Bore Finishing: Five Routes Compared by Cost | HENTRY

Every finishing route can be made to look cheap with its own arithmetic. Reaming quotes tool cost per hole; honing quotes surface; burnishing quotes cycle time. Put them in one model and the ranking stops being a matter of opinion.

This page applies a single cost model to five routes on the same bore: reaming with PCD, reaming with carbide, fine boring, honing and roller burnishing. Every input is stated, so the table can be recomputed with plant values.

Rates, prices and lives below are examples, not HENTRY values. Machine purchase and depreciation are excluded on purpose; they belong to the single-station versus two-station case on the two-station cost page.

The cost model

The model has one line and four terms. Cost per finished bore equals tool amortisation, plus machine time, plus scrap, plus gauging.

Tool amortisation is the only term that is specific to the route. A reamer is one tool per diameter; a boring bar is a body with replaceable inserts; a honing head carries stones; a burnishing tool carries rollers.

Machine time uses the cycle of the finishing operation only. If a route needs a preceding semi-finish pass, that pass is added as its own line rather than hidden inside the finishing cycle.

Scrap is the term most often left out and the one that changes rankings. A route that holds a tighter band has a lower scrap rate, and on an expensive part that difference can outweigh the tool cost entirely.

Gauging is small per bore but not zero. A route that needs a per-part gauge and a route that needs a sample check do not have the same cost, and the difference should be stated rather than assumed.

Keep the units consistent before comparing totals. Tool cost per bore, machine time per bore, scrap per bore and gauging per bore are all per-bore figures; a quotation that mixes an annual tool budget with a per-part cycle cannot be put in the same column.

The model also needs a stated boundary. If a route requires a semi-finish operation, that operation is a line of its own; if it requires a new fixture, that fixture belongs to the qualification cost, not to the per-bore figure.

The five routes on one page

The five routes are compared on the same bore and the same drawing. The capability columns are industry ranges; the cost columns are structures, because a single annual figure would be false precision.

The two cutting routes are described separately in fine boring versus reaming, and the burnishing route, including what it cannot correct, is in reaming versus roller burnishing.

Two rows need a note. Honing's tolerance is often quoted as tighter than IT6, but the bore must also be straight and round before honing can deliver it; the route corrects form, not position.

Roller burnishing is listed as a finishing operation, not a standalone route, because it needs a pre-hole good enough to be worth improving. Its cycle is short, but the reaming cycle before it still has to be paid for.

The worked example

The bore is 25 mm H7, a band of 0.021 mm, in a steel part at 150,000 holes a year. The machine rate is 45 EUR per hour, the scrapped part is valued at 12 EUR, and gauging is charged at the stated rate per bore.

Tool lives are examples: 8,000 holes for the PCD reamer, 3,000 for the carbide reamer, one insert per 800 holes for the boring tool, one stone set per 1,500 holes for honing, and 30,000 holes for the burnishing tool.

Recompute the first row to check the model. The PCD reamer costs 420 EUR, takes two regrinds at 120 EUR and produces 8,000 holes between regrinds, so 24,000 holes per purchase cycle: 660 EUR divided by 24,000 is 0.0275.

Machine time is 6 s at 45 EUR per hour, which is 0.075. Scrap is 0.3 percent of 12 EUR, or 0.036, and gauging is 0.01, so the total is 0.149. The other rows use the same arithmetic with their own inputs.

The ranking is PCD reaming, carbide reaming, ream plus burnish, fine boring, honing. The gaps are large at the top and small in the middle, which matters when the decision is between adjacent routes.

Sensitivity: where the ranking flips

Three levers move the ranking. Each has a threshold, and the thresholds are more useful than the example totals.

The first is volume. PCD tooling has a high unit price and a long life, so its advantage grows with volume. At 5,000 holes a year the same tool produces 0.132 per bore in amortisation and the carbide route overtakes it.

The second is the tolerance band. Every route's scrap rate rises as the band tightens, but not equally: honing and fine boring hold a tight band better than reaming, so their scrap term stays flat while the reaming routes climb.

The third is the surface requirement. If the drawing asks for 0.4 micrometres Ra, reaming alone is out and the choice narrows to honing, burnishing or a two-operation route. If it asks for 1.6, three routes qualify and cost decides.

A fourth lever is part value. Scrap cost is a multiplier on every route's scrap rate, so on a 200 EUR part the routes with the lowest scrap rate move up the ranking even if their cycle time is longer.

A fifth is the pre-hole. When the pre-hole is drilled on the same machine as the finishing cut, the reaming routes keep their advantage; when it has to be produced separately, the difference between the routes narrows because the handling cost is charged to all of them.

State the lever next to the ranking. A table that says "reaming is cheapest" without a volume is not a result; it is a coincidence of one set of inputs.

How to use this with your own numbers

The model is only useful if it is recomputed. Ten inputs are enough, and most plants already hold all of them.

The list is: bore diameter and tolerance class, bore length, material and heat treatment, surface requirement, annual volume, machine hour rate, current cycle time, tool price and life, regrind price and count, scrap rate and scrap value.

Two of these are usually missing: the scrap rate by route and the regrind count. Both can be estimated from the tool records if they exist, and both should be marked as estimates if they do not.

Keep the gauging term separate until the end. It is small, but it is the term that differs most between a route that needs a per-part gauge and one that needs a sample check.

The division of labour with the other cost pages is deliberate. Cost per accepted hole compares PCD with carbide on one route; this page compares five routes; the equipment decision is on single-station versus two-station cost.

Once the route is chosen, the next question is whether it can hold the drawing on the machine in front of you. That decision is a lookup rather than a comparison: hole route selection by tolerance and volume gives one route per tolerance and volume cell, with the fallback stated.

Send the ten inputs with the drawing through the custom cutting tool RFQ and the table can be rebuilt against your rates instead of the example ones. The route matrix behind the five rows is on hole machining process route.

What the model does not include

The model is a per-bore cost model. It is not a business case, and four effects sit outside it.

Equipment is excluded. Honing needs a machine that reaming does not, and that capital belongs in a separate comparison, not in a per-hole rate that quietly assumes the machine exists.

Floor space, labour and work in progress are excluded for the same reason. They are real, they are large, and they are already counted on the equipment page.

Qualification is excluded. A new route needs a first article, a capability study and sometimes a customer approval; those are fixed costs per part number, not per bore, and they dominate at low volume.

Risk is excluded, and it is the hardest to price. A route with one supplier and a long lead time carries a different risk from a route with three suppliers, and no per-hole model captures that.

State these exclusions next to the table. A per-bore ranking presented as a total cost of ownership is the most common way this kind of comparison misleads.

What published sources say about this

These pages were used for the route capabilities and the process context. Each is cited for what that page states, under its own conditions.

• Roller burnishing tools (toolmaker technical site): burnishing described as surface smoothing without material removal, with a stated finish improvement and a surface reach of Rz below 1 micrometre, the basis for the burnishing row.
• Honing machines, tools and abrasives (manufacturer site): honing presented as a machine-based route with its own tools and abrasives, which is why honing carries a fixed cost the other routes do not.
• Reaming and fine boring (toolmaker competence page): the two cutting routes described together, the reference for their tool structures.
• Tools for fine machining bores (toolmaker interview): the single-bladed reamer and the handling effort of fine boring tools, the background to the adjustable-body cost structure.
• Reamers, machine reamers (toolmaker technical overview): reamer designs and flute shapes, which set what a reaming tool's life and regrind cost look like.
• What is Process Capability? (NIST/SEMATECH e-Handbook of Statistical Methods): process spread against specification limits, the method behind the scrap term by route.
• Dimensioning and Tolerancing (ASME Y14.5): the form and position definitions that decide whether a route's capability actually meets the drawing.

Outbound references are listed because the comparison depends on them, not as endorsements. All prices, lives, rates and cycles on this page are examples and are not taken from these sources.

Frequently asked questions

Updated 13 November 2026: first publication. Scope: the four-part cost model, the five-route capability and cost table, the worked example, the volume, tolerance and surface thresholds where the ranking flips, and the model's exclusions. All prices, lives and cycles are examples, not HENTRY values.