Primitive Archer

Main Discussion Area => Horn Bows => Topic started by: stuckinthemud on July 02, 2017, 06:49:44 am

Title: hornbow project numpty questions
Post by: stuckinthemud on July 02, 2017, 06:49:44 am
Ok, so, when processing horn, you need a strip of horn about 6mm thick, is that measured from the top of the crown, or the edge?. Also, do you run the thicknessing cut right to the end of the horn or do you cut off the tip and save it for other projects? Do you cut a few mm oversize and use abrasives to get to the final thickness?  Finally, some sources advocate a sacrificial jig to mount the horn on before band sawing but is it ok to just use the saw fence? Thanks, Andrew
Title: Re: hornbow project numpty questions
Post by: Pat B on July 02, 2017, 07:46:23 am
Just guessing...I think you want the horn "lam" to be even thickness through out when you cut it from the raw horn then grind it to it's glue up shape and size.
Title: Re: hornbow project numpty questions
Post by: stuckinthemud on July 02, 2017, 08:16:09 am
Hi Pat, yup, I have back strips to process, each one going from 2mm thickness at the wide end, to full thickness about 6" from the tip. I think I'm supposed to make a second cut?
Title: Re: hornbow project numpty questions
Post by: mikekeswick on July 02, 2017, 12:53:15 pm
Hot melt glue and a piece of ply are what to use to keep the cut true. Do not use the fence. A 3/8th blade about 10 tpi with a good set to it is what you want and free hand the cut.
Try to envison on what plane the longest, widest, straight strip is.
A horn strip does not need to be 6mm thick. 6mm thick horn would be suitable for a bow of around 100# If you are aiming for something around 50# I wouldn't go any thicker than 4mm. You want to have the core as thick as possible as wood is the most stable and stiff material in a composite. Sinew thickness is more or less set at 2 - 3mm over the center of bending sections so you can really only alter the core to horn ratio. More horn will have less string follow but will be harder to stabalise. Typical core woods will be around 0.65s.g. horn is more like 1.3 s.g.
It is best to cut all the way to the tip, even though it narrows too much to be in the finished bow, it is useful for clamping later when flattening and prepping the strips for grooving.
Yes cut oversize on the bandsaw. Then use, rasps, files then 40 grit to get perfectly flat. At this point you will see that you will have a tapered strip anyway. Once you have it perfectly flat use a very sharp scraper to get them completely smooth. At this point you should not touch the strips with bare hands(important!).Then groove.
Title: Re: hornbow project numpty questions
Post by: stuckinthemud on July 02, 2017, 02:15:05 pm
Thanks Mike, that's exactly what I need to know. Target weight is between 40 and 50 for my first one as I  shoot 45# max at the moment. Probably look for 70 from the second one but that's a way off yet.
Title: Re: hornbow project numpty questions
Post by: stuckinthemud on July 11, 2017, 08:30:59 am
I cut the horn plates a long way too thick (11mm)so I'm gonna be a long time rasping them down to thickness; my question is, the concave hollow section at the end of the horn, what do I do about it?
Title: Re: hornbow project numpty questions
Post by: mikekeswick on July 11, 2017, 11:15:22 pm
Just keep grinding/rasping until it is flat. This is the part where your lovely long horn becomes shorter! the internal concavity is one of the reason why the Turks (and others) used concave horn/convex core.
You can use the bandsaw to make further cuts on the thick proportion too.
You need to stop and continually check you are removing material on the same plane through the whole strip.
I use my edge sander to get the strips really close. A standard belt sander with 36 grit paper is very useful.
Title: Re: hornbow project numpty questions
Post by: stuckinthemud on July 12, 2017, 12:00:36 am
Thanks Mike, hollowing the horn is an option I'm fine with as my mate with the power tools is an hour away. Presumably where the horn tapers the depth of the hollow reduces?
Title: Re: hornbow project numpty questions
Post by: mikekeswick on July 12, 2017, 10:12:05 pm
You are better off making it flat throughout its length.
Title: Re: hornbow project numpty questions
Post by: stuckinthemud on July 12, 2017, 11:29:09 pm
Ok, I've filed the horn into 5mm plates and straightened them with steam, they are 18.5" long including a 4" taper and a 4" concave section that i guess I could use for the handle. This leaves 10" of  32mm wide parallel sided working section??
Title: Re: hornbow project numpty questions
Post by: stuckinthemud on July 13, 2017, 11:10:47 am
Any tips on getting the horn plate perfectly true?
Title: Re: hornbow project numpty questions
Post by: mikekeswick on July 13, 2017, 11:45:55 pm
I always grind away material to get a straight, untwisted strip. You need to stop regularly to give it a good eyeballing for straightness. It is tempting to follow any minor twist to get a longer/wider strip and heat to straighten but unfortunately the twist will come back and lead to a twisted bow.
Again as heat is used for a large part of the tillering this heat will lead to any earlier heat corrections going back to their original twisted shape. Indeed this can happen when the horn is heated for the gluing process. You need to get it to 50 degs Celsius.
These sort of issues show why every step has to be perfect or else the house of cards starts getting unstable! 
Title: Re: hornbow project numpty questions
Post by: stuckinthemud on July 14, 2017, 02:22:31 am
Yup, this learning curve is huge!

This is where I am, the heat correction was for the curve of the horn rather than twist, still not totally straight though. The photo is deceptive, there isn't any twist as such, should I cut to size then finish grinding? The bottom piece is 40mm wide, the top one is slightly narrower but is a 1/2" longer at the tip end
(https://stuckinthemudsite.files.wordpress.com/2017/07/win_20170714_10_17_52_pro-2.jpg)
Title: Re: hornbow project numpty questions
Post by: mikekeswick on July 14, 2017, 11:21:00 pm
They look pretty good.
I would continue removing horn on this side to remove the concavity totally first. Then start working on the other side to get it completely flat and thicknessed. Then once it is perfect in thickness remove any extra width down to the size you want.
Remember that extra width is no problem. it is actually very useful to have extra width during the glue-up to the core. Once the horn is glued to the core and dry you can then reduce the core/horn for sinewing.
Title: Re: hornbow project numpty questions
Post by: stuckinthemud on July 15, 2017, 06:12:18 am
Thanks Mike, will do. Going back to the hollow limb section. If the olden-days buyers hollowed their horn plates, in addition to getting greater length from a given horn, might there also be a mechanical advantage to using this form - flexing tubes is much more difficult than flat plates, so you might get a stiffer/quicker bow.
Title: Re: hornbow project numpty questions
Post by: mikekeswick on July 15, 2017, 10:33:38 pm
No the stiffest cross section is a rectangle. More material at the surfaces to resist tension and compression. The problem with a rectangular limb is the poission effect. The upturned edges on the bent limb then take more stress. The flat back/round belly cross section pretty much eliminates this problem but is less stiff than a rectangular section.
Title: Re: hornbow project numpty questions
Post by: bjrogg on July 16, 2017, 04:40:23 am
Thanks for sharing this stuckinthemud, someday this is on my bucket list and I really haven't a clue so this is very helpful.
Bjrogg
Title: Re: hornbow project numpty questions
Post by: stuckinthemud on July 16, 2017, 08:57:44 am
Big thanks to all who have/are guiding me along this path! I'm really struggling with the final dressing of the horn plate. I keep trying to tack it down to a base board to be able to perfect it but the centre bellies up when I tack down the ends. Any suggestions?
Title: Re: hornbow project numpty questions
Post by: mikekeswick on July 16, 2017, 11:30:42 pm
Steam it flat. Remember that it will spring back if you just clamp it between flat surfaces. I heat the horn then bend it past straight by hand, hold it there and then run cold water over it. It will 'set' very quickly into its new shape.
Title: Re: hornbow project numpty questions
Post by: stuckinthemud on July 19, 2017, 06:51:13 am
Not a question, just an update. Rasped and scraped the plates down to 4.5mm, the hollow section has reduced to 2" length, giving a 13" length 35mm wide plus a 4" taper to the tip. Time to sort the core
Title: Re: hornbow project numpty questions
Post by: Del the cat on July 19, 2017, 10:43:19 pm
Great Q and A thread for us armchair, would be hornbow makers.
I'm looking out for local maple... damn council cut down a lovely one about a month back, I got there too late it was cut into stupid short sections  .... grrr.
People with chainsaws who don't know the value of what they are cutting down ... grrr  >:(

Del
Title: Re: hornbow project numpty questions
Post by: stuckinthemud on July 24, 2017, 05:00:10 am
So, these horn plates are quite short, I'm thinking a Magyar style might be the best option?
If I do go with this form, then, is the outside timber of the lath on the back like a Turkish bow, or belly side like a self-bow, and if on the belly, I'm guessing I need to de-crown the core-lath? I was thinking of a three-piece or 5-piece using v-splices throughout.
Title: Re: hornbow project numpty questions
Post by: BowEd on July 24, 2017, 05:25:55 am
Stuck....The outside of your core on a turkish is on the belly for form bending reasons avoiding splinters.An end view look of the core should look slightly oval to avoid the poissen effect.It reduces that extra mass weight off the corners and puts a stress line straight accross through the core from side to side looking at it from the end.
Most times both surfaces of the core are violated getting sinew and horn over it anyway.
Title: Re: hornbow project numpty questions
Post by: stuckinthemud on July 24, 2017, 08:22:01 am
So, does that mean you would slightly hollow the horn plate?
Title: Re: hornbow project numpty questions
Post by: mikekeswick on July 24, 2017, 10:06:10 am
You use either a flat joint or a convex core,concave horn joint. Both work.
There are a few reasons for the convex/concave way. As Beadman mentioned the outside of the tree is the belly of the bow because this is the best way to bend the cores eg. the outer fibers of the lathe are then uncut and able to conform to the bends without excessive splintering. The outer surface of lathes from small trees are naturally convex. Buffalo Horn is naturally concave on its interior. Therefore you can get more length and thickness from your available horn and have to remove less material from the formed and joined core.
However for a first bow it is easier to make flat mating surfaces.
A Magyar style bow is much easier to make than a Turkish bow (from a core point of view) and would be more suited to short horns.
Title: Re: hornbow project numpty questions
Post by: stuckinthemud on September 24, 2017, 07:25:16 am
OK, I have finally sorted out some wood for a core (apple) so its time to make a little progress, and, I have some questions about scrapers.  What do you make them out of and how do you cut the teeth, and, finally, I want to go with non-matching grooves but I'm not sure precisely what that means: does that mean that one scraper has 2mm deep triangular teeth at, say, 16 points per inch, while the other scraper has 2mm deep triangular teeth at, for example,10 points per inch?
Title: Re: hornbow project numpty questions
Post by: BowEd on September 24, 2017, 08:19:20 am
I used a Saws All type blade that I triangular filed the teeth[10 or 12/inch groove over 1.5"width of limb] for flat grooving of horn and core.A concave/convex scraper with the teeth filed into it with a fine triangular file for concave and convex grooving would be needed.Done by hand.Around 2mm or 1/32" deep.
Some prefer to have many more grooves per inch.
Here's my grooving tools.
(http://i920.photobucket.com/albums/ad41/Beadman1/DSCN1802_zpskwk0t17h.jpg) (http://s920.photobucket.com/user/Beadman1/media/DSCN1802_zpskwk0t17h.jpg.html)
This did'nt cost much to make.
(http://i920.photobucket.com/albums/ad41/Beadman1/DSCN1803_zpsactf2xnu.jpg) (http://s920.photobucket.com/user/Beadman1/media/DSCN1803_zpsactf2xnu.jpg.html)
(http://i920.photobucket.com/albums/ad41/Beadman1/DSCN1804_zps2wpqazpe.jpg) (http://s920.photobucket.com/user/Beadman1/media/DSCN1804_zps2wpqazpe.jpg.html)
These I acquired through a trade from a good bow making friend.Both styles will work.
Title: Re: hornbow project numpty questions
Post by: stuckinthemud on December 27, 2017, 11:21:03 am
I give up trying to source green timber for a core!  Just checking, a timber merchant not too far away has acer saccharum in stock.  Assuming its perfect, straight and rift or quarter sawn, am I correct in asking them to mill me some laths to 20mm thickness, or is it OK to go for 12mm for a 45#@25" Magyar-style bow? 
Title: Re: hornbow project numpty questions
Post by: Bjoern Sofeit on December 27, 2017, 10:30:31 pm
I bought some material from smith-lumber dot com

Their website seems to be under maintenance atm, but you could write them an email, and get some 2x4 hard maple bow staves. They also ship green wood.