2021 what did you do today?

EvilDogBeast · February 17, 2021, 02:41:42 PM

Heh...

Buemaker · February 17, 2021, 02:49:32 PM

For that too?

williwaw · February 17, 2021, 04:03:09 PM

Quote from: Shredd on February 13, 2021, 10:27:46 PM
Mattox- Good luck with removing a percentage to back peddle and get the exact same bend while narrowing the limb by 1/32" off each side... There are so many unforeseen things... The odds are that you will not get the exact same bend and if you did the odds are that you will not get the same speed... Not saying that it could not happen but I believe the odds are not...

shredd,

what does a "mapping" of the limb consist of?
a tracing of the bend? a numerical formula? your thickness and width recipe? a model in a spreadsheet?

Crooked Stic · February 17, 2021, 04:08:01 PM

Check you limb bend every inch. some trace it on paper and fold it in half and get each limb the same all the way thru the draw. What the end is each limb returns to brace at the very same time.

Longcruise · February 17, 2021, 04:33:15 PM

Quote from: Crooked Stic on February 17, 2021, 04:08:01 PM
Check you limb bend every inch. some trace it on paper and fold it in half and get each limb the same all the way thru the draw. What the end is each limb returns to brace at the very same time.

Wonder if that return will vary with the grip?

Roy from Pa · February 17, 2021, 04:39:48 PM

Yup and where you pull the bow string from.

Buemaker · February 17, 2021, 06:22:26 PM

Here is how I map limbs. I map at brace, at 20 inch draw and at 28 inches. Let us take one of my take down glass recurves. I strive for an even tiller and the deep part of the grip is the bow's center. At brace I lay the bow flat on a long piece of paper, mark where the handle ends and draw a line along the limbs belly. Then flip the bow over so the handle is in the same place and draw a line again, I want the lines to correspond. Then I draw the bow on a 20 inch long stick and draw lines again and finally on a 28 inch stick. Even with limbs made on the same form, using exactly same thickness of lams and glass the limbs usually bend a little different and adjustments can be made if you find it necessary. Sometimes the bend is quite a bit different ( headscratcher) I am not sure, but to my way of thinking it is most important that both limbs bend the same at full draw. But then again when someone shoots the bow,hand placement, nocking point and technique must come into play on how the limbs bend. Anyway I strive to have both limbs bend the same when I map it. I do the same with RD bows. My 2 cents.

Roy from Pa · February 17, 2021, 07:32:37 PM

But then again when someone shoots the bow, hand placement, nocking point and technique must come into play on how the limbs bend. Anyway I strive to have both limbs bend the same when I map it. I do the same with RD bows. My 2

Exactly Bue and that is how my tiller tree is setup, taking into account that I will place the arrow string nocks at 3/8 inches above the arrow shelf, and I tiller for equal limb timing.

Shredd · February 17, 2021, 08:23:39 PM

The boys mentioned some good reasons for mapping limbs... Here is another reason and my process...

I sometimes map limbs when I am testing and looking for performance... I take a piece of paper and I have three tiller sticks... 18", 22" and 26"... I put the bow on the paper at brace and trace the top limb on the back side of the limb onto the paper... I flip the bow and see if the bottom limb matches the top limb bend which was drawn on the paper, for tillering reasons... Then I will trace the top limb using all three tiller sticks... Then I will take another bow of the same design and with a different lam layup and possibly different performance and compare the bend to the one drawn on the paper... If one bow is shooting faster than the other I will stay away from the slower bow's limb bend and try to tweak the next bow I make limb's bend similar but slightly different from the faster bow's bend hoping to gain a bit of performance... Thousandth's of an inch can effect the bend and performance of a bow...

** Warning **

Messing with tiller sticks could be very dangerous (especially at full draw)... Treat with lots of caution as if it were a loaded gun... Stay out of harms way as much as possible... Make sure your tiller sticks are solid...

williwaw · February 17, 2021, 11:25:10 PM

Quote from: Buemaker on February 17, 2021, 06:22:26 PM
Here is how I map limbs...... draw a line along the limbs belly.Then flip the bow over so the handle is in the same place and draw a line again, I want the lines to correspond. Then I draw the bow on a 20 inch long stick and draw lines again and finally on a 28 inch stick.

that's how I trace the limbs when tillering a wood bow for evenness. I also like to have an unbraced tracing to reference for seeing set.

Quote from: Shredd on February 17, 2021, 08:23:39 PM
If one bow is shooting faster than the other I will stay away from the slower bow's limb bend and try to tweak the next bow I make limb's bend similar but slightly different from the faster bow's bend hoping to gain a bit of performance... Thousandth's of an inch can effect the bend and performance of a bow..

Tweak the next bow by varying a thickness taper?

Heres an example stress curve. Stress varies between otherwise similar bows if you change limb width, thickness, shape, r/d or length. It might be an informative way to see what part of the limb is working harder.
Below it is the associated profiles for the example.

Shredd · February 18, 2021, 12:19:26 AM

Yes... I change the hyper lam (super lam) a hair...

Interesting diagrams you have there... Maybe you can open up a thread and explain in more detail how to work with that graph and how you plot it out, how you can gain performance using it and what to look for and what would be an optimal curve... When I look at the WTT contest pics there is a question I always ask myself... Some of the highest performing bows appear to be bending a lot right off the fades... It seems to go against a basic rule of what a lot of guys think on here and also what I think what a bending limb should look like for good performance... Am I missing something here?? Limb shapes can be deceiving... Maybe your method could help explain how those limbs are being stressed...

As for me I use a good old dfc... It's not an absolute but in general it is a good tell tail on performance and how the limbs are working...

Any tool that you can use to plot some accurate numbers to get a better view of the inner workings of a limb is a good tool to me...

Bowyer's Alchemy - Going deep into the inner workings and manipulating what you want in a limb...

Flem · February 18, 2021, 11:49:14 AM

Good luck mapping asymmetrical limbs

Roy from Pa · February 18, 2021, 12:02:51 PM

kennym · February 18, 2021, 12:06:16 PM

I'm gonna throw a bow together and see how it turns out. All this engineering is makin my head hurt.

Mad Max · February 18, 2021, 12:08:47 PM

That's a good looking bow in that graft

Roy from Pa · February 18, 2021, 12:11:34 PM

Me too Kenny.

Flem · February 18, 2021, 01:02:58 PM

How about a Blindfold tiller challenge? See if it can be done by feel alone. We are bowyers, not cartographers.

I bet this guy could get one dialed in
[attachment=1]

Buemaker · February 18, 2021, 02:01:22 PM

Heat treating the Norwegian way. It is not me, I'm showeling snow.

Shredd · February 18, 2021, 03:08:15 PM

No wonder I keep getting Headaches...

williwaw · February 18, 2021, 05:09:48 PM

Quote from: Mad Max on February 18, 2021, 12:08:47 PM
That's a good looking bow in that graft

that's a tweaked "design" taken off a bow I bought years ago. BTW, handles do not render well in the program, but are under such low stress I do not think it matters much.

The untweaked model is shown below for comparison. The graph shows a stress concentration at the fades.

Modification of limb crossection in my tweaked example lowers max stress and distributes it out more along the limb. Whether the changes would make the bow shoot better is anyone's guess. The model is somewhat imprecise because I had to guess at glass thicknesses when measuring out the bow.