Those arrows on your grinding wheels are extremely important when it comes to getting the job done well.
By following the appropriate guidelines and making sure the "Mount Up" and "Mount Down" arrows are always pointed in the right direction, you'll continue to produce high-quality work.
The Truth About Truing
Truing is the process of making the newly mounted wheel concentric to the center axis of the machine spindle by dressing away abrasive material, as shown in the illustration. In precision wheels the “Mount Up” arrow ensures that abrasive material is removed from the heavy side of the wheel, improving dynamic balance and reducing overall machine vibration. Mounting the arrow the wrong direction will actually worsen dynamic balance.
Typically, rough grinding wheels with “Mount Down” arrows are not trued so correctly mounting them ensures the heavy side of the wheel is closest to the center axis of the machine spindle. As long as the arrow is pointing in the right direction the dynamic balance will be within an acceptable range thus greatly reducing machine vibration.
Wheel and Hub Tolerances Are Essential to Good Dynamic Wheel Balance
The outer diameter of mounting hubs is typically manufactured to an undersized tolerance, while the hole of the grinding wheel is manufactured to an oversized tolerance. This creates "clearance" between the hole and the hub which is important for safety. However, it also creates eccentricity (i.e. off-center condition) with the center axis of the machine spindle, like you see in this illustration, which produces imbalance and vibration.
Another source of imbalance comes from the fact that all manufactured wheels have small variations in density throughout. During manufacturing, the light side of the wheel is identified and the mounting arrow is applied there. For precision grinding wheels, such as surface grinding wheels, the arrow says to “Mount up.” For rough grinding wheels, such as foundry snagging wheels, it says to “Mount down.” By following this arrow the amount of imbalance in the machine spindle will be at its lowest and the grinding process will not suffer from excessive vibration.
Proper Mounting Procedures: What to Do when Using the "Mount Up" and "Mount Down" Arrows
It's time to learn the correct procedures to ensure your work is quality at all times. The following three procedures will show you the correct way to mount your large precision grinding wheels.
(Please note: when mounting foundry snagging wheels, mount directly onto the fixed machine flange, and then position the arrow on the wheel in the indicated direction.)
Method 1: HORIZONTAL MOUNTING
- Lie the mounting hub horizontally on a firm, flat surface. Slide a new blotter over the sleeve of the hub and against the rear shoulder, making sure it lays flat. Next, slide the wheel onto the hub, ensuring the side with the arrow is visible.
- Apply the second blotter then install second flange. Make sure the blotter fits freely and that the paper hasn't moved. Use a soft mallet to seat the flange properly, and then insert the flange bolts and tighten them by hand.
- Place the hub-wheel assembly onto the machine spindle. Rotate the assembly to position the arrow on the wheel in the directin indicated (up or down). Loosen the flange bolts slightly to allow the wheel to fall into position on the wheel mount. Notice that the top side of the hole firmly sits against the top side of the hub sleeve and that there is a space between the bottom of the hole and the bottom of the hub flange.
- Following a star pattern, tighten the flange bolts to the required torque (20 foot-pounds or in accordance with the machine builder’s recommendations). Finally, tighten the machine spindle nut.
Method 2: VERTICAL MOUNTING
- On a firm but padded surface stand the wheel upright on its periphery and position the arrow downward. Slide a new blotter over the hub’s sleeve and against the rear shoulder. Again, make sure the blotter is lying flat against the sleeve's shoulder. Insert the hub sleeve into the wheel’s hole until the shoulder contacts the side of the wheel. Make sure the sleeve is not cocked inside the hole.
- Place a blotter on the second flange and install it , once again making sure it seats properly. If positioned correctly, the hub sleeve sits firmly against the bottom side of the wheel’s hole.
- Insert all of the flange bolts and tighten them as stated above. Last but not least, place your wheel mount assembly on the machine spindle, position the arrow on the wheel in the indicated direction, and then tighten your machine spindle nut.
The Final Result
Maintaining good dynamic wheel balance when using a large-diameter grinding wheel is essential, and aligning your wheel with the mounting arrows positioned correctly ensures the job gets done right. Whether you're working on a rough application such as foundry snagging or a precision application such as cylindrical or roll grinding, good dynamic wheel balance makes a big difference in overall performance. Not only does good balance keep your machine from vibrating, it also increases metal removal rates and extends wheel life, allowing you to produce quality parts on a continual basis.