shimming

[wind_comm]

negatory, you need to start with the bevel and pinion! the "traditional" method just isn't as good and tears up pinions like crazy.

[boogiebot]

Originally Posted by wind_comm

we all had to start somewhere. not all of us were birthed into the airsoft world with dual sector gears, frankentorques, massive lipos and r-hops.

Yeah it was tricky but you're right I had to start somewhere. Still gots lots to learn so getting the knowledge from the members here is much appreciated

Originally Posted by ThunderCactus

Well since everyones looking at this thread, everyone does it different but here's how I shim a gun;
remove all the internals
put a .1-.3mm shim under the spur gear, then shim it from the top
I just close the mechbox shell and hold it shut myself, and check for axial play and if the gear spins freely
then remove the spur gear
throw a .4-.5mm shim under the bevel and sector gear, and I shim those at the same time
Then throw the whole set in, close the mechbox and put 3 screws in, then check to see if the whole set spins freely

Also important to note, once you re-assemble the mechbox, push back on the air nozzle to see if it moves back and forth freely, just incase you shimmed the sector gear too far into the tappet plate.

And speaking of that, I came in right when everyone was making the switch to NiMH, and the word was to always put stock parts in your gun. Our gunsmithing knowledge was crap back then lol

Thanks for tips ThunderCactus. This will definitely come in handy.

[wind_comm]

Gear Shimming Tutorial - YouTube
Bevel Gear Shimming Revisited - YouTube

do it like this! it should end up sounding like this:

http://youtu.be/hGe-tPycrfw?t=27s

shimming it spur first ends up whiny/chirpy and overall just bad.
also ALL gearboxes are different. because somebody used .5 here and .3 there doesn't mean yours will be the same! my old gearbox needed 2mm of shims on each gear! x.x

[ThunderCactus]

Odd, since I've been shimming guns for 5 years and have never done a bad one using my way. The only times they sound whiny is when people are using flat gears and there's lots of slop in the meshing.
The reason you think it'll sound chirpy is because some people overshim the bottom of the bevel and then are never able to get proper pinion engagement on it no matter how high the motor sits. If the motor doesn't engage perfectly I'll drop it down to a .3mm shim, but I've never had to go below that.
But like I said, everyone's going to tell you to do it differently

[wind_comm]

the bevel-pinion method results in full engagement of the motor pinion. way quieter, way more efficient, less wear all around. you really need to try it and see the results.

The only times they sound whiny is when people are using flat gears

...sooooo...everybody?

believe me man, in the 3 or 4 years I've been working on my gearbox(es), I've taken it apart and reshimmed it so many times, trying to get it right. a bevel shimmed gun (preferably with a mosfet) is something special to behold.

[L473ncy]

Not to discredit you but I'm pretty sure that TC has a good idea of what he's doing. He kind of does similar stuff for a living and I'm sure that he's experimented a hella lot with different methods and has settled to his method.

[MaciekA]

When you shim starting from the spur, you are obscuring the path to the optimum shim solution because the spur's location is at least somewhat if not wholly dependent on the pinion-bevel mesh (depending on brand/fitment/gearbox type).

When starting with the spur, you're "winging it" to some degree, which hugely extends iteration time. If you can test a greater number of shim solutions than your competitor in a given amount of time at the work desk, then you will have a better shim solution faster.

Worst of all and most importantly, shimming from the spur will make it impossible to test your shimming solution "from the bottom up" as you go. Testing from the bottom up quickly informs you whether you've got problems.

I think we should be suggesting the method which is well-known to be more reliable across a wider range of brands, tolerances/precision, workloads, and skill levels... and is less likely to lead newbies astray.



Shimming from the pinion-bevel mesh first enlightens people as to why they're shimming, because the results of bad positioning are the most obvious at that mesh. The pinion-bevel mesh is the most difficult shimming in the system, and the remainder of the gears are dependent on the bevel being set correctly.

Proper shimming is like a search algorithm which explores all the permutations of positions to find the best solution. The possibilities are arranged as a tree from most-influential to least-influential (or most-dependent on the next influencer over). Spur-shimming advocates starting several levels into the tree instead of at the root, which is wrong.

Instead, by starting at the pinion-bevel point, (the root of the tre), no further motor adjustment will be required once you've "solved" this point. Also, since you've only got one gear in your gearbox at the beginning, you will be able to quickly test whether everything is good by slapping your motor grip on there and checking if it sounds correct. A bad pinion-bevel mesh can be detected very easily at this point, especially if your shimming has left no possibility of movement. As you progress to the dependent gears, you will require less time to test each solution because everything you've passed is already "solved" and you can leave it be (assuming you don't end up with a high sector, but this can be avoided by keeping the spur as low as possible while still engaging the bevel with as much contact as possible).

Think about it: If your bevel's range of movement has already been limited by your spur and none of its available positions are optimal for the motor's pinion gear, then all you can do is worsen the situation by moving the motor downwards (a common piece of bad advice). This lowers torque, increases stress, greatly increases the likelihood of slip, which leads to the stripping of your pinion gear or too much load on your motor. You can avoid even having to make this mistake in the first place.

Pinion-bevel shimming can be done almost mechanically with no thinking. Just a simple loop of adjusting, observing, testing and re-adjusting. We should be telling everyone to do it.

[MaciekA]

Originally Posted by L473ncy

Not to discredit you but I'm pretty sure that TC has a good idea of what he's doing. He kind of does similar stuff for a living and I'm sure that he's experimented a hella lot with different methods and has settled to his method.

This is a fallacious argument of appealing to authority. Are you certain you want to pursue this line of thinking? I don't think it will be a fair debate, since those of us who are ASM readers can simply checkmate everybody by name-dropping ASM members, who collectively have thousands of times more experience, proof and authority than anyone on ASM. If we're debating shimming techniques in public view of newbies, I say we keep it scientific and practical...

[MaciekA]

Also to not discredit TC, I will agree that he's been doing this for a long time and that his method might work for him, but that doesn't mean it isn't trumped by pinion-bevel shimming in the grand scheme of things. Different or new ideas overturn existing ones all the time.

[ThunderCactus]

Yes that is the better, more exact way

[L473ncy]

Originally Posted by MaciekA

This is a fallacious argument of appealing to authority. Are you certain you want to pursue this line of thinking?

Well, to be honest I'm not a "do-er" I'm a "follower" so yeah I do usually appeal to authority. Too many "wasted" hours and sleepless nights of experimenting wondering why I'm doing this. I just want a solution that is validated and works. If I can get a solution that's approximately right (maybe not 100% optimal) that's usually good enough. Basically like an NP Hard problem being solved using Heuristics.

Don't get me wrong I still like experimenting and all but I'm now a really big fan of validated off the shelf stuff that just works or easy to follow instructions.

[ThunderCactus]

Either way reaches the same result anyway lol
Starting from the bevel just prevents you from having to take it apart later when you realize the bevel isn't in the adjustment range of the motor

[boogiebot]

more good info. and i am sure that both methods have their pros and cons. from what i have seen and read both methods are used by various techs and enthusiasts with success.

that said i do have a questions regarding shimming and starting with the bevel gear. if you start from the bottom and add a shim and put your pistol grip back on how can you see how close the motor gear aligns with the bevel?

[ThunderCactus]

leave the mechbox open, or close it up and see if your bevel gear has any axial play
anyway you always check motor height after reassembling the gun anyway

[boogiebot]

Originally Posted by ThunderCactus

leave the mechbox open, or close it up and see if your bevel gear has any axial play
anyway you always check motor height after reassembling the gun anyway

Thanks for the explanation :tup: