# Taper By Cutting



## Charles (Aug 26, 2010)

Today's project was an investigation of the results of taper by cutting. Here are the rigs I used.










The bottom rig you will recognize as my Zen PFS. Yes, I know, one band is broken ... more about that later. The bands were cut from ONE Alliance 105 band. I stretched a 105 band and cut it at what appeared to be its weakest part, yielding a strip 10.5 inces long. I wanted 1.5 inches at each end to allow for tying, so I measured 1.5 inches and marked that at each end using a ball point pen. I used wide packing tape to tape down one end of the band, stretched it lightly, and taped the othe end down as well. Then I used a steel rule and a rotary cutter to slice the band diagonally between my two marks. Stretching the band made it easier for me to get a straight, proper cut. That gave me two bands from one Alliance 105. I used an extra strip of another 105 over the forks to prevent chafing, and used a standard rubberband tie with Alliance 64s to attach the bands to the forks. The taper was so great that I had to use small rubber bands to tie the bands to the pouch. The band length, from fork to pouch tie, was 7 inches.

The top rig is a new PFS I made from a bamboo scraper I scored at a thrift shop yesterday ... and it has a shoestring lanyard, also from the thrift store. Each band was cut from a single Alliance 105. In each case, I began with a strip 10.5 inches long as before. I marked off 1.5 inches from one end. At the other end, I marked the band in the middle of its width. I stretched each band and cut as previously described. I used standard rubberband ties to attach the bands at the forks, but had enough length I could just double the band under to provide the cushioning from chafing at the fork. The bands were attached to the pouch using cutoffs from small diameter Chinese tubes, as I have described elsewhere.

I took a few shots with each to warm up, and then fired 20 shots through the Chrony. Here are the figures:

single band------------------------156 fps
tapers cut from one band------172fps **
tapers cut from two bands-----165fps **
taper by half doubling-----------184fps

The results above marked by ** are the results from today. The other two results I reported in other threads.

The draw weights are also interesting to compare:

single band------------------------6 pounds
tapers cut from one band------3.5 pounds
tapers cut from two bands-----4.5 pounds
taper by half doubling-----------14 pounds

Frankly, I was amazed at the performance of the tapers cut from just one length of Alliance 105. Essentially, you are using half the amount of propellent material as with the single band setup ... remember, the single band setup had two bands, each of which was an Alliance 105. And yet the velocity was significantly higher!

But now for the bad news. The bands cut from a single 105 broke after about 30 shots. One band broke near the pouch, but not right at the pouch tie ... I do not think the pouch tie had anything to do with it.

I have not shot enough with the tapered set cut from two 105s to have a good feel for band life. All I can say is that so far they look just fine. The pull is amazingly light compared to the uncut bands, and the tapered bands do give a 6% increase in speed. Cutting them was not too big a pain. Still in my view, the band life would have to closely approach that of the uncut bands to be worth a mere 6% increase.

If I were going into the field with any of these bands, I would carry an extra set, complete with attached pouch. Changing bands with a rubberband tie is actually pretty quick and easy if you use a string loop to pull the free end of the tie under the last layer or two of wrap.

Cheers ..... Charles


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## dgui (Jan 12, 2010)

Nice Little Rigs you got there. I will stick with square cutting bands, it's easier and I generally cut 4 widths. 1/4, 1/2, 5/8, 3/4 inch and that's it. If I want taper I buy them from Tex.


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## Papa G (Aug 19, 2011)

thanks for all the good test you have been posting Charles.


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## AJW (Apr 24, 2011)

Thanks Charles, really enjoyed your set of tests with the 105's and 107's. I was surprised that your little PFS stood up to the partial doubling taper.

When Henry made my first set of 107's for me, he doubled half the band to get the tapered effect. I loved the feel that the extra mass added to the pull weight, it did make me feel like I was contributing to the performance of the bands. At the same time I knew it would be a chore to use fully doubled 107's for any length of time.

I still use Henry's original configuration but I'm using it on a full sized frame, where I get a fist full of handle to make an easier pull. I would imagine that your PDF is pretty hard on your thumb.

I have it on three frames now and do appreciate the extra life I get out of a set of 107 bands. With TBG I wasn't getting 200 shots, and I have had as low as 50. I have repaired the original set of 107's (which I which was never possible with TBG) and only now need to replace them. If I remember correctly, that has to be about 2 weeks of use.

Thanks for your studies Charles.


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## Charles (Aug 26, 2010)

AJW said:


> Thanks Charles, really enjoyed your set of tests with the 105's and 107's. I was surprised that your little PFS stood up to the partial doubling taper.
> 
> When Henry made my first set of 107's for me, he doubled half the band to get the tapered effect. I loved the feel that the extra mass added to the pull weight, it did make me feel like I was contributing to the performance of the bands. At the same time I knew it would be a chore to use fully doubled 107's for any length of time.
> 
> ...


Those bamboo PFS rigs are very tough indeed. Those scrapers are at least 1/4 inch thick at their thinnest part, and the grain runs longitudinally. It would take a LOT more force than what can be supplied by those bands to break one, especially given the way one holds a PFS while shooting.

And actually, my bamboo scraper PFS rigs are very easy on my hands. For one thing, I grip them fairly high up. For another, I point them forward. Both of these techniques lower the forks and so give less torque on the wrist. And that sort of hold means that a great deal (probably most) of the force on the forks is along the longitudinal axis of the PFS, rather than perpendicular to the forks. Also, I do not shoot vertical as does Dgui. I find I have a lot of hand tremor when I try to shoot vertically with heavy pull. I have been shooting with a sideways hold for some time now, and it is much easier on my wrist with heavy bands ... I get much less hand tremor with a sideways hold. And I am an aimer, not an intuitive shooter; so I am much more accurate with a sideways hold than with a vertical hold.

I note that my recorded velocities are not as high as reported by some others ... no doubt due to slight differences in draw length and other matters. So I am trying to be consistent as much as possible with things like band length, draw length, pouch size and material, and attachment methods. I am not totally consistent on all these matters from one rig to another, but not too bad. I am also using bands from the same box, so that hopefully the band composition will be the same from trial to trial. I am not so much concerned with the absolute numbers as with the comparison between different setups.

I have more tests in mind, but do not have the time to do them today.

Cheers ...... Charles


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## pop shot (Sep 29, 2011)

could you explain "half doubling? or a photo?


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## pop shot (Sep 29, 2011)

disregard- saw the post


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## philly (Jun 13, 2010)

Great write up Charles, enjoyed the read. Thanks for sharing. Love my Bamboo PFS, mine were from a cutting board.
Philly


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## Dayhiker (Mar 13, 2010)

Thank you Charles. I have no patience for research myself so I very happy to have guys like you and Henry and ZDP189 around to do it for me.


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## ZDP-189 (Mar 14, 2010)

Charles, that's a great post. It is inspiring. It fills me with questions and desire to do my own testing. There are a couple of big areas that I need to fully explore before I can say that I've got a proper idea of how flat bands work and tapers is one of them.

I think that your results demonstrate several things:
The aggressive taper offered more velocity from less draw than the medium taper and that in turn better than the straight bands
Aggressive tapers have shorter band life, failing at the pouch
Double straight bands (data taken from you other thread) are more efficient than single straight bands because the dead mass of the pouch is split between twice the amount of rubber band
You can get more performance out of a generic band with creative methods of cutting and tying
I would very much like to explore this in detail. In order to understand it properly I need to standardise testing and plot a surface. What I need is curves of velocity against projectiles of 4 or more masses for 4 or more degrees of taper for the same elongation at similar draw forces of around 60 Newtons with a draw length of 76cm in TBG. I'm a bit short on time, so if anyone with a chrony wants to do this for trade, money, or pure gratitude, please PM me.


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## Charles (Aug 26, 2010)

This sounds like a good project for collaboration. I cannot do it immediately, but would be happy to work on it in a month or so. I do have some Theraband gold, so I could cut the bands. My proposal would be to set up a rig on a 2x4 backbone ... fixed dowel forks on a short crossbar at one end ... draw to a mechanical release anchored at the other end of the backbone ... release through a chrony after some fixed time, say 15 seconds. I have 3/8 inch steel and can cast lead balls of various weights. Since we are talking "muzzle velocity", I do not think air resistance of the projectiles will matter, so I would not worry about dimensions of the balls but only their masses. Perhaps you could suggest the sorts of tapers you have in mind for the bands.

Cheers ..... Charles


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## Imperial (Feb 9, 2011)

slingshot science terminology has officially gone over my head on this day, 11-2-2011.


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## Charles (Aug 26, 2010)

Imperial said:


> slingshot science terminology has officially gone over my head on this day, 11-2-2011.


Only because you ducked!!!









Cheers ..... Charles


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