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ribbon mixer formula

rbregn

Aluminum
Joined
Jan 8, 2014
Location
Montana
Does anyone know where I can find a formula so when I roll some flat bar and stretch it, it will come out to my desired diameter. I tried Google, but don't know how to ask what I want. :scratchchin:
 
This strikes me as the sort of thing that doesn’t lend it self to a formula.
Probably trade secret and simple hard earned skills.

Maybe start with some smaller material and get a feel for it.
You can start by calculating the length of the helix, then maybe use volume to get a heads up on the diameter.
 
I used to have a DOS program, punch in the numbers and it would spit out the answer. No longer have it and don't remember what it was called
 
I will been doing more research, have not found an app. But I can describe what I am looking for with better terminology. Say I want to make a Helix out of 1 1/2 x 1/4 inch flat bar, that is 12" in diameter and has a pitch of 12" also. What is the diameter of the circle I want to roll the flat bar to, before I stretch it out to a 12" pitch? In theory if I find the length of the od of the finished Helix, that would give me the circumference of the circle I want to roll the flat bar to. But I think I might still be missing something.
 
I will been doing more research, have not found an app. But I can describe what I am looking for with better terminology. Say I want to make a Helix out of 1 1/2 x 1/4 inch flat bar, that is 12" in diameter and has a pitch of 12" also. What is the diameter of the circle I want to roll the flat bar to, before I stretch it out to a 12" pitch? In theory if I find the length of the od of the finished Helix, that would give me the circumference of the circle I want to roll the flat bar to. But I think I might still be missing something.

That will get you as close as you can expect.
Figure some weirdness in stretch...go a little large on the flat, you can always cut it down.
 
It sounds like you are using a 9" shaft to wrap the 1/4 x 1 1/2 around on a 12" pitch. So 1 revolution of the bar travels 12" down the pipe. Use a piece of string to wrap one complete revolution around the pipe, start and stop 12" away. What is the length of the string, this will be ID of your circle, with :some weirdness in stretch". Should be distance around the pipe plus the distance travelled.
 
Rob F's method is an excellent solution. The only problem: by the time you find a 9" mandrel to form the ribbon you will have more invested in time and material than the cost of a new snow blower.

You might consider buying flighting and cutting to width for your ribbon.

Have you done an internet search for ribbon flighting?
 
Look up surface-flattening algorithm or surface-flattening software.

I came up with 10.4149" diameter for the roll to be stretched out and 35.14" length for each complete wrap (assuming the neutral axis is in the center of the bar when rolled the hard way. Make it longer).
 
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Lookup surface-flattening algorithm or surface-flattening software.

I came up with 10.4149" diameter for the roll to be stretched out and 35.14" length for each complete wrap (assuming the neutral axis is in the center of the bar when rolled the hard way. Make it longer).
These numbers need explaining. Also looks like you forgot the 12" pitch?
ID of the part should be more like 12.8" and if you add 1 1/2" to get to center of axis it is 14.3" Or OP wants to measure OD then 15.8" or so
 
These numbers need explaining. Also looks like you forgot the 12" pitch?
ID of the part should be more like 12.8" and if you add 1 1/2" to get to center of axis it is 14.3" Or OP wants to measure OD then 15.8" or so

Let's see.

I think his od is 12", so his id is 9". My number is for the id that is needed to close down to 9" when stretched to a pitch of 12". You can add 3" to get the od.

Here is a (too) simplified way to think about it:

Take 10.5" * pi (circumference at the neutral axis) to get one leg of a triangle and use 12" (pitch) for the other. The hypotenuse will be: 35.1" That is the length of the material needed to make one pitch length wrap assuming the neutral axis is at the mid point.

Look at these that I did using Rhino and its 'Unroll Surface UV' command:

snow_ribbon0.png photo - David photos at pbase.com
snow_ribbon1.png photo - David photos at pbase.com
 
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OK, simple math.

You want a helix with a 12" diameter; lets call that d.

And with a 12" pitch; call that P.

The length of that helix is L

L = sq rt [ (d * pi)^2 + P^2]

Or in your case L = sq rt [ (12 * pi)^2 + 12^2]
L = sq rt [37.70^2 + 144]
L = sq rt [1565.22]
L = 39.56

Now you need the size of a circle with that circumference. Just divide by pi.

D = L / pi

Or in your case D = 39.56 / pi
D = 12.59

The overall, one step formula for D would be:

D = (sq rt [ (d * pi)^2 + P^2]) / pi

I did it with a calculator. I don't know if it is worth creating an "App". Besides, I HATE that word.

I did that assuming that I was working with the outer diameters. There is going to be some kind of fudge factor due to the bending of a flat, rectangular bar into that initial circle and probably another, smaller one when you stretch it.
 
a = (9" + 1.5") * π
b = 12"
c = sq rt(a² + b²)

c ≈ length of ribbon

((c / (a / c)) / π) - 1.5" ≈ inside diameter needed to roll ribbon to before it is stretched to length so that it fits the 9" diameter roll.

I know I'm late with this.

This is an approximate way to get results though not as accurate as the iterative process used in post 15
 








 
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