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Old 01-24-2017, 11:04 PM   #106
popgun pete
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Re: Trigger Mechanism Design Rules

Checking out the availability of spare shafts I found this morsel of information on the JBL "Adapta-shaft" page. These "Adapta" shafts are basically the matching stainless steel tail ends to the original fitment shafts that can be combined with a threaded connection to make up a replacement shaft of any length you desire in heat treated spring stainless steel at the front end. What is interesting is that at some time the eurogun shaft "standard" changed to a shorter tab section behind the spear tail notch, and that will be when the "Canon" received its new stainless steel innards. You can see the length change here in this combined image. Dacor used to sell rebadged Cavalero spearguns, that is why Dacor is included in the listing.

When the spear tail pushes on the sear lever's backing projection it has to be of the correct length for the sear tooth to roll up from underneath and enter into the spear tail notch. In spearguns of the dipping sear tooth type there is no backing projection, so instead the spear tail runs into a stop or lug inside the handle frame or sear box and the sear tooth can then find its way up into the spear tail notch. I have examined guns where some strong individuals have rammed the spear so hard into the sear box that they busted off that lug and then wondered why the spear tail was not always latching.
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Last edited by popgun pete; 01-24-2017 at 11:35 PM.
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Old 01-26-2017, 08:18 PM   #107
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Re: Trigger Mechanism Design Rules

The original "Champion Arbalete" invented by Rene Cavalero used a brass (or bronze) sear lever with an alloy trigger and that dictated the shape of the spear tails that were used in these guns. That shaft went on to be a standard for the "universale gachete" trigger mechanisms which often operated in different ways, but still used this spear tail.
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Old 01-27-2017, 03:34 PM   #108
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Re: Trigger Mechanism Design Rules

The "Champion Arbalete" trigger mechanism is of a pull down sear lever type which was adopted from the very similar trigger mechanism used in the spring guns of the period, which was during the mid-forties. One important aspect of the essentially in-line and shallow trigger mechanism was that the hand grip was positioned high up behind the drive line or propulsion axis for the shaft. This had been done deliberately in order to reduce muzzle flip or toss of the gun during the shot. In-line band pull kept the shaft off the barrel tube as the first models were only around a meter long, which meant that essentially the "Arbalete" was a slingshot or catapult mounted at the end of a long pipe which replaced your outstretched arm. Instead of holding the spear and stretched band fitted with a tail cup back with your other hand the new "gun" had a handle and trigger mechanism to hold the spear tail. Thus for shooting the gun was basically a catapult, and for band cocking it was like an arbalete or crossbow. However arbaletes cock the bow string and only then the bolt or arrow is fitted, whereas the "Arbalete" attaches the drive directly onto the shaft and the shaft is then held by the trigger mechanism instead of the mechanism holding the bowstring. Thus was created a simple and very effective underwater weapon that spelled the end for the previous bulky underwater rifles that had been powered by springs or multiple endless loop rubber bands.

Last edited by popgun pete; 01-27-2017 at 03:55 PM.
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Old 01-29-2017, 11:36 PM   #109
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Re: Trigger Mechanism Design Rules

If you have ever wondered why the earliest reverse trigger mechanism in mass production did not take advantage of making the wishbone draw longer then you only have to look back at how it began. The "Sea Hornet" trigger mechanism designed by Wally Gibbins was originally constructed completely out of stainless steel with the "cassette" built on the stainless steel top tube acting as the "spine" with rectangular metal posts welded/brazed on at either end. The covering side plates were spot welded to the posts and that formed the completed sear box. Rather than weaken it by cutting the tube back (as indicated by the thin blue line) it was just used with longer spear tails from the last wishbone notch back. You wanted a longer wishbone draw, then you made yourself a longer gun, these guns all being cocking stock guns and parts to build your own gun were always readily available from sports stores (there were no dive shops as we know them today).

When economic considerations meant a switch to an injection molded plastic cassette was the way to go rather than spend a fortune continuing the making of the stainless steel cassettes the basic shape was still retained, even though the end posts were gone (replaced with ribs as interior "walls"), however the plastic cassette needed the integral molded top tube for strength, so it was not cut back.
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Old 10-09-2018, 08:21 PM   #110
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Re: Trigger Mechanism Design Rules

I just recovered what I thought were lost files from a tower computer's hard drive that seemingly expired many years ago. Among them was this "Bandito" handle composite image (also sold as an "Aquacraft" years earlier) which shows a very compact "cam lock" trigger mechanism. If you go back to the first page of this thread then you will see a drawing of this trigger mechanism.
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Old 10-10-2018, 02:43 AM   #111
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Re: Trigger Mechanism Design Rules

Hi Pete, Thanks again, I just re-read all.
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Old 10-11-2018, 01:41 AM   #112
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Re: Trigger Mechanism Design Rules

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.

https://www.planetdivestore.com/dive...25941/84478/sc
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Old 10-11-2018, 01:48 AM   #113
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Re: Trigger Mechanism Design Rules

Hi Pete, I see you do a lot of theoretical testing but do you do any bench testing?
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Old 10-11-2018, 01:57 AM   #114
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Re: Trigger Mechanism Design Rules

Quote:
Originally Posted by Rob Allen View Post
Hi Pete, I see you do a lot of theoretical testing but do you do any bench testing?
With this one I may have to, but the answers lie in the geometry, assuming that it is made of the right stuff, which I am sure that it is. The US square cut spear tail probably works because the tails tend to lean outwards imperceptibly and at high loads that is all that is needed to push the roller tooth down and out of the way.
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Old 10-11-2018, 02:45 AM   #115
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Re: Trigger Mechanism Design Rules

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.
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Old 10-11-2018, 10:31 AM   #116
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Re: Trigger Mechanism Design Rules

I love this thread!
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Old 10-16-2018, 04:48 PM   #117
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Re: Trigger Mechanism Design Rules

Jack Prodanovich said that the higher up on the sear tooth that the spear tail notch engaged it then the harder the trigger pull. That makes sense as the lever input length is longer. Usually we don't think too much about the sear tooth to spear tail notch interaction due to the use of "universal" spear tails, but in Prodanovich's own "balanced sear" gun the spear tail notch was part and parcel of the design. Spear tails can jump out of the sear box if the sear box mouth is too short as is often the case with reverse trigger mechanisms, although the longer mouth in say a Sea Hornet/Biller makes for a longer spear tail rearward of the wishbone notches or shaft tabs.
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Old 10-17-2018, 06:39 AM   #118
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Re: Trigger Mechanism Design Rules

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.
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Old 10-17-2018, 08:43 AM   #119
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Re: Trigger Mechanism Design Rules

Probably a genius...
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