This is a CNC machined auto lathe 640 type round bore collet chuck built for high-speed turning and bar-feeding operations. We machine the body from 42CrMo steel, harden it to HRC 58-62, and grind the
This is a CNC machined auto lathe 640 type round bore collet chuck built for high-speed turning and bar-feeding operations. We machine the body from 42CrMo steel, harden it to HRC 58-62, and grind the bore to a 0.005 mm total runout — that is a 4x tighter grip accuracy than standard commercial chucks. Every unit ships within 10 days, and we keep zero inventory because we cut each chuck only after your order is confirmed.
The 640 series uses a straight round bore, not a tapered or hex-shaped aperture. That bore is ground in a single pass on a CNC internal grinder, holding a tolerance of +0.005 / -0.000 mm. The round bore distributes clamping force evenly around the workpiece circumference, so you avoid the three-point distortion common in 5C or ER collets when gripping thin-wall tubing. If you feed 10 mm round bar, you get a consistent grip length of 28 mm — enough to hold a 3:1 length-to-diameter ratio without chatter.
Our 640 chuck uses a hardened steel spring sleeve with a collapse range of 1.0 mm (from 9.0 mm to 10.0 mm bore diameter). At the top of the collapse range, the sleeve exerts 4.2 kN of radial force. That force is repeatable across 50,000 open-close cycles because we grind the spring slots with a 0.2 mm radius at the root — a detail most factories skip. A sharp slot root creates stress risers and cracks; our radius triples the fatigue life of the sleeve.
We start with 42CrMo (AISI 4140) round bar, not cast blanks. Castings have porosity; bar stock does not. After CNC turning and milling of the body and slots, we vacuum harden to HRC 58-62. Vacuum hardening prevents surface decarburization, which would soften the outer skin and cause wear. The final grinding step removes 0.15 mm from the bore and the outer taper, giving you a surface finish of Ra 0.4 on the gripping surface and Ra 0.8 on the taper.
Every chuck goes through a 6-point inspection on a Zeiss CMM. We measure the bore diameter at three depths, the taper angle to ±0.1 degree, the runout of the bore relative to the taper, the hardness on two spots, the surface finish with a portable profilometer, and the spring collapse range with a calibrated plug gauge. You receive a PDF report with the actual measured values, not a certificate of conformity. If any value exceeds our spec, the chuck is scrapped — not reworked.
The 640 type is a standard spindle-nose mount, so it fits most Japanese and Korean auto lathes — Citizen, Star, Tsugami, and Hanwha. The taper angle is 16 degrees included, and the back face has a pilot diameter of 42 mm. We machine a locating spigot on the back plate to 0.003 mm concentricity with the bore. That spigot is what guarantees your tool centerline stays dead-on after mounting. If you have a non-standard spindle, send us your spindle nose drawing and we will adjust the back plate geometry at no extra cost for orders of 5 pieces or more.
The bore is not just ground — it is honed with a 400-grit diamond stone. Honing creates a cross-hatch pattern that holds oil film, reducing galling when you grip stainless steel or aluminum. The cross-hatch angle is 30 degrees, and the resulting Ra is 0.4. If you run dry cutting, the honed surface still works, but we recommend a light oil mist. For aluminum bar, we can apply a hard anodize coating (50 microns) on the bore to prevent aluminum cold-welding to the steel.
We do not have a minimum order quantity. One piece or one hundred pieces — the price per piece stays the same because our CNC setup time is identical. Standard lead time is 10 working days for any size within the 640 series (bore sizes from 3 mm to 42 mm). If you need a rush order, we can ship in 5 days for a 15% expedite fee. The expedite fee covers overtime labor, not machining shortcuts — the inspection process remains identical.
| Specification | Value |
|---|---|
| Type | 640 series round bore collet chuck |
| Body Material | 42CrMo (AISI 4140) bar stock |
| Hardness | HRC 58-62 (vacuum hardened) |
| Bore Diameter Range | 3.0 mm – 42.0 mm |
| Collapse Range | 1.0 mm per chuck |
| Total Runout (bore to taper) | 0.005 mm |
| Bore Tolerance | +0.005 / -0.000 mm |
| Surface Finish (bore) | Ra 0.4 (honed) |
| Surface Finish (taper) | Ra 0.8 (ground) |
| Clamping Force (at max collapse) | 4.2 kN |
| Standard Lead Time | 10 working days |
| MOQ | No MOQ |
ER collet chucks grip with a tapered cone, which gives you axial pull-back. The 640 round bore chuck has no axial pull-back — it grips purely radially. That is an advantage for bar feeding, because the bar does not shift backward when you clamp. It also means you can grip shorter lengths without losing positional accuracy. If you are already using ER collets and want to switch, check our CNC cutting tool selection guide for a comparison of grip geometries. For general tolerance limits on the parts you will hold, read our CNC machining tolerances guide.
We are a precision manufacturing facility in Dongguan, China, with 20 years of experience in CNC machining, stamping, springs, and heat sinks. The 640 chuck is machined on our own Mazak CNC lathes and ground on Studer internal grinders. We do not outsource any critical step — heat treatment is done in our in-house vacuum furnace. That is why we can hold the 0.005 mm runout consistently. Made in China does not mean compromised; it means we control the entire process under one roof.
No MOQ — we accept one-piece orders at the same unit price as bulk orders.
Yes, we can machine any bore size from 3 mm to 42 mm, and we will modify the back plate spigot to match your spindle for orders of 5 pieces or more at no extra cost.
Every chuck is inspected on a Zeiss CMM with a 6-point check, and you receive the actual measured values in a PDF report before shipment.
Standard lead time is 10 working days; expedited 5-day shipping is available for a 15% fee.
Send us your spindle drawing or your required bore size, and we will reply with a firm price and lead time within 12 hours. We do not quote ranges — you get a fixed price per piece. Email your drawing to sc@bquq.com or WhatsApp us at +86 13713157787. We will confirm your 640 type round bore collet chuck spec the same day.
| 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 |
