How Much Reflex?

[mmattockx]

So I tried heat treating bow #2, a 65" red oak pyramid bow drawing 37lb@28" before heat treat. The caul has about 2.5" of reflex in a smooth radius (~180" radius if anyone cares). Because of work commitments I ended up leaving the bow on the form for 4 days after I did the heating. When it came off there was no spring back at all and the bow held all the reflex of the caul.

Due to my inexperience with heat treating I managed to scorch the back of the lower limb near the tip and it ended up breaking at the scorched area when I was working it on the tree. No surprise there. Chalk it up to experience and the cost of an education... I put several hundred shots through the bow before this and was quite happy with it for a second bow so it does suck that I lost the bow, but I can make more.

My question relates to the reflex amount. Since I had shot the bow a reasonable amount I was familiar with bracing it. After heat treat it was a complete bitch to brace and I thought I was going to have to use my stringer to get it. Between the reflex trying to flip the string and the extra weight it had gained it was a different animal.

How much reflex is reasonable for a simple board bow like this, both in terms of over stressing the wood and making bracing difficult? After this experience I am thinking I will heat treat the next one after I get it to brace (or at least well floor tillered), but how do people manage a reflexed bow on the tillering tree and how much reflex is reasonable before the wood simply can't handle that much extra strain?


Thanks,
Mark

[Del the cat]

Just my opinion:-
I like reflex to be balanced out with some deflex near the grip such that the tip pretty much still line up with the back of the grip.
My reasoning is that you don't get something for nothing... so reflex gives early draw weight but sacrifices draw length. That's fine if you have a short draw, but if you want a long draw then you'd have to have longer limbs to make up for the bend you'd lost by having reflex.
To justify this opinion, bear in mind that the tips of a bow only come back about 1/3 of the draw length although TBF, the tip movement to brace a straight limbed bow is only the same as the brace height.
So by reflexing, say, 2" of tip movement you are potentially throwing at least 2" of draw and arguably more.
A short static hook, doesn't really effect the brace height ( as the string is still on the belly at the root of the hook), but it gives some softening (let off) of the force draw curve as the string lifts off the hoks at or near full draw.
Del

[mmattockx]

My reasoning is that you don't get something for nothing... so reflex gives early draw weight but sacrifices draw length. That's fine if you have a short draw, but if you want a long draw then you'd have to have longer limbs to make up for the bend you'd lost by having reflex.

Fair enough and that seems reasonable to me. My draw is 28", so pretty much in the middle of the range. In the end it is just a simple board bow, it is never going to set any performance records and I am not trying for any. The reflex question came up unexpectedly for me because I was expecting the bow to spring back a fair amount off the caul and it didn't, so it kept all 2.5" of reflex when I was just looking to end up with all the set removed and back close to straight. That put me in a different position than I had been expecting and I figured I would ask about it. I think I will re-cut the caul to more like 1.5" of reflex and avoid problems due to excess reflex on future board bows.

A short static hook, doesn't really effect the brace height ( as the string is still on the belly at the root of the hook), but it gives some softening (let off) of the force draw curve as the string lifts off the hoks at or near full draw.

So you are suggesting it would be better to put static hooks in to get the nocks 2.5" ahead of the handle than to reflex the whole limb?


Thanks,
Mark

[Del the cat]

No, I'm not suggesting you put static hooks on (unless you splice and extra 2.5" onto each end)....
You don't get something for nothing.
Del

[scp]

I would glue on a siyah on the broken tip. It can take long time, at least many days, for heat treated oak to re-hydrate completely. I would weigh the bow everyday until the weight starts to go down instead of going up.

[Bryce]

Anymore than 4” and I don’t find tillering very fun.

[DC]

Anymore than 4” and I don’t find tillering very fun.

Bryce, and anyone else that finds this, can you go into a little more detail about what isn't fun about tillering more than 4" reflex.  I think I notice the inner half of the limbs start bending too much. Also things seem to happen rapidly which I've mentioned before on my "all of a sudden" posts.

[mmattockx]

I would glue on a siyah on the broken tip. It can take long time, at least many days, for heat treated oak to re-hydrate completely. I would weigh the bow everyday until the weight starts to go down instead of going up.

The limb broke about 6-7" from the nock, so it would be a very large siyah. Otherwise that would be a very reasonable plan and I will keep it in mind for any future mishaps of a similar nature. I wasn't home to weigh the bow, but it did sit for 4 days in an unheated wood shop (ie - full outside humidity) before I pulled it off the form.

Anymore than 4” and I don’t find tillering very fun.

How do you keep the bow steady on the tree with that much reflex? Clamp it down or something else? Any tips or things to watch out for when tillering a reflexed bow as compared to a flat bow?


Mark

[bownarra]

The problems come when you are trying to bend a too thick stave! Obviously!
With practise and feel you will know when it is ready to brace. Bracing early is never a great idea as it strains the wood unnecessarily.
To get to this point I use my vice to clamp the handle and just bend the limb by moving the tip.
A stringer and a set of temporary nocks are the key to controlled bracing.
For an unbacked bow a pre-tiller reflex of 2 inches is plenty. 1 inch might be better until you have made more bows.
Also don't add the reflex in an arc of a circle it should increase as you move along the limb. Thinner outer limb wood holds reflex better.
 

[mmattockx]

The problems come when you are trying to bend a too thick stave! Obviously!
With practise and feel you will know when it is ready to brace. Bracing early is never a great idea as it strains the wood unnecessarily.

You misunderstand. I wasn't bracing early, the bow was done and had shot several hundred arrows. The heat treat and resulting reflex was an afterthought and an experiment that ended up failing due to my inexperience with the heating.

For an unbacked bow a pre-tiller reflex of 2 inches is plenty. 1 inch might be better until you have made more bows.

Thanks for the guidance, I am definitely going to cut the caul down to around 1.5". Again, I wasn't actually after reflex, I just wanted to pull the bow back to flat and heat treat to harden the belly wood. Getting all the reflex was an accident and I will be better prepared for it next time around.


Mark

[DC]

How do you keep the bow steady on the tree with that much reflex? Clamp it down or something else? Any tips or things to watch out for when tillering a reflexed bow as compared to a flat bow?
Mark

I use 5 min epoxy to glue a flat piece of wood to the handle. Make it about 1 1/2" wide. It will keep all but the worst from flipping. Just rasp it off once it's braced.

[bownarra]

The problems come when you are trying to bend a too thick stave! Obviously!
With practise and feel you will know when it is ready to brace. Bracing early is never a great idea as it strains the wood unnecessarily.

You misunderstand. I wasn't bracing early, the bow was done and had shot several hundred arrows. The heat treat and resulting reflex was an afterthought and an experiment that ended up failing due to my inexperience with the heating.

For an unbacked bow a pre-tiller reflex of 2 inches is plenty. 1 inch might be better until you have made more bows.

Thanks for the guidance, I am definitely going to cut the caul down to around 1.5". Again, I wasn't actually after reflex, I just wanted to pull the bow back to flat and heat treat to harden the belly wood. Getting all the reflex was an accident and I will be better prepared for it next time around.


Mark

Well what I said still holds true. It is about feel. Once you've done a few you will get the hang of it. What you describe as being hard to brace wouldn't be hard to brace for me! So we come down to how we use different words to describe the same thing. Again a set of temp or secondary nocks makes even 100lb+ reflexed bows easy to brace.

[mmattockx]

What you describe as being hard to brace wouldn't be hard to brace for me!

Very likely true. I was mostly surprised by how much harder it was to brace compared to pre-heat treat. Before it was no problem at all to brace it.

Again a set of temp or secondary nocks makes even 100lb+ reflexed bows easy to brace.

I do have a stringer but testosterone poisoning took hold and I managed to grunt through it. If I had failed that attempt then I would have pulled the stringer out and done it the easy way.


Mark