First R/D: Hickory backed ipe - your thoughts please

[Freeflynick]

I am trying my first R/D bow (6th bow total) and put together the jig in the photo and before gluing it up would love to get your opinions. Too much, not enough, just right, doesn't matter....??
The support at the tip is around 3.2" high, and standard 2x4 in the middle. I pre-cut the ipe (on my new bandsaw....where has THAT been all my life!!?) quite thin based on other builds I have seen - worried it may be too thin, but will have to wait and see.
Thanks guys!
Nick

[DC]

I like the look. I know nothing about either wood except they look great together.

[bownarra]

Try to make the reflex more evenly spread. Past the block the outer limb is too straight. You want the reflex to start very gradually and increase slowly as you progress towards the tip. As the limb gets thinner it can safely bend further thus keeping reflex better.

[bownarra]

What draw weight are you aiming for?
How thick are your lams? What taper rate?
Ipe is very stiff and as long as you are close to dimensions you are unlikely to run out! You can also trap the back to lose some weight if needed.

[mmattockx]

Does anyone have any comment on the straight handle and then bending the limb back into deflex off the fades? Usually the deflex portion comes mostly straight off a bent/curved handle area then just sweeps forward into reflex. To me that looks like a failure waiting to happen right where the limb hits the fades, but I've never tried this before to know firsthand.


Mark

[DC]

Which one looks like a failure and why ?

[willie]

Which one looks like a failure and why ?

I think Mark is making a good point. The fade area and just outside of it, is being bent to make the glueup. My concern is that the handle area will spring straighter than planned when unclamped, and the tips will set forward more.

[mmattockx]

Which one looks like a failure and why ?

The picture posted by OP. On an R/D lam bow the limbs almost always sweep back off the handle in a straight line and are not bent back right beside the fades.


Mark

[DC]

I'm still not sure why you think it would fail. As long as the tiller matches the shape shouldn't it be OK?

[mmattockx]

I'm still not sure why you think it would fail. As long as the tiller matches the shape shouldn't it be OK?

This is based on my engineering experience and the bow analysis work I have done. I have designed a lot of structures and looked at a fair number of others that have failed. The deflex bend just looks like a stress concentration to my eye and the base of the limb sees a lot of stress on an R/D design (significantly worse than a flat bow of the same back profile).

Maybe tillering will sort it out, it just looks like trouble to my eye.


Mark

[bownarra]

As long as the lams are thin enough going over the back of the riser it is ok but bending a thick piece like that isn't ideal.
These bows are really best built like the majority of r/d glass bows. A riser with belly ramps and thin lams (that will conform to any shape ). They can then be made accurately to stack numbers and basically pretillered with the correct use of tapers.
A r/d bow doesn't see more stress than a flatbow.
Wood can only take a given amount of compression or tension. It doesn't know what design it is in All bows should be built to the same strain - the level is dictated by the material not the design.

[mmattockx]

A r/d bow doesn't see more stress than a flatbow.

It certainly does.

http://www.primitivearcher.com/smf/index.php/topic,68269.0.html

I post an experiment where I analyzed several bows with the same back profile, draw length and weight, etc. but made one flat, one with flipped tips and one R/D. The flat bow had the lowest stresses and the R/D the highest stresses.

Wood can only take a given amount of compression or tension. It doesn't know what design it is in All bows should be built to the same strain - the level is dictated by the material not the design.

I agree 100% with this, but that is not the same as saying different side profiles all have the same stresses when braced or drawn.


Mark

[Freeflynick]

Thanks for all the detailed responses, guys! Some are a little beyond my understanding at the moment, but I think the gist is to maybe reduce the thickness of the block under the handle to decrease some of the initial deflex, and use some extra clamps to get a more gradual transition into the reflex tips?
The dishwasher has turned into an indoor sprinkler system, so that's my day shot unfortunately, but I will try another mock-up later and repost.
I am humbled by the time you guys give to help out newbies like myself - it really is appreciated!
Nick

[willie]

but I think the gist is to maybe reduce the thickness of the block under the handle to decrease some of the initial deflex

maybe not the block, but the ipe in the handle, a smoother slimmer swell? for a two piece lam bow you should consider shaping the ipe to the proportion you would want it to have in the end before glueup. you might not want to actually bend the ipe too much, (as in doing a "pretiller" like you would do with a more flexible wood), but you could make a pattern out of spruce or pine to pretiller so you can find the desired shape .
If you decide to slim the handle area ipe more before glue-up, post a straight-on pic of the handle area. Posting a few pics with a question will always get you more comments.

[Freeflynick]

There have been a few comments about the handle section that I dont quite understand.....I am planning on gluing on a multi-layer handle after gluing the hickory to the ipe. Should I be removing the handle profile from the ipe now to get it to bend for some reason? I was planning on a non-bending riser section, flat bow deisgn, but I am not married to that - do you guys think a bend thru the handle design would work better?

Like I said, I am still in my infancy of bow making, so some of these suggestions are just a little out of my knowledge range.

Thanks again!

Nick