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    Straight grain walnut suitability

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    Moon
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    Straight grain walnut suitability

    Post by Moon on Mon Sep 13, 2010 3:15 pm

    I would appreciate feedback from those that have used walnut for medieval crossbows. I want to use walnut but I suspect it may not be tough enough for the prod end. Thank you in advance for your thoughts and advice.
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    Re: Straight grain walnut suitability

    Post by Todd the archer on Mon Sep 13, 2010 3:33 pm

    Hi Moon, still trying to get mine together (can't seem to find time with family and work). While I am no expert, I think any straight grain wood would work. Consider that almost all the load is in compression and how short from prod to nut. You are familiar with traditional bows look at riser of a longbow and the leverage the limbs put on it. Hope this helps.

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    Geezer
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    walnut?

    Post by Geezer on Mon Sep 13, 2010 3:48 pm

    Yes, walnut will do just fine. Geezer
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    walnut?

    Post by Geezer on Tue Sep 14, 2010 7:28 am

    Geezer here, adding a bit to my very brief response above. You want the grain in your stock to run more or less from top to bottom, rather than side to side. A 45 degree angle is okay, but straight across may result in cracking along the grain. If you work it right, walnut will do fine.
    Having restated my previous comment, I will continue. Very strong medieval bows ran an iron rivet from top to bottom, a couple of inches behind the prod-socket (sometimes it's two pins, side by side, more commonly one). I do something similar with bow-iron mounted prods, since it's possible to drive the wedges in really tight, resulting in high stress over the narrow area at the front of the keyway (slot that the wedges and keepers fit into) In that case, I insert a 5/16 in. lag-bolt, from bottom, to within about 3/8 inch of the top. (not quite to the bolt-groove) I've never had a socket split on any bow that was reinforced with a lag-bolt. So if you're worried about resilience/strength of a walnut stock, just figure to put in a lag-bolt. You probably won't need it, but what the heck, better safe than sorry on a project you're spending a lot of time on. Geezer.
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    Thanks

    Post by Moon on Tue Sep 14, 2010 8:25 am

    I'm thinking about epoxying a nut in under the Delrin (or other material) arrow groove insert and using a machine thread bolt from the bottom with it's socket head (with a flat washer) seated deep enough to put a wooden plug over it so the bolt is not visible.

    I will be using a fairly straight grain walnut for my first one. I'll try to explain to the supplier the grain direction I'm looking for. I'm thinking that by using a rifle stock blank turned backwards I'll have all the material I need for the medieval Max design. Your thoughts? Thanks again.

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    Thanks-Moon

    Post by Geezer on Tue Sep 14, 2010 8:45 am

    Putting a nut under the arrow groove and epoxying it in place shouldn't do any harm, and tightening the bolt up enough to get some compression on the assembly might strengthen things a fair bit. A walnut rifle-stock blank oughta do very nicely. That'll put the tall butt-section at the head, where you'll want to mount your prod, and leave plenty of mass around the lock as well. I say go for it. Geezer.

    ps. This is just a crossbow, not a rocket to the stars. Try not to worry too much about minor details, and remember, errors simply lead to ingenious saves, covered by beautiful decorations that you can claim were intentional in the first place. :-)#
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    Moon
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    Post by Moon on Tue Sep 14, 2010 9:42 am

    My problem is that this hunting medieval will be void of decorations so covering things up will be tough Wink

    I'm a little concerned hearing about Alchem not responding to calls and emails. I'm going to need 2 175 lb prods, bow irons, wedges, etc. We shall see how it pans out. Thanks
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    Re: Straight grain walnut suitability

    Post by basileus on Thu Sep 16, 2010 12:12 am

    Moon wrote:I'm going to need 2 175 lb prods, bow irons, wedges, etc. We shall see how it pans out. Thanks
    Responding in case you don't get prods et al from Alchem or somewhere else. Or if you feel like "doing it yourself" Smile... Anyways, making bow irons is pretty simple, even with very simple tools (hacksaw, file, vise, hammer):

    • http://users.utu.fi/sjsepp/paja/making_bow_irons/making_bow_irons.html

    You can also design and make a prod from a leaf spring relatively easily, if you got an angle grinder:

    • http://users.utu.fi/sjsepp/paja/designing_crossbows/designing_crossbows.html
    • http://users.utu.fi/sjsepp/paja/making_a_steel_prod/making_a_pyramid_profile_steel_prod.html

    I've used my own bow irons and bows with great success on three different crossbows. The benefit with making your own is that you don't have to be content with what's available commercially. I'd estimate that making a set of bow irons takes 4-8 hours and making the prod about the same.

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    Post by Moon on Thu Sep 16, 2010 6:49 am

    but I have too many "irons in the fire" already Very Happy
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    Re: Straight grain walnut suitability

    Post by basileus on Mon Sep 20, 2010 8:01 am

    Geezer wrote:Very strong medieval bows ran an iron rivet from top to bottom, a couple of inches behind the prod-socket (sometimes it's two pins, side by side, more commonly one). I do something similar with bow-iron mounted prods, since it's possible to drive the wedges in really tight, resulting in high stress over the narrow area at the front of the keyway (slot that the wedges and keepers fit into) In that case, I insert a 5/16 in. lag-bolt, from bottom, to within about 3/8 inch of the top. (not quite to the bolt-groove) I've never had a socket split on any bow that was reinforced with a lag-bolt. So if you're worried about resilience/strength of a walnut stock, just figure to put in a lag-bolt. You probably won't need it, but what the heck, better safe than sorry on a project you're spending a lot of time on. Geezer.

    I don't think the wood type itself matters much with relatively low-powered crossbows (e.g. ~150 pounds at ~32cm / 13" draw). If you use a very light wood, e.g. most conifers such as pine or fir (SG of ~0.4 - 0.5), then make sure there's plenty of wood between prod and the bow iron wedge slot or the bridle hole. Alternatively you could just make the stock a little wider. I don't think any species of walnut can be considered an especially weak wood, so you should be fine. I've sometimes reinforced the front part of the stock with vertical screws, bolts or round wooden dovels like Geezer, but I don't think that's necessary in most cases.

    For example, I've had no issues with my ~300 pounder (@25cm / 10" draw) although there's only 5cm (2") of wood (birch) between the wedge slot and the prod and there are no reinforcements. That crossbow has experienced 10+ accidental dry-fires and has been dismantled ~7 times, so it has really been tested. The angle between the slot and the grain probably makes a difference, though; the slot in that crossbow is canted slightly, so the wedges can't as easily push the two halves of the stock apart and split it. If the grain and the slot are perfectly parallel, then using reinforcements probably makes sense.
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    Post by Moon on Mon Sep 20, 2010 1:16 pm

    What do you do with a 300 lb draw crossbow? :-) I'll probably ultimately settle on 180 lbs but even the 160 that I have now will be sufficient for close range deer hunting.
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    Re: Straight grain walnut suitability

    Post by basileus on Tue Sep 21, 2010 3:20 am

    Moon wrote:What do you do with a 300 lb draw crossbow? :-) I'll probably ultimately settle on 180 lbs but even the 160 that I have now will be sufficient for close range deer hunting.

    Well, I shoot with it Smile. That said, I'm way more interested in making crossbows (and other historic projectile weapons) than shooting them. I guess this is analogous to why some people tune their cars endlessly, rather than just use them to get from A to B every day. Also, 300 pounds is not that much: maximum power output (in joules / foot-pounds) is only 50% more than that of my ~150 pound crossbow, the reason being 300 pounder's noticeably shorter draw length. Full stats are available here, if you're interested.

    Even the heavy medieval crossbows with ridicuously high draw weights (1500 pounds and so) were not that powerful, as their draw length (and thus energy storage) was severely limited.
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    What was the most used prod/limb material

    Post by Moon on Tue Sep 21, 2010 8:53 am

    for those monsters?

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    Re: Straight grain walnut suitability

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