When you decide to customize the internals of an electric airsoft gun yourself, I think the first hurdle for many people is how to adjust the shims (that was the case for me).
Regarding shim adjustment, I've seen many resources that rely heavily on intuition, which I think isn't very helpful for beginners.
So, although it's my own method, I'd like to share it because I believe anyone can do it if they're willing to dedicate enough time to measuring and quantifying the gaps using tools, rather than relying on intuition.
There are various methods, but I will introduce a method based on the bevel gear, which is basically the biggest source of noise.
I think the work would be faster if I used the spur gear standard, but since I'm doing this on my own, I prioritize accuracy and quiet operation over saving time, so I'm using the bevel gear standard.
*This article aims to provide educational explanations from a mechanical engineering perspective regarding the safe hobby use of airsoft guns.
This does not promote acts of violence, the use of weapons, weapon modification, practical evaluation, or violation of laws and regulations.
What to prepare
First, as preparation, in addition to the complete gearbox assembly you'll be customizing, I'll introduce some recommended accessories.
Thickness gauge used in the maintenance of motorcycle and car engines
- A sheet (paper) for sorting the adjusted shims.
- A box with dividers that make it easy to see the thickness of the shims.
Sim
Sorry the paper is dirty (I've used it many times).
A thickness gauge is a measuring instrument used to measure gaps, and you can probably find them for under 2000 yen at home improvement stores, auto parts stores, or on Amazon. Ideally, you should get one made of iron.
Thickness gauge
A cage that's too large won't fit in the gearbox, so a smaller one would be better.
Any shim will do, but I use Lilac's shims because they're readily available (thicknesses are 0.5, 0.3, 0.2, and 0.1).
I think there are some that are divided into even finer thicknesses, but I haven't had any particular problems with this one.
Sim
Any product from a well-known manufacturer should be fine.
Finally, a divider.
Measuring the thickness of each SIM card is a hassle, so having one ready is very convenient. For example, ice molds for refrigerators and other kitchen utensils often seem to be inexpensive and easy to use.
Now, let's go through the shim adjustment process.
This explanation will use Gearbox Ver. 3. The process is basically the same for other versions.
Review of the names of the components in the gearbox for the purpose of explaining shim adjustment.
To explain, let's first review the names of the various parts inside the gearbox.
As shown in the picture, the muzzle should be on the right side, with the lower gearbox on the left (L) side and the opposite side on the right (R) side.
There are various ways to refer to it, but here we will use the terminology shown in the diagram.
Positioning the pinion and bevel gears (shim placement in the right gearbox)
First, we'll position the bevel.
Assemble the bevel gear (without shims) into the R-side gearbox, which is the opposite side from where the anti-reverse latch is located.
The motor is then installed.
Here, we change the position of the motor to adjust the meshing between the pinion gear and the bevel gear.
Adjust the pinion gear so that it fills the tooth width of the bevel gear (by turning the screw on the bottom where the motor is attached).
Next, I will post photos before and after the adjustment.
Before adjustment
After adjustment
You should be able to see that the position of the pinion gear has changed. Let's try looking at it from a different angle.
Before adjustment
After adjustment
herePlease be careful not to hit the protrusion of the anti-reverse latch.
A gap of approximately 2mm between the latch and the motor pinion is sufficient.
I won't go into a technical explanation of gear noise here, but from an engineering perspective, the noise from spur gears tends to decrease as the meshing width and face-to-face meshing ratio increase.
The front meshing ratio is determined by the gear specifications and cannot be changed, but the meshing width can be adjusted, so we maximize the width.
If you are interested in this kind of thingMy Mechanical Design CoursePlease take a look.
Now that the positions of the pinion and bevel gears are determined, the next step is to measure the gap between the gearbox and the bevel gear to determine the amount of shim needed.
Insert the thickness gauge into the back of the bevel, adjusting its thickness as you go.
Stop when you feel it's getting a little too tight to insert.
If you try to force it in, the gauge will go in too, so stop when it's thick enough to offer a little resistance.
Based on my experience, the most common thickness seems to be around 0.6 to 0.8 mm.
In this sample, we found a gap of 0.9 mm.
If we insert a 0.9mm shim here, there will be no gap, so we'll leave a 0.1mm gap to make it 0.8mm.
In my case, I'll go with two SIMs, one 0.5 and one 0.3 (I try to use as few SIMs as possible).
Now that the positions of the pinion, bevel gear, and gearbox are determined, we'll determine the positions of the remaining gears.
Sector and spur gear positioning (shim setting for the right gearbox)
Next, we'll decide on the sparring positions.
Now, we'll assemble the bevel gear (with the shims we decided on earlier) and the spur gear (without shims) into the gearbox.
In most cases, there is no gap between the bevel gear's anti-reverse latch and the spur gear.
Therefore, insert shims until a gap is created here.A very small gap is sufficient.
Conversely, if you leave too much space, the gear meshing width will decrease, so please minimize it.
Can you understand this from the image? This determines the thickness of the spur shim.
Next, we determine the shim size for the sector gear.
Attach a shim to the spur gear you just decided on and install the sector gear into the gearbox. (The bevel gear is optional.)
When you assemble it, in most cases the gap between the spur gear and the sector gear will be larger.Insert shims until the gap is minimized.I'll go (just barely avoiding contact).
It's hard to tell from the photo, but the gaps have been reduced.
This determines the sector's simulation.
Let's organize the Sims here.
This completes the determination of all the shims on the right side of the gearbox.
Shim setting for the left gearbox
Next, without inserting any shims, assemble the spur and sector gears on the left side of the gearbox, which is the opposite side from before.
If the spur gear rubs against the gearbox wall, insert the smallest possible shim (in most cases, a 0.1mm shim).
Next, since there is often no gap between the spur gear and the sector gear, insert a shim to create a gap.However, please keep the gap to a minimum. Just a tiny bit is fine (it's okay as long as you can't touch it).
The position of the left bevel gear is determined by the motor's pinion gear, so I don't use shims.
This determines the basic shim thickness.
Now, we'll put all the shims we've decided on into the gearbox and assemble it.
You can start from either side of the gearbox, but lightly tap the spur and sector gear axes with a screwdriver or punch.
In most cases, there will be some play, so adjust it by inserting shims of the same amount into the left spur and sector gears of the gearbox so that the play is approximately 0.1 to 0.2 mm.
This will determine all the Sims.
Finally, as a final check, insert the shims you decided on, assemble the gearbox, tighten the bolts on the gearbox, and rotate each gear to check it.
In the photo below, the motor is connected to power to rotate the gears, but if that's too much trouble, you can remove the motor and rotate the gears by hand to check. Also, if tightening all the bolts in the gearbox is too much trouble, just tightening the bolts around the gear shaft will suffice.
If you have any resistance here,Basically, adjust by reducing the shim on the left side by 0.1mm at a time.I will try to avoid touching the settings on the R side as much as possible.
This is because the position of each gear is determined based on the bevel gear on the right side, so if the reference point is off, there is a high probability that everything will have to be redone.
If each gear rotates smoothly, the shim adjustment is complete.
The effect of shim adjustment
Let's check the effect of the shim adjustment before and after the adjustment.
The contents have changed this time, so it's not really something that can be directly compared, but I've included a video for reference.
The model is the LCT AK74. Both use the same battery.
This is the video before adjustments were made.
LCT AK74 straight out of the box
This is the video after adjustments.
LCT AK74 Custom, slightly high-cycle, after adjustments.
You should be able to confirm that the noise from the pinion-bevel gear has decreased.
Basically, the sound will be so quiet that you can barely hear anything other than the sound of the pistons striking.
If the noise is still too high after this, the only option is to change the motor's pinion gear.
Also, the anti-reverse latch may make a clicking sound, but I don't think there's any way to eliminate that sound other than replacing the latch.
Summary
In summary, the general order is as follows:
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If possible, even if you're only changing the motor, we strongly recommend performing shim adjustments.
Many overseas-made electric airsoft guns are quite noisy, so adjusting them can be very effective, and you'll likely notice a significant difference before and after the adjustment.
Furthermore, while the products from Japan's largest manufacturer perform wonderfully right out of the box, as they are mass-produced items, there is still room for improvement, and I believe they can be made even better with some fine-tuning.
However, just because it's noisy doesn't mean it's completely unusable right out of the box. The presence of noise simply indicates that mechanical loss is occurring.
If any of you are having trouble with sim adjustments, please use this as a reference.
Once you get the hang of it, the shim adjustment itself can be done in about 15 minutes and you can get it right on the first try.
Moreover, the noise is almost completely eliminated, and all you hear is the clicking sound of the anti-reverse latch. If you feel like it, I think you'll find it surprisingly easy and fun to try.
Thank you for reading this lengthy explanation.
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