Primitive Archer
Main Discussion Area => Bows => Topic started by: stuckinthemud on March 16, 2019, 04:57:51 am
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Hi guys,
This is a yew and sinew bow for a crossbow, still in the early stages of tillering, not got to brace yet, I know, I know but bare with me ;D . The bow is 29" ntn and will need to draw to 11", so it should fall well inside the double draw length plus 10% rule. I am looking to use heavy hunting-weight bolts with bodkin heads. The tiller looks to me to be a bit thick on the right fade - the bow will be slightly stiff at the centre so as not to throw off the lashings - but the bow also looks like it is a good arc of circle so I do not know if I should remove much more material here. I am thinking I should be looking to tiller for an ellipse rather than an arc ? I would be very grateful for your opinions.
Thanks,
Andrew
(https://stuckinthemudsite.files.wordpress.com/2019/03/20190316_110129-1-e1552734554396.jpg)
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It'll flex in the middle regardless, the bindings will be fine especially if you put a bit of leather underneath 'em for the m to bite into.
It's so hard to judge tiller on such a short bow, I'd go arc of a circle, but would suggest doing a temporary lashing so that you can get it off and re-tiller if necessary once it's had some shots through it.
Del
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I agree with Del
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I reduced the centre a little, now drawing to brace height at 4.5 inches, any thoughts?
(https://stuckinthemudsite.files.wordpress.com/2019/03/20190324_210753.jpg)
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Looks good.
Maybe go over it measuring thickness every couple of inches checking for even taper, slide the verniers along feeling for thick spots/discontinuities.
Brace it and gently ease it back looking for any sign of uneven tiller.
It's hard to see on V short bows, so measuring may help.
Make haste slowly!
Tips can maybe be slimmer?
Del
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Thanks Del, I'll do as you suggest. I've been leaving the tips alone until the lath was at brace but once I've made up a string I will slim them down to fit it. Was thinking of 50 loops of 18/3 linen.
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Right, so, now I am in a quandry. I have the thing tillered out to 6 inches of tip movement, which is full draw, but still on the long string. Draw weight I have only been able to test to 3" of STRING movement and it is 60lb - so over 100lb to brace it and north of 200lb at f/d. This is WAY over my target draw weight of 150lb. Would you guys de-power it or call it done and learn to love a hugely overpowered crossbow?
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Like most probs it's a compromise.
Have you actually braced it?
If not, all bets are off, 'cos it so short, all the guestimates and long string figures are IMO just a guide.
Until you have actually braced it you just don't know, it may take a load of set, it may be a ludicrously high draw weight.
I'd say brace it and draw it to you target weight NOT over.
Then if it is over weight, take a tad off the belly, review and repeat until, you reach target weight and draw length or you or the bow explodes >:D
Del
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I'm enjoying this bow Tom. (-P I've been thinking about making one myself. I'd like to see what the wheelie bow guy's that complain about the guys hunting with crossbows that "aren't really bows" reaction would be. :o should make a interesting conversation. :BB
Bjrogg
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Why brace it at all? Could you make the stock a bit longer and just use a long string, tight but long.
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+1 with DC I have seen crossbows that are not braced shoot amazing! if it starts to stack or is about to break you should consider it.
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Haven' braced it as i wanted to see how strong it is so i could work out the number of strands i need, a 200# string is quite a bit more chunky than a 150# . Any mileage in making a temporary short string from paracord just to get a more accurate idea of draw weight?
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I think you would find that the paracord has more stretch than the bow has bend. It would be more like a sling shot than a bow :)
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Agreed, but i dont want to shoot wirh it, just see whats going on at brace height
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Why brace it at all? Could you make the stock a bit longer and just use a long string, tight but long.
...Because the limbs would flex the wrong way when the bow was shot and probably smash eventually.
Del
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Thank you. I figured there was a reason. So a low BH is OK then?
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Thank you. I figured there was a reason. So a low BH is OK then?
As low as you dare >:D
I've had some prods throw the string off, just twist it up a tad and try again (if the prod hasn't exploded)
Del