Saved one today and learned a big lesson
Posted: Tue Sep 30, 2014 12:10 pm
Morning all,
I had an order from a mate for a 90lb warbow, done in spotted gum, backed with hickory.
Settled on a bow 80 inches total length (hes a bit shorter than me) with handle dimensions 32 wide and 28 thick for a 6 inch block then following Dennis's template tapered the thickness down to 12mm at the tips, figuring that it should work out nicely.
Glued it up Sunday, out of the wrapping Monday, cut out rough dimensions, rough shaped the belly round and crowned the back (always crown the back on these now, cant explain it, it just works!!)
Measured out the thicknesses along the limbs to check how even they were, 12.4 or so on one and around 14.3 on the other. The limb that was 14.3 was somewhat thick over its entire length so I started scraping to even them out. Completed that and put a long string on... tips were coming around early, maybe even a bit much but I figured when I got the handle bending all would be ok... WRONG!!
Put the short string on and nothing but the last 8 or 10 inches of tip was bending... CRAP!!
The Problem:
Since the tips were so small compared to the handle there was no where near enough stiffness in them to make the handle bend a bit. Also, when the short string goes on and your getting a bow to brace the force vectors on the tips are different to when you pull the bow to a brace height with a long string...
Should have know about the vectors, im an engineer!!
The remedy for this bow:
Scraped out the belly around the handle to mid limb to get it bending as required to save the bow, And heres the result... Brace height is around 6 inches here.
And here we are at 28 inches pulling 48 pounds.
The tiller is not quite perfect but its ok for a saved bow I think.
Let me know what you guys reckon. Any suggestions on fine tuning the tiller or just leave it as is??
The Remedy for Future bows:
Will be up-ing the tip thickness to 14mm thick and wide to give the tips a little more stiffness to get the handle bending for any bows over around 60lbs to make sure they don't end up like this one did.
Now I need a new piece of spotty for round 2.
Colin
I had an order from a mate for a 90lb warbow, done in spotted gum, backed with hickory.
Settled on a bow 80 inches total length (hes a bit shorter than me) with handle dimensions 32 wide and 28 thick for a 6 inch block then following Dennis's template tapered the thickness down to 12mm at the tips, figuring that it should work out nicely.
Glued it up Sunday, out of the wrapping Monday, cut out rough dimensions, rough shaped the belly round and crowned the back (always crown the back on these now, cant explain it, it just works!!)
Measured out the thicknesses along the limbs to check how even they were, 12.4 or so on one and around 14.3 on the other. The limb that was 14.3 was somewhat thick over its entire length so I started scraping to even them out. Completed that and put a long string on... tips were coming around early, maybe even a bit much but I figured when I got the handle bending all would be ok... WRONG!!
Put the short string on and nothing but the last 8 or 10 inches of tip was bending... CRAP!!
The Problem:
Since the tips were so small compared to the handle there was no where near enough stiffness in them to make the handle bend a bit. Also, when the short string goes on and your getting a bow to brace the force vectors on the tips are different to when you pull the bow to a brace height with a long string...
Should have know about the vectors, im an engineer!!
The remedy for this bow:
Scraped out the belly around the handle to mid limb to get it bending as required to save the bow, And heres the result... Brace height is around 6 inches here.
And here we are at 28 inches pulling 48 pounds.
The tiller is not quite perfect but its ok for a saved bow I think.
Let me know what you guys reckon. Any suggestions on fine tuning the tiller or just leave it as is??
The Remedy for Future bows:
Will be up-ing the tip thickness to 14mm thick and wide to give the tips a little more stiffness to get the handle bending for any bows over around 60lbs to make sure they don't end up like this one did.
Now I need a new piece of spotty for round 2.
Colin