Robin bamboo build along

[Sam Harper]

Robin Tan, whose username I can't remember, sent me some of his bamboo from Singapore saying it's better than the bamboo I get at Franks or other American suppliers.  He said it's harder, and there's better node spacing.  He wanted me to do a build along and review.  That works out great for those of you who like this sort of thing.  Who doesn't like a build along, though, am I right???

This may take me a while (like weeks) because I've been working out of town lately and only come home on weekends, and I'm not free to play every weekend that I'm home.  But maybe I'll get laid off and have more time to make bows.  :-)

Feel free to comment, critique, offer suggestions, or ask questions, and if I don't know the answer, I'll make something up.

Here's the package he sent it in, which I just got today.  It's wrapped in mailing paper and taped up.

 

It came with two black rectangles where the addresses are supposed to be, but those postal workers are wizards, and they managed to get it to me anyway.

It's about 31.5" long, which is shorter than I would like.  I can splice it together, though, and get 63" (actually 62.75" when you consider the splice), so about the longest bow I can make is 62" nock to nock, assuming I cut my nocks about 1/2" from each end (or 3/8" when you consider the splice).  I'm probably going to make a 60" bow, though.  Or maybe I'll do something really crazy and make an odd-numbered-inched bow, like 61".  Oooo!  How unconventional!

 

To avoid stacking at my 28" draw length, I'll probably have to reflex the tips.  That's okay, though.  Last year, I made a  58" bamboo backed Osage bow , and it turned out well.

As you can see from the picture, he sent me matched sets so the node spacing will be the same on both ends of the bow when I splice them together.  :-)  And, like he said, there's lots of space between the nodes, which is a good thing because it makes it easier to tiller.  Nodes create stiff spots.

There's plenty of thickness as you can see.

 

The diameter is a little more narrow than I am used to, giving it a higher crown, but it's close enough to not really have anything to complain about.  A higher crown limits you on how thin you can get the bamboo because if you try to get it too thin, you'll begin to lose width.  I think these will be fine.

The narrowest one is 1.5".  

 

The stuff I usually buy is 2" wide, but these are fine.  My bamboo backed ipe bows are usually 1.25" wide, and my bamboo backed Osage bows are anywhere from 1.25" to 1.5" wide.

Next, I'm going to flatten this bamboo, then splice it together.  Stay tuned, but be patient.

[macbow]

Looking forward to this Sam.

[MoeM]

Nice to read you again Sam- your BAs always contain a lot of knowledge and your writing is very entertaining- even English aint my mother tongue...

[takefive]

X 2 what macbow said ^.  I've only made two bamboo backed bows and tillering them gave me fits.  I'll be following along with great interest.

Nothing wrong with your English at all, Moe.  It's much better than my German.  I visited Germany many years ago (my Grandparents were from Esslingen and Stuttgart area) and would love to go back someday.  Beautiful country.

[Trux Turning]

You're right... We like build alongs! Should be interesting.

[Sam Harper]

I arbitrarily picked a matching pair and flattened them.  First, I used the bandsaw to cut off the inner part.  The better you are at the bandsaw, the more you can cut off without the risk of ruining anything, and the less work you have to do on the belt sander.

I was impressed right away.  This bamboo is a lot less pithy than other bamboo I've used.  Whenever I bandsaw the inner stuff, it curls up, leaving the bamboo backing kind of straight.  This stuff didn't curl, and the fibers seemed to be more dense where the pith is supposed to be.  It was nice and stringy.  That stringiness (fibers) are what give bamboo its crazy tensile strength.  I like it so far!

Since the inner part didn't curl, I decided to make a template out of it.

 

First, I drew a straight line as close to center as I could with the aluminum yard stick so it would be nice and straight.  Then I measured 1/2" wide at the tip, 1-1/4" wide 10" from the tip, and 1-1/4" for the rest of the length toward the handle.  Ordinarily, I'd start my taper farther than 10", but since this is going to be sort of a recurve/hybrid, I left it wide closer to the tip to give it more stability.

Since I don't like to have my nodes too close to my overlays (because it makes it hard to do the overlays), I decided the ends with the nodes closer to the end would be the handle, and the other ends would be the tips.

 

I put those clamps on there to hold the template still while I drew the lines.

On the last bow of this style I made, I didn't pre-taper the bamboo.  I left it parallel from end to end because I intended to make a recurve and wanted to make sure I could line my tips up after glue up.  But I decided to go ahead and pre-taper these because with the higher crown of this bamboo, I wasn't going to be able to get it very thin toward the tips unless I pre-tapered it.

After drawing the lines, I cut it out with a bandsaw and took it to the line with the belt sander.  Then, I used the belt sander to thin the bamboo some more.  I ground it down until I had a knife edge on the sides, and the thinnest I was able to get it was a little over 1/8" thick, which is thicker than I like.

 

But since I tapered the width toward the end, I was able to taper the thickness as well.  With this bow being shorter than usual, the overall thickness of my limbs is going to be thinner than usual.  That means my belly/core wood is going to be thinner than usual, and that means there could be an unfavorable ratio of thickness between the bamboo backing and the belly wood.  And that could cause the bow to fail in compression or create an unexpected hinge or something like that.  I can avoid that by tillering carefully, making the limbs more narrow (instead of thinner), and using a wood that's really strong in compression.

I know what you're thinking.  You're thinking, "Osage!"  Well, that's what I was thinking, too!  And I got some Osage lumber from Terry Dunn in La Vernia, Texas, so I'm all set!

So there they are, all nice and thinned and tapered.

 

The next step was to join these two pieces of bamboo together, and I did that with a scarf joint (or at least I think that's what it's called).  I used to have a difficult time getting my two ends to match and be squared up, but Bob Sarrels of    Sarrel\\'s Archery  showed me how he did it with just a stick of wood clamped to the table of his edge sander, which I replicated on my disc sander.

 

And look!  I got a perfect fit the first try!

 

It was such a good fit, I had to pull it apart a hair just so you could tell there was a joint there.  :-)

[Sam Harper]

When I glued these two pieces together, I wanted the tips to be lined up, so I took a piece of cedar slightly longer than the two pieces of bamboo when placed end to end, and I used a string with squeeze clamps hanging off of both ends to make center marks on each end of the board.  That way, I could line the tips of the bamboo up with the marks, and that ought to make the tips line up.

 

At this point, I went back and forth over whether I should use 5 minute epoxy or Smooth On.  Some people don't like 5 minute epoxy because it's brittle, and some people claim to have lost tip overlays over it.  But this joint isn't going to be under much stress if any at all since it will be at the thickest part of the handle, which will be stiff.  Plus, with 5 minute epoxy, I could work on this bow just as soon as I get the Osage ready whereas Smooth On takes a few hours in the hotbox and longer at ambient temperature

But I went with Smooth On anyway.  It doesn't take much.  A little dab'll do ya!  Here it is all glued up with wax paper around it.  I put that piece of leather right over the joint.

 

Then I stuck it in my solar hot box.

 

I had to drive my car around the corner to do this because there's too much shade on my street.  But I was uncomfortable with it, and with the sun on its way down and the clouds in the sky, I figured it wouldn't get very hot anyway, so I took it back in and put it in the garage.  Smooth On will cure without a hotbox; it just takes a lot longer.  I'm reluctant to put it in my proper hotbox because I don't want the bamboo to warp or curl or anything.  But it's summer, so it'll be fine in the garage.  I'll be able to tell when it's cured from the Dr. Pepper cap I mixed the glue in since there's a smidgeon of glue left in it.

The next step will be to prepare the Osage.  I may not get to that this weekend.  Tomorrow, I'm taking a leather working class at Tandy in hopes of improving my ability to make cool sheaths for my knives.  On Sunday, I'm going to a 3D shoot at the Austin Archery Club, then going to see Earth to Echo with a friend.  I've got to squeeze laundry in there somewhere, too.  On Monday, of course, I'm going back to work.  So I'll get back to this when I get back to it, which I realize is a tautology, but since it has found its way into the American vernacular, it's a socially acceptable tautology.

[Ice Mike]

Glad to see you building again Sam!! I'll be following this like Santa on a Christmas list!!

[Mad Max]

yea SAM
why does everybody make 62 64 66 68" bows  

 
what's wrong with 61 63 65 67" bows    :confused:

[Sam Harper]

Here's my big ole piece of Osage I got from Terry Dunn.  I have a longer one, but the longer one is an inch or so shorter than my bamboo, and my bamboo is short enough already.  Besides that, I wanted to show you how I do a Z-splice, so I went with the shorter piece of Osage.

 

I set the rip fence on my bandsaw to 1-1/4" and ripped out a piece.

 

That's Osage is 2-1/8" thick, and my bandsaw cut through it like butter.  Ah, it's nice to have a good bandsaw!  A sharp blade helps, too.

The sides of this piece of Osage were a little wavy.  If I had a jointer, a planer, or a drum sander, I would've used it to true this up before ripping any further, but I did the best I could with my belt sander, and this was the result.

 

After truing it up, I set my rip fence to 3/8" and ripped out two slats.

 

So, those slats are 1-1/4" wide and 3/8" thick.  It's important that they be at least 4" longer than your intended bow if you're going to do a Z-splice because a Z-splice takes up about 4".

Now, I want to say a few things about Z-slices, because they can be kind of tricky if you're like me, and you're stingy with wood.  If you make your wood nice and wide you don't have as much to worry about, but I waste as little wood as possible.

To do a Z-splice, I stack one piece of wood on top of the other and cut them both at the same time. That way, they match better, and I only have to cut once.  I put a clamp around the middle, far enough back so it doesn't interfere with the table of the bandsaw.  I also wrap some tape somewhere behind where I'm going to do the cutting.  That way the two pieces won't slide around while you're trying to cut them.

This is how I trace it out.  I draw a line across the board about 4 or 5" from the end.  Then I draw a line perfectly centered from the end of the board to the line I drew before.  Then I draw my diagonal lines.

 

The first cut I make is along that center line.  But this is where you have to use your head.  Remember that the bandsaw blade creates a kerf, and that line is perfectly centered.  So imagine if you cut straight down that line.  I'm going to exaggerate here so you can see the problem.

 

The problem is that by cutting through the center of the line, with there being some width to the kerf, the joint is going to be off center resulting in to the two pieces of wood being misaligned like this.

 

That wouldn't be a problem if your wood was wider than you needed it to be in the first place.  You could just cut off the excess, and everything would be fine.  But like I said, I don't like to waste wood.

To avoid this problem, you want to cut in such a way that the edge of the kerf goes straight down the middle of that line. That means you're going to cut slightly off center of the line.

 

When you cut out those angled parts, leave the end of the centered one about as thick as the kerf so when you join the two pieces, it'll seat neatly into the bottom of that neck.

[Sam Harper]

And for heavens sake, be careful which side of that center line you cut.  You want to cut toward the side where you're going to remove that triangular piece.  If you cut the wrong side, you're going to end up with what I ended up with.

 

This is why I don't make bows for a living.  See that big ole gap?  That's because I cut to the wrong side of that line.  I could push the two pieces together, but then they would be misaligned.  To keep them aligned, I've got to live with the gap.  I decided to just fill it with epoxy.  Since it's in the middle where the handle is going to be, nobody will ever know.

I clamped the pieces to the edge of a table so they'd be lined up and so they wouldn't slide around when I applied the clamps to the splice.

 

Do try to cut straight lines so everything will fit together nicely.  Smooth On fills gaps, so it doesn't have to be perfect, but you can get it pretty close to perfect just by cutting carefully.  Some people like to boil the ends, then clamp them together while they're wet, hot, and swollen, but not glued.  That gives them a perfect fit.  Some people like to use a jig.  There's a pretty simple jig you could find using google.  I just free hand it because I don't do too many z-splices.

That's all for today.

[BMN]

I know what you mean about cutting on the wrong side of the line! Been there done that! I filled my gap with a thin piece of osage.

 

[Eric Krewson]

I have added an osage shim to fill gaps more than once.

[macbow]

I'd been struggling with my splices.
You've already helped me.

[robin]

Hi sam great build along, you really want to be careful at the node area as this species of boo the thickness on the left and right of the node area is normally one side thicker than the other during the growth cycle of boo.

[robin]

Hi sam great build along, you really want to be careful at the node area as this species of boo the thickness on the left and right of the node area is normally one side thicker than the other during the growth cycle of boo.

[inksoup]

play it again sam  

you are good on this...

[Sam Harper]

Thanks for the tips, Robin!

Yeah, I guess it would've been better to put a shim in there instead of just filling it up with epoxy.  Oh well.  Today, I cleaned it up on the belt sander, and this is what it looked like:

 

It's got a little bubble in there, but that's okay.  i'll fill it with 5 minute epoxy.

I made a mark 1 inch from one end of the splice.  That'll be the middle of the bow.  That way, when I cut my arrow shelf in about 1.25" above center, none of the splice will be in the site window.  it'll all be under the handle.

 

Then I put the bamboo on top of it, lining up the center of the bamboo with the center mark on the Osage.  I made a mark on the Osage at both ends of the bamboo and cut the Osage to the same length.

Then I decided to do something I've never done before.  I wanted to taper the Osage before putting in the curves and gluing it up, and usually I'd use a bandsaw and a belt sander for that, but this time I decided to try the Dean Torges method that he shows on his video, "Hunting the Bamboo Backed Bow."  He uses a jointer and makes multiple passes, progressively starting each one closer to the handle, to get an overall taper.

I don't want to go into all the details of the math, so I'll just tell you the bottom line of what I did.  I made three marks on either end of the Osage that were 8-3/4" apart.  I set the jointer to 1/16", and I made three passes.  The first one, I started at the first 8-2/4" mark.  The second one, I started at the second 8-3/4" mark, etc.  I forgot to take any pictures, so I made an illustration so you could visualize what I did.

 

That basically reduced the thickness by 3/16" from about 26" to the end.

I didn't like this method, though.  I don't know if the problem is me, the jointer, or the Osage, but it was a bit chippy.  Check out this big chip it took out of the end of one end of the Osage.

 

It's not a deal breaker, so don't stress out.  :-)

My bamboo was just a smidgeon more wide than the Osage, so I made it more narrow, being careful to remove the same amount from each side so the tips would stay lined up.  Then I noticed my Osage wasn't straight, so I used the string and squeeze clamp method to make center marks on each ends that lined up with the center of the handle area.

 

Then I lined the bamboo up with those end marks and traced a line kind of wide of the bamboo, and I cut that out with the bandsaw.  I thought it would be better when I do those recurves if the bamboo is already straight and centered.  I don't know if makes a difference or not.

Speaking of doing the recurves, this is the same form I used on the last one, and it worked out, so I'm using it again.  I made this out of a 2X6.

 

I put an aluminum strip next to the Osage, clamped the tip end to the form, and put another clamp on the other end of the aluminum.

 

That way, when I start to bend the Osage, that aluminum will be pressed tight against the Osage, preventing any splinters from lifting.  Also, the aluminum stays hot when you heat it up, and it conducts that heat to the Osage, keeping it hot while you're bending.

Some people leave their Osage kind of thick when they do this so if it lifts a splinter, they can just rasp it off, and still have plenty of thickness left.  I saw one of J.D. Jones' static recurves at OJAM earlier this year.  His Osage was thick, and his bend was almost 90º.  It was such a sharp bend, the back of his Osage was wrinkled from the compression.  So you can do some crazy stuff.  I haven't tried anything that radical.

Anywho, I used my heat gun to heat it up a little at a time and apply clamps until I got the whole thing clamped down.  Of course I had to remove that one clamp so I could get it to go down all the way in the end.  Since my Osage was pretty thin, it didn't take long.  Just a few minutes.  I can't explain when it's ready to bend.  I just apply a little pressure, and when I feel it begin to loosen up, I apply a clamp.  I guess it's the sort of thing you have to do to figure out.  I always cringe a little when I'm applying the clamp because I'm afraid of breaking it.  That would be such a disappointment!

I got it all down without any cracking noises, though.

 

It helps if you have that form nice and rounded with no sharp spots.  You can feel them by running your finger along the curve, so just file them away if you feel them.

After I get it all clamped down like that, I put the heat gun on the aluminum a little more in hopes of loosening it up a bit so it'll hold the curve better when I unclamp it.  I'd like to have as little spring back as possible.  The longer you leave it clamped up, the better.  I'll probably unclamp it in a few hours and do the other end even though it would probably be better if I left it over night.

I don't know whether I'll post more tonight or wait until tomorrow.

[soy]

This is a good one ....thanks  

[Sam Harper]

I decided to leave it clamped up over night, and this morning I barely got any spring back at all.  Maybe I'll end up with a recurve this time.  I had intended the last bow like this to be a recurve, but so much curve came out by the end that it wasn't really a recurve anymore.

 

I just clamped up the other end, so I'm going to wait until the end of the day to unclamp it and continue.