Opening Up a Gearbox Bore… Without Opening the Gearbox Sometimes the fix isn’t complicated… it just has to be right. We were brought in to machine an aft low speed bore on a large gearbox that needed to be opened up for a sleeve. The requirement was simple on paper… increase the bore by 5mm and maintain alignment to the existing forward and aft bores. In practice… that’s where things get interesting. The Challenge This wasn’t a “set it on a machine and hit go” situation. The gearbox stayed intact. Everything had to be machined in-place while holding alignment to existing geometry… the same geometry that determines how the entire system runs. No room for drift. No room for guesswork. When you’re working with bores in this size range (roughly 8.250” ID)… even small misalignment becomes a big problem fast. The Setup Before any cutting starts… the real work begins. Our team manufactured custom fixture plates to mount the boring equipment directly to the gear case. That created a rigid foundation… which is everything in portable line boring. From there: Boring bar installed and secured to the gearbox Alignment taken from existing forward and aft bores Setup dialed in to maintain concentricity across the entire cut This is where experience shows up… not in the cutting, but in making the setup behave. The Machining Once aligned… it came down to execution. Aft bore machined +5mm over existing size Bore approximately 8.250” ID × 2.500” long Forward bearing face lightly machined for cleanup No hero moves… just controlled cuts and disciplined machining. Because accuracy isn’t about one pass… it’s about everything leading up to it. The Result Two technicians. One shift. Job done. The bore was opened to spec, alignment maintained, and the gearbox was ready for the next phase of repair. No disassembly. No unnecessary downtime. Just machining where it sits. Why In-Place Line Boring Matters This type of work doesn’t always look flashy… but it’s critical. When bores and bearing fits are involved, everything downstream depends on accuracy. On-site machining allows that precision to happen without removing the component… reducing downtime while maintaining alignment integrity. The Mactech Approach We keep it simple: Good setup…Solid equipment…Experienced machinists… That combination shows up the same way every time… in results that hold up in the field. Line boring setup mounted directly to the gearbox using custom fixtures Precision machining in progress with portable boring equipment gearbox Maintaining alignment across bores is critical during machining Machining completed in-place without removing the gearbox