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Discussion Starter · #1 · (Edited)
Hi guys!

I got stuck in sixon's thread http://www.airsoftsniperforum.com/43-longrange-aegs/7606-hk417-dmr-2.html#post94007 talking about a mod that replaces the old Sorbo-mod lots of guys use.

Check out my post in Sixon's thread for links to facts and examples. (link above)

Most of you guys already know and use the sorbothane-mod to save your
gearbox from cracking and it also helps with AOE but it's an old method that
needs to be rethought.

Why? well Sorbothane is a visco-elastic material that compresses quickly but
resets slowly, ideal for damping in most situations but in AEG's when the piston
constantly puts force on the sorbo when in "relaxed mode" it compresses
and once you start shooting there's no time for the sorbo to actually decompress and reset.

Sorbo has been the best sollution out there for quite some time but we need
to think outside the box and not only focus on what material to use, but how
to shape it to give the piston a gradual damping, using a material that resets
quickly!

I have been doing this mod to all of my builds for several years and i build
about 2-3 rifles a month and none has failed or even showed signs of
wear and tear.
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For this guide i will be using an old random noname cylinderhead with a flat
rubber damper, slightly thicker than they usually are.



I use a vice to secure the cylinder head and then pries off the rubber pad which
is superglued in most cases, all cylinderheads are different.



doesn't matter how careful you are, you'll always get residues left if the pad
is glued to the cylinder head.



I use a flat head screw driver to scrape off most of the glue making sure the silicone
wont stick to something that's loose.




The cylindrical rise in the center is not needed so i just used a drill or similar to
cut it down and instead make a slight countersink



take some shrink-tube and slide it over the nozzle tube to protect the surface.



Use a regular screwdriver with variable speed control and fit the cylinder head
loosely making sure you dont damage the nozzle tube.



Take some sanpaper like 500 grit or so and "lathe" the surface a bit, clearing it
from most of the residues plus giving the silicone a good surface to grip on



Now, apply a generous amount of silicone to the cylinderhead - i use a 8$
aquarium/window-fitting silicone readily available in any hardware store.

Here's a hint from BuMS - Thanks for letting us know

I've just tried this mod again, and I've learned something.
Normal building/universal silicone won't work, only glass/aquarium silicone will work.
The building/universal silicone is a lot softer, stickier, and is very hard to work with.
I was close to dismissing this mod, as being close to impossible.

Hammar: You might want to underscore, the importance of the right choice of silicone,
in the first post. So anyone(else >:D) don't think that silicone is just silicon.



now turn on the screwdriver at low speed, wet your finger with saliva and start
molding, keep it wet so it doesn't stick to your fingers and create this shape.



Better to add too much silicone from the beginning and then remove small amounts
as you go, than to add silicone to an already applied surface, it will not be as strong
or solid as one proper application.

Bare in mind, some builds need more AOE and some less, if you run a high
power setup then the resting-point of the piston will be further in than if you're
building a high-speed setup so shape the silicon-dome accordingly.

Let the Silicone rest and cure for 24 hours before doing anything to it.



When the silicone is cured then use a hole-punch to cut out the center.
I use 8mm most of the time.



Center it carefully and use a hammer to knock out the center part, make sure you
get all the way down to the plastic, when you've done this a couple times you'll know
how hard you have to hit to get to the plastic without damaging it in one punch.



Then use pliers to grab the center part and rotate to get it out.



And wolah!




Here's a video of me making a quick mold.

The whole idea behind this design is to gradually increase the braking-force of the piston
reducing the energy transferred into the gearbox, and instead of using a visco-elastic
material like sorbo, changing the actual design and using a material with no memory
is a far better sollution.

This works, and since it's silicone it resets immediately, making sure the cylindervolume
stays the same for each shot - consistency is the goal here.

Sorbo is a thing of the past and should stay there since it's a material that has a slow
inertia, when your battery is getting tired and the cycles aren't as fast, the sorbo
has more time to reset, taking up more volume in the cylinder, and if it's one thing
we don't want, then it's a variable cylindervolume..

Give it a go and let me know what you think!

Once i find a camera that can zoom in and video i will show the softness and compression
of this thing, giving a clearer view of how it behaves.
 

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That is a fantastic write up & idea!

Vindi introduced me to a similar solution some months ago but instead of shaping it we have been flattening it and like how sorbo is now.

I'd like to point out that you need to be sure to do this with a high quality sealant! If you use a low quality sealant it will take considerably longer to cure all the way through or may not cure at all! I speak from experience here, I bunged up my gearbox twice before I discovered the issue ;-)

May I also recommend this article for stickying by the mods.
 

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Discussion Starter · #3 ·
That is a fantastic write up & idea!
I'd like to point out that you need to be sure to do this with a high quality sealant! If you use a low quality sealant it will take considerably longer to cure all the way through or may not cure at all! I speak from experience here, I bunged up my gearbox twice before I discovered the issue ;-)
Hehe true that, I only use Casco products since they have been around for almost 100 years now, they know what they're doing! i stamp the center after about 24h and try not to install it in a gun before 48h

thanks for the feedback mate :)

gonna make a test with 2 sportline gearboxes and a 130 spring in both, this mod in one ofem, and one stock. gearbox and motorgrip, full auto :)
 

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I have been thinking of the same exact thing! I've also noticed that sorbo doesn't reset very fast and I figured that silicone would absorb impact as well as reset much faster than sorbo. I was just thinking of using a flat sheet of silicone with an airbrake piston head with an o-ring glued to the front to reduce the slapping sound. Great minds think alike! :tup:
 

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I was contemplating this myself. I used a flat facing version of this mod in my g&g m14 but there is no reason why you couldn't replicate this shape and then remove the section for the nozzle from the raised portion rather than the centre.

I would like to note that it'd be a good idea to work out how much aoe you need before you do this.

Afterthought on the afterthought is we need to work out how big the compressed silicone is... Cause you could get your aoe right without spring pressure and then discover that it's not enough when the spring is in.

Sent from my HTC One using Tapatalk 2
 

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After doing some research and some calculations. Keeping it a flat surface with a conical middle actually improve this for surface area. Also mixing in dish soap and molding it to with your hands works nicely and helps it cure withing 15-30 minutes but I say do not test till 10 hours.
 

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Discussion Starter · #11 ·
hmm Sanguinor:

There's no real way of telling how much further in the piston is gonna be, you're gonna haveto do this by feel, ive tried like 10 different profiles and most of them (part from flat surface) compress about 3mm at the most, as long as AOE is in the ballpark it wont make much of a difference.. :cheers:

i havent experimented with V7 cylinderheads yet so i cant really tell how it would deform if the cutout for the air outlet is off-center but my guess is it wont matter much, as long as it deforms reasonably even around so the piston has a fairly even and centered bumper stopping it.

Deathfinder, What type of calculations did you do? .. And what does it improve? your post is a bit confusing hehe

i wouldn't say dish soap would help much in terms of curing but it sure becomes easier to work with. :shot:

it takes at least 48 hours for the silicone to really firm up and grip on to the plastic cylinderhead, so even if it is "solid" after 10 hours i still dont think it would be a good idea to actually put it in a gun since it might slam the whole bumper off the cylinderhead due to vibrations and tearing when expanding and contracting.

Surely this depends on what silicone is used, but with the casco Glass-silicone im using, 10 hours is way too early =) :tup:

Next week my other V2 sportline Gearbox will arrive =) then let the testing begin! (errh, well ive tested it for a year now but i meant the video hehe)
 

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just a small question, is it take-off a lots of air-volume ?
 

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Shucks. I guess I'll have to get rid of my 50 dollars worth of sorbo pads i've stockpiled up now.

Imm attempting this mod within the next month. Gotta clear the workbench first.
 

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I think I'm going to try this on my BASR VSR-10 Cylinder head!
 

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Discussion Starter · #16 ·
Thanks for making this a sticky =) I'm honored!

just a small question, is it take-off a lots of air-volume ?
well, yes of course it takes up volume in the cylinder, but i'd say it's enough air left for most barrels from 500mm and below, fixing AOE by putting spacers between the piston and pistonhead also takes up volume, cant really escape from it...

Shucks. I guess I'll have to get rid of my 50 dollars worth of sorbo pads i've stockpiled up now.

Imm attempting this mod within the next month. Gotta clear the workbench first.
Sorry bout that mate, maybe you could use it as inserts in the motorgrip or something to reduce vibrations and also resonance? Sorbo can be used to alot of things hehe, cheer up!

Let me know how it turns out, document it and share =)

I think I'm going to try this on my BASR VSR-10 Cylinder head!
It'll be interesting to see how it performs in a Bolt-action rifle =) same goes for you, Document the work and share!
________________________________________________________

Just received a call from my local HOBBEX-store and they have another gearbox waiting for me, so if i have the time tomorrow i'll go get it, lets start testing and see what's what =)
 

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Hi ! Just a quick question. Could this be done on the V7 cylinder head ? As you may know on the V7 cylinder head, nozzle tube is located in the top of the head not in the center.
 
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