Intermediate level build/help-along - Laburnum Pyramid - UPDATED WITH PART 3!

[NicAzana]

So, inspired by the excellent build alongs by Gordon, Bryce and others on this site, I've decided to try to give something back to the community by doing a little build along thread here.
If finished, this will be my forth or fifth successful adult bow (depending on other projects), so consider this an insight into the process of someone who maybe has most of the fundamentals down, but still needs a lot of practice.

The stave is a laburnum stave from a tree that was cut on my land a couple of years ago. It is the same wood that I tested in this thread:
http://www.primitivearcher.com/smf/index.php/topic,68656.msg963505.html#msg963505

I recently worked on another laburnum stave from another tree that had a sapwood back. It tension snapped during floor tillering and smacked me pretty hard in the ribs.
I THINK this sapwood might have been compromised by some rot in the tree, but I'm not taking any chances with this one, so I've chased a ring on this stave before beginning this build along.


The stave is 70" long, and is pretty clean, with no major knots, however it has some uneven reflex, that I will probably try to reduce a bit after roughout, in order to match the limbs a little more.
I think this will make tillering much easier for me. Here's a pic of the end grain:


It is also pretty straight, with a wiggle in the middle that will be handled (very much pun intended) later on.
One limb has a bit of a roller coaster wiggle on one side, right in the middle of the limb.
It doesn't pose a risk for the bow, but will complicate tillering for me, so I marked the middle of the stave following the grain, trying to place the middle as far from that side as I could.


Before laying out the bow, I squared up the stave, making it a uniform 2" width, and 2/3 thick for the whole of the stave.
I don't have much thickness in the handle, only about 1 1/16", so I'll probably either have to glue on something later on, or else keep the handle a little wider than usual. I'm planning to make this bow about 1 1/2" wide just out of the fades, and should end up at less than half an inch thick. As I'm told that wood is eight times as strong when the thickness is doubled, compared to only twice as strong when the width is doubled, that *should* make a 1" wide, 1" thick handle plenty strong?
We'll se if anyone here with more experience can chime in on this.



Anyway, I then marked an inch on both sides of the center line, by using my calipers every few inches, and then following up with a pencil. Time to go to the workshop!


Faugh! What a mess, good thing I'm only here by myself... This is my little shed, where I have my tillering setup, and my supply of bow wood. Mostly Laburnum staves and billet sets, with some elm, and a bit of plum, white oak and yew.
I made the shave horse a few years ago. Not a beauty by any means, but it does the trick. When it eventually dies, I have a long list of Improvements.

I carefully used my drawknife to get close to the lines. I've noticed that laburnum tends to tear a bit in some spots, so I used my shinto rasp close to the lines. I know I'm late to the party, but I just LOVE this tool.


Remember, safety first when creating dust!


Then It was time to lay out the back of the bow. This will be a pyramid bow, with a 4" handle and 2 1/2" fades. As the whole bow will be 69", that leaves us with 30" limbs.
First I marked each limb every 7 inches, creating four evenly spaced marks along the limb, with 2 inches surplus at the tips.


I then calculated the total width of the limb at each point up to a width of 3/8" 2 inches from the tip, using this formula:


The one behind the multiplication sign means this is the width at the first point, 7 inches from the fade. Substitute the one with 2,3 and 4 to get the other measurements.
I then measured out these widths along my marks on the back of the bow, and, using my finger as a guide, drew parallel lines from each point towards the tip.


These parallel lines then worked as guides for free-handing the width taper:


For now, I left the last 9 inches wide, about 0.65", leaving me some room to play with later. In these last 9 inches, the width taper will be "stretched" a little, giving the bow a slight eiffel tower shape to the outer limbs.
I then started roughing out the bow, using the drawknife to remove the bulk of the wood. I first removed wood at an angle, to not accidentally "reverse trap" the bow, and to prevent a tearout ruining the bow. Then i carefully took more wood out until I was close to my pencil line, and finished it up with the shinto rasp.


Then it was time to rough out the thickness. As this bow is a pyramid design, a uniform initial thickness is probably an okay starting point before floor tillering.
I'm aiming for somewhere around 50-55# of draw weight, and so I think roughing the bow out to a little over 1/2" thick is appropriate. I marked down the side of the bow using my calipers:


I again used my fingers as a guide, checking against my caliper marks to mark a consistent thickness.
Once again, I start by carving at an angle, leaving me with a diamond-like cross section:


I then carefully worked my way down to a flat belly, leaving me with a roughed out bow:


For now, I've left the handle square, not sure how I'm going to do that one, but there's no rush.
As it is, it is juust starting to bend a little when I lean on it. Next time, I think i will do some steam bending, to remove some of the uneven reflex, aiming to make tillering easier for me later. I might also add a touch of reflex to the tips as well, just for looks, and as there is a small amount of deflex there currently.

Anyway, that's it for now folks!

See you next time.

/Nicolas

[Hamish]

Looking great so far.

[bownarra]

Labernum likes to be narrow and thick.
wide and thin limbs can make it a bit doggy.....
The best design for labenrum in my eyes is one that you would use with yew. It has pretty much the same properties. Low bend resistance. Great elasticity etc....And sinew/labernum is a marriage made in heaven.

[NicAzana]

Bownarra, what do you mean by doggy? Regarding the characteristics of laburnum, that is also what I've found through research and testing, although laburnum tends to be denser than yew. This bit should be around 0.68, which I think is a little on the low side, while yew is 0.55-0.67, according to TBB4. This is my first bow of the stuff, though. I've laid it out to 1.5" wide to give myself some margin for errror, I might reduce the width a bit during tillering.

Anyway I guess people still make yew pyramids and flat bows that shoot alright, right? This will be a pyramid with slightly drawnout tips, so the outer tips should end up plenty light.

[NicAzana]

Part II: Heat corrections and floor tillering.

I got to work some more on the stave. As you can see in my last post, the stave had quite a bit of character, a lot of uneven reflex (>5" overall), and some deflex in the tips.
To help myself with tillering, I decided to steam out some of the worst reflexed kinks in the stave. First, I decided to deal with a short, highly reflexed section in the middle of one limb.
I first dry-fitted think on my caul, to check that everything was ready:


Then i suspended the limb section over a pot of boiling water, and wrapped bowlimb and pot with a couple of layers of tinfoil.
After 40 minutes of steaming, I quickly transferred the stave to my caul, and secured the limb in its new position, using a couple of clamps. After, the limb looked much straighter:


I wanted to get rid of the tip deflex, and decided to flip the tips a little at the same time. However, in order to not have prohibitive amounts of reflex, I first steamed and bent the handle section to remove some of the reflex there:


I forgot to take pics when I steamed and bent the tips, but here is the result after all the steaming:


I ended up overdoing the flipped tips a bit in the heat of the moment, so afterwards, I relaxed the bent tips a bit with the heat gun and some clamps, and straightened one tip that had a strong sideways kink slightly at the same time.
I also removed some twist in one of the limbs, again using the heat gun.


After that, it was back to the workshop to refine the thicknes. Since this is very close to a pyramid shape (just slightly extended tips), I made the thickness almost uniform throughout, but maybe 1/16 thicker in the inner limbs, to not risk weakening them from the start.
Again, remember to mask up when creating dust, even for woods that are less immediately toxic than Laburnum:




Here's the stave, ready for floor tillering, note that I left the tips wide, to allow for adjusting string alignment later, and to allow me to cut temporary nocks, which can be removed later on.
Overall, I ended up with about 4 1/2 inches of reflex, which is a lot for me. I'll have to go slow, long string tiller a little bit longer than I usually do, and try to have as even tiller as I can manage all the way.
The risk is that I end up underweight, as it is hard for me to string the bow with this much reflex, untill it is is bending quite a bit. I think overall the stave should be able to deal with the reflex.
As Bownarra noted, Laburnum is flexible stuf, and this stave is fairly long and wide (~69" ntn, 1.5" wide at the fades).

After some rasping, the tips was moving about four or five inches when floor tillered, and looked okay bend-wise. I did a little bit of rasping with the shinto rasp, trying to make it bend a little more, keeping the bend fairly equal between the limbs.
I don't really trust myself with floor tillering, as I find it really hard to judge the bend, so I tend to go to long string tillering fairly quickly.

I then rounded the back corners with a scraper, and cut some temporary nocks for the tillering string.


Here it is on the tiller for the first time:


I always start by drawing the back profile on my blackboard tillering background.
Whenever I manage to reign in my impatience, I like to judge tiller using as many of the following methods as possible:

- First I judge the bend by eye on the tiller, and mark out weak and stiff spots with a pencil.
- After drawing the bow, I compare the relaxed profile with the chalk line, and use this to monitor set.
- I also go over each limb width my fingers and/or calipers, to find thin or thick spots.
- Finally, at least 3-4 times during the tillering process I take pictures of the bow relaxed and drawn. I then go superimpose the images like in the image above.

If all lines of evidence points to the same result, I am confident going foreward. As long as I manage to stay patient, this method has turned out to be fairly reliable for me.
I hope my eye judgement will improve over time, practicing like this 



Anyway, I'm seing that both limbs are bending mostly from 1/4-1/2 out towards the tips, and the thickness taper agrees. I've marked the bow like in the image above (x for don't touch, shading to be removed), and will do a little rasping with the fine side of the shinto rasp next time I have time to work on the bow.
Then It'll probably be the scraper from then on.

Stay tuned for more!

/Nicolas

[bownarra]

I mean they can be slow and handshocky. Narrow thick limbs give the wood the return speed it needs. Thinner wider limbs don't stress the wood appropriately. It took me a while to figure it out, 3rd bow from labernum was the charm!

[NicAzana]

Surely that depends on other variables than thickness and width!

A long bow will have thicker and narrower limbs for the same strain, and, conversely, a short bow need wider and thinner limbs to experience the same strain as a longer bow.

Same goes for reflex/recurving - if the stave has a lot of reflex (like this one), it must bend more to be braced, therefore requiring thinner, wider limbs to be equally strained, compared to a straight or deflexed bow.

I guess for laburnum (or yew), with its low bend resistance and high elasticity, the real answer is that it should be thicker and narrower than an otherwise identical bow of a stiffer wood? In this case, I have four inches of reflex, a pyramid taper, and will have very slim/light and stiff tips. It might be a little long, but I can shorten it a bit if it turned out to be understrained later.

Does other people also think that this is way overbuilt?

[simk]

really nice piece of wood - that's gonna be a screamer for sure

I have two laburnum bows started, now sitting in the unfinished bows corner - not the easiest pieces and tricky to remove rings also - they just overstressed my patience. hope one day they will shoot...

cheers

[NicAzana]

I sure hope so Simon! We'll see, I have yet to f*** it up, I think 

I too hate chasing rings - but once this was dry, it was actually surprisingly easy to carefully cut it free with my dull-ish drawknife. I think you can treat it like a lot of folks describe chasing Osage rings - as long as the rings aren't too thin.

[simk]

sure wish you luck 
I have hard times chasing the rings here despite thick rings....there's almost no early wood on mine and the color differences between the rings are marginal - almost invisible. also I hardly feel the early wood between the rings with my drawknife nor really see it with my eyes. to me it feels much harder to chase than any wood I did before. with osage I can do it almost blind...we will see....
cheers

[bownarra]

Surely that depends on other variables than thickness and width!

A long bow will have thicker and narrower limbs for the same strain, and, conversely, a short bow need wider and thinner limbs to experience the same strain as a longer bow.

Same goes for reflex/recurving - if the stave has a lot of reflex (like this one), it must bend more to be braced, therefore requiring thinner, wider limbs to be equally strained, compared to a straight or deflexed bow.

I guess for laburnum (or yew), with its low bend resistance and high elasticity, the real answer is that it should be thicker and narrower than an otherwise identical bow of a stiffer wood? In this case, I have four inches of reflex, a pyramid taper, and will have very slim/light and stiff tips. It might be a little long, but I can shorten it a bit if it turned out to be understrained later.
Does anyone else think this is way overbuilt.

Of course bow design is a combination of many factors.
Really bow making is about judging maximum thickness for the wood you are working and marring width taper and tiller profile.
you aren't telling me anything I don't already know re. reflexing/recurving etc been there done that many times.
I'm simply trying to help you by telling you (all other things being equal)that labernum bows should be thicker /narrower than virtually all other woods - due entirely to the properties of the wood. I've probably made around 10 labernum bows. I've had 185fps @ 10gpp with the later ones.
Anyway I hope it works out for you.

[NicAzana]

Shortish update:

Tillering is progressing along - When I first got it braced, the stave/bow was very twisted:



I'd monitored the limb sides, and they were equally thick, so the twist was a little bit of a mystery to me.
I then realized that the crown is a little uneven - it slopes a little more gradually on one side of the limbs, making it effectively thicker on one side.

Bows with this much reflex is a challenge to me - My ability to judge the bend is limited untill I get in on the tiller, but to get it there, it has to bend much more than a straight stave.
I think I've finally learned my lessen this time - next time I'm going to wait with flipping the tips untill I'm further along, and have the limbs already bending evenly.

Feeling whith my fingers and looking at the tiller, comparing with photos on the computer, and watching for set, I slowly try to get it bending more, without taking too much set.


Here it is, marked for another round of scraping.

It still has developed about 1-1 1/2" of set, subtracted from the original 4 1/2. But I've now have even thickness taper, and the twist is much reduced.
Here's my latest set of image analyses:



First I superimpose the braced and drawn profiles on top of the unbraced image. This way it is much easier for me to judge the bend on a stave with some character.
You can judge the set based on the chalk line behind the stave. The set is happening in the inner third of the left limb, and in the right limb, at the two kinks.



I can also compare drawn circles that touch each end of the bending part of the limb.
As you can see, the right limb is stiffer (circle is larger), and how the limb follows the cicle can help identifying stiff and weak sections (but remember to account for reflex/deflex and wiggles).



Finally, I'll "walk" the cut out bent stave along the unbraced bow in my program, help to see the details of where the bow is bending.

All, in all, these images, along with set, and what I can feel with my fingers, tells me that:

1) right limb is currently stiff
2) right limb needs to bend more on both sides of the wiggle, and is a little weak in the outer part of the bending limb.
3) left limb is stiff in the outer 1/3-1/2

I think this bow should ideally have almost circular/slightly elliptical tiller, so I've got some scraping to do.

I don't dare drawing it to full weight, until the bend is better, but I'm a little worried that it is approaching target weight fast.
But I think it is long enough at 68" NTN, that I'll be able to plug an inch off each end, as long as the tiller is good.

We'll see!

Stay tuned!