Elm Stave

[Richard B]

Not sure what sort of elm it is. The draw weight I achieved with the miniature bow suggested similar properties to English elm, but its all fairly approximate with am 18" long bow. The stave was big enough for me to cut enough for the bow, a miniature and enough left over to make up one of the test pieces describes in TBB vol 1. Haven't got round to this but should be able to estimate the strength of the wood, density etc which might help me identify it (there I go, on about numbers again!). Should really do this before proceeding with the tillering, I guess as it would give a better idea of what draw weight I should be able to safely achieve before I go and break it. I am brand new to this and so don't have the experience to be able to look at a stave and assess its strength (also I'm a geeky engineer and like doing sums!)
My most time consuming hobby is building model boats, again with lots of numbers. Have a look at my website and you will see what I mean!
http://richardsmodelboats.webs.com/

[Sidmand]

Richard, send me a PM with your address (if your stateside) and I will send you some B55 or B500 to make you a string.

[Richard B]

Sidmand,
Unfortunately, I'm in the UK, but I think I can buy some locally. Many thanks for the kind offer though.

[zenart]

Yeah Richard, does sound like you're over thinking a bit on this. I'm new as well. I've broken enough of these to know it's better to go by feel than try to make too much of a science of it. You may be able to engineer using certain materials but this is working with organic variables. It will require you to think differently. Making bows is truly a tactile art.

I don't know if this is true for all woods or with all designs but to get at least a few actual bows completed I approached it this way, and this is speaking in a broad sense:

When you get to floor tiller try to really feel the wood's elasticity. At floor tiller if it's bending a lot while still thick than it's saying it has a weaker composition, so don't ask it to be a heavyweight. If it's getting thin to get to floor tiller than it's saying it's sting and loves to bend so you can ask more from it.

Of course, sometimes there are 'unseen' forces within the wood, a splinter lifts out of nowhere or grain looks great but inside it's brittle (coarse as opposed to dense long fibers), but you won't know until you either go too far or get close to where you're asking it to be which will really only come with experience. You gotta break 'em to make 'em. Part of the game. 

[Richard B]

One of the disconcerting things is that it is difficult to know whats inside a stave (without radiography, which would be a bit pricey...). I had a couple of tiny knots on the belly which grew into huge knots as I removed wood. Fortunately they both disappeared completely before I reached floor tiller. With all the uncertainty over the material, and the fact that the difference in the strain in the outermost fibres and the failure strain is going to be small in an efficient bow,  all one can do is try to tiller as carefully as possible to keep the strain even and compensate for knots and other flaws as they appear. I suppose that it is this risk/uncertainty that makes creation of a working bow so satisfying. But I haven't got there yet!

[Richard B]

Basic question
The back of my bow undulates both along and across the bow. I have tried for an even taper measuring the thickness at the centerline.
Should I go for the same thickness at each side, which would mean the belly twisting to match the twist (propeller?) of the back?

Also, the thickness of the rings varies from one side to another so that aiming for even thickness across a section can result in the rings running off to one side.

Am I making sense?

[Del the cat]

Keep the thickness even across even if it leaves it looking twisted. There is a HUGE difference between:-
1. A bow with twist that draws true and straight (my fave' bow is called "Twister" http://www.primitivearcher.com/smf/index.php/topic,28324.0.html  )
and...
2. A bow with no twist unstrung, but twists (or tries to bend sideways) as it is drawn.

Having one edge thinner than the other is a recipe for number option 2.

If the back is a continuous ring, you adjust the belly to maintain even thickness, of course there are cases where for some reason this won't work or you have to make a compromise. If you have ring violation running along the bow that's not so bad. Sometimes there are several ways to tackle a problem, sometimes all or none are good, and often it's a little of option A with a little of option B,,, it's called "experience"... enjoy

You can use heat to take out the twist if you want to.
Have a shufti at this post in my blog http://bowyersdiary.blogspot.co.uk/search?q=dealing+with+the+dip
Del
BTW the bug marks under the bark look like Dutch Elm disease to me, first Elm bow I ever made was like that, I went down a few rings and it was ok.

[Richard B]

Many thanks Del. I will go with even thickness on both sides and follow the twist on the back. Yes, I thought dutch elm disease as well. Have gone down 3 rings and the back is clean now. There is a very slight staining through the thickness at one end, which I am a bit concerned about. However, I used that end for the miniature bow and it seemed to hold up OK...

[Richard B]

2mm removed from the thickness of both limbs. Thickness is now 19.5mm at the fades tapering to around 13mm at the tips. At the fades the section has about 7mm of crown (i.e. is about 12.5mm thick at the sides). The crown varies along the length of both limbs due to knots on the back surface and some deep blind knots (now dissapeared from the belly), which makes going for an even taper a bit tricky.

Still using the (rather elastic) long sting. Nearly bent enough for bracing with a short string (picture below) pulling 55lbs (target weight at 28"). Both limbs seem to be bending evenly (although a little stiff at the end of the right hand limb around the knot?). Have maintained an even thickness on each side, so the belly twists around following the twist of the back as discussed with Del (above).The tips dont seem to be twisting as the bow bends, so hopefully under control(?).

Probably take another 1mm off both limbs before it will bend enough to brace safely without overloading? 

[Richard B]

Shaved another small amount off both limbs and draws another 2 inches with the long string (still at target weight of 55lbs)
Do you think it is ready for a low brace height with as shorter string?
I think the right hand limb is a bit stiff around the knot (near the tip)?
I have some additional width here (having followed the grain around the knot), but a bit nervous about removing too much thickness.

[Richard B]

After a nervous afternoon of tillering, now have the bow at full brace (hard work!, hopefully a bit easier when I have it to full draw) and drawn to 23 inches at 55lbs. Great relief to have got so far without disaster ! And still have 5" of draw to play with to, hopefully, end up with a nice even tiller at 28".

Nervous about breaking it after having got so far, so would welcome any advice on where best to remove wood.

[Pat B]

Your tiller looks pretty good to me.
 You are holding the draw pics statically with the set up you have. Add a pulley and rope so you can stand back, exercise the limbs and hold it just long enough to take the pic.

[Benedikt]

This looks very good!
I think, the last third is a little bit to stif, there is much bending near the handle for me.
Looks like it is becoming a great bow!
Benedikt

[Richard B]

Pat,
Yes a pulley arrangement would be good. I guess I would have to fix it to a wall somewhere. Does leaving the bow drawn for any length of time make string follow worse?
Benedikt,
I am trying to match the target tiller curves I have plotted on the piece of paper behind the bow. In theory, this should give me an even strain along the bow for the width profile that I have. I agree, however that the ends are a bit stiff still and I guess I could scrape something off the outer third of both limbs. Its a bit more difficult to judge with the right hand limb which has a few knots and weaves about a bit. I have followed the grain around the outermost knot, as best I can, which seems to have left the bow a bit stiff there. Do you think it would be OK to scrape a bit off the belly there and let it bend through the knot?

[DarkSoul]

Does leaving the bow drawn for any length of time make string follow worse?

Yes, it does! You're fine at 23" maybe, but it will induce set when you're approaching full draw. From now on, you should no longer use the tiller stick. It's best to use a tiller tree. That way you can also attach a scale and monitor draw weight more easily. If you can't make a tiller tree, you should use the reflection of the bow in a window/mirror when you draw the bow by hand. You could even use the shadow when you're working in the sun.

I can't tell from the pics, but now is also the time that you should make sure all the edges are nicely rounded. Especially the back edges should be smooth and round. Scrape away all the tool marks, if you haven't done so. This could easily gain you another inch of draw length. The midlimbon the right hand side is a bit stiff. Near the knot. Make it bend a bit more, but be careful not to let this knot bend too much. The same holds true for the outer limb on the right side. Since I can't see how big those knots are (there's no recent pic of it), I can't tell you how much the bow should bend there. Remember that the knot itself stretches only one inch of limb length. So if you want to tiller a knot to be stiff, the bow should have a section of only 1" that remains stiff. Not the current 5" as pictured in the right mid limb.

You can go and shoot some arrows at 23" draw length now, but please be very careful not to overdraw the bow! Mark every arrow carefully at 23" (with some tape or a rubber band).