dimensions are as follows: 25" (width) by 38" (height) by 3-11/16" (depth). If all goes according to plan, I should have 3" of interior depth for tool storage.

Two Important Questions

Before we get started, there are two very important questions that need our attention:

  1. How do I design the door so it will support the weight (tools) that will be stored in it?
  2. Will I be able to glue it up as planned?

Failure to be cognizant of these elementary questions before you begin can lead to serious problems later on. These questions are so interconnected that I really consider them to be one and the same. In other words, ignore one and the other will make you regret your oversight. For instance, a poor design that results in a time-intensive glue-up that exceeds your glue open-time can ruin your project. It is imperative that your design will keep you safely within your glues open-time.

All glues have an open time that is inversely proportional to the ambient temperature in your shop. High temperatures make for very short open times and low temps will extend open-time. Take a minute to read the instructions on the bottle for this crucial info.

If your design results in an overly complicated glue-up process you could be heading for disaster. If your glue begins to set before you have all the components coated with glue and in place you may have just ruined your project. Being aware of glue open-time while in the design stage will make for a predicable glue-up procedure.

The very best way to avoid this disaster is to go through the complete glue-up procedure without using glue. This is a sure-fire way to uncover potential pitfalls in the process. This will, however, not overcome a poor design that ignored the glue-up process.

I work alone, so I always design my projects so that I can safely manage glue-ups on my own. If you have help, then you can design and plan accordingly.

Lastly, if we were going to use metal fasteners we would not even be talking about all of this. But we're not and that is why we have to design our project with all these pitfalls in mind.

Woodworking Physics

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Drawing 1
This drawing illustrates a typical rail-stile mortise-tenon joint with potential real world stress configurations. For the sake of this discussion, the stile is the fixed member and the rail is free to flex on its right end.

To help us understand these problems more clearly I have created a simple drawing that will help us visualize the four basic stresses we must take into consideration in our design.

Looking at the stress-force in Drawing 1, the assumption is that the stile - the vertical board, is the fixed member. The rail - the horizontal board, is the free member, meaning that it is only attached on the stile end. The right end is free to flex with the racking forces placed upon it.

In general, all forces come about due to the racking that takes place on the free end of the stile. If a downward force acts on the free end of the rail the tension/compression forces will increase as shown. If an upward force acts upon the rail the forces are equal but reversed: The tension is now compression and the compression force becomes the tension force.

In both cases, shear is a constant because the racking force being applied creates horizontal forces and not vertical forces. If you were to hit the stile-to-rail joint with a large hammer then that would definitely create a vertical shearing force. But that is not a force we would normally have to worry about.

The plan is to use only very short dominos to handle all the stress that will be placed on this door. It could be argued that the glue placed along all the mitered joining edges will also help support the door. While that may be true to some extent, I cannot take that into consideration because (1) edge-to-edge bonding is a very weak bond at best and (2), there is no guarantee how tight the edge-to-edge surfaces will end up being.

So for these reasons I am assuming that this bond will be negligible. My assumption will be that the real support will come solely from the domino joints and nothing more. If the edge-to-edge bond ends up being beneficial that's great. But I'm not counting on it being additive in any way.

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Drawing 2
This drawing illustrates our door less stress and with real-world stress forces being applied (in red).
Drawing Details

Looking at Drawing 2 above, we see the door frame (in black) less any external forces being applied to it. The red-frame depicts the result of a racking force being applied to the door.

The drawing also shows that the piano hinge, on the right edge of the door, attaches the door to the fixed member.

More importantly, as the door distorts due to the racking force: Angles A and C become greater than 90 degrees. Likewise, angles B and D become less that 90 degrees. This is critical information to know because (1) we now know where the greatest distortion is taking place and (2), this will help us determine where to place our dominos to combat these distorting forces.

With this rudimentary knowledge, lets take a closer look at how these stresses will affect our door.

Shear

Looking at the stress-forces in Drawing 2, we can see that there is no change to the shear as the door distorts. Because of this, we can ignore the shear force. Shear will always be a real force, but one we can safely ignore in this project.

Tension

Tension is a force we do need to be concerned with. As the weight due to the door contents (the racking force) tries to pull the door downwards, the tension at the top right-edge of the door will try to pull itself free from the piano hinge.

To exaggerate for a minute, if the upper part of the piano hinge was adhered with rubber screws you would clearly see the screws stretch until they broke. That's tension.

We also need to keep in mind that with good joinery at the corners (our goal) the door may not distort, but the racking and tension forces will remain constant.

Compression

Generally speaking, compression can be ignored for a project of this type. This is not to say that compression is not a real force because it is. A normally jointed door is more that able to withstand this force.

Racking

It should be obvious by now that racking is the greatest of all of our distorting forces. The heavier the door contents, the greater will the racking force be. And speaking of heavy, the further away we place heavy items from the piano hinge, the greater will be the racking force. This is due to cantilevering, so heavy items should be placed as close to the hinge as possible.

Great! We now know a boat-load about forces that will be affecting our door. So lets put this newfound knowledge to work and design our door.

Design

From the onset our goal was to bevel all the joining surfaces to hide the edges of the plywood. Now, we need to determine where we want to plunge our dominos to keep the door rigid and undistorted during its lifetime.

We have also learned that the areas of greatest concern are the corners which distort due to the racking force caused by the weight of the door contents.

Reality Check

This is a good time to take a minute to try to figure out just what we are going to store in this door. If we have some idea of what this is going to be then we can come up with a rough estimate of the weight we are expecting the door to support. In truth, we oftentimes are not quite sure what we are going to store in a cabinet much less its door. However, it would help us to have some idea of the potential weight of the items we want to store in the door and design it accordingly.

I am planning to store all of my woodworking chisels in this door. This includes my Japanese dovetail and mortising chisels. And, to be crystal clear - I do not want any of my chisels hitting the concrete floor of my shop due to a poorly designed door.

The (unfinished) cabinet shown below shows the planes cabinet. The door to this cabinet will be used to store my chisels.

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Image 2
This photo shows the cabinet that will house all of my planes. As seen, it is not quite finished but will be in the near future. It will also hold other related items such as spoke shaves, plane irons and so on.

I took the time to weight all of the chisels I plan on storing in this cabinets door and the total weight came to 19-lbs. This knowledge gives me a very good idea of the weight this door must be able to support.

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Image 3
This photo shows how I spaced the dominos from the corners of the plywood door. The center of the first domino is 1-11/16 inches from the end. The second is 5 inches from the end.

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Construction

The first step is to dimension each side member and the door face. The door face will be 25" by 38". All of our stock is cut to spec. Great.

Now Step 1 of the tricky process. (Once the door is done I may look back and think that the process was not as tricky as I am now thinking it is. We will know about this soon enough.) Step 1 is to 'build' the door by standing the sides vertically as they will go when assembled. (Marking each member at this time is a good idea so that you will know where each member goes later on.) Then we place the top over the sides and align carefully. (I put a heavy weight on the top to keep all the members in alignment.)

Okay, we have our door setup correctly and now we want to mark - across the edge of the top and the side members, where we want to plunge each domino around the edges of our door. I used five dominos on each side. This was just my choice and nothing more. Whether I could have used more or less dominos is something that we will know later on. Keep in mind that the more dominos you use the more difficult the glue-up is going to be. Five domino's per side means that when the top is glued on you will have to deal with twenty domino's at once.

Assumng that all of our domino markings are completed (and correct!), we now want to plunge each mark with the Domino. Plunging the domino into the sides of the plywood requires a very careful plunge. I think that I will need to plunge the sided to a depth of 5/8". This will leave 1/8". I am aware that this is very shallow, but the domino has to have some glue area and I think this will work just fine if I work carefully.

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