## Opening
Your drawing defines the geometry. We define the tolerances. Every ER extension holder set is machined to your exact print, then verified with a CMM before shipment. No surprises at your
## Opening Your drawing defines the geometry. We define the tolerances. Every ER extension holder set is machined to your exact print, then verified with a CMM before shipment. No surprises at your spindle.
This is a custom CNC collet chuck, not a catalog item. We machine the taper, thread, and runout to your spec. You get a holder that repeats within 0.003 mm at 2.5×D from the nose.
| ## Specifications | ||
|---|---|---|
| Parameter | Value | Notes |
| Material | 42CrMo4 (AISI 4140), 20CrMnTi (AISI 8620) | Carburized or through-hardened |
| Hardness | HRC 52–56 | Case depth 0.5–0.8 mm for carburized |
| Machining | 5-axis CNC, turning, grinding | Mazak and DMG MORI |
| Taper accuracy | AT3 per ISO 7388/BS 1660 | Ground, not turned |
| Runout (TIR) | ≤0.005 mm at nose, ≤0.008 mm at 2.5×D | Verified on CMM |
| Thread accuracy | 6H per ISO 965 | For pull studs or retention knobs |
| Surface finish | Ra 0.4 µm on taper, Ra 0.8 µm elsewhere | |
| Coating | Black oxide, TiN, or none | TiN adds 0.001–0.002 mm thickness |
| Batch size | 1 to 5,000 pcs | No MOQ, same process control |
| Inspection | 100% critical dimensions, CMM report per batch | PDF or hard copy |
We grind the internal taper after heat treatment. That is the only way to hold the 0.005 mm runout. We do not skip this step for small orders.
## Three reasons buyers send us their drawings 1. Batch-traceable quality. Each bar of steel has a heat number. Each batch gets a production card. If a holder fails on your machine, we trace it back to the heat, the tool, and the operator. You get a root-cause answer, not a shrug.
2. Inspection report per batch. Every batch ships with a dimensional report. Taper angle, runout, thread pitch, hardness—all measured and recorded. You do not need to re-inspect on arrival. We have done it already.
3. One factory for CNC, stamping, springs, and heat sinks. Your CNC tooling project might need a spring collet, a stamped retention knob, or a heat sink for a spindle motor. We make all of those in-house. One purchase order, one quality system, one shipping address. Less coordination, fewer delays.
## Where these parts are used Custom CNC collet chucks and ER extension holders are not just for standard milling. Our parts go into:
We also make custom pull studs, collet nuts, and coolant-through versions. If your spindle takes a BT30, BT40, HSK, or Capto interface, we can match it.
## Questions buyers ask before ordering Q: Do you really have no MOQ? A: Yes. We have shipped single-piece orders for R&D labs. The setup cost is absorbed into the unit price. For production runs, price drops significantly at 50 and 200 pieces.
Q: How do you guarantee tolerance on a custom collet chuck? A: We grind the taper and bore after hardening. Then we measure on a CMM with a calibrated master collet. The report shows actual values, not just pass/fail. If you need better than 0.005 mm, we can grind to 0.003 mm, but it adds 2 days and 15% cost.
Q: What is the lead time for a custom ER extension holder set? A: Standard ER sizes with black oxide: 7–10 working days. TiN coating adds 2 days. Complex geometries (coolant holes, special threads) take 12–15 days. We quote firm lead time with your drawing, not an estimate.
Q: Can you provide material certificates? A: Yes. We supply EN 10204 3.1 certificates for the raw material. Hardness test reports and dimensional inspection reports are included free with every batch. Third-party inspection (SGS, TÜV) is available at cost.
## Send your drawing Email your PDF or STEP file. We will check for manufacturability, confirm material and coating, and send a firm quote within 12 hours. No obligation, no design fees.
Precision manufacturing made in China does not mean cutting corners. It means 20 years of CNC experience, one factory, and a CMM report on every batch. Send us your drawing—we will make the holder your spindle deserves.
Looking for a different part? We also machine Custom CNC Machined ER32 Collet Nut with Spanner Wrench Tooling in the same Dongguan factory.
| 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 |
