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    Beechwood Prods

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    GodricSwin
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    Beechwood Prods

    Post by GodricSwin on Sat Feb 28, 2015 6:22 am

    Hi Friends,
    I'm new here . . . and want to get started on a medieval-style crossbow.  I've done a lot of reading and looking at pictures and have learned a lot - but certainly know it's only a small bit of what I need!
    I will continue with the researching but want to begin making a prod.  I was in the local hardware store looking for wood for the stock when I found a piece of very straight grained quarter-sawn beech.  I Googled beech and generally am lead to believe that it's not the best for a prod but several bowyers commented that it works well (for bows).

    I would appreciate very much any suggestions:
    1. general dimensions (I'm hoping for a strong crossbow - limited only by the use of a wippe)?
    2. would it be best with a flatter belly or more rounded?
    3. should I put a small recurve towards the tips? and can this be done after the prod is carved?
    4. where the handle would be (on a regular bow) should I do anything special or just continue with a (gentle) curve?

    Help with these questions will get me started . . . I hope!
    I thank you in advance for help with this.

    Incidentally, this is a great site!
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    Re: Beechwood Prods

    Post by Anatine Duo on Sat Feb 28, 2015 1:02 pm

    Quarter sawn?  The grain in classic quarter-sawn will not be optimal for a prod (at least what I have pictured in mind but the piece you have might be from the right part of the tree) 

    Normally you want the bow to have as flat grain as possible, with the outer growth ring forming the back.
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    Re: Beechwood Prods

    Post by mac on Sat Feb 28, 2015 1:14 pm

    Godric,

    I recommend limiting the number of technological problems you tackle in a project; especially if its your fists crossbow. 

    Beach is not counted among the first-rate bow woods, so trying to make a bow on it at all might be a bit much for a first go. Trying to make a powerful bow on it sounds like a recipe for failure. 

    Stick with your original idea of using the beach for the tiller.  It will work OK there and look nice as well. 

    For the bow its self, you can do a lot worse than to start with a commercially available prod.  There will still be plenty of pitfalls and stumbling blocks ahead of you without having to make the prod.  If you feel that you must make everything yourself, you should hedge your bets and start with a  can't-fail wood like hickory.

    The other thing you need to know about using wood for a powerful prod is that it will have to be deflexed.  The ends may be recurved if you like, but overall, it must already be curved in the direction it will be when drawn.  

    I recommend a rectangular cross section.  The "D" section that the longbow guys use will lead you to grief in a crossbow.

    I like to see the middle of the prod just a bit thicker so that it does not flex much.  This will keep your bindings from working loose as quickly.

    If you "tiller" the prod so that it bends nicely, you can then steam bend the whole thing into its final shape, and it will still bend nicely.  I use a two piece form made out of plywood to do this. 

    Mac
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    Re: Beechwood Prods

    Post by kenh on Sat Feb 28, 2015 9:03 pm

    Godric -- from your initial post points 3 and 4, it's apparent that you have never made a "self bow" for conventional archery.  For one things, you don't "carve" recurves into a bow, you steam or otherwise bend them.

    That being said, I would not suggest you try making a wooden crossbow prod until you've successfully made at least half a dozen full-size bows.  The problems inherent in trying to make a short (30-36") all wood bow are magnified several times from those of trying to make a 5 ft or 6 ft bow.

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    Re: Beechwood Prods

    Post by GodricSwin on Mon Mar 02, 2015 9:44 am

    Hi again,
    Guys, I appreciate the feedback.  Having said that, you all will probably think I’m nuts but I want to go ahead with the crossbow prod and by that I mean to make it myself.  Yes, I could buy a prod, or for that matter a completed crossbow but there wouldn’t be much challenge or satisfaction in that – except to my bank account.  I want the experience of doing the work myself.  I’m semi-retired and usually have too much time on my hands as it is.  I suppose failure with a prod(s) is very likely but I’m stubborn enough to keep trying.  (I’ll set a limit, however, and if no success after X number of failures I’ll buy the thing!)   Another “challenge” is that I now live in Central Europe where various supplies are more difficult to come by.  For example, no hickory - with which I am acquainted and liked using – a great wood to work. I used it, besides other things, for handles for high-end croquet mallets (laminated, and turned on a lathe).  There is ash and yew here but I’ve yet to find them.  Another “challenge” is that at the moment I’m limited to dried stock from a lumber yard (I hope to get some fresh ash, but later in the year).  I will certainly continue the search . . .
     
    Questions:
    1. I don’t see polyurethane glue mentioned in reference to bow making – has anyone tried it?  I’m wondering about its ability to ”move” (flex).
    2. Mac, you said that deflex should be built in.  I realize there are many more factors involved here but can you give me a kind of “rule of thumb” as to how much, maybe your best guess?  I’m thinking of the prod’s flat length at about 32” tip to tip; I’ll begin with a blank of about 1 1/4” width, and 7/16” thickness – hopefully that will give me enough wood to begin working. (Obviously, I won’t know finished width and thickness until I have started cutting and tillering.)
    3.  I will stick to your recommendations for a rectangular cross section, and thicker middle.
     
    Thanking you all for your help.

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    Re: Beechwood Prods

    Post by Hermit on Mon Mar 02, 2015 10:30 am

    I am by no means an expert on wood bow construction,there are others on here far more experienced than I,but I would think that if you want a crossbow,as opposed to a child's toy the raw bow stave would need to be both thicker and wider than the dimensions you quoted.
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    Re: Beechwood Prods

    Post by mac on Mon Mar 02, 2015 12:59 pm

    Godric,

    I wish I could offer some rules for you, but I really haven't got enough information.

    I can show you what I have done that has worked.  Here is a hickory bow that draws about 150lb.  It is unstrung in the pics, and the bastard string is under no tension.



    The deflex is about 80 or 85mm



    The thickness...


    The width....


    And here is a pic of something that did not work.  I tried to make something a bit more powerful out of yew.  On the tiller board it was drawing something more than my body weight.... probably a bit over 200lb.  I set the project aside, un-assembled for a couple of years, and when I finally got back to it... there was a disastrous incident.  I don't know if the wood dried out in the intervening years, or whether I made a fatal error in measurement.  I did not make any notes about the tillering, but I may not have allowed for the diameter of the nut when I figured the draw length.  In any case, I drew the bow up to the nut, and it started getting pretty stiff.  I gave it one more heave, and it blew up, right there between my knees.



    My camera batteries ran out.  I will get the pics of the prod thickness and width later.

    Mac

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    Re: Beechwood Prods

    Post by GodricSwin on Mon Mar 02, 2015 3:13 pm

    Mac & Hermit
    Thanks!  That was what I need!  If you two hadn't replied I would have begun tomorrow with a stave way too small.  I found an article on bow (prods) design on Wiki that is seemingly very good (at least in the reading) but what I really needed was some example of basic dimensions which you've supplied.  I know I'm starting too soon but I can't wait to get my hands working.

    Mac, what's the length of that bow (the one that's not broken!!)?
    Thanks, again
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    Re: Beechwood Prods

    Post by mac on Mon Mar 02, 2015 5:24 pm

    The distance from working nock to working nock is about 35inches (885mm).  

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    Re: Beechwood Prods

    Post by GodricSwin on Wed Mar 04, 2015 4:59 am

    Mac,
    Thanks!
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    Re: Beechwood Prods

    Post by kenh on Wed Mar 04, 2015 7:26 am

    Mac -- Just to be  clear on something, because Godric was talking about "carving" recurves and such.

    On the rectangular prod that worked... did you steam that deflex in to a 'thin-wide' board and then tiller away the excess wood?  Or did you 'carve' the deflex into a 3" deep  block. 

    From the look of things you steamed a nominal 1x2 and gave it the 3" of deflex, then tillered that down to the dimensions and taper shown.

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    Re: Beechwood Prods

    Post by GodricSwin on Wed Mar 04, 2015 8:49 am

    Kenh,
    Forget about my use of "carve" - it was just a poor choice of words; I'm not only learning about crossbows, but needing also to learn the correct vocabulary as well.
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    Re: Beechwood Prods

    Post by kenh on Wed Mar 04, 2015 8:54 am

    OK Godric.  I understand.  I spent my working career as a science and technical writer, and getting the right jargon and vocabulary right for each of the myriad subjects I wrote about, was always a big deal...
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    Re: Beechwood Prods

    Post by mac on Thu Mar 05, 2015 8:56 am

    kenh wrote:Mac -- Just to be  clear on something, because Godric was talking about "carving" recurves and such.

    On the rectangular prod that worked... did you steam that deflex in to a 'thin-wide' board and then tiller away the excess wood?  Or did you 'carve' the deflex into a 3" deep  block. 

    From the look of things you steamed a nominal 1x2 and gave it the 3" of deflex, then tillered that down to the dimensions and taper shown.
    I did all the tillering on a normal flat stave, and then steamed it into shape.   It's easier to see if every part is flexing the right amount if your starting point is flat.  Giving it a permanent bend afterwards does not change anything about the bow as a "spring".

    If I were going to put significant recurves in the tips, I think I would do it differently.  I would get the back down to a single growth ring and cut the profile to about what I think is a good starting point, but with some extra material on the belly side of the recurves.  I would then bring the bellies of the recurves to a single growth ring.  This would make them less likely to fail when steaming in the recurves.  After the entire bow was steamed to shape, I would finish the tillering and remove that extra wood I left on the bellies of the recurves.   That may be fussier than it needs to be, but it's certainly a safe way to do it.

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    Re: Beechwood Prods

    Post by mac on Sat Mar 07, 2015 10:47 pm

    I have posted scans of an article about a wooden crossbow prod in this thread. http://thearbalistguild.forumotion.com/t1363-the-berkhamstead-bow-fragment#12881

    Mac

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    Re: Beechwood Prods

    Post by GodricSwin on Sun Mar 08, 2015 3:44 am

    Mac,
    A lot of good stuff in there, especially for a newbie. Thanks!
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    Re: Beechwood Prods

    Post by mac on Sun Mar 08, 2015 11:21 am

    There's some good stuff in there, but don't believe every word they say.......

    Mac
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    Re: Beechwood Prods

    Post by mac on Sun Mar 08, 2015 11:26 am

    Here is another wooden crossbow prod.  Unfortunately, I can't remember where I found this. (my only other clue is that the name of this JPG is "page 65") The author of this catalog believes it is a handbow, but that seems pretty unlikely. The overall length of 89cm gives it away.

    The bow appears to have a full-blown "smiley" profile, but its not clear how much of that is an artifact of the camera angle.

    Mac


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