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Vollmer Basics

Basic Knowledge

Machining Circular Saws

Machining Band Saws

Sharpening the tooth face of carbide-tipped circular saws

As a rule, tooth faces are sharpened straight; however, sometimes they are also sharpened at an angle.

Tooth face machining also includes hollow face grinding. This is carried out using a grinding point at high speed. However, this method cannot be used for every saw blade. There must be a certain amount of chip space available in order to be able to machine the tooth face using peripheral grinding. In particular, it must be ensured that the grinding point is positioned exactly in the middle of the saw blade diameter and the cutting width.

 

1. Tooth face (tooth breast) / 2. Negative tooth face / 3. Concave tooth face (hollow face)

Machining the tooth face in a face grinding process

Different tooth geometries for tooth face machining

1. Flat / 2. Single-sided angled right / 3. Single-sided angled left

Different tooth geometries for tooth face machining

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Grinding the clearance surface of carbide-tipped circular saws

Machining the clearance surface can be done in a wider variety of ways than grinding the tooth face. The geometries can be designed to be straight to almost round, depending on the range of applications of the carbide-tipped saw blade. Machining is carried out with a face grinding or peripheral grinding process.

Machining using a face grinding process is particularly time-saving. Using this method, the grinding wheel must simply be turned through a certain angle in order to produce a wide range of tooth shapes (such as trapezoidal, roof, etc.).

1. Clearance surface (top of tooth) on the blade / 2. Clearance surface (top of tooth) on the carbide tooth

Different tooth geometries for clearance surface machining
1. Flat / 2. Single-sided angled right / 3. Single-sided angled left / 4. Alternating angled

Different tooth geometries for clearance surface machining
5. Trapezoidal / 6. Group toothing flat-trapezoidal with tooth height difference / 7. Group toothing flat-roof with tooth height difference / 8. Group toothing trapezoidal-trapezoidal with tooth height difference

1. Machining the clearance surface in a face grinding process / 2. Machining the clearance surface in a peripheral grinding process

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Side grinding of carbide-tipped circular saws

The flanks of a saw tooth are ground to a tapered shape in the cutting and feed direction, in order to prevent the cutting edges from pressing into the material. The precision of the tooth flanks significantly influences the surface quality. Grinding is carried out once when the circular saw is manufactured using a face grinding or peripheral grinding process.

1. Tooth flanks downwards, in feed direction, tapered / 2. Tooth face / 3. Tooth flanks backwards, in cutting direction, tapered / 4. Tooth face

1. Side grinding in a face grinding process / 2. Side grinding in a peripheral grinding process

1. Flank clearance surface / 2. Raised tooth flank / 3 - 4. Possible machining of the flank clearance surface

5 - 7. Possible machining of the flank clearance surface

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Soldering carbide-tipped circular saws

The body of carbide-tipped circular saw blades consists of pre-tensioned tool steel. Raw saws have a tip groove, onto which no cutting plates made of carbide can be precisely soldered. Soldering takes place during production using automatic machines. However, for service work, it is carried out manually with the aid of machines, as this only involves replacing individual broken cutting edges. Silver or a sandwich alloy is used as solder.

1. Prepared blade with tip groove / 2. Saw blade with soldered teeth

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Types of Band Saws

Depending on price, there are three different types of band saw:

1. Swaged/set band saws made of CV steel (chrome vanadium steel)
2. Stellited band saws
3. Carbide-tipped band saws

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Sharpening Band Saws – Profile Grinding

Band saws are highly sensitive. If maintained incorrectly, they may break. The reason for this is that band saws are subject to a constant bending cycle. This can cause hairline cracks to form in the tooth gullet, the area of highest tensile stress. If the saw is not resharpened on time, these cracks grow and cause breakages. To prevent this, the whole profile, i.e. all of the teeth (irrespective of their shape), of band saws made of CV steel and stellited band saws must be regularly resharpened – even when the usual degree of bluntness has not been reached in some places. If grinding is not carried out professionally, problematic scratches and grooves form, while excessive chip removal hardens the tooth gullet. With grinding machines from VOLLMER, you can be on the safe side and sharpen band saw blades correctly and extremely efficiently.

In order to prevent saws from becoming stuck during use, you need a side projection. Therefore, band saws made of CV steel must still be set, or alternatively, swaged and levelled after profile grinding. In contrast, stellited band saws and carbide-tipped band saws require side grinding.

1. Tooth face (tooth breast) / 2. Tooth tip / 3. Clearance surface (top of tooth) / 4. Tooth flank / 5. Tooth gullet

Profile grinding sequence

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Stelliting Band Saws

Stelliting refers to the process of applying stellite® to the saw teeth and thereby hardening them. This increases the abrasion resistance of the saw cutting edges, which in turn leads to longer machine service life, increased cutting accuracy and reduced set-up times.

Stelliting is especially advantageous when particularly abrasive and hard woods are to be sawn. Stellite® no. 12 (containing 59% Cobalt, 29% chrome, 9% tungsten and 1.8% carbon) has proved to be extremely successful for machining wood. It is wear-resistant while not being too brittle, and can be ground without problems. In some cases, stellite® no. 1 is used: This is an extremely hard alloy, which is primarily used for sawing wood with a high proportion of silicate.

In addition to painstaking manual stelliting, there are two types of machine stelliting: The resistive and the plasma welding process. During the latter, the saw tooth is heated and the required amount of stellite is melted. The liquid stellite® is guided into forming jaws, where the raw tooth is shaped into a finished tooth. The grinding work required is therefore reduced to a minimum. In contrast to the resistive process, fully automated plasma welding has the advantage that it forms a completely solid compound layer between the stellite® and the base material. Last but not least, repairs or replacements are cost-effective, as new stellite® is simply applied to the existing tooth, and the costly process of grinding off leftover stellite® is not required.

1. Raw tooth / 2. Tooth stellited into shape / 3. Annealed and ground tooth

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Sharpening Carbide-tipped Band Saws

For carbide-tipped band saws, only the carbide-tipped tooth tips are ground. When doing this, the following sequence must be observed: First the tooth face, then the flank surface and then the clearance surface.

This is not a problem with VOLLMER technology.

Unmachined saw blade

Machined tooth face

Machined Flank

Machined Clearance Surface

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Side Grinding Band Saws

Stellited saws must also be ground on the flanks after profile grinding. Even carbide-tipped band saws require side grinding. Irrespective of which tipping your band saws have, with VOLLMER grinding machines, you can machine the flanks correctly and extremely efficiently.

Four possible grinding programmes
1. Grinding downwards, lift-off, return in rapid traverse / 2. Grinding downwards, without lift-off and return / 3. Grinding downwards, with feed, and return / 4. Oscillation grinding with free selection of the number of feeds and strokes

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Setting Band Saws

In order for a CV saw to be able to cut freely during machining, the saw kerf must be wider than the body. One possibility is to set the saw teeth, and therefore the alternating bending. When doing this, it must be ensured that the teeth are not set too much, otherwise the cutting quality will be reduced. However, if the teeth are not set enough, the saw heats up, develops burn marks and loses tension. As a general rule, only the top third of the teeth should be set. However, the set width depends on various factors:

  • Type of wood: The softer the wood, the more the set
  • Wood moisture: The wetter the wood, the more the set
  • Resin content: The higher the resin content, the more the set
  • State of the wood: Frozen wood requires less set

Set saw teeth

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Swaging and Levelling Band Saws

1. Anvil / 2. Swaging bolts / 3. Swaging curve / 4. Equalising jaws / 5. Saw tooth

Swaging saw teeth is another possibility, along with setting, for ensuring that the saw can cut freely during machining. For the swaging process, a swaging bolt is placed in front of the saw tooth. The saw tooth is held in place with an anvil. By turning the eccentric swaging bolt, the sawing material is pushed towards the tooth tip. When the swaging process has ended, the swaging bolt turns back to its starting position.

Levelling takes place after swaging, i.e. the material which was pushed towards the tooth flanks is pressed together with the appropriate equalising jaws, so that the tooth tip is conically tapered downwards and backwards. As the swaged saw tooth works on the entire kerf width, it carries out the same work which would be carried out by two teeth on a set saw. The cutting power is increased thanks to the greater number of main and minor cutting edges. In addition, the hardness grade of the base material is increased thanks to the swaging process.

The swage must be adjusted for different types of wood in order to achieve the best possible performance.

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Levelling, Tensioning and Straightening Band Saws

1. Levelling /// 2. Tensioning /// 3. Straightening

Levelling refers to the process of eliminating irregularities (dents/bumps) in the saw blade. This is usually carried out as the first maintenance work. After being located with a straight edge, dents can be “hammered out” using a ball or club hammer, whereby the weight of the hammer must be matched to the blade thickness. The following guidelines apply when doing this:

  • Hammer weighing 1250 g for blade thicknesses ≤ 1.65 mm
  • Hammer weighing 1500 g for blade thicknesses > 1.65 mm

Hammers should have soft, rounded striking surfaces so that they do not leave any imprints on the blades, as this could negatively impact on the service life of the blade.

Tensioning or stretching means extending the middle zone of the saw blade. This is carried out by rolling using a rolling machine. By stretching the middle zone, the toothing side and the rear edge become shorter in relation to the middle. As a result, when fitting the saw blade to the rollers in the sawing machine, the compressive stresses are released and the saw blade forms a curve in the middle. This prevents the saw blade from shifting back and forth at the most convex contact surface of the roller.

When tensioning is carried out correctly, the blade has the following characteristics:

  • The tooth edge is rigid and runs especially quietly during operation.
  • The blade lies correctly on the rollers and withstands the stresses caused by high feed rates.
  • The blade is not prone to drifting. Cutting accuracy is maintained thanks to correct tensioning.

During straightening, the top of the band saw receives a slightly convex bowed shape using rollers. This balances out the extension of the toothing side when the saw is used. The final grinding process for the tooth gullet also causes the tooth baseline to be extended compared with the top. The condition of the saw blade must be checked along the entire top edge.

Measuring, straightening, tensioning and levelling: What used to be a labour-intensive manual task is now possible in one clamping operation – thanks to VOLLMER.

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Welding Band Saws

Welding is required to join band saw blades or repair cracks. The ends of the saw blades must be cut exactly square beforehand, and the cut surfaces must be cleaned. When this is done, the welding seam is laid on the top of the tooth. The point to be welded is then preheated to approx. 100 °C using a heating plate. After the welding operation, the blade must again be annealed to approx. 450 °C, so that the hardened structure returns to normal and the weld bead does not tear.

VOLLMER also has the right solution for this: Automatic welding machines for welding using a cost-effective MIG welding process.

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Saw Tooth Shapes for Band Saws

The following tooth shapes are usually used for band saw blades:

Acute angled tooth

Curved tooth

PCP (Profil á copeaux projetés)

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