Silent M4 Build - Discussion of parts

[Tad]

Hey guys,

Looking to silence my M4's gearbox and was taking a look at the various ways to do so.

Obviously one major part is the Piston head when it slams into the cylinder, and to stop that I was looking at either getting some Neoprene (I think it's Neoprene) foam as some searches on google have guides to using this for a quieter slam effect, or this -- http://www.taiwangun.com/en/piston-heads/silent-piston-head?from=listing&campaign-id=20.

I'm kind of thinking that I also need to take a look at the motor also, as it makes a nice whirring noise when it spins, does anyone have some suggestions for a quieter motor? Or how to silence it?

 

[Monty]

Perfect shimming and a high toque motor will make it very quiet.

 

[cyrexx]

Airbrake to silence pistonhead.

http://www.leesprecision.com/collections/aeg-internal-parts/products/cnc-machined-v2-v3-acetal-airbrake-piston-head-aoe-shims

Perfect shimming/meshing, helical gears, glueing in bushing.

 

[Lozart]

As you correctly suggest the main source of noise in an AEG is the piston impacting the head. Part and parcel of getting the best out of your gearbox though is correcting the AoE which would involve fitting a sorbothane pad http://airlab.parts/collections/gearbox-parts/products/sorbothane-pad-70d-hardness which will help reduce that noise. An airbrake piston head will also help but be aware that both mods WILL decrease your FPS as a side effect.

Helical gears can help too but MUST be perfectly shimmed to be silent, otherwise they will sound like a tin of wasps.

 

[Samurai]

All the above plus correct cylinder-barrel ratio and a foam filled suppressor will eliminate the piston's sound.

I found that bearing instead of bushings are quieter but those should be at least 8mm. Maybe good quality bearings and 7mm for normal AEG is fine too.

Thick grease on the gears.

Don't forget proper motor height.

 

[cyrexx]

Using standard sorbo pads will reduce the effectiveness of the airbrake. Also if you anything above an M100 with the airbrake it is less effective.

 

[geoffreym]

any reason for an M4 silent build? P90's could be a lot quieter as you can do all of the above, fill the space between the gearbox and body with sound insulating foam, and the way you naturally hold a P90 means your body takes up a lot of the of the vibrations?

 

[Tad]

I'm going to compile a quick list from all of these.

- Shimming - Needs to be spot on

- Airbrake / Sorbopad (I thought it was Neoprene cheers!)

- Helical gears (Not sure what these are to be honest will look).

- Glue in bushings (What does this add?)

- AoE

- Cylinder / Barrel teeth ratio

- Fixed suppressor (Would assume this muffles the snap of air out of the barrel rather than the gearbox itself)

- Motor Height

- Grease thickness (Would this not deteriorate the internals? Too thick would stop it spinning at all)

...

Suppose i should mention my GB has a 110 in it then.

 

[Tad]

any reason for an M4 silent build? P90's could be a lot quieter as you can do all of the above, fill the space between the gearbox and body with sound insulating foam, and the way you naturally hold a P90 means your body takes up a lot of the of the vibrations?

Personal preference is all, I am more comfortable running my CQB M4 than I am running a sub-style weapon. I have no idea why...

 

[Samurai]

- Grease thickness (Would this not deteriorate the internals? Too thick would stop it spinning at all)

That's called glue.

Not that thick. Just some high speed lithium grease or similar.

 

[Lozart]

I'm going to compile a quick list from all of these.

- Shimming - Needs to be spot on

- Airbrake / Sorbopad (I thought it was Neoprene cheers!)

- Helical gears (Not sure what these are to be honest will look).

- Glue in bushings (What does this add?)

- AoE

- Cylinder / Barrel teeth ratio

- Fixed suppressor (Would assume this muffles the snap of air out of the barrel rather than the gearbox itself)

- Motor Height

- Grease thickness (Would this not deteriorate the internals? Too thick would stop it spinning at all)

Suppose i should mention my GB has a 110 in it then.

Helical gears - normal gears have the teeth cut straight across the thickness of the gear wheel. Helical gears are cut at an angle so that when they mesh they have a greater surface area in contact. They're more usually associated with high torque gearsets in sniper rifles etc. To be honest, setting them up perfectly so they are silent is a MASSIVE pain in the arse, a well shimmed standard gearset should be almost as quiet and a lot easier to achieve.

Grease - you need a lubricant sufficiently sticky to stay on the gears and not fling off, but with low coefficient of friction. Lithium grease always works well for me or standard Abbey CT2. Silicon is not really robust enough for gears, fine for piston runners though.

 

[Lozart]

- Airbrake / Sorbopad (I thought it was Neoprene cheers!)

Neoprene pads can help but don't "squish" as much as a sorbothane pad. They do however last a bit better so if you buy a cheap sorbothane pad (like the ones from Pro Airsoft) you should ALSO get a neoprene pad to glue over it in order to protect the sorbothane from damage. As cyrexx said though, a sorbo pad will reduce the effectiveness of an airbrake piston head so it's kind of an either/or not as well as.

 

[Tad]

I've done a bit of a look around for helical gears and every post baring thos in here state they are louder than standard gears. Even when shimmed correctly.

For example - http://www.airsoftforum.com/board/topic/178949-extremely-irritated-helical-gears/

There most posts about them are nearly 3+ years old also, so are they really beneficial or is this just the old goto which is no longer relevant?

 

[Lozart]

I've done a bit of a look around for helical gears and every post baring thos in here state they are louder than standard gears. Even when shimmed correctly.

For example - http://www.airsoftforum.com/board/topic/178949-extremely-irritated-helical-gears/

There most posts about them are nearly 3+ years old also, so are they really beneficial or is this just the old goto which is no longer relevant?

If you get them spot on, they are spectacularly quiet. It's just really hard to get them spot on. I've tried (and failed) and went back to standard gears and a decent shim job.

 

[Tad]

If you get them spot on, they are spectacularly quiet. It's just really hard to get them spot on. I've tried (and failed) and went back to standard gears and a decent shim job.

Does the installation of these require short stroking the pistion? It seems like they are for a high Torque ROF build, pulling the stronger spring back and releasing it quicker.

 

[Lozart]

Does the installation of these require short stroking the pistion? It seems like they are for a high Torque ROF build, pulling the stronger spring back and releasing it quicker.

No.

Also High torque builds are for high FPS not high RoF. This is a mistake people seem to commonly make - one way to achieve a high RoF is to use a low ratioe gearset (13:1 or similar) and drive it with a high torque motor. This doesn't make it a high torque gearbox! You need higher torque gears AND motors if you're pulling a strong spring for high FPS but the down side of that is a reduced RoF.

 

[Tad]

I shall investigate the usage of the Helical gears, but it may be a future project that they get used on as it seems to be a large time sink for the "perfect" shimming, and not much gain.

Although if the noise in my gearbox is reduced and the gears are causing the noise, I shall add them after the rest of the options.

As for the Greasing, would this be suitable? -- http://www.halfords.com/motoring/engine-oils-fluids/grease/comma-cv-lith-moly-grease-500g

I realise it is a lot, but if it's perfect for the usage I will have it spare for other guns I end up maintaining.

 

[Lozart]

I'd go for this: http://www.abbeysupply.com/airsoft_gun_grease_lt2.html

 

[Lozart]

Or for those magical moments when you get the whole thing back together for the 98th (and final) time but suddenly realise you forgot to grease your gears - this: http://www.halfords.com/motoring/engine-oils-fluids/grease/3-in-one-professional-white-lithium-grease-400ml

 

[Lozart]

I'd say the CV joint stuff you've linked to is too heavy for an AEG gearbox, personally.