Request for advice: backing wood with wood & maple/white oak backings

[Aussie Yeoman]

Hi folks,

A couple fo short requests today.

1. backing timber with a lam of timber.
When backing a lumber stave with another timber, and you wrap with tire strips in the glue-up, do you do anything to prevent excess pressure on the edges of the backing from squeezing out too much glue? Like, put it backing down on another piece of timber or something?

Theoretically, the tire strip applies more pressure around the corner of the backing strip. The stave too, but being thicker the effect is reduced.

2. what would you not put white oak or maple on?
What would you suppose is the reasonable upper limit of timber that can reasonably be backed with rock maple and/or white oak?

Would you back Ipe with these timbers? Bulletwood? What sort of ratio of stave:backing?


Thanks,

AY

[Hamish]

Rubber bands : starving the glue joint wont be a problem, as its not really possible to put too much pressure(glue on both surfaces, some people only butter one side).

You can add a pressure strip if you want, just make it thin(3mm) so it will bend if you are adding reflex in the glue up.

I found maple to be quite temperamental when making Elb's . 50% broke, despite appearing flawless, so I stayed with hickory, boo.

I have a bunch of other incredibly straight maple boards, that I might give another try with, but I will be using it for wider flatbows.

I think white oak would be a better choice for a backing, many Americans rate it a close second to hickory. I haven't gotten around to testing it though as I still have a bit of hickory kicking around. Hickory isn't the easiest timber to procure in straight grain, in Australia.

1/4" thickness max, 3/16 or 1/8 would look better.

[Don W]

i think your first question depends on the type of glue. With some thicker two part epoxies, it's possible to starve a joint, although i'm not sure a rubber band will do it as long as you coat both surfaces. For wood glues like titebond it's been tested and shown you really can't starve the joint as long as both surfaces has come in contact with the glue. Again, coat both surfaces. I don't always coat both sides, bit for bows i always do. In either case make sure both surfaces are clean and roughed with a course sandpaper helps

As for backing, i think there is some latitude in judgment, opinion and wood condition. I've had failed backings from both white oak and maple, but they were imperfections in the wood ( i make my own) that i didn't notice. The thickness also plays a big role. It's important to know what woods are good in compression and what are good in tension. I typically search on phrases like "bow backed with white oak" to get a sense of what others have done, but sometimes you just need to experiment.

Keep notes on what works and why or how it failed.

[bownarra]

You won't starveanything with innertubes.
Very good idea to use a pressure strip. 1/4" thick piece of wood the same width as your lams will work - this is more important with thin backings as the edge pressure will cause the lam to 'cup'.
Pull on the tubes as hard as you can. Wrap one way up the limb...then back towards the handle revrese the wrap direction. This will elliminate any induced twist.
You can use maple or white oak to back anything Especially ipe or massa. Of course the grain must be super straight, grain orientation of the boards doesn't matter, flat,rift or quarter sawn - the wood don't care! What matters is that the grain is super straight.

[Aussie Yeoman]

Thanks folks.

I use Smooth On as my epoxy. Usually I butter up only one side, but might try both and see what difference it makes.

I've used rubber strips since about 2004, and have made perhaps a hundred bows with this method. I've also been teaching classes for about 10 years with the same, but have always used bamboo.

I've tried gluing up backing lams onto staves before with rubber strips and, while the dry fit was perfect, I did end up with small voids along the edges after clamping. I put it down to excess pressure right at the edges where the rubber comes around the corner of the backing. But perhaps it's more a function of not 'buttering both sides'.

I'll try using a pressure strip and applying glue to both surfaces and see how I get on.

I might keep my maple for selfbows and look for more white oak for backings, then. The local place does get pecan and hickory, but it's usually rough-sawn and it's hard to see the rings.

Thanks again,

AY

[Aussie Yeoman]

In people's experience, just how close to Hickory is White Oak as a backing? I know Tim Baker rates it very highly.

AY