First steamed tips!!

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hunterguy1991
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Joined: Mon Jul 09, 2012 10:18 am
Location: Woodford Queensland

First steamed tips!!

#1 Post by hunterguy1991 » Sat Jun 28, 2014 7:28 pm

Hi all,

Here is the latest project I've been working on for the last couple of days. It is a bow made of a Red Oak board from Masters, backed with 100% linen, 66" ntn pulling a whopping 15lb at 28 inches!!

The design was based off Greybeard's "Bamboo, hard rock maple and steam" bow as I really like its simplicity and elegance.

The last 8 inches of the tips were steamed into an 8 inch radius and the last 12 inches of limb are a constant 7mm thick.

Here's a shot of the bow at 28 inches on the tiller stick. Let me know your thoughts then I will let you all in on how long the tiller job took to complete :)
DSCN0406 (640x480).jpg
DSCN0406 (640x480).jpg (171.33 KiB) Viewed 1690 times
I have some ideas on how I could potentially up the draw weight a little but would love some input from you all. I would ideally like to have it pulling 40-45lb@28"

Straight shooting as always,

Colin

Dennis La Varenne
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Location: Tocumwal, NSW. Australia

Re: First steamed tips!!

#2 Post by Dennis La Varenne » Mon Jun 30, 2014 12:00 am

Colin,

Very good work indeed on your tillering. I have imported your picture into Photoshopand drawn some lines on it which show the degree of symmetry between the limb on the right opposed to that on the left.I have also rotated your picture so that the tiller is exactly vertical and square to the edges of the picture to minimise the chances of optical illusion.
Screen Shot 2014-06-29 at 11.33.23 PM.png
Screen Shot 2014-06-29 at 11.33.23 PM.png (753.12 KiB) Viewed 1649 times
I notice that a fair amount of your recurve has come out at full draw, but enough remains to help keep the string angle at full draw acceptably shallow. If you compare the limb position at vertical line No. 9 on both sides, you can see that the curvature on the right hand limb is beginnig to flatten out compared to its mate.

I have drawn red lines from the stiff part of your riser section to your string nocks on both limbs. Happily, both limb nocks tend to align horizontally demonstrating that they have the same amount of rearwards movement when fully drawn as you can see at horizontal line No. 5, and the deepest part of the arc of each limb is at the middle of the working part of the limb which is also excellent. You can see this where I have drawn the thick red line at 90 degrees to the thin red line from the string nock to the riser.

One thing to note is that the amount of gap beneath the right limb compared to the left limb is greater on the left. This means that the right limb is taking less load than the left limb which has a greater bend. This is telling me that the right hand limb is slightly longer than the left limb.

Having a longer upper limb is not problematical in itself as it tends to bring the arrow pass closer to the middle of the bow as measured from nock to nock. However, wood bows tend to compensate for the different amount of applied force at the handle by rocking slightly forward to tilt the upper limb slightly forward which evens out the amount of arc in each limb. It is a lesser version of what happens to a Japanese Yumi bow at full draw where the upper limb tilts forward a great deal, but the line between the string nocks is vertical and that line crosses the line of the arrow at right angles, thus equalizing the thrust of the bowstring on the arrow.

I would suggest that though your bow has a shallower arc in the right hand limb, that with normal shooting, the whole bow will tend to tilt slightly forward in the upper half of the bow to compensate for an otherwise asymmetrical pair of bends and end up shooting true by bringing the nocks into vertical alignment at 90 degrees to the line of the arrow.

So, I think you have done a good job indeed.

So far as increasing this bow's draw weight to 45lbs from 15lbs, you will have to do two things. Firstly, you may need to shorten the bow by 2 inches at either end to bring it back to 62 inches and reduce the length of the riser by one inch at each end. Following that, you will need to add a backing material such as a Hickory lamination of greater than 3mm thick whilst holding the bow in considerable reflex. I would bring the tips to as much as 6 inches ahead of the back of the bow whilst the backing lamination is applied and glued in place. Even the application of 2 laminations may be necessary, but I think one would be sufficient if enough reflex is built into the bow. The amount of recurve you have is quite sufficient and is not a working recurve, so do not make it too severe or you will seriously lessen the amount of actual working limb you have. Static recurves put a lot of bending load in the inner limb and their only benefit is to allow a shallower string angle at full draw. They do not shoot faster.

Regards,
Dennis La Varénne

Have the courage to argue your beliefs with conviction, but the humility to accept that you may be wrong.

QVIS CVSTODIET IPSOS CVSTODES (Who polices the police?) - DECIMVS IVNIVS IVVENALIS (Juvenal) - Satire VI, lines 347–8

What is the difference between free enterprise capitalism and organised crime?

HOMO LVPVS HOMINIS - Man is his own predator.

hunterguy1991
Posts: 859
Joined: Mon Jul 09, 2012 10:18 am
Location: Woodford Queensland

Re: First steamed tips!!

#3 Post by hunterguy1991 » Mon Jun 30, 2014 6:34 am

Hi Dennis,

Thanks for your critique on my work. After looking at the bow with the grid behind it and the chord lines put it I can see some small improvements that could be made, however I think that they're not worth doing at the moment and since that bow was just an experiment I think I'll leave it as is for a display piece.

Wasn't bad for a 5 minute tiller job though!! I guess the more even the limbs come out of rough shaping the less is needed to get them to bend even. Roughing out the limbs to thickness took me nearly 3 hours with hand saw, chisels and a rasp so little tillering was nice.

More timber will be acquired through the week for a shot at a second version that will be 62" ntn and slightly thicker (maybe 1mm) extra in the limbs to see what the resultant poundage is. hopefully it goes up a bit. I had not considered shortening the handle but since you mentioned it and thinking about it for a while it seems like a wise move, so thanks for that advice!!

As for the hickory backing, I would love to do that, but unfortunately I have no source of hickory or the tools to cut accurate laminations... the tools issue I could work around but I have no idea where to source it. Had tried Lazarides Timber as they stock some exotic and imported stuff but not hickory. Could maple be used as a substitute?

if I wanted to allow the recurve to work more during the shot cycle would the process be to thin them slightly to allow more bend under load?

Again, thanks for your input.

Colin

morganp

Re: First steamed tips!!

#4 Post by morganp » Mon Jun 30, 2014 10:07 am

The more I look at this bow, the more I like it. And Dennis' grid and explanations help me understand why bowyers do all that, lining up the nocks and more! I made my own bow on the 'wow, what a surprise, it acksherly *+%$#*ng works!' method. Followed by the 'ah yeah, that'll do' method of fine-tuning. Still works, five years later but I wouldn't dare let Dennis anywhere near it ...

One source of hickory is in the tool handle bin at good hardware stores. Mine still has a few axe handles, pick-axe handles and so on coming through in hickory. Not as many as they used to but they still get them in. You could maybe choose a good one and split it?

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Gringa Bows
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Re: First steamed tips!!

#5 Post by Gringa Bows » Mon Jun 30, 2014 11:37 am

Lookin good Colin :wink:

hunterguy1991
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Re: First steamed tips!!

#6 Post by hunterguy1991 » Mon Jun 30, 2014 1:08 pm

Morganp, I enjoy the shape of this style bow as well. Might stiffen the tips on the next one a little more to get an even better shape.
I had thought of using handles but will be tricky to find a couple of decent ones I would imagine. If my searches come up nothing I will definitely look into the handles as a resort.

Thanks Rod. Already stoked to try another one now and hopefully get some more poundage.

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bigbob
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Re: First steamed tips!!

#7 Post by bigbob » Mon Jun 30, 2014 2:21 pm

as Dennis displayed great job on the tiller especially given the duration spent on it !
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Dennis La Varenne
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Re: First steamed tips!!

#8 Post by Dennis La Varenne » Mon Jun 30, 2014 2:30 pm

Colin,

Maple can be used for backing.

Also, remember these basic rules of bowyery -
1. Where two bows are equal in every respect except width - the bow which is twice as wide will be twice as heavy.

2. Where two bows are equal in every respect except thickness, the bow which is twice as thick is eight times as heavy.

The second of these rules means that the draw weight of a bow doubles for approximately every 17% in thickness.

3. Never bend a bow in progress past its intended draw weight.

To get the recurves to work or unwind like a modern recurve requires the limbs to have a similar shape to the modern recurve. Short recurves like yours are non-working or 'static' recurves. Their historical purpose was to allow a short bow to have a shallower string angle at full draw than a straight ended bow of the same length. But that benefit came at the price of a much higher loading on the limb between the recurve and the riser.

Over time, I have noticed from measuring my bows, that generally, they seem to have a thickness taper of 0.008" per inch. I therefore mark my limbs in 3 inch increments and mark each increment on the sidewall to be 0.024" thicker as measured from the highest point on the back if it has a convexed crown. 24 thou is a poofteenth over 0.5mm. I make the same marks on BOTH sides of the limb, both top and bottom starting from the nock. When rasping the thickness of the limb down, I am able to ensure that I do not make one sidewall of the bow thinner than its opposite which can result in a cast in the bow limb if severe. To make a heavier bow, I start with a thicker tip. On a bow of 70 inches with a rigid handle, beginning with tips of 3/8" or 0.375" and increasing the thickness by 0.008" per inch will produce a bow pretty close to 50lbs depending upon the density of the wood and its width at its widest at the flares. I am doing such a bow at present. It is 1 1/4" wide at the flares.

The most remarkable thing about doing the shaping so carefully is that when you begin to bend the bow, the amount of tillering required is minimal until the bow is perhaps 3/4 drawn and even then it is often minimal because working to a known thickness taper takes care of one of the greatest variables in bow making. Wood is much more homogenous than we often believe and it is very satisfying to watch your bow take a beautiful symmetrical bend right from the outset and continue all the way through.

Commonly, I have found that the bow only needs sinking as the limbs bend to keep it within required draw weight.

MorganP,
The purpose of the drawing I did above is purely to show how evenly a bow is bending. Symmetry of bend means that each limb is doing its proper amount of work and sharing the bending load equally. If they do that, then the propulsive force to the arrow from the bow is applied with equal force from both limbs and over exactly the same period from loose to the string departure of the arrow, which phenomenon I have previously referred as limb synchronicity for want of a traditionally used term.

Such a picture as that above can demonstrate easily and clearly what would take many hours of verbal and hand-on demonstration to teach.
Dennis La Varénne

Have the courage to argue your beliefs with conviction, but the humility to accept that you may be wrong.

QVIS CVSTODIET IPSOS CVSTODES (Who polices the police?) - DECIMVS IVNIVS IVVENALIS (Juvenal) - Satire VI, lines 347–8

What is the difference between free enterprise capitalism and organised crime?

HOMO LVPVS HOMINIS - Man is his own predator.

hunterguy1991
Posts: 859
Joined: Mon Jul 09, 2012 10:18 am
Location: Woodford Queensland

Re: First steamed tips!!

#9 Post by hunterguy1991 » Mon Jun 30, 2014 3:38 pm

Dennis,

Lazarides do stock rock maple so I will endeavour to give that a crack in the near future. I imagine that I would have to be careful with the way I cut the maple to use it as backing so it doesn't lift splinters?

I Will persist with the linen backing and see how far I can push it before too much set becomes apparent. Will also give me a good opportunity to fine tune the belly blank.

As a Civil Engineer I was very much aware of the first 2 rules you mentioned as they are to do with second moment of inertia of the cross section in question, however had not heard of the 3rd rule... something I will keep in mind in the future most definitely.

Thanks for the advice on the thickness taper, this will be a big help in predicting the strength of a bow rather that just going for it and having it come up short. And now thinking about it, that taper is about what I have in the section of this bow where the limb sides are parallel. Where the limbs width begins to taper in I kept the thickness constant. That might be why the mid and inner limb came so close to a circular tiller??

Colin

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