tiller/design help needed

[stuckinthemud]

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  .  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

[Del the cat]

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

[Badger]

   I agree with Del

[stuckinthemud]

I reduced the centre a little,  now drawing to brace height at 4.5 inches, any thoughts?

[Del the cat]

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

[stuckinthemud]

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.

[stuckinthemud]

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?

[Del the cat]

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 
Del

[bjrogg]

I'm enjoying this bow Tom. 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. should make a interesting conversation.
Bjrogg

[DC]

Why brace it at all? Could you make the stock a bit longer and just use a long string, tight but long.

[Deerhunter21]

+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.

[stuckinthemud]

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?

[DC]

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

[stuckinthemud]

Agreed, but i dont want to shoot wirh it, just see whats going on at brace height

[Del the cat]

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