Red Sal Wood (Shorea robusta) for Bows

[Preston]

I just bought a Red Sal Wood (Shorea robusta) board 2" wide x 1" depth x about 7 feet long..... I would like to know if anyone built a bow out of this wood and if its suitable and do I need to keep the width 2" or will 1-3/4" or less be ok?
thanks....

[perry]

I have not made a Bow of this Wood, a quick look around the Net showed its used in construction compression Modulous of 41, Elasticity was buried in the Text somewhere, could not find it - I'd give it a go, all you can do is learn from it.

I'll assume grain is straight / no knots. If possible cut your stave with Edge Grain showing the length of the Staves Back with no run offs. The standard advice I give for for UNPROVEN TIMBER is to make it double your draw length plus 12 at a minimum. 72 - 74 " ntn would not be to long. At this length make it 1 1/4" wide for most of the Bows length, I'd leave it a working handle, spreads the stress better and makes for an efficient Bow. Taper the last 8-12" of the Limbs. I like lenticular cross sections as they go naturally with hand tools. Tiller it to resemble the Capital letter D at full draw

If your tempted to make it a Ridgid Handle Bow I suggest a Pyramid Limb design Capital C Tiller and 76" ntn and see what happens.

regards Jacko

[Preston]

Hello Jacko, thanks for the suggestions... I'll probably try that.. after I posted this question I thought of making a small bow with the same type of wood and testing that unfortunately it broke while tillering but I learn't a few lessons this is my first time trying to build a proper bow from hard wood..... I got one more small piece of wood i'll try making one more atleast I can try my hand at tillering and try to make it succcessfully to the finished bow, after which I'll do the full size one... that's my plan...

[Dennis La Varenne]

Preston,

Perry's advice is well followed on untried wood. I have just looked up your wood specie on The Wood Database http://www.wood-database.com/wood-ident ... ific-name/. Robusta is not listed, but the Shorea species is also known as Meranti. Bootle lists S. robusta as having an air dried density of around 800-880kg/m^3 and a Modulus of Rupture (MoR) of 128MPa which is quite strong.

Very heavy woods of close to 1000kg/m^3 and higher which start to sink in water often have MoRs of this level, so unless the grain direction in your board is running out of the board less than around half the bow-length, you should have good luck with it especially if you overbuild it as Perry suggests.

Bootle also suggests that care be taken when using bladed tools such as planes and draw knives on this wood because it has a tendency to rip splinters up. Abrading tools and rasps sound to be your best bet with removing by-wood. Nothing wrong with a farrier's rasp or an angle grinder at the early stages either.

[Preston]

Hello Dennis,
I have been searching for information on this wood but with no success... I made two small bows to test the wood the first one broke whille tillering the wood split from the corner and it broke at about 6" draw length so the next one that I made I rounded the top edges a bit and that helped me tiller it to a DL of about 6" after shooting it for some time I was able to draw it to about 7.5" the bow length was 20" ntn ..Its hard to know how much i was pulling the second one and i felt sorry that I didn't check the draw weight I was shooting it with an arrow which was too heavy and stiff it shot the arrow about 40FT almost horizontal till it hit a wall but that was at about 7" drawlength.... and then I tried pulling it to about 9" without tillering it for that DL and it broke... again the break was a tension break this time the split started from the center of the back. I think it would make a nice bow wood... however, I have a few questions.... how can I get a draw weight of about 50# ?... Do I just start with the measurements given by Jacko and while tillering draw it to not more that 50# and do that till I reach my Draw length?, Is there a test I can do to find out how much DW is possible with little set...for this wood for a bow of about 70" ntn?
Regards,
Preston

[Dennis La Varenne]

Preston,

I could go on for pages on that subject and I would need to look up a bit more info to pass on, but for the time being, go with Perry's recommendation as a starter. There is a bending test you can use which technique was explained by Yeoman - http://www.ozbow.net/phpBB3/viewtopic.php?f=34&t=5450 - which you may want to read up on. It will let you know just how much load any specie of wood can stand and give you something to work with in laying out the design of your bow of whatever draw weight.

One other thing I would ask is whether or not your board is quarter sawn or not. if it is quarter sawn, you stand a much better chance of a successful board bow since you can chase a growth ring along the back surface if the annual rings are horizontal to the bow or, you can lay it on its side with the reed of the grain showing and use that surface for the back and belly. This is the same principle used to orient the grain of arrows for best resistance to the violent flexing of the arrow as it leaves the bow.

Your testing on miniature bows indicates that this wood is not strong in tension and most likely needs to be backed. Miniature bows take the same loads that full sized bows do and are an excellent indicator of what your wood will do. If you make a moderately oversized bow as Perry suggests, you should be able to get it to brace height without trouble, then back it with linen bed sheet in two or three layers or light canvas using PVA glue or Titebond or other reasonable glue, then proceed with the rest of your tillering.

[Preston]

Hello Dennis,
Thanks for the link the maths looks a bit complicated....Thanks for the suggestion to back the bow after floor tillering it....that should work. Now I just got to get down to doing it..by the way I ordered the "Traditional Bowyers Bible Vol4" its a great book filled with some eye opening stuff I highly recommend it to anyone who doesn't have the book.....In it on page 307 how to make "Your First Wooden Bow" I'm wondering if I should try it with this wood....with a backing offcourse.....
Regards,
Preston

[Dennis La Varenne]

Preston,

Remember that for all their obvious value, these are US books writing about indigenous wood species which are mostly deciduous unlike Australian and most tropical hardwoods which are perennials. Their properties are very different. I have found that with the few of our hardwoods that I have used are nowhere as likely to failure if growth rings are not followed as is so often the case with northern deciduous species.

For example, years ago, a friend of mine who was just starting out with advice from me, starting making Cherokee styled bows from Eastern Red Ironbark (tricarpa spp.). He simply made boards from split narrow tree trunks by using an electric planer to flatten them (not my advice), then prodeeded to tiller them and they turned out beautifully.

Because he planed them flat, these bows broke every rule about following growth rings. The back and belly surfaces had chevrons running in all directions, but they never broke and stayed amazingly straight.

I still have two of them at home and they have taken a mere 1/2" of set despite my friend drawing them to 31". They were originally 70" long, but I have shortened them a bit to suit my usual shorter draw of 26". They were 1 1/2" wide tapering to 5/8" wide at the nocks with thickness tapers from 1/2" thick at the handle to about 1/4" thick at the nocks. The have no rigid handle as the Cherokee bow does not.

We have a huge and largely untapped range of hardwoods here and very few of them have been tried in bowmaking. The piece of wood you have can still be made into a bow and I strongly suggest that you go ahead with it and let the rest of us know how it turned out even if it does fail.

From failure, you always learn something and it may have nothing to do with the wood specie itself. Many of us who have been making bows for decades will be able to give some advice and a possible diagnosis of what went wrong as well as what you did correctly.

[Preston]

Hello Dennis,
You are right about the wood....we have different wood in this part of the world... Thanks for the help I appreciate that... I will start off on the bow...and let you all know how its coming along...I checked but cannot find any growth rings on this wood its just a bit course grained and the grain seems to run straight...I think I'll just pick a side for the back and go from there!! I will make it a Rigid Handle Bow with a Pyramid Limb design Capital C Tiller as Jacko suggested...I hope I can do it right!!!
Regards,
Preston.

[perry]

Preston, I don't mean to confuse you but due too past experience with beginner Bow Makers a Rigid Handle Bow is not the best choice for your First Bow, this is why I said earlier "if you are tempted" I should have spelt it out more clearly. Many are drawn to Rigid Handle Selfbow's as they closely resemble the modern norm of the Hill Style Flatbow and they feel they need an Arrow Shelf. I am firm that until a beginner understands the Art of Tillering they are better off with a work through the Handle Bow as they are easier to Tiller. It can get a little tricky Tillering a Selfbow but more so a Rigid Handle regardless of how long the Limbs are. Tillering will give you Kittens for a while yet, after more than 20 Years Tillering still gives me plenty to stop and think about.

Working Handle Bows occasionally scare some People away because they perceive they are less comfortable to Grip and don't like the Arrow passing over there Knuckle. This is easily solved by using Strips of Cork Tile or Leather carved to a comfortable rounded Shape and then a String Grip Bound on. A properly Spined Arrow will not take pieces out of your Hand. For insurance you can add an Arrow Shelf by placing a Wedge to make an Arrow Shelf under the Binding. I used to Stitch on a Leather Grip but now don't bother, I have grown used to the smaller Grips and the Bows look more Paleo.

Can you post Pics of the Board so we can have a look for Grain and Fibre direction and assist you looking for the best Back for your Stave. If not I recommend a Backing as Dennis suggested. Rip Stop Nylon is cheap and effective, you can Source Rawhide from large Dog Chews tied to resemble a Bone. Lots of threads here about Backings, Tillering and Selfbows in general. Sounds to me a Backing will be a top idea regardless of the Grain and Fibre direction.

The best advise I can give the new Bowmaker is to have a Bucket of Water Handy to stick your Head in when ever you start to feel unsure or impatient. It's hard to walk away sometimes but you need that Bucket, saves turning the Stave into Firewood

regards Jacko

[Preston]

Hello Jacko,
You are right the rigid handle bow appeals to me more than the bend through the handle bow...it looks so good!!,
ok so i'll go with the first plan you laid out since its my first bow with an unknown wood and like you say it will be a safer bet... atleast till I know this type of wood better....if i'm successful then the next one out of this wood will be the rigid handle type.... I just checked the density of this wood and its around 0.87 SG.

DSCN0035c.jpg (291.6 KiB) Viewed 8460 times

DSCN0041.JPG (96.02 KiB) Viewed 8460 times

regards,
Preston.

[Preston]

I made another small bow to check... and the specs are as follows

DSCN0053b.JPG (188.49 KiB) Viewed 8429 times

Length 52.75 inches
Width 1.125"
Depth 0.375"
Stiff Handle Length 4.625"
One limb longer than the other by 0.125"
Tip Width 0.25"
Pyramide Design
Jute Backed
15# at 20" Draw Length
String Follow 1.375"

DSCN0050b.JPG (187.89 KiB) Viewed 8429 times

From the above is there any way I can enlarge the specs to get a 40# Bow at 28"
meaning can it be calculated from the above information.....

[perry]

Encouraging Preston, Jute Webbing Backing also - that will test the Compression Modulous. Constructive Critique - Fadeouts are too Steep and too Short and you have a lot of work to get those Outer Limbs working. You have got to get all preconceived Modern Hill Style Riser lookalikes out of your mind. Rigid Handle Selfbows must have shallow angles and long Fadeouts or you will run into issues with the Lower Limbs being too Stiff.

Did a quick Google Search http://www.instructables.com/id/Red-Oak-Pyramid-Bow/ this is the Design you should use if you must Tiller a Rigid Handle Selfbow Its adaptable enough you could use a Rigid or Slightly Working Handle The last Pyramid Limb Selfbow I made had a 4" Grip Section and each Fadeout was nearly as long. A Trap is making the Grip too Narrow, leave it at least 1 1/8" Wide, 1 1/4" for Heavier Bows.

regards Perry

[Preston]

Hello Perry,
Thanks for your reply and advice...I made that bow out of a 3/8" thick piece of sal wood just to test the wood...the bow is still shooting good. So you suggest that I do some more tillering to get the outer limbs working?... The handle was just left over wood that I stuck on for some thickness and comfort...but I see that its not how it should be thanks for pointing that out.
I liked the Link you sent me a nice bow...
I started on a bigger bow of the same wood....Do you think Jute backing is not good for the belly?...can I glue on some cow leather as backing? its about 1/16" thick...or use cotton twine?
I have a question.... since I cannot know in advance how much Pounds the next bow will be... I was wondering if after I rough shape it and do some floor tillering I could find out by measuring the pull within limits offcourse so that I DON'T STRAIN THE BOW and take set... then keep it at that weight and tiller till draw length is reached will this plan work? so that I can get a decent weight bow? I was also wondering if this method will work to get the maximum poundage out of a floor tillered stave... I look forward to your advice...Thanks.
Regards,
Preston.

[perry]

[/size]

Hello Perry,
Thanks for your reply and advice...I made that bow out of a 3/8" thick piece of sal wood just to test the wood...the bow is still shooting good. So you suggest that I do some more tillering to get the outer limbs working?... --the outers are stiff and need to bend evenly to with 5 inches or so a full length Bows Tips, think a Capital C or Circular Tiller for Rigid Handle Bows The handle was just left over wood that I stuck on for some thickness and comfort...but I see that its not how it should be thanks for pointing that out. -- Be carefull with Glueing on Handle Sections, in my experience unless the Timber is thick enough not to bend glueing on a piece od wood to make it rigid will fail. An exception is when it is sandwiched between Backing or Belly Lamination's like Bamboo, Timber or Fibreglass


I liked the Link you sent me a nice bow...


I started on a bigger bow of the same wood....Do you think Jute backing is not good for the belly? -- Jute is a fine backing material , just be aware that it is very strong in tension - use with confidence ...can I glue on some cow leather as backing? its about 1/16" thick...or use cotton twine? If you want to but Jute is great - glueing Twine onto a Bows Back strand by strand is painfull to say the least - stick to weaves.

I have a question.... since I cannot know in advance how much Pounds the next bow will be... I was wondering if after I rough shape it and do some floor tillering I could find out by measuring the pull within limits offcourse so that I DON'T STRAIN THE BOW and take set... then keep it at that weight and tiller till draw length is reached will this plan work? so that I can get a decent weight bow? -- Thats the way to do it, experience will tell you how your going, floor tiller often and take note of the pressure you are applying. I have a vision of the finished Bows apperance and Draw Weight before I start. You could decide you want a 55# Bow, use a set of suspended Scales when checking Tiller and never draw beyond that weight. I like to get a Bow Braced Early and Tiller till the Tiller is perfect, then increase Draw Length

I was also wondering if this method will work to get the maximum poundage out of a floor tillered stave... I look forward to your advice...Thanks. -- Yes it will, with experience you will look at a Stave and see if you will get a heavy Bow from it


Regards,
Preston.

[Preston]

Thanks Perry,
I appreciate all your support and advice got to go back to work , The bow I was doing developed chrysals!!!!!. I stopped working on it...I got to go back to work (I work on the oil rigs) so I won't be able to start a new one...till march.....
I think this wood is too weak in compression compared to the tension limit. Do you know if I can try something else to be able to make a decent weight bow from this wood? I want a 35 to 40# bow to practice with...
Regards,
Preston

[Preston]

I just came off the rig today will be home tomorrow!! I searched for wood suppliers in Bangalore and it turns out that there are suppliers of the following wood...

Red Oak
American Ash
American Walnut
American White Oak
Maple (sycamore)
Wenge

I will try to get some wood when I get back home but first which wood would be the best one to start with...Please advise....
I want to build a pyramid bow as I like its shape but a bend through the handle flatbow will be fine too... for that matter any bow of around 40# is what I want to build...

[hunterguy1991]

In my opinion the American Ash would be the best for flatbows like you are making in that list mate...

Just follow Perry's advice he gave on the smaller bow you made and you should be sweet.

Colin

[Preston]

Thanks man, I'll do that and let's see how it turns out, today I found some nice videos on youtube on making a flatbow that will certainly help... Perry was telling me for a for a first bow a bend through the handle would be the wat to go....

[hunterguy1991]

Yes definitely listen to Perry's advice on this.

The ridged handled bows (howard hill style) are a little more tricky to make because you have to be careful to get the fade outs right for the weight and length of bow you're making. Also because of the rigid handle you lose some working limb length so its more stressful on the timber to make it back to full draw.

Once you knock out a couple of bendy handled bows and your confident in your tillering skills then have a crack at a rigid handle version.

Looking forward to seeing what you come up with mate!

Colin

[greybeard]

........I searched for wood suppliers in Bangalore.....

Hi Preston, it may be worth your while to source some split logs or larger branches of the following;

Following information from; http://www.arvindguptatoys.com/arvindgupta/mccann.pdf

BABAL or BABHUL

Acacia arabica Willd. (Order: Leguminosae).
Acacia from Latin acus, needle, in reference to the spines. Arabica, pertaining to Arabia, the country from which it was first described.

Description: A small spreading very spiny tree, 20-40 ft., with dark brown longitudinally fissured bait. Leaves bipinnate, 2-5 in. long, main rachis downy, often having glands: petiole 1-2 in. long, leaflets small very numerous; stipular spines variable 0.25-3 in. long, greyish white, smooth, straight, sharp: pinnae 4-9 pairs. 0.75-2 in. long: leaflets 10-25 pairs. 0.125—0.25 in. long. Flowers small, arranged in fluffy round heads, yellow; peduncles in fascicles of 2-6; calyx minute, cupped; corolla with short triangular lobes. Pods 3-7 in. by 0.5- 0.625 in. moniliform, flat grey downy: seeds 8-12, flat.

Distribution: Throughout the greater part of India, Ceylon, Arabia, Egypt, and Tropical Africa.
Gardening: Propagated by seed (seldom planted in gardens), self sown in many areas. Makes an impenetrable fence. The plant is salt tolerant and grows near the sea, even along salt marshes.

Uses: Almost every portion of the tree is used for various purposes. The gum is used medicinally and by calico-printers and as a substitute for gum Arabic. The green portions of the plant and its fruit form a valuable fodder in arid areas. The timber is hard and durable, extensively used for wheels and well curbs and largely for fuel. The young branches are used as tooth brushes and are sold in the markets.

TAMARIND or IMLI

Tamarindus lndica Linn. (Order: Leguminosae.).
Tamarindus is derived from the Arabic name tamar-Hindi meaning Indian Date; indica, pertaining to India.

Description: A large deciduous tree reaching 100 ft. in height with a large spreading crown. Leaves compound, paripinnate, 2 to 5 in. long: leaflets 10 to 20 pairs. 0.3 to 1 in. by 0.2 to .33 oblong, rounded at both ends. Flowers in few-flowered racemes at the ends of the branchlets. Calyx 0.5 in, long. Sepals 4, ovate-lanceolate, tip acute. Petals only 3 developed, ovate-lanceolate, somewhat wrinkled along the margins, pink-lined. Stamens only 3 developed. Fruit a pod. 3 to 8 in. long by 0.75 to 1 in. wide, somewhat flattened, scurfy, curved and constricted at intervals. Seeds 3-12, ovate-oblong, truncate at both ends, compressed, smooth and shining.

Distribution: Believed to be indigenous in Abyssinia and Central Africa. Largely planted in India along roads and around villages and frequently it runs wild. Tamarind groves in forests often mark the site of deserted cultivation or village.

Gardening: Propagated by seed, thrives only in the warmer parts of India. In the Punjab it does not ripen its fruit. It is one of the commonest village trees in Burma but in the dry zone.

Uses: The timber is hard and close-grained and is used for rice-pounders, oil and sugar mills, tools, furniture, and turnery. The fruit is used as an aperient and as an astringent, for making condiments and in general cooking.
Note: The young leaves and flowers appear almost simultaneously and the transition from the old to the new foliage is not always well defined. The pale green of the tender leaves is a beautiful sight.

Following information from; http://www.wood-database.com/

Common Name(s): Tamarind, Spalted Tamarind
Scientific Name: Tamarindus indica
Distribution: Native to tropical Africa; widely planted throughout tropical regions worldwide
Tree Size: 50-80 ft (15-24 m) tall, 2-3 ft (.6-1 m) trunk diameter
Average Dried Weight: 53 lbs/ft3 (850 kg/m3)
Specific Gravity (Basic, 12% MC): .68, .85
Janka Hardness: 2,690 lbf (11,970 N)
Modulus of Rupture: 16,090 lbf/in2 (111.0 MPa)
Elastic Modulus: 1,918,000 lbf/in2 (13.22 GPa)
Crushing Strength: 8,640 lbf/in2 (59.6 MPa)
Shrinkage: Radial: ~3%, Tangential: ~7%, Volumetric: ~11%

Timber Qualities
Tamarind timber is prized for its strength and termite resistance. It has a beautiful grain, yellow with red streaks, and is hard and durable. Furniture made from this tree indicated wealth in ancient Sri Lanka, where it was used to make rice pounders, mortars, side planks for boat wheels, axles and naves.

There are probably several local trees that could be suitable for self bows.

Daryl.

[Preston]

Daryl I don't know BABAL and I've heard of it... it may be a North Indian grown tree but Tamarind is all over the place overhere in Bangalore. I will try my best to get a suitable branch for a selfbow, I have never heard of tamarind wood boards being sold like other commercial woods.... I have seen some other trees that grow wild which are definately Acacia and I will try to get a branch to make a bow from one of them....Thanks guys I appreciate all your input and help. I leave for home today morning....

[greybeard]

......I will try my best to get a suitable branch for a selfbow.... I have seen some other trees that grow wild which are definately Acacia and I will try to get a branch to make a bow from one of them....

If you can, try to get manageable sized tree trunks as well.

Daryl.

[Nezwin]

TAMARIND or IMLI

Tamarindus lndica Linn. (Order: Leguminosae.).
Tamarindus is derived from the Arabic name tamar-Hindi meaning Indian Date; indica, pertaining to India.

...During my time there we built bows from tamarind timber, although this can be difficult to get due to the commercial cropping and/or religious association of the tree...

Funnily enough, I broke my Tamarind bow in a motorcycle accident halfway between Bengaluru & Chennai...

You know what they say about 'great minds'...

http://www.ozbow.net/phpBB3/viewtopic.p ... 9&start=30

[Preston]

I tried doing a test on redsal wood and it was disapointing...the wood is good in Tension it will not break but it takes set early and is weak...
So I went out and tried to get any other wood and bought some Padauk as I couldn't get any other suitable wood in smaller sizes..I have been trying to get Babool or Tamrind wood will let you all know if I'm successful..

I done a wood test with the Padauk (Using Maths in Making Bows) the results as as follows:

Padouk.JPG (28.21 KiB) Viewed 8189 times

I would like to build a bend through the handle bow with this wood as I think it might give me a better chance of success as Perry pointed out in the begining of this thread. The piece I have is about 13mm thick by about 60mm wide and about 65 inches long Please let me know what should be the design of this bow... I am anxious to have a successful build and to be shooting a bow before I go back to work by the end of this month.... around 40 to 45Lbs bow is what I would like to have.... the Thickness I got is 5.43mm by 117.84mm for the width of a 26" radius Pyramid bow!! is something wrong with my calculation? increasing the radius(length of the bow) reduces the width I need according to the spreadsheet...and a bendy should give me that I think...

I plan on backing this bow as the test piece broke in Tension the wood split/cracked around halfway from the top with the bottom half still intact

P.S I had a thought last night what if I laminated a thin strip of RedSal as a backing strip for the Padauk Bow.....

[Dennis La Varenne]

Preston,

Backing your bow is probably not a bad idea but if you are able to work out a proportional difference between the load at which the Salwood starts to take set and that loading where it eventually breaks in tension, you can make the weaker (belly) much wider than the back by making a trapezoidal limb section.

Averagely, most wood tends to be somewhere around stronger in tension in a ratio of 5:4, or about 25% stronger in tension than compression (leaving out the less common exceptions), so you could start with a belly which is 25% wider than the bow's back and see how that goes.

[Preston]

Hello Dennis,
That would be a great way to balance out the forces for the bow...but the problem is that the board of Redsal I got maybe too weak.... it may be just this piece of wood or it may be that this is the average properties of the wood, it just bends too easily and I cannot make a 40# bow unless I buy a thicker piece of wood and maybe wider too.

I just went out and bought some Acacia wood I believe... I don't know which tree it came from but its not Babool which is what I was trying to source. I will let it dry out for some time before I do a test and see if its suitable......I saw some Babool today but its in big Planks and I got to buy the whole thing just for a piece to try, and the other thing was that I couldn't find a suitable piece free of knots and most were very wavy grained. I actually felt very disapointed I wish I could get a log that I could pick myself and then split it to staves to try out that maybe the best way to find suitable Babool wood.

The redsal test is as below.....Let me know if you think it can be made into a sucessful 40 to 45# Bendy Bow...

RedSal03-Mar-2015.JPG (29.96 KiB) Viewed 8167 times

[Dennis La Varenne]

Preston,

I think you are right. What a sag it took at after 26lbs. Heavens!!!

[Preston]

Yeah that's how I felt not to mention the wasted time... but its all good experience.... The padauk bow will benefit from an Inverted trapezoid crossection since its weaker in Tension. So a rounded off Inverted trapezoid crossection Belly should be about the same thing and it will look better... I think I should try it then... the difference is about 83% between the point of first set and breaking point.

For the thickness should I use the first set point thickness( 6.89mm ) or the one where it broke (8.42 ) or an average of the two thickness...

what do you think?......or maybe use 83% of the calculated thickness for the point where it broke (~7mm ) or just use the thickness of the break point..... the reason I want to use as thick a limb as I can get away with is so that I can reduce the limb width....

I think I'll settle for 8mm thickness and a width of about 55mm and use the Pyramid Design, I'll Reduce the belly width and round it off and also back the bow with either Jute or RedSal.... Do you think this will work?
The reason I'll use the pyramid design is because of the excessive width I got to use... I hope that this will give me a 40# Bow

[Dennis La Varenne]

Preston,

Ideally, I would base my calculations on where the stave just begins to show set. Yeoman does the same as I recall. He did some bending work a good while back and came to a tentative conclusion that the maximum stress at that point on a sample beams he tried was roughly 66% of the MoR number, which is a handy reference and is much the same as your 'set-point thickness'.

Just recently, I started reading a chapter in 'ARCHERY - THE TECHNICAL SIDE' where he makes the point from an engineer's standpoint of looking at the bowlimb shape promoted by Hickman and Klopsteg (the wide pyramidal shape) was incorrect and that the ideal shape is to have both a tapered thickness as well as a limb which has a somewhat barrelled shape, ie. that the sides of the limb should form a short of shallow parabolic shape (if that is the correct term) starting at the flares and tapering slowly to about mid-limb, past which the limbs begin narrowing at an increasing rate to the tips.

However, to plot that shape well, requires the use of some fairly complicated maths so that bending load is equal right out to the nocks.

Nagler's thesis is that the bowlimb works as a cantilever rather than a beam and that changes the maths. This is at the higher end of bowmaking technique, but for the average person, the pyramid shape works well enough.

No harm is ever done by backing a bow with a material which matches the compression strength of the belly. It won't improve cast of course but will help prevent tension breaks.