Horn bows....They are weirder than you think

I've been thinking about horn and sinew bows again.  There are some really great pictures in Richter's  "Die Hornbogenarmbrust".  On jpage 89,he shows a pair of pics of the belly of the bow fragment in the Statsmuseum of Köln.  This bow is has lost all of its sinew and covering, and one can clearly see the individual horn plates all interdigitated into one another.



 

I used Microsoft Paint to reassemble the limbs into one picture and then traced out the joints between horn plates in red lines.   I am pretty sure of most of the lines, but there certainly some errors.  The overall picture it the important thing.  These plates are not laid out in straight lines like bricks.  Instead they have an organic look like cells in a tissue.

You need to click the image full size to really see the lines.






Mac

Hi Mac! 

Nice work you have done! Yes it's interesting to see that they don't seem to have made them with any kind of symetry in the bow arms. They have taken all the horn they have, short and long pieces, and just built a horn core with them. 
When I'll try to make one I will probably match to two bow arms a bit more. 

Micke D

Thank you, Micke!

This is an on-again off-again project I have been persuading for decades now. Every couple of years I think about it again.  Recently, I think I have made some progress understanding what needs to happen.

Yesterday I did a little experiment in making matching grooves in some horn scraps.  The teeth of my scraper are a bit too pointy, and that is making a gap down in the valleys.  It's encouraging, none the less.

I have also had some ideas about making a guided scraper based on the bolt fletching jig in the Löffelholz manuscript.




Mac

Here's a quick sketch of my proposed horn grooving machine.  

The horn plate is held by the clamp at the end of the bed.  A suitable scraper is clamped into the two handled "stock".  The cheeks of the stock guide its travel down the length of the bed.  The bed is provided with grooves which have been cut in by the same scraper.

 Once grooves are established in the horn plate, it is turned over.  The grooves in the horn key into the grooves in the bed.  This insures the correct relationship between the grooves on both sides of the plate.  This is essential  for subsequent assembly of the plates.  

The horn plate may be turned either end-for-end, or top-for-bottom at any time as is convenient.  The grooves on the bed will assure accurate alignment.




Mac

Your proposed design is reminiscent of planes for grooving or smoothing crossbow bolts. I'd say you're on the right track, and having the plates mate up is probably absolutely necessary.  As for making horn-sinew prods myself, I say... "Have fun stormin' the castle."  Carry on.  Geezer.

Geezer,

This is my jumping off point, of course.



  I am intregued by your mention of "smoothing" as well as grooving.  Are there any other examples of tools like this that you know of?

I have been preparing to storm this castle for quite some time now. I am hoping to actually set hands to the task within the next year or so. I have a couple of water buffalo horns that the carpet beetles have not found yet.  The next wave of experiments may involve cutting them up and getting some grooves on them.

Mac

Mac: somewhere... maybe Josef Alm's "Survey of European Crossbows" I have seen references to spoke-shave jigs being used to rough out crossbow bolts from square stock.  Of course the author may have been referring to the grooving jig for cutting slots for vanes, but using a jig to rough-round shafts might make sense.  Geezer.

I'll have a look in Alm, and see if it's there.  Thanks!

I am exited by the idea that the Löffelholz manuscript tool might not be an isolated example, and that these "guided" scrapers might be something that bowyers and fletchers used for different tasks. 

Mac

Yup, wouldn't be at all surprised.  I'm gratified to see you working/thinking so assiduously.  Geezer

I must say that I have not seen anything about using a skraper to rough out crossbow bolts Geezer, and I have most of the easy to get crossbow books, so I don't know where it's from, it's not from Josef Alm at least.

Your grooving jig design looks good Mac.The only weakness I can see,is in the clamping.Seems to me that when you are grooving a piece of bone for the first set of grooves,the workpiece could possibly move from side to side.A solution could be to have adjustable 'finger's on each side of the support legs of 'spokeshave' type cutter holder,butting against the sides of the workpiece,this should prevent any side to side movement.
                                     Hermit.

Thank you, Hermit!

The thing you pointed out has nagging me as well.  Here are my possible solutions to that potential problem.

The first is to put a temporary clamp on the free end of the horn until the grooves are well established.  Then the horn would get turned over and would key into the bed grooves.  After the second side was complete, you would turn it back over and finish the first side.  The grooves of the second side would key to the bed and hold it straight.

The second is to do basically the same thing, except instead of the temporary clamp, you would just hold the free end of the horn with one hand and ply the scraper with the other until the grooves were sufficiently deep to turn the work over and carry on as above. 

Mac

It turns out that once the grooves are established, they will remain pretty straight even with hand held scraper.

For my test pieces, I used a variation on the method that Adam Karpowicz mentions in his book on making Turkish bows. http://www.ottoman-turkish-bows.com/   That is to use a straight edge and a scribe to make one good straight line in the horn and then use that line to guide the first tooth on the scraper.  By gradually bringing the scraper to level, the other teeth are brought into play a little at a time.  Once the grooves are established on one side of the guide line, you do the same thing by moving the scraper over and gradually initiating the rest of the grooves. 

Once the grooves are all there, it's just a question of continuing to scrape until they reach their full depth.   Most modern horn-bow makers use some sort of guide to establish their grooves, and then remove the guide for convenience. They are either using a tool like this one.  https://img.photobucket.com/albums/v709/Smokeys/TorysCamera002.jpg  or else just holding the scraper blade in both hands like this.. http://i.ytimg.com/vi/IZ2lzEhvRro/maxresdefault.jpg  The limiting factor here is getting enough force on the tool. As a result, these guys spend hours grooving the relatively small amount of surface in a hand bow's limbs.  A horn crossbow is going to have 5 or 10 times as much grooved surface as a hand bow does.  Using the technology that the modern guys are using would be a real source of repetitive stress injury as well as taking a very long time.

I am hoping that my proposed machine will allow a good, powerful, and comfortable two handed grip while still maintaining the truth of the grooves. 

Mac

(Note:  I revised my estimate of the total grooved surface comparison between hand bow and crossbow. )

Whichever system you go with Mac,it has to be better if you have both hands free to guide the cutter.
                           Hermit.