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All About Guns What's your weapon of choice, and why? Discuss the beloved speargun here! |
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01-09-2022, 09:18 PM | #196 |
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Re: Trigger Mechanism Design Rules
I have been asked for a full diagram of the Ermes Sub Double Roller mech so here is an approximation of it. The important part of this mechanism is the shape of the top of the trigger which has a cup shape for the sear lever nose roller to press against, but the nose roller cannot move past it. However pulling the trigger revolves this cup away from the nose roller which provides a clearance and the sear lever can then fall. Either gravity during dry firing or band power pushes the sear lever down as it has no biasing spring. The trigger has a biasing spring of the torsion type as does the line release lever (not shown).
The roller tooth has a pin driven through it to keep it captive in the side slots or windows in the cassette walls, otherwise it would fall out of the mechanism. The roller tooth moves the force from the spear tail down to the cup cut-out in the sear lever arm so that it effectively is the tooth holding the spear tail, the roller just being an intermediary element. The roller tooth does not necessarily sit snugly in the cup, any clearance to the sear box roof will roll the roller forwards causing it to wedge the spear tail between the sear lever arm cut-out and the sear box roof. Hence there is some accommodation for different diameter spears and their tails. During relatching the nose roller acts on the trigger which has a curved ramp below its cupped retention step so that the sear lever revolving upwards can push the trigger out of the way and allow the nose roller to sit once again in the latched position. |
01-10-2022, 12:19 AM | #197 |
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Re: Trigger Mechanism Design Rules
This second diagram shows how the "mobile" roller tooth can accommodate different diameter spears by riding up inside its cradle or cut-out in the sear lever arm to jam spear tails against the sear box roof (or ceiling). The curved euro spear tail notch is what makes this work as it drags the roller tooth forwards and up if there is any ceiling gap. The curved rear of the spear tail notch creates a force component that pushes the sear lever down as was shown on an earlier post once you finally pull the trigger.
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01-11-2022, 07:05 PM | #198 |
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Re: Trigger Mechanism Design Rules
A few years back Sea Hornet Australia were developing a eurogun style speargun which was a first for them as previously their range consisted of cocking stock guns. Some of these guns had a very short cocking stock by butting the rear loading pad tight up against the rear grip handle, but they were still the same layout of parts.
The prototype eurogun was sent out for trials but very little was heard of it and unfortunately the company went into closedown and ceased operations, so that was the end of that, well for now that is as the company's tooling is all in storage. The only freely available info was that the gun used an upside down trigger mechanism with the sear tooth dropping into a spear tail notch from the top rather than from underneath. By way of someone stumbling across a diagram we now know what it was going to look like. The sear lever is a big yoke with a ramp on the lower arm that acts as a backing projection when you load the spear tail into the gun. This resets the sear lever revolving it down for its square cut tooth to engage the shaft notch. With the bands applied the shaft tail drags forwards out of the back of the yoke so that it can now revolve when you pull the trigger. The retention step is on the front of the sear lever yoke's lower arm and the trigger’s catch element drops down a window cut in the front of the lower yoke arm's tip, just rearwards of the retention step when you pull the trigger. Certainly a rather different arrangement, but the sear lever would not be so easy to make, especially with that hole in it that creates a window whose "frame" you would not want to bend, otherwise big problems! Last edited by popgun pete; 01-11-2022 at 08:16 PM. Reason: adding the advert page |
01-11-2022, 11:25 PM | #199 |
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Re: Trigger Mechanism Design Rules
Note that there does not appear to be any cam locking of the levers here, the mechanism seems to rely on the force at the sear lever's lower tip, or retention step, not being great enough to roll the trigger when pressing on the "locking" tip that extends out behind the trigger when the gun is cocked ready to shoot. Any problem with the trigger biasing spring and it would appear that the gun would shoot without you pulling the trigger! This also breaks one of the trigger mechanism rules that the trigger should revolve in the opposite direction to that which the mechanism under band pressure is trying to urge it when you come to shoot the gun.
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02-24-2022, 09:38 PM | #200 |
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Re: Trigger Mechanism Design Rules
While discussing the above mechanism with someone else it occurred to me that the force on the sear tooth with the bands cocked would close the sear lever rather than open it up as in essence we have a single-piece trigger sitting upside down if you just consider the top part of the sear lever. Now if the line of contact of the band force runs above the sear pivot pin then the torque thus created will hold the spear tail by the sear tooth pressing down on it. The only way this set-up is going to shoot is if the tooth rocks at a slight angle emulating a worn sear tooth and creates a component of band force that runs under the pivot pin which then provides a net torque which will open the sear lever, or the force runs right through the sear lever pivot pin creating zero torque and acts as a hook on which the spear can dangle! Either way it seems not a very promising design as you don't want the spear to hang up when you pull the trigger!
The horizontal spring sitting at the rear may give the sear lever a push, but using springs to make the gun shoot is also not a good idea as springs lose their power over time. Last edited by popgun pete; 02-24-2022 at 09:46 PM. |
01-06-2023, 04:50 PM | #201 |
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Re: Trigger Mechanism Design Rules
Trigger mechanisms can have a high pull if pulling the trigger drives the mechanism backwards against the band pull. Ideally when you pull the trigger it revolves and the sear lever just sits there without moving at all as the arc that the trigger contact sweeps through does not lift the sear lever tail which in a reverse trigger mechanism points forwards. Even if the parts were designed correctly a tiny error in the pivot pin spacing can result in the levers trying to push each other instead of sliding past each other. A roller on the sear lever tail still needs to obey this sliding rather than pushing aspect which it may on paper but not in practice. Wide levers in terms of thickness should provide a greater bearing surface, but they won’t if the surfaces are not flat to each other and that includes any mould parting lines which create a mini hill. Other problems can occur when the pivot pins are not parallel and may be slightly tilted in the housing frame, it does not take much when the band loads are high to expose shortcomings in the trigger mechanism in terms of pull required to fire the gun.
Jack Prodanovich, one of the great contributors to the sport of spearfishing and heavy equipment design for shooting big fish rather than tiddlers soon recognised the importance of curve matching in his trigger designs. He had been making guns when the sport was just beginning and his mechanism were built using grinding tools and jigs to get around meshing problems. That meant his two piece trigger did not drive the mechanism backwards because when cutting the tripper profile the trigger piece revolved on what was the trigger pivot the holes being cut first and all the shapes generated with respect to the holes. He knew that even the best designed forms were no good if the holes were drilled slightly out of position or they did not match the pin spacing in the housing in terms of lever separation in the housing. One gun that was notorious for pushing the trigger mechanism backwards was the Sampson gun, a gun for big hitters that was based on an up scaled and redesigned French Arbalete on steroids. The French gun also pushed the spear back slightly against the band pull, but mitigated it with a curved sear tooth profile engaging a matched spear tail notch whereas the Sampson had a V shaped tooth and spear tail notch. The curved notch “euro tail” is still with us today. Last edited by popgun pete; 01-06-2023 at 05:06 PM. Reason: typo |
07-22-2023, 06:30 PM | #202 |
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Re: Trigger Mechanism Design Rules
Interesting air rifle triggers that show the multi-lever force reduction principle. Similar to Kitto's M series that fit in the back end of a ballasted, enclosed barrel tree trunk.
https://community.fortunecity.ws/oly...b20_album.html While crossbows had similar requirements to spearguns for their trigger mechanisms I never realised that air rifles used such designs. Too tall for a speargun in terms of Arbalete style weapons, but shows a convergence of thinking. I know nothing of air rifles except that when as a kid one of my friend's owned one and we had some shots using its tiny metal pellets and ended up putting a hole in a coiled up garden hose hanging near the rear fence. That was the first and last time I touched an air rifle! Apparently these break action cocking weapons compress a big internal coil spring that is already under some pre-tension in the gun and when released it drives an air pump that blasts the captive pellet out of the gun barrel. Just reading up on these weapons this fancy looking trigger has a pre-movement to first load up the levers and then a final push to activate them. Due to the considerable energy stored in a speargun designed to shoot a big length of steel shaft compared to a tiny metal pellet in the far less dense medium of air compared to water I don’t think we need that in a speargun. Hair triggers are dangerous and put too much load on the lever release edges consequently damaging them over time. Last edited by popgun pete; 07-22-2023 at 07:54 PM. Reason: more info |
08-20-2023, 05:00 PM | #203 |
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Re: Trigger Mechanism Design Rules
Thanks to Mel Brown of the AUF, who runs their spearfishing museum, we now have a parts diagram of the original Sea Hornet trigger mechanism before it went into production. These were made at John Lawson’s workshop when he and Wally Gibbins were trying to do the same thing in reverse as was accomplished with the Undersee cam lock trigger mechanism.
The production Sea Hornet trigger mechanism was brazed and spot welded together, but here we can see the parts were originally mechanically assembled and the sear box is cut back on the top. In those early days the line slide had not been the first approach to tethering a spear with a shooting line, instead the line was tied behind the spear tip. However Wally Gibbins put a lateral lug on his spear tails to trail the shooting line from and the accommodating slots in the mechanism housing are clearly seen as in the matching one in the muzzle to let the spear tail out. |
10-11-2023, 07:45 PM | #204 |
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Re: Trigger Mechanism Design Rules
The Voit-Swimaster gun, which then became the JBL, needs a better cam lock trigger mechanism. Re-engineering the handle innards we obtain a trigger mechanism using the Aquacraft basic lever shapes, the only drawback is the existing safety lever may no longer work, but should be easy enough to change. The line release lever will still work as before. This mechanism uses the same ideas suggested for the P3 Prodanovich gun which employs a buried trigger which in turn is pressed by the usual external trigger. This allows the trigger mechanism pivot pin spacing to be lengthened by utilizing more of the real estate available in the cast alloy grip handle.
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10-11-2023, 11:55 PM | #205 |
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Re: Trigger Mechanism Design Rules
And after a few more lever shape adjustments.
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10-14-2023, 05:09 PM | #206 | |
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Re: Trigger Mechanism Design Rules
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I have been guilty of this myself until the realization that given the lengthy reloading time one begins to be reluctant to pull the trigger as a parade of ever bigger fish pass by the muzzle of your cannon waiting for the right target. Then you swim back in never having fired a shot and the cannon goes in the storage cupboard making way for more user friendly weapons. Some of the bigger guns needed two handles to swing for course changes, not target tracking, and a cocking stock that ideally could be folded or removed for the hunt, but you found them a chore to carry to the dive site as they had to be ballasted when blasting shafts of nine millimeters diameter, or even ten. Last edited by popgun pete; 10-14-2023 at 09:00 PM. Reason: added John Warrens Supergun photo |
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10-25-2023, 10:54 PM | #207 |
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Re: Trigger Mechanism Design Rules
Another trigger mechanism brought to my attention, the Torelli K handle which appears to be a derivative of the latest Rob Allen triggers, but has a rather unique plastic trigger combined with a lower metal trigger finger hook. Don't know anything else about it. Rob Torelli is a well-known Australian spearfisherman and spearfishing champion.
May have been inspired by the previous triggers of an earlier model which busted. Last edited by popgun pete; 11-03-2023 at 07:44 PM. Reason: spring left out on RA mech, added another photo |
10-26-2023, 01:50 PM | #208 |
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Re: Trigger Mechanism Design Rules
Note that the above two trigger mechanisms don't have a biasing spring on the sear lever, they only have one spring acting on the trigger. That means for keeping the sear lever rolled forwards prior to relatching the shaft tail they rely on gravity. As you are unlikely to be reloading your gun while upside down this works OK, however these mechanisms will not dry fire. However if you reset the mechanism by pushing the sear tooth back with a thin metal rod then pulling the trigger will roll the sear lever as with no spear to push gravity will do the job.
Plastic triggers are most likely broken when strong fingers try pulling the trigger with the safety still engaged. Some trigger mechanisms with top mounted safety slide button safeties had a habit of walking around on their biasing springs and applying themselves if they were not pushed fully back so that their friction end tabs locked them back in the window that they slide back and forth in. |
10-26-2023, 03:01 PM | #209 | |
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Re: Trigger Mechanism Design Rules
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The roof might get a little tight sometimes but that's mainly because of how the handle sits on the tube in relation to the track. |
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10-30-2023, 11:37 PM | #210 |
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Re: Trigger Mechanism Design Rules
MVD now has a double roller trigger mechanism, but it does not have a floating sear lever tooth, instead the roller tooth is mounted on the sear lever arm. The advantage of a roller here is a different surface can be presented each time and spreads out the effects of any wear, provided that the tooth keeps turning after every shot.
Last edited by popgun pete; 10-31-2023 at 12:01 AM. |
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