Primitive Archer
Main Discussion Area => Bows => Topic started by: Del the cat on October 29, 2011, 02:15:01 pm
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31" ntn with some built in deflex Laburnum (from one that died in the garden a year or so back) backed with rawhide.
80# @ 12.5"
No metal in the construction. The bow curved upwards so the string doesn't press down hard on the stock, and there are a few nice touches like a sliver of Ivory to stop the bolt being push back too far.
A full build along is on my Bowyers Diary starting here. http://bowyersdiary.blogspot.com/2011/10/graingram-scales.html (http://bowyersdiary.blogspot.com/2011/10/graingram-scales.html)
I'll take it up the club to the Samhain festival tomorrow.
It certainly shoots clean and fast, no real kick, just a nice click & twhack.
(http://i411.photobucket.com/albums/pp195/Del_the_Cat/Website%20stills/PrimitiveCrossbow.jpg)
(http://i411.photobucket.com/albums/pp195/Del_the_Cat/Website%20stills/prod.jpg)
I'll post the speed tomorrow, anyone care to guess >:D
The butt end looks a bit white as it isn't properly finished/varished yet.
Full draw shot ..
(http://i411.photobucket.com/albums/pp195/Del_the_Cat/Website%20stills/PCrossbowFD.jpg)
Just did some chrono tests. With the heavy bolt in the pic (it has a flat head nail in the butt end for added weight) it was only about 125 fps, but going to a V light bolt (50gn point) it shot upto 170fps. With such a short power stroke I s'pose the heavier bolt slows it down a lot.
I had a couple of dry fires as trigger groove needed a bit of fettling... dind't scare the cr*p out me at all O:).
BTW the string is 90 strands of linen thread. The binding for the prod is hemp twine soaked in a mixture of beeswax & linseed oil.
All fixed now :)
Del
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Cool Del....more photos? How bout a full draw :)
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I've just added full draw and I'm going to edit in the chrono results.
Del
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thats pretty cool there "cat daddy", i half expected to see a clothes pin on top >:D
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That's incredibly cool, I'll take a look at your build-along. I'd love to make a crossbow, so I'll be adding this to my bookmarks :)
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SWEETTTTTTT
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That is awesome! I am curious though how much the bolts weigh?
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That is awesome! I am curious though how much the bolts weigh?
The heavy bolt (11/32") in the picture is 440gn @ 125fps = 20.7 Joules of energy
A ight bolt (5/16") 150gn @ 170fps = 13.0 Joules of energy
The heavy bolt goes pretty slow, but being 4 times heavier ends up having much more energy.
It would be interestion to plot loads of different weights and see which actually gives most energy.
BTW the bolt has just 2 flights fixed at a slight angle to help it spin.
Del
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Really cool Mr. Cat, that binding for the prod is sweet looking. whole thing is top shelf .
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That is awesome! I am curious though how much the bolts weigh?
The heavy bolt (11/32") in the picture is 440gn @ 125fps = 20.7 Joules of energy
A ight bolt (5/16") 150gn @ 170fps = 13.0 Joules of energy
The heavy bolt goes pretty slow, but being 4 times heavier ends up having much more energy.
It would be interestion to plot loads of different weights and see which actually gives most energy.
BTW the bolt has just 2 flights fixed at a slight angle to help it spin.
Del
Cool, I think Im gonna have to try this sometime.
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that'a sweet cross bow del, did you wrap the rawhide with cord to get the corregated look, Bub
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Very nice!
Any shooting video? I'd like to see how you hold it.
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that'a sweet cross bow del, did you wrap the rawhide with cord to get the corregated look, Bub
Yup, spot on, that's exactly what I did.
Del
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Very nice!
Any shooting video? I'd like to see how you hold it.
None yet, but I hold it like a modern rifle, the butt droops down about half an inch and has a bit of a cast off to the right so with my cheek on the butt my eye is right in line with the bolt.
It's a bit of a mix of styles really, it doesn't look that primitive and there's a hint of the Gothic in that bolt clip. Early crossbows had a dead straight norrow stock, but would imagine it wouldn't take longe before some guy made his a bit more comfortable to shoot. The long straight stocks are a pig to shoot as it's not comfortable however you hold 'em.
The bigger one on my website is a bit of a cheek rattler, there's a vid of that one on my website and it shoots pretty similar to this one.
Del
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Yes I saw that video "game over" :)
Must be difficult to hold a straight stock crossbow against you shoulder. Is it not sufficient to rest it against your cheek. (maybe grow a beard or something if it hurts to much)
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Yes I saw that video "game over" :)
Must be difficult to hold a straight stock crossbow against you shoulder. Is it not sufficient to rest it against your cheek. (maybe grow a beard or something if it hurts to much)
Yeah, one reason for building these things is to see how they actually feel.
I shot the cross bow a fair bit today at the club and ir felt pertty good, either grouping tight or in a vertial line as the height estimation is tricky without sights. It's fairly smooth to shoot and there's a longish, but light squeeze on the trigger, one of the ladies had a go too and didn't have any problem with cheek rattling. There were a lot of visitors to the club as it was the Samhain festival and the bow drew a fair bit of interest.
Del
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Most of it is worked out from the actual bow (prod) dimensions and just sketched out by eye.
I looked at images of primitive crossbows on the internet for the trigger and coupled that with the experience of the similar mechanism on my Chinese Repeating Crossbow. If you haven't seen that, then look at my website (google delsbows to find it). The trigger mechanism works surprisingly well, the slot is cut square down into the stock, just deep enough for the string to drop into, no need to go down too deep else you end up with a very long trigger pull. You need to round off the corners of the slot so that it doesn't wear the string too much, but if you round them off too much the string can jump out on it's own! If that happens a little re-shaping of the slot will solve the problem. Facing the groove with horn or somesuch is a good ide as it will polish nicely to avoid string wear.
Anyhow here are some dimensions (mixed imperial and metric for convenience)
Prod:-
31.5" long.
36mm x 16mm at the centre
17mm x 12mm at the tip
Bracing height 3.6" from back of bow, the string pops off if it is much less than this (happend twice at about 3", so I twisted up the sting a bit more)
Draw, (back of bow to trigger slot) 12.5"
Stock:- all dimensions from front of stock (prod end) unless otherwise stated
Overall length 28.5" (I like a shortish stock and that felt comfortable to me)
Prod mounting slot about 1" deep.
Distance to prod binding hole 4". Hole about 15mm diameter (round off the corners)
Distance to small hole which is the start of the tigger 9 3/4" (I drilled a hole to help avoid splitting)
Overall trigger lever length 11" (trigger is about 11mm thick and 23mm wide.. tapering here and there to look pretty :))
Depth of stock about 2 3/4"
Width of stock 1 1/8"
Trigger slot depth 4.9 mm
Gap between top of trigger lever and underside of stock 4.9mm this gives just enough lift on the peg to push the string up and out of it's slot.
The Binding for the bow can look really nice, but it's tricky to get it tight, a piece of leather between bow and stock helps but it's one of those fiddly jobs that you will probably end up doing twice to get it right. The ideal material is sinew, maybe rawhide. I've used well waxed hemp twine before and it was fine. The first stage of binding gets it tightish, the zigzag binding the clenches the main binding even tighter.
If you don't mind what it looks like rubber strapping to bind it in is very effective as it hold it's tension.
Bolts, I just use 11/32" arrow shaft and some 100 gn points I had lying around (125 or 150 would prob be better). The trick is to match the bolt weight to the bow, heavier weight bolts will be a bit slower but will shoot smoother with less rattle on you cheek, the ywill hit home harder too. As for length it depends how cheap I'm feeling you can get 2 bolts from a standard arrow shaft, or 3 if you don't mind 'em a tad short. The one in the pics on the thread is a short one.
Del