Hinge on brace but not tiller

[MattZA]

Hi everyone!

I'm hoping someone can give me some advice on what caused this issue I had yesterday.

I'm building a pyramid bow out of a massaranduba board (bulletwood). It's 60" tip to tip, and 58 nock to nock. Fades 1 3/4" wide, narrowing down to 3/8" at the tips. Pretty dainty, I know.

With the longer string on the tiller, I had it looking pretty good at 26". The string was pretty much the length of the bow. I decided to then brace it to normal height (about 6"), and when I strung it, it suddenly developed a huge belly hinge midway down the one limb.

I know I'm an amateur, but I'm pretty certain it wasn't visible on the tiller. The limbs are about 3/8" thick, aiming for 40# at full draw, so nothing crazy. Massaranduba is also a very dense wood.

Any idea what it could be? I strung it up in the correct 'step through' method.

Thanks in advance!

Matt.

[Del the cat]

You have jumped some vital stages, without pics I can't tell exactly where you went wrong, but here's my guess list.
1. Long string was too long! It should only just be long enough to slip onto the bow and shouldn't dangle down more than about 5".
The forces on the bow limbs are at a different angle with a long string compared with brace.
Say it takes 40# on your very long string to pull the bow so that the tips come back 6". You then brace it at 6" and the draw weight at 6" is now zero (or st a couple of pounds at 1", if you say you cant measure it at brace). Where has the 40# gone? It's all stress in the wood which is what will show up your small tillering errors which weren't obvious before.
2. You went straight to full brace, much better to go to low brace, say 4". This will be applying a lot of extra force to the bow so you need to observe carefully when you start drawing it again.
3. You weren't always pulling to the same draw weight. Much more important to always pull to the same weight (as long as it looks ok) rather than pulling to the same length.
4. I'd say you are making rather a short bow for a beginner. I'm currently making a 40# Yew primitive for a 26.5" draw. It's only 61" long and I'd rather have another inch!

The problem with tillering is that when you first start and you haven't "got your eye in" you can't see the problems until they are glaringly obvious, by which time it's too late. You have to catch the problems when they are just a suspicion of a problem, the merest hint.
That's why we are all grumpy, twitchy and hard to please

Note, we are all still learning
Del

[MattZA]

You have jumped some vital stages, without pics I can't tell exactly where you went wrong,

Hi Del,

Apologies for the lack of photos, I'm stuck in the office. I'll try and get some up asap.

My long tiller string was pretty tight on the bow. If you can imagine a 0" brace height, haha.

Apologies, I should have clarified - I didn't go straight to full brace height. I first braced it at about 3" and exercised the limbs (~50 times per inch) up until about 24".

Regarding pulling to weight, just to make sure I understand you. As an example, should I:

1. Draw the bow to X weight with the loosest string.
2. Take off the belly where tiller is uneven.
3. Shorten the string by an inch.
4. Draw the bow to X weight again.
5. Repeat.

Please do post those links, I'd love to give them a read and absorb your knowledge. Thus far I've potentially ruined 2 of the 3 bows I've made! Ironically the one that survived was my first one. It was just a test, so I used a pine plank. It's a damn cumbersome 72", with almost 3" of set. But it's still shooting at 36# @28". Crazy.

Thanks a lot!

[Del the cat]

Yeah, that sounds right.
Basically always pull to full target weight unless you see a problem.
That way you'll see the draw length slowly increase and you'll get back to your target weight and length.
So on the bow I'm currently working.
First time on the tiller 40# at about 2" . It looked relatively even so I took a decent amount off all along the belly.
Next time 40# @ 10", then I can see more how it's bending, take more off look again etc.
After a few rounds of up and down on the tiller it's now 40# at 22" and the tiller looks really good.
https://bowyersdiary.blogspot.com/2018/06/yew-primitive-started.html
I also wonder if maybe you have a long grip section? that's one of my pet hates bows with about a foot of wasted timber in the middle!
The longer the limbs the less stress.
I've just found that post about draw weight... it's embarassingly wordy
https://bowyersdiary.blogspot.com/2013/12/yew-stick-bow-and-draw-weight-to-brace.html
I do have 2 video series on Youtube for an English longbow which may be of interest. It's about 10 short videos each. You'd probably want to skip the first ones! There's a series for a Warbow too which is similar.
https://www.youtube.com/watch?v=XgG0M--KCZE&list=PLBz2tD9476KQFyMBLEylQGh952tBT_mZB

There have been long discussions on here about the merits or otherwise of the long string and plenty of people prefer to floor tiller, it's down to personal preference.
There is close correlation between the draw weight and draw length on a long string (if it is a short one) and the draw weight and length when braced (I argued against this being true initially, but checked it and found it was right). But the stresses on the bow and the curve of the limbs will be different.
Del
PS. On that 61" bow, the grip is about 3" with 1" fade either side. The heel of the hand sort of overflows down onto the fade. E.G the curve where the fade rounds over into the grip fits snug into the palm.

[MattZA]

Well that in itself was extremely useful - and I haven't even read your blog yet! I've been going about tillering in the completely wrong manner.

I've been using the draw length as my base marker. I've been drawing it to 28" with a longer string, and then steadily shortening the string once I've got the tiller looking okay. Whatever poundage I end up with is a mystery until I get there.

Blimey, reading through that makes me feel stupid!

I feel I also need a more reliable scale. I've been using the Mrs' digital bathroom scale and balancing the tillering stick on a wooden block on the scale.

I knew I was doing something wrong, because there's no way I should be breaking Brazilian Ash or Massaranduba bows at less than 40#.

Is it possible that there was a hidden weakness in my Massaranduba bow, and the angle of force when being braced made it show itself?

[Del the cat]

Plenty of cheap scales out there... even those dirt cheap baggage scales that only go up to 50# are surprisingly accurate!
I think you want to make it easy on yourself. Go for a long bow say 70". You can always cut it shorter, but adding length after they've exploded is tricky 
I generally start with a bow 2" longer than I actually want, to give me some leeway.
Good luck.
Del

[MattZA]

Yea I think I'm gonna buy one of those travel scales. And my next bow will start off at ballista size. I'm tired of cocking this up!

I'm also going to give heat treatment to my hinge problem and see what difference it makes. Maybe I'll even glue some more wood on the belly.

Thanks a lot!

[bushboy]

Learn to floor tiller,it's a handy tool!

[Del the cat]

Learn to floor tiller,it's a handy tool!

Yeah, I don't floor tiller, but I do get my face up close to the bow on the tiller and look down the limbs same as when you floor tiller.
It lets you see the movement along the whole limb.

Del

[MattZA]

My floor tillering skills are rudimentary at best. I effectively check whether or not I can bend the bastard.

Apart from heat treatment, does anyone have any recipes to repair hinges on the belly?

I intend to heat treat it, shave off weight elsewhere and then potentially glue a 'patch' bit of wood on.

Am I missing anything?

[bushboy]

Has the suspect limb taken set?

[MattZA]

Has the suspect limb taken set?

The overall limb has set about an inch. The hinge itself only very slightly shows itself when unstrung.

[bushboy]

Yes a heat treating may do the trick,but I have little experience with heat treating exotics.a thin hard maple or the such backing would be the way to go rather than messing with belly lams is the way I would go if it all goes to hell.

[simk]

Matt, i'm not a pro but would never tiller on the long string until 26". Always brace it (low) as soon as possible. the long string is cheating you. cheers

[MattZA]

Unfortunately in South Africa it's almost impossible to get simple backing like hickory. Hickory itself is rare, and if you manage to find it, it'll be in board form. I'll also have to buy about about 20 feet of it. So backing is probably out of the question. I'm investigating a bamboo retailer though. Although that might overpower the belly?

I appreciate all the advice so far though.