What kind of prod could I make? (Small pistol crossbow)

I'm making a small medieval-style crossbow with a very simple push-up pin mechanism. Now the little stock is pretty much done (just needs some work for the looks). But I don't know what kind of prod I could make. Do any of you have any ideas? It need to be made from easily accessible materials (no spring steel  ). I do have an old hockey-stick made of carbon fibre, could that work? Would take away some of the medieval feeling though   . The distance from trigger-mech to front of stock is 10-12 cm. 

I would be really grateful for any ideas  I'd like to post some pics once it's finished!

Regards
//FIAAO

(Sorry if there already is a thread like this here, I could not find anything)

Quick cheap and simple is some 1/4" fiber rod from driveway markers. Cover them in leather and they look OK for a toy. I have used sawblades in the past for toy bow prods. Ebay and the crossbow store have little pistol crossbow prods that pack a whollop. Other than that, bamboo is a great choice and seems fo be a favorite around here.
cheers,
chriso

PVC, properly flattened and shaped, makes great pistolbow prods.  Properly sanded, filled and painted black or dark brown and it can look very much like a wooden prod.

Failureisalwaysanoption wrote:I'm making a small medieval-style crossbow with a very simple push-up pin mechanism. Now the little stock is pretty much done (just needs some work for the looks). But I don't know what kind of prod I could make. Do any of you have any ideas? It need to be made from easily accessible materials (no spring steel  ). I do have an old hockey-stick made of carbon fibre, could that work? Would take away some of the medieval feeling though   . The distance from trigger-mech to front of stock is 10-12 cm. 

I would be really grateful for any ideas  I'd like to post some pics once it's finished!

Regards
//FIAAO

(Sorry if there already is a thread like this here, I could not find anything)

A while back on ebay, I saw an 8' piece of fiberglass slat, 1/4" thick, and if I remember correctly, it was 1 3/4" wide. Its purpose is for supporting boat covers, you might have a boat shop locally that would carry them. The ebay one was around $25-30 USD, but the problem was because of the length, the shipping was about the same. I emailed and asked what they would charge if they sawed it in 3 equal lengths but the answer they gave was not definite since they had never done it. I'm thinking this could be good material for larger rainbow [as opposed to recurve] prods as well, possibly could be resined together to make a quite powerful prod.

Jack ><>

That fiberglass slat sounds really interesting.  I've used 1/4" x 3/4" solid fiberglass chain-link fence tension bar for regular crossbow prods  (see my avatar picture).  That stuff is so strong it would be nearly impossible to string 12" or even 16" section.  I've got a spare piece if anyone wants to try!.  My 28" + 16" loose laminate prod made from he stuff draws well over 250#s.

kenh wrote:That fiberglass slat sounds really interesting.  I've used 1/4" x 3/4" solid fiberglass chain-link fence tension bar for regular crossbow prods  (see my avatar picture).  That stuff is so strong it would be nearly impossible to string 12" or even 16" section.  I've got a spare piece if anyone wants to try!.  My 28" + 16" loose laminate prod made from he stuff draws well over 250#s.

Kenh, I read about the chain-link bars on here, but can't find them anywhere, they seem to be replaced by steel bars.
Jack ><>


adding the link   http://www.ebay.com/itm/Fiberglass-bow-slat-8-long-/270409921275?pt=Boat_Parts_Accessories_Gear&hash=item3ef5aff2fb&vxp=mtr

Has anyone tried laminating 2 or more "slats" or fiberglass chainlink bars together? I wonder if it would work without shearing at the glue joint between the lams when the prod was drawn? Could they be glued directly together or would a lam of fiberglass cloth between be required?

Jack ><>

I don't think I'd want to go that route Jack,2 radiuses of different lengths,working against each other,same as a car leaf spring,would you weld the leaves together?
                                                          Hermit.

Hermit wrote:I don't think I'd want to go that route Jack,2 radiuses of different lengths,working against each other,same as a car leaf spring,would you weld the leaves together?
                                                          Hermit.

No but I have to wonder if 2 leaf springs welded would function as 1 heavier spring, and if 2 or 3 lams [fiberglass] "welded" [resined, glued] together would function as one unit without self-destruction?  Welding would be along a thin line on the edges, gluing would bond the entire mating surfaces; wouldn't that tend to unify the structure?


Jack ><>

I don't think it works that way Jack.      If you "weld" laminations together, the strength increases much more than just arithmetically and the welds would be prone to break.  I build nominally long bows as wood-fiberglass composites and there is very little glass seldom more than .10" in a bow.  What gives a bow it's strength is the separation between the two pieces of say .05 glass by relatively weak wood.  The glass supplies 88% of the strength and the wood only 12%.  

Where are you Jack.  Send me a PM with your address and I'll get a tension bar for you.  IIRC a 6 ft bar was about $8...

kenh wrote:I don't think it works that way Jack.      If you "weld" laminations together, the strength increases much more than just arithmetically and the welds would be prone to break.  I build nominally long bows as wood-fiberglass composites and there is very little glass seldom more than .10" in a bow.  What gives a bow it's strength is the separation between the two pieces of say .05 glass by relatively weak wood.  The glass supplies 88% of the strength and the wood only 12%.  

Where are you Jack.  Send me a PM with your address and I'll get a tension bar for you.  IIRC a 6 ft bar was about $8...

KenH, thanks for the offer; can I get a raincheck? Living in the boons, I have only looked at one place and not exhausted my opportunities yet, and if I can get one locally, that would make it easier on both of us.
On the prod in your avatar, do you have any material separating the lams, and what material are the black bands, simple duct tape or some kind of shrink material, or other?

Jack ><>

Thanks for the answers guys! I tried PVC two times now but it won't work… (I'm not the best with PVC obviously   ) What length should the prod have to accommodate a 10 cm draw?

Jack - No problemo.  There's nothing between the two lams, and they are just held in alignment by the bands of shrink-wrap tubing.

Failure--- length of prod for a given draw length can only really be answered if you specify prod material and desired draw weight.  10 cm is about 4 inches.  With many materials a 20 cm (8") prod would give you that draw length but it still depends on draw weight.  A 28-30 cm prod should certainly be enough. 

If you made a 12" prod from 1/2" PVC as Nick Tomihama shows in his PVC pistol crossbow YouTube you should have plenty of power and draw length.  PVC needs *gentle* heating and working.  Check out the Google + group called PVC Archery & Crafting where a number of folks have made PVC prods for both pistol and full suze crosbows.

Fibregass is made by completely impregnating glass fibres with resin.When the resin sets up,it forms a surface that is non porous.Joining 2 already formed non porous surfaces with just a thin layer of adhesive,even though it is fibreglass resin,is something I would not be happy with in bow construction,bearing in mind the kind of stresses the a bow has to take.There would have to be a perfect bond,something that would be difficult,if not impossible to obtain,and as the surface of the fibreglass when finished is already non porous,would the bond be good enough to stand the stresses that a bow would put on it?I don't think I'd bet on the bond holding for long.
                                                      There is a way that would work tho'.
Instead of laminating and glueing the 2 pieces together,put one piece on top of the other,with a gap,and join the limb tips together so that a single string pulls both,that way,the stresses on both are equal,and the power is doubled.The disadvantage is that the width of the bow is increased,and has to be allowed for where the bow is attached to the tiller,something that seems to be fairly easy to overcome.
                Hermit.

Hermit said:  "put one piece on top of the other,with a gap,and join the limb tips together so that a single string pulls both,that way,the stresses on both are equal,and the power is doubled."

That's exactly what a loose laminate bow is and how it works.  Except that normally the two or more pieces (laminations) are usually successively shorter to get a more efficient drawn shape to the prod.

Putting ideas into words is not easy,but a loose leaf bow was not what I was suggesting,and the clue was'joining the limbs together at the tips'.On a loose leaf laminate bow,the laminates would not be permanently joined together,rather ,held in position.What I was actually suggesting,was in effect two bows,one upper,one lower joined together at the limb tips with a single string nock at each end of the bow,enabling both bows to operate as one,and so equalizing the stresses.Some compound bows operate this way,so that the cams can be accomodated in the limbs.appologies for any misunderstanding.
                                   Hermit.