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CALCULATOR · REGRIND OR REPLACE

Regrind it or buy new? Find the break-even on your own numbers.

Enter what a new tool costs, what a regrind costs and how long each lasts on your job. The page gives the cost per part both ways, the saving per year, and the tool life a reground tool has to reach before regrinding stops paying.

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01 · THE CALCULATOR

Regrind or Replace Calculator

Inputs

Result

Fill in the first five fields to see the result.

Cost per part, buy new only(P + C - S) / L
n/a
Cost per part, with regrinding(P + N×R + (N+1)×C - S) / (L × (1 + N×f/100))
n/a
Difference per part
n/a
Difference in percent of buying new
n/a
Break-even life of a reground toolf* = 100 × (R + C) / (P + C - S)
n/a
Cost per year, buy new only
n/a
Cost per year, with regrinding
n/a
Difference per year
n/a
New tools bought per year, buy new only
n/a
New tools bought per year, with regrinding
n/a

Every field is in your own currency and your own life unit. The page has no prices of its own.

02 · HOW IT IS CALCULATED

The formula behind the numbers

Each tool is bought once. Regrinding gives it N more lives of f percent of a new tool, and each of its N + 1 lives starts with a tool change. Cost per unit of tool life, with P the price of a new tool, R one regrind, C one tool change, S the scrap value of the worn-out tool and L the life of a new tool:

buy new only = (P + C − S) / L
with regrinding = (P + N × R + (N + 1) × C − S) / (L × (1 + N × f / 100))
break-even life f* = 100 × (R + C) / (P + C − S)    (percent of a new tool)

With a yearly volume A in the same unit as L, the cost per year is A times the cost per unit, and the number of new tools bought per year is A / L when buying new only and A / (L × (1 + N × f / 100)) with regrinding. If f is below f*, the page says regrinding costs more and shows no saving.

WHAT THE NUMBERS DO NOT SHOW
  1. A regrind removes material. Drills and end mills get shorter with every regrind, and an end mill reground on the diameter cuts under nominal size, so length and diameter offsets have to be measured again before the tool goes back in the machine.
  2. Life after regrinding depends on the grind quality and on whether the tool is recoated. Enter the percentage you measured on your own parts, or the figure your grinder commits to in writing.
  3. A tool run until it chips loses more material at regrind, or cannot be reground at all. The number of regrinds you enter assumes tools are pulled at a planned wear limit.
  4. Tools at the grinder are not in the machine. Count the extra tools you need to cover the turnaround before you compare.
03 · FAQ

Common questions

How do I work out whether regrinding pays?

Compare the cost per part of both routes. Buying new costs (price + tool change - scrap value) / life. Regrinding costs (price + regrinds x regrind cost + (regrinds + 1) x tool change - scrap value) / (life x (1 + regrinds x reground life / 100)). The cheaper figure wins on your numbers.

What is the break-even life of a reground tool?

It is the life, as a percent of a new tool, at which regrinding and buying new cost the same per part: 100 x (regrind cost + tool change cost) / (price + tool change cost - scrap value). Below that figure regrinding costs more, above it regrinding pays. The number of regrinds does not change it.

What does the page leave out?

It does not know how much material your regrind removes, how well your grinder holds the geometry, whether the tool is recoated, how much stock you need to cover the turnaround at the grinder, or what happens when a tool is run to a chip instead of a planned wear limit. The notes under the formula list these.

NEXT

The arithmetic is fixed. The measured tool life is yours.

This page compares two routes on the numbers you enter. Which tool type, grade and coating gives the tool life you enter is the advisor's job, grounded in catalog data and brand-neutral.

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