# Home Made Draw Board for Measuring Draw Force Curves



## SD40 (Dec 25, 2005)

HDT,

Very nice!, I made something similiar awhile back for the wheel bows. Barebow setup also it is/was was handy for checking the eccentric timing. I like the ruler and the worm gear winch
if you still have the winch model number PM me please.
I used the finest smallest gear tooth boat winch I could locate at the time also a Dutton Lainson 600#. Your worm drive is a much better
set-up. I used a arrow marked in inches for measurement. If one of the kids stops home this weekend I'll get them to take a pic and I'll try get them up.


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## Hank D Thoreau (Dec 9, 2008)

Here is the model info on the Dutton Lainson Worm Gear Winch. I bought if directly from the Dutton Lainson website. The worm gear is what makes this really nice and provides the precision needed to draw carefully and precisely so that you can really see what is going on. I would expect it to be even better for a compound. I drew one of my compounds and was really cautious to start out so that I would not overdraw the bow. I shoot old wheel bows with fingers (must figure since there is a barebow in the winch of the picture) so it is not like there is a really hard stop to tell you that you are fully drawn. I am also a novice with compounds, I shoot old bows but have not done much work with them. I would be interested in any tips that you have for drawing a compound on a board - specifically, how do I know when I have it fully drawn. The only flaw so far is the scale. Archery scales have short shutoff times and they freeze on peak weight. I want to go up and down and record weights. I have a mechnical scale on order that I will have on Tuesday. It is a bit large but will measure to 1/10th of a pound, which is fine for a draw force curve. I am planning to produce DFC's for compounds as well which should be interesting.

By the way, the clamp is am important part of the design. It is there to keep the bow from rotating since the grip is not in the center of the bow. As a result, I am not pulling parallel to the winch. I considered a few options including: two supports and a movable sinle support as well. I needed flexibility to test many bow and riser designs and the clamp ended up to be the simplest and best solution. I flip the clamp to the other side when drawing a right handed bow.

Part Number: 11011
Product Name: WG1500 w/HEX drive, bronze
Quantity: 1
Unit Price: $89.99


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## SD40 (Dec 25, 2005)

HDT.

Sorry for the tardy reply, I've yet to get any photos of my ******* engineered draw board. I used some .100 aluminum and formed it like a three finger draw and lined the string contact area with moleskin.
It attaches/slips over the hook on my hanson bow scale and the other end of the scale is tied off to my winch rope. Its crude but with the simulated draw hand if you will?, the wider contact eliminates the need for a clamp to prevent the bow from rolling back when being drawn. I know a pic is worth a thousand words, I'll get some pics taken tomorrow.
Wheel bows and full draw?, parallel, step, and even most mild energy wheels usually also a step wheel (reduced diameter cable side) if you were to draw a line through the center of the axle hole directly across or 180 deg. to the other side of the wheel. At the "point the string or cable teardrop with string attached leaves the wheel directly opposite the axle as mentioned above, is the bottom of the valley for a given draw length". Round wheels have a very generous valley probably 3/8" + either side of that mark without any loss of gain of weight or performance. I know a pic is worth a thousand words!. Tomorrow.


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## Scott.Barrett (Oct 26, 2008)

I have the same setup for my compounds....got a worm gear winch at Harbor Freight for $20....best investment I've ever made!


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## Hank D Thoreau (Dec 9, 2008)

My mechanical scale should be here on Tuesday. That should solve my scale problem. I tried tying my Easton scale to the winch cable with a nylon cord, but it turned off as well and also would only report peak weight (no backing up). The scale I am getting is big, over 9 inches in diameter, but that should make it easier to read. I am eager to see a picture of the simulated draw hand that SD40 is using. I may need to try the same. Once I get the scale worked out, I will repeat some of my limb studies that I performed in the past. I am also planning on measure drawforce curves for my compound bows and calculating the stored energy. I will be interesting to correlate stored energy to initial velocity measured with my Chrono. I wish I had a hooter shooter to ensure that I am getting the best velocity data.


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## SD40 (Dec 25, 2005)

Hope these come through!


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## pilotmill (Dec 10, 2008)

Hank,

I use a similar set up. One thing to add is a safety line between the hook and the string. I just put a loose piece of paracord tied to the main hook and the string in case the scale should let loose, the safety line will catch the bow from letting completely loose. Gar.


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## SD40 (Dec 25, 2005)

HDT,

Simulated draw hand may have not been the best choice of words, not a work of art but the concept works!. Probably closer to a fat two fingered draw.


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## Hank D Thoreau (Dec 9, 2008)

Here is the mechanical scale I received today. It came 2 days early from UPS -- go figure. The scale seems to work fine. The biggest issue is accurately measuring the draw stops in one inch intervals during the length of the draw force curve. For this I have returned to a method I use when doing DFC's by hand. I place a round metal refrigerator magnet clip on a Easton draw length arrow at the distance that I am measuring. I then winch the string until the round base of the magnet touches the back of the riser. It does not have to be a magnet, it just turned out that I had a magnet that really worked well for this. Move the magnet in one inch intervals and measure until all points from brace height through about 33 inches are measured (I have a 32 1/2 draw so I need to go long). The other problem is moving back and forth between the winch and the string (or draw length arrow) to fine tune the stopping point for each measurement. I am going to hook up an electric buzzer to the magnet so that it will go off when the magnet touches the back of the riser. That should work really well and save me a lot of time. Here are some more pictures. I will update this when I have the buzzer in place (after a trip to Radio Shack). You can see the round refrigerator magnet on the Easton draw length arrow in the second picture.


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## Hank D Thoreau (Dec 9, 2008)

By the way, is this a barebow thing? I have a Best Moon with Border HEX5 limbs on the board; SD40 has a Greenhorn Sirius with HEX5 limbs; and I know that Gar (Pilotmill) is a barebow shooter as well.


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## pilotmill (Dec 10, 2008)

I like the scale, where did you get that Hank?


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## Hank D Thoreau (Dec 9, 2008)

I got it from Amazon per a recommendation from someone who responded to a query I made on the DIY forum. I have not been able to get around problems with digital scales turning off or measuring peak weight. There is a pricey digital scale that is an alternative if this scale does not work out. It has a 10 minute shutoff (which I was told could be turned off) and will go both up and down. Also, got that recommendation from my post on the DIY forum. I am still testing the reproducability of the Taylor scale versus the digital. Also, the scale is large and weighs a lot so that may affect the readings. So far it does not seem to affect the weight.

Taylor Dial Style Industrial Hanging Scale, Weighs to 70-Pound


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## SD40 (Dec 25, 2005)

HDT,

It appears the barebow guys have similiar limb tastes!.  Actually I bought mine (Borders 2pr not at the same time tho) after following your limb thread @ Archery Interchange, Thank You!. 

The reason I was excited about your winch is I'm pondering how to mount it underneath or along side the jig up front where I can watch the draw arrow, stop as needed, then record the weight.

I think a simple hole and a pulley would permit that or maybe some type of idler around the very end then underneath?.


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## Hank D Thoreau (Dec 9, 2008)

Okay, so here is my latest innovation. I have hooked the clip on the Easton draw arrow to a buzzer so that when the round disc hits the foil on the back of the riser, the buzzer goes off. I can put the clip on at any point. I will move it an inch at a time to construct a draw force curve. This keeps me from having to go back and forth between the bow and the winch so that I can be sure of hitting my marks. I had to tape foil to the back of the riser to get sufficient conductivity to set off the alarm. The yellow alligator clip is attached to the foil (blocked from view). So far my measurements with the big mechanical Taylor scale are consistent. I got the same values at 28 and 32 inches today that I got yesterday. I will measure the full draw force curve when I have enough light to see what I am doing.


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## Hank D Thoreau (Dec 9, 2008)

SD40 said:


> HDT,
> 
> It appears the barebow guys have similiar limb tastes!.  Actually I bought mine (Borders 2pr not at the same time tho) after following your limb thread @ Archery Interchange, Thank You!.
> 
> ...



Creating all those draw force curves on the Archery Interchange thead was a real challenge and very tiring...without a tool like this draw board. Now if only I could get Sid to send me some HEX6 limbs to test .... and shoot.


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## lizard (Jul 4, 2003)

I'll take a picture of something that looks pretty much like these things, and was given to me by one Darrell Pace! Will post it very soon, so keep checking! It is VERY fancy, and VERY precise! I am certain yours is very precise too, but this one is just plain neat, I think made by, the late, CHARLIE PIERSON!


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## Hank D Thoreau (Dec 9, 2008)

Liz, looking forward to seeing your drawboard. Maybe, there are some ideas I can take from it to make mine better.


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## Hank D Thoreau (Dec 9, 2008)

Here is my first drawforce curvce using my drawboard. I chose my field bow, a Bernardini Nilo with 34 pound PSE ProElite limbs. My draw is 32 1/4 inchs.

With the mechanical scale I could see noticeable, and sometimes quite large, creep that was not visible with a bow scale. Bow scales measure peak weight. I am still testing to see where the creep is coming from. I reinforced the drawboard base just in case it was bowing. I found that the Nilo would lose a couple of tenths of a pound after each movement and then stay steady. I took the steady weight. I put a Pearson Pro Classic compound bow on and it lost considerable weight after each movement. So did a one inch tubular climbing sling. I am not sure if the creep is coming from the bow or the drawboard. The fact that I get differents degrees of creep depending upon what I pull seems to point toward the bows. I am still investigating.

The DFC that I measured was much smoother than previous curves that I have done by hand using an Easton scale and draw length arrow.

The brace height for the bow was 9 3/4 inches
As a validity check, I measured the draw weight by hand at two lengths using my Easton scale.
28 inches 32.3 with Easton scale; 32.7 with Drawboard
32 inches 41.3 with Easton scale; 40.5 with Drawboard

Included in the chart are draw weight in pounds, stored energy in ft-pounds (both using the axis on the left); and store energy per weight on the fingers (displayed on the scale on the right)


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## beleg2 (Dec 31, 2005)

Hi,
I found some creeping on my scale and it was from the coil as it moves in the cylinder of the scale.
Thansk for sharing your info.
Martin


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## Hank D Thoreau (Dec 9, 2008)

I have discovered the major source of creep, the cable. I changed to a smaller 1/8 inch cable, this time uncoated. I used a swag and thimble which gave me a nice tight end loop. I could not get a tight enough loop with the fatter coated cable. I am still picking up a small bit of creep that stabilizes pretty quickly. I believe that it is coming from the spooling of the cable. A flat unstretchable strap might work better than the cable. I have found that the setup creeps less if I run the bow to full draw and then back down before I start. That seems to get the little pops out of the system resulting from the spooling of the cable. I tested a compound bow which was giving me more problems that the recurves and it worked really well. Now I need to redo my draw force curves for my stable of bows...including, this time, the compound bows that I could not do using my previous method. I am interested in comparing the strored energy of the compounds to the recurves. The compounds are old finger bows and run about 53 pounds and less so they are not that much different than the recurves.


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## SD40 (Dec 25, 2005)

Hank D Thoreau said:


> Creating all those draw force curves on the Archery Interchange thead was a real challenge and very tiring...without a tool like this draw board. Now if only I could get Sid to send me some HEX6 limbs to test .... and shoot.


 HDT,

Yes I can only imagine, I Thank You again for being the beneficiary of your research!. The Border limbs, and being able to talk with the Sids @ Border has been huge!.
Oh, when your done with the Hex6s I'd like to try them also!. 

All Good,
Don;


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## Hank D Thoreau (Dec 9, 2008)

Below is a paste of a post that I did on the ArcheryTalk forum. I am comparing HEX5 to conventionally shaped limbs much like I did a year ago in this thread http://www.archery-interchange.net/f127/hex5-alternative-use-first-impression-26106/. I think that the curves are much smoother using the drawboard than my previous curves done by hand.

From AT:

Here is what you can do with recurve limbs. Next I am going to measure some compound bows which I could not do before.
I am comparing the radically recurved Border HEX5 to the conventional recurved PSE ProElite. I show the drawforce curve for the HEX5 followed by a DFC with both the HEX5 and PSE ProElite together. The HEX5 DFC shows stored energy and stored energy per pound on the fingers as well.

You can see that the HEX5 DFC does not have quite the sigmoidal shape as the coventional limbs (more flat). This is due to the fact that the HEX5 limbs are uncoiling the recurve for a much long portion of the draw (if I recall it is about 26 inches versus a conventional 20 inches). You can really see the difference in the first derivative curves which essentially are a measuring of stacking, i.e. how many pounds per inch the bow weight changes at each point in the draw. The normal rule of thumb is 2 pounds per inch. These curves show that you get a lot of loading early in the draw that then reduces until a valley is hit. This is the smoothest part of the draw cycle. The weight then starts to climb until the onset of stacking. The ProElite line is the same as all conventional recurve limbs I have tested including Border CXB. The HEX5 recurve pushes the valley to longer distances (since it is uncoiling the recurve for a longer distance). In this case the valley falls in the 27 to 28 inch draw ranges. The onset of stacking is also delayed to longer draw lengths. These results are consistent with previous tests I did comparing four limbs on the Border website about a year ago.

One issue I need to look at is that the HEX5 draw weights at 28 and 32 inches using an Easton scale and draw length arrow were much higher than produced on my Drawboard. The relationships look good though. I will need to run some tests with multiple scales to validate the abosolute numbers.

Here are the charts.


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## Hank D Thoreau (Dec 9, 2008)

Here is the final design. You can see the reinforcement with the 2x4's and the clamp holding down the back of the winch. Not sure how much they were needed. The big change was going to a lighter, uncoated 1/8 inch cable and using a swage and thimble for the end loop. The picture below does a better job of showing the buzzer hookup which really makes creating the curves much easier. The extended legs are so I can stand the drawboard up if desired.


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## Borderbows (Apr 4, 2009)

Hank D Thoreau said:


> Now if only I could get Sid to send me some HEX6 limbs to test .... and shoot.


Hank, you have certainly helped us disseminate information about how smoothness comes about, your 3rd party impartial information has been usefull and helpfull to many. We have had many a call to talk about these things, If your on the internet, download skype, lookup "borderbows" and you can talk to my dad, Sid, about such stuff. He knows more about these things than i do.
As for your question, what would you like, i'll see what we have? I know we have some 70" 38lbs that were the first of the final product prototypes.
We help those that help us, and without promting, or i suppose even knowing, you have helped us. for this we are greatfull. and for this, i suppose, your in our "to help" books. Part of our Border Family.
You dont have to say anything other than what you think is true. no more and no less. if we fall down on any such matters, its up to us to work hard and improve our product


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## Hank D Thoreau (Dec 9, 2008)

I am stuck here doing an all nighter for work. I was tempted to go out and test more limbs during a brief period of calm, but I would probably disturb the neighbors. I ran three scales against the HEX5 limbs today and got pretty consistent numbers. I validated at 28 and 32 inches using the mechanical Taylor scale, an electronic X-Spot scale and an Easton scale. I think the weight difference that I saw in my previous DFC's has to do with finding an accurate zero point on the scale -- especially when the apparatus is used horizontally. The consequence is that the weight difference is just a linear offset and the relationship between draw weight and force is not affected. I set up the board so that I can stand it up and winch down. That will provide the best and most consistent zero point if absolute values are critical. Actually, I am more interested in the profile of the curves which drives the feel and physics of the limbs. That relationship is more obvious with compound bows where cam design drives radically different feels. The effect of recurve limbs is more subtle but just as important since recurve shooters do not have the benefit of letoff.


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## Borderbows (Apr 4, 2009)

Have you looked into that hump that developes in the hex5 smoothness graph. the subtle hump at 21-22" This hump is something we find interesting, and it might be related to the angle of draw, and the angle of the tip. the two co-incide to make a mid draw odditie. It has been evident in every smoothness graph we have seen.
As for the cam profile, its an expensive game for those that have tooled up for mass production. i wouldnt want to retool all my limb presses for one model range. then retool again for a different one.
Limb profile in my opinion is a small scale production advantage.


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## Hank D Thoreau (Dec 9, 2008)

The hump is present in my previous curves (post #51 page 4 of the Archery-Interchange link). In those curves I started at a lower brace height and was able to show a peak at the start of the stacking curve (or smoothness curve depending on your perspective). The initial loading peak is followed by a valley and then another peak at stacking. Somewhere around the valley is a slight bulge that also shows up in my previous measurements. For the HEX5 it preceeds the valley. For the PSE Carbons I tested, it came after the valley and before stacking. It is more subtle but appears to be there after the valley for the Border CXB and Winstorm limbs that I tested. This could be the superposition of two limb behaviors - that of the recurve and straight limb. I think I will try a measurement at 1/2 inch intervals to see if I get more or less clarity in that feature. A second derivative curve may bring out the feature. I could produce that if I measure smaller draw intervals.


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## Borderbows (Apr 4, 2009)

did you get my question about hex6 limbs...
As for your question, what would you like, i'll see what we have?


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## Hank D Thoreau (Dec 9, 2008)

I see above. I appreciate all the support you have provided as well. 34 to 38 - 34 would be best, but all would work. These weights would be comparable to what I have been testing. Let me know and I will send you a check to cover shipping since I am on the other side of the pond.


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