Building bows on an adjustable form.
Posted: Wed May 27, 2020 9:19 am
The following is an overview on how I construct multilaminate bows of natural materials using an adjustable form.
I adapted Dean Torges’ form method for constructing bamboo backed bows. There are no doubt other methods to achieve the same end result but this evolved as an easy but can be a time consuming method that works for me.
The form consists of a beam and a pairs of posts of various heights. By moving the posts to different positions you can form or change the bows limb profile. Use as many posts as you need to obtain the desired profile.
Image 1 I like using speed clamps to pull the laminations down on to the lower posts and spring clamps between the posts to bring the limb laminations together.
Limb width is usually governed by the diameter of the bamboo pole i.e. the smaller the diameter the higher the crown. For a standard type of longbow three inch diameter poles are ok, use larger poles if you have access to them.
Note that with some bamboo the large diameter pole is usually from the bottom end of a longer pole and the nodes will have a closer spacing. Ideally poles with nodes that are spaced somewhere from 12 to 15 inches or more spacing are preferable.
With the use of two pack epoxy glues choose one that gives sufficient pot life. Check the manufacturers’ specification sheets to find one that suits your needs.
With a first attempt I would suggest building a long bow/flatbow.
The bow in the following will have a pole bamboo back, two core laminations of vertically laminated bamboo (one being tapered) and a Balau belly. The Balau lamination will wrap around the belly of the handle.
Pole bamboo also makes an excellent belly but make sure nodes are spaced between the backing nodes.
Image 2 When preparing core laminations for a long bow/flatbow I have an overall width about 1 ¼” to 1 ½” by the required length. Using two core laminations allows you to end for end the laminations to help minimise weak spots although I prefer three laminations.
Tapering the core laminations will help to achieve a more elliptical limb profile.
Split or saw your bamboo pole into suitable widths and start flattening the inner surface with whatever suitable tools you have available i.e. belt sander, electric planer, spoke shave etc. Mark the limb plan [slightly oversize] on the bamboo and cut to shape. Apply masking tape down the length of the bamboo; draw a centreline down the back and one across at the halfway mark.
Draw marks across the bamboo at six inch intervals; these will be used as checkpoints to control the thickness and taper of the bamboo. Continue flattening the inner surface until the edges of the bamboo is about 1.5mm thick.
Image 3 Design and shape the handle.
For this project off cuts of timber were used. Make the handle the same width as the core laminations.
Glue a core lamination to the back of the shaped handle. When the glue has cured you can refine the fadeouts to blend in with the lamination. In hind sight each fadeout for this project should have been about 1 inch longer and the handle not quite as deep. A shaped grip will help reduce the overall bulk of the handle.
Image 4 The second lamination is then glued up.
Image 5 Change the post positions and turn the bow blank over to glue the belly lamination.
Image 6 When the glue has cured move the posts back to their original position and glue the pole bamboo to the back of the glued up blank.
Image 7 After the bow blank has cured you can start shaping the plan of the bow.
Image 8 When the blank is worked to shape you can put it on the tiller stick using the tillering string. I prefer a double pocket tiller string as it allows you to bring the bow into tiller without having to cut string nocks in the bows tips. Because of the softer characteristics of bamboo this style of bow requires tip overlays.
Image 9 I have found that a string nock filed at 35 ̊ appears to suit a 68” n to n bow with a 6 to 6 ½̋ brace height. To determine what angle best suits your bow bring the bow down to the desired brace on the tiller stick and mark a horizontal line at the string nock points.
Handle shape is a personal choice and wether it will be shot off the knuckle or a shelf. For this project the handle will be shaped to allow for shooting off the knuckle. The shaping is such that it can be shot either hand.
Image 10 Image 11 Although the tiller looks out, the lower limb (right hand side) belly fade is not symmetrical with the upper limb.
Upon loosing an arrow the bow is virtually dead in the hand with the exception of a slight hum from the string, possibly due to a sloppy release. Until a lot more arrows pass over the knuckle I will not play around with the tiller.
Overall I am reasonably happy with the results; just a little disappointed that final draw weight came in at 34# @ 28”. Fortunately I have an outlet for lighter draw weight bows.
The bow is finished with two coats of Minwax Wipe-on Poly.
Things I would do differently include having the handle flat on the back so that the core laminations weren’t forced into a deflex direction, move the outer posts in a little and taper the core and belly laminations.
Daryl.
I adapted Dean Torges’ form method for constructing bamboo backed bows. There are no doubt other methods to achieve the same end result but this evolved as an easy but can be a time consuming method that works for me.
The form consists of a beam and a pairs of posts of various heights. By moving the posts to different positions you can form or change the bows limb profile. Use as many posts as you need to obtain the desired profile.
Image 1 I like using speed clamps to pull the laminations down on to the lower posts and spring clamps between the posts to bring the limb laminations together.
Limb width is usually governed by the diameter of the bamboo pole i.e. the smaller the diameter the higher the crown. For a standard type of longbow three inch diameter poles are ok, use larger poles if you have access to them.
Note that with some bamboo the large diameter pole is usually from the bottom end of a longer pole and the nodes will have a closer spacing. Ideally poles with nodes that are spaced somewhere from 12 to 15 inches or more spacing are preferable.
With the use of two pack epoxy glues choose one that gives sufficient pot life. Check the manufacturers’ specification sheets to find one that suits your needs.
With a first attempt I would suggest building a long bow/flatbow.
The bow in the following will have a pole bamboo back, two core laminations of vertically laminated bamboo (one being tapered) and a Balau belly. The Balau lamination will wrap around the belly of the handle.
Pole bamboo also makes an excellent belly but make sure nodes are spaced between the backing nodes.
Image 2 When preparing core laminations for a long bow/flatbow I have an overall width about 1 ¼” to 1 ½” by the required length. Using two core laminations allows you to end for end the laminations to help minimise weak spots although I prefer three laminations.
Tapering the core laminations will help to achieve a more elliptical limb profile.
Split or saw your bamboo pole into suitable widths and start flattening the inner surface with whatever suitable tools you have available i.e. belt sander, electric planer, spoke shave etc. Mark the limb plan [slightly oversize] on the bamboo and cut to shape. Apply masking tape down the length of the bamboo; draw a centreline down the back and one across at the halfway mark.
Draw marks across the bamboo at six inch intervals; these will be used as checkpoints to control the thickness and taper of the bamboo. Continue flattening the inner surface until the edges of the bamboo is about 1.5mm thick.
Image 3 Design and shape the handle.
For this project off cuts of timber were used. Make the handle the same width as the core laminations.
Glue a core lamination to the back of the shaped handle. When the glue has cured you can refine the fadeouts to blend in with the lamination. In hind sight each fadeout for this project should have been about 1 inch longer and the handle not quite as deep. A shaped grip will help reduce the overall bulk of the handle.
Image 4 The second lamination is then glued up.
Image 5 Change the post positions and turn the bow blank over to glue the belly lamination.
Image 6 When the glue has cured move the posts back to their original position and glue the pole bamboo to the back of the glued up blank.
Image 7 After the bow blank has cured you can start shaping the plan of the bow.
Image 8 When the blank is worked to shape you can put it on the tiller stick using the tillering string. I prefer a double pocket tiller string as it allows you to bring the bow into tiller without having to cut string nocks in the bows tips. Because of the softer characteristics of bamboo this style of bow requires tip overlays.
Image 9 I have found that a string nock filed at 35 ̊ appears to suit a 68” n to n bow with a 6 to 6 ½̋ brace height. To determine what angle best suits your bow bring the bow down to the desired brace on the tiller stick and mark a horizontal line at the string nock points.
Handle shape is a personal choice and wether it will be shot off the knuckle or a shelf. For this project the handle will be shaped to allow for shooting off the knuckle. The shaping is such that it can be shot either hand.
Image 10 Image 11 Although the tiller looks out, the lower limb (right hand side) belly fade is not symmetrical with the upper limb.
Upon loosing an arrow the bow is virtually dead in the hand with the exception of a slight hum from the string, possibly due to a sloppy release. Until a lot more arrows pass over the knuckle I will not play around with the tiller.
Overall I am reasonably happy with the results; just a little disappointed that final draw weight came in at 34# @ 28”. Fortunately I have an outlet for lighter draw weight bows.
The bow is finished with two coats of Minwax Wipe-on Poly.
Things I would do differently include having the handle flat on the back so that the core laminations weren’t forced into a deflex direction, move the outer posts in a little and taper the core and belly laminations.
Daryl.