First attempt at sinew back... Xbow

[IsaacW]

It has been a LONG time since I have been on the board and am trying to catch up.  I recently put up a new shed and have a space to easily stretch out and work on some bow making again!!! YEAH!  I may even try to put in an little indoor "range" for shooting in winter (if winter ever comes).  Anyway... I am starting my first attempt at a medieval crossbow.

Yesterday I finished working down a hackberry stave for the prod.  The tiller was okay but not perfect but I did not want to take any more wood off at this point.  I then applied the first layer of sinew to it.   It is my first time ever sinew backing.  The first layer was a bit rough but after a few hours I added a bit more to the middle of the stave (that I want to beef up a little) and it went a lot better.

I am not letting it set well before I add another layer.  While I wait, I will start on the tiller/stock of the xbow.

[Del the cat]

Interesting... I'll follow this one.
Del

[Urufu_Shinjiro]

Ditto, cool stuff.

[MXer]

Yeah I'll follow too!

Give us more... What is the tip to tip length and what kind of draw weight are looking for?

I've also thought about something like this too.

I will be especially curious how you do the trigger mechanism.

[IsaacW]

Give us more... What is the tip to tip length and what kind of draw weight are looking for?

I've also thought about something like this too.

I will be especially curious how you do the trigger mechanism.

The prod here is about 36 1/2" tip to tip.  I am not worrying too much about weight other than I want to make sure it is heavy enough to hunt with for bear or deer.  For WI, it needs to be at least 100 pounds and with a 14' bolt (12+" in draw).  I am wanting somewhere closer to 150# at a 13-14" draw.

For a trigger, I am going with a simple push pin style with a wooden tickler/trigger. I will keep everyone posted.  This is a first for me as I have not made a crossbow before.

[cadet]

Watching with interest!

I had a go at a light prototype timber crossbow recently, and used a timber pin/skane-type lock.  I'll fabricate something with a roller nut next.

[IsaacW]

Three layers of sinew on, dried, and a slight retillering (looks good).  I gave it a good check on the scale and it was disappointingly a good bit weaker than I wanted.  At 14" it is only 70#.  I am going to take an inch from each limb, add a horn belly, and add another layer or two of sinew.  We will see if I can bring it up a bit.  I really would like to get it a bit over 100# if possible.  If not... it will be a nice little lighter crossbow to shoot around and I will have to make another, shooting for heavier.

[PatM]

You need to reflex it and let it dry for a bit longer than a week if you want more weight. Heat treating would have done a lot for it as well.

[bradsmith2010]

ok it will be about 80# at 18 inches of draw,, and maybe more because the sinew is not dry yet,,
that is double what you need to kill a deer,, that will kill two deer with one shot at the 80# weight,,
that being said, as suggested,, if you  reflex the next one it will have more weight,, and add a couple more layers of sinew that will help too,,
if the stave was longer and you could draw to 26 inches you would have your 100#,,
if you draw the bow to 20 inches, and it holds , it will be at 85, and when the sinew dries about 90,,,,
so I dont think you missed your weight by much,, considering it is your first try,, congrats, B
also you could pull the bow into reflex and put more sinew on and get more weight,,,its not over till its over,,,

[PatM]

The problem is that it's a crossbow prod. It will be held at full draw for extended periods of time and plummet in weight as a result.

[bradsmith2010]

ok I understand,, thanks Pat,,

[IsaacW]

The problem is that it's a crossbow prod. It will be held at full draw for extended periods of time and plummet in weight as a result.

Indeed and will have a shorter draw length, therefore less power/poundage per inch.  To be legal in WI, it has to be over 100# which makes sense when you think of the short stroke on a crossbow.  Anyway, more sinew, more drying, and perhaps some horn on the belly... it should be better.  It is not over until it is over.!!

[IsaacW]

Also... for those that do sinew backs:
How long do you let the sinew dry?  I have made a number of selfbows, but sinewing is new to me and I tend to be impatient to a fault. 

Isaac

[mullet]

I let it dry anywhere from 3 to 6 months.

[Danzn Bar]

I let it dry anywhere from 3 to 6 months.

Eddie ... I couldn't wait that long but the RH in the house was 15-20% for about 4weeks 
DBar