THE 1: 0.625 or 5/8 BOW.
Posted: Tue Apr 14, 2020 2:58 pm
I am not sure of the exact time line of when and why this ratio for limb cross sections came into being. Reference has been made that it was used in target archery during the Victorian era to define what constituted a target longbow. If anyone as more information could you please let me know.
Perhaps this ratio was best suited to target longbows made from northern hemisphere woods.
The ILAA and BLBS use this measure in their definition of a longbow. Building a laminated longbow using hardwoods for belly material could create its own problems. Unless we try we will never know.
Pole bamboo was used as a backing, tapered vertically laminated bamboo as core material with Balau and Purple Heart for the belly. The bow was glued up with approximately 1 ½ inches of reflex built in. With the belly wood being quite a bit over thickness most of the reflex was lost when the bow blank was taken off the form.
At this stage the belly timber overpowers the backing and core. However the backing and core retain a ‘memory’ of being in reflex. As the belly wood is gradually removed the reflex starts to return.
Once the blank was sanded to the limb plan belly wood was removed to bring up a ‘D’ section. A Spokeshave is an excellent tool for removing excess wood.
My first attempt at the tiller stick indicated that a lot more timber would need to be removed. When finally getting the limbs to bend to brace height I estimated the draw weight at this point was in the vicinity of 40 to 50lbs.
Obviously a lot more belly wood needed to be removed to get the draw weight to around 50# @ 28”. At this stage it may be necessary to reduce the limb width in order to maintain the 1: 0.625 ratio as belly wood is removed. The narrower a limb becomes the more susceptible it is to twisting. During the process of removing belly wood it is important that the ‘D’ cross section remains symmetrical.
The limbs were bending fairly evenly to brace height so now was the time to go to the correct length string.
Tip overlays are fashioned from African Blackwood. This timber is extremely hard [Janka Hardness: 3,670 lb (16,320 N)] and is ideal for tip overlays when low stretch string material is used.
From the Wood Data Base. The actual number listed in the wood profile is the amount of pounds-force (lb) or newtons (N) required to imbed a .444″ (11.28 mm) diameter steel ball into the wood to half the ball’s diameter. This number is given for wood that has been dried to 12% moisture content, unless otherwise noted.
After bracing the bow, with difficulty and exercising the limbs tiller was just less than half an inch out. First task was to get the limbs into tiller and continue on reducing the draw weight. Presently the bow draws 56# @ 28” DLPP and has zero tiller.
As the draw weight is far too heavy for me the bow can go on the rack and the tiller can be adjusted if I get a buyer.
I will endeavour to get a younger club member who shoots 60# plus traditional bows to shoot the bow in for me and see if the tiller changes.
Daryl.
Perhaps this ratio was best suited to target longbows made from northern hemisphere woods.
The ILAA and BLBS use this measure in their definition of a longbow. Building a laminated longbow using hardwoods for belly material could create its own problems. Unless we try we will never know.
Pole bamboo was used as a backing, tapered vertically laminated bamboo as core material with Balau and Purple Heart for the belly. The bow was glued up with approximately 1 ½ inches of reflex built in. With the belly wood being quite a bit over thickness most of the reflex was lost when the bow blank was taken off the form.
At this stage the belly timber overpowers the backing and core. However the backing and core retain a ‘memory’ of being in reflex. As the belly wood is gradually removed the reflex starts to return.
Once the blank was sanded to the limb plan belly wood was removed to bring up a ‘D’ section. A Spokeshave is an excellent tool for removing excess wood.
My first attempt at the tiller stick indicated that a lot more timber would need to be removed. When finally getting the limbs to bend to brace height I estimated the draw weight at this point was in the vicinity of 40 to 50lbs.
Obviously a lot more belly wood needed to be removed to get the draw weight to around 50# @ 28”. At this stage it may be necessary to reduce the limb width in order to maintain the 1: 0.625 ratio as belly wood is removed. The narrower a limb becomes the more susceptible it is to twisting. During the process of removing belly wood it is important that the ‘D’ cross section remains symmetrical.
The limbs were bending fairly evenly to brace height so now was the time to go to the correct length string.
Tip overlays are fashioned from African Blackwood. This timber is extremely hard [Janka Hardness: 3,670 lb (16,320 N)] and is ideal for tip overlays when low stretch string material is used.
From the Wood Data Base. The actual number listed in the wood profile is the amount of pounds-force (lb) or newtons (N) required to imbed a .444″ (11.28 mm) diameter steel ball into the wood to half the ball’s diameter. This number is given for wood that has been dried to 12% moisture content, unless otherwise noted.
After bracing the bow, with difficulty and exercising the limbs tiller was just less than half an inch out. First task was to get the limbs into tiller and continue on reducing the draw weight. Presently the bow draws 56# @ 28” DLPP and has zero tiller.
As the draw weight is far too heavy for me the bow can go on the rack and the tiller can be adjusted if I get a buyer.
I will endeavour to get a younger club member who shoots 60# plus traditional bows to shoot the bow in for me and see if the tiller changes.
Daryl.