Introduction: Two structurally similar engine lathes differ in one bore size and one speed ladder, and that gap decides which workpiece each one suits.
Learners comparing the CQ6280B and CQ6280C usually start with the number that looks bigger. The CQ6280C carries a 105 mm spindle bore and the CQ6280B carries an 82 mm bore, so the easy assumption is that the larger hole makes the larger machine the better one. That assumption falls apart on the shop floor. Bore and speed steps answer two different questions: what can pass through the spindle, and how closely spindle speed can be matched to a workpiece diameter. Working out which of those two questions your job keeps asking is the whole decision.
The spindle bore is the hole that runs straight through the headstock. On the CQ6280B it measures 82 mm; on the CQ6280C it measures 105 mm. Twenty-three millimetres of extra clearance sounds minor on a lathe that swings 800 mm over the bed, but it decides whether a length of pipe or bar can be pushed back into the spindle and clamped close to the chuck. That one detail changes how a long workpiece behaves in the cut, because the portion hanging out in open air is the portion that vibrates and deflects.
Hollow stock separates the two models cleanly. Any tube with an outside diameter under 82 mm passes through either spindle, so small pipe and thin-wall tube gain nothing from the CQ6280C. Stock between 82 mm and 105 mm outside diameter only enters the CQ6280C, and that band is where the decision becomes obvious rather than theoretical. Solid shaft work behaves in the opposite way. A shaft held in a chuck or between centres never needs to enter the bore at all, so a 105 mm opening adds nothing to a 60 mm shaft job. Shaft turning cares about how the spindle speed lines up with the diameter as the shaft steps down, which is a speed-step question rather than a bore question.
A bore is a passage, not a rigidity rating. It changes what fits inside the headstock; it leaves the bed, the carriage, the cross slide and the tool post doing exactly what they did before. A trainee who expects the 105 mm model to leave a cleaner finish on a 50 mm shaft is reading the wrong number. The internal taper does track the bore size, at 90 mm 1:20 on the CQ6280B and 113 mm 1:20 on the CQ6280C, so the larger-bore model also accepts larger centres and reducing sleeves. Even so, the surface a tool produces comes from spindle speed, feed, tool geometry and how firmly the workpiece is supported, not from the diameter of the hole behind it.
The CQ6280B runs from 9 to 1400 rpm across 24 steps, while the CQ6280C runs from 30 to 1400 rpm across 12 steps. Those step counts describe the geared headstock: each step is a fixed ratio you select, and the count tells you how many choices sit between the bottom and top of the range. Twenty-four steps spread over roughly the same top speed means each jump is smaller, so an operator can land closer to the spindle speed a given diameter wants. Twelve steps means wider jumps, so the nearest available speed is chosen and the cut is adjusted around it. The bottom of the range matters as much as the count. Surface speed climbs as diameter grows, so a large flange or a big-diameter tube needs slow rotation to keep the rim from running away from the tool. The CQ6280B reaches down to 9 rpm, which leaves more room at the large-diameter end of the work. The CQ6280C starts at 30 rpm, still a slow speed, but the first step above it is a bigger move. Neither arrangement is a defect. Where a shop repeats the same few diameters all week, twelve well-spaced speeds are fast to select and cut down on hunting through the gearbox. Running for long stretches near the top of the range puts the demand on spindle bearing lubrication, so oil condition and service intervals belong to the upper speeds on either model.
Both models use an ISO702/II NO. 8 Camlock spindle nose. That shared interface sits inside the ASME B5.9 family of spindle nose dimensions for engine lathes, which is why backplates, chucks and faceplates mount in a predictable way across machines built to the same standard. For a buyer or a trainee, the practical result is convenience: a chuck that mounts on the CQ6280B also mounts on the CQ6280C. The mounting question drops out of the comparison entirely, and what remains is bore and spindle speed. SENMO lists both models with the same 800 mm swing and the same Camlock nose, which keeps the difference down to those two variables. The shared nose does not make every accessory shared. Because the bore differs, a chuck with a small through-hole will quietly cap the 105 mm passage and turn the CQ6280C into an 82 mm machine in practice, so chuck bore deserves a look whenever tube work is the reason for choosing the larger model. The internal tapers differ too, at 90 mm and 113 mm on a 1:20 ratio, so centres and sleeve sizes are model-specific. Think of it as two layers: the outer mounting is common to both, while the capacity inside the spindle belongs to each model alone. A clear specification sheet from a heavy duty engine lathe supplier will separate those layers instead of folding them into one line.
Bore and speed steps are the two places where these lathes genuinely part company. A horizontal gap bed lathe with an 82 mm bore and 24 closely spaced speeds suits solid shaft work and large-diameter facing where fine speed selection and a slow bottom end earn their keep. A 105 mm bore with 12 speeds suits work that has to pass through the headstock, where the opening decides what the machine can hold at all. Neither is the better lathe in general. Matching the bore to the outside diameter of the work, and the speed ladder to the range of diameters the shop actually turns, settles the choice faster than any headline number, and a conversation with a CQ6280C lathe manufacturer or a look at the published specifications will confirm both figures before anything is ordered.
A: The CQ6280B has an 82 mm spindle bore with 9–1400 rpm in 24 steps, while the CQ6280C has a 105 mm spindle bore with 30–1400 rpm in 12 steps. Both share an ISO702/II NO. 8 Camlock spindle nose, so the real split comes down to how much stock can pass through the spindle and how finely the speed can be matched to the work.
A: Yes, the CQ6280C offers 12 steps against 24 on the CQ6280B, and its range starts at 30 rpm rather than 9 rpm. Fewer steps means wider gaps between the available ratios, which is quick to work with for repeated diameters but gives less room to fine-tune speed on large-diameter work.
A: The ISO702/II NO. 8 Camlock nose is a standard interface, so chucks, faceplates and backplates mount the same way on either lathe. Keeping the mounting identical removes tooling from the buying decision and leaves bore and speed steps as the only structural differences worth comparing.
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