Domino-Plywood Joinery

WOOD WORKING BY DESIGN

Background

January 2017

Welcome to this Domino joiner woodworking project.

Before we get started I just want to make it clear that this project is about domino-plywood joinery and not the construction of anything specific. It's the 'finessing' of the Domino joiner to plunge mortises in thin plywood stock that this project is dedicated to. This is more of a demo than a project, but I'll stay with project.

In truth, this 'project' did come about while I was constructing a plywood cabinet for my wife, but I felt that the solutions I came up with were worthy of their own webpage. Hopefully, a reader could save him or herself some time by learing from my experience.

Our Goal

The goal in this project is to learn how to overcome the Domino's minimum fence-to-cutter distance so that we can center a mortise in the edge of thin wood stock. In this project I will be using plywood, but the results would apply equally well to all projects that require thin wood stock joinery.

The Festool Domino is an extremely versatile tool, but like any other power tool, it has its shortcomings. Fortunately, I think the fence-to-cutter distance or height, is its only drawback. It could be argued that its hefty price tag is a drawback, but I'm not here to debate that.

In my opinion, I do not think that all the possibilities that this power tool brings to the woodworker can ever be exhausted. Let's get started.

Metrics

First of all, lets define some terminology so we'll all be on the same sheet of music.

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IMAGE 1
Inches vs Centimeters vs Millimeters

Festool power tools are based on the metric system. So for the sake of simplicity, I'm going to forsake the British system and stick with the metric system. It's really quite simple as follows:

1 inch = 2.54cm = 25.4mm

To further simplify things (in this project only) I'm going to refer to 1 inch as 24mm, not 25.4mm. This means that 1/4-inch = 6mm which follows that 1/2-inch = 12mm and so on.

Note!
For those of you who are worried about the missing 1.4mm (25.4mm - 24mm = 1.4mm), let me be clear. As we proceed, you will see that this numeric simplification will only serve to make the position of the Domino mortise along the plywood edge easier to understand. It is much easier to refer to 1/4-inch as 6 mm rather than 6.35 mm along a 17.5 mm edge which is the thickness of the 3/4-inch plywood we will be using. In no time we would be splitting millimeters and we're not going to do that. We'll adhere to the K.I.S.S principal - Keep It Simple Sam.

Construction Material

For this project I chose to use 3/4-inch cabinet grade plywood. The "3/4-inch" is actually about 11/16-inch. As noted above we are going to use the metric system to keep things simple. That said, 11/16" is approximately 17.5 mm.

What we are about to learn can be applied equally well to any thin stock project that the woodworker plans on joining with the Festool Domino.

Design Layout

The following image shows the typical Domino joinery that we will be defining in this project.

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IMAGE 2
This image shows the edge and face views of the stock with all surfaces marked. The domino (dotted line), scribe mark and blue tape are are also shown. I will be referring to this image and its contents throughout this project so take a good look at it.

Domino Minimum Fence-Height Details

The first thing I want to do is to determine what the actual minimum fence-to-cutter-center height actually is using each of my Domino cutters.

If you look carefully at either side of your Domino, just below the fence, you will see a notch. This notch represents the center of the mortise. We can change the position of the fence, but the mortise will always be centered in this notch. The next image shows the notch against a metric rule.

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IMAGE 3
This image shows the Domino fence at its lowest setting. The metric rule shows the fence-to-centerline-notch height to be approximately 10 mm. This is the base info that we need to proceed.

Next, we want to draw a pencil mark that matches the Festool cutter center-line notch along our test board. This will be the bench-line that will help us visually determine the differences in each cutter's mortise in relation to the fence's lowest setting.

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IMAGE 4
This image shows the pencil mark we made on our test board aligned with the Festool mortise center-line notch.

We will now plunge mortises in our test board with each of our cutters and see how they compare. More importantly, we really want to know what the cutter-top-edge to the fence distance is with the Festool fence locked at its lowest setting.

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IMAGE 5
Here we see (from the left) the 8mm, 12mm and 14mm mortises with their respctive cutters. It can also be seen that each mortise was made with the Domino fence set at its lowest setting because each mortise is centered along the horizontal pencil mark we scribed above. To be clear, the fence was rested on the upper surface of the test board shown above.

Note. Festool also makes a 10mm cutter, but I did not purchase it so, unfortunately, is not included in this project.

Now that we have plunged our mortises we want to measure the distance from the upper edge of each mortise to the surface that the Festool fence was resting on. These measurements are shown in the next three images.

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IMAGE 6
This image shows the 8mm mortise upper-edge to fence height in millimeters.

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IMAGE 7
This image shows the 12mm mortise upper-edge to fence height in millimeters.

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IMAGE 8
This image shows the 14mm mortise upper-edge to fence height in millimeters.

Plywood Mortising Details

Note!
Before we begin, drag Image 2 to your desktop. This will make it much easier to follow along without having to scroll up and down as we progress through the rest of this project.

Mark Each Member CORRECTLY Before You Begin

As Image 2 shows, we need to put a short strip of blue tape on both the D and B-surfaces of our stock. And, it goes without saying, that each mortise position must be pencil-marked on both board members.

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IMAGE 9
This image shows my Lee Valley Veritas Saddle Square resting on the edge of the plywood 'Common Surface'.

Looking at Image 2 it's easy to see that we need mortise's in the D-surface and the edge of the C-B board where it joins surface D. While this is easy to understand when looking at the image, in practice the C-B edge can be problematic if it is not marked correctly before the mortise is made.

The D-surface mortise is a no-brainer because the mortise has to be made on only one side - the D side. However, when plunging the C-B member edge mortise, the Domino fence can be rested on either side of the C-B board. Only one side will be correct because the cutter is not precisely centered in the the edge of the board. If the cutter were perfectly centered in the edge of the board it would not matter which side we rested the Domino fence on when we plunge the C-B edge mortise.

That said we need to mark, with a bit of tape (as shown in Image 2), both the the B-surface of the C-B board and the D-surface of the A-D board before we begin. So looking at the image once again you will note that I have noted a 'Common Surface'. This 'Common Surface' includes the edge of the A-D member and the B-surface of the C-B member where the two members meet. Our goal is for this 'Common Surface' to be flush when the boards are joined. And, this is why we are marking each surface carefully before be make each mortise.

That said, it's obvious that the Domino fence needs to rest on D-surface to make that member's mortise. To make the edge mortise in the C-B member the Festool fence must rest on the B-surface. If the mortise is made with the Domino resting on C-surface the joint will not match. In other words, the seam will not be flush because the cutter is not centered perfectly in the plywood stock.

Which Mortise Do We Make First?

The C-B edge-mortise must be done first because its position is unique. The distance from the upper-edge of its mortise to the B-surface is what will determine the position of the D-surface mortise. In other words, once the C-B edge-mortise is plunged, its position will determine where we plunge the D-surface mortise. So lets figure out how we're going to do this.

Making The C-B Edge Mortise

Plunging the C-B edge-mortise is not difficult, but as noted above, the B-surface should be marked so that you will be sure to rest the Domino's fence on that surface and not on the C-surface. However, the first thing we need to do is to make a few test mortises in the edge of the plywood stock we are using in this project. These test mortises are necessary so we can get the mortise centered in the edge of the plywood.

Centering the 8mm Domino Cutter In The Edge

For this project I have chosen to use the 8mm cutter because it is approximately half the thickness of the plywood stock (17.5mm) we are going to use. So, the first order of business is to get the 8mm mortise centered in the edge of our plywood. To do that we need to make a test mortise in the edge of our plywood stock with the Domino at its lowest setting and work from there.

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IMAGE 10
This image shows two domino mortises made with the Domino fence resting on the upper surface of the plywood. The one on the right is the default lowest-set mortise. The left mortise was made using the spacer we will be discussing next.

Just to be clear, the fence was not changed for either of these mortises. The only difference was that the mortise on the left was made with a spacer and the one on the right was not.

Its obvious by looking at the above image that the left mortise is nearly centered in the plywood edge. The 'default' mortise on the right is too close to the lower edge of the plywood. I would prefer to have at a minimum 1/4-inch of stock on each side of the mortise, but that is not possible using the dimensiions of the plywood we are using and the 8mm cutter. The best we can hope for is that the stock between the mortise and the plywood surfaces be as uniform as possible.

We are using the 8mm cutter for this project. We know that the thickness of the stock is 17.5mm, so the 8mm mortise is roughly half of the thickness. That said, if we can plunge the 8mm mortise in the center of the edge that will leave us roughly 4.5mm on each side of the mortise. (17.5mm - 8mm = 9.5mm / 2 = 4.75mm) This means that we will have less than 1/4-inch (6mm) of stock on each side of the mortise, but this is the best we can do in this case.

Therefore, to center the cutter in the plywood edge we need to raise the cutter up and the simplest way to do that is to use a spacer between the Domino fence and the common surface of our stock.

Acrylic Spacer Details

I opted for thin acrlyic sheeting that was approximately 0.71mm in thickness. I found this acrylic sheeting at Hobby Lobby. The cost was approximately $6 for a 12-inch by 16-inch sheet (as best I recall).

One of my woodworking buddie's suggested using pieces of scrap veneer for spacers. I had already purchased my acrylic sheet so I continued on with that. However, for really fine-tuning the position of the mortise, veneer would certainly work. So keep that in back of your mind.

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IMAGE 11
This image shows the default thickness of the stock between the mortise and and the common surface as seen in Image 9 above.

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IMAGE 12
This image shows the mortise-to-common-surface thickness that was plunged using the spacer. We were trying for 4.75mm, but 4.85mm will suit our proposes just fine.

The next two images will clearly show the use of the acrylic spacer in use.

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IMAGE 13
This image shows the Domino fence resting on the B-surface of the plywood and the acrylic spacers ready to plunge the edge mortise.

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IMAGE 14
This image shows a close-up view of the Domino fence over the two acrylic spacers.

OK, the C-B edge-mortise is a done deal. Now, let's tackle the D-surface mortise. This one will require a bit more work.

Making The D-Surface Mortise

By this time, we should have the D-surface marked with blue tape. We now have to figure out how we are going to plunge this mortise so that it aligns perfectly with the C-B edge mortise we just made. The solution is not too difficult, but will require a simple wooden guide and a router bench setup to tweak the guide - and our mortise, to perfection.

In a nutshell, the guide will serve two purposes: (1), It will be used to rest the Domino fence up against guaranteeing that each mortise will be parrallel to the edge of the stock and (2), the guide will be be such that it will allow the Domino to be positioned a pre-determined distance away from the edge of the stock. This will insure that when the Domino tenon is fitted between the two boards the resultant seam will be flush.

So looking again at Image 2, if the D-surface mortise is too close to its edge the C-B board will be proud of the A-D edge and vice-versa. This means that our guide has to position the Domino perfectly so that when the boards are joined the two surfaces will be flush. This is not as difficult as it sounds, but - there is always a 'but' to deal with, to achieve this requires a bit of careful trial and error. However, this is not a big deal.

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IMAGE 15
This image shows the Domino resting on the D-surface and the aforementioned guide which is the light-colored board on the left edge of the plywood.
Making The D-Surface Guide

I made my guide out of a poplar stick. Once the stick is squared on all sides, then you can run it through the router bench. This is shown in Image 15 below.

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IMAGE 16
This image shows the guide being fed past the router bit. The router fence is on the left and the feather-board is on the right.

The image above shows our guide stick being passed through our router bench. The surface of our guide that is riding along the metal surface of the router bench top is the edge that will be clamped against our plywood stock.

Looking at the image, to move the mortise closer to the D-surface edge we raise the bit. After trimming the guide, we must make a test mortise, and repeat, until we get a flush fit.

The next image shows the guide in its working postion against the A-D board edge, D-surface up, of course.

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IMAGE 17
This image shows that the guides horizontal surface is slightly lower than the plywood surface. I did this on purpose so that it would not interfere with the position of the Domino fence while it rests on the D-surface of our plywood stock.

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IMAGE 18
This image is a closeup of the guide with the Domino flush againist the guide while resting on the D-surface of the A-D member. The poplar guide is much easier to see in this image.

So, as noted above, you will have to trim your guide, plunge a mortise and check the joint. It may take 2-3 trials until your joint is flush.

Your guide will work for all the 3/4-inch plywood Domino-joinery you may need to do in the future. We've jumped through all of the hoops in this project, but learning how to use Domino tenons in plywood makes for solid joinery that is a snap to do once you have your spacer and guide.