crab bow (nearly) strung

Adam Karpowicz · Post by **Adam Karpowicz** » Thu Jun 30, 2011 3:21 pm

JJ,

The bow will not be over-stressd at full draw. Since the limb thickness is about 1.2cm now (to increase to 1.3 with sinew on belly), the min. radius of bending will be (1.2/2)/0.10 = 6 cm, where the 0.10 is 10% max strain (actually sinew and horn can withstand more than that). Even with the belly sinew the min. radius will be only about 8.5cm.

The prototype of the bow is the one pictured on page 19 of my book - some differences, but the recurvature is very close. Note the original had most bendng in the middle of the sals where it shows some string follow, not close to the kasans. This means the original's brace height was probably even greater than in the replica.

As to drying. I do not think it could be possible with the thickness of the bow at the bend. Even if possible, I would expect serious damage to the paint there, but the finish is completely intact, there is only cracking of paint in the bending sections. If the bow was recurving itself so much, then the paint on the back side would come off.

Adam

Alessi Francesco · Post by **Alessi Francesco** » Fri Jul 01, 2011 10:03 am

Hello Adam,very interesting bow,nice work(as always).Was it difficult to "tame"?I bet it would tend to twist like crazy the very first times you bend it.I think less extreme crab bows are quite fast,I would like to make one someday:they are attractive.Have you got some pictures of the core(at the knee in particular) before gluing?Your book is really brillliant:it covers every detail in a very scientific way.I started making bows again(after a too long pause) thanks to it.Congratulations.
Bye

Francesco

Adam Karpowicz · Post by **Adam Karpowicz** » Sun Jul 03, 2011 2:05 am

I an sorry Francesco, I have not made any pictures. The core in this bow was a little thicker than in some of the originals - less sinew, more wood. The splices were similar.

Adam

geoarcher · Post by **geoarcher** » Tue Jul 12, 2011 3:34 pm

Adam,

Are your tips and kasan ridges both at about 1.5cm thickness?

Matt

Adam Karpowicz · Post by **Adam Karpowicz** » Wed Jul 13, 2011 10:15 am

Matt - the total thicknes of kasans was 20+mm and the tips a little less.

Adam

geoarcher · Post by **geoarcher** » Wed Jul 13, 2011 12:48 pm

What were they at pre-sinewing but post shaping sans the horn?

Adam Karpowicz · Post by **Adam Karpowicz** » Wed Jul 13, 2011 3:47 pm

I do not remember (I made the bow a few years ago). Prob. 4-5mm less.

Adam

geoarcher · Post by **geoarcher** » Sun Sep 11, 2011 9:17 pm

ok last question about the kasan ridges: what are their length?

dragonman · Post by **dragonman** » Tue Sep 13, 2011 6:39 pm

beautifull bow, expert work, you really got the perfect crab bow form, with a nice even tiller and looks to bend in the right places.
The only thing I dont like about crab bows is the name 'crab' sounds kind of derrogatory to my ears? I think they should have a better name!!!

Uli · Post by **Uli** » Tue Sep 13, 2011 8:49 pm

so call it Mughal - like Mongol

Btw is this a correct linguistic explanation ?

Persian ‏مغول‎ mughul means ?Mongol?
Gurkhan (‏گوركانى‎) = Mughal King comes from mongolian k?r?g?n = ?brother-in-law", pointing towards the relation with Chinggis Khan's family
?Mog(h)ulistan? = Tschagatai-Khanate, home of Tamerlane

Kviljo · Post by **Kviljo** » Sat May 25, 2013 7:09 am

Any news on this bow? I'm intrigued by the stability of the design. Your bow sems to have a fair amount of horn, which according to the rumor would make it very unstable while keeping a lot of reflex. Got any thoughts on these bows ability to keep reflex while being used, versus stability? What feature of the construction in these bows would you say gives them stability?

Adam Karpowicz · Post by **Adam Karpowicz** » Sun May 26, 2013 8:02 pm

The rumour comes from Kani (If recall this detail correctly), which is true, since the horn, together with sinew both have the modulus (stiffness) lower than wood, so more of each would make a bow softer. Since the sinew layer was nearly always the same thickness in all Turkish bows, the horn was the culprit for them.

The crab bows have lots of sinew and this will make them less stable as well, unless the humidity was lower for the sinew to get stiffer. I think the low humidity plus the greater thickness of the limbs overall would make the bows more stable.

I strung my crab with some difficulties again (see pic) and decided to do a bit of more drastic heat treatment of the sals to force more bending close to siyahs. It helped and I saw old bows with similar bending before.

The bow stacks horrible beyond about 21-22in. I drew it to 26 so far - nearly 100lb! Anyway, this design is the worst imaginable with the un-necessary and excessive recurve at the siyahs, which as a result make the bow behave as a shorter bow than it is. And the high brace (8.5in here) reduces the power stroke. I can not help thinking of those exaggerated fantasy weapons made in India (swords and such)...

Adam

Adam Karpowicz · Post by **Adam Karpowicz** » Sun May 26, 2013 8:04 pm

picture

Kviljo · Post by **Kviljo** » Sun May 26, 2013 9:15 pm

Cool

So a high amount of wood in these might be the factor to pay attention to in making them behave stable.

I think your "all show, no go"-idea about these bows is pretty much it. Especially your bow seems to show this. I guess mine, with the 10-11" brace height also shows that it could not be a type of bow designed with mainly performance in mind. - however, I wonder if the geometry of these bows make them rather good with light arrows, in spite of the heavy "kasans". I'm curious to test-shoot it, but mine is still too unstable to dare to loose some arrows.

My bow is now braced and strapped to the workbench, where it will stay for a week. After staying braced for a week I hope it will be ready to give off a force/draw-curve and maybe some test shots. Like yours it seems to want to stop at 27-28 inches. - which I guess indicates that it can not be a great shooter with a only 17-inch powerstroke.

Is there any chance to get a report on how much overall reflex your bow has kept after staying braced a while and having been drawn some times? Adding to the "performance-disappointment" with the design is the rather large string follow mine showed.

What design-pressures that shaped these bows is quite baffling to me. - other than the rather large show-off factor, hehe.

Adam Karpowicz · Post by **Adam Karpowicz** » Wed May 29, 2013 11:27 pm

After about a week strung and drawn a few times (110lb at 27in, 60%RH), the immediate unstrung reflex is 2in. If I did not do the extra heat bending on the limbs close to kasans, it would be about 5-6in (not too far from the fresh after tiller). I could have thinned the sals there instead of doing the heat corrections to keep the reflex, but then the thinner limbs would be less stable (and the bow would probably stack even more), so I opted for the heat.

I was tempted to test the bow and compare with other styles, but it would not be a fair comparison at this time (high RH, strung so long). Maybe some other time once the belly sinew is in place.

Adam