As we age, our skin inevitably changes—wrinkles, age spots, and dryness become more common. However, not all skin reactions should be dismissed as simple signs of aging. For many people in their 40s and beyond, an unusual response to sunlight could point to a deeper issue: photosensitivity, or sun allergy. So, how can you tell the difference between natural skin aging and abnormal sun reactions?     Typical Signs of Skin Aging Skin aging tends to progress slowly and predictably. The common changes include: Fine lines and wrinkles – Especially around the eyes and mouth Hyperpigmentation – Dark spots from years of UV exposure Loss of elasticity – Skin becomes thinner and less firm Dryness and dullness – Due to reduced oil production These changes are often symmetrical and consistent, and they don’t usually cause pain or itching.     What Is Photosensitivity? Photosensitivity refers to an abnormal skin reaction to s...

When connecting 18650 battery cells, the most common method is soldering. But you've probably heard the warnings — "Don't solder on cells," "Soldering causes explosions." Are these claims true? If so, what are the alternatives? In this post, we’ll explore the real risks of soldering and walk you through three safe ways to connect lithium cells without using a spot welder.     Why is Soldering Considered a Problem? Soldering involves applying heat to melt the solder onto a connection. The problem lies in that very heat . 18650 lithium-ion cells are highly sensitive to temperature, and anything over 60°C can start to break down the internal electrolyte. Improper soldering can cause the following issues: Gas Expansion: Excessive heat causes the electrolyte to vaporize, increasing internal pressure and potentially swelling or leaking. Reduced Capacity and Lifespan: Heat stress deteriorates cell performance and lifespan. Fire Haza...

Technology is evolving at breakneck speed. Smartphones are thinner, appliances are interconnected via IoT, and cars drive themselves. Yet, ironically, we often hear people say, "The old version was better." Why does this happen? In this post, we explore why technological progress can sometimes make things more inconvenient and uncover the hidden truth of design regression .     More features ≠ More convenience We tend to believe that more advanced technology means better products. But that doesn’t always translate into better user experience. Technological advancement does not always mean improved usability . In fact, we often see increased complexity, user confusion, and unintended limitations. For example, older refrigerators used mechanical door sensors that physically detected whether the door was fully closed. Simple, but reliable. Modern electronic sensors, while sleek in design, often fail to detect partially open doors—causing energy waste ...

When working with circular materials, the very first step is setting an accurate center coordinate. Whether you're using CNC milling, laser cutting, or 3D carving, even a slight deviation can result in off-centered designs or cumulative alignment errors. That’s why precise calibration is critical in any digital fabrication workflow.     Why Is the Center Coordinate So Important? Rotational or symmetric designs lose balance with center offset Symmetrical patterns may visibly shift to one side Misalignment in early steps leads to accuracy loss in later processes 3 Practical Ways to Find the Circle Center in CNC Work Manual 3-Point Edge Measurement — Mark three points on the edge, draw perpendicular bisectors, and find their intersection. Using a 3-Axis Touch Probe — Let your CNC machine scan edge points; software auto-calculates the center. Camera or Laser-Based Vision Systems — Use vision tools to detect the full cir...

Many users encounter situations where a 21V lithium-ion drill battery pack doesn't charge, despite the charger showing a green light. In such cases, the issue often lies not with the charger, but within the battery pack's BMS (Battery Management System). This post outlines how to determine whether the BMS or internal FETs are malfunctioning, and how to measure them using a multimeter.     Understanding FET Behavior Inside a BMS, there are typically two FETs (Field-Effect Transistors): one for charging and one for discharging. Each works like an electronic switch that turns on or off depending on the gate voltage supplied by the controller IC. Charging FET: Controls the return (negative) line from the charger to the battery pack. Discharging FET: Controls the negative line from the battery to the drill or load. When charging or discharging is allowed, the controller supplies around 10V to the gate of the respective FET. If the gate voltage is miss...

End grain cutting boards are prized for their durability and knife-friendly surface, but they require more care than ordinary boards. With the right maintenance, they can last 10 years or more. But if neglected, they can crack, mold, or warp. In this post, you'll learn the 4 key practices to keep your end grain cutting board looking and performing like new.     1. Oil It Regularly The golden rule of end grain board care is oiling. Because the wood fibers are exposed on the surface, they absorb moisture easily—and dry out quickly too. Apply food-grade mineral oil or a beeswax blend every 2 weeks to maintain moisture and protect the board from water damage. Tip: Let the oil absorb for at least 2 hours, then wipe off any excess with a clean cloth. 2. Wash It by Hand Only Never put your end grain board in the dishwasher. High heat and water pressure will cause the wood to warp or the glue joints to fail. Use warm water + mild dish soap + soft s...

We usually assume that if something is big, it takes up more space — and if it's infinite, it's beyond measure. But in mathematics, such intuitions can be shattered. A prime example is Gabriel’s Horn , a shape that stretches infinitely but has finite volume while possessing an infinite surface area. In this post, we explore the math behind these counterintuitive forms and the deeper meaning they reveal.     1. Gabriel’s Horn: Finite Volume vs. Infinite Surface Area Created by rotating the curve y = 1/x (for x ≥ 1) around the x-axis, Gabriel’s Horn has a finite volume of π but an infinite surface area. This leads to the paradoxical conclusion: it can be filled with paint but never fully painted on the outside — an impossible yet mathematically sound structure.     2. Mathematically Valid, Physically Unreal While such shapes are rigorously defined through limits and infinite integrals, they cannot exist physi...