Straight Grind Rail
Case Study (Centerless Grinding) {Coated}
Theory of Operation
What is Centerless Grinding?:There are three basic methods for cylindrical grinding and finishing: centerless grinding, centered grinding, and planetary grinding. The most widely used technique is the centerlessmethod. Centerless grinding is defined as the dimensioning and /or finishing of the outside diameter (OD)of a cylindrical part which is supported on a work rest blade and rotated by a regulating (or feed)head. The abrasive belt direction is downward, against the work piece, giving the tendency topush the work piece into the regulating head, which in turn, forces the work piece into theabrasive belt. Also, the regulating head is set at a slight angle to that of the contact wheel, so asthe work piece rotates, it is made to transverse through the machine. This combination generateshigh unit grinding pressures making centerless grinding a very efficient method of utilizingcoated abrasive belts. This is in contrast to centered grinding where the parts are mounted "on -centers" within a lathe and then finished with a tool post mounted grinder. Within cylindricalgrinding in general, there are three categories of abrasive operations. They are grinding /dimensioning, finishing / blending and polishing. These can be done in either wet or dryenvironments and on single or multiple head machines. The three basic elements of a centerless grinder include the regulating head, the work restsupport, and the grinding head. Figure 1 shows the basic parts of a typical centerless grinder.Centerless machines come in various sizes and configurations but all operate on the sameprinciples. The work pieces are constrained as they travel through the machine by special stops, adjacent work pieces, and by the friction of the regulating head. This makes the operationcompliant to both long and short cylindrical parts.

Grinding Head
The abrasive grinding head can be either of two configurations, slack-of-belt or contact wheelsupported, as illustrated in the following diagram. With slack-of-belt processing, it is a low tomedium pressure OD finishing operation where the abrasive belt is held by idler and drivewheels and is semi-wrapped around the part being processed. The abrasive is not supported fromthe backside. The method is primarily considered a surface leveling and finish refinementprocess.With the second configuration, the abrasive belt is supported by a contact wheel. The selectionof contact wheel and abrasive to match the grinding parameters required for a specific operationis very critical. Dimensioning / stock removal generally requires a harder (~90A Dur.), serratedrubber contact wheel, and coarse grade 3M Cubitron abrasives, while, blending / finishinggenerally requires the use of a softer (60 - 90A Dur.), smooth faced contact wheel and 3MTrizact abrasives.Regulating Head
The regulating head rotates the cylindrical work piece at a constant speed and controls thethrough-feed rate of the work piece past the abrasive belt. It should be noted that the abrasivebelt runs at a much higher speed than the regulating head. There are two common configurationsfor the regulating head. It can consist of either wheel or a belt (leather, rubber or abrasive)running against a steel platen. With both configurations, the head must rotate upward which is inthe opposite the direction of the abrasive belt.The regulating head can also be of a floating (constant pressure) or fixed (dimensioning) positiondesign. Examples of a constant pressure design would include Hammond, Loeser and Ran Brightcenterless finishers. In this configuration, the regulating head maintains a constant pressure ofthe work piece against the abrasive head, removing stock and refining the surface finish, but notcorrecting for work piece concentricity or out-of-roundness. It will simply follow the partsoriginal geometry. With a dimensioning design, such as an ACME 910 or 1212, the regulatinghead is actually positioned in order to remove a set amount of stock off the OD of the part beingprocessed. It will correct for part geometry (roundness / concentricity) as well as refine the finishof the parts surface.Surface speed, helix angle and horizontal angle govern the operation of the regulating head.Each is adjustable to fit the specific operation. The helix angle is the angle of the head in thevertical plane parallel to the centerline of the work piece. The actual through-speed isdetermined as a function of the helix angle and the regulating head rotational speed. In general, by decreasing the helix angle and increasing the regulating head speed, better surface finish, dimensioning capability, and through-feed of work pieces can be obtained. The horizontal angleis the sideways adjustment of the regulating head in the horizontal plane to provide for evenpressure across the entire face of the abrasive belt. This insures for uniform cut and evenabrasive belt wear. This feature also gives the constant pressure, floating head, machines theability to finish tapered parts such as golf club shafts. Dimensioning machines do not have thisability. They are designed strictly for straight shaft parts.Work Rest
The purpose of the work rest is threefold: (1) to provide firm support of the part, (2) to properlyposition the work piece height, and (3) to align the part with the equipment as it traversesthrough the machine past the abrasive belt. The work rest blade supports the work between theregulating and the grinding heads. It is adjustable in order to raise or lower the center of the partin relation to the centerline between the contact wheel and the regulating wheel. Generally, thedistance between the work rest and the grinding head should be no more than one-third of thepart diameter to be finished. Also, the centerline of the work piece should be no more than 1/8"above or below the centerline of the regulating/grinding heads. For recommended set upparameters on a specific machine, always consult the operating manual supplied with theequipment or contact the machine builder. Of the three components, it plays the largest role inthe proper alignment of the work piece with the equipment. Most centerless grinding problems(barber poling, etc.) can be traced to poor alignment. Work rests can be made from variousmaterials including tungsten carbide, amcon bronze, UHMW plastic, leather, etc. The materialused is dependant on the centerless operation being performed.General Recommended Centerless Equipment Parameters
Parameter Recommendation NotesAbrasive Speed: 6000 - 7000 SFPMRegulating Wheel Speed: 100 - 200 SFPMReg. Wheel Helix Angle: 3 - 5 DegreesPart Through Put Speed: 10 - 20 FPM We have run up to 60 FPM.Lubricant: 5% synthetic, semi-synthetic or water miscible oilPressure / Motor Load Light to Medium 10 - 20% over motor idle drawContact Wheels Aggressive Stock Removal: 90A Dur. Serrated Rubber (Should notbe used with 953FA)Dimensioning / Blending: 90A Dur. Smooth Faced RubberFine Finishing / Polishing: 60 - 70A Dur. Smooth Faced RubberIndustry Applications
What Type of Industries Utilize Centerless Grinding?:Hydraulic Bar StockElevator Shaft ManufacturingConstruction EquipmentAgricultural EquipmentBathroom and Bus Grab RailsAutomotive Components - i.e. Shock Absorbers, Engine Valves, Piston Pins, etc.Appliances - i.e. Washing Machine Agitator ShaftsElectric Motor Components - i.e. Stator Cleaning, Rotor DimensioningNuclear Fuel Rods and TubesSports Equipment - i.e. Baseball Bats, Fishing Rods, Golf Club ShaftsTruck exhausts, motor vehicle exhausts, motorcycle exhausts, engine exhaustsAnd Many More!What Type of Materials Will Be Involved?:
Mild and Hardened Carbon Steel Stainless Steel: Brass Aluminum Titanium* Zirconium / Zircalloy* Ceramics** Composites** Glass* Acrylic Many MoreSonic Riders 2 - Snowy Kingdom
Next page: Challenge 20 Inch Dual Suspension Girls Bike
Straight Grind Rail News
Baby's First Christmas - Gift Ideas

Cutie Pie video for my Cuties- Get your daily peek into mommyhood and my day at: www.kandeeland.com Since it will be baby's first Christmas, I ...
Christmas Gift Ideas

PLEASE EXPAND THIS BOX ♥ Sometimes it's hard to think of what gifts to give or for yourself, so I thought I would show you a few things that I ...
Christmas gift ideas for girls and mums

Don't forget to subscribe, like and comment... Or you'll ruin Christmas for everyone! Blog/Website: jimchapman.co.uk Twitter twitter.com ...
Christmas Gift Ideas For Guys Part 1

CLICK ON 'show more' FOR LINKS TO EVERYTHING MENTIONED Don't forget to subscribe, like and comment... Or Santa will definitely not be ...



