Yew Composite prod:help needed

First topic message reminder :

Hi there

I am new to posting in this forum but have used it in previous builds. I am looking to build crossbow prod useing  Yew and sinew only. Horn seems too time consuming. 

I would like to follow a build I have seen by the user OrienM:

https://thearbalistguild.forumotion.com/t1655-yew-and-sinew-prod-help-needed

However i would like the draw weight to be at least 250lbs. I know this is a lot to ask without useing horn but is anyone able to give me a guess as to the dimensions for what that might be before tillering.

On a side note the design of the crossbow is very unique as it allows the crossbow to cocked in under 3 seconds with a draw weight of 400lbs and utilises this speed of draw with a magazine of bolts. The materials used were available to anyone living in the period of when crossbows were still used on the battlefield and so from a historic sense this build is very interesting. The design is relatively compact and very easy to use with minimal effort in the loading process. 

I'd very much appretiate any advice/help, and would be happy to reveal the design in a PM

Regards

Ed

yes i will score it. when you day check that there are no lumps, would the lumps occour because the sinew might not be split enough resulting in a tough bit

Yes but, the lumps will be the remains of the sheath around the sinew, it will need to be pulled off, it feels different when you run the sinew through your fingers you can even scrape it off with your thumbnail

To score the back I've seen bowyers get a hacksaw blade, and run it along from one end of the bow to the other. Just to let you know if you were wondering.

And wash it to get rid of any grease off your fingers

I heard acetone is a good way to clean oil off of the backs of bows for gluing prep.

what about useing a combe just on those bits? want avoid coming as it makes the strands smaller in length

No need for the comb, wet the sinew and pull it through your fingers to get rid of the excess water, as you do that you'll feel any coarse pieces or lumps . Acetone is for naturally oily timbers, dish soap or sugar soap is fine for yew

stuckinthemud1 wrote:No need for the comb, wet the sinew and pull it through your fingers to get rid of the excess water, as you do that you'll  feel any coarse pieces or lumps . Acetone is for naturally oily timbers, dish  soap or sugar soap is fine for yew

ok so its ok to wet the sinew. do i need to dry it before glueing it?

No, best done when its damp, its a very scary build up but actually a very easy job, keep a towel near by and a bowl of water as your hands are going to get wet and sticky and you need to frquently clean your fingers. Keep the glue at a good working temperature, not too hot as your hands are going to be in that glue. Dont rush, smooth the sinew down and work out any air bubbles as you go, run the sinew off the edge of the lath and file it back once its dry. You can sand the sinew smooth and to shape if need be so dont get too stressed about a perfect finish

Here read this it might help you. 
https://sensiblesurvival.org/2012/03/06/how-to-sinew-back-a-wooden-bow-part-1/

This is kind of off topic, but are you going to add tip over lays?

Hey. Watched lots of tutorials on the gluing process so I'm a bit more confident. I'll read that link

Making good progress!

Excellent tips from stuckinthemud1...the sensiblesurvival.org link is quite a good one, too.

The wood prep is an important step...I score the back lengthwise with a hacksaw blade, size the surface with thin glue, and let it dry before starting on the sinew glue-up.

The sinew gets soaked in warm glue until soft and flexible, then placed on the back and gently pressed down. At the ends, I wrap over the tips, and down onto the belly a little bit. I apply single threads at a time, and only pause briefly during the process, so the backing never dries out completely until finished.

I keep mixed hide glue in a tupperware container in the fridge, and heat it with short bursts in the microwave to get it to the proper working temp. It should never exceed "comfortable", or it will cook the sinews...they will curl up and become unusable.

This may sound weird, but with sinew-backed bows I don't raise knots on the back...I plane them down flat and sinew over them. At most, I'll add a bit of width at a knot to compensate. The sinew should do the vast majority of the tension work, and is plenty strong enough to make up for violated rings.

I absolutely won't flex a sinew-backed prod until it's sinewed...no pre-tiller done at all. Instead, I establish an accurate front-view profile shape, carve nocks, and pre-taper the limbs by eye, but leave lots of excess thickness (back to belly), and do all the tillering after the sinew cures. The way I see it, a powerful prod NEEDS sinew to function, and pre-tillering just risks breakage at a vulnerable stage. After the sinew cures (3 months minimum), the tillering can be done by drawing with a cocking rope (or your own method of choice) on a dedicated tillering jig.


Keep up the good work!

This would also be the time to steam-bend in deflex, if you intend to do so. Personally I like to use a bent-in deflex (typically about 1" less than the brace height) because I think it results in less wood damage than allowing 'natural' set to occur. It also helps a lot with the stringing process when using a bastard (2nd) string.

Hi there

I want the end result to be a straight piece of wood when unstrung. 

Today I added the first layer of sinew.

Here is the end result.

Tell me what you think 

Tel

[url=https://servimg.com/view/20097012/9][/url]

[url=https://servimg.com/view/20097012/10][/url]

Looking good

Thanks for- that orien. I have taken heartwood off the knots for the sinewing as you can see. The tips will be a little thicker as I have had to take wood out of the back for the string groves. There is about 2mm of sinew that flows over the back onto the side of the bow. The knot in the middle is untouched and I have added resin into the hole. The sinew thickest at this point and I have used my longest strands for the knot.

That is looking nice...keep up the good work!

I do highly recommend double nocks, though; I fear it will be extremely difficult to brace your prod otherwise. My own prods can only be braced by using a bastard string and pulley rope...the 'step-on' method doesn't flex the limbs enough to get a string on. Without any deflex, your prod may be even more stubborn to string.

Hi

We will be making two little metal plate hook type things that catch the tips. Don’t want to loose any strength if we don’t need to with the bastard notch

Ah, good...that should work just fine. I have dealt with steel prods that way, but not wooden ones.

The step-on method of mounting a string is Very Risky and limited to lighter draw weight.  Use a bastard clamp or cobble up a drawing-bench.  My old Journeyman, Lightly has one mounted to the wall in her shop.... two thick pegs the right distance apart and right height. Stand the stock on a bottle-jack directly underneath, with ends of the prod against the pegs..... crank up the bottle-jack till the bow-limbs are sufficiently bent to do your business.  Geezer.
ps: If I could figure out how to add pics to these posts, I could include some pics of bastard clamps... I'll look into it. Geezer, the luddite.

Well durn: that was easy.  Let's see if it comes up.  Geezer.