Building a crossbow

Hello,

I'm new in making a crossbow but i came far. Here are the resultes that i have now.
But i came at a problem about the bow itself i don't now what the measurements are.

https://servimg.com/view/18923679/7
https://servimg.com/view/18923679/8
https://servimg.com/view/18923679/9
https://servimg.com/view/18923679/10

I want to build a composite wooden prod for a crossbow. I have experience building laminated flatbows but I am not sure about the sizes and materials for making a crossbow prod.
 
I have a 5mm hickory strip available which is quarter sawn for the back of the bow, I want to use massaraduba aka bulletwood (Manilkara bidentata) for the belly of the bow since it is strong in compression. Do you think this is a good combination? I will use titebond III for the glue up. This combination of woods&glue sure works on long/flatbows.
 
I did some browsing on the forum and I calculated that the length of the prod should be 3 or 4 times the length of the arrow groove/stroke. Am I right? Is there a formula for calculating the correct length of the prod? What draw length/stroke is normal for a medieval crossbow (12 inch/30,5cm)?
 
We are aiming for a prod of 40/50# any suggestions about the with of the prod and thickness? When gluing should we glue the prod straight or glue in some deflex (bend towards the bowstring)
 
We would like to hear your input.


Caspar Staal

Hi Caspar;

Most of the people here are not building wood-wood composite prods; and only a very few are making wood-fiberglass prods.  From my bowbuilding experience, your hickory/bulletwood should make a good prod.  But I haven't any idea of the proper dimensions for the two laminations.  Titebond II or III is good.

You want a prod that only draws 40-50 pounds?  That VERY lightweight. Or do you mean 40-50 kilos (88-120 pounds)?  I would guess your 5mm hickory and an equal lamination of bulletwood to be far too strong for only 40-50 pounds draw weight.  That would make a 40-50 pound full-length flatbow!!  For 40-50 pounds I might use a 3-4 mm strips of each wood.

Length of prod can be anything you want from about 28" to 36".  Since you're using wood I would suggest 36" or a 1 meter long prod about 1.5" or 35 mm wide.  If you have a flatbow made from those woods, you could estimate draw weight for a short prod by deducting 10 pounds for every 2" of length that a prod (of the same width and thickness) is shorter than the flatbow.

I would glue a little deflex into the prod; that will make it easier to get the string on to start.

Thanks voor the info it really helped.
I'm now finished whit my crossbow and it shoots really nice

Bravo!  Very nice job.  Looks very good!

ooh, is that a double horn anvil?! I'm jealous, I only have an old 35 pounder.  The nut is steel? looks very nice.

Jup the nut is made of steel and the anvil isn't mine a friend of mine is a blacksmith its his anvil.