One Station or Two: Combination Tool Cost | HENTRY

Saving a machine is a capital argument, not a cycle-time argument. The cycle time decides whether one station can absorb the volume at all; the capital, floor space, labour and work in progress decide what the second station was costing while it existed.

This page puts the five cost lines of a three-year comparison on one table, shows the arithmetic line by line, and names the four situations in which a single station costs more than it saves.

All amounts are example assumptions, stated so the arithmetic can be checked. They are not HENTRY prices and they are not a quotation for any machine, tool or service.

The five cost lines

The comparison is only as good as its boundaries. A three-year window is long enough to include one machine's depreciation cycle and short enough to stay inside a planning horizon.

The first line is machine capital: depreciation plus the interest on the capital employed. Depreciation is purchase price divided by service life; interest is charged on the average book value over the period, not on the purchase price.

The second line is floor space and logistics. Space is charged per square metre per year, and the figure should include the aisle, the coolant unit and the chip container, not only the machine footprint.

The third line is direct labour. Operators are rarely dedicated to one machine, so the honest unit is a fraction of a full-time equivalent, loaded with employer costs and indirect time.

The fourth line is work in progress. Two stations hold at least two parts between them, one station holds one, and the difference is charged at the cost of capital.

The fifth line is tooling. It is the only line that can favour either side, which is why it deserves its own section rather than a footnote.

The worked comparison

The example is a cell making 200,000 holes a year, with a cycle that fits inside one machine's capacity. That last condition is the one that makes the capital line real, and it is checked in the next section.

The machine is 450,000 EUR with a seven-year life, which is 64,300 EUR a year in depreciation. Interest at 4 percent on the average book value adds about 9,000 EUR a year, so the capital charge is 73,300 EUR per machine per year.

Space is 12 square metres at 120 EUR per square metre per year, or 1,440 EUR per machine. Labour is 0.6 of a full-time equivalent per machine at 55,000 EUR loaded, or 33,000 EUR per machine.

The total difference is 312,600 EUR over three years, or about 104,000 EUR a year. Add the context: the two-station cell carries two machines, two spindles, two coolant systems and two sets of fixtures for one operation pair.

Only one line favours the two-station layout, and it is small: tooling is 4,500 EUR higher for the single station over three years, because one combination tool costs more than a drill and a reamer and is reground as one item.

Check the arithmetic before using it. Depreciation is 450,000 divided by 7, multiplied by 3, which is 192,900 per machine. Interest is 450,000 times 4 percent times 3, which is 54,000 per machine. The two together are 246,900 per machine, and the table doubles that for two stations.

The capital line behaves differently from the others as volume changes. Below the capacity of one machine it is a real saving; above it, a second machine is needed either way, so the line falls to zero and only space, labour and work in progress remain.

On the example the volume of 200,000 parts fits in 3,450 hours at 21.8 s per part, which is 1,211 hours. There is room before the second machine becomes necessary, which is the condition under which the capital line can be claimed at all.

Tooling cost inside the TCO

Tooling is the line most often argued about and least often measured. It belongs in the comparison at the level of cost per accepted hole, not at the level of tool price.

A combination tool costs more than a drill and a reamer bought separately. It also replaces one tool holder, one set of presetting data and, in many cells, one tool-life record, so the premium is smaller than the price difference suggests.

The measurement that settles the argument is cost per accepted hole: tool price plus regrinds, divided by holes produced, with scrap and rework counted against the tool that caused them. The method is set out in cost per accepted hole for PCD reamers.

Use one method for both options. Two quotations that compute cost per hole differently will produce a comparison that cannot be audited, and the difference usually sits in whether regrinds and scrap are included.

On the example, the combination tool carries a 4,500 EUR disadvantage over three years. That is 1.5 percent of the total difference, which is why a tooling argument alone rarely decides the layout.

When one station does not pay

Four conditions reverse the table. Each one is common enough that the comparison should be checked against all four before it is presented.

The first is volume below the break-even batch. Below roughly 2,500 parts, including the proving run, the tool premium is not recovered by cycle time alone, as the arithmetic in cycle time calculation for combination tools shows.

The second is a shop that already runs both operations on one machine in two programs. In that case the second machine does not exist, so the capital line is zero and the saving is the cycle time only.

The third is tool life. If the combination tool's life is shorter than the sum of the two separate lives, the tooling line can outweigh the cycle gain, and the three-year total moves toward the two-station layout.

The fourth is inspection between stages. If the process requires the bore to be measured after drilling and before reaming, a combination tool removes that checkpoint, and the cost of the alternative method has to be added to the single-station column.

A fifth condition is less financial than organisational: two stations can run different parts when one operation is idle, while one station cannot. Capacity that is shared with other work is not saved capacity.

If the volume is below the break-even batch, the tool can still be justified on setup and reach grounds, but the case has to be made that way rather than through the capital table. The screening rules for whether to combine at all are in when to use a combination drill-reamer.

How to present this internally

The three cost models answer different questions, and presenting them out of order is what makes capital requests fail. The order is cycle time, then equipment, then cost per hole.

Start with the seconds. One table like the one in the cycle-time page, rebuilt with the plant's own change time and gauge routine, settles whether the volume fits in one station.

Then the capital table. Five lines, three years, one difference row, and a note that says which conditions would reverse it. Finance teams accept a table with stated assumptions far more readily than a percentage.

Then the per-hole figure. Cost per accepted hole is the number production will be measured on after the investment, and it is the number that survives the first quarter.

Keep the three numbers separate in the memo. Mixing a cycle-time gain into a capital payback is the fastest way to lose the argument when someone recomputes it.

The tooling part of the case belongs on the combination drill-reamer page for the tool family, and the per-hole arithmetic belongs on the cost page linked above. Regrind cost, which is where a tooling line usually surprises people, is set out in regrinding limits for combination tools.

When the comparison moves from the machine to the finishing method itself, the per-bore model is in five bore finishing routes compared on cost.

Send the volume, the change time, the machine rate and the tool-life records through the custom cutting tool RFQ and the same three tables can be recalculated against your plant instead of against the example.

What the three cost models do not settle

The comparison says nothing about quality. A single station removes the chance to correct the bore between stages, so the process capability of the pre-hole becomes part of the business case rather than a shop-floor detail.

It says nothing about flexibility. Two stations can be reallocated to other parts; a single station with a dedicated combination tool cannot, unless the tool is changed with the part.

It says nothing about the qualification path. A new layout needs a first article, a capability study and, in regulated industries, a process change notification that costs time rather than money.

It also says nothing about the tool's own risk profile. One tool that stops the station is a different failure mode from one of two tools stopping one operation, and the difference shows up in delivery performance before it shows up in the TCO.

What the table does settle is the size of the prize. If the prize is small under the plant's own assumptions, the layout decision should be made on quality and flexibility grounds and stated as such.

What published sources say about this

These pages were used for the tooling, operating-cost and process-capability points. Each is cited for what that page states, under its own conditions.

• Overall operating costs (toolmaker application report): a case in which a replaceable-head drill cut machining time by more than half with a stated tool-life increase, and tool-data transparency reduced downtime, the kind of line that sits behind direct labour.
• Tool life up, costs down (toolmaker application report): a case in which revised tools and parameters doubled tool life in production, cited for the link between tool life and operating cost rather than for a price.
• Digitalised regrinding management (toolmaker report): reconditioning described as a significant expense whose registration and turnaround are the critical parts, which is why regrind cost belongs in the tooling line.
• Tool refurbishment (toolmaker service page): regrinding and recoating described as costing a fraction of a new tool and extending tool life, the basis for treating refurbishment as a recurring cost rather than a replacement.
• Reamers, machine reamers (toolmaker technical overview): reamer designs and flute shapes, the reference for what a reaming tool's life depends on.
• What is Process Capability? (NIST/SEMATECH e-Handbook of Statistical Methods): process spread against specification limits, the method behind the scrap term that the TCO table keeps separate.
• Levene test for equality of variances (NIST/SEMATECH e-Handbook): a test for whether two processes have the same spread, useful when comparing two stations on the same bore.

Outbound references are listed because the comparison depends on them, not as endorsements. All figures on this page are illustrative assumptions and are not taken from these sources.

Frequently asked questions

Updated 13 November 2026: first publication. Scope: the five cost lines in a three-year single-station versus two-station comparison, tooling inside the TCO, the conditions that reverse the result and how to present the case. All amounts are example assumptions, not HENTRY prices.