What This Collet Set Does and Why It Matters for Your CNC Lathe This is a complete mid-series collet set covering 25 mm, 28 mm, 30 mm, and 32 mm bore sizes for automatic lathes a
BQUQ CNC Machined Auto Lathe Collet Set 25-32 Mid Series
What This Collet Set Does and Why It Matters for Your CNC Lathe This is a complete mid-series collet set covering 25 mm, 28 mm, 30 mm, and 32 mm bore sizes for automatic lathes and CNC turning cente
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What This Collet Set Does and Why It Matters for Your CNC Lathe
This is a complete mid-series collet set covering 25 mm, 28 mm, 30 mm, and 32 mm bore sizes for automatic lathes and CNC turning centers. You get guaranteed 0.005 mm TIR (total indicated runout) at the nose, a hardness of HRC 58–60, and a surface finish of Ra 0.4 µm on the gripping diameter. That means your bar stock stays centered, tool wear drops, and you hold ±0.01 mm part tolerances without re-fixturing.
We machine these collets from 42CrMo4 alloy steel in our Dongguan factory, then grind and hone the bore. Lead time is 7 days for standard sizes, 12 days for custom bore profiles. No MOQ – order one set or fifty.
How the 25-28-30-32 Mid Series Grips Without Distortion
Each collet uses a 12-slot design with a 30° taper at the rear, matching standard auto lathe spindles. The slots are wire-cut, not milled, so the spring action is uniform across all four sizes. This prevents the "egg-shaping" you see on cheaper collets when you tighten the draw tube.
For the 25 mm and 28 mm sizes, we use a 0.5 mm slot width. For 30 mm and 32 mm, the slot width is 0.8 mm. This gives you enough flex to compensate for bar diameter variation up to 0.1 mm without losing grip force. You can run at 6,000 RPM with coolant on – no slip, no vibration marks.
Materials and Heat Treatment We Use for the Collet Bodies
Base material is 42CrMo4 (AISI 4140) – not mild steel. We pre-hardened it to HRC 28 before machining, then through-harden to HRC 58–60 after slot cutting. The final hardness range is verified on every batch using a Rockwell tester, not a sample.
The gripping surface is not just hardened. We grind it to Ra 0.4 µm and then apply a light phosphate coating to prevent galling on stainless steel and aluminum bars. No chrome plating – that flakes off and ruins your spindle. The 30° taper is ground to an angular tolerance of ±0.005°.
Runout Control: How We Hold 0.005 mm TIR on Every Collet
Runout is the enemy of precision turning. We measure each collet in a calibrated test holder, not in a free state. The test procedure: insert a ground master bar (diameter tolerance ±0.002 mm), tighten with a calibrated torque wrench, and read TIR at 10 mm from the nose. If it exceeds 0.005 mm, we reject it.
For the 32 mm size, we hold 0.007 mm TIR because of the larger diameter. This is still tighter than ISO 15488 class A (which allows 0.015 mm). You can use these collets for finishing passes without a second operation.
Inspection Before Every Shipment – What We Actually Check
Every collet in the set – all four sizes – goes through a 9-point inspection. We check: bore diameter, taper angle, slot width, slot depth, slot count, hardness, surface finish, TIR in test holder, and concentricity between taper and bore. Results are printed and included in the box.
We also do a functional test: we mount each set on a CNC lathe and machine a test bar to verify the part tolerance. If a collet fails the functional test, it is scrapped, not reworked. You get a signed inspection sheet with your shipment.
Specs and Dimensions for the Full Set
Parameter
Value / Range
Collet sizes in set
25 mm, 28 mm, 30 mm, 32 mm
Material
42CrMo4 (AISI 4140) alloy steel
Hardness (after heat treatment)
HRC 58–60
TIR (runout) at nose
0.005 mm (25/28/30), 0.007 mm (32)
Surface finish on gripping bore
Ra 0.4 µm
Taper angle (rear)
30° ± 0.005°
Slot count / width
12 slots; 0.5 mm (25/28), 0.8 mm (30/32)
Max spindle speed
6,000 RPM
Standard lead time
7 days (custom bore: 12 days)
MOQ
No MOQ – order 1 set or more
Why This Set Beats Buying Single Collets or Imported Brands
Buying a four-piece set saves you about 18% compared to purchasing each collet separately. More importantly, the set is matched – all four collets are ground from the same batch of steel, so thermal expansion is consistent across sizes. You do not get surprises when switching from 25 mm to 32 mm in the middle of a job.
Imported German or Swiss collets cost 2.5 to 3 times more for the same runout. Our precision manufacturing in China uses the same grade of steel and the same grinding equipment. We are not a trading company – we machine these in our own 20-year-old factory in Dongguan. That is why we can offer no MOQ and a direct factory price.
Customization Options for Non-Standard Bore Profiles
If your bar stock is hexagon, square, or has a special diameter like 25.4 mm, we can grind the bore to your profile. We hold the same 0.005 mm TIR on custom shapes. The lead time is 12 days, and the price increase is 15% over standard. Send your drawing with the bore dimension and tolerance – our engineers will confirm within 12 hours.
We also make stepped collets for double-diameter parts. These are ground in two sections, each with its own runout control. We have done stepped collets for automotive fuel injector bodies and medical screw blanks.
FAQ: Ordering, QC, and Lead Time
What is the minimum order quantity?
No MOQ – you can order a single 25 mm collet or the full 25-28-30-32 set.
Can you customize the bore for my specific bar size?
Yes, send your drawing – we grind custom bores (round, hex, square, stepped) within 12 days, holding 0.005 mm TIR.
How do you guarantee quality on every collet?
Each collet is inspected per our 9-point check and tested on a real CNC lathe before shipment; we include the signed inspection sheet.
What is your lead time for a standard set?
7 days for the standard 25-28-30-32 set, 12 days for custom bores – shipping from Dongguan via DHL or FedEx.
Get Your Firm Quote Within 12 Hours
Send your drawing or just tell us the bar sizes and material you are cutting. We will reply with a firm price, lead time, and a technical recommendation. For reference on tool selection or tolerance design, read our CNC cutting tool selection guide and CNC machining tolerances guide.
Email your drawing to sc@bquq.com or reach us on WhatsApp at +86 13713157787. We respond within 12 hours, even on weekends. This is a direct factory offer – no middlemen, no MOQ, made in China with a 12-month warranty against manufacturing defects.
