Questions about lamination

reini · November 21, 2017, 02:33:00 AM

Hi there,

building a D/R longbow I recently ran into a big problem with one limb laterally deflecting. Unstrung, the limbs were straight, when strung the upper limb leaned to one side, with almost no twist.

I'm using a bow form with airhose.
Stack from back to belly was: glass, veneer, carbon, actionboo, walnut, veneer, glass
Glue was SmoothOn.

The checks i did: tips ok, grooves equal, bow form ok, limbs unstrung not tilted/twisted or such.

Question 1: What could be the reason for this?!
As it was a bi-lam, could it be the walnut-lam causes such a deflection? Or even the glass?

Question 2: To avoid such problems, i'm thinking of building my walnut-lams out of multiple stripes (like actionboo). What kind of glue should be used for that? Epoxy? Or Elmer's glue? Anything else (e.g. edge/flat grain) to pay attention to when building this 'action-nut' lams?

Thx reini

mikkekeswick · November 21, 2017, 03:27:00 AM

I can't think what else it could be but I doubt it is the walnut.
How thick is this lam?

reini · November 21, 2017, 04:25:00 AM

walnut is 2.7mm (.1"), taper .003
boo same as walnut

glass both 0.8mm (.035")
carbon 0.5mm (.02")
veneers both 0.5mm (.02")

monterey · November 21, 2017, 10:35:00 AM

Where did you purchase the glass?

Did you do any or possibly too much sanding of the glass surface?

I may not understand, but it seems like you have a total of .006 taper in the limbs. That seems like a lot. .003 would be more typical of an R/D bow.

How wide are the limbs at the fades?

reini · November 21, 2017, 11:31:00 AM

hi monterey,
glass was purchased in Germany, Bearpaw Power glass, i did not sand it.

Total taper was .003,
and width at fadeout was about 1.38", at the tips 0.63", bow length 66".

Mysterious case, isn't it?

Crooked Stic · November 21, 2017, 01:26:00 PM

Pictures? I assume you worked everything off a center line?

Crooked Stic · November 21, 2017, 01:31:00 PM

If you walnut and your boo are both .003 then you have .006 total. Measure the weak side and compare with strong side thickness.

reini · November 21, 2017, 02:46:00 PM

Sorry, no pics as i've already cut off the limbs to reuse the riser.

Total taper was .003 (.001+.002)

Think the center line was ok, checked it with a string from mid tip to mid tip. Unstrung i couldn't see any problem, so the center line should have been right?

thx reini

November 21, 2017, 04:51:00 PM

Welllll.... I guess that solves that...

Most guys drag a thread on and on about how they are gonna fix their problem or save their bow... You are like, 'Screw It', just make a new one... LOL...
Good for you Bro... Already moved on...

reini · November 22, 2017, 01:37:00 AM

Welllll...., Shredd: my intention wasn't to save that one bow? Trying to correct that deflection i ruined the limbs, they got too narrow.

I'm just searching for a solution to avoid such problems in the future.

Dazzad · November 22, 2017, 02:29:00 AM

Hi Reini,

The limb that demonstrates a non-twisting, sideways 'lean'..........If you still have it, have you taken a thickness measurement on one side of the limb, and then a thickness measurement of the same section of the limb but on the other side??
I would be hoping to discover a differential in limb thickness across the width of the limb, with the thinner side of the limb being the direction of leaning. I say 'hope' because that would be a nice and obvious reason for this strange happening, and it would point to a fault in the production of one or some of your laminations.

At least this would be easy to check prior to assembly on your next bow, and would be very unlikely to be an issue again...

Darren

reini · November 22, 2017, 02:57:00 AM

Thx Darren!

Yes, i still have the limbs and will check this asap.

I'm making the lams myself on a thickness sander and they should be ok. But could also be the veneers or glass thickness, let's see ....

Crittergetter · November 22, 2017, 08:41:00 AM

I've had this happen recently. After all the investigation I could do I determined it was the veneers themselves. I used some b/w ebony veneers that a buddy gave me. It has quite a lot of character on one end with streaks running off of center. I "think" the grain structure made the side with character more dense than the side without therefore weakening the one side.
It's the only possible explination I could come up with. Luckily it wasn't very drastic and I was able to correct it with a little heat.

November 22, 2017, 10:26:00 AM

Hey reini I hope you know I was supporting you not making fun of you... True meanings can get lost in posts sometimes... I just found it funny that you were so casual about it where some guys take a loss of a bow way too serious and spend way too much time trying to fix a a F-up that will never be right and that they could have built two bows by then...

By the way I would check limb thickness side to side... Don't assume that they are even... Maybe even run a lam or two thru your thickness sander and check them for even thickness...
Double check your form for squareness and straightness... Also putting a form in an oven... The heat may warp it especially if the light bulbs are on one side...
Just some ideas I am throwing at yah...

Crooked Stic · November 22, 2017, 11:52:00 AM

Dazzad exactly wha I suggested.

reini · November 22, 2017, 01:53:00 PM

Hi again,

checked the limbs as Darren+CrookedStic suggested and yes, i found a difference in thickness between sides!

Only .006" but exactly in that area where the limb was bending sideways.
I can't exactly determine now which part of the stack was causing that, but for the future i'll check all parts especially in this respect.

Also checked my form again as Shredd suggested and also yes, it had slight inaccuracies!
Seems that some areas have minimally changed in the oven, I've corrected that now.

Many thanks, seems we've solved that mystery.

@Shredd: everything ok! I'm from Austria, so my English (writing AND understanding) just isn't the best. Hope i didn't step on someone's toes!

kennym · November 22, 2017, 02:12:00 PM

You might put the stack together next time and measure before gluing, might be able to flip a lam or two to get uniform stack.

November 22, 2017, 09:10:00 PM

No reini... You're Cool Bro... I just wanted to make sure that that you did not think I was messing with you...

What Kenny said is a good idea...

Also... I don't put my form in the oven because of the fear of warping... I post cure my bows after I take them off the form...

If this happens again for some reason... Maybe some strategic sanding in the faulty area could possibly solve the problem and save the bow...

Good Luck on your next build...

Holm-Made · November 22, 2017, 10:16:00 PM

When you initially profile the limbs, leave the tips a little wide. Cut the string grooves, string it and check it. Having an extra 1/16-1/8th inch to work with will allow you to be able to straighten the limbs out.

reini · November 23, 2017, 01:07:00 AM

Thank you all!

Next bow will be started this weekend and I'll include all your suggests.

I'm confident now, this one will get perfect ....