This time, I'll be introducing a custom build of the ICS Sportline M4 CQB.

It was discovered that the part was damaged during the customization process, so it could not be completed.

This model is made of resin and has been in use for about 10 years, so please consider this as a way to share some know-how about what tends to break down.

Let's begin the customization process.

Custom

In my custom build, there's nothing particularly unusual about it; I simply change the parts and assemble them carefully.

This time, I'm aiming for a high-response, high-cycle setup by replacing old parts, mainly with a 13:1 high-speed gear and an SHS short-stroke switch.

The process follows the basic steps: gearbox modification and polishing, electrical work, component assembly checks, shim adjustment, and final assembly.

This time, I'll be focusing on the damaged areas, so I'll only briefly introduce the customizations.

This involves crack prevention processing for the gearbox and polishing of the sliding parts.

Processing the window frame of the gearbox

Polishing of sliding parts

This time, instead of using sandpaper as usual, I tried buffing with a rotary tool. It turned out quite nicely, so I'll be using buffing from now on.

Next, we'll build the electrical system.

I made this using Eagle Force's 1.25 sq silicon wiring.

Next, we will check the assembly of each component.

Check the area around the switch

Check the mechanical systems.

Since we use parts from various manufacturers, we perform a test assembly to check for any problems. We always do this because assembling without checking could lead to major issues later.

Since I'm using a Ronex A4 motor, the pinion gear isn't very good, so I'm going to replace it with an Eagle Force carbide steel machined gear.

If you install this motor directly into a 13:1 gear ratio, it will definitely cause piston failure, so you need to cut the sector gear.

This time, we'll go with the standard strategy of cutting three cards: one to draw and two to release.

The final step in the preparation is adjusting the AOE (Area of ​​Effect).

My method involves attaching Haneite rubber to the surface of the piston head to adjust it, as I don't want to make the piston too heavy.

After adjustment.

Performing a sector cut will inevitably shift the area of ​​effect (AOE), so it is highly recommended to check and adjust it.

It's obvious that the second tooth of the piston's rack gear needs to be filed down, but the third tooth also needs to be filed down a little because the sector gear sometimes interferes with the top of the third gear.

Now that we've reached this point, all that's left is shim adjustment.

I'll break in the motor while I'm adjusting the shims. The shim adjustment takes about 20 minutes, so it fits perfectly in terms of timing.

Now that we've reached this point, all that's left is to apply grease and assemble the parts, and the gearbox will be finished.

Lower gearbox assembly

Assembling the upper gearbox

This is completed.

The rest is the assembly of the hop-up chamber, which is the same as always.

The article is titled "G-HOP," but the method is the same, just using a commercially available hop packing.

This meant that 9% of the customization was complete, but then a problem arose. I was shocked because it had taken quite a bit of effort.

Now, let me introduce the damaged parts.

Damaged part

The damage occurred in the neck area, which is considered a weak point of the M4 series due to its resin frame.

The most critical damage was the broken screw threads that secure the delta ring.

I had heard that the neck area of ​​the M4 was weak, so I tried to tighten it as much as possible by applying threadlocker, but the threadlocker seeped into the crack and I discovered it.

I'm so disappointed.

Here's a brief explanation of ABS resin, which is commonly used for airsoft gun frames.

ABS resin is basically made up of a mixture of acrylonitrile (acrylic), butadiene (rubber-based), and styrene (expanded polystyrene-based).

It is very easy to mold, durable, and readily available, and is used in many products, but it does have a few weaknesses.

will be important.

Ozone-induced cracking

Ozone cracking is a phenomenon that occurs in all types of resins, including rubber, and is a fundamental cause of fracture in resin-based materials.

Ozone is represented as $O^3$, and the ozone layer that you are all familiar with is precisely that. Even near the Earth's surface where we live, when exposed to intense sunlight, a chemical reaction occurs and a very small portion of the oxygen in the atmosphere is converted into ozone.

Unfortunately, ozone has the effect of breaking down the chemical bonds (molecular bonds) in resins. Therefore, if resins are exposed to the elements on a sunny day, they will gradually deteriorate due to ozone.

One way to prevent this is to avoid exposure to ozone, which specifically means storing it in the shade or indoors.Is to do.

Generally, natural rubber is resistant to ozone, but many rubbers and resins used in industrial products are based on petroleum components.

UV degradation

Next, regarding the effects of ultraviolet light, it hardens all types of resins, including rubber.

This is a characteristic used in gel nails and 3D printers, but it's a rather troublesome trait from the perspective of resin durability.

If resin is continuously exposed to ultraviolet light, it will gradually harden and lose its toughness.

If this hardening process progresses to an extreme, even a slight impact can cause it to crack due to its excessive hardening.

The way to prevent this is the same as with sunburn: avoid direct sunlight.There is only.

Oil loss from internal components

The hardening occurs when the oil content of the final resin component is removed.

Generally, some types of resins absorb oil and are therefore considered strictly oil-free. However, in reality, all resins, including rubber, contain oil as an internal component, and this oil provides the appropriate toughness.

If this oil is left for a while or forcibly removed, the resin will harden.

If this hardening process progresses to an extreme, the material itself becomes too hard and cracks spontaneously.

Summary of basic properties of resins

These three main factors inevitably cause degradation in any resin.

A simple example is the cracking of rubber products, especially tires, on a car that has been left unattended for many years, which occurs due to a combination of these three factors.

This will inevitably occur with any resin, not just rubber.

Since I was designing engines for automobiles, I was particularly careful when using resin materials, including rubber.

Specifically, we made sure to keep the area away from direct sunlight that generates ozone, from ultraviolet rays, and to ensure adequate lubrication (using engine oil).

However, some resins, such as nylon (66 nylon), have high water and oil absorption properties and swell on their own, so the design takes the swelling rate into account from the beginning.

If you're using materials like silicone rubber in an airsoft gun, be careful because it will absorb silicone grease. A little swelling is probably okay, but if it swells up too much, it will throw off your aiming accuracy and stop working.

In this case, the damage occurred due to a combination of these three factors over a long period of 10 years.

IfIf you want to use your resin model for a long time, store it in a place where it is not exposed to direct sunlight as much as possible.

We will explain the more detailed properties of resins as mechanical materials in a future installment of our mechanical design course.

Adhesives (such as threadlocker) and resin

I've received some valuable insights from readers after the article was published, so I'm adding them here.

I was told that adhesives such as threadlockers contain ingredients that attack certain types of resins.

My investigation confirms that there is indeed such a warning label, and it appears to dissolve materials such as acrylic, polystyrene, and polycarbonate.

Apparently, this phenomenon is called chemical cracking.

As an engine designer, I have some experience handling metals and resins like rubber and nylon, but I haven't used ABS resin much, so I'm embarrassed to admit I didn't know much about it (I thought ABS was much more durable).

This seems to be related to the damage that occurred this time.

If you are reading this article,When using adhesives or threadlockers on resin, be sure to choose products that are suitable for resin.

However, since this damage was discovered immediately after applying threadlocker and tightening the screws, it is believed that the damage was caused by a combination of factors: aging deterioration due to ozone and ultraviolet rays, and the attack by the threadlocker.

However, even if threadlocker is aggressive towards plastic, it's hard to imagine that it would cause such a decisive damage as shown in the picture within three minutes of application.

However, since it gradually attacks the resin over time, it might be difficult to notice if used incorrectly, so I think it requires careful handling.

In any case, when using chemicals, including adhesives, in addition to resins, including rubber, it is best to exercise extreme caution.

I apologize for expressing my gratitude on this blog, but I am extremely grateful to the person who provided the information.

Thank you all!

Bonus troubles

The bearing surface in the gearbox was rough, making it impossible to adjust the shims properly.

The cause was that the bearing surface was not flat and the fixing was loose.

The bearing is not securely fixed.

After going through the trouble of adjusting the shims and doing a test run, the shims burned out because the force wasn't being applied evenly.

It's probably due to deterioration from long-term use. If you're experiencing noise or other issues with an electric airsoft gun that's been used for a long time, you might want to check the bearings in the gearbox. When replacing the bearings, be sure to assemble them carefully so that they are flush with the surface.

In summary, please be careful when handling resin models.