Model 4R 2.25 BLOCK-HEAD®

The model 4R 2.25 combines the familiar mounting features of the model 4R with a larger diameter bore. Increased radial load capacity and clearance for fixturing make this spindle a useful tool in the optics industry.

Specifications (at 150 psi)

Load Capacity Ultimate Working
Radial 125 lb 63 lb
Axial 175 lb 88 lb
Tilt 150 lb-in 75 lb-in
Stiffness Radial 0.8 lb/microinch
Axial 1.0 lb/microinch
Tilt 1.7 lb-in/microradian
Error Motion Radial < 1 microinch
Axial < 1 microinch
Tilt < 0.1 microradian
Total Weight 16 lb
Rotor Weight 7 lb
Rotor Inertia 0.77 oz-in-sec2
Maximum Speed 7,500 rpm
Air Consumption < 2 scfm
Metric Specifications


Load capacity and stiffness are approximately linear with air pressure.

Ultimate load capacity is measured when metal-to-metal contact is made across the bearing surfaces. Working load capacity is half of the ultimate load capacity. Rotor weight must be included as part of total spindle load.

Axial and tilt loads are supported by the same bearing surfaces. Consequently, a load applied in one mode reduces the other mode proportionally.

High speed or high inertia applications require rotor containment. Maximum speed is dependent on application. Consult Professional Instruments for further information with regard to speed.