working details for higher poundages

[willie]

I am in the process of building a lighter weight 70#  "warbow" . this is a sort of trial run for a full size 120??pounder yet to come

As most of the bows I have ever built have been approx 40-45 in the past and I am finding that most everything I have in the past has to be rethought. First I had to rebilld my tiller tree. then I had to rethink what I usually do for string nocks, as I blew a tip, and grooved another with an undersized string loop. Del suggested some glued in reflex in another thread, which is new for me, and with the higher poundages, I find myself like a kid trying to string a mans bow. I going to have to make some adjustments to my methods when I undertake the full size warbow project, for sure,  so here is my question

Does anyone have any links or can point to a resource that might be helpful with working at this scale?

Do most use a double block on the tiller tree? and how the heck does one guy string a heavy bow?

willie

[Del the cat]

Here are my thoughts:-
Glue on temporary nocks with double grooves that allow you to use a stringer.
Avoid cutting nock grooves into the side of the bow.
Personally I get the middle of the bow moving (having got a rough thickness taper before putting it on the tree) and work outwards, may be less likely to blow a tip that way.
I'm not in favour of reflex on the heavy bows (above 90#).
Make 'em long and leave the tips wide until well past brace height. I narrow them and fit horn nocks when they are drawing about 26"
2:1 on the tiller is a good idea.
Always pull to full target weight, unless there is a visible tiller problem.
The process of tillering a heavy bow is the same as a lighter one... BUT the feel is totally different... it's a pig to get it braced, and once braced you are 80% there!
Most of this is on my blog (Google Bowyers Diary) if you trawl around it, or do a search on the blog for tillering warbow (the search facility works quite well).
All just my opinion of course, terms and conditions apply, contestants must be 18 years or over etc
Del

[colin1991]

Hi Willie,

A few questions first.

What are you building the bow from?? Lams or a stave?

If lams, what timbers are you using for them, particularly the belly?

Personally I make quite a few lams over 100lbs using a template I was given from an Aussie bowmaker for ELB's which I have since tinkered with to improve.

I glue my staves in reflex to negate string follow and get better performance and have never had an issue with it.

Bows are always cut with nocks in the sides of the timber for tillering (even across the back of the hickory back lam, but others will disagree with this) and a second nock for stringing when I can get the bow to brace.

I use a long string to get the bow bending to just past brace and then get a short brace with a short string and continue tillering as you would a light bow, upping the brace height to full as you get it bending further.  If you have a target weight, don't ever pull it past that weight as it stresses the limbs unnecessarily.


I Always use a stringer to string big bows, its safest for the bow and the shooter and far easier than the step through method.

Hope that helps a bit,

Colin

[willie]

Del
I have read your thread some in the past, but will take a closer look now that i see how much you have posted there.
Thanks for the pointers too, as I was just about to booger the tips some more. Temporary double tips seem to be the order for the day.

what do you mean 2;1 on the tiler is a good idea? are you recommending a bow length to draw length ratio? the bow is now 72 long overall and I intend to tiller out to 27"

thanks

 willie

[Del the cat]

I mean a 2:1 pulley system, as you had mentioned improving your tiller tree... Here:-
http://bowyersdiary.blogspot.co.uk/2013/11/tiller-improvements.html
Bow length to draw length ratio is nearer 2.4 : 1 for a warbow
Del

[willie]

Colin

to help answer your questions, I will point you to a few threads in the bow section, I hope you forgive that some of my experiments in materials and methods are not too traditional, they are just some ideas I have been meaning to try.  I am hoping to tiller to a traditional bend profile, and maybe keep a similarity in appearance.

http://www.primitivearcher.com/smf/index.php/topic,54581.0.html
http://www.primitivearcher.com/smf/index.php/topic,54495.0.html

hopefully my soon to be made double nocks will allow the use of a proper stringer. I was leery of doing the step thru, as I have barely got the bow bending, and I could see problems if I over stressed a limb before I even got a chance to start tillering it.

thanks
willie


Del- thanks for the clarification

[meanewood]

Hi Willie

What Del said plus
To avoid some of the effort when stringing the bow, I have found by continuing to use the long string quite a bit past brace height it makes it easier and you can give it a good long bend when stringing and know that the tiller is good while doing so!

[willie]

meanewood-

yes that would make things easier for sure, and I suppose that I could learn to judge tiller both with a long string and a short string  (by putting a finished bow back on the long string) so that I would not be tempted to thin the limbs too much. I presume you are advising a "short-as-possible" long string.?

Btw  can you over stress the center of a bendy handle bow by pulling out too far with the long string? I suppose that you might have to pull much harder with the longstring than you would with a normal string to get the same bend?

thanks

willie

[Del the cat]

Have a read of this post:-
http://bowyersdiary.blogspot.co.uk/2013/12/yew-stick-bow-and-draw-weight-to-brace.html
Del

[colin1991]

Willie,

Firstly, don't be discouraged by mistakes, that's how you learn.

Second, Try not to drive yourself mad by overthinking it all and trying to crunch numbers, just make it and see how it goes. Even if it breaks there was a lesson to be learned.

Your long string should be nearly straight along the bows belly when its on the bow... excessively long long strings will give a very different bend profile to a short string because of the force vectors at the tips.

If you over stress a bows handle on the long string your tips were far too stiff so you should be able to pick that up fairly fast.  Just remember that going from long to short string will make the outer mid-limb and tips bend a bit more (again, force vectors at the tips do this)

I personally don't ever go over desired weight when tillering, even before brace, doesn't matter if its 40lbs or 140lbs.

Can you post photos of the bow so we can see what its looking like?


Del, I read through the thread on bowyers diary you posted and found an error in it.  You say towards the end that "80# on a long string is less strain on the bow than 80# on a short string, due to string angles etc. In the same way that at brace there is 40# of tension on the sting but no draw weight."

I agree with the first part, 80lbs on a long string is less strain at the same stress than a short string, but I disagree with the second part about there being 40lbs of string tension... because of string to tip angle and line of force (and the vectors the force splits into) the string tension is higher than half the weight it took to brace the bow.

Colin
Colin

[Del the cat]

Yes, you are correct.... BUT
It's not supposed to be a an exact analysis of a specific example (the exact figure would presumably depend on the bow), more an illustration of the general point that there is string tension, but virtually no draw weight at brace.
Thus the figures aren't correct, but I can't be bothered to make up a rig that allows me to put a scale in line with the string at brace, but trust me I did look to see if it could be easily done.
I just read my blog entry. Initially I say "probably about 40#" which is IMO reasonable.
Later where I say 40# of tension I've amended it to read "substantial tension"

OK... So I caved in and used two bow strings and my cheapo scale to measure brace tension. I got it to a low brace and was turning the scle in the manner of a tourniquet to twist up the strings and increase the height, when it went BANG!
Frankly I no longer care what the exact figures are ... there is plenty of tension in a bow string.
For the record, this part tillered bow is about 50# @ 21" and needs 35# on a long string (short as possible to just slip on) to brace it.
Dunno why the scale exploded, it should go up to 50# and was only up at about 15# at about 4" brace... maybe twisting it up unscrewed something.... just done an autopsy. The twisting load broke the plastic housing
Maybe someone else would like to do the experiment ?
Del

[willie]

Del- thanks for the link,  some good reading at your place.

Colin-  your input is appreciated. I guess it would be easy for someone reading those two threads to think that I was a new guy trying to figure it out by the numbers, and overthinking everything. I have made a few bows out of  staves and a few board bows years back. I suppose that I kind of got carried away in the experimental mode with this one. I started out building this first elb as a practice bow for a bigger one that is on the list, and then I thought , why not use some wood I have never used before, then I thought that I would try tillering a regimen ( badgers no set) that I have never used before, and of course had to learn the mass principle along the way. I have never really tillered a bow out just to see how much the wood could take.... and on and on. In fact if I could learn a new way to approach every single operation with this bow, I would try it. For instance I have ditched my belt sander for a spokeshave, and I like it better, but I must say that it took quite a while to modify the off the shelf tool to make it useful....

this bow showed me that I need a new way to floor tiller If I am going to build an actual warbow. It was not too clear in the other post, but I laid the stave horizontal between two boxes supporting the tips, about 16 inches off the floor. A bathroom scale on each box, to weigh how hard I was pushing down to deflect the bow,  while taking a measurement from the bow hand to the floor. I like the ease  of method and consistency of measurement, but I then realized that I was doing the same thing as I would on the tree with a very very long string, and of course the scale weight only bears a slight resemblance to draw weight, but it should be proportional.
I have the bow up to about  14" draw, and have some tiller adjustments to make. After lowering my goal and thinning yesterday, am pulling about 2.5 lbs per inch with a low brace. I will try to post a pic later, but my camera is not much

Bob

[meanewood]

Hi Willie

Just another point about the long string.
I only use linen strings now and I make one up to suit the bow as a long string and then it becomes the short one when needed.
The advantage of this is the tillering process stretches the string out and by the time the bow is ready, the string has done most of its stretching so any adjustments are done by twisting.
This will happen even if using Fast-Flight on the higher poundages.
Its like Colin, said, the long string is only long enough to fit on the nocks!

[WillS]

Just to add one minor thing - I've found using side nocks makes life much easier at all stages of bow making, but especially tillering heavy bows.  A single groove on one side of the bow tip makes bracing very easy, doesn't affect the back of the bow and supports the string nicely.

I use horn sidenocks on all my bows now, but even if you don't want to use them at the end of the process and put a more modern nock on, the side nock you cut at the tillering stage disappears instantly once you shape the tips to fit the horn. 

They're not for everyone, but its worth trying a few times to see if you can get them to work.  I've never looked back since using them for tillering nocks!

[willie]

Thanks Meanwood

I do have some linen  twine I bought a while back. Its probably not the best as is came bleached even though it was not advertised as such. but I need to get it out as to stay in keeping with "everything  is an experiment" with this bow. I was having trouble with the dyneema I was using as it kept slipping, and no two braces were alike.


Colin
I made a pull to 17" when I had the tiller looking better, but the same uneveness between limbs came back. Need to work on the left limb and maybe reduce poundage some as the bow just took some set at midlimb. each outer limb droops about a 1/4"  more than before I made the pull. Middle half of the bow is has not taken near as much set. bow is now 70" ntn.

Will
I got some really ugly temporary nocks that are held on with hot melt glue. (so ugly that the camera refused to let them in the picture), but it seems like a good idea. Do you need quite a thick string when using softwood with high poundage designs?

willie