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Old 11-18-2013, 10:57 PM   #61
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Re: Trigger Mechanism Design Rules

spearq8 suggested I take a look at the Abellan trigger, so here it is. Not sure where the sear tooth is with respect to its height in the sear case, so I just made a guess, the horizontal band pull (red) line may be lower down than shown here. Rivets stop the mechanism being pulled apart, so this will have to do. Plastic load bearing trigger no doubt made of the right stuff as there was some discussion about what was needed on the web-site.
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Old 11-18-2013, 11:54 PM   #62
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Re: Trigger Mechanism Design Rules

Quote:
Originally Posted by popgun pete View Post
spearq8 suggested I take a look at the Abellan trigger, so here it is. Not sure where the sear tooth is with respect to its height in the sear case, so I just made a guess, the horizontal band pull (red) line may be lower down than shown here. Rivets stop the mechanism being pulled apart, so this will have to do. Plastic load bearing trigger no doubt made of the right stuff as there was some discussion about what was needed on the web-site.
I haven't read the thread, do you mind explaining what you did there?
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Old 11-19-2013, 04:06 PM   #63
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Re: Trigger Mechanism Design Rules

Well the thread is here to be read, but it is about defining the travel arcs of the sear lever tip contact where it presses on the trigger and that of the sliding surface on the trigger itself as it is revolved under load by you pulling the trigger. Doing that you have to work against friction with the leverage advantage of the trigger itself and any torque coming through the trigger from the band load, unless the torque has been reduced to near zero. A torque is a force at a right angle to the radial distance out from the pivot pin in the direction of rotation if the component was free to move. In cam lock trigger mechanisms to minimize torque going into the trigger, which you will have to pull against, the force applied by the sear lever tip is made low by the gearing or leverage reduction in the sear lever itself and by passing that force as close as possible to the trigger pivot pin which makes the torque going into the trigger close to zero. The force from the sear lever tip still creates pressure and hence friction on the trigger sliding surface, but next to no torque . To achieve that the contact between sear lever tip and trigger sliding surface has to lie somewhere on the light green circle, which on these shallow reverse trigger mechanisms you cannot do, so the force needs to be lowered by having a long sear lever arm and a sear tooth that passes the band pull close to the sear pivot pin in terms of the offset of the line of action of that force to the sear pivot pin axis. That is what these "circle analysis" diagrams try to depict, ideally you need to see the levers in their entirety, not just sections of them.

As the trigger is rotated by any non-zero torque it needs to either lock on the sear lever (cam lock) or bind on the frame of the sear box or sear case so that the trigger can only swing so far forwards at the bottom before it is halted by the rigid contact.

Last edited by popgun pete; 11-29-2013 at 04:19 PM.
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Old 03-21-2014, 12:10 AM   #64
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Re: Trigger Mechanism Design Rules

For interest here is a reverse angle tooth, single-piece trigger, it is obsolete these days, but was used in some early band guns, particularly those without a sear box "lid", i.e. they have a completely open top with the spear tail resting on the gun's top deck. It was used in early tail-pusher spearguns without any sear box as such. A diagram for it is attached.

To be on the "safe side" often a strong biasing spring was used, which meant that extra fingers were needed on the longer than usual trigger. The long forward arm mounting the sear tooth requires less degrees of rotation to drop sufficiently to release the spear tail notch. The tooth angle aims the largest vector component through the sear pivot pin to eliminate that component from the torque loading on the trigger resulting from the band pull.

Also used in some weaker crossbows, the diagram shows why you need to be careful with it, as if the spear tail lifts up off the deck then both force components will turn the trigger to shoot, maybe more than the biasing spring can oppose!
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Old 03-22-2014, 07:33 AM   #65
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Smile Re: Trigger Mechanism Design Rules

Thankyou Pete for keeping this thread going, I really love it. Nice single sear design btw, understand most of it thanks to your diagram.

All hail PopgunPete, master of the Trigger Mechanism Design Rules thread
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Old 03-22-2014, 06:17 PM   #66
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Re: Trigger Mechanism Design Rules

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Originally Posted by lordyaussie View Post
Thankyou Pete for keeping this thread going, I really love it. Nice single sear design btw, understand most of it thanks to your diagram.

All hail PopgunPete, master of the Trigger Mechanism Design Rules thread
Thanks, but I am only documenting the work of the great pioneers who perfected these trigger mechanisms through long trial and error. A lot of early spearguns misfired as soon as they were banded up, so the safety mechanism often ended up being the real trigger, if the gun had one! Not too many trained engineers were working on spearguns in the early days, it was all home workshop tinkering and seeking inspiration from anything with a mechanical catch on it. Many accidents were prevented by weak band loads being unable to roll the poorly held sear levers, but as band loads went up all that had to change as it was soon realized that mechanism friction was all that was holding the spears back in many guns. The big change was when the "cam lock" two-piece trigger mechanisms arrived on the scene, all the loads were then held on and by the pivot pins that could not be pushed apart in the sear box housings provided that the sear boxes were strong enough, that includes their sidewall thicknesses as well as the sear box roof. Square cut sear teeth could hold a spear tail without a sear box roof, but any forward leaning sear tooth or spear tail notch angle and you had a "stump jumper" on your hands, so most guns got a sear box roof, although the Florida Reef Rifles just used a short metal cap end to hold the rear end of the spear tail down as they used reverse angle sear teeth (with a very substantial safety bar swinging up and in behind the trigger). When the spear passes over the top of the trigger (NB. not a remote trigger) you cannot put the sear lever pivot pin behind the spear, it has to go underneath if you are using a single-piece trigger.
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Old 03-23-2014, 01:25 AM   #67
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Re: Trigger Mechanism Design Rules

An interesting trigger is Innovation by Ermessub. The shaft must be modified a little, but it connects the bands directly to the trigger allowing for more band stretch. Not sure how it adheres to normal trigger designs but pretty funky I think!

http://www.ermes-sub.net/innovation.html
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Old 03-23-2014, 06:12 AM   #68
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Re: Trigger Mechanism Design Rules

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Originally Posted by spearq8 View Post
An interesting trigger is Innovation by Ermessub. The shaft must be modified a little, but it connects the bands directly to the trigger allowing for more band stretch. Not sure how it adheres to normal trigger designs but pretty funky I think!

http://www.ermes-sub.net/innovation.html
I remember this type of trigger mechanism from the old Arbalegno site, same ones judging by the ERMES-SUB logo. This mechanism is for a tail pusher speargun, it holds the wishbone rather than the spear with the twin sear teeth, if we can call them that. Crossbows use the same method, the bowstring is held and not the shaft/bolt which fits in later after first cocking the weapon. You have to relatch the mechanism by hand, that is why there is a pull lever on top. Not sure if this is a good idea as the bands stabilize the shaft on the cocked gun when they pull on shaft tabs or wishbone slots, i.e. they clamp the shaft down onto the guide track, so if you get rolled or tumbled the shaft stays in the gun. Admittedly that is a rarity unless you swim around surge washed rocks and find yourself in the world of foam and bubbles when a comber rolls through every now and then (been there, done that). Otherwise about the same leverage applies, although sear lever gearing may be worse (high tooth to sear pivot pin height, short sear lever tail length) and the wishbone slides up the ramp of the rotating teeth as they descend when the sear lever rolls forwards. A more complicated way of making something which is usually simple, but each to his own. Pneumatic guns are tail pushers, but the shaft there is in a totally enclosed track, so it cannot depart from the axial drive line whereas it can on a band gun, so an axial tail drive is not necessarily an advantage here.

Interesting mech and looks well made with attention to detail and finish.
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Old 04-10-2014, 01:20 AM   #69
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Re: Trigger Mechanism Design Rules

A summary of sorts of reverse trigger mechanisms and the arrangements required for them to lock.
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Old 04-10-2014, 05:24 PM   #70
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Re: Trigger Mechanism Design Rules

The "reverse mechanism" is not new, the "Sea Hornet" mech was around since 1967 and there have been some earlier variations. The reason that the much shallower reverse mech versions are around these days is that the levers are precision cut, whereas the "Sea Hornet/Biller" levers are simply stamped out. Cost of production determined the "mass market" designs in the past, guns had to be both economic to make and sell at a good price which was competitive and still profitable for the companies making them. These new mechanisms are much more expensive to make, so maybe that is why they are coming from Greece. I would think that they are an order of magnitude more costly to produce, when the previous wisdom had been "quality fit for the purpose", i.e. if the mechanism did the job then there was no need to go to more "extreme" versions.
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Old 04-11-2014, 03:46 AM   #71
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Re: Trigger Mechanism Design Rules

IMPO, no matter how you slice it…the main disadvantage of the Reverse trigger mech is in its release action.
During the initial stage of trigger pull, the trigger actually elevates the tip of the sear momentarily (opposite to the direction where the sear is to rotate) before the sear is completely disengaged from the trigger….increasing the centrifugal force between sear & trigger thus increasing the initial force (produced by the bands) required to pull the trigger.
This is the exact opposite to what happens during trigger pull of regular mechs where the sear is gradually steered towards its normal direction before full disengagement.
This is one of the main reason Reverse mechs are more suitable for lower powered guns.
While fiddling around with the concept of “Roller” mechs…I’ve been testing the roller action on the Reverse mechs and the results are encouraging.
It’s nothing new…..a couple of European brands have already used the roller action with their reverse mechs but due to design there is a limitation of surface contact between sear & trigger which only slightly improves trigger pull.
I’ve taken this concept 1 step forward and increased the contact surface to almost 1.75 that of most brands and the difference now is clear…the roller action has a much smoother trigger pull at higher loads.
Problem is its more expensive to produce than conventional triggers….and design could be a bit more demanding….but then again you get a very crisp trigger pull which could contribute to better accuracy at higher loads.
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Old 04-11-2014, 08:02 AM   #72
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Re: Trigger Mechanism Design Rules

On a reverse mechanism the reason that the sear lever tip elevates is if the curve matching on the levers is slightly out, or the pin locations in the housing do not reflect the geometry of the levers. This results in a situation described as "pushing the mechanism backwards" against the band pull. One of the reasons the "Sea Hornet" mechanism was a success is it never used curve matching at all, but it made for a deeper mechanism housing to accommodate the travel arc of the sear lever tip as it rolled through the angle required to lower the sear tooth and let the spear tail notch escape. I discussed this aspect with its inventor, the late Wally Gibbins, many years ago. If you "flatten" a reverse mech and make it much shallower then the sear lever has to avoid running into the trigger pivot pin and the metal around the trigger, so the lever's forward arm has to be shorter than the pivot pin spacing. That means the lever tip cannot intersect with the "green circle", so the force on the tip cannot be directed at the trigger pivot pin and will therefore transit a non-zero torque onto the trigger created by the band pull. To lower that torque effect the leverage in the sear lever is made much larger, which lowers the force applied by the lever's tip and that requires a long forward arm and therefore an even greater pivot pin spacing which makes the trigger mechanism housing shallow, but relatively long. This is all shown in the diagrams if you study them, note the orange line on the bottom row, middle diagram in the summary diagram above.

There is no centrifugal force involved, it is simply having to drive the sear tooth against the band pull by pushing the spear backwards, even if only fractionally, by lifting the sear lever arm when it should remain stationary. Conventional trigger mechanisms are less susceptible as the curve matching is only required in the very short trigger retention notch that the sear lever tail engages to lock into the trigger. If that retention notch is not curve matched then pulling the trigger can force the sear lever tail down and move the sear tooth backwards against the band pull, so you get exactly the same problem.

Roller topped triggers or roller-nosed sear levers tend to be used in "frame lock" mechanisms, there is no double contact at the lever intersection that creates the lock in a "cam lock" mechanism. An example where there is a double contact on a roller is the Bluetec "Raptor" that I last showed , but the retention step is very small, almost too small, where the two levers interact, but the levers are wide and so is the roller. If the roller axle bends, or the axle mountings bend, then the geometry of the mechanism changes in mechanisms using rollers and can create problems with the lever travel. The roller pins are usually much smaller than the trigger mechanism pins, they don't see the same loadings, but they can be damaged.

However I must say your roller axles seem quite robust, and they are tubular as well.

Last edited by popgun pete; 04-11-2014 at 08:14 AM.
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Old 04-11-2014, 10:03 AM   #73
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Re: Trigger Mechanism Design Rules

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Roller topped triggers or roller-nosed sear levers tend to be used in "frame lock" mechanisms, there is no double contact at the lever intersection that creates the lock in a "cam lock" mechanism. An example where there is a double contact on a roller is the Bluetec "Raptor" that I last showed , but the retention step is very small, almost too small, where the two levers interact, but the levers are wide and so is the roller. If the roller axle bends, or the axle mountings bend, then the geometry of the mechanism changes in mechanisms using rollers and can create problems with the lever travel. The roller pins are usually much smaller than the trigger mechanism pins, they don't see the same loadings, but they can be damaged.

However I must say your roller axles seem quite robust, and they are tubular as well.
Roller pins used for the Nile Tec Reverse or regular mechs are 4mm in diameter...same pin diameter used for the sear & trigger (trigger mechanism pins)....which is not the case in all Euro roller mechs.
The contact surface is also 4mm so pressure is distributed more evenly along that surface. Basically due to the fact I use 8 mm sear & trigger giving more leverage to a more robust design.

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Old 04-11-2014, 03:16 PM   #74
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Re: Trigger Mechanism Design Rules

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Roller pins used for the Nile Tec Reverse or regular mechs are 4mm in diameter...same pin diameter used for the sear & trigger (trigger mechanism pins)....which is not the case in all Euro roller mechs.
The contact surface is also 4mm so pressure is distributed more evenly along that surface. Basically due to the fact I use 8 mm sear & trigger giving more leverage to a more robust design.

Ihab
I think for a period the "bean counters" gained control of the product line in some companies, hence we got plastic load-bearing triggers and tiny pivot pins. A case of the minimum quality needed for the purpose. It might be asked just what that purpose was; maybe it was to make a better profit and a slightly reduced life span gun which needed replacing more frequently, but not so soon that the product was rejected by the market. Fortunately competition, from products such as your own, has enforced a return to quality and durability in spearguns (well some of them anyway, of course some never departed from the high standards that they have always maintained).
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Old 04-11-2014, 09:43 PM   #75
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Re: Trigger Mechanism Design Rules

It's got to be an improvement on the last wide throat reverse mechs you had Ihab, I needed two hands to pull the trigger with 1 band loaded, and that was out of 4 mechanisms.

I use meandros mechanisms now and they are smoother than butter even when loaded up.
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