R/D Tiller Discussion Continued

[gfugal]

Greg:  "But I guess different stiffness of materials could throw that off."  It could, and I'm pretty sure variations in limb length and working limb length will affect it too.  But, we still have to TILLER wood bows, so the idea is to get close.

This is one of the reasons (of many) fiberglass bows don't appeal to me. Sure you can tiller them a little bit by adjusting width or doing minimal sanding on the belly, but they are pretty much set when they come out of the form. Drastic changes in tiller shape just aren't going to happen so you have to have your design right from the start. At least that's my understanding, I could be wrong as I've never tried to tiller a fiberglass bow. Wood, although much easier to break, is much more flexible (as in easier to adjust).   

[Springbuck]

  Yeah, some guys making fiberglass traditional bows, I remember specifically 21st Century Longbows, did use reverse tapers to thicken/stiffen the tips, thereby also moving mass toward the handle, but there is only so much you can do of that in a glass bow.

[gfugal]

Parallel limbs will have a more aggressive thickness taper on my self bows.It's hard to judge.When width taper takes over taper thickness wise slows down a little.

I've wondered about this. How much does width effect tiller? clearly it has a substantial impact. However, I've heard of people saying that their Pyramid Bows are uniform thickness with width being the only variability in tiller, but I can't remember who I heard that from, or if they had actually measured for taper. even a 0.1" inch difference (which is close to a 0.003" taper) may be easy to miss with the naked eye. 

[Springbuck]

Anyway, here is my lam-tapering method. Don't judge me by my garage, please. 

 I invented a little rocking table I usually set up on sawhorses.  It consists of two 6 foot  2x4's glued and screwed together in the middle, and two 8 foot 2x4's on the outside.  The long ones have a large carriage bolt and wing nut on each end so they can be loosened and tightened easily.   When loosened, they allow the  six-foot doubled up boards in the middle to move freely.  When tightned the outside boards hold the inside boards very snug and square.

The outside boards are also braced crosswise at the bottom by two short 2x4s, screwed down with long construction screws.   The short crosspieces have a hole in each with a tee-nut installed, and an eye bolt through the tee-nut.

The idea is that I can loosen each end and then adjust the height of the middle of the table on each end turning the eye bolts from underneath.  The middle section can be tipped up, down, or flat and adjusted for any thickness of lamination.

Next, I installed wheels on my power hand planer.  I wanted 4, but 2 turned out to work just fine.   On a full length lam, I can smooth and thickness it after sawing, then tilt one end of the tape up and taper in several passes from middle to tip.

It's pretty handy.  It's a little hard to taper two half laminations the same because you have to clamp it on the thick end.  I sometimes have start with a few extra inches, drill a hole in the thick end and screw it to the table  with a countersunk nylon nut so the planer will ride through without trouble.  I can usually just fiddle with the tilt and height enough to clamp the back end of a longer lam with a c-  clamp.   With this set up, I could even start tapers halfway out the limbs.   Sometimes, too, that e ends get roughed up a little because of how the planer tilts without the back wheels, but once the infeed plate at the nose of the planer is firmly up against the work piece, it's fine.   

I can put down scrap pieces to protect the table, and produce my wedges and powerlams the same way, planing them down to paper thin at the ends to save time on the beltsander.

Anyway, as I said, not as precise, but very adjustable, and I can easily produce a lam that is 3/8 in the middle, 1/4" at each tip, and 5/16" halfway out as near as my caliper will measure.

Pics are coming.  I'm on mobile, so bear with me......

[Springbuck]

See the slight incline?

[Springbuck]

Top view.

[Springbuck]

Underside.

[Springbuck]

Tilt.   The planer wheels just ride on the two outside boards like rails, planinG the middle.

[Badger]

That is a hard question to answer depends a lot on working limb and design  the tapper rate changes but I just measured 1 of my osage lever bows with a 20 in. working limb  68 in TTT and the average taper rate is  0.012  I'm seeing a average more like 0.010 for my self bows maybe I'm wrong Steve ?

  That sounds right, it just depends on the bow and the tiller you are after. Most of mine are what I would call semi pyramid. slight limb taper most of the way down. Parallel would likely come out around 10 but I never measure.

[Stick Bender]

 Steve that makes sense , it took us a couple post to get to the point of what Ed said in 2 sentences...lol !

[BowEd]

Parallel limbs will have a more aggressive thickness taper on my self bows.It's hard to judge.When width taper takes over taper thickness wise slows down a little.

I've wondered about this. How much does width effect tiller? clearly it has a substantial impact. However, I've heard of people saying that their Pyramid Bows are uniform thickness with width being the only variability in tiller, but I can't remember who I heard that from, or if they had actually measured for taper. even a 0.1" inch difference (which is close to a 0.003" taper) may be easy to miss with the naked eye. 

Width will affect the poundage more so than the actual bend or tiller.It'll store more energy then.I should say meaning that with parallel limbs using the same type wood.
I don't make true pyramids.Even then the width taper goes to 1/2" wide at tip so a little thickness taper is still needed I would say.Your right though making self bows is more fun especially when you use combinations of width tapering.Parallel from fades to mid limb but slightly a width taper of 1/8" maybe to midlimb nowadays lately on mine then into pyramid towards the tips with very little thickness tapering leaving the tips a little stiffish.

[Springbuck]

  Greg:  "I've wondered about this. How much does width effect tiller? I................."

Now hold on!  This IS tiller.  This is bow design 101, from the TBB Vol 1.  This concept is THE thing you have to know to tiller bows.  This is essentially Badger's rule' "thickness determines how much wood CAN bend, width determines how much it WILL bend."    This is THE difference between a pyramid, flatbow, and a longbow.  Front profile, which is essentially how much width and where) determines tiller shape (how much bend is allowed, and where).  We tiller TO the width.   Width and thickness are interdependent.

The reason that a pyramid bow (having even side taper) theoretically bends to the arc of a circle is that the thickness is the "exactly" the same.  The other reason is that, since the width increases proportionally from tip to handle, the stiffest part is the widest part.  The middle is half as stiff as that.   Each part of the limb is  strained the same amount.  Get it?  Theoretically, of course.  You have fadeouts to work with, and the tips can't actually come to tiny points.

The reason a more parallel sided bow like a longbow has a different tiller is that the thickness varies, and evenly straining each portion of the limb means that some portions are bending more and some less.  Guess which portions should be physically bending less?

[BowEd]

See the slight incline?

I have a power planer like that too only a dewalt for laminated bows and bamboo/maple/hickory backings.Nice set up you made.I just use a wide big saw horse with same thickness material on the end of lam or backing so the planer does'nt gouge the last couple inches.

[Springbuck]

The wheels solve that on the far end, but can cause it on the starting end.  The good thing is being able to start in the middle.  Planing without any real jig, or with just a backing for stiffness works great for parallel slats.   

As I said, planers save a lot of sanding, too!  One of my favorite parts.   

If you have any insights on using a planer on bamboo backs, let me know.

[BowEd]

Yep from the fades out with the planer.Usually 3 staggered passes at 1/64" then I see what I got.