Tech Tip courtesy of Goodson Tools.
Working in technical support, hardly a day passes without at least one crank grinding question. For the most part, these questions involve properly using, dressing, mounting and balancing the crankwheel.
The other question we’ve been hearing a lot lately is, “What can I do with my grinding wheels that aren’t the right size? Can they be changed to fit another machine or another application?” The short answer is, YES. With our expanded resizing services we can easily extend the life of a wheel. We’re able to make arbors bigger, reduce the thickness, reduce the diameter, change the profile, and so on. Not only will this save the environment, it’ll save you money as well. For more information, call Goodson at 1-800-533-8010.
The importance of crank grinding wheel selection
Wheel selection is critical and often overlooked. Take into consideration a high-performance engine rebuild. The correct components for a race engine are distinctly different from those of the family car. Going for the checkered flag involves much more than going for the groceries. Therefore, it wouldn’t make any sense to build a 12:5 to 1 compression engine for a grocery-getter.
In the same respect, using a grinding wheel intended for grinding cast iron crankshafts won’t have the right stuff to do the job correctly on a high-performance crank. Grinding wheels come in a variety of abrasive grains, grit sizes, hardness grades, structures and bond modifications. It is important to select the proper grinding wheel for the intended application. One wheel cannot do everything.
For cast iron crankshafts, you need a wheel that can be used on journals with a Rockwell hardness of 35Rc or less. Goodson’s GCS-wheels are ideal for these applications. They feature a blue-gray, semi-friable abrasive for standard cranks and are specifically designed for straight journals with a minimum of radius and / or thrust grinding.
For more versatile crankshaft grinding, you may want to step up to a better wheel. Goodson’s GCH-wheels are ideal for domestic, import or high-performance crankshafts made of cast or forged steel and nodular iron. They feature a slate-gray abrasive that removes more material, loads less and holds shape longer. GCH-wheels are specifically designed to handle large radii, as well as thrust and plunge grinding common for high-performance crankshafts. Like the GCS-wheel, the GCH-wheel can be used on journals with Rockwell hardness of 35Rc or less.
For diesel crankshafts, you need a wheel that can be used on journals with a Rockwell hardness of 35Rc or more. Goodson’s GCD-wheels are a premium grade wheel ideal for harder materials such as diesel, high-performance, industrial and billet steel crankshafts. It features a mixture of premium white friable and black semi-friable abrasives. In addition to having better form holding capabilities, GCD-wheels cut cooler and require less dressing. These distinctively “salt & pepper” colored wheels are specifically designed for grinding harder crank materials and crankshafts with large radii journals.
Crankshaft grinding techniques
Once you have chosen the proper wheel, the following steps must be taken to safely and successfully grind your crankshaft.
Before mounting any grinding wheel, inspect it for cracks or damage. This can be done visually or by giving the wheel a “Ring Test.” A good vitrified wheel with no cracks will give a clear ringing tone when tapped with a wooden or plastic mallet. A cracked wheel gives off a dull sound which is quite different.
Every wheel is marked with its maximum operating speed in RPM. This rating must be checked against the actual RPM of the spindle which will drive the wheel. The spindle speed should be checked from time to time with a tachometer to be sure nothing has changed.
The majority of on-machine wheel breakages are caused by incorrect mounting. Pay special attention to the condition of the flanges. They must be flat and of equal diameter plus have full contact with the sides of the wheel. The flanges must also be relieved so that they do not contact the grinding wheel in the area of the arbor hole.
Use a new blotter every time the wheel is mounted. The blotters are made of compressible paper which takes up any high points on the side of the grinding wheel. Direct contact between the flange and the side of the wheel could cause a stress point where a crack could begin.
In order to achieve the best results from your grinder, every grinding wheel installed on the machine must be balanced. Rebalancing wheels is a good habit to get into and balance should be checked each time a wheel is reinstalled on the machine.
Wheel balancing is a relatively easy process. First, install the grinding wheel on a wheel center and snug the cap screws. However, do not tighten the screws yet. Then mount the wheel on a balancing arbor and place it on the balancing stand. With the arrow on the wheel pointing as directed. Loosen the cap screws so the wheel will settle downward on the wheel center, then gradually torque them all to recommended specification in ft./lb. Do not rotate the wheel until all fasteners are secure. Remove the balancing weights from the wheel center and let the wheel rotate to its rest position. Mark the 12:00 position (the lightest part of the grinding wheel) on the wheel using a piece of chalk. Install two balance weights approximately on the horizontal centerline and then move the weights up toward the top of the wheel hub.
Double check the wheel balance again. If the wheel will hold position at 12:00, 3:00, 6:00 and 9:00; the wheel is properly balanced. If the chalk mark still comes to rest at 12:00, move each weight upward slightly again until balance is achieved. If the chalk mark moves to the bottom 6:00 position, move the weights the opposite directions. If two weights are not adequate to achieve balance, use additional weight.
Install the grinding wheel on the machine and true the wheel to clean up its grinding face and sides. After truing, remove the wheel and recheck the wheel balance. Adjust the weights as necessary.
Do not allow grinding coolant to run on the grinding wheel when it isn’t rotating. This will cause the wheel to become saturated with coolant on one side and the wheel will be thrown out of balance. This condition can be corrected by turning off the coolant and running the wheel until all the coolant has been removed.
Manual dressing of the grinding wheel is another important factor in producing satisfactory work on your crankshaft grinder. The wheel must be dressed each time it is placed on the machine, even though it may not have been removed from the wheel center. Mount the wheel dresser on the grinder table. Bring the rotating grinding wheel up close to the diamond and start the coolant flow. Never dress without coolant! Frictional heat buildup can cause the diamond to come loose or separate from its mount. Lack of lubricating properties (along with cooling) abrades diamond needlessly.
Best results will be obtained if the diamond is brought into contact with the center of the wheel, feed in a maximum of .002″ then traversed each direction (left and right) off the edge of the wheel. Learning the best traverse rate for dressing the wheel is a matter of trial and error for each operator. You have to be fast enough to prevent glazing, but slow enough to minimize spiral lead marks. Dressing from the center of the wheel outward to each edge helps minimize the effect of the spiral lead marks on the finish of the workpiece. Do not remove over .002″ per pass. Excessive in feed will cause the wheel to act like it’s loaded. This results from wheel material being “pasted” into new exposed wheel porosity.
The type of dress applied to the grinding wheel may be changed to suit different grinding needs. A rapid traverse will remove large amounts of material quickly. A slower traverse will produce a more desireable finish, but won’t remove material as rapidly.
Whenever the sides of a grinding wheel are found to run out, they should be dressed. With the dresser mounted to the table, bring the diamond into contact with the grinding wheel near its front corner, feed in a maximum .002″. The wheel is then fed in and out until the necessary amount has been dressed from the wheel. Dress off enough material to provide a continuous, smooth surface on each side of the wheel.
When regrinding a crankshaft, every attempt should be made to duplicate the original corner radii to prevent the crankshaft from being weakened. Position the diamond in the holder facing out the front. Slide the holder back, position and lock the radius adjuster at the desired dimension. Then slide the diamond holder forward until the diamond contacts the radius adjustment stop. Tighten the diamond holder, unlock and retract the adjustment stop. Feed the wheel into position fully forward.Using fine feed, bring the diamond into contact with the front face of the wheel and dress full width. Then back the wheel away from the diamond .004″; loosen the swivel lock and remove one of the stop pins so the upper swivel can be rotated though 90° of travel. While pivoting the diamond through its 90° arc, bring the wheel into contact and dress off the required amount from one corner. Repeat this process for the opposite corner by replacing the first stop pin and removing the second pin to provide 90° rotation in the opposite direction.
Be sure to keep your diamond dresser tools sharp. Rotate the diamond 30-45° after each dressing operation.
Final words of advice …
When you shop for crank grinding wheels, you need to take into consideration the overall-quality of the wheel; its abrasive composition, grit, bond, hardness and application. As important as wheel selection is to quality crankshaft grinding work, so is working with a reputable supplier. Be sure that your supplier cannot only sell you the wheel, but can also offer technical support, wheel shaping and resizing services and fast, reliable delivery.
The true value of a grinding wheel is not simply based on price, but on a combination of all of these attributes. A top-quality, well-selected wheel for the application will deliver excellent results and trouble-free operation.