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

10 Responses

  1. Dovetails are rip saws.

    • Technically, I do agree. They have the same form and tooth structure and count as crosscut saws, just used for a different purpose.

      • I agree that dovetail saws are rip saws but coping saws don’t get used to cut the dovetails (they wander too much), they typically get used to remove the waste which is a crosscut.

        • Think we are talking about two different things here. However, whether this coping saw can be used to cut a dovetail would be interesting. Normally, a coping saw has two reasons to wander. Firstly, blade tension. With the tension this saw can achieve, that is unlikely to be a problem. Secondly, whether the operator can keep the blade cutting in a straight line. This may not be a problem depending on how straight you can cut, and the width of the blade you use.

          Coping saw blades come in a variety of widths, and a wider width will allow a straighter cut, even if the operator is less skilled.

          Given my lack of experience in handcutting dovetails, perhaps this would be a good experiment. If I can handcut one with this saw, well, you an draw your own conclusions.

          • Main reason coping saws tend to wander is because there is no saw plate to guide the saw cut path; which is why it is much easier to cut a circle with a coping saw than a tenon saw.

          • What I wonder is how much the saw plate provides support during a cut – the kerf of the blade is wider than the body of the blade, so in theory, it shouldn’t touch the sides anyway?

  2. Thanks for this post , not so much for the saw but pointing out another woodworking company here in Adelaide.

    • Dangerous – such desirable tools!

  3. Checked out Henry Eckert website.
    Good looking saws, but now I am a bit confused about Fret / Coping saw definition

    • Fret saws are used mainly for marquetry. Think of it as the manual scroll saw. Blades are thinner and the back has more clearance than a coping saw.

      The coping saw is designed to cope (cut) the cope portion of ‘cope and stick’ and also mouldings.

      If used to cut out the waste of hand cut dovetails, then sometimes a fret saw blade will break when turning the corner too abruptly whereas the coping saw will be more resilient but will not cut as small a radius or turn a corner as tightly as a fret saw.

      A good solution is to install spiral blades in a fret saw then you don’t have to turn the blade at the corner, just change direction.

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