MrFluffy - it doesn't really matter what the classification is as the process of making the bow is pretty much the same - in the end it is just laminating wood and fibreglass on a mold. Glad to see your interest.
Grinding laminations
Laminations for bow limbs can be made from a variety of woods including yew, rock maple, ash, elm, zebrano, black walnut and exotics. My preference is for light in weight strong woods with good flex. If clear fibreglass is used usually the wood underneath will be chosen for pattern and beauty. A plain piece of maple may give good results as far as speed and durability but does not look that good under clear glass - of course stains and the like can be used if needed.
As mentioned previously we will use a layer of 50 thou glass on each side of the bow and 4 pairs of wood laminations between the glass. In this case we are aiming for a bow of about 60 to 65 lb. - this is determined by glass thickness and wood thickness (all other things being equal). With this bow we want a wood lamination thickness of about .336 in. measured at the thick end of the tapers. Being that we will use 4 pairs of laminations we are aiming for two tapered pairs (one will also work well with this design) of about 0.100 at the thick end and two (.336-.100-.100)/2 = 0.068 in. thick parallels. This total thickness can be a bit less or more (say 5 thou or a bit more either way and be compensated for when finishing the bow - more on that later).
Note that the total wood thickness is the key - the figures above are just estimates as I don't like to go less than 0.100 on tapers - less and the thin end is extremely thin. We could use 3 pairs of laminations or 5 however thicker laminations become difficult to bend and 5 pairs become somewhat difficult to get into the mold before the epoxy starts to thicken.
I rip laminations from 2 in. thick x 36 in. long stock with a well tuned bandsaw aiming for a finished thickness of about 0.135 in. or so. Once cut they are run through a thickness sander to get the final thickness.
Running a pair of laminations through the thickness sander.
A poor pair of book matched osage orange laminations shown as they would be placed in the bow limb (overlapped just for the photo).
Adjoining laminations will be book matched in the bow limbs so that they are in the same position in the limb but a mirror image of each other - for example the first lamination cut from a given block will be on the lower limb against the fibreglass at the back of the bow and the adjoining piece will end up against the fibreglass on the back of the bow but on the upper limb.
72 in. laminations can be cut and used however they will not be book matched and they are difficult to handle so I seldom use them. 36 in. laminations will be scarf joined before glue up if necessary.
I use a drum style thickness sander get good accuracy on the laminations as long as I run them through the sander several times once they reach a point near the final thickness. It is best to use fairly aggressive sandpaper (60 grit) as that roughs the wood up for the epoxy. It is a bit of a slow process to grind a few pairs of laminations.
All laminations are run through the sander using a board underneath - the board has sandpaper glued on it so that the laminations stay onboard - otherwise they may shoot out of the sander like a small projectile. The photo shows two laminations beside the sandpaper covered boards.
Tapers are created by running laminations through the sander with a tapered board underneath. I commonly use tapers that are tapered 0.002 in per 1 in of length - others may use 0.001 per inch. My bows have the tapers arranged to be thick end in the centre of the bow and thin end at the tips. One company I know of tapers laminations from thick at both ends (middle of bow to each tip) to thin in the middle. That particular model shoots very well.
Bow Glass:
Fibreglass is available in different widths, thicknesses and colours. I normally use clear and black and have 0.040 and 0.050 thick for bows. Since my molds are 2 in. wide that is the width I use. For longbows (thick limbs) I use 0.040 or 0.050 depending upon the desired bow weight, for flatbows and recurves (bows with thin wide limbs) I use 0.040 glass.
John.
