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Old 10-24-2018, 08:23 PM   #121
popgun pete
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Re: Trigger Mechanism Design Rules

Originally Posted by Rob Allen View Post
Agreed. Years ago, the most common handle in South Africa was the old Champion Cavallaro handle. The original ones only accepted a spear with a longer tail section (behind the spear notch) this caused problems when the spear pushed up against the roof of the sear box as it could affect the way it lay if the spear was not machined straight (commonly they were not straight). This was especially the case with older ones where the roof would wear. They halved the length of the tail section and this reduced that potential load flexing a lot. All Euro spears are now at the same measurement. I’m not sure who started to keep measurements uniform in Europe.
There was a move to a "universal gachete" or universal trigger in terms of the sear tooth shape and I have seen this term inscribed on the housing of a few "second stringer" European spearguns as distinct from the mainstream Cavalero and Beuchat spearguns. The rationale would be that a gun was then not restricted to its original spear and for a time it seemed that there was a "universal shaft" to fit these guns (in the same diameter shaft) and it was very much like the Cavalero shaft with a flat tail and a wedge shaped tail notch. My recollection is that these guns usually had a rear plastic grip handle, a plastic trigger and that often the dipping sear tooth design was employed where the spear tail on insertion into the sear box pushed the tooth down and then springs pushed the tooth back up to engage the spear tail notch when it slid into the correct position. The plastic grip handles were clamshell moldings and the overall construction was very light and some would say flimsy. These guns, I recall one brand was "Crawl", seem to have disappeared as well as the term "universal gachete" from the speargun world.

Last edited by popgun pete; 10-24-2018 at 10:08 PM.
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Old 10-25-2018, 10:48 PM   #122
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Re: Trigger Mechanism Design Rules

Originally Posted by Marco View Post
Probably a genius...
Yes a genius, Marc Valentin
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Old 10-26-2018, 04:32 AM   #123
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Re: Trigger Mechanism Design Rules

Originally Posted by Rob Allen View Post
About a year ago we changed our spear sear notch to a more square shape after doing destruction testing on our handle using different shaped notches. The "more square" notch increased the mechanism "hold ability" on average by around 40kg.

That is interesting … I would have thought that a C shape would be stronger than a square cut because there are no sharp corners that can propagate a weakness. I did some stress analysis testing on a computer and I always found that the weakest point in the sear shaft is the area between the shaft sear pin and the shaft sear and not the notch itself. Obviously it would be different from mech to mech as they have different measurements and different angles of attack with regards to how the spear shaft sits on the notch. In the test study, I was able to dramatically improve the stress analysis data by simply adding a bigger fillet on the right angle between the shaft sear back stop and the shaft sear. You can get away with a 2mm fillet and maybe even a 2.5mm fillet before touching the spearshaft back end. That little tiny change dramatically increased the strength of the shaft sear.
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Old 10-26-2018, 04:49 AM   #124
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Re: Trigger Mechanism Design Rules

Hi Spearq8,

When overpowered to destruction, the part that destructs is not the shaft. I agree, a square will have sharp edges and be weaker than a C shaped, but the fail is not the shaft. The sear in the mechanism itself distorts and or, bends the sear pivot pin. Our "square" sear notch in the spear does have rounded corners. The degree of glass content in the glass filled nylon cassette also plays a huge part in the mechanisms "hold-ability" as does the corners in the roof.
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Old 10-26-2018, 09:17 PM   #125
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Re: Trigger Mechanism Design Rules

The squarer shaft tail notch probably engages lower on the tooth. If you looked at a fully loaded up spear tail and sear tooth of the square cut type you would see that they would connect low on the tooth as the sear lever under extreme pressure tilts forwards slightly (1/4” sear lever pivot pin). Bill Kitto found that when he applied thousands of pounds of spear pull the slightly tilted tooth was torn off the sear lever by the spear tail which cut through the tooth, however these are not spearfishing loads and are for test purposes only. One way to lift the point of destruction higher was to square the flat faces up to each other so that the force is evenly spread which in turn meant that an over pushed sear lever for mechanism relatching could not be tolerated, over pushing being used in the heavy duty M3 Mechanism. Kitto developed the M5 two-stage locking derivative of the M3 for this very purpose, however anyone wishing to push these “MBT” trigger mechanisms to their limits will be handling a gun with scary band loads. One spearfishing identity, whom I will not name, put aside his vastly overpowered M Mechanism cannon when the creaking and groaning emanating from the laminated timber weapon had him in fear of his life and he quickly abandoned any plans to shoot one monster with another.

Note that heavy side plate trigger mechanisms are for ballasting purposes in extra heavy duty or "Main Battle Tank" underwater weapons.
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Last edited by popgun pete; 10-28-2018 at 07:19 PM. Reason: added photos of M5 "MBT" two-stage mech (Kitto's images)
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Old 10-28-2018, 07:02 PM   #126
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Re: Trigger Mechanism Design Rules

Originally Posted by popgun pete View Post
In the interests of Science I have ordered an Ermes-Sub Double Roller mech and plan to "put it to the test". Planet Multi Store, whom I have dealt with before, have a special price offer at the moment on this product.

The Ermes-Sub Double Roller mech arrived yesterday and now I can finally see what had been hidden from view in previous threads on this mechanism. These Ermes-Sub reverse trigger mechanisms are not “dry fire” mechanisms, although if you pull the trigger on an upright mechanism on its own then the sear lever falls due to its weight. More later once I figure out how to remove the pivot pins which appear to have peened over ends, no doubt to prevent them falling out, or being pushed out. The sear “tooth” roller is a bit smaller OD than I thought it would be, but the pivot pin spacing is good.

Last edited by popgun pete; 10-28-2018 at 07:21 PM.
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Old 11-25-2018, 07:17 PM   #127
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Re: Trigger Mechanism Design Rules

An old email which may be of interest here.

I spoke with Wally Gibbins many years ago and asked him about his
trigger mechanism design and the mechanisms that were contemporaneous
with it, both at the time and before. Wal actually documented it all
later in a personal letter to me which I later had published
posthumously by Wal thanks to Barry Andrewartha of IF&SN so that Wal
could speak directly to the “brotherhood” and in a sense, in his
farewell salutation, “sign off” for a last and final time. In the old
days they would have regarded an Omer “Cayman” as a childlike weapon
no better than a toy, being of a flimsy construction that would not
last a week, much less a season. Of course that would be judging it
by the plastic guns of the time, the feeble and simplistic
holidaymaker's guns from the Europeans that shot fork head tridents on
top of skinny shafts and were a low cost option to their more serious
weapons such as the legendary “Champion Arbalete” with its socket
head muzzle, preferably the version with four sockets. A gun was
expected to use either 5/8” or 3/4” solid bands of gum rubber and
either a 5/16” or 3/8” diameter shaft just in case any sharks had to
be seen off with a shot driven through them.

The square notch spear tail is a direct carry lover from the
single-piece trigger, as any significant angle on the tooth and the
mechanism shoots without you pulling the trigger. The angled sear
tooth used by the Europeans is a direct carry over from the pull down
sear, spring gun mechanism, as with a square cut tooth pulling the
trigger would otherwise drive the shaft back against the spring
loading/band pull. Once cam lock mechanisms were created they were
two state, i.e. either cocked or discharged, and why divers like them
is that they can be “dry fired” to check the latch and release action
on the spear without any band load. As timber guns of any reasonable
length (in excess of a metre) are going to have some depth to the
stock, the “real estate”already being there it makes sense to fill it
up with the mechanism. A sear box is not only held in with the
transverse pins, its forward edge presses hard on the stock, hence a
deep mechanism case transfers its load into the stock by butting
squarely into the pocket cut for it in the timber. You can see this
very clearly in the Riffe Metaltech as the sear case in its plastic
isolation cradle butts directly to the stock.

The reason why Wally Gibbins made his reverse mechanism, seen in the
“Sea Hornet” and “Biller” in somewhat economy versions, is that he
wanted that two state mechanism with a distinct “cock” and “release”,
in fact the spear could cock the mechanism with a “slight push on it
with one finger” was a familiar phrase used by Wal. I have used that
trigger mechanism, in its all metal case configuration, ever since I
started diving nearly fifty years ago, with the Undersee mechanism
being used in my long range cannons until I replaced the sear pin
“rivet” with something more substantial, just as Jay Riffe did with
his own version of the Undersee which is fully made from stainless
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Old 12-19-2018, 08:47 PM   #128
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Re: Trigger Mechanism Design Rules

Some history which I recovered from an old computer hard disk. Here is the model in clear plastic which Mori created that eventually became the Kitto M6 through to the M8 multi-lever trigger mechanism, now used for some years in the latest JBL timber (woody) spearguns. At the time Mori was working on a mechanism cassette/sear box housing and figuring out the auto-line release action in terms of which lever to drive it off.

When I first saw Mori's model I was concerned that it was a hooking mechanism and not a cam lock as the locking lever does not roll into the trigger, instead they are one and the same thing. However time has proven that it was not going to be a problem provided all the levers are fully engaged when locked.

At the time I was working on a four pivot pin, two stage mech, but thought the close set and "lean on each other" levers could be used in a four lever mech using the general shapes of Mori's levers. The parts ended up being too small and the demands on precision were great, so this "fourpin" mech never got beyond some plastic models to check it out, aided by the addition of “timing bumps” on the levers to “short circuit” the cocking or relatch action.
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