Primitive Archer
Main Discussion Area => Bows => Topic started by: mwosborn on December 28, 2014, 09:40:40 pm
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Just wondering if anyone would give suggestions on tillering out this osage mostly sapwood bow. It was cut last April - about a 3" diameter sapling. Split and clamped to a caul for a couple of months to keep from warping badly. Then has been drying in the shop since then. 63" tip to tip. 1-1/4" wide to midlimb then tapers to 1/2". Back of the bow is just under the bark. Most of the heartwood has been removed to this point although some does remain. The larvae had eaten some holes/trails in the sapwood - these were filled with titebond 3 and sawdust. Bow was then backed with rawhide.
Currently I am out to 23" and it is pulling just over 50#. I am wanting to get to 27" or 28" and 48-50#. The upper limb is on the right. The arrow pass is centered on the tree. The original unbraced profile showed just a bit of relfex. Starting to show a bit of set - more on the upper limb.
At 63" do you think I need to get the fades and handle bending some to get to 28"?
Thanks,
Mitch
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Just my 2 cents, if you know where your arrow pass is put the hook/rope where your nock point will be...This will change things some...It couldn't hurt to get those fades moving a bit more...Making the handle bend would be some insurance.
Don
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if the bow is showing set,, then listen,, it may not be long enough for your 27 or 28 inch draw,, especially since it is all sap wood,,
I would even the tiller and leave it there,, and use another piece of wood for a longer draw,, :)
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Donald's on the right trail, but, since you've got it to 20" I'd shoot it a bit to determine where the best nocking point is and where the center of your hand's pressure is on the bow's grip. Use those points on your tillering tree- with a fulcrum where your center of hand pressure is. The pulley rope should come straight down as you draw the bow on the tree and the limbs shouldn't rock on the fulcurm as the limbs return to their braced postion. Looking in a mirror helps some folks but it just confusing me.
Since the limbs are constant width to the midpoints, the tiller should ideally be more ellipitcal than circular. i.e. more bending from mid-limb out. Judging by the set in the unbraced photo (assumming the limbs were straight...), it looks like they are stressed enough there already so I'd gingerly thin the fades and maybe the handle to get a longer draw length. Based on the set, I suspect it'll be a slow shooter if you can get it to the draw length you want. Given the short length, the set, the grub holes, and sap wood, I have doubts you'll get the 27"- 28" draw lenght.
Please post on how the grub hole filling holds up. Titebond creeps when stressed....
c.d.
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right limb is bending more at the fade and less in the outer third. So, after getting right outer third bending a little more, the whole left limb will need some scraping to keep them even.
The above will get you another inch or two of draw. If things look good then, you could scrape both limbs evenly to gain some more draw length. Be very careful about scraping near the fades and on the handle. A little reduction there will make a big difference and could lead to a hinge at the fades.
I think you ought to be willing to consider calling it finished if you get to 26". But, with the right thickness (or thinness) shorter full draw bows have been made. Making any bow is a risky endeavor. Making a short full-draw Osage bow with sapwood in the mix just makes it more interesting!
Jim Davis
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Thanks for the help guys - will work on it some more this afternoon hopefully.
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Mitch I'm glad you posted this mostly sapwood bow. There was some discussion earlier on another thread about using osage sapwood that wasn't directly related to this bow but it is interesting that your making one mostly sapwood. Are you going to heat treat it? I will be interested in hearing how it performs. I think the tiller advise given does'nt need any more elaboration so I'll watch and see how your finished product satisfies you. Hope it turns out good. Danny
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Worked on it a bit. The first pic here is the same one in the original post except with an oval added. The second pic is after a little bit of scraping. I pulled to 24" now and it is currently at 50#. I think I will slowly reduce some weight and see if I can get it out to 27" without going BANG!
Danny - I think I may heat treat it just to see. I think it is going to be sluggish so I might as well try. I have had good luck heating ash and hackberry, but have never worked with hedge sapwood before (and only a few heartwoods). I cut this sapling because it was so darn straight and I thought it would dry relatively fast. I cut some nice staves from a fairly straight section of a 10" trunk at the same time - will be working on one of those shortly!
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Think a few scrape on the outer third of right limb yet?
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Have you tried Eric's Tillering Gizmo? He has a "How To" in the "How To" section.
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Yes I have Pat - thanks. The gizmo is showing the limbs to be bending pretty close to the same now. I am still trying to develop a "tillering eye" so can always use some help from those that have developed one. ;)
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Looks pretty dang good
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Think a few scrape on the outer third of right limb yet?
Yes, I said that before you drew the elipse (not oval, btw).
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Will do Jim - thanks. I did take several scrapes off that section already - will do a few more. You are correct an "elipse" is the correct term. :)
Thanks Joe.
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I got it out to 27" without breaking it (right at 50#) - however it did take quite a bit of set - 1-1/2 to 2". Especially in the outer 1/3 of each limb. Shot it a few times in the garage at 7 yards (it is below 0 here today) and it draws nice and doesn't have much hand shock. However, the set was bothering me so I decided to clamp it down flat on the bench and toast the belly. I will let it set a couple of days and revisit the tiller.
In hind site I might have been asking too much of this piece of wood given my level of skill! Stiff handle design with the wormy sapwood and 63" total length pulling 50# at 27" resulted in lots of set. :-\ I post some pics when I get back to it.
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I think you did push the stave to its limit. You did well to get to 27". 2" of set is not a failure. You may gain some draw weight with the toasting. In that case, you will need to approach the 27" draw very carefully, because the wood will be more stressed than it was before the heat treatment.
Jim
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maybe consider drawing less than 27 if you heat treat,,
you may be able to get good cast at a lower draw without taking on more set
why compromise the set and cast to get to 27, when performance may not increase with the longer draw,,
maybe even have less cast per # if it takes on too much set or breaks
if you find a sweet spot as you re tiller,, let the bow dictate the draw,,, :)
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I went ahead and "carefully" heat treated this bow. It took quite a bit of set and was "sluggish" and I wanted to see how the rawhide would hold up to heating. It came out of the heating looking pretty good - rawhide remained in good shape and the limbs back to straight. I let is sit a few days and then strung it back up - tiller did not seem to change much, but it did gain some weight. I gradually got it pulling to 25" and was removing some weight. I decided to drop down to maybe 45# or so to take a little stress off the limbs in hopes of less set. At this point the limbs were holding well with not much visible set.
It was looking good at 25" and pulling right at 45#. The tips were still pretty rough and bulky so I decided to thin and shape them a little bit at this point. After doing this, I strung it back up and gave a little pull to exercise the limbs a bit and I heard the dreaded "tick". The back gave away about 8" from the top tip. It did not break completely, it cracked though the first couple of rings of sapwood that had been damaged by the bugs.
I decided to "dissect" the bow and learn what I could. I scraped the rawhide off and scraped down through the surface sapwood a bit. Under the surface that I added originally added sawdust and titebond was not pretty! See first picture.
I then went ahead and cut the limb in half at midlimb to see what the inside looked like (there was no sign of surface damage at the point I cut). Lots of internal damage that could not be seen until it was cut in cross-section. See second picture.
Lessons learned...
Osage (even "wormy") is some tough wood.
If there is insect damage on the surface, it is probably worse inside.
Select quality wood with no insect damage.
Heating osage sapwood will increase weight.
You can heat treat the belly without damaging the rawhide on the back.
I do have another sapwood sapling stave that is insect free - it is only 53" but I think I will try a bending handle bow out of it some time in the future.
Thanks for the help.
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Dang it! The worms had that one from the start...I hate it man, A+ on effort and trying though...That's how bowyers are made... 8)
Don
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No way that honeycomb was going to have any integrity.
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You are correct Pat - glad it broke when it did. It didn't "explode", it was actually only a small crack through the first ring or two of damaged sapwood. Just goes to show how tuff wood can be.
On second thought, it could have broke earlier in the process and saved me some time!
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Oval was the correct term, and SO was ellipse. Ellipses are a subset of ovals, just like osage is a subset of 'tree'. All ellipses are ovals, but not all ovals are ellipses.
Brave effort on this stave -- Hard to know in advance when you're doomed.