trouble spanning bow

I'm building my first rolling nut crossbow and have just got to the stage were I was ready for a trial assembly and to test the lock today. To my surprise I couldn't span the bow. Its a nominal 150lbs standard fibre glass prod, braced at 3.25" with a 9" power stroke and although it goes off my bow scales I reckon the weight at full draw is a bit less than 150 - though it is definitely stacking at the end of the stroke. I'm 5' 10" 170lbs and used to pulling longbows up to 70lbs so I didn't expect this to be a difficulty.

I'm wondering if this is a question of technique and geometry - I've left the tiller quite long - 32" from prod to but and the stirrup is copied off one of Todd's medieval bows bolted in front of the prod which is held by wedges secured by the stirrup - this makes the length from the bar of the stirrup to the tiller butt 39", and the butt end of the tiller comes up pretty high when I try to span.

So - help please: will it help if I shorten the tiller so I can get down lower? Do you use the strength of your arms to pull the string, or your back or your legs by bending down and standing up? Our am I just being a wimp who needs to get down the gym :-)

Thanks - I will try to post some pics later so you can see the proportion.

Stan

Hi Stan,

Consider doubling your strength with pulleys:
http://www.excaliburcrossbow.com/catalog/crossbow/rope_cocking_aid

The rope aid is arguably even more useful for unspanning without discharging a bolt.

The only modification needed is somewhere on the tiller to loop the rope. Check out the video on that link.

I imagine they would be simple to fabricate, but for speed and ease I just purchased the Excalibur ones (avatar)...
Ernest

Thanks for the advice Hotspur - trouble is I will be using the bow (with a few modifications) for NFAS field shooting in UK and the rules forbid any spanning aid. I did finally manage to span it later this evening, but only with a lot of difficulty. Maybe I just need to work at it.

You can't use even a hook on your belt, as a spanning aid. Is that right?

There seem to have been a number of bracing techniques, but the best ones for 'heavy lifting' would involve the shoulders/back/waist rather than the arms. So I'm thinking trimming the tiller back will help. Try even just taking 2" off the butt end and see if that improves things.

Where is the butt of the tiller when you're in firing position now? Atop the shoulder? Free of the body? Touching the front of your chest?

KenH: You're just about my height, and I assure you a 39 inch tiller is way-way too long for me to span by standing in a stirrup and drawing with both hands. My rule of thumb for customers is to buy a stock no longer than your trousers inseam. For me that's about 30 inches. If the stock is too short, you'll have the long lever-trigger snagging against your trousers-leg. If the stock is too long, the butt gets in the way of your hip or whatever, and even if you can span it, you'll end up over drawing one side or the other.
Like it or not, you're just gonna have to saw some wood off the butt. Take it in 2 inch increments and see what feels right. Geezer.

My two cents, I made my own rope and pully cocker and it works wonders. A simple slot filed in the end of the tiller is all it takes to get it to work.
https://thearbalistguild.forumotion.com/t956-diy-rope-cocker

Yeah Geezer, I know. I wouldn't want to be trying to bend over a yard of tiller, let alone a meter! The tiller is just a hair over 30" on my recent full-size build with the loose-lam prod. The same as my inseam.

My apologies KenH. That comment should have gone to backgarden bowyer. Ahh well, he'll probably read it anyhow. I Know you've got the proportions down. Geezer.