Published:2026-09-28 12:00:00
NUT BRACKET INSTALLATION AND BALL SCREW RESISTANCE
Find the tightening step that introduced the resistance
If rotation is smooth during preliminary assembly but starting torque or rotational resistance increases after tightening, inspect the mating faces, centre heights and axis relationship. Identifying when resistance first changed is more useful than immediately increasing motor torque.
01 / HOW RESISTANCE DEVELOPS
The bracket connects two sets of mounting datums
The guides constrain table travel, the shaft-end supports locate the screw axis, and the nut bracket connects the ball nut to the table. Before tightening, clearances may temporarily accommodate an offset or angular difference. After tightening, the nut, bracket and table constrain one another. The resulting additional off-axis load or moment can increase running resistance.
The HZMotion manual highlights the perpendicular relationship between the nut flange connection face and the table connection face. Bracket geometry is only one part of this relationship. Table distortion, debris between faces, different axis heights and support installation errors can also introduce unwanted constraint.
Separate three connections: nut flange to bracket, bracket to table, and screw support to machine base. If resistance changes after installing the motor or coupling, inspect motor bracket shaft alignment rather than assigning every source of resistance to the nut bracket.
A reduction in resistance after releasing one connection shows that the constraint changed. It does not identify which part is out of tolerance. Use drawings, measurements and a staged record to establish the cause.
02 / LOCATE THE TRIGGERING STEP
Record when the change occurs, where it occurs and in which direction
Review the assembly record and identify the first step with a clear increase in resistance. During an authorised recheck, change only one controlled connection state at a time and keep load, lubrication, temperature and measurement method consistent. Do not run the drive with loose fasteners. Independently support vertical axes or externally loaded tables before releasing a connection.
| Observed change | Check first | How to distinguish causes |
|---|---|---|
| Hard spots exist before connecting the nut to the bracket | Nut and screw condition, lubrication, contamination, guides, seals and shaft-end supports. | Separate resistance sources using a manufacturer-permitted inspection method. Do not assume bracket tightening is the original cause. |
| Resistance rises after tightening the nut flange | Flange contact, nut envelope interference, holes, threads and bolt length. | Check whether tightening pulls the faces together forcibly, bottoms bolts or presses on recirculation or sealing parts. |
| Resistance rises after attaching the table | Table face, burrs or debris, bracket orientation, centre height and table distortion. | Compare contact and measurements before and after connection. Check whether an offset hole pattern pulls the bracket sideways. |
| Resistance increases towards one stroke end | Screw axis relative to guided travel, end-support location and local interference. | Record horizontal and vertical changes along travel and rule out hoses, covers and limit hardware rubbing. |
| A hard spot repeats at a position or rotation angle | Possible local damage, contamination, screw bending or runout, or rotating-part interference. | Distinguish repeated table position from repeated screw angle. Neither pattern is a complete diagnosis by itself. |
| Cold motion is acceptable but rotational resistance increases after warm-up | Thermal changes, lubrication, preload, support arrangement and changing external load. | Record temperature and operating time rather than treating it only as a cold mounting-face problem. |
Hand feel can reveal a problem, but results from different operators, handle lengths and checking speeds are not directly comparable. Where appropriate, use a suitable instrument to record starting torque from rest separately from resisting torque during continuous rotation. State which components are included and do not compare readings from these two states as if they were the same measurement.
03 / GEOMETRY CHECKS
Separate seating, centre height and changes along travel
1. Do both connections seat without being forced?
Clean the nut flange-to-bracket and bracket-to-table contact surfaces. Inspect for burrs, dents, coating buildup, chips and trapped residue. Use the specified inspection method, such as a straightedge, feeler gauge or contact check, to assess seating. Do not pull visibly raised faces flat with bolts. Protect locating surfaces and do not rework precision datums without an approved process.
2. Are centre heights referred to the same datum?
The bracket centre height may be measured from the table connection face, while a support unit centre height may start at its base mounting face. Translate the base, rails, carriages, table thickness and installation orientation into one coordinate system before comparing the nut axis with the support axis.
Free motion at one position does not rule out an angular difference. Similar readings at the two ends do not rule out table distortion, guide errors or interference in the middle.
3. Does the screw axis agree with guided travel?
Follow the assembly inspection plan. Use guide travel or the specified machined datum as the reference and measure the axis relationship at stations in both horizontal and vertical directions. Measure a designated surface or test mandrel that represents the axis; record positions, span and screw angle. Indicator fluctuations from a ball raceway groove are not a direct parallelism measurement.
If the screw must be rotated for a runout check, record that separately from measurements taken along travel. Otherwise runout can be mixed into the apparent alignment result. The selected product and machine drawings must define instruments, datums, spans and acceptance limits.
4. Do bolts, holes or lubrication fittings interfere?
Check that flange bolts and table bolts have not been mixed up and that thread size, usable depth and length match. Tightening must not press on seals, return components or fittings. Compare bore D1 with the full nut envelope; initial insertion does not rule out interference with a projecting feature.
IT6 is a dimensional tolerance grade, not one universal acceptance value for flatness, perpendicularity and parallelism. Record each measured feature, datum, drawing limit and method separately. No single alignment limit in this article applies to every model.
04 / INSPECTION SEQUENCE
Inspect one interface at a time and correct the cause before final tightening
- Establish safe and repeatable conditionsStop and isolate the drive from unexpected startup. Support the table and external load. Record orientation, load, temperature, lubrication and the original connection states, and confirm the permitted manual checking method.
- Verify complete interfacesCheck model, flange, holes, centre height and bolts against the nut and bracket drawings. Resolve a model or hole-pattern mismatch before assembly; do not enlarge holes or pull parts into place as an improvised remedy.
- Identify datums and the triggering stepFollow the machine assembly procedure to establish the fixed-end, guide and table references. Recheck only connections permitted for adjustment while preserving other datums. Do not alter bearing or nut preload arbitrarily.
- Measure and correctInspect seating, the dimension chain, axis direction and interference. Use an approved adjustment or rework process. If shims are permitted, define material, support area and retention rather than stacking loose pieces to hide skew or inadequate support.
- Tighten in stages and recheckUse the drawing-specified sequence, torque, thread lubrication condition and locking method. Record changes at each stage and complete every connection before final operational checks.
- Verify the full strokeUse the permitted method for low-speed checks throughout travel, in both directions and at critical positions. Restore guards, then carry out low-speed, loaded and warm-running checks under the commissioning procedure. Retain before-and-after data.
This sequence organises troubleshooting; it does not replace the machine assembly procedure. Stop if there is a clear hard spot, unusual noise or abrupt resistance increase. Do not force the motor through it or assume that running-in will remove the cause.
05 / FINAL CHECKS AND RECORDS
Compare before and after tightening under the same conditions
A useful record preserves the order of cause and effect: which connection changed, when the resistance changed, where it occurred and which acceptance criterion applies. Transfer the following fields to the inspection sheet and fill in limits from the confirmed drawings and process.
| Record field | Information to enter | Purpose |
|---|---|---|
| Models and revisions | Nut, bracket, support and guide models, with drawing revisions. | Confirm that interfaces and inspection criteria belong to the same configuration. |
| Connection state | Tightening stage for flange, table and supports, required torque and execution record. | Identify the first step that introduces the problem. |
| Measurement conditions | Load, orientation, temperature, lubrication, instrument, checking speed and coupling connection state. | Make before-and-after data comparable. |
| Geometry | Seating and centre-height results; horizontal and vertical measuring stations, readings and drawing limits. | Separate positional offset, angular change and local distortion. |
| Running resistance | Turning resistance in both directions at the start, middle, end and abnormal positions, identifying the included components. | Determine how resistance changes with position or direction. |
| Correction and recheck | Location and method of correction, final tightening, full-stroke and warm-running results, operator and date. | Confirm recovery and support later maintenance. |
Servo current or estimated torque can provide a trend during powered commissioning, but acceleration, gravity, seals and control settings also affect it. It is not a direct measurement of nut friction. Make powered comparisons only after every connection is fully tightened, protection is restored and operating conditions are consistent.
Combine these checks with the support unit runout, clearance and temperature acceptance checklist so that shaft-end support problems are not overlooked.
06 / COMMON MISTAKES
Temporary smoothness is not proof that the fault is corrected
- Leaving bolts loose: this changes load transfer and location and is not an operating solution.
- Pulling parts into place with bolts: closing a gap may only deform the table, bracket or screw. Establish the underlying geometric cause.
- Fitting a larger motor first: more drive torque cannot restore incorrect mounting geometry and may mask increasing resistance.
- Checking one direction at one position: local interference and axis relationships near the stroke ends may remain undetected.
- Using the opening to adjust preload: the MC opening is not a clamping adjustment slit. MGD, MGS and NH must not be forced into an unspecified fit either.
If the interfaces do not match, return to the MC, MGD, MGS and NH interface selection guide. When contacting HZMotion, provide nut and bracket drawings, mounting-face photos, the tightening sequence, and the position and direction of binding.
07 / FAQ
Frequently asked questions
Does increased rotational resistance after tightening prove the bracket is defective?
No. Table faces, holes, bolts, supports, guide alignment and surrounding interference can all contribute. Identify the triggering step and use measurements to distinguish causes.
Can the machine run with the table connection loosened if motion becomes smooth?
No. The released state only provides information during controlled inspection. Operation and delivery require the specified fastening condition and verification after full tightening.
Does resistance near one end mean the bearing at that end is damaged?
The support may be involved, but screw-to-guide misalignment, local interference and other causes are also possible. Record the position trend and check geometry and components before concluding that a bearing is damaged.
Can shims correct centre height?
Only where the design or assembly procedure permits controlled adjustment. Confirm support area, flatness, retention and the final dimension chain. Improvised shim stacks must not hide incorrect holes or distorted parts.
How is successful correction confirmed?
Meet the drawing requirements for geometry and fastening, then complete full-stroke checks in both directions and any specified loaded or warm-running checks. Keep before-and-after records rather than relying on one manual movement.