Grinding

Surface Grinding

Surface GrindingMetalmite Corporation — a full service CNC machine shop located just outside of Detroit, Michigan — offers full surface grinding processing on any job that requires it. A surface grinder is a machine tool used to provide precision ground surfaces, either to a critical size or for the surface finish.

The typical precision of a surface grinder depends on the type and usage, however /- 0.002 mm (/- 0.0001”) should be achievable on most surface grinders.

The machine consists of a table that traverses both longitudinally and across the face of the wheel. The longitudinal feed is usually powered by hydraulics, as may the cross feed, however any mixture of hand, electrical or hydraulic may be used depending on the ultimate usage of the machine (ie: production, workshop, cost). The grinding wheel rotates in the spindle head and is also adjustable for height, by any of the methods described previously. Modern surface grinders are semi-automated, depth of cut and spark-out may be preset as to the number of passes and once setup the machining process requires very little operator intervention.

Depending on the workpiece material, the work is generally held by the use of a magnetic chuck. This may be either an electromagnetic chuck, or a manually operated, permanent magnet type chuck; both types are shown in the first image.

Aluminum oxide, silicon carbide, diamond, and cubic boron nitride (CBN) are four commonly used abrasive materials for the surface of the grinding wheels. Of these materials, aluminum oxide is the most common. Because of cost, diamond and CBN grinding wheels are generally made with a core of less expensive material surrounded by a layer of diamond or CBN. Diamond and CBN wheels are very hard and are capable of economically grinding materials, such as ceramics and carbides, that cannot be ground by aluminum oxide or silicon carbide wheels.

Our Okamoto and Ried Surface grinders offer the application of coolant as well as the extraction of metal dust (metal and grinding particles).

CNC OD Grinder

CNC OD Grinder

Inner and Outer Diameter Grinding

Metalmite has several Inner and Outer Diameter grinders in house. They have a maximum work area of 10” diameter by 40” between centers. We offer CNC grinding as well as conventional grinding capabilities. Our Jones and Shipman grinders have been industry leaders for years and the addition of our Toyoda Universal Grinder has made our grinding department one of the strongest around. With the ability to hold tenth limits and extremely fine microfinishes our customers have been very satisfied.

JigGrindJig Grinding

Metalmite uses a number 3 Moore Jig Grinder to hold tenth limits and finish bores and radii to customer specifications. The jig grinder is very similar to a jig borer, in that the table positioning and spindles are very accurate (far more so than a manual milling machine or lathe). It is almost exclusively used by tool and die makers in the creation of jigs or mating holes and pegs on dies. There are usually many peripheral elements to a large jig grinder, including separate hydraulic motors, air compressors, and various cooling systems for both the hydraulic circuit and supplying coolant to the work and machine itself.

The machine operates by a high speed air spindle rotating a grinding bit. The air spindles are removable and interchangeable to achieve varying surface speeds. Some spindles are fixed speed (60000 rpm), others are adjustable (30000-50000 rpm), and still others are very high speed (175000 rpm). The machines have a standard X-Y table with the notable exception of knee travel. All axes are indexed to .0001” via a vernier scale on the handwheels, with higher accuracy available with the use of measuring bars. The machine head has two vertical travels, one rough head adjustment and the other a precise spindle adjustment. The spindle to which the detachable air spindle mounts also rotates at a variable speed and can typically outfeed .100” while running, again with an accuracy of .0001” on the handwheel or greater, for very precise hole, peg and surface grinding. A well-kept jig grinder will reliably position work to a higher degree of accuracy than is possible with handwheels alone. These features are all critical in positioning a hole and peg system a precise distance from a reference surface or edge.

Jig Grinding

Jig Grinding Sample

The most important factor on a jig grinder is the dual-spindle configuration. The main spindle is roughly positioned with between 1” or 2” of travel for setup, and then the .100” of outfeed is used during machine operation to outfeed into the work. A spacer bar may be used between the grinder and main spindle, allowing large (9” radius or larger) work to be completed. The main spindle has a wide range of speeds to ensure proper grinder feed rates are maintained.