by Ran Lancon
Carbide Saw Blades
Thin Kerf Saw Blades
Basics on Carbide Saw Blades
The request is usually the same - "Just give me a blade that will cut everything." The response is just as simple - "there's no such thing!" Carbide tipped saw blades are used to cut almost everything from asbestos to Zirconium, including paper, plastics, rubber, steel, insulation, aluminum, and even food, as well as every kind of wood in the world and all the wood composites. Sure, almost any of the dozens of blade styles will actually cut all of these materials, but when you consider accuracy, finish, tool life and safety, there is no blade that will do everything.
The variety of machines carbide blades run on is just as diverse as the materials they cut. On a table saw, for example, the material is pushed through the blade and the cutting action is downward, whereas the radial arm saw is just the opposite - the blade moves into the material and the cut is upward. It only makes sense that the same style blade will not work equally on both. Because of this wide variety of materials and machines - with new ones being developed all the time - the saw blade industry is constantly updating and modifying blade designs. For our purposes here we will consider blades for cutting wood and wood composites. The first consideration in a carbide saw blade is quite simple - diameter. Use the saw diameter the machine was designed for. Cutting the cost by going to a smaller blade is not saving anything. Even if the material being cut doesn't require the depth of cut you will get from the proper size blade, you want the rim speed attained by a full diameter blade. The reduction in blade life and the likely decrease in cut quality will more than outweigh the initial saving. Next consider tooth count. The basic rule is the more teeth the finer the cut, but you also have to consider the thickness of the cut and the cutting feed rate. The fine tooth saws do tend to leave a smoother finish, because each tooth takes a smaller bite. However, if the material is too thick (remember, it's the overall thickness when it's stacked that's important), or if it is being fed at a high rate, the gullet capacity of fine tooth blades is too small. The gullet is the open space between the teeth and inadequate gullet capacity will cause burning, poor quality cut, and possibly heat damage to the blade. Conversely, not enough teeth will cut aggressively, at lower feed, or on thinner materials and leave a rougher finish.
If you are cutting material that is finished on two sides, the tooth count may have to be higher and/or the feed rate lower, unless there is a scoring blade. Pre-scoring will allow a coarser tooth count and therefore a higher feed. So. if you make any changes to the material thickness, feed rate, or finish requirements,you may want to adjust tooth count accordingly.
The last consideration is the tooth style. Blade manufacturers usually have specific brand names or numbers for the various tooth styles they offer. Generally, however, they fall into one of three categories: Square Top style - rip saw, for downgrain cutting of solid wood; Alternate Top Bevel (ATB) style - cut-off saw, for cross grain cutting; and Triple Chip style - designed primarily for composite board cutting. In addition to these basic designs there are specialty blades for specific applications that represent a small percentage of the saw blade market. These are often overlooked, yet can be very useful for solving specific problems, improving the product, or even eliminating a manufacturing step. The following is a few of the more common specialty blades available at most saw blade suppliers.
Thin Kerf/Thin Rim Saws - These blades come in all tooth styles, depending on the application. Thin rim saws have a thick body core, but the plate is thinner at the outer rim. On thin kerf saws the entire plate is thin. Thin rim blades have a maximum cutting depth limited by the depth of the rim. They can be used with standard saw collars. Thin kerf saws have no preset depth of cut limitations, but usually should be used with larger and very accurate saw collars or stabilizers for strength and accuracy. Neither of these blades is recommended for deep cutting. Thin Kerf/ Thin Rim blades are very popular in the plastic display business, but can also be very useful in fine woodworking, thin material cutting, and even cutting melamine and other laminates. The advantages are low resistance cutting, low waste, and generally an excellent finish. Overheating, running them too dull, pushing them too hard, or running them on poorly maintained equipment and/or collars will take away all the advantages of thin kerf sawing and could cause permanent damage to the blade. Attention must be paid to setting the blade height correctly, and they should never be used on unstable or green material. Sharpening is also critical, as the tooth geometry must be maintained. Thin blades should only be used for finish cutting.
Chip Limiter Rip Saws - These blades are more widely used in Europe than North America. Between each tooth there is a hump-like shape, designed to limit the amount that the tooth following the hump will bite. The primary purpose of this is safety in hand feed ripping applications. The chip limiting hump will resist over-feeding, jamming and possible kick-back by controlling the in-feed rate of the material.
Double End Tenon Saws - The tooth style on these is usually 3 or 4 teeth all top beveled one way, and one tooth beveled the opposite way. The purpose is so that 75 to 80% of the teeth are giving a clean finish on one side of the material, because the other side is waste. For obvious reasons, these blades come in left and right hand for each side of the tenoner. This style is also used on edge banders for trimming, and has also been used on other types of machines when one side is always waste.
Negative Hook Saws - These blades are available in Alternate Top Bevel and Triple Chip tooth styles. There are two primary applications for this type of blade - the first being on overhead machines, particularly miter saws ( they are absolutely necessary on sliding miter saws) and often on radial arm saws. On these machines the negative angle of the tooth prevents the material from lifting and jamming the blade, plus the surface finish is usually better than the standard positive hook blades. The other application for negative hook blades is on table saws cutting double sided melamine board where there is no pre-scoring. In this application, when the blade is set at the correct height, a satisfactory surface finish can usually be achieved, as well as a reasonable life to the blade's cutting edge.
Hollow Ground or Hollow Face Saws - These are specifically used for cutting double sided composite board, usually melamine. By design, the edges are very sharp and they do an excellent job of leaving a chip-free finish, top and bottom. The downside is that they tend to wear faster than some other styles and are little more expensive to sharpen. When conventional blades designed for this purpose will not work satisfactorily on a particular machine, usually the hollow ground blade will solve the problem.
High ATB (Alternate Top Bevel) and Alternate Face Bevel Blades - These are used in composite board applications where surface chipping is a problem. Each tooth is ground to a very sharp and fragile point for cutting the surface fibres as cleanly as possible. They should never be used for solid wood sawing as the intermittent cutting resistance can cause tooth breakage.
These are just a few of the many designs of carbide saw blades. Combinations of these tooth styles and others, along with variations in hook, kerf, clearance angles, carbide grades, and tooth pitch, make it possible to solve most sawing problems in wood and other machinable materials.
Go to TOP of page
Thin Kerf
Saw Blades
Thin Kerf Sawing is the principle of
reducing the thickness of the saw tooth., which reduces the width of the cut.
This reduction in kerf can have a significant effect on waste reduction. For
example, a standard 12 inch diameter Rip Saw has a kerf of approximately
0.155". A Thin Kerf Saw at 0.095" would reduce waste by almost 40%.
This would also create an increase in either finished size or, quantity of
pieces produced.
Thin Kerf Sawing is primarily used in Multi-Rip applications, because the gains
are more predominant. Ripping 6 inch wide material to a finish of 3/4's of an
inch would produce one full extra piece, if using the example above. At 50 ft. /
min. this translates to 3000 lineal ft. per hour that you are getting paid for,
with no increase in material or labour cost. Unless your goal is to increase
finished size there may be little to gain in single or even double line ripping,
or for that matter in cross-cutting, or trimming applications.
The upside to thin kerf sawing is quite simple and obvious, so why isn't it an
accepted normal practice? This is where it can get complex and why in some
applications it just won't work. Every application for thin kerf sawing is
unique, in that there is such a large number of questions and specifics to be
considered, there is always some variations.
The kerf you are trying to achieve is probably the first thing to consider. The
finish size and the raw board size will determine the ideal kerf. In the example
above, reducing the kerf further would not improve yield, and since the kerf
required is inversely proportional to the degree of difficulty, there is little
benefit to asking for 0.070" kerf, and a whole lot more to be addressed.
The biggest obstacle to overcome is dealing with the body weakness of extra thin
saw blades. The tooth is not the problem. It's the saw plate supporting the
tooth that fails if the correct conditions for cutting are not maintained.
Whatever the kerf is, the saw body has to be even thinner, to provide adequate
side clearance (how much thinner depends on the material being cut) . Without
side clearance, friction would occur between the saw plate and the wood, causing
heat generation. Heat is your worst enemy. If heat is created in the body,
expansion and warpage will follow, creating even more heat, by friction and
cutting resistance. In heavy kerf saws a limited amount of heat can be absorbed
and dissipated by the heavy body, but with thin bodies the heat builds faster,
has no place to dissipate, and will do more damage because the blade is more
fragile.
It is well known that different materials have different machining properties.
Also, different materials have differing affects on the on the cutting tool.
Harder woods have more cutting resistance and require a stronger blade. All
other conditions being equal, you could reduce kerf a little more when ripping
softwood. Factor in moisture content here. Dry wood machines better (unless, of
course, it is too dry) and is a lot easier on the blades than wet wood. The
higher the moisture content the more side clearance is required (therefore
higher kerf) to keep the material from rubbing on the plate. Wetter wood also
greatly increases the wear on the teeth, again increasing the cutting
resistance. Dressing is critical before thin ripping. Rough material will not go
smoothly through the feed system and the material needs to be fed into the
blade(s) firmly and securely, without any movement or vibration, therefore it
must be D4S before ripping. How thick is the cut? This can affect how the blade
is designed and how it is mounted. If, for example, the depth is 3/4", the
blade could be designed to be thin only on the outer 1 to 1 1/4 inch of the rim,
giving it greater strength and a bit better at heat dissipation. In lieu of this
stepped body, or in conjunction with it, the spacers or saw collars could be
made larger, strengthening the saw and absorbing some heat.
Feed and Speed. The feed rate is dependant on several factors. Higher blade
speeds allow higher feed rates, but, particularly with thin kerf sawing,
material dimensions have a significant affect on the rate of cutting.
Over-loading the blades will damage them - often irreparably - and under-feeding
can cause substantial increased wear on the teeth.
The last thing we need to know is the type of machine and blade diameter. Thin
kerf ripping can be done on a Multi-Rip or a Moulder. Moulders have certain
advantages over Rip Saws in that they usually run at higher RPM. This allows for
either increases in feed and/or using smaller diameter saws. The smaller the
diameter, the more stable the blade is.
Although thinner blades offer less cutting resistance a gang of them can require
a lot of power to drive them. Inadequate horse power will result in too much
load on the blade. The blade will bog down, and heat up. Heavier blades, again,
may be able to absorb a certain amount of increased cutting pressure, but not
extra thin blades, and depending on the job, a standard machine may not have
enough power to achieve the desired productivity from thin kerf saws.
Go to TOP of page