Limb thickness question.

[autologus]

How would the limb thickness look on a bow with parallel limbs to midlimb then straight taper to the tips.  I know a pyramid profile has a uniform thickness.  I have been having a devil of a time with my bow designs they all seem to be overpowering the bellies and fretting.

Grady

[blackhawk]

Sounds like thickness taper is the least of your problems and worries...besides,it'll be whatever it wants to be when properly tillered and you'll get there by tillering...now you should be able to "feel" a nice subtle even thickness taper with your fingers. Keenan just posted a video in his most recent thread sneak peak to his yew bow about this. But,it sounds like you have a design(improper width),wet wood,or improper tillering problem or all. Are you making selfbows or laminates,and what kind of wood are you using? Is it seasoned? What's the exact dimensions that you are trying to use? Is your tillering good?

[autologus]

I am using boards, I think most of my problems is in design.  I understand tillering pretty well I think, although I am probably too impatient and can correct that.  Proper design is I think my biggest problem as I don't have the general design principles as a base to start from.  I don't think being able to tiller properly will help much if the basic design will not support intended goals.  Am I making any sense?

I can look and other peoples bows and see where the flat spots are and where to take off the wood, I see the hinges and understand elliptical vs. circular tiller.  I guess I am just having a hard time with getting every thing right before the tillering starts.

I hope I am not rambling incoherently and am making some sense.  I guess I just don't have the concepts of what are the rules of basic design for the different styles of bows.

Grady

[Del the cat]

I generally rough out to an even thickness taper of about 1.5mm change for every 6".
On an ELB it of ten ends up as about 1mm every 6" in the final bow.
Another way is to just measure the thickeness at the fade and what you think will be about right at the tip and work out an even thickness change every few inches or whatever is convenient depending on limb length.
I use mm for thickness as it's convenient working to approx the nearest 0.1mm. I still like inches for the longer measurements.
You've got to realise that getting it nice and even before it goes on the tiller (or very quickly afterwards) is probably 60% of the process. by the time it's on the tiller and the tips are coming back to brace height you are probably 75%-80% there and it's already getting a bit late to sort out any big problems.
It's easy to see hinges and problems, the trick is to see 'em before they have developed.
Del

[Onebowonder]

What species of wood boards are you using?

Have you tried trapping the back of the board yet? (I.e. - Narrow back, wider belly)  Like this: (only don't leave sharp edges obviously...)


          __________
        /                      \
      /                          \
    /                              \
   __________________

OneBow

[blackhawk]

What kind of boards,and what exact dimensions did you try,and what intended stats are you trying to reach? That will tell us a lot as to what's going wrong for you.

Also,reading and understanding bowyering jargon and terms is different than being able to execute them properly and understand by hand. A lot of Boards are much more suceptable to fret and have a very small room for error. Proper grain choice in the board,design,and executing both thru proper tillering is crucial.

[BowEd]

Nice even taper,No abrupt changes.It's hard to break a bow with nice even taper to it.I go over my belly with a block of wood and 36 grit sandpaper to assure myself of that nice even taper.I cheat too and use a calipers......LOL.

[Maxspin]

Grady,
Do you have a bow scale?
Could you be pulling way past draw weight in your early tillering stages?

Keith

[autologus]

Yeah I have one.  I think besides the design issues, I am impatient and try to go too far too fast.  I think part of what causes that is I really am struggling with is how to start the basic limb thickness (even thickness or taper depending on design) and that leads to tillering taking forever because I am trying to get the wood to bend with a scrapper when I probably should be using a rasp because I started with even thickness instead of a taper.

This is where most of my problem lies I think, what kind of limb thickness should I start with depending on design (parallel limb, pyramid, mollegabet, ect).

Grady

[Gordon]

Limb thickness for a pyramid design is not necessarily uniform. Maybe that's your problem - are most of your fretting issues happening in the inner limbs?

[autologus]

They do typically fret toward the inner 1/3, I know it is probably not exactly uniform but more of a starting point in general.  I am definitely going to have to be more patient and learn more.

Grady

[Pat B]

I never consider limb thickness! I remove wood so the limbs bend evenly and together and I have the draw weight I want and the tiller fits the bows profile.
 Please post pics of your bow(s), braced, unbraced and full draw. That will show us how you are tillering the bow and then we can be more accurate at figureing out what is going on with the fretting, etc.

[bow101]

How would the limb thickness look on a bow with parallel limbs to midlimb then straight taper to the tips.  I know a pyramid profile has a uniform thickness.  I have been having a devil of a time with my bow designs they all seem to be overpowering the bellies and fretting.

Grady

If you chek out  Bingham's Website  they have a chart somewhere that states what limb thickness will add to draw weight.   My first bow was 5 lams that totalled a limb thickness of .390 which for that lenght would be about 50#. Of course you have to take into account other variables like wood species, width, design etc...etc.......

[SLIMBOB]

Pat's right.  The thickness of your limbs needs to be "just thick enough and no thicker", and what that measurement is can only be known after the fact.  I never measure the thickness beyond roughing it out.  I will check to see that the limbs are uniform in thickness from side to side, and that there are no shallow spots or humps through out the process, but I care not what that measurement is until I'm done.  Even then the values are mostly irrelevant to the next bow you make.  Focus more on good tillering and less on the mathematics involved.  Post pictures and let's see what you got.     

[Jim Davis]

I think autologus is trying to avoid scraping when there is still 1/4" that needs to be removed. Flat bow designs are pretty thick out of the fades, but pyramids are in the neighborhood of 9/16" thick from the fades to the tips (the design goal of a pyramid bow IS to have uniform thickness and straight side taper. If the thickness varies, the whole reason for being is gone.)

Tim Baker and many other respected and experienced bowyers note that there is one best thickness for a given degree of bend, and this is the same for most varieties of wood for a given design. Increased weight has to be gained by increasing the width, not the thickness. If weight is gained by designing and making limbs thicker, the result will be chrysaling or fracture.

So, in the interest of not having to scrape or rasp off wood that could be removed by faster means, certainly any flatbow can be reduced to 3/4" or a little thinner with a band saw, hatchet or  drawknife. I take my pyramid limbs down to 5/8" or so at the edges with the band saw, leaving the middle of the limb thicker to take down with a rasp.

Jim Davis