Enclosed Track material

I dont know how much better that would be. epoxy with graphite is pretty slick already. The metal track would be loud. The shaft would rattle and scrape on the shot. Another problem is the expansion and contraction rate of wood when its wet and as temperature changes. The epoxy tracks dont have a problem with this, the UHMW have a slight problem and as a result cant be glued in. I would imagine you would run into some kind of problem with this. Also by looking at your diagram there is a small gap between the metal and the wood. This could potentially hold water and cause the metal to rust. Its stainLESS not stain proof it can still rust although this is obviously a long term not short term problem. Its also heavy, some guns would have a problem floating that extra mass.

Try it see how it works.

pretty interesting idea.

my first two thoughts are that it will be loud, metal on metal.

and second is that you risk a lot of galvanic corrosion since the likelihood is that the SS will be different.

i feel like the benefits of having a temp solid material might outwieght the noise but i hope someone smarter than me also chimes in (edit, Xan was typing while I was...he qualifies as much smarter )

By enclosing the spear in a cylinder you get the generation of a squeeze film between the shaft and track, like someone slipping over with smooth leather sole shoes on a wet tile floor (which is tantamount to moving across a smooth sheet of ice wearing just ordinary shoes), and this squeeze film limits the frictional effects of the track. When an automobile engine first turns over squeeze films in the residual oil in the bearings create reduced friction before the oil pressure builds up from the oil pump to the running pressure and the plugs begin to ignite the fuel-air mixture. The squeeze film is the result of the velocity differential across the thin fluid film, say the enclosed track being stationary and the shaft accelerating inside it. Point or linear contacts at three points on the shaft will have more friction, not less. For the record the first enclosed track band guns had metal tube tracks, slotted at the sides. The modern enclosed track band gun started with top slotted metal tubes. Consideration had even been given to non-cylindrical shafts and tracks, such as hexagons and octagons, but of course a round shaft is the easiest to make as metal rod is available in many diameters, lengths and materials. Also cylindrical bores are easy to generate compared to barrel tube cross-sections shaped like polygons.

Im not sure a squeeze film is forming in this scenario. Most enclosed tracks that I know of are intentionally made larger than the shaft so that they can function with slightly bent shafts or sand/debris in them. A good quote I read once was that you want your enclosed like an ak-47. It needs to be able to shoot every time even if there is a slight flaw in the shaft or barrel etc. Under ideal conditions a squeeze film might form and in the field you may see a partial squeeze film but I dont think this happens in most if any guns. Another problem with the squeeze film model is that it requires the shaft to move parallel to the track but it is known that on overpowered guns (one of the big reasons people choose enclosed track) and even normally powered guns the shaft flexes and does contact the track walls. If you watch slow mo videos of open track guns you can see how much the shaft flexes. The ability of the track to contain that flex and direct the forces into moving the shaft instead of flexing it. Additionally the oil used in engine lubricants is significantly more viscus and is chosen for its cohesion and ability to form a film. Water is not nearly as good as a lubricant.

Like you mentioned Dustyyoungblood track material wouldnt matter if that was the case but experimentation has shown that the UHMW and epoxy are the best.

Pete you really a great wealth of info and a great resource for this forum

Great discussion gang

Quote from dustyyoungblood

So, in an enclosed track with a circular cross section, and in very close tolerance to a shaft with a circular cross section, then we have a squeeze film of water between them. During acceleration then, is the shaft perhaps not contacting the track at all? But just gliding in perfect equilibrium inside the enclosed track? If that is the case, then using a low friction plastic is not relevant. The only important feature of the enclosed track will be it's shape/size/accuracy of fabrication.

Not at the start as the shaft initially goes from zero, but the squeeze film will form very fast. Then there is the loading of the gun, the plastic tracks make it easier to push the shaft in, plus no shaft is ever truly dead straight. Some enclosed tracks are loose, like the optional one on the Riffe "Metaltech", so that it can take a couple of different diameter shafts. However a light section track will be less effective on shaft whip as the shaft will distort the track temporarily. The Riffe enclosed track is mainly intended to keep the shaft on the gun in the absence of a shooting line holding the shaft at the muzzle.

Quote from Wishihadgills

Im not sure a squeeze film is forming in this scenario. Most enclosed tracks that I know of are intentionally made larger than the shaft so that they can function with slightly bent shafts or sand/debris in them. A good quote I read once was that you want your enclosed like an ak-47. It needs to be able to shoot every time even if there is a slight flaw in the shaft or barrel etc. Under ideal conditions a squeeze film might form and in the field you may see a partial squeeze film but I dont think this happens in most if any guns. Another problem with the squeeze film model is that it requires the shaft to move parallel to the track but it is known that on overpowered guns (one of the big reasons people choose enclosed track) and even normally powered guns the shaft flexes and does contact the track walls. If you watch slow mo videos of open track guns you can see how much the shaft flexes. The ability of the track to contain that flex and direct the forces into moving the shaft instead of flexing it. Additionally the oil used in engine lubricants is significantly more viscus and is chosen for its cohesion and ability to form a film. Water is not nearly as good as a lubricant.

Like you mentioned Dustyyoungblood track material wouldnt matter if that was the case but experimentation has shown that the UHMW and epoxy are the best.

I studied Applied Physics at university for my degree and the squeeze films are not some figment of my imagination, however I have not seen the topic of spearguns subjected to any experiment on this matter. As for water, well that is what an ice skater slides around on under the blades of their ice skates, the squeeze film supports their weight to reduce friction on the ice.

I wasn't saying that squeeze films don't exist only that they arent really present in a speargun. Many aspects of modern life wouldnt be possible without squeeze films and their application in hydrodynamic bearings and lubrication.

The experimentation I was referring two was more the trial and error of different builders trying different materials and techniques for building tracks and arriving at the current solutions. I guess it would be more of an evolution in that regard.

I didnt say that water cant work as a lubricant or form a film but Im sure you can agree that oil is a better lubricant. Your right about the ice skates but the shape of the blade plays an important role. If the bottom of the blade was rounded or sharp like some people think they wouldn't work. As Im sure you know for the squeeze film to form the shapes need to be very close and the gap between the surfaces has to be very small. Also having a higher viscosity liquid helps. I wasnt suggesting that a squeeze film cant or doesnt form only that because of how wide the gap is relative to the spear diameter makes it easier for the water to flow around the shaft and makes the effects of the the squeeze film minimal compared to other forces. Squeeze films and hydrodynamic bearings require much tighter tolerances than are found in speargun tracks.

This is further reinforced by the trend to use low friction materials . A squeeze film would reduce the friction to the point that material choice would have minimal effect and the extra work to make a the track out of a different material wouldnt be worth it. It would be easier to just make it out of wood.

Quote from dustyyoungblood

Well, as a speed skater in my high school days.... you have used an analogy that I can relate to:D

Now, even in a "loose" enclosed track, where some shaft whip is occurring, and perhaps the track is a bit warped also...... can we imagine the squeeze film still acting in places along the track, even just for an instant, as the shaft is forced to contact the track? I picture a shaft kind of bouncing around in the track as it accelerates, but the squeeze film does what it can to cushion the shaft as it moves forward, reducing impact, kind of like Magnetic Levitation....

Yes you can. This is known as squeeze film dampening. It will have some effect and there are instances especially towards the end of the shot, once the shaft has started moving and there is less flex, where the squeeze film will occur.

Quote from Wishihadgills

I wasn't saying that squeeze films don't exist only that they arent really present in a speargun. Many aspects of modern life wouldnt be possible without squeeze films and their application in hydrodynamic bearings and lubrication.

The experimentation I was referring two was more the trial and error of different builders trying different materials and techniques for building tracks and arriving at the current solutions. I guess it would be more of an evolution in that regard.

I didnt say that water cant work as a lubricant or form a film but Im sure you can agree that oil is a better lubricant. Your right about the ice skates but the shape of the blade plays an important role. If the bottom of the blade was rounded or sharp like some people think they wouldn't work. As Im sure you know for the squeeze film to form the shapes need to be very close and the gap between the surfaces has to be very small. Also having a higher viscosity liquid helps. I wasnt suggesting that a squeeze film cant or doesnt form only that because of how wide the gap is relative to the spear diameter makes it easier for the water to flow around the shaft and makes the effects of the the squeeze film minimal compared to other forces. Squeeze films and hydrodynamic bearings require much tighter tolerances than are found in speargun tracks.

This is further reinforced by the trend to use low friction materials . A squeeze film would reduce the friction to the point that material choice would have minimal effect and the extra work to make a the track out of a different material wouldnt be worth it. It would be easier to just make it out of wood.

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There is a squeeze film even on the bottom of an open track, just slide two wetted glass plates over each other. In tire tread pattern design I did a lot of work on squeeze films and how to disrupt them for better braking with fully locked wheels, so I know something about it.

I have no friggin idea of gun construction or enclosed tracks, but do you know that now there are "Ice skating rinks" without ice?

They use a special kind of UHMW with additives that improove sliding properties. It is totally "green" as no power is needed.

I am related to a Factory in Germany that does that material.

More info here: http://www.simona.de/static/si…e/PraxisStudie26-engl.pdf

I think it would make the very best enclosed track material. Ever!

Found this string from pro machinist...
"I went to my local plastic supplier for Delrin, told them what it was for, and they recommended UHMW. I was warned that it is a little more difficult to machine than Delrin but that it would last longer and have less friction.

This website seems to agree:
Page not found- Johnson Plastics & Supply- Evansville, IN

"UHMW has one of the highest impact strengths of any thermoplastic and has excellent abrasion resistance, tensile strength, energy absorption, resistance to stress, cracking, and coefficient of friction properties. UHMW coefficient of friction is significantly better than nylon and acetal and is virtually the same as Teflon® but has superior abrasion resistance.

UHMW in sliding applications will out wear steel 10 to 1 and stainless steel 6 to 1."

BTW, acetal is the generic name for Delrin.

I see that there is now Delrin AF, which has threads of Teflon added. Based on the quote above, however, I'm sticking with UHMW for now.

Also, UHMW cost me $3 a pound versus regular Delrin for $8 a pound."

Also this is the BOMB Comparison Table for Plastics.
It is a string about best track materials after all