Crab Bow Measurements

Bede · Post by **Bede** » Mon Feb 01, 2010 8:03 am

Regarding the horn insert in the tips of the crab bow:

I have seen some variation. I have probed into the damage tip of the measured bow and the width of the horn is 3.5 mm.

The bow mass is 450 grams. The next two posts will have the cross sections.

Bede · Post by **Bede** » Mon Feb 01, 2010 8:04 am

These are the cross sections of the measured crab bow.

Bede · Post by **Bede** » Mon Feb 01, 2010 8:08 am

This page covers down to the centre of the grip. These cross sections used a profile gauge for data. The profile gauge is only accurate to about 1.5 mm so I visually corrected the drawing from the bow. I will be refining the cross sections later.

Dusan · Post by **Dusan** » Mon Feb 01, 2010 9:03 am

Thanks, Bede. Very usefull information.

Daniel T. · Post by **Daniel T.** » Tue Feb 02, 2010 8:37 pm

Yes, that's great, thank you very much!

Kviljo · Post by **Kviljo** » Sat Mar 06, 2010 3:47 pm

I've started making one of these, but am struggeling with deciding how to make the "kasan" core piece. All the "kasan eye"-bend is made on the kasan piece, I guess.

Is there any evidence that this was steam-bent from a straight piece of wood, or have they used a naturally bent piece? If it is steambent, how thick is the core at the center of the bend? I'm just not sure if I will be able to bend such a sharp bend with the required thickness? Perhaps the wood is not that thick, and that the ridge is mostly made up of sinew?

I've also been wondering a bit why the limbs are straight at the outer presumably non-bending parts, while the bending section of the limbs have a lot of reflex. Perhaps the added shear and tension on the glue line is not such a big problem with these sinew-wrapped bows? And perhaps having the bending section close to the grip makes the bow more stable? - is that a bit issue with these bows?

Adam Karpowicz · Post by **Adam Karpowicz** » Mon Mar 08, 2010 1:12 am

The reflex in these bows in mostly concentrated in the kasan eye, not in the sal. That, with the reflex in the grip, makes the sal quite straight. It would be quite Ok to start with the sal nearly straight in these bows, with some reflex added as the sinew dries. As to the kasan's core thickness, it is probabbly no more than 1/2 inch, the rest is sinew and (very thin) horn.

Adam

Bede · Post by **Bede** » Mon Mar 08, 2010 12:22 pm

The one I saw cut up had the kasan core only about twice the thickness of the sal core and less than one third the thickness of the kasan with sinew. If there was any horn, it was paper thin. I could not see any horn past the splice.

I don't think this was the only way to make them or the best. I think Adam's advice would make a better bow.

Kviljo · Post by **Kviljo** » Tue Mar 09, 2010 9:30 pm

Thanks for the brilliant responses, guys.

That cut-up bow should have been published somewhere! The information that the cut up chinese bow (at atarn.org) gives is priceless.

On bending the kasan piece - I guess one could shape the kasan ridge before the bend, to prevent splinters.

And, I forgot to mention it: Thanks a lot for publishing the dimentions and cross sections. The cross sections will be especially helpful.

JJ · Post by JJ » Wed Mar 10, 2010 11:20 am

Bede,

somehow I have missed your last posts....

Thank you very much for the cross sections, they?re brilliant. That?s a lot of work... I?ve never seen before so many, and precise cross sections of a crab bow. That?ll be a great help for bowyers.

Hope to see you on atarn.

JJ

Bede · Post by **Bede** » Thu Mar 11, 2010 12:59 am

Kviljo,
The ridge I saw on the cut up bow was only about a millimetre high on the core despite the thickness of the ridge on the completed bow. To make that, I think the core of the kasan was made a millimetre thicker for bending and then adzed away afterwards. Splinters could be removed at the same time.

Possibly the kasan core was made even thicker for bending. This would allow differential thickness being used to affect the degree of bending at each section.