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Old 03-01-2012, 09:30 PM   #31
popgun pete
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Re: Trigger Mechanism Design Rules

Here is something that should make Jeff (Tin Man) happy, his mech from a while back subjected to "circle analysis". It follows the short in-long out arm length criteria on each lever for good gearing and is a hooking mech like the Kalohi mech made by Kitto (M6 through to M8).
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Old 03-01-2012, 09:43 PM   #32
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Re: Trigger Mechanism Design Rules

Funny that you posted that Pete! When you started this thread, the first thing I did was find my little prototype / model and look it over based on all you've shared.
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Old 03-01-2012, 10:31 PM   #33
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Re: Trigger Mechanism Design Rules

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Originally Posted by Tin Man View Post
Funny that you posted that Pete! When you started this thread, the first thing I did was find my little prototype / model and look it over based on all you've shared.
The "Force" must be with us, or great minds think alike. No doubt someone else will now chime in and say "fools seldom differ"! Anyway I had done your mech some time back, but never did it on the actual computer drawn graphic, so there you go.
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Old 03-03-2012, 11:45 PM   #34
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Re: Trigger Mechanism Design Rules

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Originally Posted by popgun pete View Post
That is pretty much the "Undersee" layout which started the progression to two-piece trigger, "cam lock" mechanisms. Riffe and Alexander are copies of it, as are many others. The sear tooth should be vertical, not tipped back as shown here. Also the trigger pivot pin is usually located higher up in the housing, that way the force from the sear lever tail can be aimed virtually right at the trigger pivot pin.
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Old 03-21-2012, 04:26 PM   #35
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Re: Trigger Mechanism Design Rules

The JBL M7 trigger mechanism "circle analysis". Note how the mechanism locks outside the green circle. The dark blue force line turns the trigger anti-clockwise as seen here, closing the mechanism. That force line needs to stay in front of the trigger pivot pin axis, or run right through it.
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Old 03-22-2012, 08:45 PM   #36
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Re: Trigger Mechanism Design Rules

This is the "Sea Hornet" mechanism devised by Australian spearfishing great Wally Gibbins. Having seen the mechanism created by Denny Wells (which became the world famous "Undersee" mechanism) and having built his own version of it, Wally then decided to try a reverse arrangement where the trigger was in front of the sear lever and not situated behind it. John Lawson's workshop facilities were being used for the development work and one outcome of this joint collaboration was the use of a single leaf spring to bias the two levers. The levers themselves had been designed to be very simple in shape as no curve matching was required on the sear lever to trigger interface. Instead all parts on the top arm of the trigger revolve forwards and downwards away from the sear lever's front tip so that there is no chance of the trigger's firing movement pushing the sear lever upwards and hence backwards against the band pull. If the top of the trigger's upper arm had extended slightly rearwards then its travel arc there would have had to have been curve matched to the sear lever as that additional section rotated upwards to reach "top dead centre". The length of the trigger arm above the trigger pivot pin is to reduce the degrees of travel arc when pulling the trigger to shoot the gun. The further out from a pivot you go then the less degrees of arc are required for the trigger to swing through in order to move a certain circumferential travel distance at the top. That aspect is what makes the "Sea Hornet" a tall mechanism as the trigger pivot pin is located towards the bottom of the sear case.
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Old 04-22-2012, 09:40 PM   #37
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Re: Trigger Mechanism Design Rules

In the "trigger mechanism design rules" I previously looked at the leverage reductions or "mechanism gearing" inherent in the lever arm lengths as various levers transferred the band load acting on the sear tooth down to the trigger, ideally reducing that force to near zero, but with enough force (actually a torque) left over to keep the trigger mechanism locked up. Another factor is sliding friction at the trigger to sear interface, or in some mechanisms the locking arm to intermediate lever interface, as that is where the loaded sliding faces move out of contact with each other to release the sear lever and thus the spear from the gun. By pulling the trigger you supply the force to move these sliding surfaces that are responsible for the locking condition. In most production trigger mechanisms these faces are preferentially smoothed or polished before the mechanism is assembled as friction there needs to be kept low, even though the force acting between them (due to the contact pressure) has been reduced by the gearing in the sear lever, or the sear lever in conjunction with the intermediate lever which both act as a combined or "folded" sear lever. Unfortunately if very big band loads are used over time then these sliding surfaces tend to roughen up due to galling or pitting and then the trigger pull exerted by the user has to overcome this extra friction as well as any reduced opposing force transferred from the band pull via the torque reduction system. Remote triggers of the swinging type usually add to the leverage applied to the true trigger in the mechanism at the rear of the gun on mid-handle guns, although in these situations the true trigger has effectively become the locking arm which is activated by a push rod (or pull rod in some guns) which is employed to connect it to the user operated trigger in the gun's grip handle.

In a "Sea Hornet" mechanism (and the near identical "AB Biller") the point where you pull on the trigger (below its pivot) is not much greater than the sear to trigger interface distance (above its pivot) in terms of the respective arm lengths to the trigger pivot pin, you can see this in the "circle analysis" diagram, the arms are on opposite sides of the trigger pivot pin and thus the trigger component has reduced leverage with respect to overcoming friction at the sliding interface. On the "Undersee" or "Riffe" type trigger mechanism where you pull on the trigger is on the same side of the trigger pivot pin as is the sear to trigger interface and as the former position is much further out than the latter, so this type of mechanism is better able to cope with the surfaces roughing up as it has greater leverage built into the trigger component. To overcome galling and provide a more resistive bearing surface both "Sea Hornet" and "AB Biller" now use different hardness materials in the sear and trigger levers (this improvement was actually developed and patented by Fred Biller in the USA). Some euroguns use plastic triggers as load bearing components in conjunction with a metal sear lever, so you don't want to overload them! Fortunately the muzzle design usually limits the bands that can be used on such guns.

Ideally you never overload your gun's trigger mechanism so that during extended service the mechanism doesn't accrue such damage at these important sliding surfaces, but over time it pays to periodically check them out. On a "Riffe" trigger mechanism you cannot knock the pivot pins out that hold the levers in, they are riveted instead, but it is a simple matter to remove the biasing spring and swing the levers out and look in at them from underneath the sear box once it is removed from the gun, then you can see the sliding surfaces very easily, including the sear tooth face.

Nothing lasts forever, so it pays to periodically check your spearguns out for accumulated wear and tear. Spearguns are made to be dismantled, they are not mysterious "black boxes" unless you treat them as such. Avoid buying guns which cannot be opened up, but make sure you use appropriate tools for the job, like quality screwdrivers (which have hardened steel tips) and needle nose pliers for removing springs and pins, although many can be manipulated by hand or unhooked or pushed out using awls or makeshift metal drifts such as small diameter aluminum rods (e.g. aluminum knitting needles after cutting off the knobs or heads).

Last edited by popgun pete; 04-22-2012 at 10:07 PM. Reason: added some refinements re torques
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Old 04-25-2012, 09:11 PM   #38
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Re: Trigger Mechanism Design Rules

Here is an "Ocean Rhino" trigger mechanism both cocked and fired, note the small angle that the sear lever has to transition through to release the shaft and conversely relatch the trigger mechanism during reloading. The sear tooth being located further forward from the sear pivot pin makes this small angular release movement possible.
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Last edited by popgun pete; 05-24-2012 at 07:38 PM. Reason: added a clearer circle analysis diagram
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Old 04-30-2012, 07:56 PM   #39
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Re: Trigger Mechanism Design Rules

How do the rules apply to the Picasso shot engine?

Its basically similar to the Undersee arrangement, but instead of having a hole in the sear, it has a slot. I imagine the sear slides during loading, and pulls forward to lock the spear. The trigger is not at all far below the axis of the spear, which makes this a convenient mech for a light gun.

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Old 05-02-2012, 02:10 AM   #40
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Re: Trigger Mechanism Design Rules

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Originally Posted by Ric.Fallu View Post
How do the rules apply to the Picasso shot engine?

Its basically similar to the Undersee arrangement, but instead of having a hole in the sear, it has a slot. I imagine the sear slides during loading, and pulls forward to lock the spear. The trigger is not at all far below the axis of the spear, which makes this a convenient mech for a light gun.

Ric
The trigger mechanisms with floating sear pin positions just relatch in a different sequence to the way that they shoot, so as you say they are like the "Undersee" type in terms of their leverage or gearing. They require two springs to work, one biases the trigger component and the other helps reset the sear lever. When these mechanisms shoot they oppose the sear lever biasing spring which is there to hold the sear lever tail down, not up, so they are momentary action mechanisms which are latched all the time, but only release when you pull the trigger and only with band pull on the spear. These mechanisms do not "dry fire" the spear.

"Beuchat" patented the sear pin moving in two curved slots on ether side of the cassette housing and Hughes Dessault (original "Sporasub") patented the stationary sear pin with a curved slot in the sear lever allowing it to move back and forth on the sear pin which pushes the sear tooth down when the spear tail is inserted. Hence the sear levers only have a sear tooth and have no backing projection like you have in an "Undersee" or a "Sea Hornet/Biller". If the springs fail to reset the sear tooth then the mechanisms can appear to be latched, but the sear pin has not completed its travel in the curved slot and may then shoot without warning as the sear tooth is not fully engaged in the spear tail notch. Everything needs to move freely in the mechanism for them to work properly and the springs need to push effectively on their lever arms. This forum has many threads where they have not, but mainly from the clones which departed from the original patents, probably from necessity in how they disposed their springs in the grip housing in slightly different arrangements.
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Old 05-11-2012, 08:39 PM   #41
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Re: Trigger Mechanism Design Rules

I thought that as I was pulling my JBL "Travel Magnum" apart I may as well do its "circle analysis". Note that most of the trigger mechanism gearing is in the trigger component and very little is in the sear lever. The green circle is very small on this mech because the pivot pins are too close together. Other than that the handle's alloy casting and levers are very well made. The trigger is biased by a large coil spring, the sear lever is biased by a two leg wire spring looped around the sear pivot pin. The pivot pins are large in diameter, so it is not a weak mechanism, but it is limited by its gearing.
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Old 05-12-2012, 06:41 PM   #42
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Re: Trigger Mechanism Design Rules

I guess I should explain what the limitation mentioned above is. The red straight lines on the previous diagram show the lever arm lengths with respect to torques as that is what the "circle analysis" diagram is all about, hence the trigger component has a tiny "in" and long "out" length which makes up for the not so large difference between the "in" and "out" lengths on the sear lever, so the trigger mechanism's gearing as a torque reducer is very good overall. However if the high contact pressure resulting from the short sear lever "tail" (the "out" length) chews up the sliding contact between the two levers then the friction between those surfaces goes up by a large amount. Then the trigger component leverage to fight this friction is the horizontal blue line from the trigger pivot pin (see new diagram attached) as compared with the distance down from the trigger pivot pin where your finger pulls on the trigger. The trigger component leverage is still good, but not as good as it was from looking at the "torque" length lines in red on the first diagram.

Another aspect is the trigger mechanism is not "curve matched", although it is very close to it as it does not push the sear lever backwards against the band pull when you pull the trigger. To be "curve matched" the sliding contact between sear lever and trigger should be on the grey circle shown around the trigger pivot pin. The more contact area you have then the lower the contact pressure, however the stamped out mechanism levers are not dead square on their edges, they have a slight taper from side to side and that means that rather than contact being fully from edge to edge on the levers it gets concentrated on one side. With enough band pull that virtually point loading tears up the sliding edges. A fix would be to curve match the sliding contacting faces and dress the leading edges of the levers so that they are pressed dead flat against each other, however you would need to start with slightly larger parts to have the material to grind away without changing the geometry of how the levers sit when latched.

Jack Prodanovich cut his speargun's trigger mechanism levers out with grinding or abrasive cutting wheels to avoid those tapered edges on the levers which can reduce the contact area where they lean on each other. Possibly if one lever was stamped out one way and the other in the opposite direction then the tapers might tend to cancel out by laying flat against each other as, and if, the two tapers matched, but it would be better if they were 90 degree cuts or grinds with respect to the large flat sides of the levers. The longer the sear lever tail is then the situation becomes less critical, for example doubling the length of the tail halves the contact pressure between the levers. That is why trigger mechanisms have a wide spacing between the pivot pins, unless you are a genius like Jack Prodanovich and use vector torque splitting to drop the sear lever to trigger contact pressure and virtually hand make each of your guns, but then wear will eventually cause the mechanism to drift away from the near "balanced sear" condition, so it is not a permanent solution unless the levers are made from extremely hard stuff and are sufficiently lubricated.
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Last edited by popgun pete; 05-13-2012 at 10:30 PM. Reason: mechanisms plural
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Old 05-13-2012, 01:19 AM   #43
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Re: Trigger Mechanism Design Rules

The spacing between the sear pin and the trigger pin in the "JBL" housing is 1.8 cm (about 23/32"). On a "Riffe" trigger mechanism this same spacing is 3.8 cm and this difference is also reflected in the sear pin axis to sear lever tail end lengths; 1.1 cm for the "JBL" and 3.3 cm for the "Riffe" mechanism. Hence for all other things being equal (which they may not actually be) the contact pressure between the sear lever and trigger will be a third in a "Riffe" of that in a "JBL" for the same band pull. That is a pretty big difference!

It is interesting to note that some changes have been made to the levers since my gun was manufactured judging by the images on the JBL spare parts page. Check the comparisons on these photos.
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Last edited by popgun pete; 05-23-2012 at 01:27 AM. Reason: more info
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Old 05-24-2012, 08:20 PM   #44
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Re: Trigger Mechanism Design Rules

Another aspect of the JBL trigger mechanism is the rather unique lever arrangement when the gun is discharged. The sear lever and trigger then press against each other to create a second cam lock condition under the action of the trigger biasing spring. This lock is used to hold the trigger in a slightly depressed state so that the safety mechanism cannot be applied. If you try then the safety lever will only move about half way and even then the mechanism will still relatch because the rear of the trigger will push the safety lever out of the way. It is all rather ingenious and has been a design consideration from the start as the levers' geometrical layout in the second cam lock is no accident (the purple and black rotational arrows cancel each other out). The attached photo demonstrates this second cam lock which can be easily released by inserting the shaft tail in the sear box (as indicated by the blue arrow). High pressure contact sliding surfaces are marked in yellow and the green curve marks the resetting cam that pushes the trigger nose down during the relatch. So there is a lot more to this trigger mechanism than you might initially think!
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Old 02-20-2013, 06:23 PM   #45
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Re: Trigger Mechanism Design Rules

Another trigger mechanism type which I did not mention before is the "frame lock" whereby the trigger is blocked by leaning on the frame or cassette housing of the gun. The sear lever does not reach an interlocked state with the trigger as it does in a "cam lock" trigger mechanism, instead the sear lever pushes on the trigger which revolves until it binds on the supporting frame. The trigger then stops turning and that in turn halts the sear lever, so you now have a "lock". Some trigger mechanisms that were intended to be "cam lock" trigger mechanisms actually only locked up when the trigger fouled on the frame of the gun. An example of a deliberate "frame lock" mechanism is the "Balco Sub" trigger mechanism used in their "Thunder" and "Arrow" spearguns. The sear lever is a brass gear wheel with six teeth, any one of the teeth can act as the sear tooth while another one of the teeth presses on the trigger where a stubby forward projection close to the trigger pivot pin meshes with this gear tooth on one side of the tooth. For this arrangement to "cam lock" the trigger would have to swing through a very large angle traversing the entire trigger finger guard space to move from "lock" to "shoot", so to shorten this travel distance the trigger binds on the frame of the housing instead with a slight bump on the front edge of the trigger (just above where your finger pulls on it) leaning on the window for the trigger provided in the alloy grip handle casting. This particular arrangement has no gearing reduction in the sear lever, the force from the spear on the sear tooth is exactly the same as the force applied by the sear lever tail to the trigger as they are of the exact same length, both being gear wheel teeth.

It is possible that some JBL tube guns are actually "frame lock" guns, depending on the grind of the flat of the trigger nose, as if the trigger can revolve forwards far enough at the bottom then the attached photo shows the true "cam lock". Note the gap now behind the trigger!

I have a "Balco Sub" that I can photograph, I just need to pull it apart.
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Last edited by popgun pete; 02-20-2013 at 09:46 PM. Reason: adding "Balco Sub" handle photos
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