Experimental Hybrid

[bwatters]

Hi All,

So a while back I was talking to one of the older bowyers at my club and he mentioned an old technique where a 'half' form was used and the bow was glued up one limb at a time. Having a very small workshop I thought this was a brilliant idea so I decided to take it upon myself to try this out with a brand new hybrid design.

So I got sketching and came up with a profile. Put some time in on Onshape and finally had a dimensional drawing I could use to make my form. I have attached a picture of the drawing if anyone likes the design.

 I wanted to keep it as simple as possible so started with a 20 degree flat section on the back of the riser for the fade and the belly side to be curved. This way it was much easier getting a nice fit on the form.
I then started working on the form, I use a inner tube/elastic method (always have, one day I'll invest in an air hose and shipping) and eventually got the form just right. You can see it below.

The interesting and very experimental thing I decided to do was to make the initial 12" or so of the form flat. This way I should shift the riser up and down the form for different bow lengths instead of piking the bow and reducing total reflex. If anything, a shorter bow now has more reflex!

I finally got both limbs glued up, cleaned up the sides and the glue lines looked awesome.

Filed in some temporary nock grooves and stuck an old string on and this is how she looked at first brace.

And then with a few more twists in the string

Unbraced profile

I'm going to keep working and see how it turns out.
Total stack was about 0.350" with 2 thou taper. We will see what draw weight we finish with.

[kennym]

Pretty innovative there!! 

I'll guess a little under 40# on a 64"

[jess stuart]

The first few recurves I built were made on the half form.  They worked out just fine.  I too used rubber bands but my form didn't use pegs, just wrapped the bands around the bow and the form.

[Stagmitis]

The most accurate R&D bows i have ever shot have have had limb tips inline with the back of the riser at rest as in your design. Did you add 4" of reflex for speed gain?-

[bwatters]

I haven't made it designed any hybrids until this so I played with the dimensions until it looked about right. My first sketch had 5" but when I drew it all to scale in Onshape it looked a tad too aggressive.

So far I have the riser roughly shaped out and it's drawing 33@28.
The riser turned out at only 16" instead of the 18" I had planned in the drawing. If the riser was 18" I think we would be pretty much bang on what Kenny predicted.

[bwatters]

Well all finished up and it came out at 33#@28",round 36#@30".
Feels like my 29" draw is nowhere near this bows maximum capacity. Might have to play around with riser size to get it optimised for more of a shorter draw length.

Full draw picture ~29"

Looks like I am only just getting all the reflex out of the limbs.

[kennym]

It looks like it has some draw left, bet she is smooth. Nice job!!

[Kirkll]

How is the vertical stability on that bow?

That limb shape reminds me of a bow I worked on years ago that a customer sent me.    Kirk

[bwatters]

At this stack height (0.350") it isn't too bad but certainly has some issues at lower brace heights. It also is quite noisy at lower brace heights as the string slaps the back of the limbs. Once you get up to 8" or so it quietens out considerably and becomes more stable.

[Kirkll]

I was just curious.... i've ran into a couple with that limb shape that lifting the string up and down you could literally flip the bow limbs over top and bottom. Same thing putting the lower limb tip on the ground just the weight of the bow would move the top limb easily.... Kinda floppy...

Yours sure has a nice string angle at 29". .. i'd bet she draws smooth to 32".     Kirk