CNC Turned Steel Threaded Flange Base
CNC turned steel threaded flange bases that mount a threaded component onto a flat face, with the internal thread concentric to the spigot within 0.02 mm and the flange face square to the thread axis within 0.02 mm. Machined in 1045 or 4140 and finished black oxide, zinc or bare for welding.
- Thread Concentric to Spigot
- Flange Face Square 0.02 mm
- 4140 or 1045 Steel
- Black Oxide or Zinc
*Tell us which feature is the datum: the thread, the spigot or the bolt circle. Mounting hubs are often checked against the OD, which is the one feature that does not control the fit.
Steel Threaded Flange Base Overview
A threaded flange base joins a threaded component to a flat mounting face, so it has to control two things at once: the thread axis and the face the mating part sits on. If the face is not square to the thread, the component leans and the load goes to one side of the thread.
The part is turned from bar or a cut blank, the thread is cut first, and the flange face and spigot are machined in a second operation held on the thread, so the face is square to the thread rather than to the bar end. The bolt circle is drilled from the same centre.
1045 Carbon Steel
1045 is used for flange bases that carry moderate load and are plated, because it machines to a clean thread and takes a uniform zinc or black oxide finish. It is the lower-cost option for general mounting work.
4140 for Higher Strength
4140 is chosen when the flange carries a bending moment or the thread has to hold preload without yielding. It can be supplied through-hardened to 28 to 32 HRC for wear on the thread flanks.
For a static mount, 1045 with zinc is enough. For a hub that sees vibration or repeated assembly, 4140 with phosphating resists galling and fatigue better.
Threaded Flange Base Specifications
Turning and threading data for flange bases, with the thread, spigot and squareness values that decide whether the mounted part runs true.
| Specification | Machining Data | Specification | Machining Data |
|---|---|---|---|
| Product | Threaded Flange Base / Mounting Hub | Machining Process | CNC Turning, Threading, Face and Spigot Turning |
| Material | 1045 or 4140 Alloy Steel | Thread Tolerance | 6H Internal, Gauged |
| Flange Diameter | 30 – 200 mm | Thread to Spigot Concentricity | 0.02 mm |
| Thread Range | M10 × 1 to M48 × 2, or BSP / NPT | Flange Face Squareness | 0.02 mm to Thread Axis |
| Spigot Diameter | 15 – 120 mm, h7 | Spigot to Thread Coaxiality | 0.02 mm |
| Overall Height | 20 – 120 mm | Surface Finish | Ra 1.6 µm Spigot, Ra 3.2 µm Flange Face |
| Mounting Holes | 3 to 8 Holes on a Bolt Circle, M6 to M16 | Hardness (Optional) | 28 – 32 HRC Through Hardened |
| Customization | Thread Size, Spigot, Bolt Circle, Keyway, Marking | Lead Time | 7 – 10 Days (Sample), 13 – 17 Days (Batch) |
| Inspection | Thread Gauge, Spigot Micrometer, CMM Squareness, Bolt Circle | Packing | Thread Cap, Oil-Filmed, Bagged, Carton |
Key Features of Our Threaded Flange Bases
Threaded first, faced against the thread, drilled from the same centre.
Flange Face Finished Against the Thread
The face is machined in a second operation held on the thread, so it is square to the thread axis within 0.02 mm rather than to the sawn end of the bar.
Spigot Coaxial to the Thread
The spigot is turned on the same axis as the thread, keeping the locating diameter and the thread within 0.02 mm so a mounted part cannot lean.
Threads Gauged Both Ways
Internal threads are checked with go/no-go plug gauges, and any thread that fails is re-cut or scrapped rather than sent with a sealant note.
Bolt Circle From the Thread Centre
Mounting holes are drilled from the thread axis, so the bolt pattern stays concentric even when the flange OD is machined to a loose tolerance.
Need a hub that mounts square to a thread?
Surface Finishes for Threaded Flange Bases
Plating builds on the thread flanks, so any coated hub is threaded to a pre-plate size and gauged afterwards.
| Finish | Main Purpose | Finish | Main Purpose |
|---|---|---|---|
| Black Oxide | Corrosion protection with no dimensional change on threads | Zinc Plating | Sacrificial protection for outdoor mounting |
| Phosphating | Oil-retaining surface that resists galling on threads | Electroless Nickel | Uniform coating on threads and spigot for cleanroom use |
| Rust-Preventive Oil | Storage protection before assembly | None (Bare) | Where the flange is welded or painted after assembly |
*Zinc plating adds 8 to 12 µm and tightens an internal thread. Coated hubs are tapped 0.02 mm oversize and the thread is gauged after plating.
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Turning Process for Threaded Flange Bases
The thread, the spigot and the flange face are cut on one axis, so the mounted part runs true to the thread rather than to the outside diameter.
01. Interface Review
Check the mating thread, the face it seats on and the bolt circle, then confirm which feature is the datum before the blank is cut.
02. Blank and Thread
Cut the blank, face it, turn the OD and cut the internal thread, holding the thread to 6H and gauging it before the second operation.
03. Second Op Face and Spigot
Hold the part on the thread, face the flange, turn the spigot to h7 and cut the relief so the face and spigot share the thread axis.
04. Bolt Circle and Deburr
Drill the bolt circle from the thread centre, deburr the holes and break the flange edge by 0.5 mm so the plated edge does not flake.
05. Finish, Gauge and Pack
Apply black oxide, zinc or bare finish, gauge the thread after coating, check squareness on a CMM, then cap the thread and oil-film the part.
Send the mating thread, the mounting face and the bolt circle, and we will quote the hub with the datum and finish fixed.
Threaded Flange Base FAQs
Usually the thread, because it is what the mounted component engages. The flange face and spigot are then machined against it, so the component sits square instead of leaning on the OD.
It can, but welding distorts the face and the thread. Weld preparation is machined and the thread is cut after welding, or the part is supplied bare and finished after the weld.
0.02 mm to the thread axis, measured on a CMM with the part held on a threaded mandrel. That is tight enough to keep a mounted motor or sensor from leaning under load.
Yes, BSPP, BSPT and NPT are cut and gauged with the matching plug gauge. Taper threads are checked for engagement depth as well as size.
Yes, by 8 to 12 µm on zinc. Coated parts are tapped oversize and gauged after plating, so the mating component still threads in by hand.
Seven to ten days for a sample including turning, threading, finishing and CMM. Batches of 50 to 300 pieces run thirteen to seventeen days depending on the finish.
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