15. 09. 2018
Our shop started the offer of our own gearbox shims recently. The shims are used to correct the movement will/gaps of electric airsoft gun between gear and gearbox. Our shims are manufactured from plated steel and they are 0,1mm thin. We do not recommend using shims made from non-ferrous metals (for example copper or zinc), because even shims are under pressure and they can cause destroying of the gears by for example: jamming the shim or cutting it. Thats why we bring to you this guide.
We recommend using 0,1mm thin shims, because of gentle setting of the gaps between the gears and gearbox.
Shimming your gears is not a big science, but if you want to do it in the correct way, you need some time with it. Gears in AEG are mostly three, there can be also four, but we will focus today on the three gear standard. For better understanding, we will show the shimming of the gears in our CNC split gearbox lower.
Picture n.1 - Motor gear is located closest to the motor and deliveres the rotation from the motor to the center gear, this gear has also the highest rotations. Motor gear has the "Cornerstop", which prevents from overturning the gears when the piston is not fully loaded, with help of anti-reversal latch.
Picture n.2 - Center gear deliveres rotations from motor gear to the piston gear.
Picture n.3 - Piston gear deliveres rotations from the center gear to the piston.
For the best performance of the gears, we need a high quality bushings or bearings, the main difference of them and how to use them are in this article, next we will need a shims and vaseline. For better manipulation and shimming, we recommend to remove most of the gearbox parts.
Picture n.4 - Lower par of the split gearbox, before change of the gears.
Correct guide for the shimming of the gears
First step is always full cleaning of the gearbox and correctly installing of the bushings/bearings, by stamping or glueing. How to do that is in this article.
Picture n.5 - Removed trigger switch and gears from the gearbox. For the cleaning of the gearbox is used Loctite SF 7063 cleaner (Picture n.6).
Picture n.7 - Cleaned gearbox. We need to remove rest of the parts and change the bushings.
Picture n.8 - Installed bushings with combination of the bearings on the motor gear.
The bushings and bearings needs to be installed correctly and they needs to be under the surface of the gearbox. If the flange of the bushing would be above the gearbox surface, it can cause jamming of the gears. If you have bushings or bearings in the right position, we can start with setting up of the two 0,1mm shims on the center gear for the left side of the gearbox (gearbox is divided into two parts, left and right, the markings of the gearbox sides is made by shooters side, because the left side is more complicated and there is installed for example trigger switch).
Picture n.9 - Correct minimal movement will between center gear and gearbox.
There must not be anything that could cause the jamming of the gear. Some of the gears could have angle teeth so the left side needs 0,5mm shim (or 5x 0,1mm shims). Do not use any vaseline.
Picture n.10 - Zero gap = jamming of the gear to the gearbox.
Picture n. 11 - Set the both sides of the gearbox together and check the gap. Count the size of the gap, remove side of the shell and add on the center gear needed shims.
Set all both sides of the gearbox together and screw it. It is more longer procedure, but we can be sure, that this work will have perfect result (yes, you can press whole gearbox in your hands, but the results of the shimming can not be precise, that is why we recommend to screw it). We can see now, if the center gear turns or not, or we can use tweezers and we can push through the bushing and finds out the movement will. If the center gear is not turning around at all, we need to remove at least one 0,1mm shim. This procedure is repeated, until the gear turns around freely and do not have any side will.
Picture n.12 - In our case, the gears have too high shafts and they look out from the bushing, that is why we need to change the ratio of the shims. This means, that we need to add 3 shims to the left side from the right side, that means that the gear will still move freely, but it will have higher gap from the gearbox.
Picture n.13 - Different ratio of shims instead of original plan. The gear has bigger gap from the gearbox now.
After finishing this procedure, we continue on the motor gear. For the left side of the gearbox where motor gear sits, we add at least one more 0,1mm shim more, than on the center gear. Otherwise the gears would be jamming on themselves. On the angle teeth gears (sometimes and on someones), there is a need of more shims, for example 0,3mm (3 x 0,1mm shims).
Picture n. 14 - Shims on the motor gear.
Picture n. 15 - Most important is the gap between center and motor gear. If there is not any gap, the gears would be jamming and that can cause breaking of the teeth on the gears.
Set both sides of the gearbox together and screw them. Like in the center gear scenario, we will do the same with the help of the tweezers and correct any movement will.
After this procedure, screw the gearbox together and find out, if the both gears turns around freely, if not, remove the shims from the motor gear, until it is turning around freely without any side will. Important part of this is to take care and look on the both gears, the gears must not be jamming together, because that would cause more pressure on the motor and the gears could grind out steel dust into the gearbox. Apply this procedure until your gears turn around freely without any side will in the screwed gearbox.
For the last gear, we apply similiar procedure. Add at least one 0,1mm shim more (than on the center gear) on the piston gear to the left side of the gearbox, set both gearbox parts together and screw them. It is important for the piston gear that it would not rub the gearbox edge and add enough shims, so there are enough gaps between gears and gearbox.
Picture n. 16 - Last gap between piston gear and gearbox which we fill with shims.
Picture n. 17 - Check with tweezers through the bushing if there is will in gears. The screws must be tightened (Picture n.18). If you did everything correctly and with care, there should not be any, or minimal (healty) will.
Correctly shimmed gears should run perfectly without resistence, even on the bushings. This video shows smooth gear run WITHOUT THE VASELINE. After lubricating with vaseline, there will be even lower resistance on the gears.
During shimming process, there could be situation, where the gear without shim has movement will and after adding shim, it will turn around badly. We recommend in this scenario skip the shim and let the gear have the "healthy movement will", than hardly tight shimmed gears. After shimming process we recommend to "glue" shims with vaseline on the gear shafts, because you need to remove gears for installation of the other inner gearbox parts and you can not drop them by this way.
Next video shows up the spin around of the gear with pressured air. It is the last proof, that the gears spins freely without jamming.
Last thing is the lubricating of the gears. Use a thin layer of vaseline on every parts of the gears where they connects together or where they touch together, for example sharfts, teeth etc. There is no need of lubricating of the gear basic surface. Overlubricating is releasing during time into the gearbox and can cause short circuit for example in the process unit/ECU, if it is integrated in the gearbox. In our service center we use Loctite 8103 vaseline (Picture n.19).
Because of huge variations of the gears, made with different tolerations with different sizes, height of the shafts, there does not exist an exact guide or count, for the used shims on the direct gear. This guide is only for explaining purpose. Direct count or configuration of the shims depends on many factors. Vaseline can be used almost everyone, but not silicon one, which has huge density and has glue effect. Silicon vaseline is used mostly for isolating of the electrical sources, thats why we do not recommend to use it for the rotational parts. There is no need of overlubrication, only thin layer of vaseline on the parts where they touches or work together is enough.
