Howard Hill Style Longbow plan advice

[bdsmith1]

Hey everyone,

I've been wanting to build an ASL in the style of Howard Hill for quite some time.  Not everything is strictly HH style, but the compromises suit my prupose.  I've decided on giving it 1 inch reflex at the nocks for a 66" design.  The form is significantly longer than that because I wanted to be able to use it for glass backed and bamboo backed bows.  I'm not sure a bamboo backed bow could take my 30" draw if I left it at 66ntn, so the form can go up to 70ntn.  I figured for the bamboo backed bows, I'd glue up like a glass backed bow, with the core lams and riser, and just leave the bamboo off the back.  I'll glue the bamboo on the old fashioned way with plenty of bands after shaping the limbs a bit.

If Ya'll don't mind, check out the link below and poke holes in this plan so that I don't waste a bunch of time and resources building a doomed bow from a doomed form lol . I'd rather post a dumb plan and get a little ribbing, than go through with it and find out the hard way.

https://a360.co/4iCWhUd

[mmattockx]

I figured for the bamboo backed bows, I'd glue up like a glass backed bow, with the core lams and riser, and just leave the bamboo off the back.  I'll glue the bamboo on the old fashioned way with plenty of bands after shaping the limbs a bit.

This is just my opinion, but for the boo backed bows I would glue the core and belly lam upside down on your form, to induce 1" of deflex. Then flip it over and glue the boo on while pulling it into 1" reflex on your form. This is called Perry reflex and it helps reduce strain on the belly to minimize set and any potential chrysalling problems. 1" either way won't make much difference, but you want every bit of help you can get with wood bows.

I did a more extreme version of this on a red oak lam bow a few years ago:  https://www.tradgang.com/tgsmf/index.php?topic=177544.msg2983379#msg2983379

It gained extra weight over my design target and has taken no set at all, which is very good for red oak in my experience.


Mark

[Stagmitis]

Bd, use an inverted form. Glue up the bamboo back and core lams as a single stave. If you induce 3” of backset you should end up with a straight to slight string follow bow. After the initial glue-up glue your handle as a square block then profile bow and shape handle. 1” shorter lower limb works but I prefer 1.5

Use a 12” handle and go 67” which will get you close to your draw length- 30” draws are not very friendly for natural backed hills

[Stagmitis]

Mark, I guess
Bdsmith is Mia but in the meantime….for years I have tried to rationalize Perry reflex- in your post are you suggesting gluing up deflex then reversing and glueing up reflex?

[bdsmith1]

Hey fellas, I'm back.  Baseball season seems like it takes me straight thru to bedtime with multiple kids to coach and chase lol.

Thanks for the tips. Seems like doing a single form for glass and wood is probably not a good strategy. Unless I run the bamboo backed as a headless form.

Should I do a symmetric form and just vary where I cut the limbs for the asymmetrical design, or should I account for the asymmetry in the form to make sure both limbs have the same backset?

[Buemaker]

For wood laminates I use a form like this, blocks are just fastened with a couple of screws and can be moved around to make all kind of shapes, straight, backset or DR. I glue with belly down and add a riser after. I know Roy does it the same way.

[Buemaker]

Sorry upside down, old pics.

[Buemaker]

DR with bamboo back

[Stagmitis]

Symmetrical form with a centerline- cut tapers from there equally then slide handle towards lower limb to your liking (1/2-3/4”). Then have loads of fun sanding bottom limb for tiller

[mmattockx]

for years I have tried to rationalize Perry reflex- in your post are you suggesting gluing up deflex then reversing and glueing up reflex?

I can show you the math if you want, but there is nothing magic about it. All you are doing is preloading the glue up so that it puts a bit of tension on the belly at the expense of greater tension on the back. There is no free lunch, you are mostly trading stresses around. This works because most of our bow woods are much stronger in tension than compression, so the back can stand the higher stresses with no problem while reducing the stresses a bit on the belly where it needs that help.

This is only worthwhile for wood bows, and probably not even for really good compression woods. I was working with red oak, so it needed all the help it can get.

Because of the way I did the glue up it also gets a bit more work out of the core wood because there is some preloading there when the belly and core are glued initially. Normally the core contributes very little to energy storage and sees low stresses.

In the thread I linked to I show pics of what I did. Going from memory, I glued the belly and core lams into about 6" of deflex, then flipped that assembly over and pulled it into about 3" of reflex and glued on the back lam. The reason for the deflex first is to maximize the tension on the belly without ending up with a huge amount of final reflex that makes the bow harder to tiller and string, etc.


Mark

[Stagmitis]

Think I got it mark. No performance gain just balancing out stresses for wood bows.

[mmattockx]

Think I got it mark. No performance gain just balancing out stresses for wood bows.

Well, you can trade the lower stresses for more longevity or you can push the wood harder for more performance. That is up to the bowyer. It is very much a wood bow thing, would have no purpose on a FG bow.


Mark

[bdsmith1]

Buemaker, I've done all my boo backed bows on forms like those. My problem is that even with a power lam, there's always a risk of popping off the riser handle. Ive glued back on risers with power lams 12 inches long that where 1/4" inch thick at mid point.  I really wanted to experiment incorporating the riser between the lams in a trilam. I had planned to glue it up much like a carbon bow, and just leave off the boo. After all was glued, I could go back and glue a very thin backing on with bands. If I heat treat the bamboo on the same form, it will better hold the shape so I shouldn't see as many issues with spring back.