Cost Reduction Through Honing Stone Quality Control

The Challenge

Cummins’ Darlington works faced puzzling inconsistencies in their wet liner honing operations. Cycle times varied from 1 to 5 minutes. Glazing appeared unpredictably on cylinder bores. Stone sets sometimes lasted a full shift, other times needed replacement after just 30 minutes. The culprit: stones supplied as a single grade varied across more than six hardness grades. Testing revealed a 240-point spread spanning readings from 800 to 1100.

The Solution

Engineer Ken Claybourne implemented GrindoSonic testing to classify every honing stone before use. Testing 1,800 J-grade stones revealed the true variation hidden within nominal grades. The solution was straightforward: use only stones reading between 850 and 950, classified into narrow bands of just 10 points. All eight stones in each set now come from a single category, ensuring uniform load distribution and consistent cutting action.

Results

The matched-stone program transformed honing operations:

Service life: Extended from 400 liners/set to 1,500–2,000 liners/set
Stone consumption: Dropped from 133 stones/week to 148 stones/month, a 40% reduction per component
Production rate: Increased from 270 to 500+ liners/shift with consistent sub-60-second cycles
Oil consumption: Reduced from 4 oz/h to under 1 oz/h
Blow-by: Improved by a factor of four
Piston ring wear: Decreased from 0.07 gm to 0.01–0.03 gm
Surface finish: Consistently 14–23 μm rms, eliminating glazed marks and bell-mouthing

Key takeaway: Classifying honing stones into 10-point GrindoSonic bands extended stone life from 400 to 2,000 liners per set and nearly doubled production output per shift at Cummins.

Frequently Asked Questions

How much variation exists in honing stones supplied as a single grade?

Testing 1,800 J-grade honing stones at Cummins revealed a 240-point spread in GrindoSonic readings (800 to 1100), spanning more than six actual hardness grades within a single nominal grade designation. This hidden variation was the root cause of inconsistent honing performance, unpredictable stone life, and erratic cycle times.

What cost savings did GrindoSonic stone classification achieve?

Stone consumption dropped from 133 stones per week to 148 stones per month, a 40% reduction per component. Stone service life extended from 400 liners per set to 1,500-2,000 liners per set. Production increased from 270 to over 500 liners per shift, oil consumption fell from 4 oz/h to under 1 oz/h, and piston ring wear decreased from 0.07 gm to 0.01-0.03 gm.

How does matching honing stones improve surface finish quality?

By classifying stones into narrow 10-point GrindoSonic bands and using only stones from the same category in each set, all eight stones wear uniformly. This eliminates mixed-hardness sets where soft stones erode faster and hard stones protrude, causing glazing, bell-mouthing, and retraction marks. Surface finish became consistently 14-23 micrometers rms.