Tilting platform jigs are by far the most versatile jig type. However they are difficult to accurately set to the different tilts for the different tool types, and the different blade thicknesses within each tool type. Aluminium oxide wheels continually lessen in diameter due to wear and dressing. Therefore a tilting platform jig can’t be permanently calibrated because the appropriate tilt for a particular tool steepens as the grinding-wheel diameter lessens. For this reason a simple 2-pin template also becomes increasingly inaccurate as the wheel diameter lessens.
In his 2001 book Woodturning Techniques Mike explained his invention of Darlow templates. These are computer designed to enable an accurate platform tilt to be set within 10 seconds for a particular tool whatever the wheel diameter. To make a template is so simple that Mike didn’t attempt to protect them. A booklet of templates was included in Mike’s DVD Sharpening Woodturning Tools. To obtain a copy of the booklet email Mike.
If you use a CBN wheel, the grinding-wheel diameter remain constant. Darlow templates are still the quickest and most-accurate way to set the appropriate tilt for each tool.
How Darlow templates work
Figure 1 shows a template. It has two pins which are pushed against the grinding wheel periphery to enable the platform tilt to be locked at the correct tilt.
Figure 1 The diagram for a Darlow template for a tool with a 30 degree bevel angle and a bevel thickness of 5 mm. Note the pink parallelogram. It’s shown in close-up in figure 2
Figure 2 Determining a Darlow template’s geometry. The pink parallelogram’s sharpening angle and bevel thickness remain constant as it is manipulated. The variables are: the length of the two opposite sides, the parallelogram’s inclination, and its position between the two arcs. The parallelogram is manipulated until all four of its corners touch the two arcs. The alignment of the bottom side is then that of the top surface of the tilting platform
Figure 2 Determining a Darlow template’s geometry. The pink parallelogram’s sharpening angle and bevel thickness remain constant as it is manipulated. The variables are: the length of the two opposite sides, the parallelogram’s inclination, and its position between the two arcs. The parallelogram is manipulated until all four of its corners touch the two arcs. The alignment of the bottom side is then that of the top surface of the tilting platform
Figure 4 Setting and locking the tilt of a two-lever tilting-platform jig