Jigs and fixtures are not the same device. One guides the tool, the other fixes position. The difference decides how rigid the build has to be, where the locators go, and why a clamp should never be the thing that puts a part in place.
A fabricated rectangle has no stiffness of its own. This article explains how a diagonal changes the load path from bending at four corners to axial load in one member, where the brace has to land, and how to read a racked frame before it leaves the bench.
Heat tint is only the visible part of the problem; under it sits a chromium-depleted layer where corrosion starts. Brushing, pickling and electropolishing remove different amounts of it, and the choice shows in service.
Build-up restores dimensions; overlay adds a surface property. Dilution, buffer layers, bead sequencing and machining allowance decide whether the deposit survives the lathe and the service that follows.
A crack is a symptom. Repair means finding the true tip, stop-drilling it, grooving back to sound metal and filling without recreating the conditions that caused the failure in the first place.
A casting is not a sheet: thickness varies, the skin is contaminated and porosity was there before the arc arrived. Pre-heat, cleaning, filler choice and slow cooling decide whether a repair holds.
Aluminium sheds heat faster than steel and wears an oxide skin that melts far hotter than the metal. Alternating current, balance control and filler choice are what make the weld possible, and appearance hides more than it shows.
Stainless to mild steel is easy to fuse and hard to make last. Carbon dilution creates a hard band at the fusion line, and the galvanic couple takes over in service. Filler, heat input and joint design all matter.
