First Bow

[Outbackdad]

Lewis has been making a few bows so I though I would have a go to.
Spotted gum with bambo backing. It is looking great so far.
See if anyone has any advice to add.

Eddie

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[Stickbow Hunter]

It's lookin' fine so far mate. Keep us up to date with your progress.

Jeff

[Dennis La Varenne]

Hullo Eddie,

For a first effort, the tillering job looks first rate - far better than my first bow for sure. It has quite lovely bends through both limbs and has the look of a "D" bow.

Firstly, I notice that the handle is glued onto the belly of the limbs with quite abrupt fade-outs which will tend to put a lot of shearing stress on the glue-line. It may pop off unexpectedly at some stage, or you may hear a crack when you draw it one day as the glue line lets go. It almost certainly won't be your limbs judging from your excellent tillering job.

I have attached two diagrams of how glued-on handles were treated in the wood bow days because handles popping off was a problem even with the best glues of those days, and there were some quite excellent glues. In those days, the handles were glued onto the belly of the limbs which were left quite thick in the handle area.

To minimise the chances of your handle coming off, I would suggest fading the handle block outside your handgrip area down in a shallow concave shape (dips is the traditional term because they dipped down from the handle and faded into the limb) and feather the ends of the riser block into your bow's belly which will allow it to flex more and take some of the shearing stress off the glue line. The first diagram shows this technique. This technique requires whipping over the fadeout to support it and prevent if from lifting off the limb. There was also the use of a small woodscrew or pin through the mid-limb into the handle riser to prevent it coming off altogether.

Further support came from the handle grip covering which was often cord or string whipped around the grip area. This gave an excellent grip feel as well as added considerable to the support of the glue line.

Don't dip your handle riser section down into your limbs with this bow as shown in my second diagram because you will have to retiller your bow and you will lose far too much draw weight. Keep this technique for your next bow.

Secondly, Spotted Gum is a good selfbow wood without any backing at all so long as there is no damage to the back (the only reason for backing a bow). It is dense and hard with very good mechanical properties in both compression and tension. Backing it with bamboo will NOT improve its performance at all unless it is used according to the Perry reflex principle which is beyond the present issue.

Bamboo is much stronger in tension than Spotty is in compression. There is not the required balance in strengths between the two working surfaces of the bow if it is bamboo backed. To bend well and keep a high degree of straightness when unbraced, the back fibres must be able to stretch (lengthen) and the belly fibres need to be able to compress (shorten).

If the material on the back of the bow is very strong in resisting stretching as bamboo is, then the wood fibres on the belly MUST shorten by compression more than they really ought in order to make the bow bend. Too much of this compression can overwhelm the natural ability of the belly wood to resist compression and the compression forces are higher than the wood's 'elastic limit' properties and it will begin to take more and more set.

Consequently, your bow will almost certainly take a 'set' or 'string follow' to a greater degree than it would have done otherwise if you had not backed it with bamboo.

If the stave really needed backing, my preference would have been for a couple of strips of sretched linen or silk which would have quite adequately prevented any slivers of wood from rising on the back, and yet still maintained a reasonable balance between tension and compression on the back and belly.

All wood bows will take some set, but backing with bamboo is not a way to prevent it, nor is it a way prevent breakage as so many seem to think. Bamboo backing will prevent breakage of the back, but the belly will begin to fail and the bow will take unreasonable set. A set of around an inch (25mm) doesn't seem to make much difference to the cast (speed and distance a bow can shoot an arrow) of a bow, but more than that will see a much slower bow because the limbs have lost a lot of their natural ability to return to original straightness.

All of this may be a bit overwhelming at first, but you will get your head around it with more bows.

But, once again, I congratulate you on your first really excellent attempt and am very impressed with your tillering job which is something which many people have most of their early trouble with. All the rest above is to help you in the future so that some unexpected things do not happen to you as they did to me.

All the very best in your bowmaking,

Dennis La Varenne

[Gringa Bows]

looks good mate,good onya for having a go ..............Rod

[otis.drum]

looking good outbackdad,
we haven't seen you or the boy on here for a while!
what's the length and poundage of that bow you have there?

dennis, i have a 64" 62#@28 tillered to 29" boo backed spotty lam bow. it has no problems handling the boo backing, there is no compression faults showing and has not gain excessive set (under an inch, and still holding some D/R). the boo is thin and tapered thinner right down to the tips. the limb cross sections and trapeziod (narrower on the boo backing than the spotty belly) and the ratio of boo/spotty would be roughly 1:3 respectively.

i'm not challenging what you say, but i haven't experienced it.

[Outbackdad]

Hi all

Thanks for the comments.
Otis the bow is 68" but I am still working on the poundage, still a bit to high.
I left a bit too much bambo on but will do better next time. I am still very happy with how this bow is working out.
Hope to have a poundage around 50-60#.
Went to the bambo back because the spotty we have that lewis has used keeps cracking, the bambo has made a lot of difference.

Eddie.

[kimall]

Good work mate it is coming along well.
Cheers KIM

[Glenn]

Eddie, good effort mate. The bow looks as though it is coming along well....Glenn....

[Dennis La Varenne]

Otis (through Outbackdad),

Not at all. What you have done is exactly how bamboo needs to be used - both tapering and trapezoiding your limbs. Doing it that way much improves the tension : compression ratios between back and belly. Not many people have the skills you have to both taper and trap their limbs.

What usually happens, is that an overly thick lam of bamboo is glued to the stave's back and some I have seen are around 5mm+ thick. It is just too thick and its tension resistance overwhelms all but very few wood species on the belly and the results are usually predictably poor.

This doesn't mean that Outbackdad's bow is an unmitigated failure. Far from it. He has done impressively well for a first attempt. I just want him to realise that there are significant problems in using bamboo as backing unless one has fairly well developed bowmaking skills and that if his bow does begin to fret, he will know why for another time.

I will also say that I am always impressed by those beginning bowyers who have the courage to post their first efforts, knowing that they may get comments both negative and positive, but hopefully constructive. I think it takes some guts to do.

Your post will put him on the right track and there will be someone up there who will be able to give him some excellent tutoring on how to use it well as a backing. If he can be shown how to trap the limbs of his bow, the chances of his bow not developing frets will increase markedly and I dare say that its cast will improve with less mass in his limbs without significant loss of draw weight.

I do still maintain however, that backing with bamboo does nothing to improve a bow's performance that I have ever seen, but it does look very nice. I would like to be proven wrong on this issue however if someone has done some decent comparative testing.

Regards,

Dennis La Varenne

[kimall]

I watched the VID by Dean Torgers on the weekend again and he said that if you have crap timber that wont make a selfbow on its own you can back it with BAMBOO to make it usable.So I would say that there is a benefit in backing a bow with it when the timber in the majority that we get here is less then ideal.Like Spotted gum most of the time.
Cheers KIM

[Glenn]

There is definately a benifit to backing a bow. It is esay to test the benifits. Just make a selfbow and a backed bow out of the same stock material and see what results you get for yourself. If you don't use bamboo and just use a suitable piece of timber you can taper the backing down by hand during the tillering process. Bamboo is harder to work with because the tapering needs to be done before it is glued to the stave. The results with backing a selfbow can be very suprising as to performance and that amount of set it takes....Glenn....

[Dennis La Varenne]

To everyone (through Eddie),

I have made bamboo backed bows as well as self-bows of the same design, the only difference being the bamboo backing and found absolutely no benefit at all. Contrary to what Kimall reports of Dean Torges, I found that poorer wood suffers more from bamboo backing than leaving it as a selfbow for just the reasons that I posted of above. I wish that I could say otherwise, but I can't, because it simply hasn't worked out that way in my practice except in one instance which I will mention later. Nor have I ever been able to discern any particular performance benefit from any kind of wood backing unless applied as I posted above using the Perry reflexing technique which I have done.

The only bellywood which seems to withstand the tension resistance of bamboo is that which has a very high density of around 1000kg/m^3 air dried and a very high modulus of rupture (MoR) similar to the various Ironbarks species and some of the tropical hardwoods. Spotted gum can come into this class, but a lot doesn't.

With Otis' deflex-reflexed bow of bamboo backed Spotted gum, my guess is that he began with a very good piece of Spotted Gum and his treatment of the bamboo was clearly cognisant of the fact of the significant difference in tension : compression between the two. His bow has held shape because of a very sound knowledge of the fundamental properties of the two materials which he has taken carefully into account.

Presuming that one of the properties of bamboo is that its high tension resistance has a certain amount of 'pulling' effect (this is only a speculation on my part, but seems to be a common belief) when bringing bow limbs back from their bent shape when braced/shot, that property, if it actually exists, is not enough to overcome the effect its high tension resistance has on forcing most belly wood to compress past its elastic limit. Even Otis' bow he says has taken about an inch of set. If the balance between tension and compression were balanced, no bamboo backed bow would ever take any set whatsoever.

Only an inch of set is very good indeed, but I have made a good few straight selfbows now which have taken only 1/2 - 3/4 inch and kept it. However, I have not made one yet with a bamboo back which took anywhere near as little unless with a very high density bellywood (bamboo backed Ipe in this instance).

For those so inclined, it is easy to find out the speific MoR of individual pieces of wood at hand by using Dave (Yeoman) Clarke's bending test which he explained in his thread on using mathematics to make bows. Sometimes you can even get individual pieces which exceed the industry listed mechanical properties. It is a simple way of testing whatever you have at hand for the quality of its mechanical properties. He also made the very useful observation that the elastic limit of the wood he tested was reached at about 60% of the MoR - something which can be easily factored into a bow's design blueprint.

It is also easy to obtain a fairly accurate ADD of an individual smaller piece (stave size) of wood by simply weighing it, measuring it to obtain a volume and then doing the sums to obtain its mass/m^3, assuming that it has been dried well. 12% moisture content is the industry standard for ADD which is difficult to measure unless you have a reliable moisture meter, but one of the small hand-held devices with twin probes is not bad for stave sized wood which has been reduced to overbuilt bow size.

Americans write about some of the northern hemisphere bow woods becoming brittle with overdrying, but the few indigenous hardwoods which I have used don't seem to suffer much from this problem - at least I have not been able to dry them to a state of brittleness yet unless I can somehow force-dry them.

Sorry Eddie if this is getting a bit complicated.

Regards,

Dennis La Varenne

[Outbackdad]

Thank you all.

I am planing my next bow already.
Will make a change or 2 but will keep with the same base plan as this has worked out well.
Shot the bow today and it went better then i hoped.
Come out to just over 50# by our dodgy scales.
A light sand and seal and i am done.

Eddie

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[Stickbow Hunter]

Looks good mate - congrats!!!

Jeff

[Steven J]

Well done mate. A fine effort.

Steve

[Gringa Bows]

does the arm holding the bow in the bottom pic belong to Lewis has he had a shot out of the bow yet.................Rod

[Outbackdad]

Rod.

Yes and yes, but he does not like the high #age.

Eddie

[Dennis La Varenne]

Eddie,

That bow looks magnificent!!! It really does. One of my favourite things (as the song says) is beautifully tillered circular bends in a bow and your bow has them. I am a bit jealous on behalf of my early days when I found it so hard to get them and you have done it on your first go.

Please take my posts above as advisory only. There was no ill-will in any of them and I earnestly hope that none of the problems I outlined happen at all and your bow lives to great old age. I do note that you seem to have feathered your dips in a bit more than on your first pics which is good.

Best regards,

Dennis La Varenne

[Outbackdad]

Dennis

Thank you.
I read everyone’s advice and go from there.
The first pics were still a work in progress.

Eddie

[Gringa Bows]

you finish the next bow yet Eddie ................Rod

[kimall]

Mate as I said on the phone VERY well done.You seem to have got the tiller really good you even got the TOP limb the stiffer one.Good on you.An afternoon in the workshop is worth more than an afternoon reading hey.
Cheers KIM

[Steven J]

Well done again on an excellent bow. My experience with backing bows with bamboo or other laminates shows a performance increase where you are using the backing to force the bow into a reflex or semi-recurve shape.

Dennis, I always appreciate your contributions. Taking the time to explain things is kind and offers emence value to this site.

Kimall, how can you tell that the top limb is stiffer from these photos? Even a reasonable camera can distort a photo beyond the 2 or 3mm of tiller that is widely accepted as the norm on a bow with even length limbs. (I don't really want to go into the merits of positive and negative tiller here as that is really like flogging a dead horse).

Steve

[kimall]

Steve J you should not take me too serious as I dont, it was a continuation of a conversation on the phone with Eddie about this bow and a joke we had about the differant tillering methods.Besides PETA wont like it if I flog a LIVE horse.
Keep smiling mate we all make em differant.
Cheers KIM

[Steven J]

Kim, there is always more to every comment that we are able to read (both yours and mine). Been working at the forge lately?

Steve

[kimall]

I need to put a handle on the bearing knife but am having fun with the new bow so got off track a bit today.Toomorrow I have to retiller a longbow a guy just got for Xmas but it is a bit heavy for him and the bowyer wont work on it.
I am moving house soon so the projects will be on hold for a few weeks but the new place has a great double shed and I have a new 100 kg anvil on order so I will be forging more than ever then.
Cheers KIM

[Dennis La Varenne]

Kimall,

I drew some red lines over Eddie's bow in Photoshop and re-posted it here. Definitely has the correct greater tiller in the upper limb in this pic. The greater upper limb bend is pretty obvious and Eddie is going to great lenghts to hold the bow as vertical as possible.

Couldn't let that one through to the keeper.

Dennis La Varenne

[kimall]

I hope you are joking Dennis as I was because surely someone with your EXPERIENCE knows that you cant measure tiller with the bow held by hand.
It is just to easy to manipulate the bend of the limbs by where you put pressure on the handle and in this pic the handle is not even straight up and down with the top of the handle being pushed away from the archer forcing more bend in the top limb.Anyway as I said I am sure you are just having a go at me and that is fine but since you did go to the trouble to put the fancy lines up I just had to make sure the keeper is actually playing cricket.
Cheers KIM

[Dennis La Varenne]

This old pot will keep boiling for years yet, Kim.

My judgement is as valid as yours based on the same pic. We're still playing cricket, its just who bowls what kind of ball up to the batsman.

Only Eddie actually knows what kind of tiller is in his bow, and he hasn't said . . . yet.

Dennis La Varenne

[kimall]

Hooray its taken all these years but finally something we both agree on.
Cheers KIM

[clinton miller]

i haven't made a bow and don't know a great deal about bowyering but correct me if i'm wrong. (i'm sure you will)

if the center of the bow is the fulcrum around which the limbs bend and we pull the string at a point above the fulcrum, (say 3/4" higher for a shelf or knuckle + 1/2" for nocking point, which is realistic) then my common sense tells me that the top limb would have to be stiffer if you want both limbs to bend the same.

maybe i don't have any common sense