Built-a-long: Bend-in-the-handle bamboo backed IPE (BBI)

[cdpbrewer]

This will start out as a built-a-long since the bow is ready to tiller.  There's a good chance it'll turn out with bad tillering, so I'm going to start the actual build-a-long then so ya'll can help me with that.

Background:  Just made my first stab at a bend-in-the-handle bow-  a BBI like the one in this post.   30# @ 27”, 59” ntn, 15/16” wide in middle 8” and a pyramid taper to 1/4” nocks.  It shoots OK but I really messed up tillering and it starts stacking at 26" and, worse, it has a weird looking tiller profile.  After ~200 arrows and at a stacked 27":

The bow is tilted in the topmost pic making the profile askew.  I can't use that excuse for the tiller tho'!    It started out with 3.25” of glued-in reflex and, with a 1/2" thick/un-tapered belly, was way too heavy at floor tillering.  My sorry tillering, being afraid of getting it too thin in the handle area and staying on the long tiller string to long I think lead to the “gull wing” looking tiller.   Might try shorten and re-tillering it someday…

Anyway, thought butchering another one like it would aid in learning (likely via more and hopefully different screw-ups) how to make bend-in-the-handle bows.  Gonna shooting for a 30-35# draw weight. 

Making the back and belly
Here’s examples of the the bamboo I started out with:

They were intended for home decor- the spots are painted on and the nodes are painted over also.  7’ long and long even spacing between the nodes but only 2.5” to 3” in diameter and kinda thin walls.   For $4 each at a local salvage store, I couldn’t resist getting a few since I'd only tried bamboo once before-  it broke straight across the grain between the nodes about 1/2 way through tillering.   At >$20 for the slat, I'd sworn-off bamboo.

Here’s what the “grain” looks like:

That’s a cut-off from the end of the piece of bamboo that was used.   About 5/32” wall thickness. 

Selected a split of bamboo that wasn’t that good- had crooks at 2 nodes and one of them had part of stem scar.   

Roughly flattened using a drawknife and coarse rasp, sanded a bit flatter using 36 grit on a 4”x36” belt sander:

Tips:  1) Don't drawknife through the nodes- it'll rip out chunks!  Instead, rasp down the nodes and drawknife between them.  2)  A belt sander works better with a foot switch- no divots from putting the bamboo on and taking it off a moving belt.   

Marked the profile for the intended bow on the INNER side of the bamboo.   It’s easier to mark there than on the curved outer side and the marks are more visible with this paint splotched bamboo.   The bow will be short- 55.75” and the nodes are not evenly spaced- 15.5” & 19.5” from tips-  owing to having to dodge the crooks and partial stem scar.  In the middle one section, the Hope that doesn't bite me later...  Wound up being 1” wide in center 8” and then tapering to 3/8” at tip ends.

Rough cut the bamboo to outside of the profile lines on the band saw and rasped and sanded down carefully to the profile lines.   Will be using the boo as a template for marking the profile on the IPE. 

Thinned the bamboo on the belt sander.    I basically get it as uniform in edge thickness (side-to-side and end-to-end) as thin as I dare and live with whatever that thickness come out to be.   Turned out about  ~1/16” on edges. 

Ripped a 3/8+” thick piece for the belly off of a 5/4” x 6” x 6’ IPE board on the bandsaw.  For wood I can’t get easily, is expensive or for making a lot of lams, I use a fence of sorts (it’s tedious to set the fence to the saw’s lead angle…), otherwise- like this IPE belly- a line is marked and freehand ripped to roughly the line.   Then sanded and flattened to about 0.325"- about 5/16"- on this using 80 grit with this:   

The thickness was a SWAG based roughly on the finished thickness of the previous bow.

Used the bamboo as a template to mark the profile on the IPE and roughly cut outside the lines on the bandsaw.   Here’s what resulted- along with an example stick of bamboo:


Finishing the profile
The IPE belly was then made to match by profile of the bamboo back.  You'll see later why this is done later.  Here's how:

First dressed down the IPE to match the bamboo on one side of the handle:

The smoother side of a farrier’s rasp was used to remove the IPE.  Tip: never rasp or sand towards the boo- it'll pull off splinters.   Before removing the bow-to-be from the vise, clamps are placed on either side of the vise to keep the two pieces aligned.  The goal is to bring the IPE down to the boo on one side of the bow then doing the same on the other side.

The tip end of the IPE was then made to match the bow:


Then did the part between the handle and tip:

The clamps plastic but are light and cheap but work better from me than spring clamps for light clamping like this.   The ends of pads on outboard one in the pic were shortened to allow clearance for the next step.  The other end is supported by the tillering tree that's attached to the end of the workbench.

The bow was left affixed as in the pic above and the side of the limb was trued-up using 36 grit cloth glued to a 2”x36” piece of 3/4” MDF (partially shown in pic above) with light pressure.  I really like that thing for such work…

The above steps where then repeated on the other side of the bow while arranging the clamping so the back and belly on the completed side stayed flush.   As usual, the sanding got into the boo a bit so the sides were checked with a straight edge and the centerline checked with a piece of string strung tip-tip.   Got a just little too much taken off at the handle to taper transition but not enough to redo the other 3 sides to match. 

Next post: Pre-tillering the IPE belly
(Shortly I hope- posting this stuff takes more effort than making the bow  )

Probably doesn't need saying but, don't be bashful about posting comments, questions and such.

c.d.

[cdpbrewer]

This is Part 2...

Pre-tillering the Belly

Pre-tillering the belly wasn’t done on the previous bow and a lot of wood had to be removed, so the belly was tapered from about 4” outboard of the handle to the tips.  To get to a floor tiller, the taper was roughed using the tools in the pic out and using a SWAG based on the previous bow's taper.

I usually leave the last 6” at the tips a bit thicker to allow for tip narrowing and tip weight reduction but decided to skip that- and adding a tip wedge- and just clean up the taper by using the 36” sanding stick thing (shown on the belly in the pic) with light pressure.

Rather than making some tied-on nocks for pulling the belly on the tillering tree, temporary nocks were made out of some fence wire- was lots quicker:

Here’s what resulted- it's pulling a whopping 4# at 24”:

The right limb looks OK but the left is bending too much close to and maybe in the handle, but I've no eye for tillering and a tillering gizmo doesn't work well on such light bows or making marks on IPE.   I went with it anyhow.  Would probably have screwed tillering up anyway 
Was also probably a mistake to pull it so far- it took about 1” of set that'll probably be reflected in the bow's set.   

Measured the thicknesses of the back and belly before glueing them together and put the data in a spreadsheet:

Got this for thickness of the bamboo back (at crown) and belly:

The data omits thickness at the bamboo nodes.  The taper is about  0.005 in/in in the outboard 20”   The cheap digital thickness gauge in the previous pic isn’t as accurate as an old fashion “analog” mike but it’s sure easier and quicker to use.  I think its inaccuracy- along with operator error and and faulty thinning of the belly-  helps explain the dips and such in the graph.  Anyway, it's close enough for SWAGing on any future bows. 

Next up (shortly I hope):  the glue-up

c.d.

[cdpbrewer]

This is part 3
GLUE-UP
Scored the glueing surface on the IPE with a 32 tpi hacksaw blade since it had been a couple of days since that side of it had been sanded.  Left the bamboo as it came from the 36 grit sander earlier that day:

Didn’t do any cleaning other than brushing the nibs off with a soft brass brush.

Always do a dry-run before gluing!  The back and belly were wrapped kind of lightly with one layer of stretch-wrap and the form was adjusted until the profile looked OK:

The joint between the back and belly were checked for glaring gaps.  After the pic was taken, the form was tweaked a bit more- basically removed the blocks under the tips that are inside the tapered looking holders.

Applied about 200 grains of Urac mixed 13 parts powder to 100 parts resin.   No pics of the gluing, so  here’s one from a previous bow:

The Urac in the cup is dabbed onto the wood with a stick then spread with a wallpaper seam roller.   The putty knife is used to wipe up any that gets on the side of the lams or on the paper underneath- it’s not used much since the seam roller works well.  The osage and maple lams in the center of the pic have already been coated with glue.   

The back and belly were then put together and clamped with two tight layers of 4” wide stretch-wrap.  The layers are wrapped in alternate directions and any that overlays the tip ends was trimmed off so that they can slide lengthwise when bent into reflex on the form.  There was a bit over the average amount of glue squeezed out.   

I typically don’t mask the back or belly since the wrap always keeps the glue off the back and belly. What gets on them usually comes from my hands during the wrapping.  The belly on this one was masked tho'.   

After clamping (not too tightly to avoid dry joints) the bow in the form with rubber strips cut from bike inner tubes, winding sticks (red box in pic below) are lashed to the bow with strips of rubber banding and eye-balled to check for limb twist and a string (red arrow) is strung between the tips to ensure the bow is straight.

Here it is on the form.   

3.5” of reflex- tip block 3.25” high, 27” from center, mid block 1” high, 16.5” from center
The form is a piece of Uni-Strut screwed to a 1”x3”.  It’s also used as the base for making endless loop type strings.  The wooden pieces on top can be adjusted left-right and secured to the Uni-Strut with 1/4” bolts and chunks of wood with tee-nuts in them. Each can hold a block which adjusts the bow vertically.

Here’s a pic of the wooden pieces the bow is clamped onto:

The arrow points to a removable wood block to set the mid-limb height.  The wooden thing at the left can hold a block to set the tip height but I didn’t use any blocks for this bow. The marks help ensure the bow's tips and handle are aligned as it is clamped down to the form.

The form was left in the sun for several hours, stuck it in the oven for 5-6 hours at ~120 degF after which the heat was turned off and left over-night to gradually cool down. 
Here's the oven:

The arrows point to two 6’ lengths of “heat rope” connected in parallel.  I think each piece puts out 75 watts at 120 vac.   The box at the left contains a light dimmer for controlling the temperature which is set manually via a kitchen type digital thermometer stuck through the foam box (on left in pic) that's the oven's top and sides.   The fan is used for curing poly finishes on bows after it’s air dried a bit.   

The blank looked good after unwrapping the next morning.  Got about 1.5" of spring back.  Typically get less than 1" with my usual 64-68" long bows.   That's the only drawback to using stretch-wrap- there's more spring back with it than without.   

The glue squeeze-out was then removed from the sides.   A before and after pic:

The glue stuck to the sides well, so, maybe skipping the usual step of de-oiling the IPE with alcohol is OK.  Used a scraper+file then cleaned and dressed down a tad with the 3 feet long, 36 grit sanding thing.

Before bending, the edges were rounded well.   I forgot to mention in part 2 that the exposed edges of the boo and IPE are rounded a bit before being glued so they'll be less likely to cut the stretch-wrap.

Found a couple of bad looking nicks (in red box in pic below) in the bamboo that had I hadn't noticed earlier.  Decided to remove the rind to see how deep the were. 

I got lucky with the nicks and learned to check bamboo more closely in the future.   The darkish splotches on the re-rinded bamboo are where the paint used for the spots on the bamboo stained the bamboo.

The blank looked good when floor tillered so put it on the tillering tree. 
Here’s what it looks like with the short-as-possible but stretchy tillering rope at 30# after being exercised: 

Shooting for finished draw weight of 30-35#.   The top pic in the composite pic above was taken just after the lower pic was taken.   Took about 1/4" of what looks to be uniform set.

Well, that's were it stands right now.   It looks a little too bendy in the center- maybe due to the longish tiller rope- but not bad enough to remove any wood.

Tillering- and especially eying tiller- is a struggle for me, so, does anyone think differently?   

In the interim, nocks/overlays will be fitted made and pics of that process should be up in a day or so. 

c.d.

[turmoiler]

Hello cd,

you did and learnt a lot of things by yourself. If you want some tips I would tell you that is better not to use too much reflex on your firsts bows because it's a little tricky to tiller them. It's better to get experience with "normal" bows. And also I will try to make them a little longer they will be easier to tiller. If you need more help with the tillering you can make yourself a gizmo:
http://tradgang.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=125;t=001047
hope this helps

BTW: I liked a lot your thicknes sander machine, can you give me more specs of it, I've been wanting to make one and I like your design.

S.P.