Circular bands cutting length

[olliric]

Hello,
I have just got a 100 cm Omer and I have to cut and mount circular bands.
I have to do a set of two 18 mm circular and one 20mm circular.
I have bought the bulk bands and I have to cut them but I am not sure about the correct lenght.
I am looking for some length table to refer to. So far I found contradicting information.
Cheers
Giovanni

 

[Dobs]

Re: Circular bands cutting lenght

Hi Giovanni,
If S is the distance between the rubber hole and the notch you will load the bands to, then the general formula most people use to measure their bands will be 2xS divided by a coefficient ranging from 3 to 3.5 according to how short you like your rubbers. Divide by 3.5 and you will have the shortest possible rubbers.
For a 100 cm gun you will have
2x100=200/3=66.66 cm (the longest)
2x100=200/3.5=57.1 cm (the shortest)

This is the measurement for a single band.
When I cut double bands I use the same formula and I take the distance to the first notch for the shorter band and the distance to the second notch for the longer band.

Hope this helps!

 

[spaghetti]

Re: Circular bands cutting lenght

Cheers Giovanni. So finally which gun did you pick? Omer which one, Cayman? Did you buy at Top Sub in Genoa, and if so, did he show you his new woody? (Top Sub woody looked lovely from pictures on Pescasub magazine...).

PS-You can trust Dobs. He's a maestro of handmade spearguns.

 

[olliric]

Re: Circular bands cutting lenght

Thanks for your reply. I have seen that formula too. The lenghts you suggest are the actual lengths to be cut? Some people suggest that you have to add 2 cm for each end before you cut it. The extra length is to allow for the wish bone mounting.
The Power 18 mm Omer circular band that came with the gun is 64 cm over all length. I have a table from an Italian company price list that for a 100 cm gun gives 58 cm (20mm dia). Quite a difference.
The formula applies to any diameter band. Would you change it a bit according to the dia?
Given that I have no problem loading the gun, in term of performance I am not sure which is more advisable. The longer one will certain make the band last longer but I wonder if the performance trade off is heavy.
Personally I would favor a progressive release with a more steady spear speed.
Difficult call,
Cheers

Hi Giovanni,
If S is the distance between the rubber hole and the notch you will load the bands to, then the general formula most people use to measure their bands will be 2xS divided by a coefficient ranging from 3 to 3.5 according to how short you like your rubbers. Divide by 3.5 and you will have the shortest possible rubbers.
For a 100 cm gun you will have
2x100=200/3=66.66 cm (the longest)
2x100=200/3.5=57.1 cm (the shortest)

This is the measurement for a single band.
When I cut double bands I use the same formula and I take the distance to the first notch for the shorter band and the distance to the second notch for the longer band.

Hope this helps!

 

[olliric]

Re: Circular bands cutting lenght

I have got the Cayman HF. Very beutiful gun indeed. I have not tried yet though. Top sub has some beautiful woodies but they won't work for me. I need to take the gun apart for travelling.
Cheers

Cheers Giovanni. So finally which gun did you pick? Omer which one, Cayman? Did you buy at Top Sub in Genoa, and if so, did he show you his new woody? (Top Sub woody looked lovely from pictures on Pescasub magazine...).

PS-You can trust Dobs. He's a maestro of handmade spearguns.

 

[spaghetti]

Re: Circular bands cutting lenght

Scusa se non ti aiuto sulla questione, ma ho solo due fucili con il circolare, che tra l'altro uso poco (preferisco le testate tradizionali), e soprattutto non mi sono mai preso la briga di misurare la lunghezza delle gomme.
(...e mi rendo conto solo in questo momento che, in vita mia, non mi sono mai misurato nemmeno il....vabbè, scusa l'Off Topic rofl)

 

[Dobs]

Re: Circular bands cutting lenght

(...e mi rendo conto solo in questo momento che, in vita mia, non mi sono mai misurato nemmeno il....vabbè, scusa l'Off Topic rofl)

rofl rofl rofl

Giovanni, I cut the exact lengths that I calculate with the formula. You loose 1 cm on each side of the band when you tie the wishbone, but then the wishbone itself gives you 2-3 cm, so it is the same.
As for the different diameter, I always cut my bands a little short (coefficient 3.5) on my shorter guns 80 and 90 cm, while on the 107 I use coefficient 3.3. I know the bands last less in this way but I like the extra punch. If you like you can try with coefficient 3 with the thicker bands and then shorten them if you think they are too weak.

P.S. I’m still laughing, Spago… rofl

 

[deep thinker]

Re: Circular bands cutting lenght

Heres a cool chart showing basic lenths and the contrictor knot for the dyneema. View attachment 12377

 

[olliric]

Re: Circular bands cutting lenght

Thanks for the table. There is a huge difference between the 16 and 20mm band lenghts. In theory they should be the same.
I suspect that by following the table the gun would turn out with about the same power no matter what is the band diameter.
I'll cut the bands according to the formula and divide by 3.
Thanks everyone for the advice.
I'll cut with more confidence now.
Cheers
Giovanni

Heres a cool chart showing basic lenths and the contrictor knot for the dyneema. View attachment 12377

 

[Dobs]

Re: Circular bands cutting lenght

I I'm not mistaking, this chart is for Rob Allen guns, which have slightly longer bands due to the muzzle design.

 

[olliric]

Re: Circular bands cutting lenght

I have cut the 18mm bands to 66 and 61 cm, the 20mm to 66cm. Unfortunately when I started grinding the ends to a 30deg taper one got caught in the grinding wheel and I damaged it. I had to cut another 1.5 cm from both 18 mm bands.
I have learned the lesson though. Grind the ends at a tangent angle to the grinding wheel and do not rest the band on the pedestrial grinding wheel rest. The band gets sucked in between the rest and the wheel and get gauged.
Now I will tie the Seatec smoby wishbone with a constrictor knot and one half hitch on both side of the knot. This way the band will be squeezed more gradually and reduce the chance of cutting in the band over time.
I have read to lubricate the line with wax before tieing the knot. I think I'll use water soluble condoms lubricant instead. It's a bit kinky but I believe will do a better job. You never know what they put in candle wax. Petroleum products will melt latex. With vaseline I broke a few condoms. It wasn't a matter of size or energy....but I took me a while to figure it out.
Cheers
Giovanni

I I'm not mistaking, this chart is for Rob Allen guns, which have slightly longer bands due to the muzzle design.

 

[Mr. X]

Re: Circular bands cutting lenght

As well as the Rob Allen chart, there is a Rabitech chart:Adrenaline Spearfishing Supplies

 

[olliric]

Re: Circular bands cutting lenght

Thank you. Again it seems that the lenght changes depending on the diameter. I am not sure what is the theory behind. I suppose it has to do with the ease of loading rather than with the maximum strain the rubber can take.
I cut and tied all the 3 bands. In a dry test they are very hard, I hope it will be better in the water. The double 18mm should a have a very stong punch.
Saturday the in the water test.
Cheers
Giovanni

As well as the Rob Allen chart, there is a Rabitech chart:Adrenaline Spearfishing Supplies

 

[Marwan]

Re: Circular bands cutting lenght

Scusa se non ti aiuto sulla questione, ma ho solo due fucili con il circolare, che tra l'altro uso poco (preferisco le testate tradizionali), e soprattutto non mi sono mai preso la briga di misurare la lunghezza delle gomme.
(...e mi rendo conto solo in questo momento che, in vita mia, non mi sono mai misurato nemmeno il....vabbè, scusa l'Off Topic rofl)

rofl mama mia! (pretending to understand italian)

rofl

 

[deep thinker]

Re: Circular bands cutting lenght

It's a bit kinky but I believe will do a better job...... Petroleum products will melt latex. With vaseline I broke a few condoms.
Giovanni

Hmm I hope this was also during the experimental stage rofl rofl You mite have offspring cruising the globe you dont even know about . Sorry if your feeling a bit worried now but I couldnt resist rofl