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Tomba - All in One barrel sealing

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.
Hello, I am new to this forum and I am interestning for the tomba for my mares sten gun. can someone make it for my gun? please reply back. Best rgs Soteres
 
I expected that I will hit target at 6 m with 6.5 mm thick shaft, but it seems that that combination is not good with so long spear. I can load spear in gun with no problems, it does not bend much as somebody would think, but shaft bends during flight in water, so because my nylon passes on left side of reel it pulls spear on left side so I fail target every time when distance was larger then 4 meters. Next time I will try with 7.25 mm.

[ame=http://www.youtube.com/watch?v=SuQ6LEAGaTs]Free shaft & Seac Asso 135 - 6.5 mm shaft - YouTube[/ame]

 
Interesting experiment, I use a 7mm free shaft in my 115 Asso & that seems to work very well up to 5mt
 
This is an idea of how combined mechanical-hydro shock absorber could be made for free shaft Tomba7easy (shown earlier). Hydro part of absorber might takeover about 10 J of piston energy, on a distance of 7 - 8 mm. Rubber tubing is 1/2 of normal length, about 8 mm. Of course, the pneumatic speargun is supposed to be loaded under water.

 
I am going to make this for my Mirage 70. Free shaft 8 mm (TombaF800) with hydro damper. This should work either vaccum barrel or water barrel. Hydro shock absorber could be replaced to regular Mares shock absorber (same dimensions).

 
I suppose I will choose this realisation: Мirаge muzzle and water exit ports covered with elastic tubing, hydro - damper and Tomba 800.



This is how I made calculation of hydro damper.

 
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tromic said:
I am going to make this for my Mirage 70. Free shaft 8 mm (TombaF800) with hydro damper. This should work either vaccum barrel or water barrel. Hydro shock absorber could be replaced to regular Mares shock absorber (same dimensions).

Click to expand...

Water imprisoned in front of the shock absorber might be a problem, not easy to solve. It could make impossible for shock absorber to move forward. Even rubber tubing over the muzzle ports could not solve the problem, because it is on opposite side of shock absorber. Only secure solution is to totally empty water from the muzzle before inserting the shaft. If not doing so, even if shock absorber would done its job, small amount of water might be injected in gun passing by the pistons sealing (if it would be a muzzle without water exit holes and elastic tubing).



My opinion is that all the free shaft vacuum barrel pneumatics has the same problem (TombaF, Evo-Air, X-power, Tovarich).
Additional problem is that it is actually impossible to empty all the water from the muzzle while the piston is in contact with shock absorber, because piston seals it and the water round the piston remains in muzzle. That amount of water might be sufficient to block (or reduce) shock absorbers movement after the gun is loaded and the water can move in front of shock absorber.

Tomba800 on the picture above, has not this problem because the water in front of the shock absorber could get out together with the sealing O-ring on the shaft.
 
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To work properly also a few recess are necessary. On the piston to allow water passage though shock absorber shaft boring. On the shaft, in total length of about 15 mm to allow input of water sufficient for hydro shock absorber to operate. Hydro - shock absorber operate on length 8 mm. Recess on the piston also allow water (salt water) to drain out from the muzzle after the speargun is out of water.



Recess on the piston might be some solution for this problem too. Water in front of shock absorber might pass through boring in shock absorber body and piston, on back of shock absorber.

 
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If this last Tomba design with hydro damper were working as I expected it would be very quiet and no water must be empty from the gun before loading the shaft. It would have a lowest stress to the piston and to the shock absorber, as well, because piston breaking distance is 8 mm, not 3 - 4 mm as most of the pneumatic spearguns have. Just before the shaft leaves the gun water from hydro-damper blows off the cone ring, O-ring and the slider from the muzzle, giving them starting speed similar to that of the shaft so the impact to the shaft-parts should be very low. Blowing of the cone ring as a shaft guide is not very good, but because only for last few cm before the shaft leaves the gun maybe would not be a problem?
 
One step to realisation...
Last phase of taking water for hydro damper, on the beginning of loading the gun. There is no mechanical shock absorber at all, just an ertacetal-C tubing to support the piston. I hope it would work!

 
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There is a problem with this design, I noticed. Water around the piston. A small portion could be injected behind the piston. Skirt on mares piston would not stop it. I could make different piston or, it would be easier to make a hole in the head with a rubber tubing, as a safety valve.
 
This will still be much better, easier to do, and safe from unwanted intrusion of water behind the piston. There will be only two holes, not four. They can serve to check the vacuum and for additional power control if the spearagun would be occasionally used as water barrel.

 
Few details were missing on a drawing, if somebody want to make calculation. For whole compensation of trigger force due to pressure in a gun also a friction(s) and spring tension should be taken in calculation. http://garpun.spb.ru/forum/viewtopic.php?p=44593#44593



Unfortunately if friction would be taken in calculation there would be dependance on pressure. For example:
atm--- kgf
15--- 3,67
20--- 1,96
25--- 0,25
26--- (-0,1)
kgf is necessary force to the trigger to shoot.
 
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