VirtualBow for modelling bows

“VirtualBow is a free, open-source software tool for designing and simulating bows. It gives users an easy way to test and optimize their designs by providing almost instant feedback about a bow’s predicted performance. The simulation results include a variety of static and dynamic characteristics of the bow such as the draw curve, limb deformation, stresses, arrow velocity and degree of efficiency.”

Something about modelling have been discussed here:

There are 3 my latest models of turkish bow with calculated strains (thanks Jano for teaching me how). I would appreciate option for D crossection in this software, for more accurate results.

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Now question for people smarter then me. Is it bad if the strain in the wooden core back is larger then 1%? If so, then all of these bow will brake. So I guess I need to shift neutral plane up to the back by rounding the belly in the real bow.

It will be in future version, but not soon.

No. If strain really is over 1 %, which I believe it really is, because the program is quite accurate, it is not a problem. Sinew layer over the core wood will affect somehow that core doesn’t break. Otherwise it would be impossible to make this kind of bows.

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Recently I noticed Jere’s question about bendmetering on facebook group and I suppose not many people truly appreciate its possibilities. IMHO this is another efficient tool for bowmakers complementary to Virtualbow ( taking into account properties of non-uniform material ) , hence I am contributing here in this thread.

( Free quote of somebody-s contribution somewhere : “Tillering Gizmo is only simplification of a bow-making bendmeter, first devised by Wilcox in the 1920’s. Russ and others refined it over the years. I seem to recall reading that Dr. Klopsteg used a spherometer for the same purpose.”)

If you do not know the appearance of bendmeter, please open the pictures - bendmeter.jpg and Elmer_book_bendmeters.jpg , from the folder - crievka - from this address :

of my selfmade one and others from R. P. Elmer-s book : Target Archery, around 1940, where he wrote about Russel Wilcox using it in tillering his Duoflex bow …

Bendmeter can be very precise, hence you can determine exact strain values at every “station” on the bending limb and “tiller” it to be precisely equally stressed ( or what stress distribution you choose ) along its length in accordance with the diminishing thickness ( elliptical tiller ). At the beginning you have to measure initial offset ( on each station along the limbs ) on non stressed bow, then the deflection and the thickness on actual station on ( partialy ) stressed bow and then compute the actual strain value ( in percent ) at this station. And so on for all stations and tillering stages .

With true bendmeter it is possible ( I hope ) to tiller the bow by amount of set/string follow , because it is so precise ( I never did it ). I used bendmetering several years ago on my wooden bows ( for hornbows probably the device with larger range of movement of the column would be needed ). I measured the bow only at about half-draw to eliminate string follow caused by long time spent at full-draw position, when measuring it by bendmeter ( shape of limb bend at this half-drawn position can be resolved through tillering programs - e.g. VirtualBow ).

It is quite “boring” and “longlegged” method of tillering ( nowadays facilitated by spreadsheets on computers ) , but gives very reliable results ( even for novices ) and should be used at least to enhance flightbow making if too laborious for common bows.


I would like to show you at least one example. Between my bendmetering attempts belongs already published - on old forum :

tillering of the experimental maple core. I liked to be more precise on short bending limbs, hence I established the “stations” every 2,5 cm ( about 1 inch ) and had to “reconstruct” my old bendmeter to narrower one - with 5 cm span ( see the picture - BTW I advice to rather buy - more handy - digital dial indicator for this purpose ). I was quite lucky and did it in only few “tillering sessions” as you can see on “small chart” on the second picture. Maximal bending strain of the wooden core was established ( not very exactly ) as 2,7 % and did not varied greatly along ( most ) bending limb.

Hope, many people ( also selfbowmakers, warbowmakers ) will be interrested in this “old masters technique” nowadays too, because it is very reliable.


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