Loose Laminate Prods?

Anyone have experience building loose laminate prods? I want to make some really small prods to fit reasonably historically accurate pistolbows like the Slurbow and Assassin's bow I posted pix of. I can't do metalwork, but I am a woodworker and thought I might try a couple of stacked prods. The Building Wiki section on Loose Laminate prods has nothing in it.

I want to make prods that are under 12" from nock to nock, with hopefully 40# total draw weight. The modern pistol bow prods are far too long - more like carbine prods than pistol prods.

I do have access to bamboo (both wild harvested and 'processed'), and I understand that constant width lams are best. I think I can find wild harvested 'boo that is more than 10" between nodes, even... If I can't, I'll put the nodes at the centerpoint of the lams. A belt sander on wild harvested splits will give me constant thickness and width lams. I'm figuring on 4 lams -- say 10", 7", 5" and 3" that are 3/4" or 1" wide. I know how to make a tillering tree, even that small, and have a scale for measuring draw weight

The big question I have is which side of the stack faces the nut -- the short lam side or the long? I can see advantages and disadvantages to each.

Other questions include brace height and draw length for this stacked creation. With a 10" length, 2" seems a reasonable fist. All I really need is space to grab the string with a cocking mechanism. On draw length, conventional wisdom for wood bows would say a draw of 50% of the T-t-T length, or 5" in my example...

Ideas anyone??

Well, I did a bunch of "mental engineering" and have an idea for very short "bundle bow" or "loose laminate" prods. Stopped at my local hobbyshop to get some bits & pieces to prove or disprove the concept. Will post photos as I go. May have to wait for hurricane Isaac to get out of my way first, though...

I don't have much experience with it, but I would think that having the smaller laminates face the nut would be better. As the prod is drawn back, the laminates will naturally begin to push back upon the next laminate in the sequence. If the smaller ones were away from the nut, when you draw it back the laminates will try to pull away from each other and create a lot more stress on whatever material you use to bind them together than if they were pushing into themselves. In either event you will need to take care to bind them well.

Ayup, that was my initial thought, based on other bows. That's the way I'm proceeding. I did get the holes drilled that I need to have in what will become the bow irons.

But you never know; physics can fool you sometimes; so I thought I'd ask.

Loose Laminates: Essentially you're making a leaf-spring, like the ones used on older cars and trucks. Back in the 60's, you could buy 'Roberts' Crossbows, made by a shop called Olsen Industries. They had a lovely modern-style crossbow with an asymmetric steel prod... the basic bow drew @ 90 lb. Stronger prods were available... they simply added a helper-leaf behind the main one... for 125, 150, or 175 lb. The helper-spring was center-riveted to the main-prod. They placed pieces of slick (Delrin?) plastic beneath the ends of the helper, where it would rub on the main prod, and secured them in place with a piece of clear heat-shrink tubing.
I have a 150 Roberts hanging on my shop wall... a nice, rugged, well-crafted piece. If any of you guys see a Roberts for sale, it might be worth picking up. A
Geezer

Hey guys. Thought I'd chime in with my newbie 2 cents worth. I just recently built a crossbow using 3 stacked lengths of loose laminate fiberglass chain link fencing tension bars. I bought the bars in 6 foot lengths and they're 5/8" wide by 3/16" thick. These bars are awesome for projects such as these as they only cost less than $2.00/length. I cut them at 28", 24", and 20" and staggered them 2" smaller at the ends with the smallest facing the archer. I bound them together using duct tape the entire length of the prod. My power stroke is at 12.5" and I can cock it manually although it's close to the limit of my strength, and I'm a pretty strong guy. I haven't tested to see what the draw weight at that stroke is as I don't have a scale yet, but she fires fast. I'm waiting for a friend to loan me a chrony and I'll post draw weight and velocity.

Fiberglass chain link fence tension bars. Now there's an innovative material easily worked with hand tools! So you basically built a prod for about two bucks -- pretty slick.

I'm experimenting with a different style of laminate for pistolbow prods -- 12" or less lengths of 1/8" diameter music wire held relative to each other by the prod irons.

I just picked up a 6 ft length of black fiberglass tension bar -- hard to find here where I live in FL, and it cost me $7 for the length, not $2.

I'm going to duplicate Rudamchu's 28/24/20" laminates for a full-size Slane style lockbow.

Any ideas on the best way to attach or cut string nocks? I read somewhere here where someone epoxied phenolic blocks to the back side tips of a fiberglass prod and then cut the nocks in that.

Kenh, what I did was pick up some extra thick heat shrink tubing and cover each end with about 2" of tubing then filed nocks in that material. Be careful with the heat gun so as not to melt the fiberglass resin. In retrospect, I would also bind the leaves with material that's less likely to stretch....over time, the duct tape does stretch some. Don't worry if your nocks cut into the fiberglass a little, as long as it's not too much. Oh, and I see you live on my left coast.....I live in ft ldle and there's a fencing supplies place here locally that has them for the price I mentioned if you're ever over here. They're called San Lazaro fencing supplies.

I'll think about the heat-shrink for the nocks. I'd almost rather use it as narrow bands where the ends of the other leaves are, rather than wrapping the whole thing in tape or something. That's the way the Chinese did their multi-lam prods back in the day. -- the lams can slide against each other a bit, the way they should.

Did you ever figure out what your draw weight is?

Nah, couldn't figure draw wt cause I don't have a scale that measures that high - I only have a fishing scale. I did get a speed test done using homemade 5/16 dowel bolts weighing 284 grains going at 210 fps

OK, so I have the three lams held together with spit and baling wire -- I mean heat shrink tubing and a bit of tape. I've got phenolic nocks glued on the back of the tips of the longest lam.

With a bastard string, I can (barely, wimp that I am) manually cock a two lam prod on a tiller stick to the point I can slip a proper length working string on.

I'd like to make the bow with all three lams (close to 200# draw?)

Now I need ideas on how to span the three lams to put the working string on.

Pictures, sketches, ideas?

* First thought -- find that really strong neighbor guy who pumps iron and see if he can 'pump' fiberglass!

* Second thought -- suspend the prod by the tips on some sort of U shaped frame and use a bar clamp or giant C clamp to pull down the center of the prod.

Don't want to spend much $$ as this is probably a one-shot deal.

kenh wrote:

Now I need ideas on how to span the three lams to put the working string on.

First, sign this liability waiver: ____________________

I did something like this with a bottle jack...

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You may find a cocking aid (silence peanut gallery) helpful...like the one in my avatar or here...
http://www.excaliburcrossbow.com/catalog/crossbow/rope_cocking_aid

Easy to make if you want the ye olde look, I just bought the Excalibur ones. It half's the draw weight. You need somewhere on the butt stock to loop the middle rope. I imagine the same concept would cock a bastard string.

I just knew those jacks were good for something besides making a rust pile in the boot of my car (when I had a car)!

Never called that a 'bottle jack' before, though. Must be one of those north-of-the-border phrases. I can see even a rack & pinion type working too, but the bottle type would be a smoother lift.

The girlfriend will never know hers got 'borrowed' for something besides changing a tire....

I do like that rope cocker though. A couple hooks a couple handles and a piece of paracord. That's cheap! And certainly worth a try. A more distant notch on the tillering stick will do to hook the cord in for the lift.

I was thinking about making a wippe for everyday shooting, but that looks like a decent alternative although I'd have to cut a special notch in my tiller for the cord.

Thanx for the ideas!

kenh wrote:OK, so I have the three lams held together with spit and baling wire -- I mean heat shrink tubing and a bit of tape. I've got phenolic nocks glued on the back of the tips of the longest lam.

With a bastard string, I can (barely, wimp that I am) manually cock a two lam prod on a tiller stick to the point I can slip a proper length working string on.

I'd like to make the bow with all three lams (close to 200# draw?)

Now I need ideas on how to span the three lams to put the working string on.

Pictures, sketches, ideas?

* First thought -- find that really strong neighbor guy who pumps iron and see if he can 'pump' fiberglass!

* Second thought -- suspend the prod by the tips on some sort of U shaped frame and use a bar clamp or giant C clamp to pull down the center of the prod.

Don't want to spend much $$ as this is probably a one-shot deal.

Hi Kenh,

How is the thing working so far ? I've decided to try this multi laminated prod too. I tried to glue wood on the fiberglass rod so I could carve nock into the wood, but I found that the bond wasn't strong enough.

Any other type of glue that would work well ?

Also, I have hard time finding a material to hod the bow together, right now I'm using tape as testing purpose, but I would want something more classic, I was thinking something like a 1inch wide leather strip every 4-5 inches, do you think it would be strong enough ?


Thanks

Keg; here's "The Rest of the Story" as they say:
https://thearbalistguild.forumotion.com/t945-loose-laminate-pinlock-build

The tension rod laminate prod works really well. Too well in some ways as it was far stronger than I really wanted (well over 200# draw). But I had to go to Plan B for the nocks -- I cut traditional sort of pin nocks in the ends and 'reinforced' them with a coat of epoxy putty. I think you could also reinforce those pin nocks with an overlay of epoxied flat phenolic like you would on a regular composite fiberglass bow.

As you'll see I used tape for testing purposes too, but finished with heat-shrink tubing as binding. I suppose you could glue strips of thin leather/suede over the tubing for a nicer look. Traditional Chinese loose laminate bamboo prods were tied with rattan cord (sort of like binder twine) and only tied near the ends of each laminate layer. I think a nice 1" wrap of thin cord of some kind would look nice too. The laminates do need to slide against each other as the prod is cocked and fired.

The whole thing works well. I'm in the process of buildinf bolts/quarrels right now using cut down arrowshafts with two fletches of thin wood.

If anyone is interested i can look up for some formulas to calculate draw, number of laminates, lenght , draw lenght and so on

Spyro.Magno wrote:If anyone is interested i can look up for some formulas to calculate draw, number of laminates, lenght , draw lenght and so on

That would be awesome!  I'm interested!  Although I'm looking at an unusual prod/bow configuration (an H bow along the lines of Nerd Flintstones Paleo Compound design).  So it wouldn't be spanned in the normal sense.

Cocking it though will very likely require an aid such as the Excalibur cocking rope (I like that - simple and elegant).

Having the information you're offering would definitely help give me some idea of what I'm dealing with.   

Ok i'll look up to it! 

Atm im working on a crossbow (i'll open a topic when is finished) and i'm strugglin to find a suitable leaf spring, or actually find a leaf spring. As i would need to do some calculations to fit it (my bad i decided the draw lenght from just thoughts, and not with proper calculations) i thought about making a quick guide with steps on how to define the dimensions for the prod (is it the prod? im not so much into the proper terms yet)

EDIT: im working on the guide and its almost finished, i'm just stuck on the actual multiple leaf spring because when looking for other resources than my book i found an other interesting method on how to calculate them but i'm missing some links between the method i learnt from the book and this one.
This last one is less ''interactive'' meaning it gives you a pretty accurate result instead of reiterate the same formula with different values until you are satisfied