The Hard Part Is the Hole
Hollow shafts and spindles need a long bore down the centre — for coolant, a drawbar, wiring, a hydraulic line, or simply to save weight. The trouble is that a conventional twist drill wanders off-centre as it goes deep, so a hole that starts true exits the side or breaks through the wall. Once the depth passes about ten times the hole diameter, ordinary drilling stops being reliable. This part lives well past that line.
The make-or-break spec: straightness and concentricity of the bore relative to the outside diameter over the full length. If the bore drifts, the wall thins on one side and the shaft runs out of balance — so the bore is the feature everything else is referenced to.
How It Was Made
1 — Deep-hole drill first
The deep bore was produced with a deep-hole (gun-drilling) process that uses a guided, single-flute tool and high-pressure coolant to keep the hole straight and flush chips out as it goes — the only dependable way to hold straightness at this depth-to-diameter ratio.
2 — Turn the outside to the bore
With the bore established, the outside diameters, shoulders and any keyway or thread were turned referencing the bore, so the wall stays even and the shaft runs concentric. This order — bore first, then turn to it — is what keeps a hollow shaft balanced.
3 — Grind to final size and finish
Bearing journals and critical diameters were ground to final tolerance and surface finish. Material is matched to the duty — commonly 4140 or stainless — and confirmed with the customer; see our shafts, gears & fittings work.
Why It Takes Real Capability
Plenty of shops can turn a shaft; far fewer can put a straight, accurate, deep hole down the middle of one and keep it concentric. It's exactly the kind of job customers struggle to source — and the reason it's worth showing here rather than another plain turned part. Tight straightness and concentricity are verified on inspection, part of our tolerance & inspection discipline.
The Workflow
Deep-hole drill the bore
Guided gun-drilling with high-pressure coolant holds the hole straight through length.
Turn to the bore
Outside diameters and features turned referencing the bore for even wall and concentricity.
Grind critical diameters
Journals and key diameters ground to tolerance and finish.
Inspect straightness
Bore straightness, concentricity and runout verified before shipping.
Outcome
Hollow precision shafts with a bore that runs true the whole way through, concentric to the outside and ground to size — a part many shops can't make reliably. Hollow shafts, spindles and bored components are core CNC turning work for us, as one-offs or in batches.
Need a hollow or deep-bored shaft? Send a drawing or a sample plus the bore diameter, depth and straightness you need. We deep-hole drill, turn and grind it true. Email [email protected] or message us on WhatsApp.
// More Case Studies