The making of fast bows, or the making of bows, fast

[yeoman]

Hi all,

well, the longbow project is on the backburner. So to are the essays on mathematically modelling bows based on bend tests.

It's all good though, as they were put on the backburner to finish these:
http://forums.armourarchive.org/phpBB2/ ... p?t=110205

But back to the good stuff.

I've been asked to make some bows as a display at an event. I agreed. I thought that it might be nicer for the public to see bows being finish tillered, rather than the whole process. To facilitate this, I'll be 'mostly-pre-making' a few bows to take along that I can just scrape a little bit, apply a finish and be done.

I'll also take a couple of bows at various stages of completion to show people what the dealio is along the way. I thought it might be nice to how the process here as well.

When you've made quite a lot of bows, you get to know just how much you can take off before getting worried about ruining it. Having a steady hand on the bandsaw helps a lot too. More than that, having a program that lets you print the profiles exactly is a big bonus too. Note to beginners: learning the hard way and the long way is the best way. I trod your path, as did your other bowyer forbears. Don't think too hard about programs and printing and whatnot. Just try to make good bows and learn from them.

What I did here was do a bend test on a sample of spotted gum, punch the results into my nifty spreadsheet and got a bunch of dimensions. Then I printed out the front and side view profiles of the bow's width/thickness and glued them on. Then, very carefully on my bandsaw, I cut them out. Two of them. Stright off the bandsaw, with no tillering whatsoever, this is what they look like with the tips bent 130mm, which is not much less than what I like for brace height:



Pretty good I think. The limb on the left is just a hair's thickness too stiff. Other than that they're ready for the short string tiller. That is, if they were to be unbacked. These two will be boo backed. That means, they are in pretty much perfect shape to apply the backing.

For the two bows so far, I've invested 2 1/2 hours time, total. I might get away with 10hrs for the both of them, completed.

More progress coming soon.

Dave

[Stickbow Hunter]

Good to see you back Dave. Thanks for sharing the build-a-longs.

Jeff

[Bill]

Hey Dave (Yeoman) I've liked what you have shown, I would like to see more, you've made it sound so simple, but still taking in the thought that there is alot of work involved.
thanks,...............Bill

[looseplucker]

Good one Dave -and at that event Tom will make some arrows, and I will make a few strings.

I may also have a bow to tiller at that event -

[yeoman]

Well, the bamboo is now on the first two bows, the second two bows are ready to be cut to thickness profiles, and I haven't decided what to do with bow 5 and 6.

I think I'll be writing a short article on perry reflexing sometime soon. Without boring you with the detail here, I have come to the conclusion that the best way to induce perry reflex is by stringing the bow backwards while the bow is in glue up. Here are the two first bows. One is strung to 2.5 inches, the other is at about 4.5 inches. Why the difference? Good question. It was not on purpose, but it will be interesting to see the difference in final thickness of these two bows which are exactly the same length, front profile and intended draw length/weight.



With the tape and glue sanded off, I gave the lesser reflexed bow about 20 minutes of tillering with a rasp. I used a 'long string' which was in reality the shortest string I could get on the bow without it having a brace height. The intended draw weight will be around 40-45lb @ 28". At this stage I'm only using about 30-35lb force to achieve enough bend to see the tiller.



As always, with a long string, the focus should be on the inner half of the limbs. You want it to bend slightly more there at this stage, because the leverage exerted by a short string is different to those of a long string. When I get this done a little more, people accustomed to normal tiller will think it looks horribly unbalanced, but when I put a short string on it will magically transform into graceful, conventioanl tiller. It took me a few wasted/awful bows to figure that little nugget out.

I have it here with the tips at about 5-6 inches of deflection, which is a nice brace height. However I will tiller it a little more so that in the bracing of the bow, there will be no surprises.

Till next time,

Dave

[greybeard]

Hi Dave,

I am not sure if [perry reflexing] [spelling], is the correct terminology when only two pieces of material have been used in an application such as yours.

Did a Google using different spelling and drew a blank.

Basically you are building reflex into the bow similar to a Dean Torges style of bow.

The application can work well in what you are doing. I made about ten bows in this manner and found that I had to get the right balance of bamboo [pole bamboo] to the main substrate. Generally I found that more reflex was better than less as you can lose a lot of reflex during the shooting in process.

Apart from a gain in performance it can add integrity to the back of the bow.

From my understanding with [perry reflexing] three or more laminations [core material] are used.

As an example; two laminations are glued up in reflex and once the glue has cured the core is pulled into deflex/de-curve and another lamination is applied. When the glue has cured the core is pulled into reflex and another lamination is added and so on going from reflex to deflex.

I was told that the theory behind the idea was that during the draw cycle the stress levels in each lamination depending on their position in the glue up process went from plus to minus stress and vise a versa.

Perhaps it has something to do with the neutral plain and/or a smoother shooting more efficient bow?


My interpretation of [perry reflexing] from what I have been told may be totally wrong and if so can someone out there please give me the correct information backed up with the relevant data.

Daryl.

[yeoman]

The Term 'Perry Reflex' was a term coined by Tim Baker after the process that Dan Perry, a once record holder in wooden flightbows, developed.

Originally the process, as used by Dan Perry, was in using a stave with a thinner backing pulled into reflex while being glued. Using more than two laminations could still technically be called Perry reflexing no doubt.

You're right on the 'more reflexing = better'. I expect the 2.5" bow to come out with up to 1/2" set, and the more reflexed bow to keep maybe 1/2" reflex or come out dead even once shot in. However there is a limit to how much reflex can be induced before it becomes unstable.

From a mathematics and engineering point of view, the correct way to lay up a bow of four or more lams would be to glue two lams together with enormous reflex, then pull them almost straight to glue on another two lams, one on the back and one on the belly. The idea behind that is to force some wood inside the bow near the neautral plane to be experienceing compression and tension before the bow even gets strung.

On a selfbow, the outer 10% of wood fibres do 90% of the stretching and compressing. By gluing up a multi-lam bow as described above, the bow will have a much higher efficiency (=faster) as less of the wood is dead weight, and more of the wood is being stressed at appreciable loads.

I have to say I've not really followed much of Dean Torges' work or lines of thinking. Doesn't mean we cn't end up doing similar things though eh?

You're right. The correct ratio of wood/backing is vital. My bamboo backing taper in thickness as well as matching the front-view of the bows.

A bow's neutral plane is shifted by adjusting the cross section or adding a backing, regardless of any reflex/deflex present. A glued in reflex adds efficiency by raising the percentage of wood which ecnounters appreciable stress throughout the draw. I'll write up a thing specifically about the mechanics of perry reflexing in a new thread when I get a minute.

Cheers,

Dave

[longbow steve]

http://leatherwall.bowsite.com/TF/lw/th ... CATEGORY=9
We may as well hear about Perry reflex from Dan Perry and save you the time writing a new essay Dave

[yeoman]

I'd forgotten how demmed hard a reflexed bow is to string. Especially with a new string.

You might be surprised to learn but a bowstring is under the most tension when it is at brace height. A lower brace height increases the tension. As a perry reflex stave increases early draw weight, this necessarily increases the tension in the string. Add ot that the factor of a new string that likes to stretch a lot, and you have yourself one difficult bow to string.

After much sweating, heaving and struggling, I finally got the string onto one of the bows.



Yuk! I thought I must have overstrained it in the stringing. I got the string off again and found that the reflex is still nice, even, and most importantly, present. Big relief!

But there's a hinge there, and one limb is definately stiffer than the other.

After literally no more than 20 minutes of tillering, here it is drawing 24lb at 19 inches. Not perfect, but looking a lot better.



If I'm lucky this one will get to 35-40lb at 28". That'll learn me for putting a hinge in the limb!

I should say...if anyone wants to buy one of these bows, gimme a holler. I have at least five on the way to be finished in the next two months or so. So if you see something you fancy......

Dave

[yeoman]

Good morning all.

Here's a quick tip for young players-

Sometimes you don't want to cut nocks early in the process. Such a reason may be that you're using English Longbow style horn nocks, or maybe you intend to put overlays on the bow's tips and have the nock wholly on the back of the bow.

However, you still need some way to affix the string to the ends of the bow to tiller it, right?

Here's a simple solution. Take a scrap of wood and cut a wedge, which has a notch in it, like this:





You fix them on by cutting about 30cm of tyre rubber, about 5mm wide, and wrapping it as tightly as possible around the wedge and bow tip. Start off the wedge, then work your way up from the thin end, then work your way back down again.

Why cut a notch in it? Why not just cut a little doorstop and use that? Well, the tension on a bow string is enormous. It really want to be slack. Even with incredibly tightly wound rubber, the string will still try to jam itself between the tied on overlay and the back of the bow, making it extremely difficult to unstring. This way, the problem is avoided.

It takes about 30 seconds to make on the bandsaw. Get a piece of wood about 15-20mm wide, cut one out to the side-view, then turn it on its back and cut it in half. There you have it, two identical temporary tillering overlays.

Dave

[yeoman]

Hi ho campers,

I have another tip for those in the bow making world.

A new bow with reflex, right off the form, is notoriously difficult to begin to tiller. The reason is the stave so desperately wants to remain in its current shape. To achieve this, it will flip flop to unstring itself when you try and use a long string. There's a simple way around it though.

Here's a nice stave with a healthy 2" reflex, right out of the form:



With the aid of a clamp to hold it fast against the tiller stick.....



...the initial bending of the stave becomes a breeze:



Some of you may already know that trick. The one thing I have to say to those people is:

WHY IN THE WORLD DIDN'T ANYONE TELL ME THIS BEFORE THIS AFTERNOON?!

I'd always struggled in this stage of the bowmaking. But no more!

Ciao,

Dave

[Stickbow Hunter]

Some good tips there Dave.

Jeff

[greybeard]

Hi Dave,

I had a bow stringer made up with oversize pockets and it is adjustable to 9'. It is the best tillering string I have ever had and it is easy to use.

Tillering String .jpg (64.49 KiB) Viewed 5477 times

Tiller String Pocket.jpg (50.63 KiB) Viewed 5477 times

The cut out in the top of my tiller stick is 'U' shaped and I have thin pieces of wood to take up the slack either side of the handle.

Daryl.

[Dennis La Varenne]

Dave,

Glad to see you are back again. I am watching with interest and wondering about some more maths at some stage. I am not the only one I think.

Regards,

[yeoman]

Hi Dennis,

thanks for the interest!

I will be doing some more mathsy stuff soon. The priority at the moment though is getting this bunch of bows ready for the folk festival.

But on the maths subject, I just wrote a little Excel spreadsheet which will tell an arrow-maker exactly what diameter his shaft needs to be to get the correct spine for a given draw weight from a given wood. I'll share it soon.

Dave

[Dennis La Varenne]

Don't you just love maths????

By the way, I had a good readup on perry reflexing by Dan Perry on the Leatherwall. It is a difficult concept to get your head around and not as simple as I first thought, but his use of the foam block analogy makes it much clearer how the preload is built into the limb, and, especially, that is should ideally be done with the limbs fairly thick. That part was a bit of a revelation to me.

Regards,

[yeoman]

Actually I kinda hate maths. I've never been good at it, and quite frankly, it doesn't like me either.

However, I do use it cos I like to get things right.

So it's good for something after all.

Dave

[Dennis La Varenne]

Dave,

I like it but I'm not very good at it either. But at the level we need for bowmaking, my brain seems to be able to cope. I like it because of the way it can predict outcomes surprisingly accurately and relieves us of avoidable trial and error.

It also allows us to analyse outcomes to see where we went wrong and why. Tomorrow, I am beingi introduced to the mysteries of Excel formula spreadsheets. Yum, yum.

[GrahameA]

Morning Dave

Actually I kinda hate maths. I've never been good at it, and quite frankly, it doesn't like me either.

However, I do use it cos I like to get things right.

Gee, that sounds familiar. I don't mind Stat's but I really have no great love for anything else. However, like you I use so I more or less have learned what I need to know.

[yeoman]

I've been away, but am now returned.

A little more progress on one of the bows. As it's been a while, I am now treating this one as my practice, or 'warm-up' bow. Here it is pulling about 30lb at 22". Even now, it sits at 1 1/4" reflex just after unstringing. Truly a testament to the qualities of a good piece of Spotted Gum backed with Bamboo.



I think I may have tillered this a little too round. However, it only needs to bend another couple of inches and the tillering is essentially done. Might be about another hour if I take it nice and slow. The string/tip angle is not yet
90 degrees, which for those following along at home is the point where stack starts to...um...stack up.

Dave

[Stickbow Hunter]

Yeah, the limbs may bend a bit much in the outer limb but it still has a nice bend Dave.

Jeff

[Darcy]

Dave and anyone else who wants to chip in,
I have some spotted gum and Bamboo in the workshop and was considering making a bow such as yours above but wasnt sure if the spotted gum would handle it compression wise. Now I have seen your post you have answered it for me with the bows above - although I understand that it also depends on quality of timber used and tillering skill.

I was hoping to build something a shade heavier, around 45-50 if possible. What dimensions would you suggest as a starting point for a 27 draw length.

Thanks all in advance
Darcy

[yeoman]

Darcy, I don't know you at all but based on the fact you want to make a bamboo backed longbow, I like you.

Please find attached a spreadsheet of very exact measurements. If you cut out a stave to these dimensions (round up to the nearest mm), you will have an excellent starting stave for a bow of the specifications you desire.

This is shared on the proviso that you share (with pictures) your progress with everyone here.

Enjoy.

Dave

[Darcy]

Dave,

Thanks for spreadsheet!
From memory (past reads) the bamboo backing should be about 3mm, is that correct?

From my past efforts I am guessing the bow will be a while in the making due to shift work (not real productive during night shifts). I have never posted pictures and I am not exactly a computer pioneer but I will make it happen when the time comes (sucess or failure). I may do another sinew backed spotted gum while I am at it to post as well

I have a largeish diameter bamboo pole. Is the bamboo best cut with a table saw or band saw?

For future reference does anyone in Aus. sell prepared backing strips?

Have you tried S.Gum and B/boo in reflex /deflex design?

Thanks again
Darcy

[yeoman]

I haven't tried deflex reflex, but I am sure that it would work.

To gat bamboo from the pole I split it with a bowie knife and a chunk of wood used as a mallet. Then I use a bandsaw.

The thickness of my boo tapers from handle to tips. Such that as the lam tapers in width, the edge maintains the same 1-2mm thickness. Easy to show, hard to explain.

http://ozbow.net/phpBB3/viewtopic.php?f ... buildalong

Dave

[yeoman]

Hi all.

I was meant to be having two days completely off to be able to work on bows. As it was, I got called in and only got about four hours worth of bowyering.

Here's a bit of progress.

I'm making a bow for Roadie. He wants horn nocks ala English Longbow.



Unfortunately, I cut the tips a little too small to fit the socket of the horn nocks. Answer? Glue some more wood on:



Then bring it all back flush, and make it square with the sides of a length the same as the diameter of the socket opening:



Measure the depth of the socket and carefully draw the correct taper on the tips:



Even more carefully, cut the tips:



Of course it has a square section and so the horn nocks won't fit all the way:



With a rasp I started rounding the square section and checking extremely often for fit. The hint is - file where the opening of the socket is touching the wood:



Eventually the nock fits on completely, and properly.

When it does fit, you can see here how the nock's string groove sits some way doen from the extreme tip of the bow:



Unfortunately the batteries in the camera died so you don't get to see the rest of it yet.

Currently long string tillered to have the tips deflected 6 inches behind the back.

Tilol next time,

Dave

[otis.drum]

dave/darcy,
i advise (though who am i to advise ) that you taper the bamboo in both width and thickness.

in regards to its thickness, i go from 4-5mm thick at the handle down to 1.5-2mm thick at the tips.

darcy i have a 62# @28" boo backed spotted gum bow and there is no sign of compression faults. the darker the spotted gum the better! also ifr making a D/R or just reflex bow, consider making it from 4-5 thinner laminations of spotty under boo.

JMO

[roscoe]

G'Day Dave
Would you be interested if i sent you a sample of acacia wood for you to do a bend test on and feed it into your computer? It would be good to know how this timber stacks up against timbers you have worked on so far...Roscoe

[roscoe]

Sorry, Thanks for the thread it was interesting..Roscoe

[yeoman]

Hi Otis,

I do taper the thickness. Once I taper the width, I thin the bamboo so that the flat edge of the boo is about 1-2mm thick. This means that by the time it's done it's about 3-4mm at the centre and 2mm or so at the tips.

Tapering the thickness of the boo in a bow that tapers in thickness is vital. If bamboo is the same thickness all along, then the netural plane shifts too far toward the back out near the tips where the most bending is done, which increases the stress on the belly, leading to set, stress fractures or breakage.

A pyramid bow, tillered to have circular bend, can have constant thickness boo backing.

Roscoe, if you want me to test some acacia for you I'd be happy to.

Dave