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In early 2005 I upgraded my shop from hobby-quality machines to a MiniMax CU410 Elite combination machine. The power, performance, and accuracy of the sliding table saw, shaper, jointer, planer, and mortiser are amazing. Jenny's reaction was that I should have bought it 30 years ago.
One of the components of the machine is a mortiser, available on several different MiniMax machines. The mortiser consists of a heavy cast unit that attaches to the side of the machine, so that a special "birds mouth" bit can be driven by a chuck at the end of the jointer/planer cutter. (Some people use an end mill rather than a birds mouth bit.) This gives me a 4.7 hp mortiser! The work piece is firmly clamped to a moving table. The height of the table that holds the work can be precisely adjusted with a crank. The table manually moves left and right, in and out, with stops to limit the left and right movement of the table (the length of the mortise) and another stop to limit the depth of the cut. The birds mouth bit looks like a long router bit, and cuts with left-right movement - it does not plunge. Different bits are used for different width mortises.
It does a superb job, making mortises so easy and fast that I now use floating tenons, with mortises on both parts. Time to do the actual cut a typical mortise is about 10 seconds. Setup time including finding and putting the bit in the chuck, etc. is a few minutes, but a change in setup (e.g. for an apron not flush with a leg) is well under a minute. I had one project that required 252 large mortises in ipe wood, but that took several hours.
This is a description of how I use the unit to do a typical table leg and apron.
I found it very convenient to make marks on the table at the left most position and the right-most position that the bit can reach - see little marks by the left and right red arrows in the picture. In addition, on my machine the stops that limit the left and right movement cannot go past the center, so I made an additional mark there, by the middle red arrow ... that center point will always be included in the mortise. Don't ask me how many times I have set up a mortise, then had to set it up again to include that point. Some of my friend's (newer) machines don't have the restriction in the middle. |
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Since the center of the table must be part of the mortise, the guide provided must be removed, since it attaches in the center of the table. I invested in a sophisticated replacement guide - a scrap of MDF and an old C-Clamp ... with the screw on the lower side, it easily attaches to the cast iron table, with the screw part avoiding the cast iron ribs. This guide stays in position to align both the aprons and legs in a typical use. Breaking news... I have upgraded the jig to a scrap of hardwood rather than MDF! I marked a depth scale on the wood (3/4, 1, 1 1/4, 1 1/2) so that I don't need a ruler to set the depth of the mortise. |
Either the leg or apron can go first, here I started with the leg. The leg is mounted against the sophisticated shop built stop described above, and along the machined edge of the table. It is clamped firmly in place with the eccentric clamp provided. The left and right stops are adjusted to the distance the mortise is from the top of the leg and for the overall height of the mortise. The maximum depth is set on that stop as well. The actual cut consists of moving the table in until the bit just touches the wood, them moving the table left and right to cut the mortise. As you move left and right, apply a slight pressure to make the cut deeper... like a plunge router without a plunge bit, you will gradually work your way to the bottom of the mortise. |
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The apron uses the same alignment - the shop-built guide still marks the distance from the top of the workpiece to the top of the mortise (the same for the leg and apron). The length of the mortise is the same. The table height is adjusted for the amount the aprons are set back from the front of the leg. The eccentric clamp cannot reach the apron, so a second sophisticated shop-built jig is called into play. This one consists of a scrap of plywood, with some sandpaper glued to the underside to prevent slippage. A scrap cut-off from the apron holds the far end of the jig, with the eccentric clamp pushing down in the middle. |
The floating tenon stock is cut in advance using the thickness planer to create stock the size of the mortising bits (usually whenever I have some scrap wood of the appropriate size). The edges can be quickly rounded on a sander, ideally leaving a small area on the top and bottom of the floating tenon for the glue and air to escape. On other pieces I round over the edges with a roundover bit or bead cutter on the shaper (I don't have a router table, but that would work, too). Note that with the router or shaper you need to use a fence, since you are cutting away the part a guide bearing would follow. |
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When the mortiser is first attached to the side of the jointer/planer, it will seem too high. It can be raised and lowered with the screws it rests on at the bottom. Don't change it like I did. The normal position of the mortiser is fairly high on the mount, and if it is lowered, you may have trouble centering the mortise in thinner boards.
To check the alignment of the mortiser, I put the largest bit in the chuck, and raise the table until it almost touches the bit (separated by, perhaps, the thickness of a sheet of paper). Move the table back and forth, in and out, so this gap is constant. No special alignment procedures... the obvious screws are adjusted for left and right slope. I haven't had to perform the "slope away from the machine" alignments on any of the four machines I have helped set up.
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©2005, 2008 by Charles A. Plesums, Austin, Texas USA. ALL RIGHTS RESERVED.
