R/D Tiller Discussion Continued

[Stick Bender]

This is the set up I use to grind lams , it's not as creative as you guys but does a great job, but can't do what spring bucks does starting in the middle which is nice for tapering a one peace lam , but to change taper rate is just a mater of changing the sled but even with the fancy equipment it's still hard to get perfect lams !

[Stick Bender]

Sled

[gfugal]

  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?

I know width effects tiller. I understand the principle as you state it but it's good to hear it again. What I meant was, could you only tiller with width. It sounds like you make the argument for this. I should try it sometime. To rephrase this I was wondering is if people ACTIVELY tiller the width like they do the belly. Most of the time I see people shaping the width first then finalize the tiller by adjusting the thickness. Have you ever shaped the thickness first then only tiller the width to get it right? I guess that's what fiberglass bow makers do, it just seems unnatural for me and less effective seeing you would have to remove 8 times the measurement of wood as you would if you tillered the belly. So yes I understood that width effects tiller, that was poor wording on my part. I should have said "how much could you actively tiller with width when making your final adjustments", that is after roughing out the shape of course. My ignorance and in-experience with pyramid or fiberglass bows may be showing. Maybe people actively tiller with width all the time, just not me. That's what's nice about this site. you can learn from other's experiences.

[BowEd]

Good set up too Rich.My friend Grant does his that way too.
All of this tapering etc. just coincides to what portion of the limbs do the most work along the length of the limbs.Highest percentage on the inner limbs but with more wood there to handle it.Less percentage as you go closer to the tips.That's why a nice even ever increasing arch for reflex works so well with it holding a higher percentage farther out to the tips.While taking less set on the inner limbs.These are all Tim Bakers' words I always remember.

[gfugal]

Bytheway Springbuck I like your lam set up. Simple and inexpensive comparatively. I'm guessing you can remove the wheels if need be. I'm in the process of making my first laminate bow, and I had no power tool method of making them or tapering them, so.... I did it the hard way with calipers, a straight edge, and a rasp. Yeah, I don't know if I will do that again let alone how accurate it was. We'll see how it works.

[PatM]

I don't think things are quite as precise as some seem to think.  A Scalloped bow is all over the place regarding width and it still bends as if it has straight sides.  The belly would be a series of ripples  if you were going to try  to follow the width and thickness proportion rules.

[JWMALONE]

I successfully tillerd one pyramid bow that way. It was red oak blew up on arrow 50 or so. Mostly I end up doing some thickness taper on a pyramid bow. I believe you would have to have the perfect width tape vs length with the right piece of wood to have no thickness tiller.

[BowEd]

  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?

I know width effects tiller. I understand the principle as you state it but it's good to hear it again. What I meant was, could you only tiller with width. It sounds like you make the argument for this. I should try it sometime. To rephrase this I was wondering is if people ACTIVELY tiller the width like they do the belly. Most of the time I see people shaping the width first then finalize the tiller by adjusting the thickness. Have you ever shaped the thickness first then only tiller the width to get it right? I guess that's what fiberglass bow makers do, it just seems unnatural for me and less effective seeing you would have to remove 8 times the measurement of wood as you would if you tillered the belly. So yes I understood that width effects tiller, that was poor wording on my part. I should have said "how much could you actively tiller with width when making your final adjustments", that is after roughing out the shape of course. My ignorance and in-experience with pyramid or fiberglass bows may be showing. Maybe people actively tiller with width all the time, just not me. That's what's nice about this site. you can learn from other's experiences.

Combination type tillering belly and width works well on self bows.Even if they are parallel limbs.Especially towards the end of the tillering to your draw weight and length.

[Springbuck]

Greg, I hope uyou caught that I was goofin' on ya a little.

[Springbuck]

"What I meant was, could you only tiller with width. It sounds like you make the argument for this. I should try it sometime."

Baker mentions this as a common method used by commercial bowmakers "way back then", esp.  for laminated wood bows.  The issue is that different woods want a different thickness or set results, and methodical thickness tillering can help us discover what that is.  More often than not "what I HAVE in the stave", like what the stave will give me determines width and I follow that.

And, yes, the FASTEST bows I ever made was with scouts.  Ahead of time, I thinned down the limbs of bamboo flooring boards to @3/8" thick, left the handle 5/8" and added handle blocks.  The boys bnacked them with linen and we tillered just from the sides with block planes making pyramid bows.

[Springbuck]

 Greg;  " I did it the hard way with calipers, a straight edge, and a rasp."  Good for your arms!  I ground out my first set of bamboo backings from Three Rivers, and boofloo lams (cut on a tablesaw) by rubbing them on a 60 grit coarse sanding belt glued to a flat board.  I feel ya!

  Pat, you are correct of course.  A lot of this is theory to be applied as it works later.  I do know that having a limb tapering in thickness grow thicker again noticeably causes me issues with tillering, like a hinge right before the thick spot or whatever.  Bows I make with a lot of small knots on the limbs end up varying in thickness like that, belly and back both a series of ripples.  It's hard to make all the wood work, and these always take some set.

[Badger]

   I made this out of a planer I didn't use. For my sleds I use two pieces of 2"X36"X1/4" plate glass glued together with different sized wire inbetween as spacers to set my taper. I usually use about 5 pieces of wire spaced at the appropriate rate of taper. Makes for a quick and easy and accurate sled.

[BowEd]

One of these days I'll get more serious about making bows and get into more different styles of bows.Nice set up too.

[Bayou Ben]

Sorry I missed all of these comments.  I was out of town....Great discussion.  That's why I joined this site!

I can't claim my grinder as my own idea, I copied what I saw from another website a couple years ago. 

There's a cabinet door hinge on the left side of that ipe board ( a board not good enough for a bow!) that allows it to swing up and down.  On the right underside there's a large bolt that adjust the height of board.  1/2 turn does about 0.01".  I have a couple bungies holding the board down so it doesn't sway side to side while grinding, and that's about it.  It's very simple, and surprisingly very accurate.  If I run a parallel lam through it, it will be + or - 0.002", sometimes less if I go slow.   
I bought a couple tapered lams that were ground precisely to 0.002".  I place my parallel lam on top of the taper and run it  through the grinder.  The force of the sandpaper rotation holds the lams together, and consecutive passes makes the top match the bottom in taper. 
I only have about 0.5" clearance between the board and the sandpaper, so I can't taper an entire board with a taper underneath it, but I really wish I could.   
I'll post more pics later in the week.

Very Nice Springbuck.  I may "borrow" that idea. 

Nice Badger.  I bet that's very accurate,  I just don't have a spare planer.

Stick Bender, you are cheating! Lol
 

[Bayou Ben]

To touch on some of the other post, yes the 0.006 taper rate just gets you close for style of bow I build, and different materials, different width profiles, etc will respond differently to that taper rate.  The bending beam theory applies more so to these bows since they are generally more uniform and more predictable than lets say a selfbow. 
All else being equal, weaker woods will require more taper rate than stronger ones.  For example an all ipe bow may require a 0.004" taper to bend in a perfect arch where as an all elm may require 0.01".
On these tri lams approximately 0.003" equals 1 pound difference in draw weight.  So if I was planning a bow and I wanted it to be 10 lbs heavier, I would make the initial stack .03" thicker (again all else being equal).  It's close enough for taking an educated guess.