First successful rekerf

[yeoman]

I have previously tried to make a recurve using a kerf to facilitate the bend in the ends of the limbs. Suffice to say, it was not successful.

Not to be swayed, I had another go. I'm glad I did because as it turns out the second time was a charm in this case. The bow is Grey Ironbark, and the lams in the kerfs are red Ironbark. Overlays are Osage. Bow is 61.5 inches around the curves. It started out with 2.5 inches of recurve and two inches of glued in reflex, ending with the tips 2.25 inches forward of the handle right after unstringing. It's 30 mm wide at the center, has no flare, and works through the handle.

It's only 39 lb at 28", but I'm not fussed. I was chasing a good tiller and a bow that'd shoot as opposed to a Mammoth Slayer. That will come later.

Given the recurve and the glued in reflex, the tillering to get the tips moving those first few inches was a real struggle. Others who've had experience with reflexed bows will attest to the extremely high string tension early on in the tillering process. For those that don't have such experience: don't be fooled into thinking the draw weight is going to be monstrous, then try to take off cubic meters of shavings to compensate. You'll end up with an horrendously underweight bow. Once I got the short string on this one, the tillering went quickly and the early string tension returned to something resembling a mortal's capacity to handle.

Here's the form I used. It's three lengths of 19 mm pine glued and screwed together before cutting out.









I love the rich brown of the timber.



Pretty happy with the shape overall





When at brace, the upper limb seems to bend a little more than the lower. However, the shape at full draw is more important than the shape at brace.

[Nezwin]

Really like this one, Dave. Nice curves, nice profile, looks to be a great little shooter. The weight would be about right for a bow to shoot all afternoon, so I wouldn't worry about it being 'underweight'. At 30mm it's also pretty narrow (about 1.25"), the Ironbark able to handle that width. That should bring the speed up a little.

I noticed you're kerfs are 'wedged' - the infill piece being thicker at one end than the other. Does the limb bend at all near the end of the kerf or is it static by that point?


Neil

[hunterguy1991]

Very nice bow there Dave, some very elegant curves!! Glad to see some others getting shooters using this method.

Going of the full draw photo I would hazard a guess and say that your recurves do work a bit during the draw. my recurves in my Bamboo/Mass bow do not open up at all, probably because they're double kerfed and quite thick.

Completely agree with you on the brace profile. With hand placement pushing slightly more on the lower limb the tiller evens out and you get perfect timing of the limbs. Have watched several videos of my bow being shot and that seems to be what's happening.

Is your 28" draw length measured AMO or true? I always measure a true draw for my bows.

Colin

[yeoman]

Thanks for the kind words guys. It's nice to diversify and make something other than flatbows and longbows for a change.

Yep, the inserts are tapered. This was mainly due to the kerf on my bandsaw blade at the time being only 0.7 mm! So I had to taper the inserts to almost nothing so as not to place undue splitting stresses in the limb. I had originally intended for these curves to be static, but in the end I chickened out and took some meat off them to spread the bending stress throughout the ful length of the bow. The last four inches is probably completely stiff...but some of the limb with inset does bend a small amount.

I tested the speed with a 495 gr arrow this morning. It was kind of disappointing...but then it did have the dacron tillering string with vinyl tube on it, so I reckon....no wait...I'll measure...........the string weighs almost as much as the arrow ( ). This sucks a lot of energy that could otherwise go into the arrow. I'll make a nice linen string just for this bow and see if that speeds things up a little. There's no other real reason this shouldn't be quite zippy with arrows.

I had originally played with double kerfing each end. I experimented with some short offcuts. I think it would make for a very striking curve if done with contrasting timbers. But I think that functionally, enough curve can be accomplished with just one kerf. If you do one kerf, and for whatever reason through the tillering it apears not to be enough, you could put a lam on the belly side as an underlay. A 'one-sided kerf', so to speak. That also could look pretty striking. Others have more patience and wood working ability than me though so double kerfing may suit them right down to the ground.

I meant to add in the original post: at brace this bow has about three inches of contact.

AMO or true? Here's a nasty little secret: I've no idea what AMO is. I measure brace and draw length from the belly, always.

I'd like to try one with more reflex and recurve, then set the bow into deflex, probably by cutting it in half and making a takedown out of it. I reckon that'd make for a screamer of a bow, like Marc st Lois'.

[greybeard]

...........AMO or true? Here's a nasty little secret: I've no idea what AMO is.......

AMO True Draw Length..jpg (59.46 KiB) Viewed 3047 times

Daryl.

[Hamish]

Have to agree with the other guys, that is a nice looking bow, and looks like it would be great to shoot.
Lovely work.