The dangers of steel and potential remedies?

I'm new to building crossbows but I have been building things for quite some time. After a few successes with traditional bows I decided it was time to tackle something more high tech. Making a wooden prod would be too similar to the bows I had already made, I wanted to go for steel.
Having some knife making experience I knew good steel could be found in the form of old car springs, so I took myself down to the junkyard and hauled a good leaf spring out.

Much to my dismay I learned that this type of steel, while amazing for knives, can be rather dangerous for crossbows.

I still want to give it a go with these springs, and to try and minimize any risks I wanted to ask about 2 things...

1) I had heard that many steel bows will break from being too weak in the middle. I plan to shore up this area by riveting a piece of leftover spring onto the center section of the prod. Does this seem like it would protect this otherwise weak area?

2) If I were to obtain some rawhide and sew it around the prod, would this be able to hold the pieces of the prod together if the prod broke? would the rawhide simply break with the prod?

Your thoughts on this matter are greatly appreciated.

gone

The question was: should I build my bow with a steel-cable bowstring? Short answer-No.
Steel strings are very heavy relative to their weight... they consume a lot of the power that would otherwise go into the projectile. Also, steel cables stretch. If you must have a strong, low-wear bowstring and you have kevlar available, just use Kevlar for your bowstring. It is much stronger, more flexible, and will in every way make a superior bowstring.
To clarify... I don't personally make Kevlar bowstrings, because the material has essentially no stretch. Kevlar strings have a reputation of being particularly hard on composite bows, not to mention the aluminum alloy I use for my entry-level bows, but for a steel bow, Kevlar should work great. So I say ditch the steel cable, go with Kevlar. You'll never look back. Geezer.

Are we answering the same question Geezer? All due respect etc etc.

Just confused as to our replies - agree with you answer thou...

Uhhh, I was answering a question about steel bowstrings, but I think the 'danger' of steel bowstaves is much over-stated, assuming you get a decent spring to begin with... without cracks or holes. Medieval steel bows often fastened a length of rawhide or other leather along the 'back' surface of the prod in case of breaking. Others covered the whole prod with thin leather and then decorated it to taste. Either of these should help reduce the danger of a broken prod, in the unlikely event something should go wrong.
Geezer.

I just read some where here that some lads in northern Europe
tested 3 mm belt leather as a backing for steel prod. They pulled the heavy prod till it broke, around 2,000 lbs. The belt leather held the limbs in place. They mentioned the belt leather was looped over tips of prod and held in place with bow string. I think they also tied strong thread around prod and leather belt in intervals along it's length. I would guess that contact cement between steel prod and leather would also help. Dynema or Fast Flite makes very good cross bow string. I have 60 strands of Dynema on my 600 lb steel prod bow made with flemish loops on either end. cheers fiddler49

I would be cautious about using an old car spring because if it has seen a lot of service it may be fatigued, cracked or be pitted with corrosion which will weaken it. I new one might be a safer bet. Admittedly, lots of eople use old springs and get away with it but theres no point having a strong crossbow if you are afraid to shoot it!

Many car springs have a hole in the middle which probably is the weak spot. If you can find one that doesnt have a hole it might be safer.



Fred

Knowing admittedly little about steel bows what Fred stated seems to have a flip side to me. It would seem that a piece of spring that had seen use but not overuse would be proven and somewhat better than a piece of untested steel. It would seem to me that as long as there are no defects in the material you would have have a bow that had already been preconditioned to its use as a spring. Is this thinking wrong?

I think back to my hotrod days talking to engine builder/blue printers who used to swear that an older block, properly remachined, was preferable to a new block since it was already proven and conditioned by use.

There may be some truth in what you say. If you trust the spring, its probably OK. If it is an old car spring with an unknown history, you take your chances.

When I was "a little younger" in my twenties, I had a lot of street rods. One of the first modifications was to go to the suspension. I have seen a lot of spring work done and know you can re-work a spring and have the "temper" put back after "re-aching". But I would think for use in crossbows, I 'd stay away from having a hole in the middle, you are just asking... "break here". besides, you see all most every one at these 'crossbow fairs' have leather on them.
What I would really like to see is "some one put rolled ends" on to a leaf spring!

Again I sort of disagree. I used to tie all my prods on but now I anchor them all with a bolt or two...right through the prod's center. If you bolt the prod down in the center hole it won't be bending there anyway. If you have a hole in the center of a tied prod...yes, it will probably flex there and fail.

Look at any commercial crossbow or take down bow...holes right in the thickest section of limb. I have never had a center hole do so much as a hairline crack.

The question is: Are center-holes in steel prods dangerous?
I have a steel bow with a hole through the middle (small though it is) that seems to function fine, but a hole through the center is an obvious weak point. When I first started making crossbows for sale, I bought ready-made aluminum-alloy prods with a hole in the middle (they were 'Jayhawk' kits, made in Afton Oklahoma. The kits were designed to have a lag-screw mounting in the center, and I made plenty, most with the screw in place and some without. With or without a lag-screw through the middle, those aluminum prods regularly failed by cracking and eventually breaking through the middle. Eventually I started making my own aluminum prods to pretty much the same dimensions, but without the hole and the prod-failures ceased. Given enough shots, they still went soft and bent, but the incidence of actual breaking went to... I dunno, no more than could be counted on one hand... I've still got one somewhere around the shop, still with it's thin-leather cover holding on.
Since I started using solid Alchem and Darkwood steel prods, I've had no prod-breaks and very few bending failures. (a handful out of LOTS of crossbows... hundreds.) From experience I would say drilling a hole through the middle of your prod weakens it at that point, and Should it Fail, it will probably do so there. Then again if your prod is fastened in securely, a break right in the center is probably much safer than a break at an end, or halfway out the limb. A leather sicher-strap down the back of stronger prods seems a wise precaution.
So yeah, in my vast experience (seriously, a couple of thousand crossbows made over 30 years) a hole through the center of your prod makes it weaker than without... a no brainer, huh? I have no doubt metal prods could be designed so that the hole was unimportant... if it's thick/stiff enough it won't bend through the middle anyway, but I'ver never seen one that couldn't bend.

Just my 2 cents. Geezer.

Obviously composite prods are different in this regard. I stand corrected. I always assume the physics will be the same but I suppose a single, fiberless material is going to behave differently. The place my bows are most likely to break is where they bend the most. I would assume that it would be the same for steel. Is it possible that the center hole failures were not properly backed or secured to the tiller? Also if a string broke I could see this destroying the bow from the center hole.

In the case of the broken prods, how were they fastened through the hole? Did the bolt clamp the bridle down into the bow or were the fastening devices beneath the bridle?

How were the prods fastened down? I put a big washer over the center-hole (as recommended by the manufacturer) then I screwed the prod down with a 5/16 in. lag-screw about 3 inches long. Over that, I fitted a 3/4 in thick by 4 inch wide bridle (binding) block, (recessed in the center to accomodate the bolt) and lashed the prod down with flax cord, much as I would do an un-bolted prod. This was in the early days, so I probably didn't get the cord as tight as I do nowadays. When the binding was tight and complete, I painted the bridle-cord with hide-glue to help immobilize it. Prods broke anyhow (after several years of shooting) when they broke, they actually pulled the lag-bolt out of the stock. On the positive side, there was no separation of prod-ends, they didn't go flying and nobody was hurt, but as the guy who made them, I was surprised. After it happened several times over the years, I got used to it. Solution: I replaced the customer's prods with new, un-drilled prods and lashed 'em down in the usual way.
My assumption is, the prods were still flexing slightly in the center, and the hole was the weakest point. After a few years of shooting, the binding-cord probably loosened up a bit, leaving the center-bolt to do most of the work. In retrospect, I wonder how many Jayhawk kit crossbows broke through the center? Not many, I think, since Jayhawk provided a steel string with swaged loops on the ends. After a hundred or so shots, the string would stretch enough to fly off at every shot. The ends of the prod were slotted, with sharp edges, so if you tried to make a fiber-string, it would cut in no time. Result... probably most people who made a Jayhawk kit gave up trying after a few weeks and the bows ended up in a garage-sale to snag some new sucker. Still the aluminum-alloy prods were what put me in business. When the old couple who owned the company retired, I bought some aluminum and started making my own. If anybody's interested, the alloy is 7075-T6. I use 190 thousandths of an inch... that's 3/16 in. And yes, the metal eventually fatigues and fails, but they're great little prods while they work. Geezer.

I know you have the experience with this geezer but I can't help thinking that if they were bolted over the bridle that the flex would not have been an issue and failures may not have been an issue. I could see hiding the bolt head beneath the binding and keeping the look intact.

Just a thought. I have a bridle epoxied to the belly of my prods and after 8 crossbows and a few phenomenal bow failures in the learning process I have never seen one center hole have the slightest problem. Fastening beneath the bridle could give a false sense of security and I could see the bridle coming loose enough to put all the forward momentum on that one washer.

Just my thoughts.

Like you say, I have a lot of experience at this. These days, would never install a prod with a hole through the middle. It's asking for trouble. When it's your own bow, that's one thing. When it's somebody else's... well that's a different kettle of fish. No center-holes, no center bolts for me. Make mine solid!
Geezer

Well one thing I really like about the way I fasten prods is they never come loose. Ever. I use leather as a gasket behind the prod and epoxy the bridle right to the bow belly. I will be selling all my bows fastened this way. For the composite prods it works like a charm. A laminated prod rattling around I'm loose bindings is doomed. Also I don't have to be period so it works for me.

Ahh yes, a prod that stays in place is a thing of beauty. Unfortunately, I find it necessary all to often to work on customer bows. It's a major reason I don't rivet parts in place, as was commonly done in period. Rivets would be easier and cheaper, but they're deucedly hard to remove when you want to do maintenance. Since I was dumb enough to offer long-term guarantee on most of my stuff, I find it convenient to be able to get inside and tinker with stuff. So I'm stuck with modern screws for the parts I need to maintain, but what can be done in period style, I'd rather do that way.
Everything involves compromise. It's the way of the world. Geezer.

olrono wrote:When I was "a little younger" in my twenties, I had a lot of street rods. One of the first modifications was to go to the suspension. I have seen a lot of spring work done and know you can re-work a spring and have the "temper" put back after "re-aching". But I would think for use in crossbows, I 'd stay away from having a hole in the middle, you are just asking... "break here". besides, you see all most every one at these 'crossbow fairs' have leather on them.
What I would really like to see is "some one put rolled ends" on to a leaf spring!

Rolled ends is exactly what i plan on making on my next leaf-spring prod!
Still finnishing up the metalwork on the tiller for now but the prod is up next!
I will post pictures of my attempts and succes or failure