How a Bore Is Made

Primary process: Broaching. The full route, materials, tolerances and design tips for a bore, with an indicative cost.

BroachingPrimary process
MachiningFamily
8Route steps
+/-0.02mmTypical tol.

A bore is primarily made by Broaching. Broaching pushes or pulls a toothed tool through or across a part, each tooth cutting a little deeper, to form a precise internal or external profile in one pass. Below is the full route to make a bore, the materials it suits, the tolerances to expect and the main design points. The route is free, from the finder.

Step by step

How a bore is made

The usual route, raw material to finished part. The amber step is where the bore gets its basic shape.

  1. Stock

    Start from bar, plate or billet sized for the bore.
  2. Broaching (roughing)

    Rough out the main shape, leaving stock on the critical surfaces.
    Tooling High (broach)   Tolerance ±0.025 to 0.1mm   Lead 8 to 16 weeks
  3. Finish machining

    Take the finishing passes that bring the bore to tolerance.
    Tooling High (broach)   Tolerance ±0.025 to 0.1mm   Lead 8 to 16 weeks
  4. Holes and features

    Drill, ream and tap, and where needed broach splines or cut gear teeth.
    Tooling None   Tolerance ±0.05 to 0.2mm   Lead hours to days
  5. Heat treatment

    Harden and temper if the bore must resist wear or load, then finish-grind.
    Tooling n/a   Tolerance can distort   Lead days
  6. Grinding

    Where the bore has bearing or sealing surfaces, grind them to the tightest tolerance and finish.
    Tooling Low (wheel)   Tolerance ±0.002 to 0.02mm   Lead days
  7. Surface finish

    Anodise, plate or coat for wear and corrosion resistance.
    Tooling Low   Tolerance adds microns   Lead days
  8. Inspection

    Measure the bore against the drawing, on a CMM for close work.

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Precision

Tolerances to expect

TYPICAL TOLERANCE IT CAN HOLD
+/-0.02mm typicalcoarsefine+/-1mm+/-0.1mm+/-0.01mm+/-0.005mm
Where this process typically lands. Tighter is possible with extra operations like grinding, at higher cost.
Materials

Materials for a bore

GradeWhy it suits this
Steels (annealed)Broach before hardening
StainlessHarder on the tool
Design

Design tips

General pointers. The full design-for-manufacturing list for a bore is in the dossier.

  • Blind internal profile. Provide tool run-out space.
  • Low quantity. Use wire EDM for a few off.
Cost

What a bore should cost

Keyways, splines, internal profiles; the custom broach is the cost, then it is very fast per part.

PER-PART COST vs VOLUME
one-offat volumeVolume per order, low to highCost per part
Per-part cost drops as volume spreads tooling and setup over more parts. The exact figures for a bore at your volume, in your currency, are in the dossier.
MODEL EST.
$60 to 165 per part at 1 off
A rough ballpark only. The dossier gives should-cost at your exact volume and currency, with the full breakdown.
GET THE FULL DOSSIER

Everything you need to quote and source it

The free route above is yours. To actually put a number on a bore and buy it well:

  • Should-cost at your exact volume in 12 currencies, with the material, processing, tooling and overhead breakdown
  • Who to source from, typical MOQ and lead time, and the exact RFQ checklist to send
  • A quote checker that tells you if a supplier quote is fair, and the red flags to watch
  • The full DFM list and a ready-to-send RFQ draft

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See also: How Broaching works and the full route for a bore in the finder.

FAQ

Frequently asked questions

How is a bore made?
A bore is primarily made by broaching. The route is: Stock; Broaching (roughing); Finish machining; Holes and features; Heat treatment; Grinding; Surface finish; Inspection.
What does a bore cost?
It depends on size, tolerance and volume. As a rough ballpark it starts around $60 to 165 per part at 1 off and falls with quantity. The dossier gives should-cost at your exact volume and currency. A model estimate, not a quote.
What material is a bore made from?
Common choices are Steels (annealed); Stainless.
What is the main process for a bore?
Broaching. Keyways, splines, internal gears and odd-shaped holes in volume.
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