Cloth backing and tite bond/wood glues, the myth!!

[dragonman]

Hi Hurlbri...thats all basically common sense put into fancy language, in my opinion...I think most bowyers here.. probably realise this..you cant argue that a backing will offer some degree of added tension and also some added protection....the  conclusion that I came to ( and  Fiddler came to , too, I think) is   that; threads of cloth ,once soaked in glue and hardened lose their tensile strength and become brittle...hence , they dont really do much at all?

[Shiloh]

Look, I'm no good with the mathematics or physics side of things, but these have been my experiences with unbleached linen backings so far:

-Out of the five or so bows I've made in the past couple months, each one has had a linen backing secured with either titebond II or III.
-One, that I made for myself as a test, had some pretty decent grain run-off halfway up the top limb, and towards the tip on the lower limb. Unbacked, with the poundage I was shooting for, I can almost guarantee you they would have broken. All of them are from store-bought, 1x2 red oak boards.
-I have not heard, seen, or been told of any cracks or splinters from the people who got my bows. I'll check them over once in a while to make sure, haven't had any problems yet.
-I took the linen off the bow I mentioned above, with the run-off, to see how it had held up after a year of shooting. No signs of undue stress, no cracks, and with average set for a 72" board bow and my mediocre tillering skills.

I'm not saying you're wrong, just that it's a pretty bold claim to make when most people have seen so much success.

[Thesquirrelslinger]

To paraphrase what Hurlbri said...
When you back a bow, you help the back of the bow overcome tension/streching forces created by the compression in the belly.
Every action has an equel and opposite reaction. When you have compression, you have tension in SOMETHING.

[bow101]

...

[bubbles]

I backed a bow with parrallel strands of linen, secured with TBIII - I had to be careful filing off the excess at the edges because the file would pull the strands of linen off the back, indicating to me that the tension strength was still in the linen, despite the glue.   

[k-hat]

Read somewhere that it's the "linen-glue matrix" that gives it strength.  Course that could be one of those unverified passed-on things, but I don't think so.  Just because it's not as "springy" doesn't mean it's lost strength.

[fiddler49]

Thats true about a fiber and glue matrix being strong but that only applies to epoxy. Wood glue/ tb 2 and 3
looses strength if you try to fill gaps and cloth is full of gaps.   cheers fiddler49

[vinemaplebows]

If you size the back proper (like applying sinew) let set till tacky then apply a wet backing (cloth prewetted with glue) WHERE ARE YOUR GAPS? I have never seen any. I don't agree.


VMB

[fiddler49]

Lad, you need to read up on glues. Tb2 and tb3 won't bridge gaps with any strength. There are lots of gaps in the cloth. People don't use tb2/t'b3 with fiber glass but do use epoxy. The reason is epoxy will bridge gaps in the fiber matrix.
cheers fiddler49

[JackCrafty]

Very interesting thread.  The only time I've had a splinter lift and cause failure was with a sinew backed ipe bow.  The splinter popped up right through 1/8" of sinew.  It didn't break but it made a nice "crack" sound.  I retired the bow and started wrapping the sinew tightly when backing all the other bows I've made.  No problems since.

I haven't used cloth, though.  Seems a little weak to me so I tend to agree with the original idea of the post.

[mikekeswick]

If you size the back proper (like applying sinew) let set till tacky then apply a wet backing (cloth prewetted with glue) WHERE ARE YOUR GAPS? I have never seen any. I don't agree.


VMB

Tb needs flawless mating surfaces for a good bond.
Every glue has a tech specification sheet - it's a good idea to get hold of one from the glue manufacturer. It can also be extremely useful to contact the makers of any glue you use and just speak to them about your intended use. Glues aren't quite as simple as people may think.

[PatM]

The problem with cloth backings is that people don't add enough depth of backing. Every other backing we use whether thin hickory, bamboo or sinew is built up to even a modest depth of fibers. Expecting a strands worth of cloth with thin gaps between each run of fiber to hold up the same way isn't really a fair comparison.
 Linen phenolic has incredible tensile and compressive strength and oddly paper phenolic tests out with higher tensile strength despite not having linear fibers.
 The "fiber" backing used in the pre fg era with great success were paper or linen but they were all much thicker than what people consider adequate now.

[bubbles]

That's a good point Pat.

What would be the best glue brand/type for applying a cloth backing then? In terms of ease of application and gap bridging?  TB is easy to just squeeze out a crap-ton to cover a whole bow back and saturate the cloth.  Epoxy to me is those little mixing syringes. I'd need a a dozen of those to do a whole backing job.

[Cameroo]

Another problem with any woven backing (cloth, burlap, that fiberglass drywall tape garbage) is that exactly half of the fibers in the material are running perpendicular to the length of the limb, and serve absolutely no function other than to add dead weight and rob your bow of performance.  I would suspect that it would also create more slack in the fibers that are actually under tension, just because of the fact that the fibers are woven.

I've never tried a fabric backing just because it doesn't seem to make sense to me when there are so many other better options available.

[fiddler49]

I think Pat M is on to something with backing thickness. Even a wood backing needs to be thick enough. Somewhere between 1/8" and 1/6" or a splinter can lift right up threw it! So what kind of glue was used on phenolic type backings?  cheers fiddler49