Force/Draw Rig. Black Widow vs Greybeard

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greybeard
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Force/Draw Rig. Black Widow vs Greybeard

#1 Post by greybeard » Sun Dec 11, 2011 9:55 pm

Here are some photos of the rig I use for plotting F/D curves. When I reorganise my workshop the rig will be wall mounted.

To make the story a little more interesting I ran a test on my 45# Black Widow recurve to do a comparison against my new 43# recurve. Both bows are 58” n to n and virtually identical in limb profile. Brace height on the Greybeard bow is 71/4” the Widow 9” because of its forward handle design.

Both bows were tested to 29” DLPP.
01 Post To Support Bow.jpg
01 Post To Support Bow.jpg (90.51 KiB) Viewed 1693 times
02 Measure From DLPP.jpg
02 Measure From DLPP.jpg (55.36 KiB) Viewed 1693 times
03 Boat Winch.jpg
03 Boat Winch.jpg (166.13 KiB) Viewed 1693 times
The blocks clamped at the back of the riser are to stop the bow accidently rotating on the post.
04 Black Widow Ready For F_DTest.jpg
04 Black Widow Ready For F_DTest.jpg (133.04 KiB) Viewed 1693 times
05 Weight At 29 Inches DLPP.jpg
05 Weight At 29 Inches DLPP.jpg (56.77 KiB) Viewed 1693 times
06 String Angle At 29 Inches DLPP.jpg
06 String Angle At 29 Inches DLPP.jpg (120.1 KiB) Viewed 1693 times
07 F D Curve 45# Black Widow.jpg
07 F D Curve 45# Black Widow.jpg (97.26 KiB) Viewed 1693 times
08 F D Curve 43# Greybeard Recurve .jpg
08 F D Curve 43# Greybeard Recurve .jpg (99.2 KiB) Viewed 1693 times
09 Stored Energy Black Widow.jpg
09 Stored Energy Black Widow.jpg (112.26 KiB) Viewed 1693 times
10 Stored Energy Greybeard Recurve.jpg
10 Stored Energy Greybeard Recurve.jpg (111.86 KiB) Viewed 1693 times
At first glance the graph appears to indicate the Widow is storing more energy but the chart tells a different story. I believe the difference is because the forward handle design shortens the power stroke.

Daryl.
"And you must not stick for a groat or twelvepence more than another man would give, if it be a good bow.
For a good bow twice paid for, is better than an ill bow once broken. [Ascham]

“If a cluttered desk is a sign of a cluttered mind, of what, then, is an empty desk a sign?” [Einstein]

I am old enough to make my own decisions....Just not young enough to remember what I decided!....
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GrahameA
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Re: Force/Draw Rig. Black Widow vs Greybeard

#2 Post by GrahameA » Mon Dec 12, 2011 6:06 am

Morning Daryl
greybeard wrote:At first glance the graph appears to indicate the Widow is storing more energy but the chart tells a different story. I believe the difference is because the forward handle design shortens the power stroke.
Yes, I agree with that conclusion - I love numbers.

It will be interesting to see the numbers with chrono. The Black Widow may gain a little back with a slighty more efficent limb design.

p.s. - The has been plenty of drizzle.
Grahame.
Shoot a Selfbow, embrace Wood Arrows, discover Vintage, be a Trendsetter.

"Unfortunately, the equating of simplicity with truth doesn't often work in real life. It doesn't often work in science, either." Dr Len Fisher.
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Stickbow Hunter
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Re: Force/Draw Rig. Black Widow vs Greybeard

#3 Post by Stickbow Hunter » Mon Dec 12, 2011 9:11 am

That looks like a sturdy and safe setup you have made there.

Jeff
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longbow steve
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Re: Force/Draw Rig. Black Widow vs Greybeard

#4 Post by longbow steve » Mon Dec 12, 2011 9:34 am

Hey Daryl, Looks like a good setup. Is 9" the specified brace for the Blackwidow? How long is the string? When you chrono them can you drop the brace on the widow aswell? Will be interesting to see the results. Steve
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Gringa Bows
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Re: Force/Draw Rig. Black Widow vs Greybeard

#5 Post by Gringa Bows » Mon Dec 12, 2011 10:17 am

looks like a top set up Daryl :wink:
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Re: Force/Draw Rig. Black Widow vs Greybeard

#6 Post by greybeard » Mon Dec 12, 2011 10:48 am

Stickbow Hunter wrote:That looks like a sturdy and safe setup you have made there.

Jeff
Jeff, the smallest capacity boat winch I could get is rated at 900kg so it should be up to the task.
longbow steve wrote:Hey Daryl, Looks like a good setup. Is 9" the specified brace for the Blackwidow? How long is the string? When you chrono them can you drop the brace on the widow aswell? Will be interesting to see the results. Steve
Steve, I can't find the specs sheet for this bow but from memory brace height is around the eight and a half to nine inches. String Length is 55 ¼”.

When we get some decent sunshine I will set up the chrony and post the results.

Daryl.
"And you must not stick for a groat or twelvepence more than another man would give, if it be a good bow.
For a good bow twice paid for, is better than an ill bow once broken. [Ascham]

“If a cluttered desk is a sign of a cluttered mind, of what, then, is an empty desk a sign?” [Einstein]

I am old enough to make my own decisions....Just not young enough to remember what I decided!....
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Stickbow Hunter
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Re: Force/Draw Rig. Black Widow vs Greybeard

#7 Post by Stickbow Hunter » Mon Dec 12, 2011 11:35 am

greybeard wrote:Jeff, the smallest capacity boat winch I could get is rated at 900kg so it should be up to the task.
Yeah, I think that should be adequate. :lol:

Jeff
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