Constrictor knots and mean green rubber

[Captladner]

Any helpful tips on perfecting constrictor knots or keeping a wishbone stopper knot stay in the tubing?
How do you determine band length with mean green rubber. My practice bands have been too extremely hard to load and my dynema wishbones are occasionally pulling out.
Any suggestions are appreciated

 

[Mr. X]

All good questions. I use RA dyneema wishbones and they have a nylon bead at each end rather than just a stopper knot. I re-use the beads, tying a double- overhand knot as the stopper within the bead.

To push the bead (or stopper knot) into the rubber, I use RA's T- shaped metal tool but snipe-nosed pliers work too. Best to lube the bead/stopper before attempting to insert it. Some use silicone but I suggest using a lube that will later become sticky: saliva or soapy water (a tip from the local motorcycle Tyre fitter).

 

[Mr. X]

Tie the constrictor knot ensuring you have at least an inch or two spare at either end. I use special Kevlar cord from spearitco.com currently, which is a bit too thin but doesn't stretch, if you use normal cord it will need to be tied even tighter to allow for stretching.

To tighten the knot, I tie one end of the cord to fixed point, usually my bench vise and wrap the other around a tool, such a screwdriver, the RA insertion tool or both sides of some snipe-nosed pliers. Then I pull real hard to tighten the knot. If you tied the knot correctly it will not loosen when you release the tension.

 

[Mr. X]

To finish the knot, I either tie an extra loop with a double-overhand knot/surgeon's knot or just cut the ends, leaving about 6mm at each end...

I then melt and mushroom the ends with a lighter flame and smear them over the knot. Take care and use some imagination. That's good enough but I sometimes superglue over the knot(s) too.

 

[Mr. X]

BTW I often wonder if Rob Allen pear -shaped beads would work better upside down: that way the tapered end should make them easier to insert and the broad end should make it harder to pull out and easier to tighter the constrictor. Anybody tried it?

 

[Captladner]

Yes, I agree with everything you said, thanks for the input. I’ve got the tool and have thought about using the beads in reverse.
Have tried the green tubing?

 

[Mr. X]

No, are they magical?

I bought my last lot of bulk rubber - which is all I use - from spearitco.com. Their rubber is really fresh. I store the excess in a sealed bag in the deep freeze. I bought 14mm, 16mm and 3/4" =18-20mm last time.

I use long 19mm rubber on my little 75cm speargun; the ends were perished this year, so I just cut the ends off and reset the wishbone. Now they are probably almost standard length ( I use Rob Allen's length chart as my guide - there are other charts and formulas - and then add a bit, as new bands can be hard to load and when the bands age I can cut them down for more power & life).

I have a 16mm bulk rubber on my 90cm speargun. Works well, I like this combination.

I plan to try 2x 14mm bands sometime, perhaps something for my son to try.

 

[MAKO Spearguns]

Tying a Double Constrictor Knot | MAKO Spearguns

Tying your own power bands is easy and inexpensive. Here are the simple steps needed to make the process a success

www.makospearguns.com

Installing Beaded Wishbones | MAKO Spearguns

Installing wishbone beads is an easy process when you know the simple techniques demonstrated here

www.makospearguns.com

 

[Bill McIntyre]

Mr X covered it well. I think a drop of super glue on the knot is good insurance.

I'm not sure if the Mean Green rubber is the same as I tried years ago, but if it is I think its worthless. You have to cut it so much longer to be able to load it, and then it doesn't have very far to contract to get the shaft moving. I gave all mine away.

I don't have any experience with the RA beads, but I'm a big fan of the stainless inserts sold by Mako. They are a lot easier to insert than a knot, and they are big enough to hold well. If you use large ID rubber, then this one:

Stainless Steel Wishbone Inserts for standard 1/8" ID tubing

These stainless steel wishbone inserts for standard 1/8" ID tubing allow you to quickly change your wishbone cordage without having to retie your bands.

www.makospearguns.com

Or is you use small ID then this one:

Q8 Stainless Steel Wishbone Inserts

These stainless steel wishbone inserts allow you to quickly change your wishbone cordage without having to retie your bands.

www.makospearguns.com

I'm using the small ID rubber and I like the fact that you can change wishbone length just by slipping the knot instead of cutting the wishbone off and replacing it.

 

[Captladner]

Thank you both for all the input. I’m starting to believe that about the green rubber. Was supposed to be everything and more. I’ve got bulk from another build and will probably go back to that.
Thanks again.

 

[Bill McIntyre]

An afterthought- I made a set of bands for a friend using the small ID inserts in large ID rubber. Mako says it doesn’t work but that was 6 months ago and they haven’t pulled out yet. Apparently you can get away with it as long as your constrictor knot is tight enough.

 

[SubSub]

I’ve used the inserts that Majd originally developed, and think they are great. Never slipped out, even though I dip the end in silicone grease to prevent water intrusion. If you’re in the US you find em here: https://www.makospearguns.com/Q8-Stainless-Steel-Wishbone-Inserts-p/mq8sswi.htm

If you’re in Europe you find them here:

Accessori

Nuova Testata modellabile, facile da piegare, far coincidere i fori di entrata e di uscita dei perni, spessore 2 mm , ospita fino a tre elastici , dotata di guidafilo destro e sinistro piegabile ed...

www.ermes-sub.net

To pull really hard on the constrictor know you can wrap one end around a object fixed to the ground and the other end around like a wrench or something and pull.

I’m using the above mentioned inserts dipped in silicone grease, a single constrictor knot with just cut and mushroomed ends but have never had a insert pop out.

If it’s to any help I have 14mm small id Primeline bands tied at 360%.

 

[Mr. X]

I see that you can also get plastic inserts in the USA. I like the idea of a lighter insert*. Some of them seem to bury the knot section inside the rubber which rather negates the benefit of using an insert, might as well use beads.

*I have some metal beads from spearitco.com but have yet to use them. I prefer to re-use my nylon RA beads.

 

[Mr. X]

I just received some of stainless steel inserts sold on eBay for £1 each.

6PCS 316 Stainless Steel Inserts Spearfishing Wishbone for 2mm Speargun Bands | eBay

6pcs of wishbone ( not including other spare parts ). Quantity: 6pcs( not including other spare parts ). Material: 316 stainless steel. Suitable for strong horse weaving thread passing within 2mm. Suitable for strong horse weaving thread passing within 2mm.

www.ebay.co.uk

The hole for wishbone is 3mm but seems just right for the 1.9mm wishbone cord I use (for notched spears). I normally use a double-thumbknot but a single thumb-knot seems to work better with these. Not ideal. They are heavy - would prefer plastic but oddly they are far more expensive - and threading in new wishbone cord is fiddly- you couldn't replace the cord while in the sea, as Pastor was able to do with his knotted loops for beads/inserts approach.

 

[Bill McIntyre]

For what it’s worth, I’m using 1.9mm stiff dyneema Aussie line in my stainless inserts from Mako. I don’t see why I couldn’t easily replace it in the water but I can’t imagine why I would ever need too. This stuff is very hard to cut with a sharp knife.

 

[Bill McIntyre]

The reason for all the extra length is that I just made new bands. If it turns out that I can’t load them I can easily lengthen the wishbones by slipping the knots in the water. After I’m sure I have it right I’ll cut off the excess.

 

[Mr. X]

Yes Bill the Mako inserts look good. I hadn't noticed the design differences in your original post, I wrongly assumed they were the same. But, as you say, perhaps it makes little difference as we're unlkely to break or fix a Dyneema wishbone at sea. I like the idea of a quick, simple, tool-less wishbone replacement though. And the ability to tweak wishbone length.

As my spearguns are superlight with relatively soft carbon barrels, so I'd rather use lighter, softer beads or stopper-knots. Spearitco.com sell a similar inserts but made of plastic, ostensibly for polespears but supposedly ok for spearguns too, provided you are careful. But the price, esp. with shipping to the UK, seems excessive. Perhaps this is the sort of thing we could get 3-D printed locally in the near future. Anyone recall what sort of cord Pastor used for his knotted & loop inserts?

 

[MAKO Spearguns]

Another benefit of this type of band construction is that it facilitates a very fast replacement of the band in a muzzle which does not have slots cut in it. Decent dynema line will show a lot of wear before it breaks, so broken bridles should be unusual, but sometimes bands break somewhat unexpectedly.

 

[sharkey]

I don’t use a constrictor knot I prefer a clove hitch & have never seen it fail. Being able to remove rubbers is great for testing & compairing things. I can use the same rubbers on equal band stretch guns to compare things like recoil & eliminate one potential bias. It also means I can get away with only a couple of dozen rubbers between many different guns I use. I can easily take two off the gun with 1.8 m 3/8 spears & put them on the one with the 1.9m 7.5mm spear. The photo is the knots on three identically set up guns we do most of our practical tests with. I don’t think “mean green” is the same green rubber that Salvimar started to distribute a few years ago. This currently available Salvimar green rubber is very progressive & IMO the best I have tried in the last few years ( I try to buy & test every rubber available ). I don’t get to caught up in putting them on scales as that doesn’t measure their speed ( I think a car tire would test well by some people’s methods). We pool test & try to eliminate bias as much as possible when compairing rubber. I have found that just one rubber on a big heavy spear ( instead of four) highlights a rubbers ability to turn the kinetic energy into results well enough to base decisions on.

 

[Mr. X]

I'm surprised that a clove hitch holds reliably, so interesting to read of your experience. I read somewhere online that a clove hitch has no recommended use (I.e. there is always a better option - I think it can change or "invert" under certain conditions) but I must say that is not my experience. In scouts they were used to finish lashings used to support some impressive, life- supporting structures. When mountaineering & rock climbing to tie in quickly to a belay point, it also allows the tie-in length to be adjusted quickly and easily.

what are you using for inserts in your pictures - 3mm hollow-spectra loops tied with an overhand stopper knot by any chance?