Grinding

Grinding is an abrasive machining process that uses a grinding wheel as the cutting tool.

A wide variety of machines are used for grinding:

Hand-cranked knife-sharpening stones (grindstones)
Handheld power tools such as angle grinders and die grinders
Various kinds of expensive industrial machine tools called grinding machines
Bench grinders often found in residential garages and basements
Grinding practice is a large and diverse area of manufacturing and toolmaking. It can produce very fine finishes and very accurate dimensions; yet in mass production contexts it can also rough out large volumes of metal quite rapidly. It is usually better suited to the machining of very hard materials than is “regular” machining (that is, cutting larger chips with cutting tools such as tool bits or milling cutters), and until recent decades it was the only practical way to machine such materials as hardened steels. Compared to “regular” machining, it is usually better suited to taking very shallow cuts, such as reducing a shaft’s diameter by half a thousandth of an inch or 12.7 μm.

Grinding is a subset of cutting, as grinding is a true metal-cutting process. Each grain of abrasive functions as a microscopic single-point cutting edge (although of high negative rake angle), and shears a tiny chip that is analogous to what would conventionally be called a “cut” chip (turning, milling, drilling, tapping, etc.). However, among people who work in the machining fields, the term cutting is often understood to refer to the macroscopic cutting operations, and grinding is often mentally categorized as a “separate” process. This is why the terms are usually used in separately in shop-floor practice.

Lapping and sanding are subsets of grinding.

Surface grinding

Surface grinding uses a rotating abrasive wheel to remove material, creating a flat surface. The tolerances that are normally achieved with grinding are ± 2 × 10−4 inches for grinding a flat material, and ± 3 × 10−4 inches for a parallel surface (in metric units: 5 μm for flat material and 8 μm for parallel surface).

The surface grinder is composed of an abrasive wheel, a workholding device known as a chuck, either electromagnetic or vacuum, and a reciprocating table.

Grinding is commonly used on cast iron and various types of steel. These materials lend themselves to grinding because they can be held by the magnetic chuck commonly used on grinding machines, and they do not melt into the wheel, clogging it and preventing it from cutting. Materials that are less commonly ground are Aluminum, stainless steel, brass & plastics. These all tend to clog the cutting wheel more than steel & cast iron, but with special techniques it is possible to grind them.

Cylindrical grinding

Cylindrical grinding (also called center-type grinding) is used to grind the cylindrical surfaces and shoulders of the workpiece. The workpiece is mounted on centers and rotated by a device known as a drive dog or center driver. The abrasive wheel and the workpiece are rotated by separate motors and at different speeds. The table can be adjusted to produce tapers. The wheel head can be swiveled. The five types of cylindrical grinding are: outside diameter (OD) grinding, inside diameter (ID) grinding, plunge grinding, creep feed grinding, and centerless grinding.

A cylindrical grinder has a grinding (abrasive) wheel, two centers that hold the workpiece, and a chuck, grinding dog, or other mechanism to drive the work. Most cylindrical grinding machines include a swivel to allow for the forming of tapered pieces. The wheel and workpiece move parallel to one another in both the radial and longitudinal directions. The abrasive wheel can have many shapes. Standard disk-shaped wheels can be used to create a tapered or straight workpiece geometry while formed wheels are used to create a shaped workpiece. The process using a formed wheel creates less vibration than using a regular disk-shaped wheel.

Tolerances for cylindrical grinding are held within five ten-thousandths of an inch (± 0.0005) (metric: ± 13 um) for diameter and one ten-thousandth of an inch(± 0.0001) (metric: 2.5 um) for roundness. Precision work can reach tolerances as high as fifty millionths of an inch (± 0.00005) (metric: 1.3 um) for diameter and ten millionths (± 0.00001) (metric: 0.25 um) for roundness. Surface finishes can range from 2 to 125 microinches (metric: 50 nm to 3 um), with typical finishes ranging from 8 to 32 microinches. (metric: 0.2 um to 0.8 um)

Creep-feed grinding

Creep-feed grinding (CFG) was invented in Germany in the late 1950s by Edmund and Gerhard Lang. Unlike normal grinding, which is used primarily to finish surfaces, CFG is used for high rates of material removal, competing with milling and turning as a manufacturing process choice. Depths of cut of up to 6 mm (0.25 inches) are used along with low workpiece speed. Surfaces with a softer-grade resin bond are used to keep workpiece temperature low and an improved surface finish up to 1.6 micrometres Rmax

With CFG it takes 117 sec to remove 1 in.3 of material, whereas precision grinding would take more than 200 sec to do the same. CFG has the disadvantage of a wheel that is constantly degrading, and requires high spindle power, 51 hp (38 kW), and is limited in the length of part it can machine.

To address the problem of wheel sharpness, continuous-dress creep-feed grinding (CDCF) was developed in the 1970s. It dresses the wheel constantly during machining, keeping it in a state of specified sharpness. It takes only 17 sec. to remove 1 in3 of material, a huge gain in productivity. 38 hp (28 kW) spindle power is required, and runs at low to conventional spindle speeds. The limit on part length was erased.

High-efficiency deep grinding (HEDG) uses plated superabrasive wheels, which never need dressing and last longer than other wheels. This reduces capital equipment investment costs. HEDG can be used on long part lengths, and removes material at a rate of 1 in3 in 83 sec. It requires high spindle power and high spindle speeds.

Peel grinding, patented under the name of Quickpoint in 1985 by Erwin Junker Maschinenfabrik, GmbH in Nordrach, Germany, uses a tool with a superabrasive nose and can machine cylindrical parts.

Ultra-high speed grinding (UHSG) can run at speeds higher than 40,000 fpm (200 m/s), taking 41 sec to remove 1 in.3 of material, but is still in the R&D stage. It also requires high spindle power and high spindle speeds.

Others

Centerless grinding

Form grinding is a specialized type of cylindrical grinding where the grinding wheel has the exact shape of the final product. The grinding wheel does not traverse the workpiece.

Internal grinding is used to grind the internal diameter of the workpiece. Tapered holes can be ground with the use of internal grinders that can swivel on the horizontal.

Centerless grinding is when the workpiece is supported by a blade instead of by centers or chucks. Two wheels are used. The larger one is used to grind the surface of the workpiece and the smaller wheel is used to regulate the axial movement of the workpiece. Types of centerless grinding include through-feed grinding, in-feed/plunge grinding, and internal centerless grinding.

Pre-grinding When a new tool has been built and has been heat-treated, it is pre-ground before welding or hardfacing commences. This usually involves grinding the OD slightly higher than the finish grind OD to ensure the correct finish size.

Electrochemical grinding is a type of grinding in which a positively charged workpiece in a conductive fluid is eroded by a negatively charged grinding wheel. The pieces from the workpiece are dissolved into the conductive fluid.

A schematic of ELID grinding

Electrolytic in-process dressing (ELID) grinding is one of the most accurate grinding methods. In this ultra precision grinding technology the grinding wheel is dressed electrochemically and in-process to maintain the accuracy of the grinding. An ELID cell consists of a metal bonded grinding wheel, a cathode electrode, a pulsed DC power supply and electrolyte. The wheel is connected to the positive terminal of the DC power supply through a carbon brush whereas the electrode is connected to the negative pole of the power supply. Usually alkaline liquids are used as both electrolytes and coolant for grinding. A nozzle is used to inject the electrolyte into the gap between wheel and electrode. The gap is usually maintained to be approximately 0.1mm to 0.3 mm. During the grinding operation one side of the wheel takes part in the grinding operation whereas the other side of the wheel is being dressed by electrochemical reaction. The dissolution of the metallic bond material is caused by the dressing which in turns results continuous protrusion of new sharp grits.

Uses for Carbide Burrs

Use carbide burrs in air tools such as die grinders, pneumatic rotary tools and high speed engravers. Micro Motors, Pendant Drills, Flexible Shafts, and hobby rotary tools such as a Dremel.

Carbide burrs are widely used for metalworking, tool making, engineering, model engineering, wood carving, jewelry making, welding, chamferring, casting, deburring, grinding, cylinder head porting and sculpting. Carbide burrs are used in the aerospace, automotive, dentistry, stone and metalsmith industries.

What cut should you choose?

Single cut (one flute) carbide burrs have a right handed (up cut) spiral flute. Single cut is used with stainless steel, hardened steel, copper, cast iron and ferrous metals and will remove material quickly with a smooth finish. Use for heavy stock removal, milling, deburring and cleaning.

Heavy removal of material
Milling
Deburring
Cleaning
Creates long chips

Use double cut carbide burrs on ferrous and non ferrous metals, aluminium, soft steel and also for all non-metal materials such as stone, plastics, hard wood and ceramic. This cut has more cutting edges and will remove material faster. Double cut also called Diamond Cut or Cross Cut (2 flutes cut across each other) and will leave a smoother finish than single cut due to producing smaller chips as they cut away the material. Use double cut for medium-light stock removal, deburring, finishing and cleaning. Double cut carbide burrs are most popular and work for most applications.

Medium- light removal of material
Deburring
Fine finishing
Cleaning
Smooth finish
Creates small chips

What RPM speed should you use?

The speed at which you use your carbide burr in your rotary tool will depend on the material you’re using it on and the contour being produced but it’s safe to say you do not need more than 35,000 RPM. If the burs are chipping easily this could be due to the speed being too slow. It’s ideal to start the bur off slow, increasing the speed as you go along. High speeds will prevent clogging in the flutes of your carbide burs.

As with all drill bits and burrs, let the burr do the work and apply only a little pressure, otherwise the cutting edges of the flutes will chip away or become smooth too quickly, reducing the life of your burr.

Our carbide burrs we manufacture are machine ground from a specially chosen grade of carbide. Due to the extreme hardness of the tungsten carbide, they can be used on much more demanding jobs than HSS (High Speed Steel). Carbide Burrs also perform better at higher temperatures than HSS, so you can run them hotter, and for longer. HSS burrs will start to soften at higher temperatures, so carbide is always a better choice for long term performance.

Click here if you are interested in dropshipping our USA made carbide burr tools.

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