SITE：Ball Screw Straightening Solution | Raceway-Safe Precision Shaft Correction | SHANGDA
The problem: a precision groove wrapped around a slender bent body
Ball and roller screws leave heat treatment with hardened raceways running along a long, slender body — a pairing few other components present. The shaft flexes easily, the working surface follows a helix over nearly the whole length, and precision grinding takes off very little stock. Four issues reach the process engineer at once.
Slender shafts, bend pointing every way
A screw is a round body many times longer than its diameter. Bending resistance falls quickly as diameter shrinks, so stresses released as the raceways cool leave bows a stiffer bar would never carry. The bend rarely keeps one plane: one screw shows a clean crown, the next an S-curve whose high spot faces a different direction at each station.
The helical track is untouchable
The ball track is the product itself: hardened, smoothly finished and later paired with a nut. A shoe crossing the groove leaves a flat spot or a bruise on the load-carrying surface, and one damaged turn cannot be repaired or ground away. Trapezoidal lead-screw threads answer to the same rule — contact must work against plain metal only.
Grinding allowance leaves no escape
Correction happens before the wheel, and the stock the grinder removes is deliberately small. A shaft left too far out, or carrying a pressed-in mark, cannot be rescued: either the bend rides through to the finished screw, or the wheel cuts into the hardened layer to erase the indentation. Straightening quality decides what the grinding shop delivers.
Manual pressing cannot be quantified
Shop-press work with a dial gauge means tracking a needle, guessing the high spot’s angle after the part rolls on its vees, and chasing the bend between tries. Results move with whoever is pressing, the track stays safe by care alone, and no load or deviation figure is kept — awkward when a buyer asks for evidence.
The rule that runs the whole station: a bent screw with a flawless thread is rejected, and a straight screw with a bruised track is rejected just as quickly. One cycle has to settle both arguments on the same shaft. How the same protection thinking applies to a different precision-rod family is laid out in our article on chrome-plated piston rod straightening, and our piece on cracking, residual stress and excessive press load explains why hardened surfaces must always work below a force ceiling.
SHANGDA builds the ball screw cell around exactly the geometry that makes the job difficult — a rotating cylindrical body carrying a continuous helical working surface, with short end journals designed to take loads. Five engineered functions make the process dependable. Held on its plain end journals, the screw is turned through a full rotation while probes read runout at measuring points along its length — 2–3 stations on short screws, 5–8 on long shafts. Turning reveals not only the bend size but the angular direction each high spot points toward — the information pressing a round shaft actually requires. The control fits the runout readings station by station, finds the maximum bend and its angle, and sets support span and ram position from them. The screw is rotated until the peak faces the ram before contact; a shaft beyond what pressing can safely recover is turned away up front rather than forced. Support and ram contacts land on unthreaded journals and bearing seats, or on profiled shoes that follow the shaft body while clearing the helical groove — never on a ball track or thread flank. A threaded-length map in the part program blocks any stroke whose shoe would cross the raceway. Correction advances creepingly: each stroke nudges the shaft, the elastic strain settles, and a fresh runout reading clears the next move. Load and travel are watched all the way; a part-specific ceiling arrests the ram at its limit, an independent travel stop traps a wrongly picked recipe instead of forcing the shaft onward, and an unexpected load curve holds the shaft and raises an alarm. Before/after runout, recipe revision, stroke count and peak force are filed against the batch and exported with the parts. No quality call depends on memory or paper notes: the evidence file comes out of the cycle that does the work, so a questioned lot is answered straight from the machine’s records. The station stands alone or runs linked, with conveyors, buffers and handshakes matched to surrounding machines. Accepted screws move on tagged for the grinder with their measurement file; transfer heights, buffer size and signals are reviewed against the real layout before steel is cut. Machine lineup for screw production. Most screw lines are configured around our Ball Screw & Shaft Straightening Machine, which completes the whole rotate–scan–press–rescan cycle unattended once loaded. Shops organised around screw rod shafts with a different diameter mix can use the Screw Rod Shaft Straightening Machine across the same part family. The wider precision-rod context sits in our chrome-plated piston rod piece, and how excessive force damages hardened parts is covered in our crack-risk piece; below we stay with what matters for purchasing. Manual stations, conveyors and gantry or robotic handling are options on one base machine, so automation follows your shift pattern rather than the reverse. Send your screw drawings with measured incoming-bend figures; our engineers reply with a layout and demonstrate it on sample screws ahead of dispatch. What arrives on your floor is a managed process, not simply a press. Every shaft then leaves on the same correction basis and the grinding shop receives parts, and records, it can rely on. Each part is runout-scanned coming in and again at the exit. Before/after straightness, recipe version, stroke count and peak force are filed against the batch and exported: 100% inspection with logged data, giving your quality team — and your buyers — acceptance evidence they can walk through. A complete cycle takes 20–90 seconds per screw, set by its length and the number of bends corrected — roughly 5–10 times what indicator work manages. One person tends 1–2 CNC machines or a row of linked fully automatic units, so headcount stops growing with output. The grinding shop gets shafts corrected on one straightness basis, lot after lot, instead of a mix shaped by whoever pressed them. Screws outside the program window are flagged and held rather than forced, so problem parts never reach the wheel and grinder input stays stable. Journal supports, profiled shoes clearing the groove, software-blocked threaded zones and angle indexing all live inside the tooling and the program, not in an operator’s concentration. The hardened track quality going in is the same quality that comes out, lot after lot. In-feed→Rotate & multi-point runout scan→Locate max bend→Press only on journals / profiled supports, light steps→Re-scan→Accept / reject output Indicative build envelope to support an early budget figure; exact dimensions are worked out from your drawings, and the completed layout is run live on your sample screws ahead of delivery. Every straightness figure is quoted together with the method used to measure it; the target assigned to your part number is documented on paper and demonstrated in the acceptance trials. Frame capacity tracks what the screw genuinely calls for, since a frame larger than needed tempts operators into heavy-handed habits rather than improving results. Diameters, lengths or targets outside the table are still worth discussing — send the drawings and engineering will answer candidly, including when no standard frame is a fit. The functional surface never meets a working face. The screw rests on plain end journals, and each stroke lands on an unthreaded journal, a bearing seat, or a profiled shoe that stands clear of the helical groove. The program holds a zone map of the threaded length and refuses any stroke whose shoe would cross a track turn or a thread flank; if the angle is wrong at loading, the part is re-indexed before the cycle starts. It is chosen from what the grinder needs: enough straightness that the remaining stock cleans up around the full circumference without the wheel breaking through the hardened raceway layer, stated with its measurement basis. Straightening is held tighter than the pre-grind condition, never looser. The exact figure for your part number is agreed in writing and demonstrated on sample screws during acceptance rather than promised on a range. On hardened raceways the risk exists, which is exactly why the machine enforces the cap instead of trusting an operator to hold back. The recipe’s force ceiling stops the ram at the threshold, an independent travel stop traps a wrongly selected program rather than driving through, and a load-versus-trace with an odd shape halts the part and raises an alarm. Moves stay short and incremental, and the control is never allowed to repeat a stroke unprompted. Our crack-risk piece explains the entire chain of causes step by step. It can. Both carry a helical functional surface, so the same rotate–scan–locate–press cycle applies; only the contact detail changes. Profiled shoes clear either the ball groove or the trapezoidal thread form, and each part number stores its own supports, spans, orientation offset and force ceiling. Roller screws belong to the same family. A genuinely new profile is qualified on sample screws before production release. Changeover between qualified part numbers is a recipe selection at the control: measuring layout, orientation offset, spans, shoe selection, force ceiling and threaded-zone map are stored. The diameter and length range is covered by the fixture family designed at order time; a truly new profile is engineered from drawings and proven on sample screws rather than dialled in on the shop floor. On your screws, not a clip. The target figure and the way it is measured are documented on paper against the drawings, sample screws from your own production run through the machine during factory acceptance, and before/after runout, stroke counts and peak-force logs travel with the parts and are verified against the agreed basis. The identical trials are run again in your workshop once the cell is installed. Start on the solution enquiry page. SHANGDA has built CE-certified automatic straightening presses to order since 2008: rotating multi-point runout scans, contacts confined to journals and profiled supports, force-capped closed-loop correction and complete logged records, with manual or automatic loading. Our engineers tell you plainly whether a screw can be corrected, dimension the press and its automation around your line, and confirm the result on your sample screws ahead of dispatch.Our solution: rotate and scan, press only plain metal, creep to target under a force cap
Rotate and runout-scan before any stroke
Press positions taken from the bend map
Journals and profiled supports carry all the load
Small steps, closed loop, fixed ceiling
A data record for every screw
Designed as a grinding-line neighbour
What you get: inspected screws, logged evidence, a steady feed to grinding
Every screw measured twice, with a file
Cycle time and staffing for precision work
A predictable handover to the grinder
Raceway protection built into the tooling
Illustrative workflow — a screw moving through the station
Configuration at a glance
Parameter Offered range Shaft diameter range Ø5–600 mm, threaded and plain round stock Shaft length range 100 mm–12 m; extra length corrected in sections Probe / station count 2–3 on short screws; 5–8 probes on long shafts Cycle per part 20–90 seconds General engineering band 0.10–0.30 mm/m Precision transmission band 0.02–0.05 mm total reading Finest band ≤0.02 mm total reading Maximum correction force matched to the part; frames reach the 1000-tonne class Electrical input 380–480 V, three phases Material handling manual stations, or automatic gantry / robotic cells Manning one person per 1–2 CNC machines or a row of fully automatic units Lead time 60–120 days from order Frequently asked questions
Will the ram or supports hurt the raceway or the thread profile?
The screw is ground afterwards — how is the straightening target chosen?
Can a high-hardness screw crack under correction?
Can the cell handle both ball screws and trapezoidal lead screws?
How does the machine adjust when we change screw size?
How is the accuracy accepted?
Send your ball screw drawings — receive a built-to-order quote
