Dummy's Guide to a HH Bow Build - Please

[longbow1964]

Hello, Trad Gang:
(Lord, I love this site.)  Anyway.  First build. Help!, please.  A little guidance - in 4-yr-old language - would be greatly appreciated.  Want a 70# HH as short as possible for maneuverability in the brushy swamps of South Louisiana. (I have a beautiful Mad Dog R/D, but the HH Bow Build Bug bit me.) Discussing details of an order with the great Missourians at Kenny's Custom Archery who sent me here for specifics on parallel lams, tapered lams, dimensions for width and length and for riser, etc.  I see Bingham's charts for the 70# at 68".  I've read Byron Ferguson's suggestions in Becoming the Arrow.  But I was hoping to go shorter - 64". Maybe 62". Do I order for a 68" at 60# and achieve my desired weight by shortening the OAL?  Could also use a dummy's guide to  building a bow form with 1" backset. Apologies for stacking my questions ... I'm sure some of this has been covered before, but I haven't been able to find exact details for what I want.  Thank you all!  And Happy New Year. - Respectfully, Mark

[bsv]

Traditional Bowyer, More unnecessary Fun. by Jack Harrison
Kustom King Archery on sale $59.00
it's a must  (IMO)

[jsweka]

Here are two builds I did a while ago.  These were for a 68" bow off a straight form that results in a touch of string follow after first stinging.  These, might help you with the process at least, but I'm not sure how both chopping length and adding 1" reflex would influence the lamination thickness you need.

What's your draw length?  If it's around 27 - 28" I definitely wouldn't try going any shorter than 64" or you'll end up with a string angle exceeding 90 degrees and a lot of stack.  Really, I don't think there is much difference in maneuverability between a 68" and 64" bow in a treestand, so I'd recommend going with a length that is appropriate for your drawlength.  If you really want a short bow for the type of hunting you do, a deflex/reflex design would be better.


  http://tradgang.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=125;t=009131;p=1#000000  

  http://tradgang.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=125;t=004759;p=1#000000

[longbow1964]

Thanks, guys!  Doing my homework now.

[longbow1964]

Thanks, John.

The physics of the lams has me perplexed. Let me get this right.

For a 68", 55 - 60 lbs @ 28", you ordered the following:

0.050 black glass
0.070 actionboo
0.080 actionboo
0.080 actionboo
0.110 curly maple (0.002 taper), and
0.050 clear glass

It ended up being 64#@28 by 68".

If I want a 70#@27 by 66, what would I order from Kenny?    
 
Thanks for your patience.

- Mark

[canopyboy]

As for how make a form, what method of clamping are you going to use?  Make a template for half the bow.  For 1" backset, I would use a parabolic curve.  If you want to make your life easier, make the curve starting at your fades.  But a little reverse taper in to the form in the riser area at the same taper as your lam stack that goes behind your riser (excluding your last lam going up the belly, 0.004/in?)  That way you can make the back of your riser flat and have good clamping.

Once you've got the curve you want, make it happen in a piece of 1/4" Masonite.  Then use a flush trim router to copy it to your rough cut form, 1/2 at a time keeping careful alignment as you flip it.

You can make your bow a little shorter and still perform at a longer draw if you shorten up the riser a little.  You need to be a little more careful with your fades, but I've talked with a couple hill style builders who support this idea -- basically you get more working limb and a little more draw before your limb tip bends around to 90 degrees with the string.  But like Sweka asked, what is your draw length?

As for scaling the Bingham's numbers, it depends.  Basic beam theory has been good to me for calculating lam stacks in a straight bow.  And each limb is a cantilevered beam, starting at the fade and ending at the string nock.  If you shorten the riser and keep the working length the same, you don't want to change the stack.  If you are shortening the working limb, you can ratio the moments (force times distance - your distance changed.)  With your reduced moment, you can calculate the required cross sectional moment of inertia (b*h^3/12) needed for the same deflection at the lower moment.  Simplifying into an equation:

new stack = cuberoot(new working length/old working length) * old stack

Hope that makes sense to other people.  If not, let me know and I'll try to do better.

-Dave

[Magnum in Ms]

Just going from a 68" bow to 66" with same stack will add about 5lbs

[jsweka]

OK - Here's my cipherin' for ya Mark....

If you start with that recipe you got from my build with a riser length of 16" and total stack of 0.440 for a 68" bow and cut the length down to 64", and using the equation Dave provided (he's a real engineer, I'm just a number crunching biologist    ), you'd need a stack of 0.430.

new stack = [(26 - 24)^(1/3)]*0.440 = 0.430

That should give you 63# @ 28".  The same bow would probably pull about 60# @ 27".

bjansen posted a stack calculator here a while ago
 http://tradgang.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=125;t=007699;p=1#000000

Inputting 0.430 stack and 60# into the stack calculator estimates a total stack of 0.453 to hit 70#.

Now that is with the design I used in that build and if you add more tapered laminations, change the length of the riser, or change the limb width, things will change. (I used 1.25" wide from fade outs to 18" from the center of the bow, then tapering to 1/2" at the nocks).

Also, the amount that you round over the edges of the limbs will have an influence on your final weight.

I'll generally try to overshoot my intended weight by a little. Once I've cut the limb profile, I'll get a string on it.  If it's more than 5 lbs above draw weight, I'll sand the edges of the limbs to knock a little more weight off and then stop when I'm about 5 lbs over the final desired weight knowing that I will lose at least 3-5 lbs just knocking the edge off the corners of the limbs.

I've gotten to where I can be within a couple lbs of a desired draw weight with the design in that build along.  However, my next bow I'm planning to build, I will be adding some more tapered laminations and decreasing the width down to 1 1/8".  So it's kind of experiment.  Once you've got that first one done, you can get a much better guess as to appropriate stack on you next one as long as you keep everything else the same.

Even the professionals miss their desired weight from time to time and those are the stock bows you see on their web sites and the bows they bring along with them to shows.

[longbow1964]

Gentlemen, I must say that ever since picking up a longbow and wooden arrows, I've felt as if I've entered a helpful, friendly universe. From Kenny at Kenny's Custom Archery and Mike at Mad Dog Bows, to Surewood Shafts, Simmons Broadheads, and Three Rivers Archery, I've met nothing but patient, kind assistance.

That sad, I'm afraid the math is lost on me.  Boxing, rugby, and law school ruined the math part of my brain - in that order, I think.  But I like the challenge!

I'm betting Kenny understands the ciphering you guys are offering. Or at least the final numbers.

Here are some answers to the questions:

Draw length: just shy of 27" at full-draw, less when the hogs charge in.

Clamp type: Plan A is my box of Harbor Freight spring-loaded clamps, unless you guys recommend otherwise.  Plan B is the innertupe strip method.

Thanks again.

[longbow1964]

Can't download bjansen's stack calculator.  Perhaps it's no longer available.  Anyone kept a copy? [email protected].  Thanks. - Mark

[jsweka]

Mark,

I'd go with the inner tube method before the spring loaded clamps.  If those clamps don't all have the same springy-ness you won't get even pressure across the entire bows and could end up with some waviness.  I think you might also have issues getting good glue lines in the fade out areas.  The best method is the air hose because that guarantees even pressure across the whole bow.

I emailed you that stack calculator.

[longbow1964]

Hunting for a bike shop.  Next build will be air hose.  Thanks again.

[bowhntineverythingnh03743]

If ya follow the guys here they wont steer you wrong. Jsweka helped me a ton on my first bow and I listen to every word he said...

 

 

 

I'm a 28 inch draw and make my straight bows at 64 inches tip to tip and have never had any issue. May try a 66 for the next one that is in the works... This is the bend I get at a 62 nock to nock...

 

Hope this helps... Justin

[longbow1964]

Justin,
Yes. I followed your build, and continue to reference it. Great advice.
How is your bow holding up?
By the way, what are the dimensions on the air hose and fixtures?  I might have access to some free air hose.
Thanks.
- Mark

[BenM]

Mark
I just glued up my first hill yesterday.  I saw you mention finding a bike shop, I did the same and the bike shop owner turned me onto "rim strips" I believe anyhow they are a rubber band that is sandwiched between the bike wheel and the tire tube.  They are varying circumferences but about 3/4" wide.  I bought a bunch for $1 a piece.  Also look for a truck tire tube. I got one from a buddy and cut it into strips.   They were quite a bit stronger.   The rim strips worked great though.

[longbow1964]

michels_benny,
Thanks!
How long did you cut the strips?
Cheers.
-Mark

[bowhntineverythingnh03743]

Bows are doing great with no issues... My form is 68 inches long. 1.25 inch gap between top and bottom form. It is 1.5 inches thick and 14 inch for height. The metal parts are just rafter supports I got from the orange box store with .5 inch holes dropped through.

Any other questions just ask.

[BenM]

I cut the truck tire tube into slices     If that makes sense.   You end up with a 12" or so rubber band.  The width is up to you.  Most of mine were 1/2"-3/4".