setting tiller weight goals for mystery wood ......bow finished, pics added

[willie]

I glued up a soft maple backing to a piece of doug fir or larch in an elb design.
It is presently 75 in nock to nock and 1.25 wide at handle with 3/4 glue in reflex
the belly wood has an S.G. of .69 @ 12 mc, which I calculate to be about .6 oven dry.

Never used a wood like this on a bow before, in fact this would be my first elb/warbow style bending handle laminated bow. I often hear that the elb/warbow is typically a highly strained design.

Having missed weight on a few bows in my time, and shooting for the most weight I can with this design..

How do I set a weight goal?      any guesses where to start with thickness?

I hope to use Badgers  "no set" approach to monitor set

thanks

willie

[Pat B]

Willie, I'm not sure how strong soft maple is in tension or larch/fir are in compression so it may not work at all for you. An ELB will need compression strong wood for sure. You'll be building an ELB but not necessarily a war bow.
 If you never draw the bow over the draw weight but draw it to the desired draw weight you should be able to reach your desired draw weight. Reduce the belly until you get both limbs bending evenly and together at your desired draw weight. Unless your belly wood is over an inch thick, don't worry about the thickness, just remove wood until you get where you are going.

[Badger]

  Willie, get the bow bending evenly at floor tiller then take the physical weight of the bow, it should give you a pretty good idea what to expect out of it. If you are looking for say 75##30"  You would need at least about 20 oz and that would be with a full arc of the circle tiller.

[willie]

Thanks Pat

I realize it may not work at all, and as I mentioned in an earlier thread, this bow is an experiment in many ways.

I fully understand that soft wood like I have will not get me into warbow territory. I guess that this bow is a test bow for seeing what I can do with the wood at hand for something bigger in the future.
I am hoping that the soft maple back will be stronger than the conifer belly,

I could pick a ridiculously high draw weight like 90# to start? and see if I could get it to brace without loosing my reflex? Thats my problem. with so many unknowns, estimating a reasonable goal.

I have found that having weight too high to start with, and constantly changing my goals leads to a bow that is "tillered to death" if that makes any sense

[willie]

Badger-

I need to get the belly down some more to floor tiller, and floor tillering at these weights is new to me.
I think that I will compare floor tiller to two of my 40# held at once, and then  weigh the stave.

thanks
willie

[Pat B]

When I hit floor tiller I'm probably 20# to 30# over draw weight(just a guess). By the time I get to low brace I'm about 10# over draw weight. As I remove wood and exercise the bow I slowly draw it to my intended draw weight or just below it and check the draw length. From floor tiller I also just use a scraper and rarely a fine rasp when needed. Taking it slow, exercising the wood and watching for any string follow is the way to go. If your bows are taking excessive set you are either using unseasoned wood or over stressing the wood.

[willie]

Pat

I slowly draw it to my intended draw weight

I follow what you are advising as a method to reach weight when you know what weight you want, and suppose most people start with a plan for a particular draw weight in mind
 
My experiment with this particular bow is to see what this wood that I have never used before is capable of, weight wise, and monitoring set is of course the way to go. I guess as an relatively inexperienced bowmaker, I find it hard to judge set taking "as you go"


Willie

[Pat B]

If you are using a tiller tree put a paper background behind the boy and draw a pencil line along the bows back on the background. After you have progressed a bit compare where the back is in relation to the last time. If the difference at the tips is more than an inch or so you are possibly overstressing the bow while you build it. You have to educate the wood to not only bend but recover also.  If you trace the outline of the back at each wood removal you can see just where the limbs are taking set and adjust your tillering accordingly.

[bradsmith2010]

just get the bow bending even,, once you can brace it,, get the tiller even and there you have it,, whatever you have will give you a starting point for the next bow,,

[Badger]

  Willie, if you want to find out what the bow is capable of standing mass weight will give you a good starting point. Now you are working with two woods that are not generally considered bow woods. If the wood is .69 sg it more likely to be larch than doug fir even though they look alike. I don't know the qualities of larch at all. I would assume it to be similar to cedar for my experience with it working arrows. For example if I were working a suspect wood I would probably add about 4" the the draw length I used in a mass calculation. It might not be necessary but I don't think anyone is very familiar with larch as a bow wood. I would say see how much it weighs and then go from there. If you start pulling on a wood with no idea how much it can stand you are just guessing. Sometimes it works sometimes it doesn't.

[willie]

thanks for checking in occasionally, I spent a little time smoothing the back and I am still "floor tillering".
since I cannot bend and look very well, I set up two milk crates with a bathroom scale on it.
pushing down on the handle with the tips on the scales, I read 40# on each scale (pushing 80?), to get 5 " bend

I lost 1/32 of my reflex doing this and the bow weighs 23.6 oz or 700 grams
your thoughts are appreciated, as I have never tried to tiller this high a poundage bow before
willie

[Badger]

 If it weighs about 23.5 oz and is just starting to flex it will likely go down to about 20 oz. If you decide to go 40# I would make the middle 12" of the handle area just barely flexing and tiller slightly elliptical from there. If it won't hold up at those dimensions it is just not good enough bow wood.

[willie]

Badger

that's 40 lbs on each scale. I am leaning on it 80# to get to brace height. shouldn't I shoot for more, like 80 final draw #?

I am not up enough on your mass formulas. I have the general idea, but not the numbers to make the calcs

thanks again
willie

[willie]

ok I got the book out now, and I see the bendy handle number in the 32 inch column reads approx 17.7 for a 50 # bow

23.6 - 17.7 = 5.9

5.9 x 5 = 29.5

29.5 +50 = 79.5

what do I do with the elb factor?  79.5 x .94 =  74.7 call it 75?


hope I am doing the calcs correctly

willie


wait,  I for got to subtract the mass I will loose tillering out

if I go with your estimate of 3.5 oz loss, then

20 - 17.7 =2.3, and 2.3 x 5 = 11.5, and 11.5 + 50 = 61.5# ?? plus or minus elb factor??

[Badger]

  As long as your close, it just lets you know if you have enough wood. You have plenty of wood so it shouldn't be an issue if the wood behaves like bow wood.