Page 18 of the Tormek Handbook (which can be downloaded for free once you register at
http://tormek.com/international/en/account/register/) explains perhaps why Tormek hasn't developed a tool rest like our homemade version.
Tool Rests and Grinding JigsTo achieve an even and sharp edge, the tool must be held steadily and with a consistent
grinding angle to the wheel. This is obtained by resting the tool on a tool rest or clamping
it in a grinding jig.
A common tool rest on fast running bench grinders is a bent plate which is usually too short
to support the tool properly. This simple tool rest can be replaced by a larger and more sturdy
support to enable you to hold the tool steadily towards the grinding wheel. The tool rest can
also have a fence which is guided in a slot, so you can keep the tool at 90° or at a specific
skew angle to the grinding wheel.
These type of tool rests have been developed for high speed grinders, where you work with a
low grinding pressure due to the high rpm. However when mounted on a water-cooled grinder
which requires a higher grinding pressure, they do not work satisfactorily. This is because
the pressure which you apply to the tool does not reach the grinding spot but instead goes
to the tool rest. (Picture no 1).
To obtain the required grinding pressure, you also need to push the tool from the handle direction
towards the wheel. Then the tool tends to climb up on the grindstone and the precision
is lost. (Picture no 2). You need to push the tool both towards the wheel and downwards so
that it does not lose its contact with the tool rest. In practice this is not possible.
This effect appears when grinding narrow edge angles and when grinding both towards and
away from the edge. The disadvantage is more severe when grinding turning tools, as they
are often made of HSS-steel which is hard and requires a high grinding pressure.
For turning scrapers which are ground at larger edge angles, this type of tool rest works
satisfactorily on dry or water-cooled grinders. The reason that these types of tool rest work
fairly well on high speed dry-grinders, is that they require a lower grinding pressure and
therefore the disadvantages can be overcome.