What Happened?!? (Draw Weight)

[Skyhigh315]

Hi,

I've taken my first shot at bow building.  I got the fist-timer outfit from Bingham's.  I did the 62" hybrid for a starter.  Two of them--one for my 11-year-old son (30#) and one for myself (50#).  I'm pretty happy with how things turned out, though I've definitely gone through more riser wood than I bet most do (mistakes here and there).  Here's the problem:

My son's came out at 28# at 28" (which makes sense because I ended up taking more width off the limbs than I meant to to get them even/straight).

MINE came out at 41# at 28" !  Nowhere near the 50# I ordered.  For the second one, it's about 1/32" wider than the plans on the limbs (learned my lesson the first time).  

I'm trying to figure out what went wrong, and I'm concerned about the Smooth-On.  On the first bow, the squeezed-out glue was rock hard when I took the bow out of the press.  On the second one, I left the bow in the oven for FAR longer than the 4 hours, and the excess glue was softer and far more pliable.  If I got the mix wrong, or left the bow in the oven too long, could that explain the light draw weight??

Thanks in advance for your thoughts.

[jsweka]

Smooth on should always be rock hard when it sets up and the longer time in the over would not make it softer. (I cook mine for 8 hours.)

Perhaps you got the mix wrong, but really that's pretty hard to do - equal parts of resin and hardener by volume.  I can't explain why it would be softer. Something's wrong.

Your low draw weight - If the bow has held together, I don't think the smooth on would explain the lighter weight.  Maybe Binghams got your order messed up and sent you the wrong thickness of laminations.  Did you measure them?  They are generally very good in their customer service, but mistakes can always happen.

[bigbob2]

mine are also cooked for 8 hours and the glue is always rock hard. my ratio for the mix is 70G part A to 58 G part B for a four lam longbow.Works out spot on.

[Skyhigh315]

Yeah, I figured something as amiss with the glue  :(

I thought I mixed it pretty even.  the amount left in the can is pretty equal, too.  I guess if I hosed up the glue, it would probably affect the draw weight.  Too bad, too, because I really like how these turned out (looks-wise).

[kennym]

Just a thought, if you have enough reflex(tips ahead of riser back when unstrung) you could pike it an inch on each end and ( on my D/R at least )will gain about 6#.

Not advising to , just a thought.

Or build another one, you know you want to...   :D

[KenH]

The glue will not affect draw weight in any way.  If one of you lams was 'off' too thin by .01 it would drop the draw weight.  Did you measure the stack before glue-up?

Were some of the lams supposed to be tapered?  If they weren't that might affect the draw too.

[mikkekeswick]

Yes there is no way the glue can affect the draweight.
what did your stack measure before glueup?

[Skyhigh315]

[Skyhigh315]

[Skyhigh315]

Umm...

Measure......  yeaaaaahhhhh.

Ok, I'm getting the impression I was supposed to measure the stack before I layer it up :/  
Too late for that now, but I'll contact Bingham's and ask what the stack SHOULD have measured at and go from there.  If I have to pike this bow, it won't be the end of the world I suppose.

Yup...  That is one of the challenges of a bowyer...  Hitting the draw weight...  That comes in time, after making several bows at the same length with the same materials...  I find for a hybrid you are generally better to error a bit on the heavier side and then narrow it down or trap it to reach your weight in which can also give you better performance...
   Sounds like you did not mix the resin thoroughly or get the proportions right... I weigh my resin out using one vessel and always put a bit more of "A" into the mix...  Example 70grams of "A" to 60grams of "B"...That way you can't go wrong...  Always use a square stick if you are using a sharp cornered container such as a dixie cup...  Make sure you scrape all the sides and bottom several times and mix very well...
   Before shortening that bow I would see how it shoots...  It may make a good practice bow...  And then just make another one...  If you have a long draw you may not want to shorten it...

[Bob T.]

Did the smooth on ever get hard? If not, I would be very careful drawing the bow as your bow might very well come apart. Safety glasses come to mind.

[Skyhigh315]

Thanks, Guys!

Yeah, Bob, I did save some of the excess to go back and check.  Yes, it's hard now.  I've put about 200 shots on the bow since I finished it on Sunday.  So far, so good...  I definitely think I'm going to pike this one if it continues to shoot well without coming apart.

My son's is awesome, though!

How do you post pics on here?

[Skyhigh315]

http://i1064.photobucket.com/albums/u375/skyhigh315/20161024_150217_zps1khi2zet.jpg

[Skyhigh315]

UPDATE:

So, after talking to the VERY kind folks at Bingham's, they've concluded that there's really just no way of knowing how/why the 50# bow could come out 40# without significant errors/mods to the design.  One interesting detail that came up, though, is that the lam thickness for a 50# bow should have been .340.  In my case, this bow came out at around .310 from the bottom of the tip overlays all the way to the beginning of the riser fade.  That's without me sanding ANY of the back or belly as Bingham's bows seem to come out pretty spot-on tillered off the press.  I looked on their chart, and it seems a 40# bow should have a lam thickness of .310.  Coincidence?

I sent them detailed pics (showing the limbs against the template to show I didn't over-sand it, and also showing the intact glass thickness on the back and belly) plus a video of me taking mic measurements along the length of the limb.  I'm just waiting to hear back what they think.

I feel like I would have needed to sand off 3/4 of the glass to go from a .340 to a .310....   :(

 

What do you guys think?

[Skyhigh315]

Here are some pics of the finished product: