Tomba - All in One barrel sealing

[Slingingsteel]

I use two different methods of attaching the line to the front of the spear.
One way is a simple hole drilled through the spear & the other is on a slider that is stopped by a ring weld about 100mm back from the tip.
I only use twin barb spears, I believe the spear will rotate or spin when fired, I never bother to place the barbs in any particular position & to be honest never noticed any difference either?

Thanks Mart

 

[tromic]

This is the drawing of a new version of TombaF7 for Mamba, free shaft Tomba adapter for Mamba, for 7 mm shaft. On shooting the friction should be half of the friction during loading the shaft, theoretically. In a real world could be different, but might not be easy to measure. O-ring is movable on the 4 deg cone of the adapter. I still prefer the slider version of Tomba.

 

[zmajmr]

New video Tomba kit

[ame=http://www.youtube.com/watch?v=bk4wxfppCzU]YouTube - Tomba kit and special stainless steel Tomba slider[/ame]

 

[tromic]

This way could be used for testing Tomba sealing too.

[ame=http://www.vimeo.com/9997697]Test di tenuta testata sottovuoto x-power(stc) on Vimeo[/ame]

 

[zmajmr]

This is the drawing of a new version of TombaF7 for Mamba, free shaft Tomba adapter for Mamba, for 7 mm shaft. On shooting the friction should be half of the friction during loading the shaft, theoretically. In a real world could be different, but might not be easy to measure. O-ring is movable on the 4 deg cone of the adapter. I still prefer the slider version of Tomba.

New video :
[ame=http://www.youtube.com/watch?v=Fj_peW6MJWo]YouTube - TombaF6.5 for Mamba (vacuum kit)[/ame]

 

[tromic]

Good Sealing:

In this case I had been using cone sliding ring with 6.55 mm ID.

Poor Sealing:

In this case I had been using cone sliding ring with 6.66 mm ID. The water in the "cup" was sucked by vacuum in the barrel.

These tests had been done with the previous Tomba10 adapter with 10.05 mm boring for the O-ring. The new Tomba10 adapter has 9.9 mm boring so it is more tolerance forgiving than this on the video.

 

[tromic]

This knot slider could be very good for Tomba, especially on high bars (near 30 bar).
This idea was by Luciano Garibbo. I used 1,5 mm spectra and double constrictor knot.
Because this is Tomba10 on 7 mm shaft, the OD is about 10 mm.


I find out that on high bars, the stainless steel slider could damage the O-ring on the shaft. I did same rough calculation and got that the slider should not be more that 1-1.5 gr not to damage the O-ring on more than 25 bars.

 

[tromic]

This is a drawing of the new cone ring for Tomba12. It's weight is 2 g. The previous was 3,7 g. If the cone ring is too heavy it will be easily damaged especially in combination with heavy slider and on high bars (more than 25 for Cyrano). On high bars it is best to use plastic slider or "knot slider" because the O-ring could be damaged too.
I measure the weight of steel ring in Mamba kit. It is 1,5 g. The sealing cylinder is 2,5 g. So the previous cone was about the same in weight as steel ring and sealing cylinder in Mamba kit.

 

[martinbar74]

Tromic,
Great!
By why this form is so complicated?
Do you think that simple ring (as standard one without using any angle ) + the slider you have made will be enough to keep the shaft centralized & not moving during loading ?

 

[popgun pete]

The weight of these slider parts is nothing compared to the shaft, so a few grams is neither here nor there as a percentage of the propelled mass that leaves the gun. Why not profile the rear of the slider face that contacts the "O" ring so that when the "O" ring is sandwiched between the metal slider and the tail cone ring at the end of spear travel (or when the fish starts pulling in the event of a hit) the "O" ring will then be compressed inwards onto the shaft. You do not want the "O" ring nipped at its outer periphery, so the tail cone ring will need a flat front face if the face on the rear of the slider is bevelled. An alternative would be to make a metal "pre-washer" that has the necessary shape to cup the front face of the "O" ring and let it be pushed along by the metal slider. So the component sequence at the end of spear travel would be metal slider, metal "pre-washer" with flat front face and concave bevelled rear face, "O" ring, tail cone ring and shaft tail with stop diameter. A replacement "pre-washer" and "O" ring could be carried as a combined unit to slip onto the shaft, it would be easier to slide this unit on than to push just an "O" ring into position when carrying out repairs "in the field" (solitary "O" rings tend to roll up on themselves, but it depends on the interference fit). Under very high compressive loads the "pre-washer" might crack, but this would not affect the holding power of the line slide on the shaft if it did break.

 

[tromic]

Tromic,
Great!
By why this form is so complicated?
Do you think that simple ring (as standard one without using any angle ) + the slider you have made will be enough to keep the shaft centralized & not moving during loading ?

Martinbar, it is possible to make what you advice, but I think this with the cone ring is better.

 

[tromic]

The weight of these slider parts is nothing compared to the shaft, so a few grams is neither here nor there as a percentage of the propelled mass that leaves the gun. Why not profile the rear of the slider face that contacts the "O" ring so that when the "O" ring is sandwiched between the metal slider and the tail cone ring at the end of spear travel (or when the fish starts pulling in the event of a hit) the "O" ring will then be compressed inwards onto the shaft. You do not want the "O" ring nipped at its outer periphery, so the tail cone ring will need a flat front face if the face on the rear of the slider is bevelled. An alternative would be to make a metal "pre-washer" that has the necessary shape to cup the front face of the "O" ring and let it be pushed along by the metal slider. So the component sequence at the end of spear travel would be metal slider, metal "pre-washer" with flat front face and concave bevelled rear face, "O" ring, tail cone ring and shaft tail with stop diameter. A replacement "pre-washer" and "O" ring could be carried as a combined unit to slip onto the shaft, it would be easier to slide this unit on than to push just an "O" ring into position when carrying out repairs "in the field" (solitary "O" rings tend to roll up on themselves, but it depends on the interference fit). Under very high compressive loads the "pre-washer" might crack, but this would not affect the holding power of the line slide on the shaft if it did break.

I had same idea on mind but didn't find appropriate solution for realization.
With this last cone ring design, and plastic or "knot slider" this will be better than previous realization. It would be even better if the cone ring would be hardened. The problem is that the inner slot of the cone ring is hammered by the impact of the shaft tail stop diameter. More mass on the shaft means more hammering. So every gram is important. That's why it is important that all parts on the shaft be as light as possible. With light slider there is no threat to the O-ring, only to the con ring itself if it is heavy.

 

[popgun pete]

If you think of the assembly as a sliding hammer then it is the weight of the shaft, spear tip and tail cone ring that act as the hammer on the restrained (by the tensioning of the shooting line) elements which are the line slide and "O" ring, however the tail cone ring's mass is very small compared to the weight of the shaft and spear tip. What will be damaging the "O" as it is being squeezed is the unyielding nature of the metal line slide. The "O" ring has an easier time with the knot slider and plastic slider as they have an element of give or yield in them. I had thought of suggesting a plastic "pre-washer", but it may be cracked by the impacts. Another possibility is a rubber washer acting as the "pre-washer", it would absorb some of the impact energy as well as the "O" ring, but would not contribute to sealing.

I know that you intended hydrobraking in the rear of the tail cone ring as it is entered by the shaft tail stop diameter, but maybe you need a small rubber washer installed in there as part of the tail cone ring. That addition would take some of the impact energy in the line slide assembly as everything is pulled to a halt by the shooting line coming under tension. So you would then have three rubber energy absorbing elements, the rubber "pre-washer", the "O" ring and the tail cone ring rubber washer inside the rear well of the tail cone ring. As the tail cone ring sits in the muzzle as the shot commences the "sliding hammer" element is the shaft and spear tip which contain most of the projectile mass. Only when the shaft and spear tip is pulled to a halt by the shooting line coming under tension does the "sliding hammer" include the weight of the tail cone ring. At this moment there is no hydrobraking inside the rear of the tail cone ring, the tail stop diameter is already inside it. However with another rubber element added in there you may take some more of the impact energy away. Due to the small annular diameter this tail cone ring rubber washer will be more like a short piece of tubing, or sleeve, or even made of some plastic material bound by the wall of the well it sits inside.

 

[tromic]

If you think of the assembly as a sliding hammer then it is the weight of the shaft, spear tip and tail cone ring that act as the hammer on the restrained (by the tensioning of the shooting line) elements which are the line slide and "O" ring, however the tail cone ring's mass is very small compared to the weight of the shaft and spear tip. What will be damaging the "O" as it is being squeezed is the unyielding nature of the metal line slide. The "O" ring has an easier time with the knot slider and plastic slider as they have an element of give or yield in them. I had thought of suggesting a plastic "pre-washer", but it may be cracked by the impacts. Another possibility is a rubber washer acting as the "pre-washer", it would absorb some of the impact energy as well as the "O" ring, but would not contribute to sealing.

I know that you intended hydrobraking in the rear of the tail cone ring as it is entered by the shaft tail stop diameter, but maybe you need a small rubber washer installed in there as part of the tail cone ring. That addition would take some of the impact energy in the line slide assembly as everything is pulled to a halt by the shooting line coming under tension. So you would then have three rubber energy absorbing elements, the rubber "pre-washer", the "O" ring and the tail cone ring rubber washer inside the rear well of the tail cone ring. As the tail cone ring sits in the muzzle as the shot commences the "sliding hammer" element is the shaft and spear tip which contain most of the projectile mass. Only when the shaft and spear tip is pulled to a halt by the shooting line coming under tension does the "sliding hammer" include the weight of the tail cone ring. At this moment there is no hydrobraking inside the rear of the tail cone ring, the tail stop diameter is already inside it. However with another rubber element added in there you may take some more of the impact energy away. Due to the small annular diameter this tail cone ring rubber washer will be more like a short piece of tubing, or sleeve, or even made of some plastic material bound by the wall of the well it sits inside.

Peter, thanks to your advices! All those different possibilities I already had on my mind. I suppose Taimen has something similar, some plastic washer. I saw something that might be that on a picture of shaft's tail. The "sliding hammer" is the main problem that should be solved. I want to find the simplest solution and to have the best performance. I think I am very close to that. If this, with the latest cone, won't be good enough I have another, pretty different solution too. But before going to another solution I would like to be sure that I considered all possibilities with the current design. Maybe adjusting just a detail would be enough to solve the problem. For example for 7 mm shaft the boring in a cone ring is 7.1, and enlarging i to 7.2 might solve the problem. Or as in last case using lighter cone, 2 g instead of 4 g. I would like to make Tomba simple and reliable for some time of usage or number of shoots. I do it for fun. It would be much easier if I had opportunity to test it myself but I have to wait for may holiday.

 

[tromic]

This is an idea for a new Tomba without a cone ring, Tomba12simple:

A green bushing inside the adapter would be made in Delrin same as the slider. A steel ring could be that already on the shaft. This is similar to one of mine earlier Tomba, that was using a cone and a plastic ring, but here the plastic ring has a role of cone ring - centering the shaft. The purpose of the steel ring is to accept the impact so it is not important to be cone shape and to be very accurate. The question is how long would the plastic bushing do its job. It should be replaced after some time of usage, maybe more frequently than the cone ring, maybe not?

 

[martinbar74]

Tromic,
As per your experience , how many shots needed to damage the o-ring (without any protection for the o-ring )?

 

[Don Paul]

Tromic,
As per your experience , how many shots needed to damage the o-ring (without any protection for the o-ring )?

I have over 25 shots in on my Airbalete with Tromic's kit at 20 bar. Unfortunately with the past heavy rain, and rivers of runoff, the 8 to 10 foot vis has kept me from further tests. So far I have no O-ring damage or deformation of metal slide ring parts. I can't wait for spring to go forward.

Cheers, Don

 

[tromic]

Tromic,
As per your experience , how many shots needed to damage the o-ring (without any protection for the o-ring )?

I was using the gun with same O-ring during my holiday for 10 days without any damage, with plastic slider. With steel slider on high pressure the O-ring could be damaged after a few shots.

 

[popgun pete]

The simplest form of vacuum seal kit is an "O" ring on the shaft sitting at the entrance to the muzzle constriction, however that "O" ring will be wiped off the shaft tail as it spreads over the shaft tail stop diameter once it gets hit from the front by the arrival of the stop ring at the end of spear travel. On your single "O" ring Tomba's you have got around this problem by moving the "O" ring further forwards in the muzzle and shifting the stop ring so that it now sits inside the muzzle behind the "O" ring. As we all know the stop ring normally sits in a recess in the front face of the muzzle, but it has to be of a smaller outer diameter if it goes inside the muzzle. With the muzzle relief ports blocked off only the gap around the shaft diameter needs to be sealed where the shaft enters the muzzle restriction, either at the gap entrance itself or some position forward of there.

This latest (Tomba12simple) version will also achieve the necessary sealing configuration, however the advantage of your tail cone ring is that it is a stop ring that will not damage the sealing surfaces as the shaft tail is inserted into the muzzle, plus it is self-centering, so the "docking alignment" can be a bit off initially as the spear tail and muzzle are brought together underwater. Also the tail cone ring gains mechanical strength by being much longer than a standard stop ring to make up for the fact that it has a smaller outer diameter, it has to be as it needs to be less than the OD of the "O" ring sitting immediately in front of it.

The new version you now propose has a small outer diameter metal washer stop ring behind what is a second and bore centralizing stop ring made using a machined delrin tube. Unless these two items are held together mechanically the metal washer could separate from the delrin tube and scratch the sealing surface for the "O" ring during muzzle loading, especially if the washer can tilt slightly on the shaft and drag on the smooth metal surface of the long muzzle bore entrance recess. So rather than the impact durability of the delrin tube, it is essentially the rear half of a split plastic line side swallowed by the muzzle with the rest of the line slide sitting outside, the durability of the surfaces that the "O" ring seals on need to be considered for the longer term. Another problem could be grit embedding in the delrin, it could scratch the muzzle bore sealing surface, as could sand grains trapped between the two, however a careful user would avoid these problems. Really depends on how low maintenance and "foolproof" you want to make it.

 

[tromic]

The simplest form of vacuum seal kit is an "O" ring on the shaft sitting at the entrance to the muzzle constriction, however that "O" ring will be wiped off the shaft tail as it spreads over the shaft tail stop diameter once it gets hit from the front by the arrival of the stop ring at the end of spear travel. On your single "O" ring Tomba's you have got around this problem by moving the "O" ring further forwards in the muzzle and shifting the stop ring so that it now sits inside the muzzle behind the "O" ring. As we all know the stop ring normally sits in a recess in the front face of the muzzle, but it has to be of a smaller outer diameter if it goes inside the muzzle. With the muzzle relief ports blocked off only the gap around the shaft diameter needs to be sealed where the shaft enters the muzzle restriction, either at the gap entrance itself or some position forward of there.

This latest (Tomba12simple) version will also achieve the necessary sealing configuration, however the advantage of your tail cone ring is that it is a stop ring that will not damage the sealing surfaces as the shaft tail is inserted into the muzzle, plus it is self-centering, so the "docking alignment" can be a bit off initially as the spear tail and muzzle are brought together underwater. Also the tail cone ring gains mechanical strength by being much longer than a standard stop ring to make up for the fact that it has a smaller outer diameter, it has to be as it needs to be less than the OD of the "O" ring sitting immediately in front of it.

The new version you now propose has a small outer diameter metal washer stop ring behind what is a second and bore centralizing stop ring made using a machined delrin tube. Unless these two items are held together mechanically the metal washer could separate from the delrin tube and scratch the sealing surface for the "O" ring during muzzle loading, especially if the washer can tilt slightly on the shaft and drag on the smooth metal surface of the long muzzle bore entrance recess. So rather than the impact durability of the delrin tube, it is essentially the rear half of a split plastic line side swallowed by the muzzle with the rest of the line slide sitting outside, the durability of the surfaces that the "O" ring seals on need to be considered for the longer term. Another problem could be grit embedding in the delrin, it could scratch the muzzle bore sealing surface, as could sand grains trapped between the two, however a careful user would avoid these problems. Really depends on how low maintenance and "foolproof" you want to make it.

One another problem with the latest design might be damaging of the back face of delrin tubing after impact with the stop ring. Also, this design wouldn't be suitable for thin wall delrin tubing. So I am going to stay with the cone ring design, just fine tuning it to make it more reliable on longer run. All this playing with Tomba design just shows how difficult is to make something really good. Peter, thanks for your comments. :friday
Yesterday I made a tiny modification to the cone ring so it might operate longer before need for some repair (using sanding paper or a file). After that it will be tested with Spark 110 on 30 bar, in Spain - I need not to wait for summer