Broaching Cost: Quoting Keyways, Splines and Internal Forms

Broaching is the operation estimators understand the least and quote the worst. The cut itself is over in seconds — a broach is pulled or pushed through the part once and the finished form comes out the other side. So the instinct is to price it as a trivial second op. That instinct is exactly backwards. With broaching the machine time is almost nothing and the tool is almost everything, which is why broaching cost behaves unlike any other line item on your cost sheet: it is dominated by a single expensive, often made-to-order tool that has to be paid for across the quantity in front of you.

This article builds a broaching price the right way round — tooling first, then cycle, setup, pre-machining, and margin — so that a keyway, a spline, or an internal hex comes out priced for what it actually costs to produce, whether you own a broaching machine or send the work out.

What you are actually broaching

"Broaching" covers a family of forms, and the form decides almost everything about the price. The cheap end and the expensive end share a name and very little else.

Form	Typical tool	Cost behaviour
Single keyway	Standard push broach + bushing	Off-the-shelf tool, arbor press, very cheap
Multiple keyways	Standard broach, indexed setups	Several pulls, more setup time
Square / hex bore	Standard or semi-standard broach	Moderate tool cost, common sizes stocked
Involute spline	Custom made-to-order broach	High tool cost, long lead time
Internal gear	Custom broach or shaped	Highest tool cost, specialist
Surface form	Custom surface broach, broaching machine	Tool + dedicated machine

The single most important question on any broached feature is: does a standard broach exist for this form and size, or does the print force a custom tool? A 6 mm keyway in a 25 mm bore is a stock broach you may already own. A 16-tooth involute spline to a specific class of fit is a made-to-order broach with a four-figure price and weeks of lead time. Pricing both as "broach a feature" is how short runs of custom splines quietly lose money.

Tooling is the line item, not the afterthought

On most machined features the tool disappears into the hourly rate. On broaching it cannot, because the tool can cost more than the entire rest of the job. Break it into three buckets and cost each one explicitly:

1. Tool acquisition — a standard keyway broach is cheap and reusable across many jobs; a custom spline or form broach is a real capital buy that must be amortised, and on a one-off it may have to be charged in full to the part.
2. Tool life and sharpening — broaches are reground on a schedule. Spread the regrind cost and the eventual replacement across the number of parts the tool produces, adjusted for material: a broach lasts far longer in free-cutting steel than in stainless or hardened material.
3. Owned versus bought-in — if you do not own a broaching machine you are buying an outside service, which carries a per-lot minimum charge and the tool cost on top. Below a threshold quantity that minimum dominates the unit price completely.

The amortisation step is where the whole quote lives or dies. A €2,500 custom broach across a batch of 20 adds €125 per part before a single chip is cut; across a batch of 2,000 it adds €1.25. Same tool, same form, a hundred-fold difference in the line — so the quantity has to drive the tooling number, exactly the way it does for any operation written into a work plan for multi-step operations.

Cycle time: the cheapest part of the job

The actual cut is genuinely fast. A keyway broach pulled through a 25 mm bore is a matter of seconds; each tooth on the broach is stepped a few hundredths of a millimetre higher than the last, so a single pass removes the full form. Add load and unload and you are still usually under a minute per part on a dedicated machine, and an arbor-press keyway is barely longer.

That speed is a trap. Because the cycle is so short, the per-part machine cost — cycle time times your fully burdened machine rate — is often a euro or two, dwarfed by tooling and setup on anything but a long run. Two things still move it. First, the length of pull: a long spline broached over 150 mm takes meaningfully longer than a short keyway, and very long forms may need more than one pass. Second, the broaching force the part needs — harder material and bigger forms mean a slower, more careful pull, and sometimes a bigger machine. But on the typical job, do not let an obsession with cycle seconds distract from the two numbers that actually matter: the tool and the setup.

Setup, pilots, and the operations broaching depends on

A broached form is never the first operation. The bore or face has to be there first, on-size and square, before the broach ever touches it, and that pre-machining is part of the broached feature's cost even when it lives on another machine:

• The pilot bore or face — an internal broach follows the existing hole; the drilling, boring, or turning that produces it is real cost and real cycle, costed the way any turned bore is in a lathe quote.
• Bushings and fixtures — push broaching a keyway needs a bushing to guide the tool; an odd part needs a fixture to hold and locate it under load.
• Setup time — mounting the broach, setting the bushing, dialling in the first article. On a small batch this setup, divided across the quantity, can rival the tooling per-part.
• Deburr and inspect — broached forms throw a burr at the exit and the form has to be checked, especially a spline or geared form to a class of fit.

Skip the pilot and the fixture in your head and the quote looks great and loses money in the shop. Broaching is an integration cost as much as a cutting cost.

Tolerance and fit: what quietly raises the price

A keyway to a loose width tolerance is forgiving. A spline or internal gear called to a specific class of fit is not — it demands a broach ground to that class, tighter inspection, and far less margin for tool wear before the form drifts out of tolerance. The print callout, not the nominal size, sets the tool cost and the inspection cost.

Reading that callout correctly is exactly where broaching quotes go wrong: an estimator prices a "spline" off the diameter and misses that the fit class forces a made-to-order broach and a go/no-go gauge per part. The GD&T-for-estimators guide covers how fit, position, and form callouts turn into tool and inspection cost rather than decoration on the drawing — and broaching is one of the features where that translation swings the price hardest.

A worked example: a 8 mm keyway and a 21-tooth spline

Take the same bored part two ways, both quantity 50, to show how far the tooling drives the answer.

Case A — standard 8 mm keyway, broach already owned:

1. Pre-machining — bore is already there from the turning op, so no added pilot ≈ €0.00 extra.
2. Broaching cycle — arbor-press pull + handling ≈ 0.6 min at a €70/h rate = €0.70.
3. Tooling — share of a stock broach you already own + regrind ≈ €0.40 per part.
4. Setup — €60 ÷ 50 = €1.20 per part.
5. Deburr + check ≈ €0.40.
6. Cost per part = 0 + 0.70 + 0.40 + 1.20 + 0.40 = €2.70.
7. Price at 35% margin — using price = cost ÷ (1 − margin), 2.70 ÷ 0.65 = €4.15.

Case B — 21-tooth involute spline, custom broach at €2,400:

1. Pre-machining — finish-bore to broach pilot size ≈ €1.80.
2. Broaching cycle — dedicated machine, longer pull ≈ 1.5 min at €95/h = €2.38.
3. Tooling — €2,400 custom broach ÷ 50 + regrind allowance ≈ €50.00 per part.
4. Setup — €140 ÷ 50 = €2.80 per part.
5. Deburr + go/no-go gauge check ≈ €1.50.
6. Cost per part = 1.80 + 2.38 + 50.00 + 2.80 + 1.50 = €58.48.
7. Price at 35% margin — 58.48 ÷ 0.65 = €89.97.

Same machine seconds, a twenty-fold difference in price — driven almost entirely by one tool spread over fifty parts. Run the spline at quantity 2,000 and that €50 tooling line collapses to about €1.30, and the part prices near €15. The margin step uses the same arithmetic as any margin-versus-markup pricing; confuse the two and a 35% intended margin quietly becomes 26%.

From a drawing to a broaching price

The hard part of broaching cost is not the cut — it is recognising, before you quote, whether the form on the print rides on a tool you already own or forces a four-figure custom broach, and then spreading that tool across the right quantity. Miss the distinction and you either lose easy keyway work on price or lose your shirt on a short run of custom splines.

QuoteBuddy reads the technical drawing and surfaces the broached feature — keyway, spline, polygon, or internal form, its size, length of pull, the bore it follows, and the fit-class callout that decides whether a standard or custom broach is needed — so the estimator builds the price from a complete picture instead of pricing a custom spline like a stock keyway. The cost engine then assembles pre-machining, cycle, amortised tooling, setup, and your target margin the same disciplined way it would for any CNC machined part, every time.

Start a 30-day trial and run a few real broached drawings through it — from upload to a complete, itemized quote PDF — and see whether the unit price it builds matches what the job actually costs across the quantity you were quoted, with the margin landing exactly where you set it.