A Woodworker’s Notebook: Fences

Timber can acquire a condition known as 'case hardened'. When the material is sawn, internal stresses are released and the wood can distort.
If the kerf spreads, one edge will tend to bear against the blade and the other will press against the kind of long fence often fitted to the type of saw illustrated below. When the wood is forced against the up-running teeth, there is a risk of a violent kickback. (In any event, the kerf will be scored by the sides of the up-running teeth).
Where the stuff is being divided into two sections by ripping, there is no need for the fence to extend any further than, say, two inches beyond the tips of the teeth. Auxillary fences are illustrated below. If this kind of auxillary ripping fence is fitted, there will be adequate space for any spreading. Some workers query the guidance of the work during the latter part of the cut. However, at this stage the riving knife offers the necessary steerage. This will not apply to workpieces shorter than the blade diameter.
On some modern saws, a two-position fence can be adjusted to enable its far end (the toe) to reach no further than as described above.
Long fences are fitted to enable work such as rebating and grooving in which the workpiece is not divided into two parts.

Fence Adjustment

If the fence is out of parallel so that it presses the wood towards the saw, there is a risk of a kickback from the up-running teeth and burning from friction between the wood and the saw's plate.

A two-position fence set up for normal ripping. Its toe extends a little beyond the cutting teeth.

The two-position fence is shown in position for bevelled cutting. This is also the best position for cutting thinner stuff since there is now adequate room for the push stick to operate during the final stages of the cut.

Left:For saws lacking the provision above, the lower auxillary fence guides the timber to just beyond the gullets of the cutting teeth.
The upper fence emulates the two-position fence in the low position. For the majority of rip cuts where a vertical reference is not required, it can serve quite well as a general-purpose fence.
Because the saw height can vary, the fixing points need to be slotted to allow fore and aft adjustment.

The right-hand diagram illustrates what can happen when a short offcut is trapped between the uprunning teeth and the fence. As the end is caught by the teeth, the offcut rotates. It deflects the blade until it is violently catapulted towards the sawyer.

It is worth noting that if the guard were to be in place, the chances of the offcut hitting the sawyer's face should be considerably reduced.

When cross-cutting with the aid of the sliding (mitre) fence, there is a natural temptation to use the ripping fence as a length stop. However, as illustrated above, this is a frequent cause of accident to the unwary. If the shaped block, shown left, is clamped to the fence, the workpiece can butt against its left-hand side. When the workpiece moves forwards there will now be adequate space for the offcuts.
The consequence of a kickback can be worse if the mitre fence is between the fence and blade. The operator will be holding the part that is ejected with consequent severe bruising the fingers, hand, and arm.
It is still wise to flick away each offcut with the push stick rather than allowing them to gather at the back of the saw.

For operations such as grooving, panel raising and so on, consult the Figure 8 and 9 of the HSE information sheet for general design details of a suitable guard/fence.HSE Information Sheet.

Given some assistance with taking off, this small section stuff is adequately guarded.

Since feeding becomes difficult, it does illustrate however, the difficulty of effectively guarding short sections.