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Simplifying Radius Grinding

Radius Grinding

The CUTTERMASTER Professional and Toycen Air Spindle has been designed for corner radius (bull nose) and ball nose grinding. Your attention to detail during set up is essential to your success. As with any surface on the cutter, grinding a radius can be tricky: although a 0.0002” nick won’t really affect the tolerance it will leave a blemish in your machined part.

The concept of this operation is that the grinding wheel and the tool must be located relative to the tool spindle pivot point so that the radius is created as the tool is rotated past the wheel.

There is a key difference in grinding bull nose versus ball nose corner rads. That is as follows:
show diagram

When grinding a bull nose you locate your wheel at angle in the y, x, and Z axes, set your indicators to zero, then move the wheel away from center (pivot) the desired radius (eg. 0.150” for a 0.150” radius), then bring the tool to the wheel using the x and y feed screws on the Radius Air carriages.
When grinding bull nose, you bring the tool to the wheel.

When grinding a ball nose, the center of the ball pivots at the center of the x,y pivot. You position the tool on center then bring the wheel to the tool.
When grinding ball nose, you bring the wheel to the tool.

True and Dress the wheel
Before setting up for your radius, make sure that the grinding wheel is shaped, trued and dressed using the Spindle Mounted Wheel Truing Device. It is important to know what part of the wheel is in contact with the tool throughout the grinding process. To facilitate this we want the outside corner of the wheel to be the farthest out with clearance on the inside. See section / diagram (.xx truing)

Bull Nose Corner Radius Set Up:
Tips to remember: the center of the arc of the corner radius is the pivot point of the radius spindle. Remember we are bringing the tool to the wheel.

Set up your CUTTERMASTER Professional like in the figure xx with magnetic dial indicators in place to keep track of both the x and y tables on the CUTTERMASTER Professional.
Tool Rest: The tool rest is not needed. The Indexing is used to position the tool.
Park the tool rest by removing it and installing it from the other end. This keeps the hole free from dust and can be used as a handle for when grinding the radius instead of holding the tube.

Backlash Compensator for z-axis indexing. If you find that there is any drift in the dial at the top of the tower

Set the Motor Rotation
Motor Tower is set clockwise ~1° to ensure the outside corner of the trued grinding wheel is proud. We want to be sure that we know which part of the wheel is grinding. Lock the motor pivot rotation.

Set the Motor Tilt Angle (Primary radius angle)
Choose an angle that suits your needs and is generally steeper than the side primary and less than the secondary. That is a starting point (most tools have different angles). Another way of saying this is take the side primary angle, plus the secondary angle and dividing by two. For example if you had a 3/4” end mill, the chart calls for 10° primary angle and a 18° clearance angle: (10° + 18°) / 2 = 14°. Therfore, you would set the motor tilt around 14°. Lock the motor tilt. This is a general rule not critical.

Locate Centers and Wheel Height at the desired height.
Install the center finder into the receiver in the center of the radius assembly. Bring the grinding wheel close to the center finder and use the z axis lead screw to set the height of the wheel. The height of the wheel should be level with the top of the center finder (center of the tool).

Bring the wheel in to the pivot center at the correct helgth and angle.
Wheel has to be at chosen angle and height to begin the center location process.

With the motor off, bring the wheel to the top corner of the center finder in both axes by feeding with the lower table feeds. Set your indicators to zero.

Move the wheel away 0.200” in the y axis to remove the center finder and return the y axis table to zero using your indicator.

The manual center finder will get you close to the center of the swing. Minor adjustments should be made if additional accuracy is needed.

Load the tool.
Move the air spindle upper y axis carriage away from the wheel to load the tool. You don’t want to move the lower table x or y feed screws after they have been positioned. Clamp the collet on the shank of the endmill and not the flutes if possible. The end mill flutes should be level with the table, or tipped slightly down depending on the tool helix Set the indexing collar to the required flute position.

Set the wheel position for your desired radius.
For this example we will set up for a .150” radius. The grinding point of your wheel has previously been located at center and your y axis indicator has been set to zero. Using the y axis table feed move the wheel away from the tool .150” according to your indicator. Now, the grinding point of the wheel will follow a .150” arc around the central pivot point of the radius spindle. Return the tool to the wheel, almost to touch, using the spindle upper carriage y axis feed screw.

Using the radius spindle upper carriage x axis feed screw, back the tool away from the wheel so that it will clear the wheel when you swing the spindle through the entire radius grinding motion.
Double check: you should see that the corner of the tool is off-set from the grinding point on the wheel by .150” when in line with the x axis and also when the spindle is swung so that the tool and spindle are in line with the y axis (fig..xx)
Double check that the settings are snug: motor tower tilt and pivot.

Once you are happy with your set up, from this point you will only use the upper carriage spindle x axis feed screw to grind.

Gibs: Once you are in position, tighten the radius spindle carriage red gib set screws to remove any play in the spinlde upper carriages. Leave the outer (black) thumbscrews just snug You don’t want any movement in the air spindle fixture except rotation.

Grinding the Corner Radius
Run the grinder at a moderate speed with the wheel turning down into the tool. Use only the upper tool spindle x-axis carriage to feed. You may find that the machine works best using a counter clockwise pivot as a roughing pass and a clockwise pivot for the finishing pass.

In this case, once you’re set up, your procedure would look like as follows:
always do a test swing with the motor off.
1. Set the indexing collar
2. Lift the motor
3. Rotate the spindle clockwise
4. Release the motor lift
5. Grind your roughing pass with a counter clockwise pivot
6. Grind your finishing pass with a clockwise pivot
7. Lift the motor and index to the next flute (without changing the position of the z axis)
8. Repeat for the remaining flutes.

Produce the radius, measure it, make the appropriate adjustment to the tool spindle carriage until satisfied with the tool geometry.

Ball Nose Set Up

Tip to remember: the pivot point of the radius spindle is the center of the arc on the ball nose. In this case we are bringing the wheel to the tool.

Set up your CUTTERMASTER Professional like in the figure xx with magnetic dial indicators in place to keep track of both the x and y tables on the CUTTERMASTER Professional.

Tool Rest: The tool rest is not needed. Park the tool rest by removing it and installing it from the other end. This keeps the hole free from dust and can be used as a handle for when grinding the radius instead of holding the tube.

Backlash Compensator for z-axis indexing. If you find that there is any drift in the dial at the top of the tower

Set the Motor Rotation
Motor Tower is set clockwise ~1° to ensure the outside corner of the trued grinding wheel is proud. We want to be sure that we know which part of the wheel is grinding. Lock the motor pivot rotation.

Set the Motor Tilt Angle (Primary radius angle)
Choose an angle that suits your needs or match the existing radius grind.

Center the upper tool spindle carriage over the pivot center. Center can first be approximated by lining up the cut out on the lead screw tray with the front face of the tool spindle carriage (figure xx).
Set the upper tool spindle carriage to the center of the tool spindle pivot point using the 5C half pin and the tool spindle pivot post (Figure 18).

Lock the y axis carriage using the thumb screw (Figure 19). Note: For a ball nose end mill the y axis remains locked on center for all operations. Also, we do not need to move the tool spindle or motor tower carriages now that they’re located in space.

From this point on you only need to feed with the upper Tool spindle carriage x axis feed.

Load the tool.
Clamp the collet on the shank of the endmill and not the flutes if possible. The end mill flutes should be level with the table, or tipped slightly down. Set the indexing collar to the required flute position.

Using the upper x axis feed, bring the tool close to the wheel. As you pivot the tool spindle carriage notice that the wheel follows your profile of the ball nose tool (Figure xx). Tilt the motor angle to grind the secondary clearance angle.

To Check for position accuracy go to a ZERO Radius setting
Using the sharp corner of the end mill using the upper Y axis feed bring the corner into the wheel, now back to the upper X away SO AS NOT TO CRACK THE WHEEL WHEN TEST ROTATING.

Rotate the assembly 90 degrees CW watching so the tool does not damage the wheel
now feed the upper X untill the tool comes close to the wheel not touching.

Since you are at zero Rad the corner of the tool should pivot at the exact outside corner of the wheel.

3.10 Corner Radius Clearance

The above instructions only address the primary angle. However a clearance angle can easily be created while the tool is still in the collet (Figure 22). It is aggressive in most cases unless you are machining hard materials.

To grind a clearance angle behind your primary.
Leave the motor at the radius that was ground on the primary.
Reposition the tool at the desired secondary angle. either by rotating the tool in the collet
or in some cases index the tool one slot (15 degrees)
Using the upper Y axis bring the tool into the wheel motor off until it touches (motor off) test drive the swing. turn the motor on take a cut , continue with both flutes untill the resired primary width is reached.

On Bull and Ball nose tools secondary clearances are generally aggressive and as is usually the case keep primary land widths to a minimum base on the material.