Spindle Finishing Process

Spindle finishing is ideally suited to the deburring a wide range of complex parts including gears, bearing cages, splined shafts, pump rotors, and jet compressor blades. It uses a flowing abrasive mass under controlled conditions to accomplish a variety of deburring and surface improvement operations.

Principle of Operation

A spindle finishing machine includes a circular rotating tub that holds loose abrasive media and rotary spindles to which workpieces are fixtured. The workpiece fixtured in the spindle is immersed in a rapidly moving abrasive slurry. Velocity of the slurry is generated by rotating the tub at a speed suitable for the specific process requirements, sometimes as high as 1,200 surface feet per minute (SFPM). The abrasive particles swiftly flow over rough edges and through holes in the workpiece, removing sharp edges and improving surface finishes. The result is a “form-fitting grinding wheel" that achieves precise, controlled deburring and surface improvements in a fast, flexible, cost-effective process.

The tub is rotated in one direction, while the spindle normally turns in the opposite direction. As the tub is rotated, the media is pushed to the outside by centrifugal force. The layer of abrasive formed as a result of this action is dense and firm, and it therefore provides aggressive action on the immersed workpieces.

Generally, the spindle is adjusted to place the workpiece as close as possible to both the outer periphery and the bottom of the rotating tub for maximum effect. There are two reasons for this placement: first, the abrasive velocity is proportional to the radius from the tub's center; and second, an advantageous pressure effect is created by compressing the moving abrasive between the workpiece and the tub bottom and side wall.

No Part-on-Part Impingement

An important characteristic of spindle finishing is that the workpieces are individually mounted for processing. The machine is equipped with two spindles, each spindle is loaded with a fixture that holds one or multiple workpieces. Compared with conventional mass finishing systems where the workpieces are free-floating in the media, in spindle finishing systems, the workpieces, being individually attached to a fixture, never touch during the finishing process, thereby preventing part-on-part contact which would damage the finish.

Fast and Efficient

Processing cycle times for spindle finishing are short. In many applications a cycle of five to 20 seconds is sufficient, although cycles up to five minutes and longer are not uncommon, depending on the complexity of the parts. Surface finishes typically range between ten and five on the roughness measurement system (RMS), with edge radii consistently produced down to 0.001 inch.

Consistant Results

Established operating procedures are controlled effectively with repeatable cycle accuracy through programmable electronic controls. At the end of the predetermined process cycle, the spindle is raised out of the processing tub automatically. A switch actuates the fixture collet to release the finished workpiece and fixture. The next process cycle begins by loading an unfinished workpiece mounted on the fixture and actuating the cycle start switch.

Technology Advantages

Spindle finishing offers a number of advantages compared to other finishing techniques for the precision deburring and surface refinement of metal parts. These advantages include:

• No damage from part-on-part impingement, workpieces are individually fixtured.


• Rapid, precise finishing of parts. Spindle finishing uses the centrifugal forces created by a rotating tub to form a compact layer of abrasive media that exposes parts to high-density abrasive action.


• Uniform deburring, radius forming, blending of machine or grind lines, and improved micro-inch surface finishes. These results can be accomplished on external surfaces in which a high percentage of the surface is recessed, as well as on internal surfaces through proper part positioning and media selection.


• Short process cycles, generally five seconds to five minutes, with an average cycle of approximately one minute. Such short cycle times result in high production.


• Process repeatability. Finishing is achieved under controlled process conditions with all aspects of the finishing cycle being automated.


• Spindle Finishing works well on workpieces with difficult to finish geometries, often obtaining results thought impossible for an automated process. Because the workpiece is held by a spindle which can be adjusted angularly and rotationally to the abrasive flow the process can be tailored to the individual characteristics of a workpiece in a way that is not possible with any other metal finishing process.

Processing Equipment

We utilize an ALMCO 2SF-36 Spindle Finishing machine with dual spindles and a 36 inch diameter tub. Our machine features:

• Fully automated digital cycle controls with timing accuracy to 1 second.


• Constantly variable tachometer controlled reversible direction main tub with a speed range of 600-1200 SFPM.


• Fully automated dual direction spindles with speed, direction, and duration controls.


• Automatic flow meter controlled fluid and compound system.


• 2J collet chuck pneumatic fixture retention systems on each spindle.

This is a late model fully optioned system capable of very high throughput and consistent results.

Fixtured workpiece in the abrasive slurry flow. The fixture is held by a pneumatic collet system hidden from view by the orange plastic protective sleeve.

Metal Finishing Services in Denver Colorado