"Rube Goldberg" Spine Tester.

How to's, questions, and build alongs for those traditional archers who are interested in building their own custom arrows.
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Captainkirk
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"Rube Goldberg" Spine Tester.

#1 Post by Captainkirk »

OK, this is a fairly simple, if not somewhat Neanderthal, spine tester I made up. It's not dead-nuts accurate, but then I didn't spend 200 bucks on it either. :roll:

Here's what you need:
*Section of board, roughly 30" long, width and thickness depending on your preference
*2 cup hooks
*A rudimentary ruler of some sort. I Googled "printable rulers" and found a site with one that fit my needs. (I can't remember which site now)
*A fraction to decimal conversion chart
*A spine conversion chart. I also found this by Googling it and printing it out (again, can't remember which site. Getting old is a bitch sometimes... :lol: )


First you cut a board roughly 30" long and mark it at mid-point. From mid-point, mark out 26" total from hook to hook (13" from center) for wood arrows, for aluminum or carbon shafts use 28" (14" from center) and a 1.94# weight. Yes, they are different.

Cup hook installed...

Image

Now, lay a bare shaft across the hooks, get a straight and level view across the top of the shaft and draw a horizontal line as a reference point. Here at this intersection of the vertical centerline and the horizontal reference line is where you will place the zero mark of the scale (ruler).

I used a scale (ruler) measured in 16ths of an inch. You can go finer if you desire, but you get to the point where you are splitting hairs; throw in a little parallax error and I think you are wasting your time... but that's just me.

Image


Now you need a weight of some sorts, to be hung from the centerline of the arrow directly below the centerline mark. If you have nicely aligned the edge of your scale with that line, it's a piece of cake to know where to hang that weight. I used an old safety wire container and the snipped-off end of a wire coat hanger. I placed the container on a food scale and filled it with #9 lead shot that was lying around on my reloading bench until it was just a hair under 2#, then screwed the top and hanger on. As you can see, there is a hole in the center (for the safety wire to come out of) that you can continue to add shot one at a time until you reach 2#...exactly. :mrgreen:
Any old container is suitable provided there is enough room for 2# of weight and a way to hang it.

Here you see the safety wire container filled with lead shot...

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...and the somewhat Neanderthal-looking, yet effective hook.

Image

There are two requirements for this thing to work;
a) Rock-solid mounting
b) Room for the weight to hang unobstructed.

I solved both issues by simply attaching the board to the front of my work bench with a couple of deck screws, who volunteered (bless their little hearts).

"So, how does it work, Captain?" you ask...

Quite well, actually... :lol: :lol: :lol:

No, seriously...it works like this:
*Center a shaft by eyeballing the distance from each end to the hook. If you want to get nit-picky you can measure, but this is trad archery..we shoot instinctively, fellers. 8-)

*Get yourself down to eyeball level and align the top of the shaft with your horizontal line.

*Hang your weight right on the vertical line and without moving your head or eye alignment, let the weight of the 2# weight pull the shaft down. Read the scale in 16ths (or whatever) where the top of the shaft now rests.

*Reduce to lowest common denominator (e.g. 10/16= 5/8)

*Find the fraction to decimal conversion (e.g. 5/8=.6250)

*Refer to your spine conversion chart; .6250 deflection= between 41 and 42 spine.
There you are, easy-peasy. I'm sure there are more accurate ways to do this, but it gets you very close, if not dead-nuts. The important thing is to not let your view change from static to weighted position. I recommend checking and double checking each measurement for consistency, maybe even 3 times. It only takes a second. Once you've done it a few times you get pretty quick at it.

The view of the shaft at static, referencing the horizontal mark with the top of the shaft...(camera parallax evident in photo)

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...hanging the weight; measurement reading is 10/16 (reduce to 5/8)

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Checking the fraction-to-decimal conversion chart...

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Finding the decimal to spine conversion...

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...and, there you have it. Between 41 and 42. Close enough for Government work.
Aim small, miss small!

Captainkirk
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Joined: Tue Aug 26, 2014 8:19 pm

Re: "Rube Goldberg" Spine Tester.

#2 Post by Captainkirk »

One more thing; When I found my printable ruler, I did a copy-and-paste so it filled an 8.5 X 11 sheet of paper (multiple scales) then printed it on peel-n-stick label paper, after printing I covered the front with clear packing tape to give a somewhat laminated effect. Cut out the scale, peel off the backing and stick it to your Rube Goldberg and it should last a very long time. And if it doesn't...you've got spares. ;)
Aim small, miss small!

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Graps
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Re: "Rube Goldberg" Spine Tester.

#3 Post by Graps »

Do I hear banjo music ?
"Maybe the truly handicapped people are the ones that don't need God as much." ~ Joni Eareckson Tada

Carpdaddy
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Re: "Rube Goldberg" Spine Tester.

#4 Post by Carpdaddy »

Good job Kirk, I'm impressed.

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Shadowhntr
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Re: "Rube Goldberg" Spine Tester.

#5 Post by Shadowhntr »

That is awesome! Cheap yet effective! I think that fits right nice in most trad shooters mind and pocket book. I like it a lot!
The element of surprise can never be replaced by persistence.

Captainkirk
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Joined: Tue Aug 26, 2014 8:19 pm

Re: "Rube Goldberg" Spine Tester.

#6 Post by Captainkirk »

graps wrote:Do I hear banjo music ?
Not just banjos...DUELING banjos.
Aim small, miss small!

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Graps
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Re: "Rube Goldberg" Spine Tester.

#7 Post by Graps »

:lol:
Ain't nutn' wrong with that .
Buy the way , I have made them with a cardboard box with a coat hanger wire indicator and a half gallon milk jug with water .
Talk about rocket science .
"Maybe the truly handicapped people are the ones that don't need God as much." ~ Joni Eareckson Tada

Captainkirk
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Posts: 12787
Joined: Tue Aug 26, 2014 8:19 pm

Re: "Rube Goldberg" Spine Tester.

#8 Post by Captainkirk »

graps wrote::lol:
Ain't nutn' wrong with that .
Buy the way , I have made them with a cardboard box with a coat hanger wire indicator and a half gallon milk jug with water .
Talk about rocket science .
As long as your rocket gets you to the moon...that's all that matters! :mrgreen:
Aim small, miss small!

Longbowfanatic
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Joined: Fri Sep 08, 2017 10:41 am

Re: "Rube Goldberg" Spine Tester.

#9 Post by Longbowfanatic »

Very cool! I like it!

cap4382
Posts: 105
Joined: Tue Sep 20, 2016 9:49 am

Re: "Rube Goldberg" Spine Tester.

#10 Post by cap4382 »

Yep, made myself one awhile back. Mines not nearly as nice though, 2-16d nails and a Ziploc filled to 2lbs.

Btw, i checked some of my 340 spine carbons @ 26" centers, deflected 18/64s (.28125"). That converts into a 92-93lb AMO spine. Oddly enough, my 90-95lb woodies take the same 275gr up front as the 340s to fly right. The woodies only weigh about 300 gr heavier. Strange coincidence....

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