# puka tapers vs cut tapers.



## pop shot (Sep 29, 2011)

call me lazy, but it's a pain to cut tapers with a 107. after reading charles' post with tbg/107 straight/107 tapered, i hypothesized that tapers are faster because of the weight difference in the tip, most importantly. so i punched holes in a 107, starting at halfway, spacing them at 20mm, 13mm, 10mm, 5mm, stopping at 5mm. i shot those, tapers and the tapers were about the same speed as the puka tapers (puka means hole) the puka tapers had less drop, but the ss was flat topped vs. chalice-angled tips. i wish i had a chrony.


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## pop shot (Sep 29, 2011)

and the puka tapers lasted about 30 shots longer- 150 total


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## Charles (Aug 26, 2010)

Personally, I think this is a BRILLIANT idea! But you see, I already tried this and posted the results ...







You will be interested in the following thread:

http://slingshotforu...by-perforation/

You obviously have a great mind, because we seem to be thinking alike!







By all means, do carry on! I am sure you will come up with things that my age-enfeebled brain will miss.

Cheers ........ Charles


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## pop shot (Sep 29, 2011)

Charles said:


> Personally, I think this is a BRILLIANT idea! But you see, I already tried this and posted the results ...
> 
> 
> 
> ...


well i'm on the right track! i just need a chrony

i wanna try a progressive taper, kinda hard to cut


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## ZDP-189 (Mar 14, 2010)

What do you mean by a progressive taper?

a curve?


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## NightKnight (Dec 16, 2009)

ZDP-189 said:


> What do you mean by a progressive taper?
> 
> a curve?


I'm not sure if that is what he means, but some of the commercial bands (like the Black Mamba from Saunders) have curved tapers on them.


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## ZDP-189 (Mar 14, 2010)

Yes, I cut curved bands. They are supposed to be 'exponentially' curved. That mean each section of band pulls a proportionally wider section of band in front of it. It only makes a significant difference from a straight cut if the bands are short or the taper is very aggressive. The level of precision required to cut curves repeatably to cut two sets the same on each side is not feasible unless you are using a CNC process, such as punched bands with a CNC-made cutting mould.

I can illustrate this with a simple picture, but in order to see the difference I'd have to post it bigger than the forum's maximum allowed image size.


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## pop shot (Sep 29, 2011)

yes, i meant a curve, a broad concave curve on the top and bottom of the bands (facing outwards) that leaves the pouch tips parallel at say, 15mm and the fork end (uncut) at 25 or 30mm. i drew it up in paint (hacked it up in paint) And yes, Z, i acknowledge this is extremely hard to do (and replicate) without some serious machinery. maybe puka tapers with tubes?


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## NightKnight (Dec 16, 2009)

ZDP-189 said:


> Yes, I cut curved bands. They are supposed to be 'exponentially' curved. That mean each section of band pulls a proportionally wider section of band in front of it. It only makes a significant difference from a straight cut if the bands are short or the taper is very aggressive. The level of precision required to cut curves repeatably to cut two sets the same on each side is not feasible unless you are using a CNC process, such as punched bands with a CNC-made cutting mould.
> 
> I can illustrate this with a simple picture, but in order to see the difference I'd have to post it bigger than the forum's maximum allowed image size.


What size is it?


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## pop shot (Sep 29, 2011)

Make it fit, PLEEEEAAAASSSEEE!


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## ZDP-189 (Mar 14, 2010)

pop shot said:


> Make it fit, PLEEEEAAAASSSEEE!


The best way is to show you a picture and then illustrate with data so you can see the difference. You need some decimal place millimeters (0.1mm is three thou') to show it, i.e. it's a rounding error.










x-position Straight Curve (all in mm)
0 27.00 27.00
5 26.82 26.80
10 26.65 26.60
15 26.47 26.41
20 26.29 26.21
25 26.12 26.02
30 25.94 25.83
35 25.76 25.64
40 25.59 25.45
45 25.41 25.26
50 25.24 25.08
55 25.06 24.89
60 24.88 24.71
65 24.71 24.53
70 24.53 24.35
75 24.35 24.17
80 24.18 23.99
85 24.00 23.81
90 23.82 23.64
95 23.65 23.46
100 23.47 23.29
105 23.29 23.12
110 23.12 22.95
115 22.94 22.78
120 22.76 22.61
125 22.59 22.44
130 22.41 22.28
135 22.24 22.12
140 22.06 21.95
145 21.88 21.79
150 21.71 21.63
155 21.53 21.47
160 21.35 21.31
165 21.18 21.16
170 21.00 21.00

Mean width: 24.0 23.9

Exponent: 0.007364343

It starts to make a difference if the bands are short and aggressively tapered:










But not so much. Therefore, exponential curved tapers are close to straights and straights are close to exponential curves.

Now, you can hand draw a more aggressive curve, but each section of band no longer draws the same amount of band in front/behind it. You can also use different mathetical models; a catenary curve for example, is not valid in this setting.

In the case of a convex section, like the one you illustrated above, that section, particularly the convex edges, are not drawing efficiently. Yet they might be faster than straights, but if so that's because you are drawing the tail end to extreme elongation. For the same draw force, _I suspect_ an exponential taper will be more efficient. I say _I suspect_, because I haven't fully explored tapers and curves. But that doesn't mean that I haven't done a fair amount of testing and modelling. I just need more before I can be definitive.

That's why I'm so interested in this thread. People like you are advancing our understanding of our sport.


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## ZDP-189 (Mar 14, 2010)

BTW for the number-phobic:

that big table of numbers is just to show there's a small but tiny difference between the two lines.
'exponential taper' simply means that the width grows at a proportionally constant rate as you go from the pouch to the fork
I can't think of a simpler word than proportional that explains the difference between the curve and a straight line. Just take it from me that it's about the same thing.


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