Introduction: A flange that will not clear an 800 mm bed swing does not end the job; the gap opening usually decides whether the lathe can take it.
Flange and disc repair work rarely arrives in convenient sizes. A pump housing flange, gearbox cover, brake disc hub, or worn register on a short heavy casting may measure beyond the bed swing of a standard lathe but still within the capacity of a gap-bed machine. Workshop supervisors then face a practical and costly question: send the part to a larger machine and lose schedule time, or use a lathe with a gap opening that can clear it. The specification sheet's swing and gap dimensions usually answer that question before motor size or spindle speed enters the decision. The key is to match the flange geometry to the gap structure, then line up the chuck, faceplate, and safety setup around those limits.
A gap-bed lathe is a plain engine lathe with a removable section of bed ways directly in front of the headstock. With that section out, the ways drop away from the workholding area, so a workpiece can rotate at a diameter that would otherwise strike the bed. The CQ6280B and CQ6280C list 800 mm swing over the bed, 560 mm swing over the carriage, and 1000 mm swing in the gap, with 240 mm of effective gap length. The extra 200 mm over the bed figure can allow a flange in the 850–950 mm range to be considered for spindle mounting rather than sent out, provided the workholding and clearance checks agree. Most flange repairs involve facing, register cleanup, groove cutting, or truing a sealing surface in a short band near the chuck. That band is exactly what the gap opens up. The useful question becomes which features need cutting and whether they fall inside the gap window, rather than whether the entire flange fits on the lathe. That check tells you which repair jobs you can accept, and it also settles the bed length decision: a machine bought mainly for discs and flanges works well with the 2000 mm maximum workpiece length, while the 3000 mm version suits shops that also run long shaft work.
Those two published figures control different things and should be read together. The 1000 mm number limits how large a disc can rotate in the opening. The 240 mm number limits how much of that disc can sit inside the opening along the spindle axis. One is a diameter limit, the other is a depth limit, and a flange setup has to satisfy both at the same time.
The 1000 mm figure is clearance, so plan to stay below it. The rotating outside diameter has to clear the gap walls while the machine is running, and the flange shares that space with the chuck or faceplate. A 950 mm flange on a faceplate with tall jaws can lose real clearance quickly, so plan the stack: flange OD, plus plate and jaw height, plus tool room with the compound set at a working angle. The 560 mm swing over the carriage also matters. A flange above roughly 560 mm cannot travel past the carriage, so the saddle stays at the gap and the work is limited to facing, stepping, and short turning work near the opening rather than long straight turning on a large diameter.
The 240 mm effective length is often the limiting dimension in flange setups. That figure has to cover the flange thickness, the faceplate or jaw height behind it, and enough clearance for the tool to reach the face. Thin maintenance flanges with a short hub, say 40–80 mm of body, sit comfortably. A flange with a long hub or a bolted boss consumes the length quickly, and a flatter faceplate or a different clamping method is often more useful than trying to gain more swing. Typical mounting is a faceplate or a large four-jaw chuck, clamped on the outside diameter or bolted through the bolt circle, with the register indicated true before the first cut. Balance also matters: at close to a metre across, rim speed climbs quickly even at moderate spindle rpm, so balance the setup and verify seating before running.
The CQ6280 series uses an ISO702/II NO. 8 Camlock spindle nose, a short-taper interface with cam pins that pull the chuck or faceplate onto the taper. That detail matters for flange work because a repair shop may swap from a three-jaw chuck to a faceplate and back within a single week. A faceplate with a matching Camlock backplate can be changed more cleanly; a mismatched backplate may require adapters, shimming, and extra runout checks. When specifying a faceplate or chuck backplate, request the spindle nose drawing from the CQ6280C lathe manufacturer and confirm the backplate specification in writing. ASME B5.9 covers the connection dimensions between spindle noses and chuck backplates and is worth referencing in that discussion. Safety planning for a large disc should start with the part. Guards must clear the swinging flange, and a guard sized for normal chuck work may need extending or reshaping before the first cut. Braking is the other half: the CQ6280 series pairs a manual brake with a foot brake, so the operator has a fast, hands-free stop when something looks wrong during a facing pass. HSE guidance on metalworking lathes covers chucks, guarding, and braking as core risk areas and is a sensible reference when writing the setup note for the shop floor. Workpiece weight, chuck size, and the final workholding plan depend on the actual flange, so confirm those details with your supplier before committing the machine to a job.
The gap on a gap-bed lathe works as a clearance window; it does not extend full-length turning capacity. Match the flange outside diameter to the 1000 mm swing, match the flange thickness plus faceplate stack to the 240 mm gap length, and keep the work in the gap band where the tool can reach it. Then build the setup around the Camlock interface, a balanced faceplate mounting, a guard that clears the swing, and a brake you trust. As a heavy duty engine lathe supplier, SENMO can send the gap dimensions, spindle nose details, and available faceplate and chuck options for the CQ6280B and CQ6280C so you can check them against the flange in front of you, along with a quotation for the bed length and tooling package you need.
A: The published swing in the gap is 1000 mm, so a flange with an outside diameter below that figure can rotate in the opening, provided the faceplate or jaw stack and tool clearance also fit. A flange above 560 mm cannot pass over the carriage, so plan to do the work with the saddle at the gap rather than along the bed.
A: The 240 mm effective gap length is the depth budget along the spindle axis. It must cover the flange thickness, the faceplate or jaw height behind it, and tool clearance at the face. Thin flanges with a short hub fit readily; thick hubs or tall jaw stacks use the length quickly, so a flatter faceplate or a different clamping method is often the better choice.
A: Use a faceplate or large four-jaw chuck with a backplate that matches the ISO702/II NO. 8 Camlock spindle nose. Clamp on the outside diameter or through the bolt circle, and indicate the register true before cutting. Check that the guard clears the full swing of the flange, confirm the foot brake stops the spindle as expected, and settle workpiece weight and the final workholding plan with your supplier before the first run.
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