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02-01-2017, 09:05 PM | #31 | |
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Re: Roller trigger thought
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02-01-2017, 09:11 PM | #32 | |
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Re: Roller trigger thought
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02-01-2017, 11:15 PM | #33 | |
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Re: Roller trigger thought
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Galling is caused by high contact pressure that microwelds the metal, you do not cause galling with sand. The way to lower contact pressure is to widen the contact area and move the mechanism quickly past the edge of the step as it releases. You do not want the trigger teetering on the edge of release as it damages the surfaces when balanced on the edges. If the surface is marked then contact pressure goes up at the high points created as you lose the width of the contact until it beds in again. The use of harder sear levers and softer triggers has been used to overcome galling, e.g. the Biller reverse mechanism, but a wider set of levers would also have helped. Although I have never found one the old "Sea Hornet" all metal trigger mechanism came in a thicker lever version for 3/4" bands, my own examples are for 5/8" bands with a maximum of two bands. Sand between the sides of the levers and the inner cassette wall is a problem when trying to relatch as the swinging levers bind in the housing. None of this hypothetical as I have speared at times in a soup of suspended sand and broken vegetation too soon after a storm and have had problems, but not very often as guns have been designed with these situations in mind years ago, however some past lessons have been forgotten as the "old guard" has now passed on. I note that Kitto's M8 has generous side clearances in the sear box to avoid sand jamming on the sides of the levers, the cassette itself having very thick walls which are unlikely to "spring". Last edited by popgun pete; 02-11-2017 at 02:33 AM. |
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02-02-2017, 12:58 AM | #34 | |
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Re: Roller trigger thought
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02-02-2017, 02:31 AM | #35 |
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Re: Roller trigger thought
The Ermesub back roller trigger does not use a sliding bar or sled. The roller just rolls down and has a pin that allows the roller to fall a certain distance via slots in the housing. It is completely different ... to my eyes at least. You can actually just remove the roller sear and install a normal friction sear on the same housing by changing two parts ... they are interchangeable.
I think the sand test where you fill the housing with sand is rather extreme and not necessary. I mean if you have sand in your mech you should try to rinse out the sand before using it. But if the sand particles did stick to the roller ... maybe that roller needs to change. Not sure what the diameter of the roller is but it could make a ton of those rollers cut from a single round rod made of 17-4 PH. As for light trigger pull ... you can easily adjust a trigger pull and make it heavier by changing the spring. But I think the point there was to show that the trigger pull was not affected even when it was loaded at high loads. A lot of trigger pulls will get progressively heavier as you start high loading the sears. |
02-02-2017, 04:43 AM | #36 |
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Re: Roller trigger thought
The sand test is worth doing as now you know that the mechanism does not seem to have sustained any crippling failure and will keep on working. What you need to do is mount it up in a gun and put it out into field testing. Hand made prototypes tend to behave themselves, but production models can have problems introduced by not so exacting standards in their construction. But that is further down the track.
I know of a new eurogun trigger mechanism out for field testing over the past year, but the outcome is unknown as the guys who have the guns are not talking, so we have to wait and see. Its existence was hinted at in a spearfishing magazine last year, but no details were given except for a not very illuminating description and a photo of the gun as projected (see image now added). I think that is the next step to take, but put a blocking safety on the mechanism, just in case, if only for the trial. Last edited by popgun pete; 02-05-2017 at 06:31 PM. Reason: added photo of new "eurogun" under test |
02-02-2017, 10:07 AM | #37 |
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Re: Roller trigger thought
Sand test passed. Jeff will need to change his middle name to Alexander.
Pete, I like the idea of wide sears, but my understanding was that there is a bad side to a Wide Trigger and Wide Shaft sear in that the interface will be more prone to binding, ie band force goes up, trigger pull goes up. Essentially you are increasing the break point? I guess you could get around it with Geometry, like your Force diagram in the Euro vs. Square cut tang discussion, it looks like a Square Cut Sear geometry would favor you whereas a Euro Round Sear the wider surfaces would stack up your breaking point?
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02-02-2017, 02:43 PM | #38 |
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Re: Roller trigger thought
Are you sure about that? Levers have been thinner to save on the amount of metal being used, reduce weight and cost and years ago make it easier to stamp them out. Although to avoid trashing a product's reputation it needed to work properly and be reliable, reducing cost was a great driver and still is as that determines the price. Plastic triggers were certainly a cost reduction measure in guns such as this "Crawl" model. It uses a dipping sear tooth lever, note the curved slots in the interior wall and the sear lever with its integral pivot pin was, bar the simple double leg springs and trigger pivot pin, the only piece of metal in the handle assembly. This gun uses the standard eurogun spear and is a "universale gachette" model. I bought it in a box of old speargun parts; the red circled item shows the plastic stop tab for the shaft tail has been busted off by an over zealous ramming of the spear tail into the sear box.
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02-02-2017, 09:50 PM | #39 |
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Re: Roller trigger thought
I ordered a few sets of waterjet cut triggers and sears today that I can retrofit to mechanism housings that I have which are outfitted with safeties. Hopefully soon I'll be able to test this design against an actual fish . . .
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02-03-2017, 12:30 AM | #40 |
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Re: Roller trigger thought
Very good, I think that they should work OK as they have survived the worst! Now to see how the pull stands up over time and whether it remains low.
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02-03-2017, 01:48 AM | #41 |
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Re: Roller trigger thought
Loose tolerance can be good ... but it can also work against you. With a loose tolerance you get less chance of particles getting entrapped inside the housing ... but also a loose fit means that the sears will not sit perfectly centered and thus might cause excessive wear on one edge rather than distribute load to the entire part. Also making the trigger wider just makes everything weaker as the housing and pins get stressed more as the distance they have to be loaded increases. I prefer good fit with minimal tolerance and if the trigger somehow gets filled with mud or sand ... just run a hose with running water inside the trigger and a little shake and dry firing should be plenty to clean off a trigger that has been buried under sand. If that is not possible or a boat doesn't have a hose, you can take out a trigger and remove the sears, clean off the sand or debris, and put it back together in about 1 minute.
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02-04-2017, 03:45 PM | #42 |
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Re: Roller trigger thought
Is this where the roller sear tooth is located in this frame lock trigger mechanism? Photo taken from the Ermes-Sub website.
If the sear tooth roller is larger in diameter then to get it into the slot the roller will have to be slid in from underneath at an angle, the ends of the roller tooth turned down to meet the fore-aft width of the slot. Last edited by popgun pete; 02-04-2017 at 03:58 PM. |
02-04-2017, 05:41 PM | #43 |
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Re: Roller trigger thought
Dipping back into the archives I found this Abellan trigger mechanism which is also a frame lock. The sear lever leans on the trigger which in turn leans on the sear box housing's transverse panel, or cross pin, at the front when the latched spear is loaded up by band pull. The trigger is blocked from moving forwards by the sear box frame. The sear lever tip points its force from the torque created by the band pull on a line behind the trigger pivot pin, hence the trigger receives a torque created by the radial offset of that force line from the trigger pivot pin axis. Cam lock mechanisms try to aim that force directly at the trigger pivot pin axis so that no torque is produced in the trigger. Thus the red lines will be just on or inside the intermediate circle (shown in pale green). Then the lever geometry has to allow for the sear lever tip to swing past the trigger pivot pin and the body of the trigger without fouling. This is why the "Sea Hornet" trigger mechanism has a tall trigger as can be seen by looking at its diagram. That mechanism also has the catching step for the sear lever tip built onto the trigger, i.e. the second step or notch in the rear of the trigger.
Last edited by popgun pete; 02-04-2017 at 05:52 PM. Reason: more info |
02-04-2017, 07:30 PM | #44 | |
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Re: Roller trigger thought
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In this picture from the Ermes-sub website of their "Ocean" model trigger, it appears that maybe a roll pin is inserted through both the slot and the roller after the roller is positioned inside the mechanism housing? I'm guessing that the pin is a press fit into the roller but slides without resistance in the housing slot. All of the different mechanism that I saw in this section of the Ermes-sub website appeared to have the arc-segment slot to accommodate the sear roller, but this was the only one that looked to have it installed. |
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02-04-2017, 07:50 PM | #45 |
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Re: Roller trigger thought
Well if you have a roller that straddles the housing and has ends that ride in the elongated slots it either has to push in from the side or, if the "tooth cylinder" is a larger diameter than the slot width, come in at the tilt from underneath, lodge one end in the slot and push it through slightly and then lift the other end up to engage the slot on the other side.
The reverse mechanism is the one shown on page http://www.ermes-sub.net/future--black--future.html. The mechanisms have an extra hole for jig positioning I would guess when bending up or holding the mechanism frame. The trigger mechanism you have shown is a "conventional" layout, if I could use that term, with a jaw type sear lever and a rear trigger. Jaw type sear levers have a high pivot pin just back of the sear tooth-backing projection yoke, you can see one in the Kitto M3 and M5 and the first version of the "Ocean Rhino". Jaw sear levers have a low rotation angle to let the shaft go. I am assuming that the three pin ends visible in the holes are the trigger pivot pin, the sear lever pin and a stop pin going from left to right on the image. There is a leg type, wire loop biasing spring on the trigger, but no other spring that I can see, although there should be another one somewhere which may use the front stop pin as an anchor. P.S. Now I see the second spring and have added a note to the photo. I have pumped up the "Ocean" mechanism photo taken at a slightly different angle and we can see a drive pin in the second hole from the left and maybe the roller mounted on another hollow drive pin in that elongated slot. Last edited by popgun pete; 02-05-2017 at 12:27 AM. Reason: annotated the photo |
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