Bearing spring guides and piston heads - do they REALLY serve a purpose?

[Flatlander]

So I got to thinking, are these even doing anything useful? First question that needs to be answered is:

Does the spring naturally rotate while it is being compressed/uncompressed? As in it rotates one way during compression, then the opposite way the same amount in decompression?

Instinct tell me the aswer to the above is no...well for the most part (ie. axial strain negligible). A stupid and poor little test of me compressing a spring by hand with a spring guide on one end revealed no visible twisting movement. Note this is a poor test - no bearing spring guide and wasn't fully compressed.

So, if the spring does not want to naturally twist/rotate during compression/decompression, then would it be a good idea to NOT use bearing spring guides and piston heads? First, the bearings are just another moving part that can fail. Secondly, they cost more. Lastly, you don't want any twisting going on in the piston assembly so a stationary spring will help prevent any.

But people report a slight FPS increase after installing a bearing spring guide or piston head? I believe this can be attributed to the 'spacer' effect that the bearing creates (spring becomes compressed a bit more = more potential energy stored).

So, if my assumption is wrong and the spring does rotate while being compressed/decompressed, then a bearing would be a good idea to prevent twisting of the piston and smoother operation. In that event, only one bearing on either end would be needed to eliminate the torsion.

[Danke]

Springs rotate under load and this results in friction where they contact a surface.

[The Saint]

Yes, fps increase after installing bearing spring guide and/or piston head is due to them acting as spacers. The opposite can be observed when removing TM piston heads, as they have a large lug inside the piston.

Yes, your assumption is wrong, spring does try to rotate while being compressed. Yes, you really only need bearing on the guide or piston head for the purpose of spring rotation. I personally use both to increase fps when the next level of spring up is overkill. Most aftermarket piston head includes them anyways.

Rarely, (very rarely) having both in addition to certain (overly-lengthy) springs can actually result in the piston not having enough room to draw back.

[ThunderCactus]

Adding a bearing spring guide and piston head made a HUGE difference in my G&G UMG. Went from 160-220 fps to 240-250fps.

[Flatlander]

Danke, Saint: I'm not saying you guys are wrong, but could you state where you get your information from or how you know? I'm trying to work out the forces the spring undergoes in my head and I believe there to be mainly two - bending and axial.

How I see things happening:
-The coils act like mini 'levers' of sorts causing bending moments on these 'levers' - main cause of the spring length change.
-Stretch out the spring into a straight wire and picture an axial force on wire. This will cause it to shrink. Now when this wire is wound into a spring the shrinkage would cause the spring to rotate during compression/decompression. I can't see this axial force/strain being great enough to really have a noticable effect.

A simple definitive test would be to chrono a gun with a bearing spring guide. Replace the spring guide with a non-bearing one but add spacers so the overall thickness is the same and compare the chorno results. Anyone ever done this?

[The Saint]

I got my information from doing a lot of reading on the subject and talking to old hats.

Originally Posted by Flatlander

A simple definitive test would be to chrono a gun with a bearing spring guide. Replace the spring guide with a non-bearing one but add spacers so the overall thickness is the same and compare the chorno results. Anyone ever done this?

You don't really need to chrony the gun, just observe whether the spring rotates when a bearing spring guide is present.

[Flatlander]

Originally Posted by The Saint

You don't really need to chrony the gun, just observe whether the spring rotates when a bearing spring guide is present.

Well it would serve as two purposes - does it rotate and how effective are the bearings (measured by the fps increase/consistency).

Also, how would you observe this? I'm assuming you're not suggesting watching the spring through the little port near the spring guide as I don't think your eye could see it as it's happening too fast?

[Danke]

I get my experience from the wonderful world of motorsports where shock spring bearings are the subject of much discussion as they degrade rapidly since they're exposed to the environment but considered a must have for those who know.

I've seen many springs "walk" themselves around a damper body and then unscrew the retainers or preload collars as they continue to spin.

I think in the world of airsoft where the bearings are going to be sealed away and the spring is subject to a very rapid and constant cycle they sure appear to me to be a good idea.

[ChiefInTrees]

Originally Posted by Flatlander

Danke, Saint: I'm not saying you guys are wrong, but could you state where you get your information from or how you know? I'm trying to work out the forces the spring undergoes in my head and I believe there to be mainly two - bending and axial.

How I see things happening:
-The coils act like mini 'levers' of sorts causing bending moments on these 'levers' - main cause of the spring length change.
-Stretch out the spring into a straight wire and picture an axial force on wire. This will cause it to shrink. Now when this wire is wound into a spring the shrinkage would cause the spring to rotate during compression/decompression. I can't see this axial force/strain being great enough to really have a noticable effect.

A simple definitive test would be to chrono a gun with a bearing spring guide. Replace the spring guide with a non-bearing one but add spacers so the overall thickness is the same and compare the chorno results. Anyone ever done this?

These are not car springs.
Irregular pitched springs have a great deal of rotation. You don't need a textbook, you just pickup an airsoft spring, put it on a rod with a bearing at the bottom, and put a bearing above it. Mark the bearings and compress it and watch the bearings move.
It also removes tension and gives the spring a straight push instead of more force on one tiny spot. Less tension during expansion means faster expansion, means more compresses per min.

[The Saint]

As ChiefInTrees said, test compress it around a rod outside of the mechbox.

[CDN_Stalker]

Springs in AEGs don't really rotate, they torque when under pressure and are released. Main reason for bearings in the spring guide and piston is for consistancy and efficeincy of the gun. Increased (in most cases +15fps) velocity is a side effect that we mostly focus on (and the fact it's good solid metal as opposed to hollow ABS of most stock spring guides), but I'm not overly sure if the thrust bearings on pistonheads do much to increase velocity at all. I'll let others answer that, and I'll give it a try next time I have an easy gun to work on that I can easily and quickly open up and close. Hmm, I have Apoc's CA M249 in the basement waiting for a new piston right now...................

[Flatlander]

Originally Posted by ChiefInTrees

These are not car springs.
Irregular pitched springs have a great deal of rotation.

A car spring (not leaf springs obviously) and an AS spring will perform the same and have similar characteristic...a springs a spring! A spring having an irregular pitch would (directly) have nothing to do with it.

Thanks Danke, you completely answered my question and clearly know what your talking about.

[ChiefInTrees]

Originally Posted by CDN_Stalker

Springs in AEGs don't really rotate, they torque when under pressure and are released.

I mean is they rotate/torque during compression and expansion. They dont spin like a top, but there is some twisting going on.

[CDN_Stalker]

Originally Posted by ChiefInTrees

I mean is they rotate/torque during compression and expansion. They dont spin like a top, but there is some twisting going on.

Wasn't exactly quoting you, more or less just putting the info out there.

[mcguyver]

Marui keeps the head-end of the spring rigid, yet puts a washer on the spring guide as a point of rotation (as the piston doesn't rotate). They do this with guns shooting sub-300 FPS. Why would they bother, if rotation isn't actually occuring?

When you look at it from another perspective, like big machinery, they usually have bearings to allow a spring to rotate, and those move slowly alot of times. An AEG spring goes from fully compressed to somewhat decompressed 15+ times per second. Rotation is a certainty.