Author Topic: Core material advice request  (Read 5960 times)

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Offline Mesophilic

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Core material advice request
« on: January 16, 2020, 08:23:40 pm »
Are modern wood laminations suitabe for a horn bow cores?  Say the lams Binghams sells?

My Grozer biocomposite looks like it has a core of two bamboo lams.  Was wondering if it would work out if I ordered some or if I'm just flirting with disaster.

If doable, what species would be appropriate?

I ask because I'm trying to find a way to work on something indoors as my knife and bow making space is currently burried in snow.

ETA: not trying to be a purist yet.  When I figure out how to make a few good shooters then I'll work on authenticity.   For example, I'm using epoxy to glue up the horns but will eventually lean the art of grooving and using fish baldder glue.
« Last Edit: January 16, 2020, 09:07:12 pm by Mesophilic »
Trying is the first step to failure
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bownarra

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Re: Core material advice request
« Reply #1 on: January 17, 2020, 02:21:02 am »
You will find that it's not really about being 'authentic' more that all the best ways have already been worked out :) Do not try to reinvent the wheel! Even if the old bowyers had had modern epoxy I don't think they would've used it, the reason being that virtually all hornbows need heat correction when tillering. Collogen glues can take it but you need a specific epoxy to do the same job. Sometimes areas need to be repeatedly heated and that is the killer for modern glues in this application.
There is no magic with using collogen glue you just need to learn its properties and how they can be used to your advantage. The grooving isn't hard either and doesn't need to be matching with the core grooves. The grooves filled with glue act as a 'core protector'.
As for cores......Binghams lams - no way! Grozers bows made with multiple lam cores need specialised jigs etc for glu-up. The old way is to benbd your core when still thick. This way the core acts as it's own form for horn gluing. The wood is the stiffest part of a composite and gives the bow its shape. Try gluing horn strips onto a thin core.....it isn't happening!
Again I highly recommend you follow the 'old' methods.
You need a diffuse porous wood, with medium density like maple/hornbeam/elder etc . The wood must accept glue well and be able to be steam bent into shape. If you can't find anything then contact wood mills in areas where there is a lot of maple and ask for perfectly straight grained wood, with absolutely no pin knots and ideally flatsawn. Wood is stiffest laterally in this orientation which is important in a core.
Boo will work but be careful on the node placement and good luck finding thick enough culms.

Offline DC

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Re: Core material advice request
« Reply #2 on: January 17, 2020, 10:59:21 am »
the reason being that virtually all hornbows need heat correction when tillering. Collogen glues can take it but you need a specific epoxy to do the same job. Sometimes areas need to be repeatedly heated and that is the killer for modern glues in this application.
Can we talk about this for a second or two. The Book says to never heat the bow above 150-160°f. I'm assuming that's the temp that hide glue will take. Any epoxy I've used will easily take that. Is there something I'm missing?

That said, there is no problem using hide glue. You're going to have to use it on the sinew anyway. Learning to trust it is the big thing :D

Offline Mesophilic

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Re: Core material advice request
« Reply #3 on: January 17, 2020, 11:43:45 am »
Just to expound on DC's question, this is from West System...they make the epoxy I use on knives and bows.

Quote
"We have glued two blocks of mahogany together with WEST SYSTEM® epoxy, allowed it to cure for one week at room temperature, and then exposed the whole assembly to 200°F for 3 hours before forcing a chisel into the glue line to fail the joint. When the joint was examined closely, we found that the primary failure was in the wood and not the epoxy. Experience has also shown that while heat tends to soften epoxy while it remains warm, if WEST SYSTEM epoxy is not exposed to damaging heat (exceeding 230°F for extended periods), it will return to full strength when cooled to room temperature."
Trying is the first step to failure
-Homer Simpson-

Offline simk

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Re: Core material advice request
« Reply #4 on: January 17, 2020, 12:39:05 pm »
the data sheet of my cheap liquid and ready to use fishglue says:

The curing time is approx. 12 - 24 hours. The cured adhesive is stable from minus 34 °C to + 260 °C.

(translated with deepl)

+ 260 °C is about 500°F

I tested that and gave a full heat treating to a laminated bow....I then reglued it after it delaminated 8). Still I'm convinced that glutine-glues are more heat resistant than standard epoxy.
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bownarra

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Re: Core material advice request
« Reply #5 on: January 17, 2020, 01:13:24 pm »
I know what you guys are saying :) I have used many epoxies over the years making carbon and various other composite parts.
I've made a few hornbows with epoxy for the horn/core joint. I know it can be done but wouldn't recommend it to anyone. There are quite a few other 'issues' as well as the need to heat the bow. The simpler the bow design you are going with the more likely it is to be suitable.
By all means do whatever you feel is going to work. I learnt all this stuff by making all the mistakes haha ;) I prefer not to re-invent the wheel now :)

By the way any 'ready to use' collagen glue eg. liquid is definitely not upto the job of making hornbows. Maybe it would be ok for the splices but even then make some good stuff yourself and then see the difference. I don't recommend heat treating laminated bows of any kind.

Offline DC

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Re: Core material advice request
« Reply #6 on: January 17, 2020, 01:24:11 pm »
Maybe I was reading too much into Adam's 150-160°. I just looked again and he actually said 50°c which is 122°f.

Offline simk

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Re: Core material advice request
« Reply #7 on: January 17, 2020, 01:43:55 pm »
By the way any 'ready to use' collagen glue eg. liquid is definitely not upto the job of making hornbows.

I dont know you nor your bows  8) But I very well know a bowyer who did dozens of scythians and other hornbows with exactly that glue  8) For me it works perfect. Did you try it?
« Last Edit: January 17, 2020, 01:52:37 pm by simk »
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Offline Mesophilic

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Re: Core material advice request
« Reply #8 on: January 17, 2020, 06:55:07 pm »
I'm just playing devil's advocate.

Does the final draw weight make a difference on how much stress is placed on the glue line(s)?  I have no idea how neutral planes play in to limbs with such a huge range of motion.

I'm guessing here, but aren't the techniqies used designed around war bow strengths? 

As far as temp ranges go, wouldn't anything above 165°F be a moot point?  Since proteins fully coagulate at 165, wouldn't anything above that potentially cook the sinew? 
Trying is the first step to failure
-Homer Simpson-

bownarra

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Re: Core material advice request
« Reply #9 on: January 18, 2020, 02:42:54 am »
By the way any 'ready to use' collagen glue eg. liquid is definitely not upto the job of making hornbows.

I dont know you nor your bows  8) But I very well know a bowyer who did dozens of scythians and other hornbows with exactly that glue  8) For me it works perfect. Did you try it?

I wouldn't know seeing as you haven't told me its particular name....:)
Do you know how liquid glues are made and how they are kept liquid. Do these processes lend themselves to producing the highest grade of glue - no, they are interested in yield and making money. Again I suggest you make your own glue then you KNOW how it has been treated
I am not hear to have pointless arguments about semantics. I am just trying to give you the benefit of my direct experience. I reserve the right to be wrong haha

A lot of this stuff will all make sense when you have made a bunch of hornbows. Theory only gets you so far. Just jump in and make one yourself and the answers to your questions will become apparent. Good luck.

Offline gorazd

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Re: Core material advice request
« Reply #10 on: January 21, 2020, 05:53:23 pm »
About using bamboo as wood core in horn bow:

I cut the core from bamboo flooring plank. The plank is vertical grain and around 8mm thick glued lengthwise with some industrial glue ( I think) - this doesnt matter in bending force ...
I grooved the bamboo/horn joint and glued it with a mixture of home made glue from cat fish bladder and cow sinew restover.
It works OK.
The only caveat - the core could not be prebended with heat - I tried it (before grooving) - with dry heat. Didnt try it with wet wood - I guess bamboo flooring wouldn stand...
So the bow is not so extremly reflexed as ussualy turkish bows.

After one year of shooting  - the bow is still OK.





« Last Edit: January 21, 2020, 05:59:38 pm by gorazd »

Offline Mesophilic

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Re: Core material advice request
« Reply #11 on: January 22, 2020, 02:05:54 pm »
gorazd, were you able to get the sinew to pull some reflex as it dried?

This makes me wonder how actionboo would work as a core.
Trying is the first step to failure
-Homer Simpson-

Offline gorazd

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Re: Core material advice request
« Reply #12 on: January 22, 2020, 05:16:48 pm »

Yes I get some reflex from sinew drying .
I did sinewing in three layers (korean style - combed sinew layers) and after puting each layer I tied the ears of the bow a bit stronger. I waited 2 weeks between layers.

Check my thread : http://www.primitivearcher.com/smf/index.php/topic,64848.0.html




gorazd, were you able to get the sinew to pull some reflex as it dried?

This makes me wonder how actionboo would work as a core.