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Old 03-30-2020, 05:08 AM   #1
Murdoch
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Join Date: Apr 2012
Posts: 10
Aimrite 85cm roller

Hi all,

I've picked up an aim rite 85cm roller. The new head on these is a vast improvement on the older heads in a number of areas. I'm looking forward to swinging it around in the dirty water, heavy current conditions we get up here. The bands on these usually come to very high stretch loads and it gets exhausting when loading 30 times per trip with lots of reef fish and loading and unloading getting in and out of the water.

Out of box measurements:
- spear 130cm 7.5mm shaft
- topside roller to first notch 70cm
- topside roller to second notch 75cm
- underside roller to band anchor 76cm
- bands 31cm 16mm rubber
- dyneema from bands to anchor point 94cm = 46.5cm each side (1cm anchor)

Changes based on my limited knowledge:
- spear 120cm 7mm shaft
- bands (here is where I am stuck)

Question for 14.5mm small ID bands:
- what length do I need to get stretch to between 320% and 350% at the first notch?

I'm not sure how to calculate this and the spreadsheets I found I couldn't interpret.

Thank you in advance for the help.
Murdoch
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Old 03-30-2020, 10:05 AM   #2
Mikel_24
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Location: Bilbao (Spain)
Posts: 445
Re: Aimrite 85cm roller

The shorter and thicker the shaft, the better. You need to add mass and reduce length to gain in ridgidity and punch. I would go as short as the gun allows (flopper resting on the muzzle or almost) as long as you can still aim well.

The rollers I have seen arround here do not sport thin bands... 14mm bands seem to be the norm currently for multi-band guns but not rollers. I think that you could benefit from thicker rubber.

And if it gets tiring... then you need to do a few more sets of rows at the gym!
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Old 04-01-2020, 06:47 AM   #3
Murdoch
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Re: Aimrite 85cm roller

Cheers Mikel,

Thanks for the tips - both spear and gym related

Regarding band length, basically the length of dyneema on the underside that anchors the bands is fixed throughout the stretch, but can be changed according to need.
The distance from the top of the roller to the spear notch is fixed, and is always the amount of stretch of the band in distance.
So 75cm of band stretch from unloaded to loaded.
So:
1) 25cm band (with no pretension) = loaded length 100cm = 400% stretch
2) 25cm band (with 5cm pretension) = loaded length 105cm = 420% stretch
3) 30cm band (with no pretension) = loaded length 105cm = 350% stretch
4) 30cm band (with 5cm pretension) = loaded length 110cm = 366% stretch
5) 35cm band (with no pretension) = loaded length 110cm = 315% stretch
6) 35cm band (with 5cm pretension) = loaded length 115cm = 328% stretch
7) 40cm band (with no pretension) = loaded length 115cm = 287% stretch
8) 40cm band (with 5cm pretension) = loaded length 120cm = 300% stretch

40cm too soft, 25cm either not possible or I'd need a lot of gym work.
Seems the sweet spot is around 30-35cm band length.
Does this look right?

Cheers
Murdoch
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Old 04-09-2020, 08:42 AM   #4
Nicholasclf
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Re: Aimrite 85cm roller

For rubber fully stretched to first notch you are looking at a full distance of 146cm (70cm + 76cm)
To get around 350% you would need a band length of approximately 42cm (146cm/42cm = 3.48 = 348%. This is assuming full pretension.
To get same 350% using a shorter band with less pretension you can as an example use a 30cm band and 5cm pretension. (70+30+5)/30=3.5 or 350%

You can use this as a guide
A = Distance at top gun from roller to notch
B = Length of rubber
C = Pretension
D = Pretension cord
E = Distance at bottom of gun from roller to notch

(A + B + C) / B = Stretch factor
B + C + D = E
E - B - D = C

You can plug that into an excel so it makes it easier to calculate.
Hope this helps.


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Old 04-19-2020, 07:05 PM   #5
Murdoch
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Re: Aimrite 85cm roller

Thanks Nicholas.
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