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    Steel Bows...breakage?

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    Post by Scott on Fri Jan 07, 2011 3:15 pm

    I have read a couple of times about a historical preference for composite bows over steel bows due to the steel ones sometimes breaking. Has anyone ever had a steel bow break on them?
    Best wishes Scott
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    Post by Vintageairguns on Sat Jan 08, 2011 8:28 am

    Hi Scott,
    I haven't had that yet!
    But apparently they did break, and as you can imagine could give a really nasty injury, that why you sometimes see on the very old Crossbows a thin platted cord running the entire length of the bow, off this cord a number of loops were attached, these went around the bow itself.
    The idea being if it did break the cord would arrest the broken steel part before it smacked you in the face.

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    Post by Geezer on Sun Jan 09, 2011 9:52 am

    Geezer here re: breaking prods.
    There's a rather famous quote... out of 15th century I believe, about Swiss and Swedes, and other folk out of cold climates who preferred horn-sinew composites rather than steel bows due to increased resistance to breaking in very cold weather. As I recall, it's quoted in Harmuth, and maybe Paterson's book as well. Whatever the case, all bows, including steel are subject to breaking under adverse circumstances. I suspect Horn/sinew composites, like some fiberglass prods, break with a crunch rather than with a sudden bang. As 'Vintage' noted above, many extant medieval/renaissance steel bows feature a 'sicher' strap running down the 'back' of the prod. The strap should prevent a catastrophic prod-failure from breaking your arm or perhaps your face. (being the likeliest things to get hit, since your prod is usually at greatest stress just as you set the lock.)
    As far as prod-weight and speed are concerned, steel bows are heavier and consume more of their spring-energy just moving themselves. So yes, they're less efficient than composite or even yew prods. What they sacrifice in efficiency, they make up in long-term reliability and ruggedness. Those beautiful Elkridge prods will definitely put more of their energy into your bolt, but they will be a bit more delicate... Don't just throw them in the trunk of your car... get or make a nice padded cover for your laminated prod and make sure to use it. Taking the string off your prod when the bow isn't in use would be a good idea.
    Keep shooting and having fun! Geezer.
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    Post by Scott on Sun Jan 09, 2011 5:40 pm

    Thanks Geezer,really interesting post. I really enjoy shooting the steel bow, but do worry a bit about something going wrong! With my bows I was suprised in a way at their quite low power approx 12ft/lb for the 90lb draw weight and 19ft/lb for the 200lb . Through reading Payne-Gallwey, Blackmore and others what sort of power were steel battle bows putting out in the 15th C? Many seem to be of fairly low draw weight to be drawn with a belt and hook or goats foot.
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    Post by Scott on Sun Jan 09, 2011 5:49 pm

    Peter, do you shoot any of your antique crossbows?
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    Post by Geezer on Sun Jan 09, 2011 7:24 pm

    Scott: Concerning Steel bows. Egon Harmuth suggests the limit for bows drawn with a belt-hook is about 150 kg for a one-foot stirrup, and maybe 200 kg for a double-wide stirrup and belt and pulley. A properly proportioned gafa might draw a bit more.. maybe 250 kg.
    Most of period steel prods I have seen have been about 30 inches long, with @ 4 inches of brace and 5 to 7 inches of power stroke. So how do they get big draws? Generally speaking with metal prods, the power is proportional to the cube of the thickness.
    For example: My 3/16 in thick aluminum-alloy prods deliver about 70 lb. at 7.5 inches power-stroke from a 3.5 inch brace (11 inches from belly to lock). A 1/4 inch thick prod of the same dimentions will draw approximately double that. (1 and 3/4 inch wide at center, 3/4 inch wide at the ends, 28.8 inches long before bending in the recurved ends.
    Typical medieval prods are 1/2 to 3/4 inch thick. Even the little Padre-Island prod is 1 inch wide, 3/8 in thick, and approx. 22 inches long, tapering to perhaps 1/2 in. wide at the ends.
    Battle bows of the 15th century generally used either the windlass or cranequin. Ralph Payne-Gallwey had a big field bow (Flemish) that drew 1200 lb. at 7 inches of power-stroke. He shot 1/4 lb. bolts 450 yards with that baby. It DID weigh in at about 15 lb. and would be right at the limit of what an archer might carry in the field. Geezer.
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    Post by mac on Sun Jan 09, 2011 9:27 pm

    A crossbow lathe is really nothing more than a funny shaped leaf spring. Do automotive springs fail more often in cold weather? I have never heard of such a thing, but perhaps it is true. Have any of you ever heard of such a thing?

    I suspect that if there really is (was) a problem with steel bows and
    cold weather it is about retained austinite transforming into untempered
    martinsite under cold conditions. This would cause the bow to become more brittle. Some additional untempered martinsite could form every time the bow experienced lower temperatures than it had ever seen before. This new brittleness could manifest its self in an increased likelihood of failure at any time after the excursion into low temperatures. This might be while the bow was being used on a cold day. On the other hand, a bow which had been exposed to extreme cold during "the off season" might fail in warmer weather.

    If this mechanism *is* the cause of cold weather bow failure, the solution might
    be to follow the usual quench and temper with a cryogenic quench and
    another round of tempering. If this is the middle ages, and a cryogenic quench is unavailable, perhaps a prophylactic re-tempering would be in order after the bow's first cold winter. Unless I am mistaken, that should take care of the problem.

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    Post by Vintageairguns on Mon Jan 10, 2011 7:06 am

    Scott wrote:Peter, do you shoot any of your antique crossbows?

    Hi Scott,
    In answer to your question not all!
    I have shot the Victorian Garden bolt Crossbow as that is a very robust beast so I don't have a problem with it as far as metal fatigue is concerned.
    As and when I manage to get some decent strings sorted out I might give the better condition bullet or a stone bow a try.
    The very early hunting one I don't think I would risk it!

    In regard to bow steel.
    Sometime back I bought a rough bullet CB somehow the steel bow itself had got bent up? How, whoever managed that remains a mystery?
    I like to see Crossbows in reasonable condition so I thought I would get the warp? Taken out.

    As I don't have the equipment to heat it up I left it with a friend of mine at the local garage.
    A couple of days later went back to pick it up, my friend stated that he has dealt with assorts of steel for years but in all that time he has never come across anything like the bow steel.
    Apparently he had one hell of a job trying to get the warp out the bow, even now its not 100% but at least it doesn't look so bad.
    So its a definite wall hanger now, just makes you wonder just how they made them in the first place!





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    Post by Basilisk120 on Mon Jan 10, 2011 4:11 pm

    No haven't had a crossbow break but have had a couple of longbows break on me and that was exciting enough.

    It wouldn't supprise me that given the rather exciting nature of a steel prod breaking that a single event have a wide spread impact. If I saw a steel prod snap at full draw I would be a little wary of using one.



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    Post by Vintageairguns on Tue Jan 11, 2011 4:24 am

    Basilisk120 wrote:No haven't had a crossbow break but have had a couple of longbows break on me and that was exciting enough.

    It wouldn't supprise me that given the rather exciting nature of a steel prod breaking that a single event have a wide spread impact. If I saw a steel prod snap at full draw I would be a little wary of using one.


    Your long bow breakage reminded me of the Longbows (over one hundred i think it was) brought up from the ship wreck of Henry the Eighth Flag ship "Mary Rose"
    There was a program on the Mary Rose along with all it armament, they were allowed to run tests one of the Yew Long bows.
    Considering they had been under sea water for 300 odd years it still functioned as well as the day it was made.
    It was put in a rig which bent it and then slackened off, it lasted numerous pulls only to break after some considerable time, it was later found that a worm of some sort had bored into it?

    Here ends today useless piece of information!
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    Post by basileus on Wed Jan 12, 2011 6:06 am

    Basilisk120 wrote:No haven't had a crossbow break but have had a couple of longbows break on me and that was exciting enough.

    It wouldn't supprise me that given the rather exciting nature of a steel prod breaking that a single event have a wide spread impact. If I saw a steel prod snap at full draw I would be a little wary of using one.

    I've had a two leaf spring steel break on me. The first one broke in the middle, because I had stupidly left the leaf spring hole in the middle and did not protect it from bending (e.g. with strong bow irons). So, this stress concentration caused it to break, fortunately not in an especially spectacular fashion.

    The second breakage was caused by the combination of an overly strong linen bowstring and a accidental dry-fire. This time the bow bent noticeably inwards near one nock at a weaker point.

    Whether a spring steel bow breaks or bends depends mostly on it's tempering temperature - given that heat treating is done properly. If it's tempered in high temperature it becomes soft and springy, meaning it will first bend permanently and only after that break. This is similar to a wooden bow getting "set" during draw when wooden cells in the belly collapse, causing permanent deflexing.

    I assume most leaf springs are tempered soft enough not to shatter when overstressed. Of course, if there are any very weak points then breakage may occur. This, however, should be easy to spot during draw. Regardless, it is probably wise to test the properties of the steel in practice before making a bow out of it.
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    Post by Vintageairguns on Wed Jan 12, 2011 9:37 am

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    Post by Basilisk120 on Wed Jan 12, 2011 4:42 pm

    Vintageairguns wrote:


    Your long bow breakage reminded me of the Longbows (over one hundred i think it was) brought up from the ship wreck of Henry the Eighth Flag ship "Mary Rose"
    There was a program on the Mary Rose along with all it armament, they were allowed to run tests one of the Yew Long bows.
    Considering they had been under sea water for 300 odd years it still functioned as well as the day it was made.
    It was put in a rig which bent it and then slackened off, it lasted numerous pulls only to break after some considerable time, it was later found that a worm of some sort had bored into it?

    Here ends today useless piece of information!
    That is impressive. Steel Bows...breakage? 602584 I would have figured that the bow would have gotten brittle over the years but I guess not and that is a testiment to bowyers who are good. I'm still learning so the broken bows were to be expected. The last one was a glue failure between the hickory backing and the Ipe body. Yeah that was excinting having the bow pop out of my hand and all.

    Ok back on topic.
    basileus, glad to hear you weren't hurt when the prod failed. But you do bring up a good point that the failure mode of the prod would depend on how it was made.
    I wonder how period prod were made? I have dabbled enough in blacksmithing and metalworking history to be dangerous so I have some ideas but nothing absolute. While the mediviel blacksmith would certianly have known his trade I belive that getting good consistant steel would have been a challenge. Inconsistant steel would lead to an inconsistant temper. And if the prod had to be forge welded the welds could be points of failure if they weren't perfect.
    But, at least, construction problems like bad temper or poor welds should show up very quickly expecially with a super heavy crossbow. They don't have much room for error.



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    Post by basileus on Fri Jan 14, 2011 11:08 am


    Ok back on topic.
    basileus, glad to hear you weren't hurt when the prod failed. But you do bring up a good point that the failure mode of the prod would depend on how it was made.
    I wonder how period prod were made? I have dabbled enough in blacksmithing and metalworking history to be dangerous so I have some ideas but nothing absolute. While the mediviel blacksmith would certianly have known his trade I belive that getting good consistant steel would have been a challenge. Inconsistant steel would lead to an inconsistant temper. And if the prod had to be forge welded the welds could be points of failure if they weren't perfect.
    But, at least, construction problems like bad temper or poor welds should show up very quickly expecially with a super heavy crossbow. They don't have much room for error.
    If homogenous steel is used and hardening is performed poorly, the bow might bend when stressed over a certain point. If tempering was done poorly, the bow could break into pieces as some parts were left too hard and brittle. Also, if the forging was done unevenly, it could cause problems. I assume that thorough annealing would solve any problems caused during forging, though. Anyways, I know about one blacksmith here who hardened his steel bow and it broke - apparently due to uneven tempering or forging.

    However, at least in some period bows the back was made from steel with (relatively) high carbon content. This meant it could be hardened and tempered so that it was hard and springy. The belly, on the other hand, was made from softer steel which was not affected by heat treatment to the same extent. So, regardless of how badly hardening and tempering were done, the bow would not explode into pieces if overstressed, as the softer belly kept it together... in theory at least, not sure what would happen in practice Smile. This is what probably allowed making durable steel bows in relatively primitive conditions (e.g. village blacksmith shops) as was done here in Finland.

    Also, I doubt the forge weld joint would be the weakest part unless really badly done. Even then it probably would work just fine if near the neutral plane.
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    Post by Vidar Halvslak on Mon Jan 31, 2011 4:02 am

    Hi guys !
    In Sweden we have to have a security chord on the whole lenght of the steelprod (including the nocks) when we compeat with our historic crossbowreplicas.
    The reason is a tragic accedent where a guy in the 80`s got the broken half of a steelprod in his head and died.
    We have made several drawtests of different securitycordmaterial and our conclusion is that normal leather you make belts of is the best. A 3x30 mm thick beltleather at the whole bowlenght broke at 170 kg force with 50% streching.
    A fullscaletest with a medieval copy of a 600 pounds stellbow revialed that this works perfectly. The broken steelprod broke att a 1200 kg (aprox. 2400 pounds) drawforce at 33 cm drawlength and stayed at place and did´nt swinged around.
    Soo, before you shoot with a steelprod, ALWAYS mount a safetychord on the back. Preferable beltleather. And bend it over the nocks so that the string "locks" it. See the lower picture at http://armborst.forum24.se/armborst-about47.html . Use Google translate Razz
    The 50 % stretching makes beltleather more suitable than rawhide or rawleather with only 10 % stretching. And easy to purchase.
    The Germans use often stainless steelwire.
    It´s strong but not medieval, so we chose leather instead.


    Last edited by Vidar Halvslak on Wed Feb 02, 2011 2:12 am; edited 2 times in total
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    Post by mac on Mon Jan 31, 2011 8:44 am

    Vidar,

    Thank you for this information. I have a couple of questions for you, if you please.

    ----When you say that you use 3mm belt leather, do you mean a narrow strap of leather, or do you cover the entire back of the bow?

    ----Do you have any more information on the bow that failed tragically? Was there any obvious flaw in the bow? Was it nicked or damaged? Was it badly designed or "tillered". Did it give way without warning, or did the guy continue to use it in spite of a developing crack?

    ----How did you induce failure in your 1200kg bow test?

    ----Has anyone tested the silk safety cords of the sort that were used on old bows?

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    Post by Pavise on Mon Jan 31, 2011 7:05 pm

    Maybe some of you will find the following link useful.
    http://www.spring-makers-resource.net/Flat-Springs.html
    And for those of us in North America: Leather thickness is measured by the ounce, with one ounce being one sixty fourth of an inch. You do the math. And vegetable tanned leather will stretch when wet and chrome (chemical) tanned leather will stretch less. So I would suggest that any leather used as a covering or safety restraint on a steel prod be suitably protected against the elements.
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    Post by Vidar Halvslak on Wed Feb 02, 2011 2:55 am

    mac wrote:Vidar,

    Thank you for this information. I have a couple of questions for you, if you please.

    ----When you say that you use 3mm belt leather, do you mean a narrow strap of leather, or do you cover the entire back of the bow?

    - A 30 mm x 3 mm belt leather along the whole back of the steelprod. Even the nocks. http://armborst.forum24.se/armborst-about47.html

    ----Do you have any more information on the bow that failed tragically? Was there any obvious flaw in the bow? Was it nicked or damaged? Was it badly designed or "tillered". Did it give way without warning, or did the guy continue to use it in spite of a developing crack?

    - It was a steelspring from an old truck pale . Full of microscopic cracks and broke at the first tension, swinging around and instantly killed the guy aiming Crying or Very sad
    We x-ray all our steelbows before use.

    ----How did you induce failure in your 1200kg bow test?

    - The 1200 pounds (approx 600 kg)steelbow was streched in a rigged "safetybox" far beyond it´s limits. 43 cm instead of 16 cm drawlenght . It broke with a bang but did´nt swing around due to the safety beltcord----

    Has anyone tested the silk safety cords of the sort that were used on old bows?

    - Not what i know. I know that Mr Jens Sensfelder (jens.sensfelder@googlemail.com) in Germany makes and sells good historicly correct steelbows is thinking of testing silk safety chord. I´ll let you know if he does. It will probably be published in the exelent yearly "medievalcrossbowmagasine" "Die Jahrblatt".
    //Vidar

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