- Theoretical part
- Tools and devices, preparation for work.
- Saw Tooth Set
- Tooth profile and sharpening angles
- Turning process step by step
- Eyeliner and edits
Like any tool, hand saws need care and maintenance. It is possible to ensure high accuracy and cleanliness of the cut only if the teeth are correctly sharpened and set. You don’t need special equipment for this, a simple tool and basic knowledge are enough..
To ensure a high quality cut, you need to understand the mechanism of the effect of the edges of the hacksaw teeth on the material being processed. Unlike steel and plastic, wood is a heterogeneous material, it is because of this quality that several types of saws have been developed, differing in the profile of the teeth, their sharpening angle and the degree of divorce. All types of hacksaws for wood, their characteristics and technical data are specified in GOST 26215-84.
The main types of hacksaw teeth for wood. 1 – for cross cutting Type 1; 2 – for cross cutting Type 2; 3 – for longitudinal sawing Type 1; 4 – for longitudinal sawing Type 2; 5 – for universal sawing
There are three types of hacksaws: cross cut, rip saw, and multi-purpose. The main difference lies in the cutting principle: when sawing wood across the fibers, fragments of different densities are encountered along the path of the tooth. On the one hand, this circumstance plays into the hands: the resulting chips are smaller and easily removed from the contact zone, which allows the presence of sharpening on both sides of the sawing tooth, both in the forward and reverse feed direction. On the other hand, cutting across the fibers takes place partly for impact, and accordingly, more obtuse angles of descents of the cutting edges are required..
Sawing wood along the grain can be characterized as repetitive micro-planing cycles. The force exerted on the tooth is in this case uniform, therefore the teeth have an asymmetric shape and are directed with the tip towards the cutting side. In this case, the edge formed at the apex of the tooth is directed strictly perpendicular to the plane of the blade. When sawing along the grain, elongated chips are formed, the removal of which from the contact zone is difficult. Also, when ripping, there is a greater release of moisture, resins and adhesives, which in combination with the first factor prevents sawing in both directions. Chip removal occurs with direct tool feed: the perpendicular direction of the edge promotes the ejection of sawdust towards the saw. Reverse movement ensures the removal of chip residues and self-cleaning of the edges.
The teeth of all types of hacksaws are set, they are alternately inclined in different directions from the longitudinal axis of the blade. Due to this, in the longitudinal profile of a row of hacksaw teeth, a kind of dovetail is formed – two sets of cutting wedges formed by the tips of the cutting edges of the teeth. Accordingly, at the bottom of the cut, the hacksaw forms two grooves, which ensures uniform step removal and effective chip evacuation.
Tools and devices, preparation for work.
Hacksaw blades for wood are made of corrosion-resistant alloy steels with a hardness of 40-50 HRC units. Thanks to the use of such material, the tool retains its qualities, even if it has not been used for several decades. To return even an old rusty blade to work, it is enough just to sharpen and spread the teeth correctly, and this will require some tools and equipment. Let’s make a reservation right away that modern hacksaws with a hardened toothed edge (where the tarnishing colors are visible) do not sharpen or divorce, unless only after annealing the blade.
Reliable fastening of the hacksaw is ensured by a piece of board, at the end of which a cut is made parallel to the wide side. The saw should be done with the same hacksaw, which is processed, the depth is about 70–80 mm. The blade must be inserted into the cut with the butt downwards so that the teeth protrude from the cut to a height of at least 50 mm. The wooden miter box itself must be clamped in a vice, or fixed to any stationary object, immobilizing the canvas with a wide and thin wedge
As a further improvement to the miter box, a similar holder can be used to quickly fix the saw blade.
Processing of metals of such hardness is possible manually and mechanically. In the first case, you can use files with a hardness of 60 or 65 HRC, or diamond files. When machining, an electric sharpener is used with a white electrocorundum stone on a vulcanite bond mounted on it. The optimal diameter of the circle is 120 … 160 mm, it is desirable that the thickness does not exceed 8 mm, otherwise it will be necessary to fill the end face to the dish-shaped profile. The grain size of abrasive particles should be P 120-140 or higher.
To set the teeth, you need a tool called a set. It is a thin plate on the handle with one or more transverse cuts of different widths. The butt of the hacksaw should fit into one of the cuts so tightly that the tilt of the handle relative to the blade is at a right angle +/- 2 °. To make the divorce even and symmetrical in both directions, an angular adjustable stop in the form of a metal arc is attached to the distribution.
Saw Tooth Set
The hacksaw teeth are set apart before sharpening. The blade should be firmly clamped in a vise, the teeth must be free of resin and fine wood dust. Before setting the teeth, you need to calibrate the tool. This requires a set of probes and a metal ruler. The amount by which the teeth should be bent is set by the standard and averages 1/10 of the pitch or distance between the vertices. Having measured the pitch of the teeth, you need to choose the appropriate set of probes or pads, the total thickness of which is equal to the divorce distance.
First, you should choose an arbitrary tooth and bend it by a certain amount, by eye achieving the correct bend size. After that, a set of spacers is pressed against the plane of the canvas, the total thickness of which is equivalent to the amount of divorce. The metal ruler must be pressed with the edge against the linings and ensure that only a light touch is provided when passing the tooth tip.
Further, everything is simple: when the control tooth is bent to the required amount, a limiter for the inclination of the setting is installed along it, it should rest against the side of the saw blade. Sometimes it is necessary to displace the stopper in order to compensate for the reverse deformation of the teeth due to the elastic properties of the blade due to the stronger bending. Starting from the control tooth, all the rest are bent, alternately in opposite directions. To speed up the process, it is recommended to first bend only in one direction, and then in the other, in both cases bending the teeth through one. It remains to add that the divorce during operation shrinks 2–3 times slower than sharpening. To check if the hacksaw is well spread, it is necessary to measure the thickness of the toothed part in different places with a vernier caliper – it should be 20% more than the nominal thickness of the blade.
Tooth profile and sharpening angles
In addition to the standard hacksaw blades for wood, there are others defined by the standards of other countries. However, despite all the variety, there is a certain common tendency in determining the angle of attack of the tooth, the angle of sharpening of cutting edges, and sometimes in the methods of finishing the vertices.
The teeth of the hacksaws of the first type have the shape of an isosceles triangle with an apex angle (the same angle of attack) of 40-50 ° for the first version and 50-60 ° for the second. For hacksaws of the second type, sharper profiles of the teeth (less than 40 °) and their inclined position towards the cut (version 1), or a rectangular profile with a shallow backing are characteristic. Hacksaws of the third type also have an inclined tooth position, but the apex angle is 35–45 °. This information is for reference only: the profile of the tooth does not change during sharpening, but the ability to understand the types of blades will help determine the correct turning technique.
The most popular non-standard types of canvases are dagger and wolf’s tooth. Hacksaws with a dagger tooth are very similar to blades of the first type of the second version according to GOST, their characteristic feature is different heights of teeth and a large blade thickness, due to which an increase in pressure is provided for removing larger chips. The wolf tooth profile consists of several pairs of teeth of the second type, alternating with the teeth of the first type, paired into M-shaped tails. The main difficulty in sharpening such saws is the need to individually select the sharpening angles of the edges for each type of teeth..
Turning process step by step
Manual file sharpening makes it easier to control material removal and set the correct edge angles. The blade must be clamped in a miter box or a vice, ensuring that the teeth protrude above the jaws of the order of 30–35 mm. The routing is done before sharpening for three reasons:
- so that the cutting edges are not subsequently damaged;
- so that a slightly stronger spread is provided in advance, which is compensated by the removal of a certain fraction of the metal from the teeth;
- so that the directionality of the cutting edges and the setting of the teeth are uniform.
The most important rule for sharpening hacksaws for wood is: the tooth should have a flat side on the side into which it was bred. Thus, the cutting edges of adjacent set teeth are directed towards each other, that is, inside the channel formed by the set.
After clamping the blade, it is necessary to specify the sharpening angle of the cutting edges. Ideally, it should be determined by the hardness of the wood being processed, but since the hacksaw is used for sawing various species, a universal value of 60–75 ° from the plane of the tooth is set for all types of profile. There is a certain difficulty in determining the sharpening angle relative to the plane of the blade for confident control of the position of the tool. This can be done using a flat metal plate, choosing the least worn tooth as the standard, usually this can be found closer to the handle.
When sharpening, you need to process those teeth that are located with the edges towards you. Maintaining the correct angle between the edge of the file and the blade, and also slightly tilting the file towards the edges, you need to remove 2-3 material from the cutting edges, applying pressure while moving away from you. After each pass, you need to make sure that the metal is removed over the entire surface of the face, if necessary, adjust the position of the file. In order for the sharpening to be uniform, the number of file movements on each tooth must be the same. A good sharpening result is a uniform brightening of the blade descent over the entire area..
Sharpening the blade on an abrasive wheel is more difficult due to the fact that the blade does not have a stop. However, with the proper skill, it is possible to achieve accurate metal removal from both sides of each tooth. As with manual sharpening, the movement of the cutting tool should be directed towards the flat part of the tooth, so the entire blade is turned twice with an overturn.
Eyeliner and edits
The steel from which the hacksaw blade is made has toughness, which can cause burrs on the cutting edge. To remove them, it is enough to clean up the flat edges of the tooth in the direction from the base to the top. Since it is very difficult to edit a bent tooth with a flat file, it is better to use 80-120 grit abrasive paper, rolling it into a small tube.
To make precise fit cuts, many craftsmen recommend blunting the tip of the teeth slightly to form a third cutting edge. It is better to do this with a miniature diamond-coated file with at least one flat edge. The file is brought to the tooth in such a way that its working surface is perpendicular to the plane of the blade (not the tooth). Then 1-2 easy removal is carried out, the movement is carried out from the base of the tooth to the top.