What This R8 Collet Chuck Does and Why It Matters This is a CNC machined R8 collet chuck for milling machines, built to hold ER collets and cutting tools with a guaranteed runout of 0.005 mm TIR (to
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What This R8 Collet Chuck Does and Why It Matters This is a CNC machined R8 collet chuck for milling machines, built to hold ER collets and cutting tools with a guaranteed runout of 0.005 mm TIR (to
This is a CNC machined R8 collet chuck for milling machines, built to hold ER collets and cutting tools with a guaranteed runout of 0.005 mm TIR (total indicated reading) at the nose. That number is not a marketing claim — it is measured on every unit before shipment. You get tool-holding stiffness that reduces chatter, extends cutter life, and improves surface finish on your parts. Hardness is 58 HRC on the taper and gripping surfaces, so it resists wear even in high-volume production. Lead time is 7 days for standard sizes, and we ship from our Dongguan factory direct to your door.
The R8 taper is a 16-degree 51-minute included angle, standard on Bridgeport-type and many vertical milling machines. Our chuck starts as 42CrMo steel, stress-relieved, then CNC turned and ground to a true R8 form. The ER collet pocket is precision bored and lapped to accept ER16, ER25, ER32, or ER40 collets — you choose the size when ordering. The combination of a hardened R8 taper and a flexible ER collet gives you both axial location and radial clamping force. That means the tool runs concentric with the spindle, not just close to it.
We use a single-piece body design, no threaded adapters or glued joints. This eliminates stacked tolerances. The collet nut is hardened and coated with a wear-resistant finish, so you get repeatable tightening torque without galling on the threads. Each chuck is balanced to G2.5 at 20,000 RPM, which covers most milling spindles on the market.
We start with 42CrMo4 (AISI 4140 equivalent) bar stock. After rough machining, we oil-quench and temper to 58-60 HRC on the working surfaces. The drawbar threads are rolled, not cut, to avoid stress risers. The taper and collet pocket are ground on a cylindrical grinder, then honed to a surface finish of Ra 0.4 µm or better. The outside diameter is finish turned to Ra 1.6 µm, which is smooth enough for chip clearance and safe handling but still grip-friendly for a wrench.
Every chuck is magnetically crack-tested after heat treatment. We reject any part with micro-cracks, no exceptions. The final passivation layer is a black oxide finish, which gives corrosion resistance without changing dimensions. If you need a different finish — zinc nickel, electroless nickel, or no finish at all — we can do that, but the standard product ships with black oxide.
| Parameter | Value |
|---|---|
| Taper type | R8 (16°51' included angle) |
| Collet size (ER) | ER16, ER25, ER32, ER40 |
| Material | 42CrMo4 (AISI 4140) |
| Hardness (working surfaces) | 58-60 HRC |
| Runout (TIR at nose) | ≤ 0.005 mm |
| Surface finish (taper & pocket) | Ra 0.4 µm |
| Balance grade | G2.5 @ 20,000 RPM |
| Lead time (standard sizes) | 7 days |
| MOQ | No MOQ — buy 1 or 1,000 |
| Country of origin | Made in China, Dongguan factory |
We do not rely on batch sampling. Each R8 collet chuck goes through a final inspection that takes 15 minutes per unit. First, we check the R8 taper with a precision air gauge — contact angle and straightness must match the print within 0.002 mm. Then we mount the chuck on a test arbor and measure TIR at the collet bore, 25 mm from the nose, using a 0.001 mm resolution dial indicator. If it reads above 0.005 mm, the chuck goes back to the grinding station, not to the shipping box.
We also verify thread fit with a Go/No-Go gauge on the drawbar threads, and check the collet nut torque repeatability. A test collet is inserted and tightened to 80 N·m, then removed — we confirm the collet seats fully and the nut spins freely without binding. Finally, every unit gets a serial number and a signed inspection report, which you can request with your order. This is how we keep our precision manufacturing promise: data over promises.
This R8 collet chuck is for vertical milling machines with an R8 spindle taper, including Bridgeport Series I, Jet, Grizzly, and many Taiwan-made mills. It works for drilling, end milling, reaming, and light boring. If you run a CNC mill with an R8 spindle, this chuck is a direct replacement for a worn or inaccurate collet holder. We also make custom versions with extended lengths (up to 150 mm nose projection) or with a coolant-through hole — just send your drawing and we’ll quote.
For high-speed machining above 20,000 RPM, consider our HSK or BT30 options. For heavy roughing with a 3/4-inch end mill, this chuck with an ER32 collet will hold up to 200 N·m of torque without slipping. If you need a shorter or longer grip length, the ER collet system gives you flexibility — use shorter collets for rigidity, longer ones for deep reach.
We understand you may need one spare chuck, not a hundred. Our no MOQ policy means you can order a single unit for prototyping or replacement. For custom designs — different length, different collet size, special coating, or a different drawbar thread — we require a simple 2D or 3D drawing (PDF, STEP, or IGES). Our engineers review it within 24 hours and give you a firm quote. Standard sizes ship in 7 days; custom orders ship in 10-14 days depending on complexity.
If you are unsure about the right ER size or grip length, read our CNC cutting tool selection guide — it covers collet types, runout, and tool holding for specific operations. For more detail on what tolerances you can expect from CNC machining in general, see our CNC machining tolerances guide.
Yes — we will machine a single custom R8 collet chuck if that is what you need, but the unit price will be higher than for standard sizes due to setup time.
Yes, we can drill and seal a coolant channel through the body and collet pocket, rated up to 50 bar (725 psi) of coolant pressure.
We measure TIR at the collet bore 25 mm from the nose with a 0.001 mm indicator on a calibrated test arbor, and we reject any unit above 0.005 mm.
For a custom design with 50 pieces, lead time is 12 days from drawing approval, including heat treatment and grinding.
Stop guessing about tool holder quality. Send us your drawing or just specify the ER size and spindle taper, and we will reply with a firm price and delivery date within 12 hours (working days, China time). Email sc@bquq.com or reach us on WhatsApp at +86 13713157787. We respond to every inquiry, even for one piece. Your Cnc Machined R8 Collet Chuck Milling Machine Cnc Tooling order starts with a quick message — no obligation, no spam, just a clear quote.
| Parameter | Capability |
|---|---|
| Materials | AL6061/7075, SUS303/304/316, 45# steel, T2 copper, H59 brass, POM, PEEK, nylon |
| Tolerance | ±0.005mm standard, ±0.003mm on request |
| Machines | 3/4/5-axis CNC, turn-mill, Swiss lathe |
| Surface | Anodizing, nickel, zinc, passivation, sandblast, polish |
| Size Range | Max 400 x 300 x 200 mm |
| Prototype | 72 hours, no MOQ on samples |
| Inspection | Full report per batch, CMM data on request |
