Ball Screw Support Unit

Tianjin OuNaiDa Transmissions Technology Co., Ltd. is one of the leading manufacturers and suppliers of Ball Screw Support Unit in China. If you're going to buy high quality Ball Screw Support Unit, welcome to get more information from our factory. Also, custom service is available.

Ball Screw Support Units - Fixed End and Supported End

A ball screw axis needs support at both ends, and the two ends do different jobs.

The fixed end handles axial positioning. It carries angular contact bearings and a lock nut that sets the preload. This end decides where the screw sits.

The supported end carries radial load only. It deliberately allows the screw to grow and shrink with temperature. Constrain this end and a long screw will bind itself as it warms up during a shift.

Get these two reversed during assembly - it happens more often than you would think - and the axis will run rough from the first hour.

Series We Supply

BK / BF - Square Block Type
The most widely used series. Square housing with clear machined reference surfaces, easy to align against a flat machine bed. BK is the fixed end, BF the supported end. Standard choice for CNC machines, general automation, and medium to large screws.

FK / FF - Round Flange Type
Circular flange mounting, installed from the machine frame side. Same fixed/supported concept as BK/BF but a different mounting interface, different flange dimensions, and different centre alignment. Choose this when your frame layout calls for a round mounting face.

EK / EF - Compact Square Type
Smaller housing and lower centre height for tight installations and smaller screws. Not simply a shrunken BK - the bearing arrangement and allowable axial load differ, so check the drawing rather than scaling down from the BK table.

AK / AF - Sealed Type
Square-type fixed and supported units supplied with shaft seals, for installations where contamination is a concern.

BK Series - Fixed End Dimensions

Dimensions in mm. Each BK unit ships as a complete assembly: housing, bearing set, holding lid, collars, seal, lock nut, and set screws.

EK Series - Compact Fixed End

Matching EF supported-end units are available for each size (EF06 through EF25), supplied with bearing and snap ring.

Matching Support Units to Your Ball Screw

The applicable shaft outer diameter for each support size:

Do not select by nominal screw diameter alone. The support unit must match the machined shaft end - journal diameter, shoulder, thread, and journal length - not the screw's outer diameter. Two Ø16 screws with different end machining need different support units.

Installation Notes

The problems we get asked about most, in order of frequency:

Fixed and supported ends swapped. The axis runs, then binds as it warms. Check which end carries the lock nut before you bolt anything down.

Misalignment between the two units. Set the fixed-end reference position first, then align the supported end to the screw axis - not to the machine bed.

Thermal expansion blocked at the supported end. The supported end must be free to float axially. If it is clamped, a long screw has nowhere to grow.

Lock nut tightened by feel. Preload set by guesswork is the most common cause of rough running on an otherwise correct assembly.

Recommended sequence: establish the fixed-end reference → align the supported end to the screw axis → connect the nut housing → check running torque across the full stroke. Smooth torque end to end is the acceptance test.

When to Consider Fixed-Fixed

For long strokes, high-speed operation, or axes needing higher axial stiffness, a fixed-fixed arrangement with a pre-tensioned screw raises critical speed and improves thermal control.

It also demands correct bearing selection, controlled preload, and tighter installation accuracy. Fitting two standard fixed-end units at both ends is not a fixed-fixed system - that arrangement will fight itself. Tell us the stroke and speed and we will advise whether it is worth the additional cost for your application.

Quotation Checklist

Send us:

1. Ball screw diameter and lead
2. Shaft-end dimensions - journal diameter, shoulder, thread, journal length
3. Support unit series preference, or your mounting constraints
4. Centre height and mounting hole spacing available on your frame
5. Load and operating speed
6. Quantity

Replacing existing units? Clear photos of the front view, side view, bottom mounting surface, and any nameplate marking will match faster than measurements alone.

Supplied as a Matched Axis

Tianjin OuNaiDa manufactures precision transmission components - since 2008, with 20 years of production and 15 years of export experience across 300+ overseas distributors, to CE and ISO 9001:2015 standards.

Support units are one part of a linear axis. We also supply the ball screws themselves, shaft couplings, and linear guideways, with shaft-end machining matched to the support units you select. Confirming the shaft-end design before the order is placed prevents the rework that makes a cheap part expensive.

OEM and ODM accepted. Samples available. Technical support 24 hours.

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