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Friction trigger
- Thread startertromic
- Start date
Thread Status: Hello
, There was no answer in this thread for more than 60 days.
It can take a long time to get an up-to-date response or contact with relevant users.
It can take a long time to get an up-to-date response or contact with relevant users.
This speargun has a piston...
Shaft D6 mm, barrel D10 mm, load strength about 250N at that time (at the end of loading). Sometimes when it's needed I increase the strength... have used 350N. To load the spear D6 to 350N it is almost impossible and dangerous with "standard" gun, but without any problems on friction trigger.
In my condition of spearfishing (rivers, lakes) it is very convenient - manoeuvrable, good-balanced and has high initial velocity of spear...
Control at a floor scales... like this
On this clip the pistonless friction-trigger gun with the shaft D8...
Mares "Cyrano" alloy muzzle weighs 49 g., including shock absorber consisting of plastic anvil and rubber sleeve which weighs 5 g. I was mainly thinking of the muzzle body and the material it would need to be manufactured from if this type of "friction sear" muzzle was used on a gun with say a 35 mm or a 40 mm OD tank which usually floats after the shot.
This muzzle body is made of aluminum alloy with 22 mm OD
In my design of "friction sear" the axles are loaded with the wedge strength about 600N (with 300N on the spear)... not too much. The wedge angle might be about 30 degrees... There is no special demands to hardness of spear and eccentric... no need for heat hardening.
The muzzle of "Osa" is made of aluminum alloy too, but axle is loaded with the wedge strength about 1500N (with 300N on the spear). The wedge angle is about 5 degrees - so spear, roller and roller ramp must be made of very firm and hard metal... Otherwise the sear might not act reliable...
How do you shape/cut stainless steel cradle parts? That is a demanding operation without specialized tools. I like your design! It is quiet in operation in contrast to mine sketches, above, which would be loud in operation, but less demanding to make.
I suppose your design would not be suitable for use in salt sea water because of electro corrosion between aluminum and stainless steel?
I suppose your design would not be suitable for use in salt sea water because of electro corrosion between aluminum and stainless steel?
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Drill, files and two ours of free time...
Cradle parts might be that
but I have removed all unnecessary metal.
It is possible to electro isolate the upper axle and other parts from the muzzle with plastic sleeve and washers...
Or to make all of titanium alloy - it is not rarity in my land...
"Oca" muzzle looked rather bulky for an alloy item, that is why I thought that the outer part was possibly plastic, but evidently there was no concern about the weight of the muzzle, particularly with that large sight positioned on top. Possibly the large profile of the front sight is to provide a top-down symmetry with the similar shape where the pivot pin for the wedge element is located (refer "processed" photo based on original from www.apox.ru). The "Oca" is a series production speargun, is there any plan to produce a production speargun based on the rocking cradle and eccentric pivoting drum method?
Not for the present...
I carry on with my work.. there is something to do yet...
P.S.
A weight of 27 g. is very light, not much more than half of the weight of a Mares alloy muzzle (49 g.), although the length of the muzzle is reduced by not having to accommodate a shock absorber body and a ring of muzzle relief ports positioned directly behind it, which is necessary in the Mares gun. I note that two guns with relief ports in a reduced diameter "neck" behind the moving parts of the "friction sear" muzzle were shown at the bottom of the page, do either of these guns float after the shot?
No... They have too thin tanks.
The barrelless gun at item #24 can float though it has OD22 tank.
Any gun that floats with a 22 mm OD tank is a significant achievement, especially considering that this example has a more complicated mechanism than is usually seen in this type of "piston-less" and "barrel-less" pneumatic speargun. The twin horizontal teeth incorporated in the sides of the flat spring underneath the muzzle that secure the swinging arms of the cradle in the forward position until the teeth are withdrawn by being pushed downwards when the control rod is pulled back by the trigger is very ingenious. As is the hooking of the horizontal section of the "multifunction" wire spring at the same time which does the actual pushing on the upturned tail of the flat spring. I assume the wire spring that is visible in front of the swinging arms replaces the short leaf spring (part 11) in the sketch of this release component. The restraining action of the twin teeth seems to be dependent on the geometry of the opposing faces as strictly speaking the swinging arms are not locked, but are hooked instead. The mechanism is very compact and now only needs a pull rod to operate it.
A pull rod inside the tank has been used on at least one forward latching pneumatic speargun which was the Technisub "Pulce" using an elliptical tank profile to conceal the pull rod. I remember seeing a parts diagram for it on a forum page, but cannot remember the trigger details beyond the muzzle employing a three ball and sliding collar system to catch an annular groove or step in the spear. If a pull rod projects out from either end of a pressurized section a change in rod and seal diameter at one end can be used to bias the pull rod depending on the difference in cross-sectional areas between the two ends that face the same internal pressure. This force differential between unequal diameter ends has been used to bias a sliding column sear, something like a "Taimen" sear, except that the top was open to ambient pressure and the trigger had to pull the column sear down rather than push it up.
A pull rod inside the tank has been used on at least one forward latching pneumatic speargun which was the Technisub "Pulce" using an elliptical tank profile to conceal the pull rod. I remember seeing a parts diagram for it on a forum page, but cannot remember the trigger details beyond the muzzle employing a three ball and sliding collar system to catch an annular groove or step in the spear. If a pull rod projects out from either end of a pressurized section a change in rod and seal diameter at one end can be used to bias the pull rod depending on the difference in cross-sectional areas between the two ends that face the same internal pressure. This force differential between unequal diameter ends has been used to bias a sliding column sear, something like a "Taimen" sear, except that the top was open to ambient pressure and the trigger had to pull the column sear down rather than push it up.
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Yes, Pete, you understood how the mechanism works right..
The operating manual for the "Oca" can be downloaded from here as a pdf file: http://www.opensea.ru/_data/documents/0000756/Instr_Oca.pdf
Although the text is in Russian, the diagrams and tables can be understood easily enough and give a good idea of how the gun works, particularly as there is an exploded parts diagram.
Although the text is in Russian, the diagrams and tables can be understood easily enough and give a good idea of how the gun works, particularly as there is an exploded parts diagram.
On the Russian forum "apox.ru" someone has recently weighed all the muzzle parts of the "Oca" speargun on an electronic scale and the result is a mass of 93 g. That includes all the items shown in the red square on the attached diagram (taken from the "Oca" instruction manual) and is thus double the weight of a Mares "Cyrano" muzzle! The "Oca" has a stainless steel inner barrel tube (11 mm ID) and the inner muzzle body (part 12) looks to be manufactured from stainless steel as well as it screws onto the front end of the inner barrel (thus same metal for screw threads). As the roller's back and forth motion is constrained by a window in the underside of the inner muzzle body which cuts away half of the tube's circumference in the front section it is unlikely to be made from aluminium alloy, plus there are two more transverse windows taken out of the rear section of the inner muzzle body that provide access to the four muzzle relief ports (two ports on each side of the outer muzzle body). Except for the aluminium alloy outer muzzle body (part 2), all the other items appear to be steel parts, stainless or non-stainless. The profiled roller/drum (part 21) will be a hardened material to protect it from irregular wear as the roller will rotate to any position and has to provide the same action whichever locations on its circumference end up performing the jamming action between the spear and the wedge element (part 23). In Mechanik's gun the roller/drum always engages at the same locations on its circumference as the eccentric pivot eliminates any change in the roller's contact surfaces. On both these guns the third contact on the shaft will be where the shaft presses up into the bore hole running through the muzzle thereby providing a "line" contact at the top rather than the two "point" contacts on the flange inner surfaces of the roller/drum where cones/cylinders with axes at right angles to each other meet at tangents.
The "Oca" has a 30mm OD tank which makes it difficult to create a floating gun after the shot, especially if the guns are shorter versions as there is insufficient tank length to offset the weight at the ends even if you can use a plastic handle at the centre as the "Oca" does. It seems that there will be later versions with more features once (and if) the gun proves itself in service, the current gun being the quickest way to place a product on the market using some existing parts adapted from previous models.
The "Oca" has a 30mm OD tank which makes it difficult to create a floating gun after the shot, especially if the guns are shorter versions as there is insufficient tank length to offset the weight at the ends even if you can use a plastic handle at the centre as the "Oca" does. It seems that there will be later versions with more features once (and if) the gun proves itself in service, the current gun being the quickest way to place a product on the market using some existing parts adapted from previous models.
I wonder if fish slime transferred from diving gloves has any effect on the spear being gripped by the "friction sear". I expect that it does not considering that experimental guns have been in use, but any lubrication on the spear or roller would be likely to lower the friction unless the high contact pressure wiped or squeezed the lubricating substance off or there was not enough of it on the shaft to have any effect.
The wedge angle is calculated with friction coefficient that takes in account any lubrication:
for steel/steel - 0,1
for titanium/steel - 0,2
And you are right - "the high contact pressure wiped or squeezed the lubricating substance off"...
Here http://garpun.spb.ru/forum/viewtopic.php?t=994&postdays=0&postorder=asc&start=0
more about "friction sear"... birth of my design.
It is enough to see images.......
May be interesting ?...