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made a new crossbow (Read 7155 times)
Hellfire
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made a new crossbow
Jun 24th, 2006 at 11:37pm
 
Me and the forum member Brainkrieg found out that we didn't live that far apart. So one lazy afternoon we went out and made a crossbow. I got to keep it  Wink. Here are some pics. Brainkrieg made the stock and I made the prod.
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Tint
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Re: made a new crossbow
Reply #1 - Jun 24th, 2006 at 11:59pm
 
Real nice! Shocked
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Slinger_Man_Dan
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Re: made a new crossbow
Reply #2 - Jun 25th, 2006 at 4:42am
 
     Cheesy Hellfire, Brainkrieg!!                                                         
         Wowie, ka-zowie!! You guys did good! That is a super cool piece of work! I have been doing some reading about crossbows and there have been some crossbow threads on this forum; interesting stuff. I've read that the simple notch lock works best with bows of low draw weight. Can you guys give us some specs ( specifications ) on your new toy? What are the dimensions of the bow and the stock? What materials did you use? What is the draw weight?                           
         Did you find a similar piece in a book or google search to inspire you? Anyway, great work! Maybe you could post some close ups of the lock and tell us how it shoots!                            .......Dan
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Mike
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Re: made a new crossbow
Reply #3 - Jun 25th, 2006 at 12:29pm
 
http://homepages.tesco.net/~tinyclanger/albini/albini_equipment_crossbows_lockbo...
http://homepages.tesco.net/~tinyclanger/albini/albini_equipment_crossbows_12th13...
The pin pushes the string out when you push up on it. These two websites will explain most of it.

The prod (bow) is made of elm. The prod pulls at about 66 pounds, and it took a set. Dimensions for the prod: It is 37 and a half inches long, 1 7/8ths inches at the center, and it tapers at the ends to about 3/4ths of an inch. It is 7/8ths inch thick.

The stock is 3 foot long, and the groove is 16 inches long. The groove was carved with a pocketknife and a 1/2 inch dowel covered in sandpaper. The stock is 1.5 inches wide, and I think it is made up of elm. The stock dips down around the end so you can aim the dowel to your eye and fire it.

How it shoots? It isn't bad, but it's not great. I didn't measure distance, but it goes the distance of about a 30-35 lb pull bow. Less that a hundred yards.

I did get some close ups of the lock. The first picture is a birds-eye view of the lock. The last picture show the lock and trigger, so I hope that answers your question.

The bolts I haven't been able to work on. All I did was take a 16 inch dowel (long for a bolt) and put a half inch nut at the end for weight. No fletching yet.

For tools- a pocketknife did the debarking, and most of the carving of the lock mechanism. I don't know about the prod, as Hellfire made it. The groove was carved with a knife and smoothed with sandpaper.

The two divets in the stock are for aiming purposes. Put your cheek down to it, aim across the bolt with your eye, and fire.
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Re: made a new crossbow
Reply #4 - Jun 25th, 2006 at 11:38pm
 
On the range of the crossbow,
When i was an undergrad back in the early to mid-'90's I did some calculations for my Physics class on my Barnett Commando ( 175 lb pull)
The calculations showed that maximum range with 0 degree elevation was only about 52 meters.
So it sounds like your about right on your range.

Ya might get some better range with a proper field point on it.

Marc Adkins

[quote author=Brainkrieg link=board=other;num=1151206635;start=0#3 date=06/25/06 at 12:29:39]

How it shoots? It isn't bad, but it's not great. I didn't measure distance, but it goes the distance of about a 30-35 lb pull bow. Less that a hundred yards.

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Re: made a new crossbow
Reply #5 - Jun 26th, 2006 at 4:25pm
 
it Lovely Cheesy i might try when i figure it out (one day you know Tongue)
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Mike
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Re: made a new crossbow
Reply #6 - Jun 26th, 2006 at 9:11pm
 
Winkleried,

I haven't taken a physics class yet, but how do you calculate the distance a crossbow should shoot a bolt at 0 degrees?
What did you use to pull back your crossbow? I am thinking about just using my fingers with a hook so it doesn't crush them. Maybe a goats-foot lever or a belt and claw. Or did you have on of those compound crossbows with letoff?
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Re: made a new crossbow
Reply #7 - Jun 26th, 2006 at 10:08pm
 
We have a 150 lb crossbow here, modern steel recurve design, and with a loop to place your foot I find it easy to cock with my hands/arms.

btw,  Great looking cross bow!
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Re: made a new crossbow
Reply #8 - Jun 27th, 2006 at 5:24am
 
Your crossbow looks great!!
It has the same lock (peg type) as the old viking crossbows.
I have made 5 crossbows with this type of lock.
Try and buy a book called:
European Crossbows By Josef Alm.  Printed by Royal Armouries. ISBN 0948092203

In this book you wil find most types of crossbows.
I recomend that everybody that is interested in crossbows must read this book.

Rune "The Reb"
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Re: made a new crossbow
Reply #9 - Jun 27th, 2006 at 10:12am
 
That book, and "The Crossbow" by Sir Ralph Payne-Galwey (I think thats his last name.)
I would like to see some pictures of those crossbows, and how much for poundage they have, unless you sold them or something. Do you know how to calculate the distance a prod can safely pull?
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winkleried
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Re: made a new crossbow
Reply #10 - Jun 27th, 2006 at 3:21pm
 
I'll try and post the formula later on tonight..... Going to have to chase it down in my physics book. From what I remember its a fairly straightforward formula used in classic ballistics.

For the cocking part i just use my arms without any cocking device.
I brace the bow against my thigh and pull the string down to where it locks.
If I'm in harness I brace the bow against my Leather lamalar breast plate and pull down.

Marc Adkins

Quote:
Winkleried,

I haven't taken a physics class yet, but how do you calculate the distance a crossbow should shoot a bolt at 0 degrees?
What did you use to pull back your crossbow? I am thinking about just using my fingers with a hook so it doesn't crush them. Maybe a goats-foot lever or a belt and claw. Or did you have on of those compound crossbows with letoff?

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Re: made a new crossbow
Reply #11 - Jun 27th, 2006 at 4:18pm
 
Brainkrieg,

Here is how to figure out (roughly) how far a crossbow should shoot, if you are shooting at zero degrees (that is, straight ahead, no elevation at all).

First off, an object falling near the earth's surface, is accelerated downward at 32.15 feet/second/second (9.8 meters/second/second). †It does not matter if it is pointed straight up, straight down, or anywhere in between. †If it is pointing upward of horizontal, the acceleration of gravity will pull the object down until it is no longer moving upward, and thenceforth it will move downward faster and faster. †But the crossbow bolt is being shot horizontally, so it is at rest as far as its vertical motion is concerned.

So. †The distance an object moves under a constant acceleration is:

†x = 1/2 a t2

The above formula assumes the object is initially at rest; there's a couple of terms I left out that deal with the initial position and velocity, if it is already moving.

If we plug in 9.8 m/s2 for acceleration "a", we see that after one second the bolt will have fallen 4.9 meters (16.1 feet).

Let us re-arrange the formula and find out how long it will take the bolt to fall 5 feet, or 1.5 meters (assuming the crossbow is held at shoulder level and you are not extremely tall).

†t = sqrt(2x/a)

Note: "sqrt" means "square root". †There's a standard symbol for it, but the computer character set used here does not include that symbol. †OK, where were we? †Oh, yeah, now substitute in the values for distance "x" and acceleration "a":

†t = sqrt(2 * 1.5 / 9.8 )

†t = 0.55 second

Now, how fast is the bolt moving horizontally? †Let's assume it's going 100 ft/sec (30.5 m/s). †Ignoring air resistance, which is probably safe to do IN THIS CASE (because it's only flying for half a second), the bolt will travel 30.5 / 0.55 = 55.5 meters (182 feet) before it hits the ground.

Thus ends today's lesson in classical mechanics (basic physics).
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Re: made a new crossbow
Reply #12 - Jun 27th, 2006 at 4:47pm
 
If you know Perl you could adapt my script with the Baatz physics.

http://www.mbsks.franken.de/slinging/slinging.html#Ballistics

Zwiebeltuete

PS: Great crossbow!

PPS: The problem with the performance of the crossbow is the small draw length compared with a bow as the stored energy is  draw length * avg. force.
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Re: made a new crossbow
Reply #13 - Jun 27th, 2006 at 5:38pm
 
ZwiebeltŁte,

I read the page describing your Perl ballistics script.  Very nice job!

However, I disagree with one thing: you assert that spin is relatively unimportant for slinging.  My experience has been otherwise.  Spin has a noticeable effect on my casts.  For instance, using the figure-8 style, I consistently put a side-spin on a golf ball.  I can cast one about 100 yards, and the side-spin moves the ball's impact point probably 15 yards to the right of its original trajectory.

Perhaps I will find that stones are not so affected.  Perhaps the ball would be unaffected, if I could figure out how to put a rifle-spin on the ball (axis of rotation parallel to line of flight) instead of a side-spin (axis perpendicular to flight).  To present, however, I have not confidence  in my slinging and so do not sling stones for distance.  All my experience is with golf balls.
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Re: made a new crossbow
Reply #14 - Jun 28th, 2006 at 5:15am
 
Flat stones are affected too. Yesterday a stone flew a significant curve to the right. I will revise my page.

Zwiebeltuete
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