CNC Turned Threaded Grooved Pulley
Grooved pulleys turned from 6061-T6 bar: Ø90 mm, four R2.0 belt grooves on a 3 mm pitch held to ±0.02 mm, an M40 × 1.5 thread at 6g over 22 mm, a Ø25 H7 bore round within 0.008 mm and 0.02 mm face runout. The grooves and the thread are cut in the same set-up, and each pulley is balanced to G6.3 at 3,000 rpm.
- Groove Pitch 3 mm ±0.02
- M40 × 1.5 Thread 6g
- Bore Ø25 H7
- Runout 0.02 mm
*Tell us the belt profile and the shaft fit. Groove pitch and depth come from the belt section, and a groove 0.05 mm deep will let the belt bottom out and slip under load.
Threaded Grooved Pulley Overview
A grooved pulley has to do three things: keep the belt in its groove, run true on the shaft, and transmit torque through the thread without loosening. All three are turned features, which is why the part is made on a lathe rather than milled from a block.
The pulley is turned from bar stock in one set-up: the OD and hub are faced, the grooves are cut with a form tool at a controlled feed, the thread is single-pointed and checked with a gauge, and the bore is drilled and bored to H7. The part is then balanced and anodized with the thread and bore masked.
6061-T6 Aluminium
6061-T6 turns to a clean groove flank and keeps a 420 g pulley light enough for a high-speed drive, while taking a hard anodized skin in the belt contact area.
7075-T6 or 6082-T6
7075-T6 is used when the pulley transmits high torque through a small hub, and 6082-T6 is chosen for anodized pulleys where colour consistency matters more than strength.
A groove depth 0.05 mm over size lets the belt bottom out and slip; the depth is set from the belt section and checked with a form gauge.
Grooved Pulley Specifications
Groove, thread and runout values, measured on the finished part.
| Specification | Machining Data | Specification | Machining Data |
|---|---|---|---|
| Product | Threaded Grooved Pulley | Process | CNC Turning, Threading, Grooving |
| Material | 6061-T6 Aluminium | Outer Diameter | Ø90 mm ±0.05 |
| Belt Grooves | 4 × R2.0, Pitch 3 mm ±0.02 | Groove Depth | 2.4 mm |
| Thread | M40 × 1.5, 6g, Length 22 mm | Bore | Ø25 H7, Roundness 0.008 mm |
| Face Runout | 0.02 mm | Radial Runout | 0.03 mm |
| Hub Width | 38 mm ±0.05 | Balance | G6.3 at 3,000 rpm |
| Weight | Approx. 420 g | Edge Break | 0.3 mm on Groove Edges |
| Inspection | Thread Gauge, Runout, Balance | Batch Size | 25 to 2,000 Pieces |
| Finish | Clear or Black Anodizing | Drawing Format | STEP, PDF, DXF |
Turned True in One Set-up
Grooves, thread and bore from one bar clamping.
Grooves Cut With a Form Tool
Each R2.0 groove is cut with a ground form tool at a slow feed, which reproduces the belt profile within 0.02 mm of pitch and leaves a flank that does not feather the belt edge.
Thread Single-Pointed
The M40 × 1.5 thread is single-pointed rather than die-cut, so the pitch diameter stays within 6g over the full 22 mm and the pulley does not wobble when it is screwed onto the hub.
Bore and Grooves on One Axis
Because the bore and the grooves are turned without re-chucking, the radial runout stays at 0.03 mm and the belt does not track to one side of the pulley.
Balanced After Turning
Each pulley is balanced to G6.3 at 3,000 rpm, with material removed from the hub face rather than the grooves, so the belt surface is untouched.
Pulley that has to run true at speed?
Surface Finishes for Grooved Pulleys
The grooves wear, the thread engages, and the bore locates; each is treated separately.
| Finish | Main Purpose | Finish | Main Purpose |
|---|---|---|---|
| Clear Anodizing | Corrosion protection, belt wear face | Black Anodizing | Machine covers and drives |
| Hard Anodizing | Wear resistance in the belt grooves | Bead Blasting | Matte before colour |
| Masked Thread | Bare thread for full engagement | Masked Bore | Bare bore for the shaft fit |
| Chromate Conversion | Conductive pulley for static discharge | Laser Marking | Part number on the hub face |
| Teflon Coating | Low friction on the groove flanks | Ultrasonic Clean | Thread and groove cleaning |
| Deburr Only | Pulleys used in a dry enclosure | Foam Packing | Protects groove edges |
*Anodizing on the thread changes the pitch diameter and the pulley will not screw on; the thread is masked, and coated threads are chased back to 6g.
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How We Turn a Grooved Pulley
The grooves, the thread and the bore are turned in one set-up, so the pulley runs true on its own thread instead of relying on a separate hub.
01. Belt and Shaft Review
Check the belt section, the number of grooves and the shaft fit, then set the groove profile and the thread class from the drawing.
02. Turn the Blank
Face both ends, turn the OD to Ø90 and the hub to width, leaving 0.3 mm on the groove area and the thread for finishing.
03. Cut the Grooves
Cut the four R2.0 grooves with a form tool at a 3 mm pitch, checking the pitch with a form gauge before the part leaves the chuck.
04. Thread and Bore
Single-point the M40 × 1.5 thread and check it with a ring gauge, then drill and bore the Ø25 H7 bore in the same set-up.
05. Balance, Anodize, Verify
Deburr the groove edges, balance to G6.3, mask the thread and bore, anodize and re-check runout.
Send the belt profile and the shaft fit, and we will quote a pulley with the grooves and thread turned in one set-up and balanced before coating.
Grooved Pulley FAQs
HTD, GT, timing and V-groove profiles from the belt drawing or a sample. The form tool is ground to the profile, so any section is possible.
A die-cut thread on aluminium tears the flank and drifts on pitch diameter. Single-pointing holds 6g over the full length and leaves a thread that screws on by hand.
Yes, a keyway or a cross hole can be added after turning, with the runout re-checked afterwards.
On a dynamic balancer to G6.3 at the working speed, with correction by removing material from the hub face.
Yes, so the thread is masked. If a coated thread is required, it is chased back to 6g after anodizing.
Yes, turned with the same thread and checked against the pulley so the pair screws together without play.
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