"Zatara," bamboo backed osage bow, part 3 - heat treating

As I learned from my experience with trying to heat my yew "fence post", you don't heat treat an already glued bow. So I'm heat treating the rough-tapered osage limb sections before I put the bamboo backing on. This should give me an opportunity to straighten the deflex out of them as well as hopefully improve the performance of these marginal leftovers.

All of the heat treating I've done before was done by simply holding the gun and waving it back and forth over the limbs until they changed color. It's tedious and time consuming. I expected the latter, but the former has got to be changed. So, I built a holding jig to keep the gun about 5 inches from the limbs, as you can see in the photo below. So as to evenly temper it, I'm heating only one inch of limb at a time. The first limb took about 5 minutes. At 29" of limb to heat, this is about 2.5 hours of time per limb! Fortunately, I had other things to do (clean the workshop), so it was not too big a deal to multi-task. Set the timer, then move the whole limb one inch to work the next section. Repeat.

 5 minutes seemed like a long time, but I was going by the color change. At some points 4 minutes seemed more appropriate, so I switched to that as needed. I think part of the reason it took so long was that the doors to the workshop were open, allowing some draft to pass through and rob the limb of its heat. However, I didn't want to overdo it, so I limited the time. The resulting limb looked somewhat splotchy, so I ended up treating it in a separate session later, at about 2-3 minutes per inch. I wanted the treating to really permeate the limb, and the result was a nice even deep brown.

Untreated handle on the left; treated limbs on the right.

For the second limb, I did the same routine of 4-5 minutes per limb -- but with the garage door closed, limiting the draft. Apparently this made a significant difference. After I nearly finished the limb I noticed that there were several small cracks throughout the wood! These appear to be small drying or stress cracks. Were they already there, exacerbated by the heating; or were they the direct result of heating?

Cracks can be seen in the limb on the right.

Upon inspecting the first limb, I discovered a few of those there as well, but localized to one small area as opposed to throughout the limb, as they are on the second one. As a result, I've decided that I should go back to the manual method of heating, or reducing the time if using the jig. I've also designated the "crackled" one as the upper (weaker) limb.

I don't know if these cracks will have much effect on the final bow. The cracks shouldn't pose a problem in tension, as the bamboo back will be doing the work there, but they may very well be a sign that the limb got over-treated and will crumble or fret in use. Or maybe not.  I could stop, but I've got nothing to lose but my time at this point, and I'll learn something in the process. I figure that once the bamboo back is glued on, I can hit the cracked areas with low viscosity super glue as a hedge against problems.

Time (and experience) will tell.

Yew "fence post" longbow, part 8 - filling time

Reducing and heat treating the belly has revealed the weakness inherent in the knot in the upper limb. The knot was pretty punky, and adding heat to it only made it crumble worse. While I've compensated for it some (probably not enough?!) by adjusting the width of the limb at that point, it makes me highly uncomfortable having this open "wound," if you will. As I started digging out the punky parts, the knot has revealed itself to be somewhat conical in nature, with the tip of the cone just protruding in a flattened point on the back of the stave, though it was not punky fully though. This results in the blister in the back being somewhat filled -- more crater like than an actual tunnel.

I've decided to try and fill this with a combination of yew wood dust (collected in the dust collector by grinding some yew offcuts on the belt sander) and super thin cyanoacrylate (CA) glue (a.k.a. "super glue"). What I've read on-line is that the wood dust should be reasonably fine and that it should be compacted in small layers, then soaked through with the CA glue.  Doing this on the back is pretty straightforward. It will also be covered by rawhide, so I'm mostly trying to fill the little crater here so that I don't end up with an air pocket after the rawhide goes on.

Filled and glued.

Leveled and sanded smooth.

The hole on the belly side takes considerably longer. I add just a bit of wood dust, then compact it down with the stem of a q-tip that has had its head removed. Glue is dribbled in a bit at a time to soak through, after which I pack down the wood dust again and use a paper towel to wick up any puddling glue before it dries. The whole process gets repeated again.

Partly filled...

...fully filled...

...being filed...

...and finished!

With luck, the filling process will provide some sort of structural support -- but I'm not going to count on it. I am learning that with bows, as each new problem reveals itself, although we may take measures to remedy it, we are constantly flirting with disaster. I feel like Odysseus, trying to navigate between Scylla on one side and Charybdis on the other. Let's hope things turn out better for this bow than for Odysseus's men...

"Zatara," bamboo backed osage bow, part 2 - rough limb tapering

As mentioned in the last post, the outside of the stave section from which the limb section was taken was in pretty bad shape. My hope was that by turning the back of the staves into the belly of the limbs, the problem areas would come off in tapering and tillering. Since this is going to be a backed bow, I can really treat these sections as lumber and go ahead and give them a rough taper before glue up. I'll refine the taper/tiller after it's all glued up and already starting to bend.

The limb thickness of the osage is currently a nominal half inch (just under), and I want to taper it out about 1/8" along the limb. I'll start the taper just outside where the handle section will get glued over the splice. The pieces are long enough that I can get a full 66-67" nock to nock length. Since the overall length is close to 69" and my handle is 9", I'll plan to taper 29" for each limb, which will give me a half inch margin on either side of the handle as a "safety zone" to eventually bring down when tillering.

The ideal way to taper this dimensional stock would be to use a planer, which would allow me to take 4 passes of 1/32" and call it a day. I don't have a planer, so I'm going to go to the bandsaw instead. When I first started building bows, I took a bow class in which we built bamboo backed ipe longbows by first tapering the stock by cutting it on the bandsaw using a .005" per inch pre-tapered piece of wood attached to the stock. On 29", I calculate that this makes closer to 5/32" than 1/8" (.145" total taper, to be exact), but in practice I have found that it is close enough to what I want that it works just fine. It generally means that most of the refining I do to the tiller happens in the inner limbs first.

This job is going to be a little trickier, as the stave originally had some good reflex to it. Since I'm orienting the grain in the the opposite direction, I'm actually fighting the wood a bit. Here is one of the future limbs next to my pre-tapered stock. One can see the amount of the reflex pretty clearly. In order to keep it in place for tapering on the bandsaw, I'm going to use my favorite secret weapon: blue painter's tape!

Here you can see the limb section taped to the pre-tapered stock. You'll also notice blue clamps in place. I use those to hold the limb in place against the stock so it is as flat against it as possible. The taping actually uses a technique I picked up from lutherie: One stretches the tape while applying it so that it exerts some clamping/pulling force. How much does it stretch? Not much, but enough to create some reasonable force on the two pieces, especially when applied in quantity as it is here. How much stretching is too much? If the tape snaps, you've gone too far. It's a nice self-correcting exercise.

 

Because the limb section is already at its maximum thickness near the handle, setting up the bandsaw fence is relatively easy: I just put the taped up piece next to the blade just outside of where I want the cut to stop, then slide the fence over until the stock is slightly snug against the blade and the teeth of the blade catch the tape when trying to pull it through. This lets me know that the blade will effectively stop cutting at that point -- plus there's that half inch "safety zone" I mentioned.

All the prep work for taping it in place took a considerable amount of time, but putting it through the bandsaw couldn't have gone smoother. Because of the direction of flex in the piece, as each part is cut and is freed from the tape, the section actually pulls away after the cut, which means that the taper is pretty consistent. Luck also appears to be on my side, as the bad sections of the piece have come just away in the tapering process. You can see the before and after in the photos below.

Limb 1: before

Limb 1: after

Limb 2: before

Limb 2: after

"Zatara," bamboo backed osage bow, part 1 - salvaging

This series of posts is really a sequel to my "Driftwood" series describing the making of a sister bow from the salvaged offcuts of that project.

In the process of getting to a thicker growth ring and a usable length from the basket-case osage piece Jarrod gave me (which yielded the short selfbow, "Driftwood"), I removed a large, flattish section of the outside of the osage (including some sapwood) by using the bandsaw. I actually had to go down a little more than a half inch deep (if you remember from this post, the stave had already been worked down through several layers on one end), and the resulting offcut was  great than 1/2" thick and a little over 2" wide.  I couldn't very well throw the piece away, so I decided to see if I could get a bow out of it by recutting and splicing, and backing it with bamboo. Here's a bit of information about what I'm working with:

First, the 9" bow handle section was removed from one end of the offcut. One can see a trace of sapwood in the photo below. This is probably the best piece of wood out of the entire original stave! I thought it would be cool to be able to incorporate more of the stave back into the bow, so this section will make its way into the handle.

Also shown is the remaining section (original stave belly side, which will end up being the back gluing surface -- more in the next paragraph), already sawn into two pieces, about 38" in length and a little over 1" wide at the widest end (the narrower end tapers to 3/4"). You can probably also see the extreme coloring in this osage piece -- lots of red streaks. One of the major ones was bad in the section that eventually became "Driftwood," but these seem pretty solid. At any rate, they'll captured in the interior of the bow near the bamboo back, far away from the compression of the belly where they could do real harm.

The original stave, as I mentioned in the post "Driftwood part 1" was pretty well worked down in odd places on the back when I first got it. Normally I would try to orient flatsawn grain so that the original stave back would be next to the bamboo backing and the original stave belly would be the bow's belly. In this case, because there is so little wood to work with and because the the back was in such poor shape, I'll need to make the stave back into the new bow's belly with the hope that all of the bad spots will come off in the tapering and tillering. You can see the spots in the photos below. They are incredibly dark, as the original stave had been sitting around for some years and the exposed wood had oxidized. It's a beautiful color -- and the bright yellow of the freshly cut osage gives you a real appreciation for just how much the color changes over time!

It's probably not apparent from the pictures above just how marginal the wood is in places. The center photo shows a fairly deep cut that looks like the back of the stave encountered a radial saw! I'm really hoping that most of that will come out in the tapering and tillering -- but it's going to be close. The bottom picture shows a nice void in the middle of the stave.

Of note: Orienting the back of the stave toward the belly of the bow in the glue up does cause the rings to travel in the same plane as the eventual radius of the belly, creating the potential problem of having large sections of soft earlywood exposed, which could weaken the bow or cause hinging. However, I'm at least aware of the problem going in, so I'll know to look for it and correct for it wherever / whenever possible.

As a further appreciation for just how marginal this wood is, I've taken a couple of photos of the sides. These were the original sides of the stave, and they had all sorts of sections missing. I'm not sure that the photos do it justice. For example, what looks like 1 3/8" width on the sawn section is really reduced to 1" of usable wood once these wood voids are accounted for...

In case you are wondering about the scrawled "NOT" on the side of the left-most piece of wood in the first picture above, it was a note to myself when preparing to cut the original stave on the bandsaw. One side of the stave had some good relatively flat spots that traveled well on the bandsaw table and allowed the stave to be stable, whereas the other side had all sorts of dips that spelled trouble. Though it was fairly obvious which was which, I did not want to leave anything to chance, so I wrote the word "NOT" to remind me not to use that side against the saw's table. I hate to think that its vestige might be a sort of prophecy, telling me not to attempt to salvage this wood as a bow!

To conclude this post, I guess I should explain a little bit about the name. I was telling my friend Nick about the "Driftwood" bow I was working on and how I thought I might have enough for a second bow. I was casting about for a potential name.  "Firewood" had made the list, as it was a) appropriate! and b) reflected the spirit of the red streaks I kept finding, but Nick suggested "Zatara," the name given to Edmond Dantes in the movie version of The Count of Monte Cristo. The name was supposed to mean "driftwood" in the movie (a search on the 'Net reveals influences of Italian, Spanish, and Arabic, and it might actually mean "raft"), though there is this tidbit from one of the Yahoo! Answers pages:

Zatara is a surname. The most famous Zatara was a magician that died on the Titanic. Shortly after his death, ther were a few jokes that came about. The most famous that stuck was: The Great Zatara was performing on the Titanic. One day a man with a parrot was in the audience. This parrot started to heckle The Great Zatara. Parrot voice: “Browk, it is in his hat!” Parrot voice: “Browk, it is his hand!” Parrot voice: “Browk, it is his pocket!” That night the boat hits an ice berg and sinks. The Great Zatara wakes up on a piece of driftwood with the Parrot. Two days go by with the two of them just staring at each other – really glaring! Then the Parrot says, “Ok, I give, Where’s the boat?” The producers of the movie The Count of Monte Cristo heard that joke and gave tribute to The Great Zatara by giving the name to Edmond Dantes and changed it to mean driftwood. (There are ancestors of The Great Zatara that have kept the name. They are mostly in Ireland.)

Regardless of whether or not it is a real word, I liked the connection to the name of its sister bow, and that making a working bow out of this other piece of "driftwood" is going to take some magic. That, and I already promised Nick I would make him a bow, and this might as well be it. (Unless it doesn't turn out!)

Yew "fence post" longbow, part 7 - resplicing

I decided to bite the bullet and cut the splice apart. I've outlined the steps below, just in case anyone is crazy enough to want to do so too!

Step one was to mark out the areas to be cut, on either side of (and parallel to) the current glue lines. By marking the new lines out a mere half inch on either side of the end of the splice along the center line, I should only end up losing about an inch in total from the length. One can note from the images that this results in a narrow (but reasonable) area in which to cut the slanted parts of the splice. By my reckoning, I should be able to cut exactly along the glue line, then pare back to the penciled lines and have a new splice joint pretty close to fitting spot on...

...but first, I'll need to drill a hole just big enough for me to snake a coping saw blade through! The hole is drilled not at the very end of the splice, but in my closest approximation to what will be a waste area (based on the penciled lines). This means I will need to saw in both directions, but I want to have as clean a spliced line as possible.

Starter hole from the back.

Starter hole where it exited the belly.

Fortunately, I was able to drill a pretty straight hole (having a wood bit and marking the start with an awl helps). Below you can see the coping saw "in action." (Actually, I had to switch hands and am not really sawing here, as the other hand is holding the camera -- but you get the idea!) This is followed by an image of the finished "inner cut."

Things got a little jagged running the other way, as I was using my left hand. It got a little detracked on the belly side, so I had to recut a section there. No worries -- I'll fill that tiny section with a wood offcut, and the glue should patch it right up. I finished up the last bit with a Japanese pull saw, as it had no back and just fit in the slot. This worked great, as it was a lot sharper than the coping saw blade, despite the latter being new. It also did wonders on cutting the slants quickly but accurately.

Below is the cut-apart splice, waiting to be trimmed up. (The blue on the interior of the right piece is paint or something from the writing on the Japanese saw. It will come off in the cleaning up.) One nice thing is that by following the previous glue lines, the resulting splice angles should line up pretty accurately and it should only be a matter of needing to refine the surfaces slightly. You'll notice from the following image that I biased my cuts to one side of the glue line so that I could just focus on cleaning up the outside edge on each joint instead of working hard to reduce the interior angles.

I apparently got caught up again in the doing rather than the recording and forgot to take additional pictures of the finished splice during fitting and the glue-up process. Suffice to say, it took a little bit of finessing and I had to use some yew offcuts to fill the gaps (most significantly, the saw kerf from the "inner cut" on the center line, as failing to do so would have shifted the centerlines of the two limbs fractionally). Mostly I think it turned out okay:  I only lost an inch (the stave is now 75 inches overall), but I did decide to add a tiny bit of reflex by joining the limbs together at a very small angle. It is probably not enough to be noticeable, but every little bit counts. I daresay that the joint looks a little more solid than it did the first time, so maybe being forced to redo it was providence?!

Yew "fence post" longbow, part 6 - handle "set back"

Normally when bowyers speak of "handle set back," they mean the shaping of the bow in such a way that the handle is closer to the archer, so "set back" from the back of the bow. In this case I mean "set back" in the sense that ordinary folks use: a failure followed by a temporary delay.

I was feeling pretty good about heat treating the belly and worked from both tips toward the handle. The tips seem to have taken a fair amount of twist correction, and some small amount of reflex was materializing. I thought the glue (Unibond 800) was not heat sensitive--but it turns out I thought wrong. The glue had darkened and bubbled in spots, reminding me of the crunchy foam structure of chocolate honeycomb candy my grandmother sends from the East Coast. On inspection, it looks like I've cooked the glue and weakened the joint. A quick search on-line shows that yes, Unibond can be degraded and weakened by heat. Unibond is a great glue, and frankly I should know better: just about any glue will weaken under any temperatures high enough to scorch wood.

Cooked glue joint!

First rule: Don't panic! All is not lost: I can cut the handle apart and splice it back together over again, but it is going to be work. For one, I could do a neat cut in half and totally recut the splices, but it means losing 4 inches in overall length, going from a 76" stave with 74" nock to nock length to a 72" stave with 70" nock to nock length. That's a considerable loss, especially considering that I fought the initial stave to retain every bit of length I could. I could try to recook the glue and hope it fails then clean up the edges and reglue, but I'm afraid that in doing so I will either a) ruin the wood by overheating or b) not be able to weaken the glue enough to simply pull it apart with my mere mortal strength. Even if I could, I'd still have to clean up the edges and get rid of any trace of the original glue, which could be problematic.

There is a third way between these two extremes, though I'm not happy at the prospect: I can cut the splice apart along the glue lines, refit the joint, and reglue. It will be time consuming and would actually mean cutting a new splice in fresh wood just outside the glue line, then cutting a matching splice in the other limb in such a way that I pare out all of the old glued sections. The advantages are being able to glue a brand new joint while retaining most of the current length (if thoughtfully done, I might in theory only lose a half inch). On the other hand, cutting the center spliced section means having to drill a small hole in the middle of the stave in order to snake a coping saw blade through. There will also be even less room for error, since the stave has already been taken down to final width at the handle. (I might end up losing some there...)

This is not the happiest thing that could happen, but I will say this: I have learned an enormous lesson about glue and heat, and it has already changed my mind about how I want to approach my next bamboo backed osage bow project. This will be a lesson I won't forget -- and I'm sure I'll learn something new in the cutting and re-splicing process.

Yew "fence post" longbow, part 5 - heat treating

Not a lot of pictures for this one... I guess I got caught up in actually doing rather than documenting!

At this point I'm heat treating the limbs for a few reasons:

1. To pull the twist out of the tips of the stave.

By using clamps and weights to create a lever to twist the limb in the desired direction, it is possible to take out some of the twist at the tips. I use the approach of not forcing the limbs against a form. Rather, by using the clamp and weights levered out at the end, the tips are gently coaxed into position as the wood is heated and relaxes. The trick is to try and coax them a little beyond where one wants them eventually, as some of the wood has memory and springs back a little bit. One can see the clamp and the weights in the picture below.

2. To try and add a little bit of reflex into the stave, as it is fairly straight limbed and slightly deflexed in areas.

I know that adding reflex can make a bow more difficult to tiller, but I'm not anticipating adding much: just enough to help make up for some of the inevitable string follow that will happen. As the bow takes set from being worked in, the limbs will start to bend toward the archer. If I can give the bow a little reflexing, the degree of string follow will be diminished in the finished bow (though the amount of string follow may be the same -- it just starts from a different place). Consequently, performance should go up, albeit only slightly.

3. To try and create a little more performance by altering the belly wood. 

Heating the wood on the belly, tempers it and makes it more resistant to compressive forces, which can also slightly increase performance by two means: 1) increasing the draw weight per overall mass or allowing a lower mass for a given draw weight, and 2) forcing the belly to do more work. For the latter, wood is usually stronger in tension than in compression, so having the belly do a little more work can help balance out the load bearing. One downside, though: I recognize that some of the effects of heat treating the belly will be diminished by the fact that the limbs are not at their final thickness, so some of the tempered parts of the belly will disappear under the rasp and scraper. Why not wait until later? I plan to back the bow with rawhide using hide glue, so I don't want to soften the glue with heat and have the backing come off. As with many things, bow building is a matter of compromises!

Diversion: PVC bows

Well, it's not woodworking, but it still pertains to bows and how they bend...

I decided to undertake making some PVC bows with an eye toward supplying those who don't have access to archery bows with something cheap and relatively quick to make. I got the idea this summer after visiting Raptor Archery. My kids were handed one of the bows -- which of course have flashy paint jobs and come in cool shapes (more than half of the appeal, if you ask me) -- and I was told that the store had a book about it. It was inexpensive, so I picked it up. (For those interested, it is Simple PVC Pipe Bows, by Nicholas Tomihama.)

For those who don't know, the basic premise is to take PVC pipe and heat it with a heat gun (or other heat source), then to flatten parts by clamping in a simple caul. The flattened sections are weaker, so allow more bend, while round sections are stronger and allow less bend. In essence, it is very easy tillering, since the material is homogeneous.

It seemed like a good way to try them out was to make them for the kids. The youngest (age 5) is pulling #9 @ 16" on our Martin all-fiberglass 50" bows. The oldest (age 9) is drawing about #16 @ 22". Hopefully I could make something that has just a slightly stronger pull at the same draw weights, partly as a way of allowing them to grow as archers and partly as a way of increasing their performance and minimizing arrow "bounce-outs."

My first try with 1/2" PVC had the usual learning-curve problems -- I heated the PVC too much/too fast, cooled it down too quickly so that it split the tube while clamping, etc. The second go was more successful, yielding a stylized "horse bow" of about 46" ntn length, #32 @ 26 on the tillering tree (though I did bring it to a full draw of 28" while shooting). This was made using 3/4" PVC, and I must admit it looks pretty cool. Sadly, it took about 3-4 hours of time (more time than I had wanted to spend on it), though that is fast compared to working with wood and probably not too bad for learning the process.

"Horsebow" at brace...

...and at 22" on the tillering tree.

At 28" draw.

A third try was made using 1/2" PVC salvaged from the first go (I cut out the bad sections.) The overall length was of only 40", yielding 39" ntn length, in "longbow style" (i.e. no recurves) and with narrowed tips (made by cutting out a section, heating to move the tips together, and then gluing the split tip back together). Of interest: Each section taken out of the tips removed about 175 grains of weight -- a significant weight savings, though it was offset by the noxious nature of the glue. This little bow ended up coming in exactly at #9 @ 16" and #16 @ 22", pretty much identical to the Martin fiberglass bows, with the downside that the PVC ended up both slower and lacking in the stability that a longer limb-length gives.

Short "lonbow" at brace.

At 20" on the tillering tree.

How did the kids take to them? All were wowed by the shape of the horse bow but complained that it was way too strong. They all liked the smaller bow, as it seemed comparatively easy for them. Interestingly, they all thought it was easier to pull than the Martin fiberglass bow, even though it is exactly the same draw weight and despite the shorter limbs creating more finger pinch. I'll have to assume that it was either a) the novelty of it creating a more favorable review or b) the comparative ease of drawing it after trying the heavier bow [or c) a combination of the above].

How do I feel about PVC as bow material? Well, it was an interesting project, and I see both the positives and negatives:

Pros:

• it requires little time commitment
• material is minimal, cheap, and accessible
• little expertise is needed
• being able to get bows into the hands of non- or would-be archers
• being able to fancifully decorate a bow (and not feel guilty about covering up beautiful wood)

Cons:

• the end product might not be durable and is not something I would want to pass on
• short limb length means less stability
• dense, sluggish material gives poor cast
• material is inorganic and creates a plastic "saw dust" that clings to everything
• possible negative environmental impact?
• skills are not very transferable to real bows

By this last point, I mean that this is a one-way street. Based on my knowledge of bow building so far, I would say that everything I have learned about the way real bows bend and work can be applied to the PVC to make a decent bow, but there isn't a single thing I learned from the process of working with the PVC that would assist me in making a real bow. So if you are thinking of trying to make your own PVC bow, just know that this is the case. PVC bows might make you an archer faster, but they won't make you a bowyer any sooner. 

Quick and inexpensive they may be, but it was a sad task working with a lifeless object with the personality of putty. There is something sacred about working with wood, knowing that nature has provided one with a bit of itself; and that this bit is a good bit compared to all the other wood that had to be rejected. Working with wood and thinking about it in this way forces one to slow down and treat the material with reverence. PVC, not so much. (Ok, so I reused the failed bow from the first trial, but only because I can't stand the idea of waste. Even my offcuts make their way into projects when I can.) Yes we can work fast, but as Dean Torges put it best, "Let's not punch time clocks in our sport as though it were indifferent to our best efforts, at least not until we also value loving and praying as fast as we can."