The kitchen knife is blunt; experts use a whetstone, I’m a novice, so build a portable rechargeable belt grinder: forward / reverse adjustable, charge display, a neat power switch, stepless like a gas pedal; kitchen knives and machetes come up sharp with a quick pass, belts are swappable, one minute and it cuts vegetables like tofu; cost ¥100-something. Core parts: belt-grinder head kit ¥44 (comes with 5 belts, drive wheel / idler); 795 motor ¥28.9 (with mount and dust cover, 200W). Assembly problems: the motor shaft is smaller than the drive-wheel bore, so buy 5mm ID / 8mm OD bushings (¥19.5 for 5), heat the drive wheel so it expands and drop the bushing in, then lock the grub screw to clamp the motor shaft; the frame holes don’t line up with the motor holes and can’t be drilled (the original design wasn’t for a 775/795), so he models a base and housing (with battery bay and slots for the electronics) plus a motor bracket, 3D prints them, and will release the models free and open source; two screws hold the bracket to the motor, the other side to the steel frame, drive wheel fitted; changing a belt means removing the idler; a quick power-up to fine-tune the idler until it runs smooth. Battery: for portability, 18650 2000mAh 5C-discharge at ¥3 each, 9 cells for 12V (3S3P, 12.6V 6000mAh); battery meter DC7-100V ¥10.9; forward / reverse via a KCD1 6-pin 3-position rocker switch, ¥13 for 10; Type-C 3S charge-management module ¥11.8. Spot-weld the nickel tabs on; note the parallel / series joins are welded in a “box” pattern so the balance BMS actually works, otherwise it only balances one group; wrap in fish paper for insulation and heat isolation; fit the 3S 60A 12.6V balance BMS (¥6.1) — separate-port, so both input and output leads must be connected; pack goes into the printed box, input side to the Type-C charging module, plug in and it charges normally. Fit the lit metal latching button ¥6.9: switch input to the pack’s output positive; button negative and meter negative twisted into one lead; meter positive, sense lead, switch output and switch positive twisted into one lead; the negative lead to the pack’s output negative; into the input of the adjustable buck-boost module ¥15.3, then the master switch; the light comes on, so the wiring is OK. Forward / reverse rocker switch: the middle pins are the power input, and whichever of top or bottom is used as output needs two jumpers crossed to the other side’s pins — the principle is simply swapping positive and negative; switch input from the buck-boost output; the buck-boost raises 12V to 24V so the 795 is more brutal and spins faster; not building 24V directly because 12V is smaller, portable use doesn’t need long runtime, and 12V parts are in stock. Output leads out of the box to the motor; lid on; the frame bottom is screwed to a bracket and strong glue fixes the frame to the box base; motor positive and negative connected; job done; test grind works really well and fast, usable for DIY too. 102 comments: this is the way, no argument (7); is a 12V motor enough? why forward / reverse for sharpening? sourcing (2) → every part has detailed sourcing info in the video; where to buy components / is LCSC reliable (2); add a rest to fix the angle (1); an angle grinder takes seconds → too aggressive, the edge quenches; does dry grinding anneal it → no; isn’t a bowl bottom good enough (many); wasn’t this on your livestream → yes; posting at 4 a.m. → afraid of copycats; which 3D printer; the kit is only ¥40-something, don’t rip people off; help fix two streetlight lithium packs.