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Old 01-31-2017, 05:32 PM   #1
Tin Man
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Roller trigger thought

I’ve been thinking about roller style trigger mechanisms. When different manufacturers coalesce around the same basic design, it’s probably a sign that said approach is the best. But still . . .

I guess it is possible to position the roller on the trigger, the sear, or potentially even both. All of the designs that I could easily find pictures of seem to have adopted the sear tip placement, though they go about the sear fabrication differently. If you looked no further than Popgun Pete’s trigger threads, you would still find examples of sears that are laminated from thin plates (C4 and Bleutec), some where the roller space is machined from a solid sear (Nile-tec), and others where the sear appears to be cast or metal-injection-molded to create room for the roller. I’m sure that each approach has its relative merits and shortcomings, but they do share some commonalities that bug me a little.

First, they require reasonably tight tolerances, and you end up with some closely fitted parts, which is something that seems best avoided in a speargun trigger when possible.

Second, as Pete pointed out elsewhere, the roller simply can’t be the full with of the sear.

Third, there’s a limit to how small the roller can be because it requires a sufficiently stout axle to carry it, and roller diameter is one of those variables that I think can influence the way a trigger feels when it “breaks” at the release.

I thought about how ball bearings are usually constructed. The balls or rollers are in firm contact with the inner and outer race, but aren’t attached to either. Instead, there is generally some sort of cage which surrounds the rollers and keeps them arranged as they should be. With that idea in mind, I thought of this:





The load bearing surfaces of the trigger and sear are both arc segments just like the inner and outer races of a bearing. Under load, the roller is pressed between them, and rolls around each piece as the trigger is rotated. The last element, a cage, requires nothing more than a circular window in the housing that is large enough to allow the roller its needed range of movement, but small enough to keep it from escaping. Once the mechanism is installed, these windows are covered so the roller cannot fall out of place.

Maybe this is a new approach, or maybe it’s not. I really don’t know, but I felt like pursuing it so I built a prototype that I could abuse on my trigger test jig.

Last edited by Tin Man; 01-31-2017 at 05:56 PM.
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Old 01-31-2017, 05:33 PM   #2
Tin Man
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Re: Roller trigger thought

For the first series of tests, I created a trigger with an arc segment load bearing surface (blue in the sketch below), but the sear was flat faced. I really just wanted to see if the “floating roller” would behave itself, and it actually worked pretty well.

I started with 100 cycles at a 500 lb load, which seems like a reasonable maximum for normal guns. The trigger pull was smooth and precise, though it did decrease slightly over the course of the test. Since I had made no effort to polish off the machining marks when I fabricated the trigger and sear, I think this decrease may be attributable to the trigger pieces smoothing themselves out from repeated contact.

So if 500 lbs works, how about 1000 lbs? Not really a problem. By this time the trigger pull was very consistent throughout the entire 100 cycles. In the picture of the trigger, you can see how smooth the surfaces look. All the parts just sort of burnish themselves. After that, I went fully into the “let’s just see where it breaks” mindset and loaded it up with 1500 lbs. It did well for a few cycles, but the roller was creating a little smashed spot at the sear tip so I called it quits.

After that test, I made a new sear with a proper radius on the contact face (red in the sketch below) and did an endurance test consisting of 1000 cycles at a 500 lb load. As you can see from the second chart, the trigger pull was very consistent throughout, except for outliers at 200 and 900 cycles. Both of those were due to spring malfunctions. In the first case, the spring had shifted and wasn’t applying resistive force to the trigger (hence the low reading). In the second case, the spring attachment had become rough and was applying excessive resistance to the trigger. I sanded the rough spot off the spring, and trigger pull fell back in line. If you eliminated those two points, I think that the trigger pull would have been very consistent at about 2 lbs throughout the test. I should note here that I was using a Lyman digital trigger pull gauge to measure trigger pull force, and it is a little sensitive to technique. Pulling a little slower or a little faster will definitely affect the reading, which is why I always averaged several readings to define a result. But still, there is a human error component involved.

As I see it, this approach “could” have a few advantages. First, it allows for simple construction because the trigger and sear are simply waterjet or laser cut from plate. Second, it eliminates some of the close fits associated with an axle-mounted roller, which might be better for a mechanism that gets dragged through the sand and muck. Third, elimination of the axle allows for either a very strong mech, or possibly a smaller one to carry the same load. And lastly, the ability to incorporate a smaller diameter roller provides flexibility in tuning the way the trigger feels when it releases.

So that’s about all I have so far. I don’t know if there is merit to the idea, or if it’s been done before, or if it has a major flaw that I have overlooked. Either way, I figured that getting it in front of the forum’s collective eyes and brains would be the best way to find out.
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Last edited by Tin Man; 01-31-2017 at 05:49 PM.
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Old 01-31-2017, 05:39 PM   #3
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Re: Roller trigger thought

Thinkin outside the box. American ingenuity is not dead. Are you making Reverse Mechs? That one I got from you years ago was smoooooth.
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Old 01-31-2017, 05:47 PM   #4
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Re: Roller trigger thought

This is awesome.
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Old 01-31-2017, 05:54 PM   #5
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Re: Roller trigger thought

Very very cool. Would you be able adjust to geometry in order to change the length of the trigger pull?


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Old 01-31-2017, 05:59 PM   #6
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Re: Roller trigger thought

Quote:
Originally Posted by jstiver09 View Post
Very very cool. Would you be able adjust to geometry in order to change the length of the trigger pull?
I think so. In my limited experience with just a few prototypes, it seems like something as simple as changing the position and radii where the roller falls off the tips of the trigger and sear can do just that. Changing the roller diameter would also have an affect.

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Originally Posted by Behslayer View Post
Are you making Reverse Mechs? That one I got from you years ago was smoooooth.
No. I do love tinkering with them, but I just don't want the liability that comes with producing them.
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Old 01-31-2017, 07:29 PM   #7
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Re: Roller trigger thought

If you are a 1970's hot rod guy, then you absolutely love roller cams. But with the roller cam's reduced friction, it is critical that the roller and the roller pin (axle) gets clean fresh lubrication or the roller will "skid". A floating roller would be 2-3 times as likely to 'skid' versus an axle roller because it will bind at the 1st possible chance under a huge load.

In salt water spearfishing, the lubrication comes from the salt water, but it leaves behind 'deposits' when dry. In a normal sear, those deposits are scraped off. In a roller cam, there is no scraping or cleaning action to either the roller surface or if you choose to use a roller axle.

I love roller cams in engines because the smoothness equals more horesepower. But if the cleaning sequence on the roller surface or the roller axle is not addressed, then longer term the roller will 'skid' against the cam. This is what we see in engines also. Given superior materials in both the roller and the axle, along the low cycles, it may not be an issue. But I would guess at some point the roller would skid. Long term wet dry testing would be the only way to find out.

But DANG, I love this IDEA !!!!
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Old 01-31-2017, 07:40 PM   #8
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Re: Roller trigger thought

Would there be any advantage to the Ball Bearing being a high density Self Lubricating Nylon?
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Old 01-31-2017, 07:57 PM   #9
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Re: Roller trigger thought

Roller sear trigger mechanisms, such as this recently patented one, US20160377063A1, require the mechanism’s internal parts to be free of contaminants. You can achieve that in a firearm trigger mechanism which can be fully lubricated and enclosed, but in a band powered speargun the trigger mechanism is usually flooded and can be penetrated by sand or fine grits and saltwater can corrode smooth bearing surfaces when trapped in inaccessible corners of the mechanism cassette. A pneumatic speargun has a controlled environment, but most of them use a single-piece trigger operated by a remote trigger beyond the pressure boundary. The reason that their single-piece trigger mechanisms last is that they are always swimming in oil when compared with the same arrangement in band guns which eventually suffer from tooth wear and can no longer hold their shaft tails.

If you could seal the trigger mechanism and lubricate it then things may be different. I note that the "Carbon C4" trigger mechanism is packed with grease, hence they must rely on there being few access points for contaminants to enter, plus regular maintenance by changing the grease keeps problems at bay. Actually although grease is a "magnet" for sand, you can use it sparingly on the rubbing surfaces between sear lever and trigger, but only the actual contacts which wipe each other.

Just another observation on the "Carbon C4". First time I saw that its trigger mechanism was loaded up with grease I thought maybe that was not such a good idea, then I realized that the rocking cradle could jam on the sear lever arm if tiny grit particles got into the gap between the sear lever and the side plates. In order to prevent that from happening all the gaps in the mechanism cassette were filled up with grease. However it seemed to me that a "Carbon C4" was not a gun to be dropped in the shore break while cocked as in that situation spearguns can fill rapidly with sand. I spent an hour or so removing the sand from my "Metaltech" when I did just that.
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Last edited by popgun pete; 01-31-2017 at 09:08 PM. Reason: further comment
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Old 01-31-2017, 08:32 PM   #10
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Re: Roller trigger thought

It may be worth thinking of how to create a trigger mechanism, like this one that you are now working on, that is relatively sealed off from the environment. Up until now the paradigm is a couple of levers swinging in an open cassette where things can go in and then wash out just as quickly. There are two main openings, the sear box mouth and where the trigger projects, plus the line release lever on some side window openings. Now how to seal them off with some simple elements that can be serviced or replaced reasonably quickly.
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Old 01-31-2017, 08:37 PM   #11
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Re: Roller trigger thought

I like the fact that there is nothing Sealed in this Rolling Bearing idea Jeff has. Like an AK-47 you can pour sand through that and it just filters out. I'd leave it open. Then you can actually spray things down, it will get rinsed. It's always going to have water moving around inside it.

Last edited by Behslayer; 01-31-2017 at 08:47 PM.
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Old 01-31-2017, 09:14 PM   #12
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Re: Roller trigger thought

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Originally Posted by Behslayer View Post
I like the fact that there is nothing Sealed in this Rolling Bearing idea Jeff has. Like an AK-47 you can pour sand through that and it just filters out. I'd leave it open. Then you can actually spray things down, it will get rinsed. It's always going to have water moving around inside it.
I think he needs to try the sand test by throwing some inside and see what happens, wet sand that is and which is "sharp" as are quartz type sand grains rather than smooth micro pebbles. The mechanism may sweep them out, rather than catch them in the "nip".
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Old 01-31-2017, 09:21 PM   #13
Tin Man
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Re: Roller trigger thought

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Originally Posted by popgun pete View Post
I think he needs to try the sand test by throwing some inside and see what happens, wet sand that is and which is "sharp" as are quartz type sand grains rather than smooth micro pebbles. The mechanism may sweep them out, rather than catch them in the "nip".
I can do that. Should be interesting!
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Old 01-31-2017, 10:39 PM   #14
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Re: Roller trigger thought

Sounds like a plan. I can provide the sand. What do you see as the test parameters? I would think that shaking the gun underwater to shake the sand out, and using typical beach sand would be part of the test procedure?
The idea of a 2-3 lb. trigger pull at those loads is in there with a decent firearm, and is maybe 1/2 of a typical sear/ trigger mech?.
If the mech is one we've been using, I could be pursuaded to install it in one of my guns for testing!
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Old 01-31-2017, 10:53 PM   #15
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Re: Roller trigger thought

Hahaha, this thread is FUUUUN. Great work as always Sir Tin Man!!!


Wood guy, ill be in touch soon. Thanks
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