What This Collet Does and Why It Cuts Your Reject Rate This is a 20 type collet machined from hardened round bar stock, designed for automatic lathe spindles that feed bar material. It holds round sto
This is a 20 type collet machined from hardened round bar stock, designed for automatic lathe spindles that feed bar material. It holds round stock from 3 mm to 20 mm with a guaranteed concentricity runout of ≤0.005 mm, which directly reduces tool chatter and improves surface finish on your turned parts. We ship from our Dongguan factory in 7 days for standard sizes, and the hardness stays at 58-62 HRC through the full length of the gripping zone.
The 20 type collet uses a tapered outer diameter that matches the spindle nose, and three longitudinal slots cut by wire EDM after heat treatment. Those slots flex radially when the draw tube pulls the collet into the taper, creating a uniform 360° grip on the round bar. We machine the inner bore to H7 tolerance, so a 10 mm bar sits with zero play. The gripping force is calculated for each bar diameter, so you do not over-torque and dent soft brass or aluminum rounds.
We start with 20CrMnTi alloy steel round bar, not cast blanks. The bar is turned, bored, and slotted on our CNC lathes, then carburized to a case depth of 0.6-0.8 mm. Final hardness is 58-62 HRC, and the core stays at 32-36 HRC for toughness. If you need corrosion resistance for stainless bar stock, we offer the same collet in 9Cr18MoV hardened to 54-58 HRC. All collets are stress-relieved before the final bore grind to prevent dimensional drift in your spindle.
The inner bore is not just turned — it is ground on a cylindrical grinder with a CBN wheel, after heat treatment. This is the step that keeps runout under 0.005 mm. We measure every collet on a precision mandrel with a dial indicator at 10 mm from the nose. The surface finish inside the bore is Ra 0.4 µm, which prevents the bar from cold-welding to the collet under high feed rates. If you need tighter than 0.005 mm, we can grind to 0.003 mm on request, but that adds 2 days to the lead time.
Most low-cost collets are machined from free-cutting steel and only case-hardened on the surface, which wears out after a few thousand cycles. Our 20 type collet is machined from round bar stock that is fully carburized and hardened through the working section. The slots are cut after hardening, so there is no soft edge. In our own test on a 20 mm brass bar at 4,000 rpm, the collet held the bar without slipping for 12,000 open-close cycles. We also chamfer the front edge to 30° so the bar feeds smoothly without catching on the slot ends.
| Specification | Value |
|---|---|
| Collet type | 20 type (DIN 6343 / ER style double taper) |
| Round bar stock range | 3 mm – 20 mm (in 0.5 mm increments) |
| Material | 20CrMnTi alloy steel (or 9Cr18MoV stainless) |
| Hardness | 58-62 HRC (carburized case), core 32-36 HRC |
| Runout (TIR) | ≤0.005 mm at 10 mm from nose |
| Bore tolerance | H7 for round bar |
| Surface finish (bore) | Ra 0.4 µm |
| Slots | 3 longitudinal, wire EDM cut after hardening |
| Lead time | 7 days for standard sizes, 9 days for custom bore |
| MOQ | No MOQ — order one piece for testing |
Every collet gets a dimensional report, not just a visual check. We measure the outer taper angle with a sine bar, the bore diameter with a bore gauge, and the runout with a mandrel and dial indicator. The hardness is tested on a Rockwell tester at three points along the body. Each collet is etched with a serial number, and the report is attached to the packing list. If you receive a collet that does not match the report, we replace it within 48 hours — that is our warranty.
No MOQ — you can order a single piece to test in your spindle before committing to a production batch.
Yes, we can bore to any diameter between 3 mm and 20 mm in 0.1 mm steps, and the lead time is 9 days instead of 7.
We machine the outer taper to the standard 20 type angle (16° included), and we check it with a sine bar on every part — if your spindle is non-standard, send us a drawing or a sample and we will copy it.
Standard sizes ship in 7 days from our Dongguan factory, custom bores in 9 days, and we send the tracking number the same day the courier picks up.
This collet replaces the stock collet on your automatic lathe (Swiss type or sliding head) that feeds round bar from the spindle. It works with any draw tube that uses a standard 20 type taper. The straight slots give a rigid grip, so you can run at higher feed rates without the bar slipping. If you are using a guide bushing, the collet also aligns the bar for the first machining operation. For more on matching tooling to your spindle, see our CNC cutting tool selection guide. And if you are pushing tolerances below 0.01 mm, check our CNC machining tolerances guide to know what is achievable.
You are buying precision manufacturing, not just a metal part. Our factory has run CNC machining lines for 20 years, and this collet is a standard item we produce weekly, so the process is stable. Because we machine from round bar stock in-house, we control the material grain flow, which gives better fatigue life than collets cut from plate. The price for a 20 type collet is typically 30-40% lower than a European equivalent, with the same runout spec. We are a precision manufacturing facility, made in China, but we ship worldwide by DHL or FedEx — 5 days to the US, 4 days to Europe.
Tell us your bar diameter and spindle type, or send the drawing of your existing collet. We will reply with a firm price, a lead time, and a sample offer if you need to test first. Email us at sc@bquq.com or message us on WhatsApp at +86 13713157787. We answer within 12 hours during the working week, and we will send you the inspection report with the first batch.
| 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 |
