Grinding Your Own Tools: From Blank to Sharp¶

CRITICAL SAFETY WARNING¶

STOP! READ THIS SECTION COMPLETELY BEFORE TOUCHING ANY GRINDER!

Grinding wheels carry enormous energy - they are heavy stone discs spinning at thousands of RPM. They demand your utmost respect and can cause severe injury or death if misused.

Mandatory Safety Equipment¶

Safety glasses or face shield - ALWAYS, NO EXCEPTIONS
Respirator mask - Grinding dust causes permanent lung damage
Proper clothing - No loose sleeves, jewelry, or gloves
Hearing protection - Recommended for extended grinding

Grinding Wheel Hazards¶

Wheel explosions - Can occur from:
- Excessive side pressure
- Material jamming between wheel and rest
- Damaged or cracked wheels
- Improper mounting
- Running above rated speed

Pre-Operation Safety Checks¶

Inspect wheel - Look for cracks, chips, or damage
Ring test - Tap wheel gently; should ring like a bell
Check guards - NEVER operate without ALL guards in place
Gap check - Maximum ⅛" between wheel and tool rest
Paper washers - Must be installed to distribute clamping force
Stand clear - Let grinder run 1 minute before first use

During Operation Safety¶

Never force the work - Let the wheel do the cutting
Keep tool moving - Prevents wheel glazing and overheating
Water container ready - For cooling, not wheel quenching
Two hands always - Maintain complete control
Face shield down - Sparks and particles fly everywhere

Equipment Selection and Setup¶

Essential Equipment¶

Bench grinder - 6" or 8" diameter wheels
White aluminum oxide wheels - 60 and 120 grit
Adjustable tool rest - Critical for consistent angles
Water container - For cooling tool bits
Wheel dresser - Diamond or star wheel type
Sharpening stone - For deburring and finishing

Wheel Selection Guide¶

For HSS (High Speed Steel):

Roughing: 60 grit white aluminum oxide
Finishing: 120 grit white aluminum oxide
Wheel hardness: I or J grade (medium)

Why white wheels?

Cooler cutting than gray wheels
Self-fracturing for consistent sharpness
Visual indication when dressing needed
Less likely to burn the steel

Tool Rest Setup¶

The key to consistent results is proper tool rest adjustment:

Set gap - Maximum ⅛" from wheel face
Adjust angle - 10° down from perpendicular
Check height - Center of wheel or slightly below
Lock securely - Vibration will loosen adjustments

10° Angle Setting Trick: Use the factory angle on HSS blanks as a gauge. Place blank against wheel, adjust rest until blank sits flat.

Material Preparation¶

Practice Material¶

Start with mild steel square bar (¼" or ⅜"):

Grinds 5x faster than HSS
Allows rapid skill development
Mistakes are inexpensive
Same grinding techniques apply

Layout and Marking¶

Identify top surface - Factory 10° angle indicates top
Apply layout dye - Blue Dykem or similar
Mark cutting edge - Scribe line at 85° from edge
This creates:
- 5° side clearance angle
- Prevents heel rubbing
- Defines grinding target

The Grinding Sequence¶

Overview: Three-Surface Method¶

Surface 1: End Relief (Front Clearance)

Creates clearance below cutting edge
Compound angle: 10° down, 5° sideways

Surface 2: Side Relief (Side Clearance)

Prevents rubbing on side cuts
Simple 10° angle

Surface 3: Top Rake (Chip Control)

Controls chip formation
Angle varies by material

Detailed Grinding Instructions¶

Surface 1: End Relief Angle¶

Position tool - Flat on rest, aligned to scribed line
Light contact - Let wheel do the work
Sweep motion - Move tool side-to-side continuously
Watch progress - Grind until reaching scribed line
Cool frequently - Dunk when too hot to hold

Critical points:

Maintain consistent angle to scribed line
Don't pause in one spot - creates hollows
Light pressure prevents wheel loading

Surface 2: Side Relief Angle¶

Rotate tool 90° - Previous top still faces up
Hold square to wheel - Rest provides 10° angle
Grind depth - Approximately ⅓ tool width
Create full facet - Top and bottom edges touch wheel
Match previous depth - Consistency matters

Result: Basic tool suitable for brass cutting

Surface 3: Top Rake Angle¶

For steel/cast iron (5-8° positive rake):

Position at wheel side - More control
Tilt tool slightly - 5-8° from parallel to rest
Light passes - This surface is critical
Blend to point - All surfaces meet cleanly

For aluminum (35-40° positive rake):

Extreme angle - Tool looks like meat hook
Multiple passes - Remove substantial material
Maintain control - Aggressive angle is correct
Sharp edge critical - Aluminum needs keen edge

Angle Reference Chart¶

Material	End Relief	Side Relief	Side Rake	Back Rake
Brass	10°	10°	0°	0°
Mild Steel	10°	10°	10°	5-8°
Cast Iron	10°	10°	5°	5°
Aluminum	10°	10°	15°	35°
Stainless	10°	10°	10°	5-8°

Finishing Operations¶

Deburring¶

Use fine stone - 400 grit or finer
Light oil - Prevents loading
Remove all burrs - Check with fingernail
Maintain angles - Don't round cutting edge

Nose Radius¶

Always required - Sharp corners fail immediately
Size guide:
- Roughing: 1/64" radius
- Finishing: 1/32" radius
- Heavy cuts: 1/16" radius
Methods:
- Hand stone for small radius
- Light wheel touch for larger
- Maintain tangency to edges

Heat Management¶

Preventing Damage¶

HSS threshold - Approximately 1000°F
Visual indicators:
- Straw yellow: OK
- Dark blue: Approaching limit
- Light blue: Possible temper loss
- Gray: Definitely damaged

Cooling Technique¶

Dunk frequently - When uncomfortable to hold
Never quench directly on wheel - Causes cracking
Air cool final - Prevents micro-cracks
Work in segments - Allows natural cooling

Common Grinding Errors¶

Problem: Chipped or Broken Cutting Edge¶

Causes:

Too much pressure
Wheel too hard
Feed too aggressive

Solution: Lighter touch, dress wheel, reduce feed

Problem: Burned or Blue Tool¶

Causes:

Dull wheel
Excessive pressure
Insufficient cooling

Solution: Dress wheel, reduce pressure, cool more often

Problem: Poor Surface Finish When Cutting¶

Causes:

Incorrect angles
No nose radius
Rough grinding marks

Solution: Check angles, add radius, finish with fine wheel

Problem: Tool Rubs Instead of Cuts¶

Causes:

Insufficient clearance angles
Heel dragging
Tool below center

Solution: Increase relief angles, check tool height

Advanced Techniques¶

Chip Breaker Grinding¶

For improved chip control on long cuts:

Grind small groove - Behind cutting edge
Depth - 0.005-0.010"
Angle - Parallel to cutting edge
Purpose - Forces chip to curl and break

Special Purpose Tools¶

Threading tools:

60° included angle
Minimal top rake
Very small nose radius

Parting tools:

Narrow width (⅛" typical)
Side clearance critical
Slight back rake

Boring tools:

Extended reach consideration
Increased end relief
Chip evacuation angles

Maintenance and Care¶

Wheel Maintenance¶

Dress regularly - When loaded or glazed
True running - Eliminate vibration
Balance check - Heavy spots cause problems
Storage - Dry location, prevent impacts

Tool Bit Care¶

Protect edges - Individual storage
Rust prevention - Light oil coating
Regular inspection - Check for chips
Resharpening - Before completely dull

Summary: Your First Tool Bit¶

For your first successful tool bit:

Start with brass-cutting geometry - Simplest to grind
Use the 10° table method - Consistent results
Three surfaces only - Don't overcomplicate
Practice on mild steel - Build skills cheaply
Take your time - Rushing causes mistakes
Safety first always - No exceptions ever

Remember: Every master machinist started with their first badly ground tool bit. Practice creates expertise, but safety keeps you alive to develop that expertise.