Horizontal spindle surface grinding is becoming ever more important as equipment and machined parts are miniaturized and dimensional tolerances shrink.
A few years ago, ;.0001 in. was considered a close tolerance. Now, half that amount (.000050 in.) is seen more frequently on drawings,
especially in the advanced technology areas. These pressures for increasingly closer work are reflected in newer, more rigid machine tools and greater concern with surface texture specification and measurement.
Avoiding damage, such as grinding cracks, is critically important in ground parts subjected to large and variable loadings such as those occurring in bearings, missiles, and aircraft applications.
These requirements for improved machine tools are also reflected in the development of improved superabrasives.
These permit sharpness to be better controlled, resulting in less metallurgical damage and easier size control. A grinding wheel made with
improved abrasives (superabrasives) will last much longer while removing a given amount of work material than one made with aluminum oxide or silicon carbide. With superabrasives, the ratio of the volume of workpiece removal to the volume of abrasive loss (the grinding ratio) is low, and the ratio can be considerably greater than 1000:1, in contrast with the considered acceptable with conventional abrasives. As there is great movement toward automation of grinding processes, more and more research is being put into making the grinding processes more predictable.40:1
All this progress relates to the task of setting up and using the horizontal spindle surface grinder. It is at this point you start putting together numerous variables that, through your skill and observation, can result in an accurate workpiece.
As the operator you will have more control of the outcome in surface grinding than in nearly any other portion of the machinist’s trade.
This is also where the wheel selection and preparation processes are put to the test.
In surface grinding it is necessary to reverse one of the more usual principles of machining used in most of the other chip-making processes. In both turning and milling for metal-cutting volume, the machinist tries to keep the depth of cut to a maximum, adjusting all the other variables such as speed and feeds to match that concept. In surface grinding, the important thing is to coordinate the action of workpiece speed, crossfeed, and downfeed to keep the grinding action as consistent as possible while avoiding damage to the workpiece.
The example in this unit will be the grinding of a vee block, but before beginning with that, other generalities about horizontal spindle surface
grinding should be considered.
Starting with a broad surface of a soft steel like AISI 1018, a suitable selection of wheel and grinding variables would be as follows: an aluminum oxide abrasive of 46-grit size in a J-bond hardness. The bond itself is vitrified. The wheel speed for vitrified wheels is usually from 5500 to 6500 sfpm; the table speed would be about 50 sfpm (and could be 625 M12_KIBB5087_09_SE_C12.QXD 6/3/09 1:36 AM Page 626
626 SECTION L GRINDING AND ABRASIVE MACHINING PROCESSES much higher when using rotary table machines). The crossfeed
rate would be .050 to .500 in. per pass, with a maximum being one fourth the wheel width.
For roughing, the downfeed could be as much as .003 in., and for finishing less than .001 in.
If the same AISI 1018 material was pack hardened (carburized) to about 55 Rockwell C, how would this change the initial recommendations? The wheel speed and the table speed would remain the same. The abrasive chosen and the grit size would also remain the same, but the bond selected would be one grade softer, or I bond. The roughing downfeed would change to .002 in. and the finishing to .0005 in.
The greatest change in recommendation other than the grade of the wheel would be in the way that the crossfeeding is done. Here the recommendation would be .025 to .250 in. with one tenth of the wheel width taken as a maximum. All these recommendations are based on a sharp wheel prepared with a dresser that is in good condition. If the dressing is done incorrectly, so that the wheel is dulled, it could make
the recommendations useless.
A general observation in horizontal surface grinding is to keep the crossfeed travel as large as possible and the downfeed adjustments matched so that you cannot hear a significant change in grinding wheel speed during the work’s traverse under the wheel. This procedure helps keep the surface of the wheel parallel to the spindle and avoids excessive dressing, providing the grade and abrasive friability are correctly matched to the workpiece needs.
At the surface grinder you will be using, familiarize yourself with the controls and tooling. If someone else is using the machine, observe the operation for a time. Check the supply of grinding wheels and determine their possible uses by observing their color and texture appearance and by reading the printed symbols on the blotters.

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