If you have ever built any piece of furniture that utilizes mortise and tenon joinery, you will know that creating the mortises and the tenons can be a time consuming process. Tenons (the part that fits into the mortises) can be made with hand saws, or powered saws with appropriate blades. Mortises (the "holes" in which the tenons fit) were traditionally made with hand drills and chisels.

Traditional mortises are rectangular or square in shape with "square" corners. Obviously, cutting a 'square' hole is not possible with your everyday drill, drill press or router. Enter the chisel mortiser... a tool that can indeed cut "square" edged holes for all your mortise and tenon joinery projects, or for arts and crafts furniture work where square wooden pegs or plugs may feature in the design.

There is a great debate between chisel mortiser users and router uses about the best way to create a mortise, however, the best way in my opinion, is the way that suits you best. I prefer the mortiser to make my mortises, and using a dado blade and tenoning jig on the table saw to cut the tenons, but you can use a router to make the mortises and then just round over the tenon. You will likely need to make a few mortising jigs if you go the router path however.

Ok, I digress... back to the mortising machine...

The TBM-160 Chisel Mortiser
Let me start by giving a quick run-down of how a chisel mortiser works, for any readers who are new to the craft. The mortiser looks a little bit like a drill press, and essentially, it is not much different. The mortiser is a drill press of sorts, but it also allows the fixing and use of hollow, square chisels. The mortise and chisel bit used in the machine consists of a hollow square chisel with a drill bit that spins within the square chisel. The drill bit, which is like an auger style bit for rapid chip removal, drills out the bulk of the material from the mortise, and the square chisel, which is set slightly higher than the drill bit "follows" behind and shaves / chisels out the round hole making it square, and hence, you end up with a square hole, all in one plunge action. You can buy kits for drill presses that turn them into a pseudo-chisel mortiser, and they can work well, but because some force is required in the squaring up of the drilled hole, the normal shorter handles of a drill press don't provide as much leverage, and setting up and removing the kit can be a bit of a pain. A dedicated machine is the way to go if you plan on making more than one or two mortise and tenon joint projects in a lifetime!

There are a number of mortise machines on the market, although they generally fall into a couple of classes, these being the budget machines, semi-professional units and machines made for industrial use. Naturally, their price tags are also in line with their class level, and the higher class machines generally have more user-friendly features and better build quality, but cost more. The TBM-160, feature wise, is probably within the realm of the semi-professional unit... i.e. a unit for the serious hobbyist woodworker, but within the budget real price range.

The TBM-160 comes shipped mostly assembled, although you will need to attach the work clamp, sliding table adjustment handle, leverage/plunge handle and mortise chisels bits etc. A basic black and white manual is included which is sufficiently worded and illustrated to make installation, setup and use relatively trouble-free. One mortise chisel and drill bit set (3.8") is included to get you started and this is quite sharp out of the box (usually the supplied cutters are not terribly sharp). Different sized chisel and bits can be purchased of course and most bit sets should fit the TBM-160 without too many problems.

The tool frame is cast iron construction, and weighs in at around 42 kilograms. It is a bit of a lift for one person, so grab another hand to help you retrieve the tool from the box and lift it onto your worktable or mounting stand. The nature of chisel mortisers is such that it must be clamped or secured to a solid work surface to be used safely. Because of the leverage applied the tool will have a tendency to rock forward when sitting on a bench unsecured in use. Holes for bolts to secure the tool to your workbench are milled into the base of the unit, and I would recommend bolting it down instead of using clamps to secure it if you can. The last thing you want is a 42 kg machine rocking and falling over on your workbench, or on to the floor and breaking a few toes, or worse! The machine is rather solid and balanced however in comparison to other similar sized mortisers I have used.

The TBM-160 features a half horsepower (370W) motor up top. This is a fairly standard size motor for many similar models in a similar price range. You don't really want anything smaller in terms of horsepower for a mortiser, especially if drilling very hard woods. However, if you have sharp drill bits and hollow chisels, the motor will certainly work its way through most any hardwoods without too much drama, even when using the largest 5/8" bits this machine is capable of using. In fact, the difference between dull and sharp bits could even, in my theoretical thoughts at least, equate to a 1/4HP motor difference. That is, a 1/2HP machine with sharp bits would probably work as well as a 3/4HP machine with dull bits. The motor drives the spindle at 1400 revolutions per minute. This is a fixed speed, and is suitable for the diameter of the drill bits that can be used in the machine. The motor casing is wrapped with aluminum cooling fins, much like you see on a computer heat sink. These fins help draw heat away from the tool and dissipate it into the surrounding air, mostly due to the much larger surface area the fins create. This helps keep the motor running cooler and extends motor life. A cooling fan up top adds to the heat reduction features as well. Power is applied via the basic ON/OFF controls on the front of the unit, just lateral to the motor. Green button for on, red for off, no rocket science there. The TBM-160 is very quiet when in use, so it's not going to annoy the neighbors too much. No need for hearing protection, but eye protection should be worn of course. The ON/OFF controls have a clear rubber dust cover enclosing them, however, I did need to reseat this cover out of the box as it had come away from its holding perimeter at the top edge. That's a two minute job and no further problem since.

If we move downwards from the motor and controls, we come to the main plunge shaft of the tool. The head of the tool (lift and drop body) moves up and down on a dovetail shaped column (also referred to as the trestle) via a circular gear mechanism seated in the trestle (rack and pinion type gear). Plunge action is very smooth and is assisted by the hydraulic lifter on the side of the machine, preventing the head sliding down under gravity on its own accord, and allowing the head to be lifted up again with relative ease. On the other side of the trestle column is the plunge lever. This is molded for a comfortable grip in the hand and is the lever by which both downward and upward plunge action is controlled. A longer lever provides better leverage and hence, more force when mortising. The lever on the TBM-160 is just about the right size given the motor power and overall size of the machine, and is slightly longer than my own mortise machine I have owned for around two years. I found it very easy to use and have no problems with the leverage it provides in use.

Just under the plunge lever is the depth stop adjustments. These comprise a round metal bar (with one edge machined flat) and two stop collars which can be tightened/released on the bar via their yellow screw knobs. The depth stop plate attached to the head of the tool rides against the bar and contacts the stop collars to provide the desired range of movement. One stop collar can be set to stop the tool at a fixed point when raised, and the other (the lower collar) is set to the depth you require the mortise to be in your workpiece. The collars are easy to manipulate, however, you do have to be careful as repeated tapping or pushing on the lower collar while plunge mortising can cause it to move if not firmly tightened. This was perhaps my only big issue with the TBM-160. It can be overcome however, as the stop collars and bar they ride on and clamp to can be easily disassembled for a different type of depth stop collar or system to be applied - You will need to come up with your own solution for this if you find it is a problem. Despite this, if you keep an eye on the depth stop collar and don't deliberately crash down on the stop collar hard each time you plunge the head of the tool, they do hold quite firm.

The TBM-160 has a spindle stroke of 100mm, i.e. the plunge range on the shaft from top to bottom is 100mm, however, with the largest chisel inserted, the maximum travel of the chisel is 75mm, still plenty for your every day mortising tasks.

Next we have the drill chuck and mortise bit holder. The drill chuck works in the same fashion as any other and a chuck key is required to grip your drill bit (fairly essential for this type of tool - a keyless chuck may not grip the drill bit as well). The chuck can take drill bits from 1.5mm - 13mm in diameter. You can actually use the TBM-160 as a regular drill press if you like, but you will need quite long drill bits for most tasks, and you can only spin them at the speed the tool is fixed at (1400RPM), so it isn't as 'flexible' as a regular drill press in this regard.

Just below is the area where the hollow chisel is seated. The hollow chisel is inserted from below and pushed up as far as it will go before you secure it via the hex screw on the lateral edge. The chisel does secure quite well via this design and I had no problems with it dislodging, slipping or falling out. Note that when you insert and secure the hollow chisel, it is important that you line up the face of the chisel to be square with the edge of your workpiece so your mortise remains square to the edge when cut. Additionally, the open section of the hollow chisel needs to be facing the correct direction for effective chip clearance by the drill bit. It either faces left or right (when standing at the front of the machine). The open side of the chisel basically faces the same direction as the movement of the workpiece as you progress cutting the mortise. It is also important to set the drill bit the right distance from the tip of the chisel. This distance can have quite a large effect on how well, or how poorly your drill and chisel work together, and hence, how easy or difficult it is to cut your mortises. The manual recommends 0.8mm - 1.6mm from the flat section of the drill bit to the chisel tips. I varied the distance but found distances closer to the 1.6mm range to work better for me, your mileage may vary!

Moving on down, we basically come to the work table. This is where the TBM-160 is somewhat unique against the competition in a similar price range. Most budget mortisers have a fixed work table. The TBM-160 however, has a 'moving' table, capable of sliding on both the X and Y axis - again using well machined dovetail-shaped slide surfaces. This is a very handy feature to have and can make your mortising tasks a fair bit quicker to complete, and with a little more accuracy and less fiddling around with moving fences etc. The work surface can be moved left and right and forward and back. A small knob on the front of the machine adjusts the forward/back movement slowly, but this allows precise accuracy. If you are cutting mortises wider than the largest mortise bits you have available, the forward/back table movement allows you to position your piece without unclamping or adjusting fences - a great time saver. A shaft and attached handle just below this provides the mechanism to slide the table left and right. You will use this axis of movement for most mortising tasks and, again, means you can keep the workpiece clamped firmly throughout the entire cutting procedure. The table slides through 230mm on the X axis (left and right), which should be more than enough for most all mortising tasks. The Y axis range (forward/back) is 45mm, again, enough for the majority of tasks (unless you are making very wide mortises) - rack and pinion type mechanism at work again here.

The fence on the TBM-160 is made of aluminum angle. It is very rigid and certainly suitable for the task, although do check that is is actually square to the worktable surface before you use the machine. If not square, it can be removed and shimmed to achieve a square face. This is an important check as anything you clamp against this fence needs to be square to ensure square mortises front to back. Remember that good initial setup generally means good results!

The work clamp is another nice feature. On many budget mortisers the clamp is a small "U" shaped device that clamps to a post and is designed to hold down the workpiece so the chisel does not lift it on exit. The clamp on the TBM-160 is definitely a "clamp" and holds your piece tightly to the fence, resisting any movement in any direction while mortising. It is adjustable forward/back via the screws that hold it to the table, and can be positioned in two locations for both wide and thinner pieces. It can also be adjusted forward/back within these two locations via the milled slots on the clamp's base (see photo). The clamp is adjusted via the large circular wheel at the front. It can be a bit slow to adjust and a crank handle on the wheel would certainly make things much simpler to operate, however, you do only need to clamp the piece once thanks to the sliding table features, so I won't be overly critical on that point. Max clamping width is 100mm.

In Use
So how did we find the tool to use overall? Setup was fairly quick and no major dramas. Once you have your tool plugged in and drill and chisel bits inserted and secured, you clamp your workpiece to the table/fence and using the X/Y table slide axis, position your piece (pre-marked for the mortise location) ready for the first plunge. Switch on, and make the first cut. Note that if you are making deep plunge mortise cuts, it is best to mill them in several shallower passes as it will cut better and be less likely to overheat and dull your drill bit and chisel. Also, deeper plunges do not clear the chips out as well as shallow plunges. If you have not used a mortiser before, you might be surprised at how much force is needed to get that chisel shaving and squaring up the cut. It is a fair bit more force than your standard drill press, hence the longer handles on a mortiser. The plunge force needed on the TBM-160 was not a lot different to my other budget mortiser model, so it's no worse than that... quite normal in fact, perhaps a shade easier. The force needed can be markedly reduced by having nice sharp bits however, and for that you will probably require a mortise sharpening kit (see below).

I digress, back to the action. You make the first plunge cut to your pre-set collar depth, then you just grab the X axis table handle and slide the table over the width of a chisel and make the second plunge cut, and so on. The TBM-160 does plunge smoother than my budget Carbatec model, and is certainly much easier to use with the sliding table - that is, in my opinion, the best feature of the tool. You wouldn't go back to a non-sliding version once you have used a sliding table mortiser, that's for sure. We made many plunge cuts in your standard off-the-shelf soft pine wood and it handles that with no problem at all. Remember that the mortiser is not going to cut mortises with as clean an edge as a router will, but you don't have to square them up or round over your matching tenon either, and given that the edges of your mortise are going to be covered anyway, know one is going to see the mortise edges. The results are quite good actually and you end up with a nice square mortise that is cut probably 20 times faster as doing it with a drill and chisel manually. Check out our close-up photo of a mortise cut in pine for the finished result.

Naturally, we also set the TBM-160 on to various hardwoods and cut several mortises as well. Not all hard woods are created equal of course and varying amount of force are required to get that chisel down into the wood. We have shown a photo here of a mortise being cut in New Guinea Rosewood. We are cutting a mortise wider than the chisel itself, and hence have to make two row passes to get it to width. We have cut the first edge and working our way along with a second pass to widen it up. Again the TBM-160 handled the task without too many problems, and performed similarly with other hardwoods such as Jarrah, and Tasmanian Oak.

The TBM-160 overall performed very well. You might get a bit of a noise in use from the drill bit touching the inside of the hollow chisel. This is quite normal, but as mentioned above, certainly no need for hearing protection here.

Given the retail price of AUD$349.00 for the TBM-160 (June 05), I believe it offers good value for money, particularly with the sliding table. You have to spend a fair bit more than that to get a machine with a sliding table function. I do think the stop collar design could be improved slightly to be more rigid and less prone to dislodgement and movement, but overall, the tool is quite well machined (the work table almost having a mirror finish). The maximum clamping width may be a factor if you are planning to mortise large table legs, but that is something for you to consider. If this is the case, you might need a larger machine with a wider throat anyway, and these generally do not fall under the budget or semi-pro category. If I had to give the TBM-160 a score out of ten considering build quality, features, value for money and overall function and use, I'd give it an 8 out of 10.

Mortise Chisel Sharpening Kit
If you are going to buy a chisel mortiser, you should also invest in mortise chisel sharpening kit. Sharp chisels and bits make cutting mortises much easier. Mortise sharpening kits are available from a number of sources, but we tested the MCS-01 set sold by Timbecon (Western Australia) for AUD$89.00 (June 05). The kit allows you to sharpen both the inner and outer edges of the mortise chisel.

Firstly, to sharpen the inner bevel of the mortise chisel, you take the countersink bit and secure the correct sized alignment bush into it for the sized chisel you are sharpening. The alignment bush helps you keep the countersink sharpening bit in line while the sharpening action is in progress. You can then use a hand brace or a drill to slowly sharpen/shape the inner bevel. You can also use a slow speed drill, or you can rig up some clamps or jigs and run the countersink in a drill press on slow speed (sub-200rpm is best), but you have to be careful and ensure alignment for best results.

With the inner bevel sharpened, you will probably have a small burr on the outside faces of the chisel. Included in the MCS-01 kit is a credit card sized diamond sharpening plate. Simply keep the chisel face flat against the diamond stone and move it over the surface to remove the burr. With the burr removed on each of the four faces, you should now have a pretty sharp mortise chisel to work with. You will need to sharpen the cutting edges of the drill bit using conventional tools as these are not supplied, but a few small diamond sharpening sticks are great for this task. Also, the diamond plate supplied in this kit can certainly be used to sharpen many other tools. Diamond plates are extremely hard wearing and don't really wear out and remain flat for a very long time (I have a couple diamond plates I have had for about 3 years and all are still flat and sharpen just as well as the day I bought them), so the diamond plate will come in handy for more than just sharpening your mortise chisels.

I noticed a good difference in cutting speed and ability after sharpening the inner and outer bevels of the mortise chisel and the cutting sections of the included drilling bit. These kits are certainly worth the asking price. I have seen the countersink bits for cheaper, but this kit includes the diamond stone which is worth a fair bit on its own. If you are going to be doing a fair bit of mortise cutting, grab a sharpening kit to keep your bits in tip-top shape.
 

Sherwood TBM-160 Photos
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The TBM-160 features solid cast-iron construction throughout.

The adjustable work clamp holds your piece secure throughout the mortising process.

The front slide handle moves the table left and right.

The gears that help slide the table left/right.

The table also moves forward and backward (Y axis) on dovetailed slides.

The two depth stop collars help limit plunge range for accurate mortising depth.

1/2 HP motor is fan cooled and metal fins help disperse heat more effectively.

Plunge handle is sufficiently long enough to provide good leverage and force.

Drill bit and hollow mortise chisel secured and ready to go...

Making a mortise in pine...

Good clean results from our first mortise!

Making a wide mortise in hardwood taking a couple of passes.

The MCS-01 mortise chisel sharpening kit.

The countersink sharpens the inside bevel and the included diamond plate handles the burrs on the outside faces.

A sharp mortise chisel ready for action!