Shimming Helicals.. High, low, or in between?
 

:confused:

I shimmed my new helicals last night... took over 4 hours... It was my first time so don't make fun of me!

Anyway, there is pretty much no lateral play, and the gears spin like 5-7 revolutions freely with the gearbox screwed tight.... The things is, when it's all assembled, those things are LOUD... way louder than normal... No grinding though... Teeth are completely contacting eachother.

I just got back from the skirmish today, and people where telling me how loud the gears were.... Surprisingly enough, I didn't get any problems, jams or lockups.

I spoke to a gundoc there who asked me how i shimmed them. I followed the guide, shimmed the spur as low as possible to clear the bearings and irregularities (if any) on the inner gearbox surface. Then, I shimmed the sector as low as possible but making sure it doesnt rub the top of the spur or cutoff lever... lastly, the bevel, as instructed.

He told me all the gears are supposed to be as centered as possible in the gearbox, not as low (to the left) as possible (for the spur and sector).

I looked everywhere for a proper guide on shimming helicals specifically. There are some threads, but none are very specific. All the guides for straight cut gears say to shim the spur and sector as low as possible. And ive skimmed throught ALOT of guides.

Your insights are greatly appreciated!

-Adam.






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+1

+2

Of all the popular shimming articles, guides and threads I only saw 2 of ~15 that actually mention starting with the bevel gear, not the spur. (Excluding this one ^:D)

I restarted, but from the bevel this time and shimmed according to its height and my gun is as quiet as a mouse fart compared to before. AND my motor doesn't heat up one bit like before, AND my rate of fire skyrocketed.

I inserted my bevel, attached the motor cage with the motor inside, and tried different shims on the "top" of the bevel gear. The 0.2 worked best. What's weird is most people say that they try to keep their bevels as low as possible, like the spur gear, which IMO is totally stupid. It's pretty much forcing the pinion and bevel together... after a full skirmish like that, I was surpised to see NOT ONE BIT of wear on the pinion or bevel and believe me, they were TIGHTLY shimmed together.


+1 for king arms gears.

Like the man with the minigun says in the video. The pinion/motor is the only gear that has ONE fixed position... Logically, it's imperative that you start with the bevel and work your way from there.

I feel this is a large issue with online airsoft-tech databases; When searching for shimming guides, 90% say to start with the spur and work out from there.... which couldnt be more wrong.
They don't even MENTION this specific method for the bevel particularly.

This whole start with the bevel gear should have it's own sticky thread and smeared all over the online airsoft world, for the good of our guns, pride and money.

Heres how i did it
http://www.airsoft-barracks.com/foru...howtopic=24099

A good video.
YouTube - ‪Airsoft Minigun V2 V3 Gearbox Shimming Different Technique‬‏

Shimming helicals is the same as shimming standard gears.
Make sure your bevel gear clears your pinion gear on your motor though. If you adjust your motor height all the way down and it still sounds screamish, you need to reshim your bevel gear.
And be sure to properly adjust motor height after shimming your gears.
Raise it up until it stops whining, but not so much that it screams.

So the spur and sector are to be shimmed as low as possible? If so, than I can rule those out of the equation... that leaves just the bevel... I can't understand how that single gear is making all the noise... well, I'll give it another try. Any other tips?

Well if your bevel gear is crammed against the motor, it's going to make a lot of noise.

Shim Bevel gear first. Raise the motor so the pinion gear is in the middle of the bevel gear, then shim the bevel gear so it's high enough to make as much contact with the pinion gear. Then shim the others as normal. Try and shim everything so the teethes makes as much contact with each other as possible. Most screeching noises come from the pinion or bevel gear.

Their is a mathematical way of shimming gears that I have used.

You will need a set of digital calipers and a way to measure the left side to right side spae between your gearbox shell bearings.

It's VERY straight forward and anyone with a high school diploma can do it.

If your gears are making a lot of noise it's very likely that your bevel gear is not properly shimmed for your pinion. Generally I start with a 0.20 shim on the spur gear, then start shimming. I have found from experience that 0.20 is near the ideal clearance between gears. Take a shim and put it onto the spur and rotate the gears while putting pressure on the axles of all the gears. The shim should clear without problems each other gear.

+1

+2

Of all the popular shimming articles, guides and threads I only saw 2 of ~15 that actually mention starting with the bevel gear, not the spur, Excluding this one ^:D

I restarted, but from the bevel this time and shimmed according to its height and my gun is as quiet as a mouse fart compared to before. AND my motor doesn't heat up one bit like before, AND my rate of fire skyrocketed.

I inserted my bevel, attached the motor cage with the motor inside, and tried different shims on the "top" of the bevel gear. The 0.2 worked best. What's weird is most people say that they try to keep their bevels as low as possible, like the spur gear, which IMO is totally stupid. It's pretty much forcing the pinion and bevel together... after a full skirmish like that, I was surpised to see NOT ONE BIT of wear on the pinion or bevel and believe me, they were TIGHTLY shimmed together.


+1 for king arms gears.

Like the man with the minigun says in the video. The pinion/motor is the only gear that has ONE fixed position... Logically, it's imperative that you start with the bevel and work your way from there.

I feel this is a large issue with online airsoft-tech databases; When searching for shimming guides, 90% say to start with the spur and work out from there.... which couldnt be more wrong.
They don't even MENTION this specific method for the bevel particularly.

This whole start with the bevel gear should have it's own sticky thread and smeared all over the online airsoft world, for the good of our guns, pride and money.

Heres how i did it
http://www.airsoft-barracks.com/foru...howtopic=24099

A good video.
YouTube - ‪Airsoft Minigun V2 V3 Gearbox Shimming Different Technique‬‏

Well done. You learned a lot with this experience.

Here are a couple of things that I have learned over the years:

A) You don't have to start with the bevel gear, just know how the AOE with the motor is going to be.

B) A lot of people fail to watch this one: you must ensure that you do not go so low as to have the sector gear rub on the cutoff lever. This can cause premature wear of the cutoff lever. This can cause more noise than you may want in your gearbox. If you have to raise the sector gear significantly to clear the cutoff lever then the spur gear and bevel gear must be raised accordingly.

This does not refer to the OP situation. He now has perfectly shimmed gears.

I agree... I didn't get any rubbing on the cutoff lever. Even on a 0,2 (final config on a 0,3 to clear the spur), the sector didnt even touch the lever with the GB closed and screwed tight....


I also had a problem with my fire selector going all screwy on me... I was about to give up and take it to a tech when I realised that the irregularity in my selector plate could be causing it.... I looked up pictures of the stock vfc selector plate and noticed that mine was in fact bent, out of the factory!!! I bent it straight like it was in the pictures and the problem was solved!

My shim job at the moment is great, but I feel it could be even better. At the moment, my gears make the same amount of noise as my buddy's G&g m4 commando running fully stock on straight-cuts.... Maybe I should take it to a tech???


Or hone and re-shim it with a better shim set... I used systemas shim set, which only had 0.2, 0.3 and 0.5.... no 0.1 (which I could do without) and no 0.15 (which i feel is absolutely necessary for helicals).


Insights?

Helical gears are designed to take more torque than straight cut gears. The nature of this theory is that the helical design allows for more contact surface area at any given time; therefore the stress needed to cause failure at a single point (usually a tooth) is increased. This increase in surface contact area also causes the gears to make more noise than straight cut gears.

The fact that your gun is much quieter than before tells me that you have a good shim job. You had a pretty good shim job and just moved it up a point or 2 of a MM. I am very impressed and if I were you I would try to ride this gear set for 100,000 cycles. If you get that then your job was superb.

I need to know: What spring and fps are you running here? What is the gun?

I just read some gear talk and I read that helical gears are quieter than straight gears in transmissions, so part of my theory could be wrong.

I can find quotes of people saying both. My thoughts in my previous post (more contact area) are why I believed the louder theory. I don't know what to think now?? ENGINEERS? PHYSICISTS?!? PLEASE WEIGH IN!

I must admit .. I beleive I fell into this too! .. however I do think my motor cage is crappy and screwing me around a bit too...

typically I start with the sector gear (for the rubbing and clearance of the lever) .. and then set the rest to match and not rub on each other, etc. and do date it was beautiful (lucky?... or I did it right .. just backwards LOL )

anyways.. my first set of helicals... motors pissed off, batteries getting hot, gun sounds like it's trying to pull a M260 or something... (this is with a 300% set, hi torque motor, and a M120 spring, on a 9.6)

anyways... I was just narrowing down on my undersight on the pinion to bevel when I caught this thread... I noticed that the helicals seem to be a bit "thinner" then normal gears and were stacked up a bit more then normal on the "top"

I think it also matter the company that machined the helical cut... I *beleive* that if the edges of the helicals are too 'sharp' they will be a little noisey till they 'wear in' ... where as they really high end helicals are softened on their edges (if that made any sense at all) part of the high pitch noise/whine of straight cuts are the super sharp edges

Helicals by nature arent as loud as straight cut
However, being fairly new to this, how do you know it's the gears making the noise, and not the pinion-bevel engagement?
There's an incredibly obvious difference in sound between a gun with a low set motor height, and a gun with a properly set motor height. It becomes much quieter once you adjust the motor.

The idea behind helical gears being quieter is due to the constant contact between the gear teeth. With helical gears, the broader contact area means that there is always a pair of teeth engaged as the gears rotate - ie, contact begins on the next set of teeth BEFORE the current set disengages. This gives a smooth and quiet transition between the teeth as the torque is gradually loaded and offloaded on each tooth pair.
With straight cut gears, as smooth as they can be made to be, there must be a clearance (and consequently, backlash) between the gear teeth to prevent the teeth from binding. This means that there is a small gap between when the current teeth are engaged and when the next set are engaged, and only one set of teeth are ever engaged at any one time. This causes extra noise and shock as the point of contact abruptly transitions from one tooth pair to the next.