The spindle moulder, part 2: designing and making spindle jigs
Words and photos: Neil Erasmus
In part 1 of this series we looked at the basic attributes and function of the spindle moulder, a machine that when properly set up and used can open up a world of capabilities.
Cutting curved edge shapes with a spindle jig allows you to mass produce identical components. This jig can in some cases be designed to cut all the edges, whether curved or not, of a piece of wood, including the endgrain. The only limitations to this kind of shaping work are that the minimum radius of the curve can’t exceed the diameter of the cutter, and the maximum height of cut is limited by the cutter height.
How to design a safe spindle jig
Here is a summary of the basic principles of designing and making a spindle jig with safety and efficiency in mind.
1. Don’t make the jig too small even for shaping small components—small jigs can allow hands to get dangerously close to the cutterblock.
2. Don’t make the jig too large and cumbersome. Remember these jigs are used cutter up/bearing down. If a large jig tilts up and off the bearing it could spell disaster as the jig will move straight into the cutter.
3. Allow for safety lead-in and lead-out at each end of each cut to guide work into and away from the cutter. Make sure when exiting cuts on component ends that any splintering will occur on yet-to-be-cut edges. This means lead-in and lead-out will both mostly be on the 1st cut side.
4. Use a minimum of 25mm thick material to offer maximum bearing contact, and to provide a rigid base for all fixings. Remember that if the jig lifts up and off the bearing follower edge for whatever reason, it moves straight into the cutter without any obstruction, turning it into a lethal workshop frisbee.
5. Space robust clamping bars every 300mm or so when clamping plates are not used.
In a past issue of Australian Wood Review (AWR#65) I showed how to make the wine table shown above. Each leg is fitted into a central, stubby post with a tapered sliding dovetail joint. I shaped the legs on a spindle jig which was made with the help of a ‘master template’.
Making the master template
This template jig is made from 9mm MDF and shaped by hand. It’s used for marking out the stock I wish to bandsaw and spindle shape using the spindle jig and it’s also how you can shape the actual spindle jig itself.
Straight edged templates can be cut with a circular saw, while curved ones like the one for the wine table can be hand drawn, bandsawed and faired to shape.
As shown above, useful sanding aid for curves can be made from a thin strip of flexible plywood or MDF, onto which sandpaper is attached with double-sided tape. This helps to fair both convex and concave shapes, into nice consistent curves.
Minimise short grain
In order to maintain structural strength in the leg, it is important to minimise short grain areas. The grain direction must run as parallel as possible along the centre axis of the leg. To better get an understanding of this, it’s time to use the master template to mark out, then plane, thickness and cut out the legs on the bandsaw, cutting to within 2mm of the line, on the waste side.
This diagram shows how to place the leg on the jig, bearing in mind the anti-clockwise direction that the cutter spins. You need to consider which face to place down: do you need to turn it over to ensure a better with-the-grain cut in the areas that matter?
Making the spindle jig
When you have decided how to orient the legs place two freshly bandsawn legs parallel on a piece of 25mm MDF. Separate them enough to leave between 200mm and 250mm between their outer edges. Mark around them with a fine pencil, then position the master template and this time, mark more heavily. Do the same on the other side.
Next draw two concentric circles 40mm apart on some 9mm MDF to create the lead-in and lead-out on the jig. The inside radius of each circle must be about 50mm greater than the radius of the cutterblock. These can simply be drawn using a compass, then bandsawn into two separate arcs and roughly sanded—no need to be too particular (photo 1).
Using the inside concave edge of the arc, draw the lead-ins and lead-outs as shown (photo 2). Each lead-in/out must extend a safe distance from the point of contact with the leg, to ensure a ‘neutral’ position can be maintained where the jig is up against the bearing surface, well before the cutter engages the leg.
Now that the radiused lead-ins and outs are drawn on the piece of 25mm MDF, lead-ins and outs must be created on the other side of the jig. These may simply be extensions of the lines where the leg begins and ends, and can be made from strips of 40 x 9mm MDF, rather than curves. I chose however to stick with the curves for this story. Simply draw a pair of straight lines on the jig, then cut two 150 x 40mm strips of 9mm MDF. These strips, together with the half circles are used later. The jig may now be cut out on the bandsaw, again leaving about 2mm waste (photo 3).
Now drill the counter-holes on the underside of the jig to take the heads of the bolts that act as screw hold-down clamps. Centre these along the length, one at each end, and the others spaced about 300mm apart (photo 4). Use a forstner bit chucked in the drill press—choose the right size and don’t drill too deep. After that, drill a clearance hole for the bolt shank through the centre of each hole.
Turn the jig back over again and fix the master template with partially driven-in nails over the 1st cut side of the jig—this is the side that allows the ends of the legs to be cut with the curved lead-ins. Next, cut the arc lead-ins to fit snugly up against the back edges of the leg master template: one at the top, the other at the bottom end of the leg (photo 5). Note: It is extremely important that these, temporary, lead-in/outs extend well beyond the jig as shown! They too must be fixed securely with nails. Tug on them to ensure that they can’t easily come loose.
The jig is now ready to shape on the spindle moulder. As the master template and temporary lead-in/outs on top of the jig guide the cutter, the bearing is placed above the cutter rather than below it. Try to get as much of the bearing to touch these 9mm MDF parts, while ensuring the jig gets properly cut underneath it.
Offer the lead-in on the left hand side of the jig up to the bearing, then, slowly move the jig towards the left until you can hear the cutter engage the jig. Keep moving, not too quickly—not too slowly, until the cutting finishes and the bearing supports the lead-out, finishing the operation. Never operate the jig anti-clockwise around the cutter, even when you miss part of the cut. If this happens, simply begin the feeding process all over again.
Now, remove all the 9mm lead-in/outs and the master template, and nail the template over the jig on the ‘second-cut’ side. Using the same 9mm MDF curves, again create lead-ins and outs at the ends of the leg template (photo 6). Repeat the process described above, but once cut (photo 7), leave the master template in place, removing only the lead-in/outs (photo 8).
Machine a length of solid hardwood, around 20mm wide and slightly narrower than the thickness of the material you wish to shape. Cross-cut this into several blocks, each of which has a corner removed from one end. Rub-glue in place the blocks against the master template, spacing them evenly around the template.
The little relieved corner should be trapped between the jig and template to allow a little space for any dust build-up to go. Position them so you can fix the leg in the same spot every time (photo 9). Once the glue has fully set, the master template can be removed (if you wish, the blocks can be screwed in place).
All that is left to do is to make the clamping bars and fit the bolts through the base of the jig. Make sure that the bolt is long enough to clamp the work between the jig and the clamping bars, leaving enough thread to fix either wing or plain nuts and washers. The clamping bars need to be robust enough not to flex—I generally use 40 x 40mm or bigger, hardwood, and cut each one well over-length before drilling a clearance hole through the centre of each (photo 10).
A quick calculation to determine the bolt length: 25mm MDF, plus, say, 22mm component thickness, plus 40mm clamping block, plus 25mm thread—this amounts to a minimum bolt length of 112mm, the closest available size being 125mm. I try to get 3/8” (9.5mm) bolts and matching washers and wing nuts. Place the bolts through the holes and epoxy glue the heads into the hole pockets, clamping them in place using the clamping bars and the roughed out legs. Apply enough pressure to pull the end of the bolt head under the surface of the MDF, then relax the pressure and allow the glue to set (photo 11). Sand the excess glue flush. Almost there!
Now, number and position the bars and jig and mark the top of each bar just inside the edge of the jig and cut them to length. Last, place a patch of 80 grit sandpaper under each bar and on top of the jig where the two meet. Also, mark the jig where it’s visible with the legs in place, on its 1st cut and 2nd cut sides. The jig is made! (photo 12)
The final part of this series will look at using the jig.
First published in Australian Wood Review, issue 67. Neil Erasmus is a furniture designer/maker in Perth, WA