High C

When sawing, a blade can either be designed to cut while in tension, or compression.  If the blade is being pushed into the cut, then it is likely to be a compressive stroke – typical for western handsaws.  Nothing wrong with this, although as a saw blade tends to be pretty thin, it will try to buckle when in a compressive load, and so the saw either needs the blade to be thick and wide enough to cope, or have some inherent features to stabilise the blade.

Hand SawThis is a typical panel saw.  The thickness of the steel, and the overall width of the blade means it can cope with the compressive forces during the cut stroke, where the blade is pushed into and through the material being cut.

211803This is a small crosscut saw (and specifically a dovetail saw, from Veritas), which also cuts on a compressive stroke.  It has thinner steel, and a narrower overall width, so uses a support bar along the length of the blade to keep it stable.

Japanese SawsJapanese blades tend to be used on the pull stroke, a tension stroke so they are significantly thinner than their western counterparts.

Some blades are attached at either end, which presents a different opportunity, namely allowing the blade to be placed into tension increasing the beam strength, and resulting in a push stroke being able to occur without the blade going into compression, despite the direction of the cut.

This is the principle that bandsaws and scroll saws work on, as well as handsaws such as the bowsaw

IMG_5918-bowsaw-turning-sawand the coping saw.

The fact that these blades never go into compression is obvious from their blades.  They can be very thin, and therefore particularly good at cutting curves.

A cheap coping saw has a thin frame, which will bend if the tension in the blade is too high.  The blade needs to stay in tension however, and this is particularly important when cutting curves in the timber.  If the blade is not tight enough, then it will wander in the cut.

To make a frame more capable of dealing with  tension conditions, you need to modify the frame.  There is a common structure in use that greatly improves the structure’s strength.  The box section design of a bridge.

 

1024px-The_Little_Belt_Bridge_(1935) The diagonal bracing transfers load, so no one area has to cope with the entire load, and therefore fail.

Knew Concepts have recognised that fact, and have produced a coping saw with the same engineering principles bought into play.

That saw is the Knew Concepts Coping Saw, sold in Australia by Henry Eckert (.com)

_DSC2465-EditThe saw has significant strength in the frame, allowing the blade to be used a lot tighter than usual.  When plucked, I swear the blade produces a high C!

The crossbracing really strengthens the frame.

_DSC2467-Edit

The saw looks bulky, but is really light – beautifully so.

To get a blade that tight needs a special mechanism.  One that can be quickly released so the blade can be repositioned at a different rotation (8 different positions at 45 degree increments), and fed through a hole cut in the object to allow internal cuts (then as quickly retensioned).

_DSC2468-EditIt works on a preset tension using a knurled knob, then a cam lever allowing that tension to be applied and released.

It is beautifully made, simple and light, and based on sound engineering principles.

Knew Concepts Coping Saw

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