# Fork to pouch angles



## Ordie69 (Aug 25, 2011)

Hello everyone. Most of you are old pro's at making slingshots. I am just beginning and have been looking at the dynamics involved in the shooting system. One thing that I continue to read about is band life. Looking at some of the designs that are available I noticed that few of them take into consideration the added pressure on a part of the bands during the draw.









I am primarily talking about tubed slingshots but I imagine the same principles would apply to flatbands. The typical setup is similar to A above. The forks are at approximately 90 degrees so during the draw you have added pressure on one side of the tube. Without uniform stress, one side of the tube will degrade faster than the other, shortening the life of the tube.

In example B above, this is compensated for by calculating the angle based on the width of the forks and the length of the draw to get as close to a perfect angle as possible. This should increase the life of the bands due to uniform stress.

I tested this on a Daisy B52 with the standard bands shooting marbles. With the original angles I got 290 shots before I detected the first signs of stress cracks. After bending the forks to the angles that would fit my draw (87 degrees) I am now on shot 330 with no signs of stress cracks. I will post the final number when I get it.

Here are a couple of web sites that can help you find your angle if you so desire. Anyway, it was something that I was working on that I thought I would share.

http://ostermiller.o...c/triangle.html
http://www.teachervi...th_6_TTT_17.pdf

****UPDATE****
Well I just changed the second band at 412 shots. The rubber next to the pouch was showing stress cracks so I changed it before it broke. Around the forks still look fine. I am going to try another band and see if I get similar results or if it was luck of the draw with that particular band.

One more thing...I have no idea if this is even a good number of shots out of these store bought tubes. Does anyone have any experience with them and if so, approximately how many shots are you getting out of them? Thanks.

****UPDATE2****
I tried this same experiment with a brand new Marksman 3061 today and got 117 shots with this result. Notice that the forks are further from the 90 degrees of the daisy. I know this probably doesn't surprise many of you but I find it interesting







The result could be due to cheap installed tubes but the stress points are the same.


----------



## brianmitchell66 (Jun 20, 2011)

If you use tubes, durability really is not an issue.

Thanks for sharing though!


----------



## NaturalFork (Jan 21, 2010)

I know trumark turns in their prongs a little to adjust for the angle.


----------



## jskeen (Feb 7, 2011)

That is an interesting point, I don't shoot tubes much, so I am curious if that area is a common failure point for tubes. I know with flat bands the normal failure point is the other end of the band, just in front of the pouch tie. I suspect that failure is more attributable to the bands and pouch impacting the frame after release, than it is to elongation pressures, evenly distributed or not.

However, in theory any point stress load that is higher than average is a cause for premature failure in any material. The question is, is the severity of that load comparable with others, or is it so much lower that some other issue will cause a failure elsewhere long before that particular one is an issue.

I'm sure that aligning the load bearing structures with the axis of force will help the bands last longer at that point, but if it causes a more direct impact with the tubes closer to the pouch, or some other second order effect, it may be decreasing overall tube life.

As with most things, an ounce of field data is worth a gallon of armchair theorizing


----------



## Papa G (Aug 19, 2011)

Worth thinking about


----------



## Charles (Aug 26, 2010)

Interesting point! And your empirical experiment seems to bear out your concerns. Thanks for this.

Cheers ....... Charles


----------



## Ace (Oct 24, 2010)

i have Marksman slingshots from 3 years ago with the original tubes only sign of wear was a bit of scuffing on the pouch side of the tube nothing major still shooting however slow they shoot


----------



## Ordie69 (Aug 25, 2011)

Ace said:


> i have Marksman slingshots from 3 years ago with the original tubes only sign of wear was a bit of scuffing on the pouch side of the tube nothing major still shooting however slow they shoot


Ace, what model Marksman is it? I just did the same test with a Marksman 3061 which failed terribly.


----------



## NaturalFork (Jan 21, 2010)

Tube shooters like that always break tubes on the fork end. Trumark makes rotating prongs and Saunders makes tube sleeves to alleviate some of the stress (watch flatbands video).

But this is just another reason to use flats.


----------



## Ordie69 (Aug 25, 2011)

NaturalFork said:


> Tube shooters like that always break tubes on the fork end. Trumark makes rotating prongs and Saunders makes tube sleeves to alleviate some of the stress (watch flatbands video).
> 
> But this is just another reason to use flats.


Thanks NaturalFork. I think that it is inevitable that any band will wear and break. I am simply looking for ways to prolong the life. I have yet to try a flatband so I can not speak to that yet, but I will soon.


----------



## Ace (Oct 24, 2010)

Ordie69 said:


> i have Marksman slingshots from 3 years ago with the original tubes only sign of wear was a bit of scuffing on the pouch side of the tube nothing major still shooting however slow they shoot


Ace, what model Marksman is it? I just did the same test with a Marksman 3061 which failed terribly.
[/quote]
It's a 3055 but my 3061 has gone for well over 1000 shots but will get a set of trumark tubes whenever i can get my hands on them my friend drew back and launched one right into the tube end it has a shallow slice in it but with 1000+ shots not bad but very slow bands.


----------



## Ordie69 (Aug 25, 2011)

Ace said:


> It's a 3055 but my 3061 has gone for well over 1000 shots but will get a set of trumark tubes whenever i can get my hands on them my friend drew back and launched one right into the tube end it has a shallow slice in it but with 1000+ shots not bad but very slow bands.


Wow, 1000+ shots. I must be doing something very wrong... Just out of curiosity, what is your draw length? Mine is between 32" and 33" and I think that might be over drawing for the default bands on the 3061. In any event, thanks for the information


----------



## Ace (Oct 24, 2010)

Ordie69 said:


> It's a 3055 but my 3061 has gone for well over 1000 shots but will get a set of trumark tubes whenever i can get my hands on them my friend drew back and launched one right into the tube end it has a shallow slice in it but with 1000+ shots not bad but very slow bands.


Wow, 1000+ shots. I must be doing something very wrong... Just out of curiosity, what is your draw length? Mine is between 32" and 33" and I think that might be over drawing for the default bands on the 3061. In any event, thanks for the information








[/quote]
MY draw length is 30" since I believe marksman bands are extruded they don\t stand up well to over drawing it maybe your problem I never liked those bands anyways it just saved me a few bucks not to buy new tubes


----------

