16 replies to this topic

[ZDP-189]

There have been a few developments in my bandset making these days. First, I have moved to a much more complex taper than before. The bands are highly engineered. They are radically tapered, mathematically curved, have straight sections for fork tying over specially coated fabric, are specially flared, doubled and feature a precise centre-marker. This is the band design I supplied to Jeff (shot in the foot) that offered superior accuracy, high velocity for low draw weight and have lasted over 5,000 shots so far without signs of wear. I appear to be onto a winner, so I have used this same pattern on all subsequent slingshots. However, there are a few drawbacks though all in the production process. Basically, they are very challenging to cut and there is no margin for error at all. The slightest imbalance, width miss-cut or a significant nick will render the bands useless and I have been throwing away three bands for every one made. It's already a wasteful design, as I can only get three sets from one 18" strip of Threa-band Gold. The cost of the materials, precise cutting requirements and labour input gave them a prohibitively high production cost.

I had to find a solution and turned to industrial rubber parts manufacturers. The solution was to make this steel rule die mould.



It cuts three pairs a minute by hand, or in an instant in a fly press.

It's all CNC laser cut to about 0.1mm precision. The fixed razor blades press through the latex into a plastic block and cuts perfect lines without nicks. It will cut any thickness or elastic you'd care to shoot. If the process can handle these complex shapes, simple tapers are no challenge at all. You could even set up a series of different tapers and lay rough-cut strips on top of the set that you wanted to use. The mould life is probably more than any one person would ever want and even the bigest Site Vendors would justify a very quick cost recovery compared to cutting by hand.

All you need to do is find a die cutting service on-line or in your vicinity and have them make you a mould to your specs. It was easy for me, I just took the lift down to the 7th floor!

[smitty]

Wow ZDP ! I like your solution to band production. I have done rotary die cutting on printing machines for decades. This might be something for me to look in to also. Thanks for all of your ideas. I also liked you taking me to school with the pics on making micarta.

[baumstamm]

that is what i´m looking 4!!!!!

[Dayhiker]

Way out of the realm of my hobby and into the realm of precision manufacturing. The skill of the shooter and the uniformity of the material are way too wild a variable to render any of this more than quite marginally useful in the real world. This exercise is purely academic in my opinion. (Please do not hate me, Dan.)

[ZDP-189]

Dayhiker, on 08 August 2010 - 03:47 PM, said:

Way out of the realm of my hobby and into the realm of precision manufacturing. The skill of the shooter and the uniformity of the material are way too wild a variable to render any of this more than quite marginally useful in the real world. This exercise is purely academic in my opinion. (Please do not hate me, Dan.)

Not at all. Let me explain a little why I had to go to all this effort.

The band design is firstly optimised for speed for low draw weight. That requires:

• Wide bands
• Aggressive taper
• Low weight at pouch end with light weight band tying
• Fast latex
• Great elongation at full draw

Then it is about accuracy (admittedly the user is more important here):

• Wide bands must cut and doubled so as to avoid rolling and achieve a more linear stretch
  
• Exactly balanced left and right bandsets
  
• Equal upper and lower bandsets

Most of all the above is inconsistent with longevity/ durability, so to enhance that:

• Fork tie portion to be exactly as wide as tips
• Pouch tie portion to be as wide as tip end to allow it to be rolled around the band to protect the elastic at the leather and under the tie
• A gradual flare at the pouch tie with the narrowest part of the taper just in front of the tie, not under it
• Gradual taper so that each section is approximately proportionally smaller than the next part in front so the elongation ratio is constant
• No single band is any weaker than the others
  
• No blade nicks on the edges

That's all academic. Either you'd want bands with these features or you wouldn't. This thread is not about the design of the bands but rather the challenges of making them and a solution that can be applied to all band making if you'd choose to.

I was having great trouble making these bands perfectly by hand. All the items in bold above conflicted with that. My bands were often nicked at the edge to the point of looking chewed up, unbalanced or narrower than the last set. Many ended up in the bin or were turned into tying strips. I tried roller cutters and steel rulers on rubber mats. I tried tape. I tried doing it sober without music playing. In the end I could do it, but it took too long and the reject rate was still high.

This solution is both fast and precise and I am now satisfied that I am making my bands to the standards required.

As for it's being an academic exercise, it's easily attainable. The cost is about the same as a couple of slingshots and the challenge of making it is just design and draw it, then wait 20 hours for the mould maker to tell me to come downstairs and pick it up. I slap the Thera-band on it and roll over it with a plastic rolling pin. Job done and complexity is no longer a factor.

[Flatband]

Now that is some high tech stuff Dan! How drastic are your tapers Bud? I have found through experimentation that too drastic a taper( I.E. more then 2.5 to 1 really is energy defeating( there are a lot of other variables though,cut,elastomer type,length,etc.. If you have found otherwise,please-I'M interested!!! Flatband

[pelleteer]

Ah! Took me awhile of looking at that to figure out what I was seeing (sort of an optical illusion). The red shaded areas are the dies for the three sets of band, yes?

Attached Files

•  SteelRuleDie_01.jpg   58.39K   79 downloads

[ZDP-189]

smitty, on 08 August 2010 - 01:23 PM, said:

Wow ZDP ! I like your solution to band production. I have done rotary die cutting on printing machines for decades. This might be something for me to look in to also. Thanks for all of your ideas. I also liked you taking me to school with the pics on making micarta.

Rotary dies would work, probably better, but I think they're technically more challenging to set up.

baumstamm, on 08 August 2010 - 02:28 PM, said:

that is what i´m looking 4!!!!!

It's surprisingly affordable. The shipping would cost as much as the mould, which is the main reason I'm not offering to help people make theirs. The other reason is that unless you have a fly press and safety guard, you're essentially pressing down hard on a rolling pin over multiple 18" razor blades. The only thing missing from this recipe for disaster is alcohol in the bloodstream and acetone on the nearest cleaning rag.

If you're familiar with British TV, watching me working on it looks like it should be in the opening 5 minutes of an episode of "Casualty". But then again that's true of just about every work process in my shop.

Flatband, on 08 August 2010 - 08:28 PM, said:

Now that is some high tech stuff Dan! How drastic are your tapers Bud?

Yes, I engineered the heck out of it. I took all the conventional wisdom I could find, identified the problems then took an out of the box approach to fixing them drawing on parallel-industry expertise. The result may or may not be better than other solutions like tapered tubes, thin tapered ribbon bands, etc. but they're distinctively mine and positively reek of my design approach. They're also impractical to copy unless you have a set to measure, a custom made mould and a source of the coated low friction weave.

Flatband, on 08 August 2010 - 08:28 PM, said:

How drastic are your tapers Bud? I have found through experimentation that too drastic a taper( I.E. more then 2.5 to 1 really is energy defeating( there are a lot of other variables though,cut,elastomer type,length,etc.. If you have found otherwise,please-I'M interested!!! Flatband

Not that radical. You are right, there is a distinct energy optimum. Also band life is reduced too much. The idea was to get pretty much all I knew how to get out of the bands in terms of speed for a given draw force but to out-last tubes and so as not to have to do butterfly. If you want, I'll send you some bands. It's the least I can do after all the free band material you gave me.

pelleteer, on 08 August 2010 - 08:34 PM, said:

Ah! Took me awhile of looking at that to figure out what I was seeing (sort of an optical illusion). The red shaded areas are the dies for the three sets of band, yes?

Yes, it's a vase-or-two-faces kind of illusion. The bands are the parts shaded for three pairs of bands. Can you see why I don't hand cut them? The inside angle by the pouch flares are potential failure points and have to be cut in one pass, not two cuts. I also make the flare on one side only because once tied, it's effectively symmetrical but it reduces the number of these angles by four per slingshot.

[Tex-Shooter]

The Saunders bands are cut in a complex shape also. I dont know if they are cut with a steel rule die or a roller die. -- Tex

[AaronC]

Wow, you are really coming up with some innovative stuff! I'll bet those are some fast bands!

[Frodo]

Wow...you are the man! Now i understand why you said that you sended me your best bandset!

Friedrich

[ursu5]

Have you tried cutting the bands directly using a laser cutting service?

[dgui]

Brilliant.

[bj000]

could there be any chance of me getting to try out a bandset? They look awesome. I doubt i would ever get to shoot something like that.

[Charles]

Wonderful work! Way to push the envelope. I can't express in words how impessive I find the band design. I would be very interested in seeing some speed tests compared to standard straight cuts.

Cheers ...... Charles

[Beanflip]

I got to chat with Z one night. I think he is working on going into production. I think they will be available soon.

[bj000]

Beanflip, on 14 September 2011 - 09:30 PM, said:

I got to chat with Z one night. I think he is working on going into production. I think they will be available soon.

hot dawg!