Making your own fiberglass lams for bowbuilding

[dfrois]

Right...I think I have the images thing sorted...just needed to wait a bit. Let`s try...

This is the fiberglass weave that I used. It was just a bit leftover from days gone by...
 
What I did was remove the transverse fibers, leaving only the longitudinal ones. They were fairly easy to remove...
 
The removed fibers are close to 3 feet long, which is the width of the weave...
 
This is the form I used: two wood bars, wrapped in plastic, with two aluminium strips screwed to the sides. The idea was to stop the fibers coming out, while allowing the excess resin to pour out through any small gaps (which it did):
 
As explained on my previous post, I first layed the fibers on the bottom of the form groove, trying to get them in 4 parallel layers, and then poured resin on top, working it downwards with a spatula and a small roller. This was probably not ideal: the resin took (I guess) many small air bubbles, which made the lam cloudy.
This is the form when clamped. Actually, this picture was taken after making the lam; during the real layup, i did not take pictures (my camera probably does not handle epoxy too well...):
 
And this what came out: ugly, but (I think) workable:
 

The thickness was close to target: I wanted a lam 0.8mm thick, and got a thickness between 0.8 and 0.9, measured in various places on the lam. As far as weight goes, the fibers weighed 39 grams, and, after trimming excess resin, I got 52 grams for the whole lam. I am fairly certain that very little, if any, fibers were removed during the trimming, because it was made only on the vertical sides, where the fibers could not go.

So, I think it works, and I think that I did several things wrong. For the next attempt, here is what I will do differently:

1 - I will lay a length of weave, slightly longer than the intended size for the finished lam and try to remove the transverse fibers in the middle, leaving about 6-8 transverse fibers in each end, to assist in maintaining the bulk of the fibers aligned. In the presen attempt, I left one end of the fibers free, and that helped in getting them all crossed over. I may pour a bit of resin on the bits of weave at each end, which would help with stretching them at layup. This is also difference n. 2:

2 - Instead of leaving the fibers trapped on one end and free at the other, I will try to trapp them at both ends, and stretching them while wetting them with resin. This should help with consistency of thickness, and maybe even with eliminating air bubbles in the resin. Which brings us to n. 3:

3 - The "lay the fibers then pour resin" approach is not good at all. I knew this from the beginning, but thought that being a very thin layup would mean it would work well. It kind of did...were it not for the cloudy looks. The next layup will be done pouring a start layer on the bottom of the form, and then laying the fibers into that, one layer at a time, 4 layers programmed.

I hope to get close to the same thickness (0.8mm), more constant, and better tranparency. We`ll see how it goes.

And thanks for all the (very helpful) inputs. Please, do keep it coming.

Daniel

[fujimo]

i have stitched fibers together- by putting paper top and bottom- helping feed it through the machine- and then carefully tearing the paper off afterwards- little bit of trial and error to get the feed rate correct.

[BenBow]

If I remember correctly gilnockie clamped one end of the fibers then combed them straight. Then stretched and clamped the fiber on the other end before adding the resin. But my memory isn't what it use to be. Good luck. BTW I'm doing something similar for the beam in my heavy weight bow risers.

[fujimo]

yup- keeping that glass under tension would be crucial in my books

[elkors]

Hi, Daniel,

I am currently in the same process as you were (a year ago) - did you finish your experiments, what were the results?

I was using a 80/20 ratio glass fiber 600g/m2(80% of fibers in one direction, 20 % perpendicular), and the result was that the lamination was not transparent where the larger fibers crossed the smaller ones due to the angle of glass. So it is clear that I need a more unidirectional fiber. I was looking for a unidirectional glass tape, but those have still some cross fibers (10%), there are also unidirectional cloth of glass fiber where there are less cross fibers.
 
Now based on your experiment I will try to trap both ends of GF strips, then remove the cross fibers, then do the lamination.