Project: Making trivets
Words and photos: Geoff Birtles
As a bachelor who cannot and will not cook I cherish every dinner invitation, and try to ensure I am asked back time and time again. My favourite expression of appreciation (and bribery) are trivets. I have found that metering them out to the host cook one at a time guarantees I am asked back!
Trivets protect tables and benchtops from hot pans and serving dishes. These trivets are small triangular wooden frames that cooks love because they work well, and are decorative and light to handle. The joinery never fails to attract attention and provoke good pre-dinner discussion.
Timber preparation is exacting and the joinery challenges are significant but not difficult. Three jigs are involved, so both beginners and experienced woodworkers will enjoy a good deal of job satisfaction, not to mention much appreciation from the spouse. Batches of four are recommended to optimise timber preparation, and to fully capitalise on the jigs. You will need a few spare workpieces for set-ups and inevitable first time errors.
Step 1: Select a hardwood that will withstand abuse from heat and moisture. It is safer and more efficient to machine longer lengths and markedly assists with good clean joinery down the track. Mill 610mm lengths to 28 x 15mm, ensuring all sides are flat and square with crisp edges. If there is a power tool for the job, I use it. A 6" jointer and 12" thicknesser make quick work of batches. Others may prefer the zen of a bench plane and shooting board.
Step 2: Chop these 610mm lengths into three equal oversize lengths of about 200mm. If the wood grain shows promise, keep track of adjoining lengths so you can run the grain around the triangle. At this stage you should have 12 workpieces (with a few spares) for a batch of four trivets.
Step 3: Time to build your first jig: a complementary angle cutting jig for your mitre saw. These trivets are equilateral triangles with three corners, each of 60°. To achieve this each side must be cut at 30° to the long axis and exactly to length. It’s more challenging than you might think. See below how to increase the angle capacity of your mitre saw with jig no.1.
Step 4: First cut one end of each workpiece to 30°, then set your stop block to length (180mm), and cut the other end to exact length, also at a 30° angle.
Trivet jig no.1: Complementary angle cutting jig for mitre saw
Trivets are equilateral triangles—each corner is 60°. To form these you need to trim each end of each side piece at 30°. First do a test cut from scrap on your mitre saw.
Set the cut angle to 30°, push your workpiece against the fence and chop it. Use a protractor to check the angle. You got 60°? Damn right you did—that’s because the angles marked on your mitre saw scale are not what they seem. They are complementary angles of 90°, the default angle of your sawblade to the fence. (A pair of angles are ‘complementary’ if the sum of their measure is 90°.) So, the saw scale’s 30° is deducted from 90° to arrive at the true cutting angle of 60°. Crazy, but that’s how the scale is marked.
Fortunately the answer is more simple than understanding the maths. An auxiliary fence allows you to align the main (long) axis of your workpiece at 90° to the mitre saw fence (ie parallel to the sawblade’s default position). Now, the angle you set on your mitre saw base scale (for example 30°) is the actual angle you get in relation to the long axis of your workpiece. It’s a lot easier than it reads as shown in the photo below.
A 240mm square piece of 18mm MDF is secured to the mitre saw fence from behind with two hidden wood screws. (The front clamp simply stops the auxiliary MDF fence from levering upwards when the workpiece clamp is in use.) The left hand side of the MDF fence sits along the 90° blade axis. A toggle clamp secures the workpiece alongside and an adjustable stop block ensures equal cutting lengths for each side.
Set the blade to 30° on your scale and this is what you will get — subject to an accurate setting. Do check, your saw scale may be out and this will affect your joinery. Important: Do use a toggle clamp because this cutting angle is not safe to use with short narrow workpieces, particularly when the rotational direction of the blade will want to pull the workpiece toward the back of the saw where it is unsupported.
Gluing up the trivets
Time to build your second jig: the glue-up press is shown below. Do not worry— having made one batch of trivets you will be called upon for many more. One caul is fixed to the base and heavily reinforced, the others are loose. I use two Festool MFT SP fixed clamps (which locate in 20mm holes) to press the trivet into the fixed stop block and force the 30° end faces together. Note: These clamps are expensive but extremely useful around theworkshop. Cheaper push-pull toggle clamps are widely available and do the job well.
Do a dry assembly to make sure everything is correct before gluing. Glue up each trivet one at a time allowing about 45 minutes for the glue set-up. Be generous with glue (these are endgrain joints) and use a waterproof product such as Titebond III. Squeeze out doesn’t matter because of the melamine jig faces and the later finishing process. You will find even the most accurate end cuts will sometimes require paper shims in the inside face of the 60° cauls to close up the joints as shown in the photo. Allow 24 hours curing time before moving to the next cutting step.
Trivet jig no.2: glue-up press
My glue-up jig is made from a 500 x 330mm scrap piece of 16mm melamine faced chipboard which support three 60° (inside face) clamping cauls (you will need your complementary angle cutting jig to make these out of 40mm wide melamine strips).
The main caul stop block is secured to the base and supported on each side to withstand the pressure required for gap free joints.
The bottom right caul is pictured upside down to show how it is constructed from two 40mm strips each end cut to 30°. The 15mm relief hole in each caul allows the trivet apex to settle in, as gaps close. The toggle press clamp on the stop block caul is optional. With practice and the use of paper shims I found it unnecessary.
Cutting keyed mitre spline slots
Keyed mitre splines serve two purposes. The first is to reinforce an otherwise weak endgrain joint, the second is a point of visual interest. Crisp edges, tight joinery and clean well fitting splines are a matter of professional pride and will provoke admiration from recipients (hey, we all need it!).
Time to build your third jig: a keyed mitre slotting jig for the tablesaw (I told you this would be fun). You can do this while
your trivet glue-ups are curing overnight. My spline cutting jig is built from MDF scraps, as shown below.
Trivet jig no.3: Keyed mitre slotting jig
This slot or spline cutting jig is designed for the tablesaw. It is made from four pieces of MDF. Overall the jig is 300 x 100 x 49mm thick. The rear piece of MDF (riding along the fence) is 18mm thick.
The two centre pieces, each with a 30° angle intersecting to provide a 60° cradle, are from 25mm board and the outside front support is 6mm thick. All are just spot glued and pinned together with brads.
I constructed the cradle to oversize height and width, then trimmed (ripped) the bottom to just under the trivet bottom line (to minimise thin kerf blade flex) and crosscut each end to flush them up. The two lines on the outside face are set- up lines. The lower line indicates the bottom of the trivet, the top line is for the top of the required slot—you set your blade height to this.
You can now proceed to cut the spline slots. I use a thin kerf blade, which is good and bad. Thin keys look good but thin kerf blades flex marginally at higher cutting heights, which results in fractionally variable spline fits (you can’t see it, but you need to be aware of it when preparing your spline stock).
Set your rip fence to centre the spline and set your blade height for an attractive spline depth (about 35mm). Use scraps to ensure you have got it right as you are deep into the project by now. Cut the first slot, rotate the workpiece, cut the second and then the third slot. Keep the workpiece pressed hard against the right hand side of the jig and rip fence.
Spline mitre keys
1. Select a contrasting wood (I used jarrah off-cuts) and rip long grain to a thickness that is oversized to your trivet spline slots (about 3mm). I resaw offcuts to approximate thickness on the bandsaw, rip to approximately 40mm width strips on the tablesaw, then run the strips through my drum sander, testing the thickness with each pass on a slotted trivet until the fit is just right. You could rip with care on your tablesaw and then sand with an orbital sander, as thickness and tolerances are not that critical (glue will expand the key later on).
Drum sanding mitre spline stock to final thickness. The MDF sled allows accurate tolerances at fine thicknesses. The test trivet sits on a WIP rest for constant checks on fit.
2. Cut spline material to oversize length (about 60mm) and get ready for the glue-up. Test each spline for a snug but easy fit before gluing, as keys expand quickly with moisture. Work some glue into each slot (one at a time), and apply glue to contact areas of the spline stock. Wiggle each spline into its slot ensuring you have a close fit at the back of the spline, ‘persuade’ it if you have to. Wipe excess glue and check for no rear gaps again. If you feel your spline fits are a bit loose, use small G-clamps to close the slots for a snug fit. This is much better than trying to hammer home splitting splines that are too tight. I hope it is clear that the long grain of the keys (ie, the 60mm length) run across the trivet ends for strength. Let the keys set for at least half a day before trimming.
Trimming splines with a Japanese saw.
3. Now trim each spline to about 3mm from the trivet sides with a dozuki or other fine blade crosscut saw.
4. Splines can be milled flush to the trivet sides in many ways—just be sure not to lose the crisp edges. You can use a sharp block plane (planing from the tip toward the centre of the trivet), or use a sharp chisel to pare away the excess. You can also do it the easiest way of all using a flat belt linisher with a light touch, square feeding and remembering at all times that a linisher takes more from the lead- ing edge, so you need to rotate the work-piece. Practise first!
At this stage your trivets are looking pretty good, but a little messy from the glue-up and maybe the odd mitre edge standing a little proud on one side if it’s a first time exercise.
Do not be tempted, as I first was, to use a 6" rotary orbital sander on the faces, you will inevitably lose the crisp flat sides. Use a sanding block or a small fine orbital small — mine is 80 x 130mm with a 2mm stroke. Work up from 180 grit to 220 and 320 if you are looking for a special appearance. Use only a sanding block on the sides, taking particular care to retain squareness and sharp edges.
Trivets suffer a fair bit of abuse so I like to spray them with a pre-catalysed clear sanding sealer such as Mirotone’s Mirocat No.3242. Two coats, wet on wet. It’s ready for sanding in 90 minutes and hand sands silky smooth in seconds with 320 grit paper. The residual surface is hard and durable. Then just wax for a luxurious soft satin sheen. I use Mirotone’s Mirowax No.738 because it’s non-toxic and silicone free. Incidentally, this is a beautiful finish for small boxes and even furniture.
With these jigs and processes you are now equipped to make small batches of trivets – could be a commercial opportunity here for someone!
Geoff Birtles is a retired marketing and communications professional who has written several articles for Australian Wood Review. This article is republished from AWR#64. Links to some of his other stories are shown above right.