The spindle moulder, part 1: an introduction
Above: Hafco SP-300 spindle moulder
Words and photos: Neil Erasmus
The spindle moulder is still widely avoided because of fear of injury, and because of that, its broad range of uses is not appreciated. When correctly set up and used, it is a versatile and confidence inspiring gem of a machine.
How it works
The spindle moulder is a stand alone machine with a vertical shaft, generally 30mm in diameter that is threaded at the top and has a stepped flange at the base (photo 1). A huge range of dedicated cutters is available, each bored to suit the shaft diameter.
These are positioned on the shaft with a range of machined spacers that are clamped in place with a nut (or screw and washer) against the flange. Years ago, many furniture manufacturers ground their own high-speed steel cutter pairs into any shape required and clamped them over the spindle shaft between a pair of slotted collars. These are now regarded as being unsafe, not least because they have no built-in safety cut limiters.
The shaft is raised or lowered relative to the machine table and locked at the set height. Newer machines may sport a shaft that tilts to 45°, and most have a micro-adjustable fence that fits around the cutter assembly. The fence assembly has a parallel pair of fences that are used for moulding or edging straight stock.
The adjustable nature of these in- and out-feed fences allows a ‘planing’ action similar to that of a surface planing machine. The out-feed fence becomes a ramp for the newly machined surface as it’s fed through, while the in-feed fence regulates the amount of stock removal. Naturally, when only part of a straight edge needs moulding, grooving or rebating, the two fences are placed in line with one another. The fences are faced with solid wood and adjust to open or close the gap between them, the smaller the better. Some spindle moulders even have a sliding carriage with a fence and safety hold-down for endgrain work such as tenoning or finger-jointing.
A special bonnet type guard is used for shaped work (photo 2). These guards sometimes have a brake to keep the outer race of the bearing follower (if used) from spinning with the cutter. Both fence types include a dust extraction port.
Most machines have stepped motor and shaft pulleys to change the shaft speed somewhere between 3,000 and 11,000rpm. The rule is: the larger the diameter of the cutter being swung around, the lower the speed you choose, and vice versa. The basic science behind speed choices is what is called ‘peripheral speed’ or the speed at which the cutter moves past a stationary point. This is a factor of length measured as circumference, multiplied by the revolutions the cutter makes in a minute.
Most modern machines have an easy to reach emergency stop switch and built-in brake that stops the machine from spinning in seconds, while others have a foot brake at the base of the machine.
In this three-part series I’ll only be showing the machine in use with a rebating cutterblock such as the one shown in photo 3. This type of cutter is made either from machined aluminium or cast iron, and features two slots across the outside edge into which are clamped a pair of chipbreakers and double-sided, disposable carbide knives. It’s much like a narrow version of a modern planer cutterblock.
I own two other cutters. The first is a special combination cutterblock that allows a huge range of moulding profiles that are available at very reasonable prices. These have to be matched with cut-limiters which act as a safety device. The other cutterblock I have is a finger jointing one shown below in photo 4 that planes a complementary profile on two edges for almost indestructible joints. Both have to be used with the adjustable, straight fence.
The rebating cutter shown in photo 3 is 100mm in diameter and has 50mm knives. For curved shaping it is used either with a bearing follower, or a curved fence to allow both convex and concave shapes. As with the cutter, this bearing follower fits over the spindle shaft and may be placed either above, or below it. The special bonnet guard keeps fingers out of harm’s way, and also keeps the bearing follower stationary.
Router or spindle moulder?
Aside from the fact that the spindle moulder is a standalone machine, let's look at the basic differences between the router and the spindle moulder in terms of how and what they can accomplish.
1. Spin speed
Compare: a 19mm dia router cutter spins at 24,000rpm and a 100mm dia spindle cutter spins at 9,000rpm. Their circumferences are 59.7mm and 314.2mm respectively, while their peripheral speeds are 1,432.8 and 2,827 metres per minute. As you can see, the spindle moulder’s cutting speed is twice as fast. As far as I know, large routers don’t spin much faster than 24,00rpm. I run my 100mm cutterblock at 7,500rpm or 2,356.5mpm, the machine’s maximum speed—enough to deal with difficult woods, even when cutting against the grain.
It’s extremely important to wind down the speed on the router when using cutters larger than 19mm in diameter. The relatively light duty capacity of the hand-held router means peripheral speeds over 1,500mpm can spell disaster, especially with some of the huge cutters now available. Because of the sheer heft and fine tolerances of the spindle moulder, a much higher peripheral speed is considered safe. Spindle moulder cutterblocks all now specify the maximum safe speed.
The spindle cutter’s larger relative diameter (as well as its faster speed), allows a gentler, sweeping cut that leaves little, if any, splintering. A router cutter removing the same amount of material from the edge of a piece of wood has a tougher job as it cuts at a more direct angle across the grain, risking severe chipping. Cutting against the grain requires much more grunt, straining the cutter especially as it gets blunter.
3. Direction of cut
Because the spindle spins anti-clockwise, the work can ONLY be fed clockwise from the right around the cutter. With the router, freehand or table-mounted, anti-clockwise feed or ‘back-cutting’ is possible.
Making jigs for shaping curves
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.
Coming up in part 2, we'll look at designing and making a spindle jig with safety and efficiency in mind. The third and final part of this series will look at using the jig.
Neil Erasmus is a furniture designer/maker in Perth, WA. His article in the current issue (110) of Australian Wood Review looks in detail at the use and maintenance of hollow chisel mortisers.