Info Favorites Register Log in
myArmoury.com Discussion Forums

Forum index Memberlist Usergroups Spotlight Topics Search
Forum Index > Off-topic Talk > Definition of draw weight and crossbow cocking devices Reply to topic
This is a standard topic  
Author Message
Helge B.





Joined: 06 Mar 2008

Posts: 73

PostPosted: Wed 11 Feb, 2009 4:19 pm    Post subject: Definition of draw weight and crossbow cocking devices         Reply with quote

How do you actually define the draw weight of a bow or crossbow? Is it the weight you need to pull back the string to the maximum power stroke?

How does this relate to the force needed to cock a crossbow with a mechanical aid? If you use a goatsfoot for example you should get a mechanical advantage of 1:5. Does this mean if you use this device to cock a 100 lbs. crossbow you would only have to lift 20 lbs.?

What are the mechanical advantages of the different cocking devices used for historical crossbows?
View user's profile Send private message
Randall Moffett




Location: Northern Utah
Joined: 07 Jun 2006
Reading list: 5 books

Posts: 2,121

PostPosted: Wed 11 Feb, 2009 10:56 pm    Post subject:         Reply with quote

Helge,

It means you need apply the draw weight to ready it. For a crossbow this is to the nut or slot. So if it is 400lb draw you need exert 400lbs to get it to the full draw.

The windlass and cranaquin could handle the most power of a mobile system but both were slower than the belt hook, belt hook with pulleys and goats foot lever but these last ones could not pull the same amount of draw weights.

If I had to guess on the pull they could generate it'd be-
Windlass/Cranequin
Goatsfoot lever
Belt hook with pulley
Belt hook
unaided.

You do have spanning tables in castles for all but the biggest great crossbows that at times were manned by two men. These could likely reload these massive weapons fairly quickly but one could not move them very far as they were rather large and out on campaign it'd be a hinderance for mobility.

RPM
View user's profile Send private message
Leo Todeschini
Industry Professional



Location: Oxford, UK
Joined: 12 Nov 2006
Likes: 1 page

Spotlight topics: 1
Posts: 1,723

PostPosted: Thu 12 Feb, 2009 12:53 am    Post subject:         Reply with quote

Quote:
Helge B wrote What are the mechanical advantages of the different cocking devices used for historical crossbows?


All were different so it depends on exact manufacture, but roughly

Windlass 140:1
Cranequin 45:1
goats foot 4 or 5:1
Belt hook and single pulley 2:1 (but legs/back are far more powerful than arms/back
belt hook 1:1 (uses back and legs
straight draw 1:1(uses back and arms

Tod

www.todsworkshop.com
www.todcutler.com
www.instagram.com/todsworkshop
https://www.facebook.com/TodsWorkshop
www.youtube.com/user/todsstuff1
View user's profile Send private message Visit poster's website
Gary Teuscher





Joined: 19 Nov 2008

Spotlight topics: 1
Posts: 704

PostPosted: Thu 12 Feb, 2009 8:25 am    Post subject:         Reply with quote

I have somewhat of an idea, but does anyone know of when these various spanning devices were first used and/or what time period they were used?
View user's profile Send private message
Sean Manning




Location: Austria
Joined: 23 Mar 2008

Posts: 853

PostPosted: Thu 12 Feb, 2009 9:32 am    Post subject: Re: Definition of draw weight and crossbow cocking devices         Reply with quote

Helge B. wrote:
How do you actually define the draw weight of a bow or crossbow? Is it the weight you need to pull back the string to the maximum power stroke?

Its the force required to draw the bow a certain distance- that's all. The distance is fixed for crossbows and flexible for other bows, which is why you'll read things like "a draw of 650N at 70 cm".
View user's profile Send private message
Jean Thibodeau




Location: Montreal,Quebec,Canada
Joined: 15 Mar 2004
Likes: 50 pages
Reading list: 1 book

Spotlight topics: 5
Posts: 8,310

PostPosted: Thu 12 Feb, 2009 10:35 am    Post subject:         Reply with quote

Leo Todeschini wrote:
Quote:
Helge B wrote What are the mechanical advantages of the different cocking devices used for historical crossbows?


All were different so it depends on exact manufacture, but roughly

Windlass 140:1
Cranequin 45:1
goats foot 4 or 5:1
Belt hook and single pulley 2:1 (but legs/back are far more powerful than arms/back
belt hook 1:1 (uses back and legs
straight draw 1:1(uses back and arms

Tod


For the belt hook method I would gess that someone used to doing it would be able to do it more efficiently than one of us trying it the first time no matter how strong our leg muscles might be.

My guess, but the way I would set up the belt hook would be for it needing only the 5 or 6 inches of draw where my legs would be bent just enough for the hook to attach to the cord and would need to just straiten up to pull.

The point being that the legs are strongest in the upper part of leg extension, in other words it's easier to do it at the top end rather than using a short belt hook and squatting deeply.

I would also imagine that the way the belt is made and adjusted would make a great difference in how much weight one could handle with the belt hook ? In my case I can do 1000 pound leg presses so I think that a 350 to 500 pounds belt hook crossbow should be easy to pull with the right equipment and technique.

( Edited for spelling mistake )

You can easily give up your freedom. You have to fight hard to get it back!


Last edited by Jean Thibodeau on Thu 12 Feb, 2009 2:39 pm; edited 1 time in total
View user's profile Send private message
Gary Teuscher





Joined: 19 Nov 2008

Spotlight topics: 1
Posts: 704

PostPosted: Thu 12 Feb, 2009 11:37 am    Post subject:         Reply with quote

Quote:
Is it the weight you need to pull back the string to the maximum power stroke?


To re-iterate what Sean said, the draw weight the peak weight on the draw.

One thing about crossbows though - for whatever reason many usually refer to the draw length is the nut to the braced position of the bow - many leave the brace out when factoring drawlength. When figuring a selfbows draweight, the draw + brace are figured in. For example, a 30" long draw on a longbow means a 22" draw or so with an 8" Brace.
View user's profile Send private message


Display posts from previous:   
Forum Index > Off-topic Talk > Definition of draw weight and crossbow cocking devices
Page 1 of 1 Reply to topic
All times are GMT - 8 Hours

View previous topic :: View next topic
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum






All contents © Copyright 2003-2024 myArmoury.com — All rights reserved
Discussion forums powered by phpBB © The phpBB Group
Switch to the Basic Low-bandwidth Version of the forum