Primitive Archer

Main Discussion Area => Bows => Topic started by: BoltBows on November 19, 2018, 07:23:34 am

Title: Interesting HLD bow explosion (Pic heavy)
Post by: BoltBows on November 19, 2018, 07:23:34 am
Hi there folks!

With a lot of inspiration from Leon (aka Leonwood) and Simon (Simson) I wanted to build a HLD elderberry bow. Leon gave me a great piece of elderberry to use and so it began.
I did try to make an elderberry HLD recurve before, but after heat treatment it failed and developed fatal crystals in the sides near the handle.
The first HLD I tried to make involved a lot of work with gouges and scrapers to get the hollowed out shape. Being a woodworker I decided that could go a hell of a lot quicker!
So I took up one of my granddad's old concave moulding planes. (Not sure what this one is called in English.) And well to put it shit way: It will save you a lot of time ;)
(https://farm5.staticflickr.com/4815/44138293110_d33f119b2c_c.jpg) (https://flic.kr/p/2afmhMC)
So this HLD elderberry made it to a 28'' tiller when I decided to shorten it a little to get a few lbs extra. It was just under 40 and I wanted about 42-44.
The left limb seems to do way less than the right, but the left limb had quite a kink which resulted in reflex exactly where the knot it, in the middle of the limb!
Quite dodgy, but amazingly it did what it had to.
(https://farm5.staticflickr.com/4805/44137828260_cfb6ba8375_c.jpg) (https://flic.kr/p/2afiUAY)

However, after shortening it, it exploded spectacularly on full draw. So now the interesting part:
It was the right limb that broke, although in the whole process I felt like the left one was gonna go.
And what's more interesting than that, is the way it broke. As you can see on the picture below it split lengthwise for almost half the limb.
It looks very much like the backing of the limb has been broken off because of the limb deformation, although it might have been that little knot you can see in the picture on the left.
however I still think that knot was not the case, because of the fact that the limb halves almost split a cm apart in width.
In my mind this confirms the theorie of the cross section tension which makes this HLD so fast, however this was probably a bit too extreme.
(https://farm5.staticflickr.com/4901/44137828370_6116fc41c2_b.jpg) (https://flic.kr/p/2afiUCS) (https://farm5.staticflickr.com/4892/44137828430_6beea1c989_b.jpg) (https://flic.kr/p/2afiUDU)
After this happened I wondered what the cross sections looked like exactly, so yeah.. here they are:
(https://farm5.staticflickr.com/4901/45904979842_3ff3716423_b.jpg) (https://flic.kr/p/2cWt2cG)
Looks pretty good I suppose. I even compared them to Simson's recommendations which are in his tutorial on his website, and I was damn close!
Keeping in mind that he makes even more extreme versions of this, mine should be okay I guess.
So yeah, I probably went a bit too extreme, wanting too much from this piece of wood. But it resulted in an interesting project I think!

Cheers guys, thanks for reading.

Jaap
Title: Re: Interesting HLD bow explosion (Pic heavy)
Post by: Badger on November 19, 2018, 07:30:25 am
  I don't believe it has ever been confirmed that the hollow limb is a fast design. Have you seen any tests done on it?
Title: Re: Interesting HLD bow explosion (Pic heavy)
Post by: leonwood on November 19, 2018, 07:40:08 am
Hey Jaap, nice to see you posting here! Sorry to see this one explode, thought you made it! The hld cross section looks pretty good to me.
However it also could have been the wood since my broken elderberry from last week and Erics from last month where from the same tree and they all broke!
Title: Re: Interesting HLD bow explosion (Pic heavy)
Post by: leonwood on November 19, 2018, 07:45:13 am
  I don't believe it has ever been confirmed that the hollow limb is a fast design. Have you seen any tests done on it?

Don't believe anyone has ever done any comparison tests, I know for sure my fastest selfbow is a HLD black locust recurve but I am not sure if that has anything to do with the HLD part.

Would be interesting to test it though... Take two staves from the same tree an tiller them at the exact draw weight and mass, one hld and one flat. Would that work???
Title: Re: Interesting HLD bow explosion (Pic heavy)
Post by: Bayou Ben on November 19, 2018, 07:47:03 am
There you have it....if Leon's bow broke from this wood, it's the wood's fault!
Title: Re: Interesting HLD bow explosion (Pic heavy)
Post by: Badger on November 19, 2018, 11:42:10 am
  I don't believe it has ever been confirmed that the hollow limb is a fast design. Have you seen any tests done on it?

Don't believe anyone has ever done any comparison tests, I know for sure my fastest selfbow is a HLD black locust recurve but I am not sure if that has anything to do with the HLD part.

Would be interesting to test it though... Take two staves from the same tree an tiller them at the exact draw weight and mass, one hld and one flat. Would that work???

  That would be an interesting test. Just bottom line performance would also be interesting.
Title: Re: Interesting HLD bow explosion (Pic heavy)
Post by: bradsmith2010 on November 19, 2018, 11:52:46 am
better is the enemy of just fine,, (SH)
Title: Re: Interesting HLD bow explosion (Pic heavy)
Post by: ohma2 on November 19, 2018, 12:00:19 pm
I agree on the test as mentioned,would be very interesting .yeah 3 bows breaking from the same tree wood does get one wondering.
Title: Re: Interesting HLD bow explosion (Pic heavy)
Post by: Weylin on November 19, 2018, 05:15:57 pm
I'm not sure how accurate the test would be (not that I'm discouraging it) You would need to take a branch from a tree to make the HLD if it's big enough to make a flat bow out of with the trunk. That's already adding another variable. I'm all for playing around with designs to get an idea of what's better or worse but it's just so damn hard with wood bows because there are too many variables that we will just never have control over. I feel like the only reliable data can come from flight shooting/chrono readings from lots of bows over time but even then managing the variables on that can be a headache.
Title: Re: Interesting HLD bow explosion (Pic heavy)
Post by: Badger on November 19, 2018, 06:10:18 pm
I agree with you Weylin, woodbows are virtually impossible to really control variables.
Title: Re: Interesting HLD bow explosion (Pic heavy)
Post by: BoltBows on November 20, 2018, 12:19:24 am
  I don't believe it has ever been confirmed that the hollow limb is a fast design. Have you seen any tests done on it?

Of course you're right there Badger and no I haven’t. Just suspicions!
I agree it would be very interesting to make a lot of HLD bows to somehow compare to ‘normal’ design bows, but yeah it would be hard to truly compare.
Title: Re: Interesting HLD bow explosion (Pic heavy)
Post by: simk on November 20, 2018, 01:35:07 am
would it be wrong to argue that a HLD profile in general needs less wood/mass to generate same strain/draw weight than other common cross-section designs and therefore should be more competitive? just asking...
Title: Re: Interesting HLD bow explosion (Pic heavy)
Post by: Del the cat on November 20, 2018, 02:39:52 am
Great pics interesting post.
Del
Title: Re: Interesting HLD bow explosion (Pic heavy)
Post by: leonwood on November 20, 2018, 05:18:15 am
You are right Weylin, you just never know with wood. There is so much difference in wood even from the same species that most tests only say something about the specific piece of wood the testbows are made from.

But specifically about HLD bows, I have done quite a lot of them in the last two years and I must say that all of them came out as really good shooters. Especially the whitewood ones from elder and hazel amaze me with the amount of set (almost none) and how they hold up even after a lot of arrows.

This bow for example: http://www.primitivearcher.com/smf/index.php?topic=61803.0

I gave it to to a fellow archer who broke his osage bow and he shoots it a lot. The bow still has no set and even after shooting for a few hours it immediately snaps straight after unbracing. And it still shoots 176 fps
Title: Re: Interesting HLD bow explosion (Pic heavy)
Post by: Badger on November 20, 2018, 07:12:05 am
That is a good report. I have always wondered of the hollow limb design might be less prone to vibration in the last few inches of the power stroke. Flat bows have some distortion here that looses energy.
Title: Re: Interesting HLD bow explosion (Pic heavy)
Post by: leonwood on November 20, 2018, 07:39:18 am
That is a good report. I have always wondered of the hollow limb design might be less prone to vibration in the last few inches of the power stroke. Flat bows have some distortion here that looses energy.

Hmm, that sounds like a good explanation, maybe I will do the test and try to arrange an ultra slowmotion camera to see the difference in vibration when the string slams home
Title: Re: Interesting HLD bow explosion (Pic heavy)
Post by: simson on November 20, 2018, 09:57:11 am
Sorry for you lost, Jaap.
I really admire what you've done, assuming this is your first HLD it is good work – even it is blown up.
You and Leon should examine exactly why it exploded. Looking at the fd, I think you are asking a lot from this bowwood. The break is at an area where the limb seems to be thinner. It started as a tension break, after that it splitted (IMO).
I personally would use a risky wood like this with all the knots. A HLD requests the best stave ever, no knots and evenly high crown.
I like the tools you've shown, but I don't think you can get with them the right depth. Wood is not an industrial product, so we have to react on the changes at the back. If there is a hump, follow the geometry on the belly. This can only be done with the scraper (at least in the final tillering stadium) and a caliper.
Back to the fd:
I couldn't find the specs, how long was the bow, how long non bending areas?
And when you draw the bow on the tiller tree, be careful to hold not that long!

I'm convinced elder is good bow wood, not osage – but good! It just needs to be a bit longer, or a bendy handle.

My HLD theory and experience:
A HLD needs less mass compared to a flat or a recurve (same weight). So there is more energy on the arrow.
Meanwhile I've made a bunch (at least about 20) of HLDs, and my experience is they all outperformed bows of same drawweight with common designs.
Example: a little elder bendy handle HLD (http://primitive-bows.com/elderberry-hld-4028-no-37/) shoots 10fps faster than a really well made osage recurve (http://primitive-bows.com/bowquiverarrow-set-for-a-my-wife-4028-no-27/).
I have some of them chrono tested, unfotunately I don't own a chrony myself.

Leon: „Take two staves from the same tree an tiller them at the exact draw weight and mass, one hld and one flat. Would that work???“
IMO: No, assuming the have same length and same length bending parts, the HLD is the lighter bow for sure.


Now let's have a look at the cross section pic:
What you've created I would call a semi-HLD. Will say, the 'moon' is too thick, the limb cannot flatten out. So you will loose same advantages from a real HLD. For further info:
http://primitive-bows.com/hld-a-new-progressive-design-for-selfbows/
Your cross section is a good mass saving design, but provokes a lot of stress in the ridges.   
It wasn't obviously not a problem on your bow, but I found some minor bow woods couldn't withstand without starting to chrysel.

At least:
Don't give up making HLDs. Lot of work – I know, but a successful is a really fun to shoot.
And you've done already great work.
Title: Re: Interesting HLD bow explosion (Pic heavy)
Post by: Weylin on November 20, 2018, 01:34:31 pm
I think the mass is one area that there can be a somewhat objective comparison. If HLD bows are consistently coming in with less mass for the same specs then that might be some indication of an advantage. That seems to be the argument for HLD being efficient, needing less mass to do the same job because of the shape. 
Title: Re: Interesting HLD bow explosion (Pic heavy)
Post by: BoltBows on November 20, 2018, 02:46:39 pm
Sorry for you lost, Jaap.
I really admire what you've done, assuming this is your first HLD it is good work – even it is blown up.
You and Leon should examine exactly why it exploded. Looking at the fd, I think you are asking a lot from this bowwood. The break is at an area where the limb seems to be thinner. It started as a tension break, after that it splitted (IMO).
I personally would use a risky wood like this with all the knots. A HLD requests the best stave ever, no knots and evenly high crown.
I like the tools you've shown, but I don't think you can get with them the right depth. Wood is not an industrial product, so we have to react on the changes at the back. If there is a hump, follow the geometry on the belly. This can only be done with the scraper (at least in the final tillering stadium) and a caliper.
Back to the fd:
I couldn't find the specs, how long was the bow, how long non bending areas?
And when you draw the bow on the tiller tree, be careful to hold not that long!

I'm convinced elder is good bow wood, not osage – but good! It just needs to be a bit longer, or a bendy handle.

My HLD theory and experience:
A HLD needs less mass compared to a flat or a recurve (same weight). So there is more energy on the arrow.
Meanwhile I've made a bunch (at least about 20) of HLDs, and my experience is they all outperformed bows of same drawweight with common designs.
Example: a little elder bendy handle HLD (http://primitive-bows.com/elderberry-hld-4028-no-37/) shoots 10fps faster than a really well made osage recurve (http://primitive-bows.com/bowquiverarrow-set-for-a-my-wife-4028-no-27/).
I have some of them chrono tested, unfotunately I don't own a chrony myself.

Leon: „Take two staves from the same tree an tiller them at the exact draw weight and mass, one hld and one flat. Would that work???“
IMO: No, assuming the have same length and same length bending parts, the HLD is the lighter bow for sure.


Now let's have a look at the cross section pic:
What you've created I would call a semi-HLD. Will say, the 'moon' is too thick, the limb cannot flatten out. So you will loose same advantages from a real HLD. For further info:
http://primitive-bows.com/hld-a-new-progressive-design-for-selfbows/
Your cross section is a good mass saving design, but provokes a lot of stress in the ridges.   
It wasn't obviously not a problem on your bow, but I found some minor bow woods couldn't withstand without starting to chrysel.

At least:
Don't give up making HLDs. Lot of work – I know, but a successful is a really fun to shoot.
And you've done already great work.

Simson, thanks for your answer! let me try to reply some of your questions!
- I will check if the pieces are still around in my dad's workshop, so I can examine it again more thoroughly. You might be right about the tension break, I hope I can find out if was indeed too thin.
- yep it was a risky stave, especially with the big knot in the middle of the left limb and the ones on the sides of the right limb, but amazingly they held their own!
- The moulding plane I use is only meant for roughly shaping the bow. I don't use it when tillering and like you said, I follow the geometry of the backing with scrapers and relatively flat gouges.
But it definitely speeds up the process of shaping, it's a replacement of what I would normally do with a drawknife.
- About the specs: Handle area is definitely 5'' long, and the fades 2,5'' each. At the fades it's about 45mm broad and midlimb about 35mm. The length when it broke was 164cm (64,5'') and it would've been about 46lbs @ 28''. I'm not entirely sure about all the measurements, but I will check soon.
- I never ever hold my bows on draw long, simply because I don't have the balls for it! Although if you make an under strained bow, with almost no set, it should be able to withstand at least a few seconds on full draw, shouldn't it?
- About the cross section: Ahaaa that makes sense! I guess I didn't dare to hollow it out too much, but I will do a better job on the next one!
- About your elderberry HLD, that one is a work of art! It's really a masterpiece to die for! I also really wonder how fast it is, considering it out shot that osage recurve by 12fps!  :o

Thank you so much for your information, I will continue to build HLD's, because the virus has caught me. Currently I'm working on two HLD deflexed recurve bows. One of yew, and one elderberry (the latter is a pretty clean stave, but is also quite flat, so it will be a flat HLD.)

Cheers,
 Jaap
Title: Re: Interesting HLD bow explosion (Pic heavy)
Post by: Jim Davis on November 20, 2018, 05:24:46 pm
One thing seems to be missing from this post mortem. When a half cylinder is bent, there is more happening than simple longitudinal tension and compression. Bending opens the radius so that the inside radius is in tangential tension---and has almost no strength to resist that tension.

Try bending a long piece of PVC that has been sawn in half lengthwise. It probably won't break easily, but it will have a nearly flat cross section where it kinks.

O.L. Adcock tried to revolutionize laminated fiberglass bows by making the limbs concave. Lots of hype, but only a memory now.
Title: Re: Interesting HLD bow explosion (Pic heavy)
Post by: BoltBows on November 22, 2018, 06:56:21 am
One thing seems to be missing from this post mortem. When a half cylinder is bent, there is more happening than simple longitudinal tension and compression. Bending opens the radius so that the inside radius is in tangential tension---and has almost no strength to resist that tension.

Try bending a long piece of PVC that has been sawn in half lengthwise. It probably won't break easily, but it will have a nearly flat cross section where it kinks.

O.L. Adcock tried to revolutionize laminated fiberglass bows by making the limbs concave. Lots of hype, but only a memory now.

Hi Jim, you have a good point on the tangential tension, something I’m aware about. I think the question is if it adds something to peformance or doesn’t. For sure it shouldn’t be overbent because like you point out, it will just flatten and break. However I think if the flattening effect is kept to a certain maximum, it might even benefit the bows peformance. If I’m not wrong it will even smoothen the draw a bit.
Enough stuff to experiment on! That’s what makes bow building fun!

Ps: please don’t take this the wrong way, but Da Vinci also tried to build flying machines. Not everything will work the first time. Maybe this also won’t! But I want to find out.
Title: Re: Interesting HLD bow explosion (Pic heavy)
Post by: Jim Davis on November 22, 2018, 01:59:06 pm
ByBolt, I am sure such a bow will hold together if the stresses are limited to what the wood can bear. Don't know what to think about a performance gain. I think any gain would be due to reduced limb weight and perhaps less hysteresis.
Title: Re: Interesting HLD bow explosion (Pic heavy)
Post by: leonwood on November 23, 2018, 05:02:54 am
My experience is that HLD bows have less set also, so the combination of lower mass, less set and les hysteresis (which are all performance killers!) when added up it is a good possibility that HLD does enhance the performance of a bow ;D
Title: Re: Interesting HLD bow explosion (Pic heavy)
Post by: Badger on November 23, 2018, 11:06:16 am
   I am curious about the mass, are there any examples that show the mass and dimensions?
Title: Re: Interesting HLD bow explosion (Pic heavy)
Post by: leonwood on November 23, 2018, 11:32:37 am
   I am curious about the mass, are there any examples that show the mass and dimensions?

I can measure the dimensions, draw weight and mass of my black locust bow if that helps?