first time build (complete newbie)

First topic message reminder :

Hi I'm new to this site and to be honest new to crossbows and im looking for some help building my first one because basically i have no idea how to even start designing one so if any one can point me in the direction of either some plans or some reading material i would be most grateful. Im in the uk and also limited in so respects as to materials and to be honest skills but i'm keen to learn new skills and work with new materials so any help anyone could offer would be massively appreciated!

I'd say your timber is too 'tall' from the bolt track groove to the underside.  You could make it a lot 'sexier' by tapering the underside of the tiller from the pin hole to the butt end.  You could easily reduce the depth at the butt by half and it will look much.  Remember, unlike a rifle, there is little or no recoil, so the tiller doesn't have to be so massive.  Similarly, reduce the depth of the trigger arm along the entire length. It only needs to be perhaps 8mm thick.  

You can also reduce the width of the tiller.  Aft of the bridle hole it doesn't have to be 12mm wide on either side of the bolt track, and near the butt end it can get thicker again to make the "buttplate".

dackieboi,
I wouldn't do much more with the tiller until you have your prod, since mating up those two elements together correctly is much more critical than how the tiller looks. Also more important than how it looks is how it feels and how it works! My first couple of builds were built to designs I labored over ahead of time and looked pretty fantastic, in my own opinion, but over time I came to realize that they handled like crap. So far my favorite weapons have been the ones where I didn't give a thought to the shape of the tiller until all of the critical work was done, mounting the prod correctly and setting up the lock/release mech. Then I took off the prod (which you can do without unstringing quite easily, by the way), put away the power tools and cut and carved and sanded the tiller till it felt right in my hands and shouldered without thought or effort. That's where the beauty of a weapon resides, in my humble opinion, in it's utility.
So my advise is to think generally about the design to start, and chunky is a great place to start since you can always remove chips and sawdust but it's harder to put it back on, Work with muscle powered tools as much as possible since it will take a lot more effort to really screw it up before you know it, and constantly handle and test the tiller as you go to make sure you're moving in the direction you want.
Best of luck with your build,
Gnome

Cheers gnome I'm probably gonna rebuild the tiller in the future anyway cause I feel like I could do it better but I've learned a lot from this one

There's a fairly fast learning curve in this business.  I still have my first crossbow hanging on the shop-wall.  It's not half bad, but no more than half-good either.  Lots of changes since then!
Congratulations on your first build.  Geezer.

ok got it all together last night but realized some kinda major design flaws:  

1. the binding hole is prob a bit too close to the prod
2. i could really do with a proper stirup rather than a piece of rope
3. the catch for the bow string was to shallow (which i've fixed now but leads onto the next problem)
4. after cuting the catch deeper now the firing pin is too narrow
5. and finally im not entirely happy with the binding seams a bit loose (was fine until i had a fight with the prod trying to string it)

 

http://www.flickr.com/photos/114412612@N02/11992742204/

String the prod before binding it.  There's probably some optimum binding hole to prod distance, but I don't know what it is.  You just have to take your time with the binding to make sure it's good and tight.

Yes, a rigid stirrup, or at least a rigid flat bar on a rope stirrup works better, as I discovered in a recent build.

The best arrangement with the firing pin IMHO is to have it sort of one-third "imbedded"  in the face of the string notch.  What diameter pin did you use?  I prefer a pin about 8mm in diameter (3/8"), with about 3mm imbedded in the face of the notch.  I mark the notch distance, the drill the pin hole such that it partially crosses that line.

Take a look at the detail photos on the build of the loose laminate pinlock in my avatar, and you'll see what I mean about "imbedded":

https://thearbalistguild.forumotion.com/t945-loose-laminate-pinlock-build?highlight=pinlock

Hmm. Your binding hole does look a bit close, but that doesn't mean you can't work with it. It is a bit trickier to bind the prod if it is already strung, since that string will be in your way, but unless you have a press of some kind to span the prod it could be the only way to do it without wrecking the binding.
I think if you had more distance between the mortice and the hole you'd have that much more space to lash the main binding, making it that much tighter and resistant to mishandling. Chances are that if it slips around on you while you are attempting to string it, it will also be too loose to shoot safely and accurately. If you don't want to start over with a new tiller at this point, it would be fairly easy to drill out the current hole and plug it with a same size dowel, then make a new hole an inch or two farther back. If you glue it well it will probably be stronger than it was before, and you probably won't be able to see it with the binding covering it.
Gnome