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The workhorse of a circular sawmill is the saw blade itself. It

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The workhorse of a circular sawmill is the saw blade itself. It Powered By Docstoc
					                                         BITE The amount that         at its outer perimeter,     speeds when gullets        without rubbing, the       the tooth out so that
  The workhorse of a circular            each successive tooth
                                         moves into the wood
                                                                      so often one of the col-
                                                                      lars is hollow ground,
                                                                                                  are too small mean
                                                                                                  fine sawdust, low pro-
                                                                                                                             saw teeth are made a
                                                                                                                             bit wider than the
                                                                                                                                                        the tip of the tooth be-
                                                                                                                                                        comes the widest spot.
                                                                                                                                                                                    Saw Blade Style
                                                                                                                                                                                    There are two styles of saw blades:
                                         being sawn is called the     while the other is per-     duction, heating, and      body of the saw. The       After swaging, the             * Those with inserted teeth (that is, the
  sawmill is the saw blade itself.       bite. Generally, for soft-
                                         woods the preferred
                                                                      fectly flat; or sometimes
                                                                      both are hollow ground.
                                                                                                  short saw life (rapid
                                                                                                  dulling). Gullets
                                                                                                                             extra width on each
                                                                                                                             side of the body of the
                                                                                                                                                        tooth is sharpened nor-
                                                                                                                                                        mally. Swaging is nor-      teeth are replaced after being sharpened a
                                         bite is 0.125 inch and       Overtightening the ar-      should be rounded          saw is called the side     mally done to solid-        few times). The saw will stay the same di-
  It looks simple—a spinning disk        for hardwoods 0.110
                                         inch. This means that
                                                                      bor nut can actually
                                                                      cause some collars to
                                                                                                  without sharp corners
                                                                                                  to avoid cracks and
                                                                                                                             clearance. The set is
                                                                                                                             the total width of the
                                                                                                                                                        tooth saws, but rarely
                                                                                                                                                        done to inserted-tooth
                                                                                                                                                                                    ameter after repeated sharpening.
                                         after 10 teeth have cut      warp and lose contact       breaks.                    teeth. Avoid large sets    saws.                          * Those with teeth that are an integral
  with sharp points on the outer         the wood the saw will
                                         have moved 1.25 inches
                                                                      and effectiveness.
                                                                      EYE The exact center
                                                                                                  KERF The width of
                                                                                                  the slot in the wood
                                                                                                                             as they will greatly af-
                                                                                                                             fect yield and profits.    TEETH The teeth are
                                                                                                                                                        the part of the blade
                                                                                                                                                                                    part of the saw, called solid-tooth saws.
                                                                                                                                                                                    Each time the teeth are sharpened and the
                                         or 1.10 inches forward                                                              As a rough rule of
                                         into the wood.               of the saw is the eye.      made by the blade                                     that cuts the wood.         gullet is ground slightly, the saw will de-
  edge. But the blade is actually        BODY or PLATE                GAUGE The measure
                                                                                                  when sawing is the
                                                                                                  kerf. For practical pur-
                                                                                                                             thumb, each 1/32 inch
                                                                                                                             of extra kerf is a 3%
                                                                                                                             loss in yield.
                                                                                                                                                        The teeth cut a slot,
                                                                                                                                                        called the kerf, in the
                                                                                                                                                                                    crease slightly in diameter.
                                         The body or plate is the     of the plate thickness is   poses, the kerf is the                                wood that is a little bit
  a sensitive and critical piece of      main piece of metal
                                         used to make the saw
                                                                      the gauge. A typical
                                                                      saw, for example, could
                                                                                                  same as the overall        SIDE CLEARANCE             wider than the thick-       Saw Diameter
                                                                                                  width of the saw teeth,    See set.                   ness of the plate, so       The diameter is chosen based on the horse-
                                         blade. The teeth are         be 7 gauge, which is        called the set. Techni-                               the plate can move
                                                                      0.180 inch or approxi-                                 SIDE DRESSING It                                       power, expected wood density, log or cant
  spinning metal, and the teeth          fastened to the outer
                                         rim. The center has a        mately 3/16 inch in
                                                                      thickness. (Table pg 14.)
                                                                                                  cally, after the teeth
                                                                                                  cut the wood, the          is often important that
                                                                                                                             the sides of the teeth
                                                                                                                                                        through the wood
                                                                                                                                                        without rubbing.            size, tooth size, and so on. The larger the
                                         hole to accommodate                                      wood actually closes                                                              saw, the slower it must be run, the more
                                         the arbor.                                                                          be perfectly aligned       TIP OF THE
  are equally important. Let’s exam-     COLLAR The washers
                                                                      GULLET The space
                                                                      between the teeth and
                                                                                                  the slot or springs back
                                                                                                  a very small amount        with one another (that
                                                                                                                             is, protrude out the
                                                                                                                                                        TOOTH The part of
                                                                                                                                                        the tooth that does the
                                                                                                                                                                                    teeth it will have, and the more horsepower
                                                                      the body of the saw.        giving a narrower kerf.                                                           required. Further, the larger the saw, the
                                         on each side of the                                                                 side of the saw the        actual cutting or scrap-
  ine the circular blade more care-      blade when the blade is
                                         attached to the arbor
                                                                      This space holds the
                                                                      sawdust while the teeth
                                                                                                  NUMBER OF
                                                                                                  TEETH Circular saws
                                                                                                                             same distance), so that
                                                                                                                             they produce a smooth
                                                                                                                                                        ing of the wood is the
                                                                                                                                                        tip or top of the tooth.
                                                                                                                                                                                    harder it is to maintain. Of course, the larg-
                                                                                                                                                                                    er the saw, the larger the piece of wood that
                                         are called the collars.      are in the cut. The gul-    are specified based on     surface. This process of   Some manufacturers of
                                                                      let must be large                                                                                             can be sawn. However, most mills will by-
  fully. The discussion here applies     The collar not only
                                         holds the blade to the       enough to hold all the
                                                                      sawdust produced. A
                                                                                                  their diameter and the
                                                                                                  total number of teeth
                                                                                                                             aligning is called side
                                                                                                                             dressing. Many saws
                                                                                                                                                        inexpensive saw
                                                                                                                                                        blades do not have ex-      pass a few large pieces of wood and use a
                                         arbor, but also stops                                    they have. Teeth           have terrible tooth        tremely sharp teeth         smaller saw, rather than be able to cut
                                         wobble and effectively       full gullet means that
  to all circular blades used in a       increases the blade
                                         stiffness.
                                                                      no further cutting can
                                                                      be done; slower than
                                                                                                  spaced too closely
                                                                                                  make more fine saw-
                                                                                                  dust and potentially
                                                                                                                             alignment and there-
                                                                                                                             fore cut very rough sur-
                                                                                                                             faces and waste wood
                                                                                                                                                        when the “new” blade
                                                                                                                                                        is shipped—this is
                                                                                                                                                        “bad news.” Even in-
                                                                                                                                                                                    everything and use a larger saw.
                                                                                                                                                                                       Detailed calculations of the best saw size
                                             The collar should be     normal feed speeds will     more heat, causing the     (and money).               serted teeth may not        can be done. For example, see www.fpl.fs.
  sawmill on green logs or cants.        as large as practical for
                                         best stability, especially
                                                                      have to be used, plus
                                                                      the blade may vibrate
                                                                                                  blade to wander a bit
                                                                                                  at times.                  SWAGE (Rhymes
                                                                                                                                                        be well sharpened.          fed.us/documnts/misc/circsaw.pdf.
                                         with thinner blades.         excessively. Larger gul-                               with edge.) This is the    TOOTH POINT
  Lets begin with some terminology ...   (Many collars are too
                                         small, in my opinion.)
                                                                      lets are required when
                                                                      making deep cuts (that
                                                                                                  SET In order to create
                                                                                                  enough room for the
                                                                                                                             process of mechanically
                                                                                                                             (with a hammer and
                                                                                                                                                        Same as “tip of the
                                                                                                                                                        tooth.”
                                                                                                                                                                                    Saw Plate Thickness
                                                                                                                                                                                    The plate transfers the power from the arbor
                                         The collar must touch        is, when sawing thick       body of the saw to pass    special tool) spreading
                                                                      pieces). Slow feed          through the wood           the metal at the tip of                                to the teeth. The plate also keeps the teeth




   The Circular Blade                                                                                                                                                By Gene Wengert




12 • Sawmill & Woodlot                                                                                                                                                                                         Oct/Nov 2007 •   13
The Circular Blade
                                            facturing profits.                       teeth with this species are Stellite.
  Birmingham Thickness                         Suggested plate size for 40-inch-     Other tooth materials include high       Hook, Sharpness, and
  Gauge for Saw Plates                      to 54-inch-diameter saw blades: For      speed steel (HSS), diamond, and          Clearance Angles
 Gauge      Thickness     Approximate       low density woods and smaller di-        chrome.                                  The angle of the tooth face, com-
          (inches)       (inches)           ameter logs or large cants, use a 9/10                                            pared to a radius from the center of
 3        0.259             17/64           gauge (9 gauge at the eye and 10         INSERTED TEETH Sawmills have             the plate, is called the hook angle.
 4        0.238             15/64
                                            gauge toward the rim); for dense         used inserted teeth for many             (Rake is the same angle, but usually
                                            woods and large diameter logs or         decades. Certainly one advantage is      rake is applied to knives and hook to
 5        0.220             7/32
                                            large cants, use a 7/8 gauge; for in-    that if a nail or other tramp metal is   saws.) The larger the hook, the more
 6        0.203             13/64           termediate density and intermediate      hit when sawing, it takes just a few     the blade wants to climb into the
 7        0.180             3/16            diameters, use an 8/9 gauge. Tradi-      moments to remove the damaged            wood; a saw with large hook is called
 8        0.165             11/64           tionally, the Birmingham gauge has       teeth (called bits) and replace them     an aggressive saw. It can feed so ag-
 9        0.148             9/64            been used.                               with new ones. The gullets do not        gressively that the saw will stall. The
 10       0.134             9/64
                                                                                     have to be ground when resharpen-        large hook also means rougher cuts
 11       0.120             1/8
                                            Saw Blade Tension                        ing the bits, although the edges of      (that is, more tear-out). Blades with
                                            When a saw blade is spinning, the        the gullets should be kept sharp.        smaller than normal hook angles are
                                            outer rim wants to fly off due to        Further, the teeth are already wider     hard to feed.
running straight. Thick plates are          centripetal force. The metal below       at the tip than further back, so they       The clearance angle is the angle
needed when the wood is dense.              the rim keeps the outer metal from       do not usually have to be swaged.        between the back of the tooth and a
Thinner plates can be used for lower        expanding, however. In order to off-     Inserted teeth can be used in saws       line drawn connecting adjacent
density woods. If the plate is too          set this centripetal force, the rim of   from 12 inch diameter and larger, al-    teeth. This angle is required so that
thin, however, it will vibrate and the      the blade can get wavy. Of course, a     though sometimes solid tooth saws        the back of the tooth does not rub
saw will wander in the cut.                 wavy rim means wavy cuts. To cor-        will have less kerf.                     on the wood as the saw is fed into
    The plate of a circular saw blade       rect this tendency, a saw blade is          When specifying an inserted bit       the wood.
is typically 1/8 inch to 1/4 inch           dished slightly when at rest. The        (and there is also the shank that           Generally, the hook is 43 degrees
thick. Sometimes the plate is thick-        amount of dish depends on the final      goes with the bit to hold the bit in     to 45 degrees. The tooth sharpness
er at the eye of the saw and then ta-       speed of rotation. As the dished saw     the saw body), the items that must       angle is 35 degrees to 37 degrees and
pers a bit toward the teeth. The            blade increases its speed, the rim       be specified are style, gauge, kerf,     the clearance angle is 9 degrees to 12
thinner plate means that there is           gets longer by becoming un-dished        type, and tip.                           degrees. These three angles must to-
less sawdust and potentially less           or by “standing up straight.” The                                                 tal 90 degrees. Generally, be very
waste. However, thin blades, often          process of dishing a saw is called       STYLE There are four common              careful not to change the angles from
called thin-kerf blades, are very sen-      tensioning the saw. It was done          styles of inserted teeth: 2-1/2, 3, F,   the factory settings.
sitive to heating and wobbling,             mainly by hammering the saw, but is      and B. The 2-1/2 and F styles are a
which in turn means non-straight            now often done with automatic            bit narrower than the other two.         Sharpening
(wavy or snaky) cuts. As a result of        rollers and tensioning devices. In                                                Sharpening can be done with a
this one factor, most people opt for a      any case, a large diameter saw must      GAUGE The gauge refers to the            handheld file, but almost everyone
thicker, and therefore stiffer, plate.      be properly tensioned for it to run      thickness of the plate at the rim.       uses an electrically powered tool
When someone comes up with a                correctly–straight and true.                                                      (that looks like a hand drill with a
thin-kerf, stiff plate, it will sell like                                            KERF The kerf is the width of the        grinding wheel) called a Jockey
hot cakes and improve wood manu-            Saw Teeth                                tip of the tooth.                        Grander. It is critical to keep the an-
                                            TOOTH MATERIAL Although                                                           gles the same as originally supplied,
                                            many saws use steel teeth, many          TYPE Each of the above styles            and to also keep the tip straight
      Tip of Tooth          Bit             modern saws use a different material     when made of HSS is available in a       across and not angled. Avoid too
                                            that is brazed onto the saw tip. The     standard shape bit, in an extra long     much heating of the metal (turning
                                            most common material is probably         shape bit, and in a Standall bit (de-    blue is too much). Although sharp-
                                            carbide. Carbide consists of a mix-      signed for frozen lumber, but often      ening is easy, it must be done care-
       Gullet                               ture of tungsten, carbon, and cobalt.    used on all lumber).                     fully and skillfully to achieve the
                                            It lasts 50 times longer when cutting                                             proper results and good lumber sur-
                                            wood than steel teeth. Carbide is        TIP The tip refers to the material,      face quality. Ask an expert (not nec-
                                            very brittle, so the saw must be han-    such as chrome or Stellite, put on       essarily your neighbor) for a quick
                                            dled carefully once off the arbor.       the tooth’s tip. Although solid tooth    lesson. I
                                            Hitting small pebbles embedded in        saws can be tipped with carbide or
                                            the bark of a log can easily chip the    other materials, it is expensive to do   Gene Wengert, Professor Emeritus, Univer-
Shank                                       carbide. Western red cedar is known      so, especially when compared to an       sity of Wisconsin-Madison, is President of
                                  Plate     to dissolve the cement that holds        inserted tooth saw.                      The Wood Doctor’s Rx, LLC, in Madison,
                                            the carbide together, so often the                                                Wisconsin.

14 • Sawmill & Woodlot                                                                                                                                                     Oct/Nov 2007 •   15

				
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