Product Reviews » JessEm Zip Slot Mortise Mills
Add a drill and the Zip Slot Mills provide an easy and effective way to do loose tenon joinery.
JessEm Tools has rolled out a couple of new products designed to make loose tenon joinery easy. Their Zip Slot Mortise Mill, $250, and Pocket Zip Slot Mortise Mill, $100, use a special drill bit, in conjunction with the mills, to create the required mortises.
|Pocket Zip Slot Mill||Zip Slot Mill|
What is Loose Tenon Joinery?
In loose tenon joinery a mortise is cut into both of the mating pieces and a separate piece of tenon material, the loose tenon, is glued into the joint (Photo 1). Many woodworkers consider this easier than cutting a mortise in one piece and a tenon on another. As long as the loose tenon material is a good fit for the mortises, you've got a solid joint. Loose tenon joinery does eliminate the fussiness of trying to produce a perfectly machined tenon to match the mortises you've made.
It also makes project math a little easier. Since your parts will simply be butting against each other, you don't have to calculate the allowance for extra material for the tenon. This can help you avoid mental errors when prepping your project parts.
The real key to loose tenon joinery is being able to accurately and easily machine the mortises. Mortises cut into face grain, like on the face of a chair or table leg, aren't too hard to cut. They can be done using a mortise machine, hand held router, or router table. But cutting mortises into the end grain of a rail is
tough. The JessEm Mortise Mills do a good job of making it easy to accurately locate the mortises and an equally good job of making it easy to cut the mortises.
|Photo 2. The drill bit used with the Mortise Mills has been specially designed for this purpose. The cutting action is similar to a router bit.|
How the Mills Work
The first step in using the Mortise Mills is locating them on the material. Two primary adjustments are required. The technique for
this varies slightly between the two mills and will be covered in more detail later.
Both Mortise Mills consist of a carriage that slides back and forth on rails. A drill bit is inserted through the guide bushing on the carriage. To make a mortise, you apply down pressure to the spinning drill bit while at the same time levering the carriage back and forth. This action forms the mortise.
JessEm's Mortise Mills rely on a special drill bit (Photo 2).
The cutting tip looks similar to that on an upcut spiral router bit, but the bit is designed for the lower speed of a drill, not the high speed of a router. Depth of cut is controlled by a stop collar on the drill bit.
The loose tenon material can also be purchased from JessEm. 50-piece bags of the 1/4" material cost $9. Bags with 40 pieces of 3/8" material cost $13. 30-piece bags of 1/2" material cost $15. Now we can look at how each of the mills is set up to make mortises.
Using the Pocket Zip Slot Mill
The Pocket Mill comes with a 1/4" guide bushing and drill bit and cuts mortises only for JessEm's 1/4" x 1-1/4" loose tenon material.
The first step is setting the depth of the drill bit (Photo 3). It should cut slightly deeper than 1/2 the length of the tenon and is locked in that position using the stop collar. Next, locate the carriage plate. This is done by loosening the lock screws and positioning the edge of the plate on the center line of your mortise (Photo 4). The maximum distance you can set this to is 1", so you can get to the middle of pieces up to
The next step is to position the Pocket Mill on your material. This is done by marking out the center line of the mortise on the face of the material, then aligning the edge of the alignment window with the pencil line
With the mill held firmly in alignment on the part, lock everything into a vise. Insert the bit through the guide bushing, turn on the drill, and apply gentle down pressure (Photo 6). At the same time, move the lever back and forth. You've formed a mortise. Now let's have a look at doing a similar operation on the larger mill.
Using the Zip Slot Mill
The Zip Slot Mill comes with a 3/8" guide bushing and bit, so is set to make mortises for JessEm's 3/8". x 1-1/4" loose tenons. Additional guide bushing and bits are available that allow making 1/4" or 1/2" mortises, (Photo 7), giving you more loose tenon size options than the Pocket Mill. Setting the cutting depth is done the same way as on the Pocket Mill.
Next, you've got to lock in three settings: the length of the
stroke, the position of the carriage plate, and the position of the mill on your material. If you love nicely engineered tools, you'll love the Zip Slot Mill.
The length of the carriage stroke is variable because this mill will handle more than one size of loose tenon material.The stroke is controlled by positioning the stop. It takes some practice to get used to the measuring system, but once you get it, it's easy. Because of the different diameter bits the mill accommodates, stroke length is based on the center of the bit, not the diameter of the bit. This is explained well in the owner's manual and the stop system includes a pointer and built-in scale that works well (Photo 8).
The carriage can be positioned using any of three methods. The simplest approach is to use the built-in scales and pointer, which indicate the distance to the center of the mortise (Photo 9). You can also lay out the center of the mortise and position the edge of the carriage plate on the line (Photo 10). Finally, you can use the 'cross hair' lines, which will provide the carriage and material stop position (Photo 11). The maximum distance you can set the carriage to is 2", so you can get to the middle of pieces up to 4" thick.
Locating the mill on your work is done with the built-in stop (Photo 12). Again, the positioning is based on the center of the bit plus the length of the mortise you'll be cutting. The owner's manual explains this well. The stop can also be flipped over to handle material cut at 45-degrees (Photo 13). Once the stop is set, it's very easy to get repeatable results with the mortise location.
Finally, clamp your material in place, connect a shop vacuum to the mill and you're ready to cut a mortise (Photo 14).
How They Differ
Obviously there's a significant price difference between the two mills. The Pocket Mill is
limited to 1/4" mortises, while the large mill
can handle 1/4", 3/8", and 1/2" mortises. Adding the 1/4" and 1/2" guide bushings and drill bits will cost $25 and $33, respectively. The large mill provides more joinery versatility, but if your work is primarily in 3/4" material, 1/4" mortises are fine.
The big difference between the two mills is in set up. Once I used the built-in scales on the large mill, I
was spoiled. It's much more user friendly than the Pocket Mill, with easier repeatability of settings. The dust collection worked great, although this isn't a tool that, like a router, sprays dust everywhere if you're not using dust collection.
Since you can customize the stroke length on the large mill you can easily make your own loose tenon material and adjust the stroke to fit. The longest mortise the large mill will cut is 3-1/2".
The large mill is bolted or clamped to a bench. You bring the material to the tool and clamp it in place.
This is easier than the Pocket Mill on which you hold the mill and material in alignment and secure them
in a vise.
The lack of a stop for locating material on the Pocket Mill made it tedious to position the mill on the material and also provided a great opportunity to make mistakes. I came up with a shop-made stop block that eliminated the need to align to a mark on every piece and this made the process a lot simpler (Photo 15).
Both of these mills do what they promise,
which is to provide a relatively easy way to cut mortises for loose tenon joinery. JessEm typically produces high quality, well thought out products and these tools don't disappoint. As an extra benefit, by drilling one hole at each end of the stroke, the mills can be used as doweling jigs (Photo 16).
The scales on the large mill made the required set up very easy to do. Changing one guide bushing for another is simple. The guide bushings on both mills are not simply bushings. They have bearings, so should be long-lived.
Having cut mortise and tenon joints a variety of ways and watched many of my students do the same, I think most woodworkers new to mortise and tenon joinery will find that using the Mortise Mills is simpler than traditional mortise and tenon joinery. My biggest complaint is that the drilling process felt slow, especially when using the 1/2" bit, but it's not a deal breaker.