What This ER8 Collet Chuck and Nut Set Does for Your Spindle This is a CNC machined ER8 spring collet chuck and collet nut set designed for high-speed, light-duty milling, drilling, and tapping on CNC
This is a CNC machined ER8 spring collet chuck and collet nut set designed for high-speed, light-duty milling, drilling, and tapping on CNC spindles with a 1:10 taper. The concrete benefit is repeatable tool centering: we hold the taper to 0.003 mm total indicated runout (TIR) at the nose, which means less tool wear, better surface finish, and fewer broken micro-drills. The chuck body and nut are machined from 8620 steel, carburized to 58–62 HRC, and ground to a surface finish of Ra 0.4 µm on all critical sealing and taper surfaces.
Lead time is 5 working days for standard ER8 sizes (1.0 mm to 5.0 mm capacity). We ship worldwide from our Dongguan factory, and there is no MOQ – you can order one set for prototype validation or 500 sets for production. Every unit is 100% inspected before packing, and we provide a digital CMM report with each order.
The ER8 collet uses a 1:10 taper angle on both the inner bore of the chuck and the outer cone of the collet. When you tighten the collet nut, the collet is forced axially into the chuck, which compresses the eight longitudinal slots around the collet bore. This creates a uniform radial clamping force around the tool shank – not just at two or three points. For a 2.0 mm end mill shank, the grip torque is 1.8 N·m, which prevents tool pull-out even during interrupted cuts at 40,000 RPM.
The nut is machined with a precision ground thread (ISO M8 x 0.75) and a hardened thrust washer face. We use a left-hand thread direction on the nut to match the spindle rotation, so the nut tightens under cutting load, not loosens. The slots in the collet are broached, not milled, to ensure the slot width is consistent within 0.01 mm – this keeps the collet segments symmetrical and prevents uneven clamping that causes runout.
Many cheap collet chucks are turned from free-machining 12L14 steel, which is soft and wears out after a few thousand tool changes. We use AISI 8620 alloy steel for both the chuck body and the collet nut. 8620 is a low-carbon alloy that carburizes well – we case-harden it to 0.6–0.8 mm depth, reaching a surface hardness of 58–62 HRC. The core remains tough (35–40 HRC) so the chuck does not crack under impact from clamping and unclamping cycles.
For the collet itself, we use spring steel (65Mn) with a hardness of 44–48 HRC. This is a deliberate choice – if the collet were as hard as the chuck, it would be brittle and crack when you clamp an oversized tool shank. 65Mn gives the collet the spring-back needed to return to its original bore size after releasing the tool. The nut is also 8620, hardened to 50–55 HRC on the thread flanks to resist galling when you tighten it with a wrench.
We grind all functional surfaces after heat treatment. The 1:10 taper on the chuck nose is ground to a tolerance of ±0.002 mm on angle and ±0.003 mm on concentricity. The collet nut thread is ground on a CNC thread grinder, not cut with a tap, so the pitch diameter error is less than 0.005 mm. The sealing bore (where the collet sits) is honed to Ra 0.2 µm to minimize friction during collet compression.
We also balance every chuck and nut assembly to G2.5 at 30,000 RPM. For high-speed spindles, unbalance can cause vibration that transfers to the tool tip. We mark the heavy spot on the nut with a laser dot, so you can index it relative to your spindle's existing balance correction. Standard surface finish is Ra 0.4 µm on the taper and Ra 0.8 µm on the outer body – no cosmetic polishing, because that adds nothing to performance.
Our ER8 chuck is dimensionally interchangeable with all standard ER8 tool holders from brands like Rego-Fix, ER, and DA. The thread size is M8 x 0.75, the nose taper length is 9.0 mm, and the overall chuck length is 31.5 mm (short version) or 40 mm (standard version). We offer both straight shank (diameter from 6 mm to 10 mm) and threaded shank styles for different spindle interfaces.
The collet bore range is 1.0 mm to 5.0 mm, in 0.5 mm increments. Each collet has a clamping range of -0.5 mm to +0.1 mm on the nominal bore – so a 3.0 mm collet holds shanks from 2.5 mm to 3.1 mm. This is a standard ER8 spec, but we measure each collet's free-state bore with an air gauge to ensure it is within ±0.01 mm of nominal. If you need a non-standard bore (e.g., 2.35 mm for metric-imperial hybrid shanks), we can CNC drill and ream that on request – lead time is 2 extra days.
We do not ship any ER8 set without a full inspection report. Every chuck and nut is checked on a Zeiss CMM for taper angle, thread pitch, concentricity, and bore diameter. Then we assemble the set with a test bar (a hardened and ground 3.0 mm dowel pin) and measure the runout at the nose, at 10 mm from the nose, and at 20 mm from the nose. The max runout we allow is 0.003 mm at the nose and 0.005 mm at 20 mm – if a set exceeds that, it goes back to the grinder.
We also perform a 100-cycle clamp test on each collet: we clamp and release a test bar 100 times, then re-measure the runout. If the runout changes by more than 0.001 mm, the collet is rejected. This is because spring steel can fatigue after repeated clamping, and a worn collet will cause tool runout to increase over time. Our rejection rate is below 1.5%, and we log the serial number of each accepted set in your order history.
| Specification | Value | | --- | --- | | Chuck body material | AISI 8620 alloy steel, carburized | | Hardness (chuck body) | 58–62 HRC (case depth 0.6–0.8 mm) | | Collet material | 65Mn spring steel | | Hardness (collet) | 44–48 HRC | | Collet nut material | AISI 8620, thread flank hardened | | Taper angle | 1:10, tolerance ±0.002 mm | | Runout at nose (TIR) | ≤ 0.003 mm | | Runout at 20 mm from nose | ≤ 0.005 mm | | Surface finish (taper) | Ra 0.4 µm | | Surface finish (sealing bore) | Ra 0.2 µm | | Thread size | M8 x 0.75, ground | | Balance grade | G2.5 @ 30,000 RPM | | Standard lead time | 5 working days | | MOQ | No MOQ (single set accepted) |To quote your exact ER8 set, send us a drawing or a simple list: (1) chuck shank diameter and type (straight, threaded, or flange), (2) overall length if non-standard, (3) collet bore sizes you need, (4) any special coating (we offers TiN, TiAlN, or black oxide on request). If you do not have a drawing, tell us your spindle model and we will match the existing interface. We are a precision manufacturing company made in China with 20 years of experience in CNC machining, stamping, springs, and heat sinks – so we can also machine the matching spindle adapter if you need it.
For engineers choosing between tool holders, we recommend reading our CNC cutting tool selection guide to understand how runout affects tool life, and our CNC machining tolerances guide to see how we hold these tight numbers in production. Both guides are written by our shop floor engineers, not marketing staff.
There is no MOQ – you can order one set for testing, and the unit price drops by about 15% at 50 sets and 25% at 200 sets.
Yes, we can modify the shank diameter, length, thread type, or add a flange – send us a sketch and we will tell you within 1 business day if it is feasible and what the extra machining time costs.
Every order, whether 1 set or 1,000 sets, goes through the same CMM inspection and 100-cycle clamp test – we do not skip QC for small quantities.
Standard ER8 sets ship in 5 working days from Dongguan via DHL or FedEx (2–4 days to most destinations); custom designs take 7–10 working days. Shipping cost for a single set is typically $35–$45 to North America or Europe.
Send your drawing for a firm quote within 12 hours. Email sc@bquq.com or WhatsApp +86 13713157787. We reply with a full technical review, not just a price – we will flag any dimension that is risky for runout or durability before you commit.
| 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 |
