11.4 Application
Tim A. Bacon
Now let’s go grind a bench block! The following is a step-by-step sequence of operations that can be directly applied to most projects.
- Safety first – Wear safety glasses, remove jewelry, and tie back loose clothing, and long hair.
- Gather equipment – Have some towels nearby to aid in coolant clean up. Create a clean location to place the tools.
- Choose a grinder – The workpiece is square, so use a horizontal surface grinder.
- Choose the wheel – The material for the Bench Block is mild steel. A straight grinding wheel will be used, with the cutting surface on the circumference of the wheel. The wheel is an Aluminum Oxide abrasive for the steel workpiece. A grit of 60 is for general purpose grinding applications.
- Perform a ring test – Ring test the grinding wheel before the wheel is placed on the spindle. If a high ring note is heard, proceed with installation. If the sound is dull, get a new wheel.
- Mount the wheel – The grinding wheel will be mounted on the grinding spindle. To tighten the nut that holds the wheel in place, turn it the opposite of the direction the grinding wheel turns when grinding. This nut usually has left-handed threads.
- Dress the wheel – Set the dressing diamond just past the center of the wheel, on the exit nip side (typically the left). Ensure that the magnet is on, and the diamond is secure. Start the wheel rotating by hand. With your hand clear of the wheel, turn on the power to bring the wheel up to speed. Bring the wheel down to just touch the diamond dresser. Move the crossfeed out towards the operator, and then in away from the operator to evenly dress the wheel. Bring the head down .0002 to .001 and move the crossfeed again. Repeat until the wheel is evenly cleaned up, then stop the wheel before continuing.
- Workholding – Ensure that the grinding wheel is not spinning; clean the table thoroughly. Place the part on the magnetic table with concave side down. Turn the magnet on, and check that the workpiece is secure.
- Touch off – While the wheel is stationary, bring the wheel head down slightly past the top of the part, and on the outgoing nip side of the wheel. “Gently”‘ move the table workspeed direction, X-axis, so that the part touches the wheel. Raise the head until the workpiece passes below the grinding wheel. This process stages the wheel within a few thousandths of the part to expedite grinding, and to avoid excessive plunging into the part on first contact.
- Instructor Note – Once a complete understanding of manually controlling the surface grinder is demonstrated, the automated functions can be introduced if the machine has the capability. Caution is strongly advised. If the grinder is not set correctly, the part may be destroyed, the machine may be damaged, and/or bodily harm may be caused to anyone nearby, including yourself.
- Turn on coolant – Position the coolant nozzle to spray at the ingoing nip side of the wheel on top of the workpiece.
- Turn the grinding wheel on – Start the wheel by rotating it by hand in a clockwise direction. With hands clear, start the motor to bring the wheel up to speed. This will help keep the wheel centered on the spindle if the electric motor has a sudden power surge.
- Start position – Start with the workpiece close to the operator, away from the side of the grinding wheel, and to the left of the outgoing nip.
- Make a complete pass – Use the left hand on the hand wheel to move the part along the workspeed direction from the outgoing nip to the ingoing side, and back to the beginning. The workpiece must clear the grinding wheel before changing direction. Now use the right hand on the hand wheel to move the crossfeed towards the grinding wheel. The crossfeed direction distance should be less than the width of the wheel to create an overlap grinding pattern.
- Repeat as needed – Continue this pattern of moving right, left, and in until the workpiece is on the far side of the grinding wheel.
- Back to the beginning – Move the part to the far left of the grinding wheel, and reposition the workpiece to its starting position.
- Are we there yet? – Turn the wheel off, and inspect the workpiece. Determine if more grinding is required. Continue alternating between making a complete pass, and checking the finish, and/or dimensions before lowering the head to resume grinding.
- Adjust the head – Lower the head down .0002 tenths to thousandths to remove more material.
- Make a complete pass – Make another complete pass, moving the workpiece right, left, and in. See description above.
- Back to the beginning – Move the part to the far left of the grinding wheel, and reposition the workpiece to its starting position.
- Are we there yet? – Turn the wheel off, and inspect the workpiece. Repeat these last three steps until the desired results are reached.
- Level one Complete – When the workpiece has a consistent finish, it may be removed from the grinder.
- Wait for it – Wait until the grinding wheel has stopped before continuing.
- Power down – Turn off the table magnet to release the workpiece.
- Clean up – Wipe down the table and the workpiece to remove the silt. This is the grinding dust mixed with the coolant.
- What’s next? – It is likely that at this point only one side has been ground. Flip the part over, and repeat the above sequence. If both large faces of the workpiece are ground, then the project will go to the mill to square up the short sides.
Author’s Tip
On thin parts, it may be necessary to take a small amount of material off of each side and flip the part over several times. This will help ensure that the part stays flat without being restrained by accounting for the stress relieving of the material being removed.
The shape is that of a bowl right-side up
the fine material that comes off of the part and mixes with the coolant.
When the part is cut, or ground, it can release the stress in the part. This will cause the part to bend.