Fibreglass cloth for woodbows

[yeoman]

Hiya all,

Has anyone experimented with using the bi-directional fibreglass cloth for backing a wood bow? I saw a demo on youtube where a guy did it with unidirectional...I think, and think it should probably work with bi-directional.

However, the mass of the backing would be double as there's fibre going in two directions.

Dave

[looseplucker]

Dave

I have given serious thought to using that stuff - as well as using the cloths used to coat wooden dinghys - saw a fair bit of it at ACT Fibreglass Supplies (where I get my techniglue).

No reason it shouldn't work with bi-directional - and given the immense amount of materials that can be used for backing all things are possible. I am sure I read in the TBB about someone using Duct-Tape (does anyone use that stuff for ducts anymore?)

[gilnockie]

Don't waste your time and money on woven fabric because it is unsuitable. It is subject to "crimping" which is the movement which occurs as the limb bends and recovers and the glass fabric tries to adapt. The over and under weave causes the epoxy to break up and the fabric will fray.

If you want to back a bow with glass, you should use uni-directional and make sure that it is sized for epoxy resin, preferably the adhesive rather than the laminating resin. If it is sized for polyester rosen, the epoxy will not adhere properly.

The best technique is to lay the srip of uni on a flat piece of steel with a smooth surface; 2mm black iron is ideal and it is cheap. Wax the surface well and allow the wax to dry; buff it to a sheen. I lay the steel onto a piece of 90 X 19 Tas Oak which is well waxed. This keeps everything straight and flat.

Tension the fabric so each thread is straight and taut. This is very important. I clamp one end to the steel and wood, pull it tight and then clamp the running end. If the threads are slack, they will not add tensile strength to the bow.

Apply your epoxy adhesive to the fabric and then place the back of the bow on the thoroughly wetted fabric. Clamp the stave in place and allow the epoxy to cure according to the manufacturer's specs.

Remove the glass/ wood composite from the steel and remove the surplus fabric and adhesive.

[yeoman]

Thanks for the advice Norman.

From where do I get unidriectional glass?

Dave

[Glenn]

Back in the mid 90's a surfboard manufacturer gave me some cloth he used in his surfboards but what I did with it as a backing was to pull the strands out and glued them on the back of the selfbows, one was a recurve. I just glued them with bondcrete and it worked very well. Those bows are still shooting today. I think if you were to use Titebond 3 that would work just as well without using epoxy....Glenn....

[ichiban]

hmmm i for get where i read it but i think i may have been sam harper (sorry really cant remember) who has used plaster board tape, and covered it in glue which seemed to work a treat.

[gilnockie]

Go to the Yellow Pages and look for "Fibreglass" in the index.

Any firm which sells epoxy resin and polyester resin should sell uni fibreglass. It is about 1200mm wide from memory and it is only a few dollars per lineal metre.

[ichiban]

how would that compair to bowtuff??

[greybeard]

This could be another option available from boat building suppliers.

Unidirectional Carbon Tapes

Unidirectional; 11. 1 oz carbon fiber reinforcing tapes are used for selective reinforcement to improve tensile strength and stiffness in one direction while adding minimum thickness and weight. Fiber bundles are held in place by a polyester fill thread for easy handling and wet out, 144,000 fibers per inch of tape width.
702-12 - 1 ½” wide x 12’ roll, 702-50 1 ½” wide x 50’ roll,
703-12 3” wide x 12’ roll, 703-50 3” wide x 50’ roll.

Carbon Ribbon.jpg (32.86 KiB) Viewed 2855 times

[ichiban]

that stuff looks very space age

[gilnockie]

I have tried the full width uni carbon of the same type to make my carbon lams.

You will have to be very careful about the weft or cross thread. I found that on the belly the threads began to come through the varnish because while the carbon was still solidy bound up in the epoxy resin, the weft thread would not bind to epoxy.

I came to the conclusion that the weft thread was either nylon or a polyester thread which was not compatible with epoxy.

That carbon did work OK on the back, but I personally would not use it on the basis that if the laminating epoxy would not bond to it the epoxy adhesive probably would not either. I did not relish a channel of unsecured nylon every 5mm along the back of the bow.

[Moss]

There are two different types of uni directional carbon tape. One like norm said has polyester or nylon thread but there is another which has fiber glass thread. if you can get the later it works to my very limited experience. I made a horse bow with it in my earlier days but didn't taper the lams it bent to a right angle one of the limb hinged literally to a right angle. But the carbon tape didn't break or show damage. i found the cheapest way two get it was to buy a wide 250mm strip of it than just cut smaller strips from the side its very easy as your only cutting thin fiberglass strands.

[gilnockie]

If you want to use uni carbon, the best material I tried was uni fabric wher the weft threads were carbon fibre.

I only stopped using it when the local supply was exhausted. I spent hours searching for an alternative supply, to no avail. That is when I started using carbon tow to make my laminates.

If you want to experiment with using carbon on the back of a bow, carbon tow can be purchased bythe lineal metre.