Swiss Type CNC Turned Pin 316L Stainless 0.005mm Small Diameter Custom

Dongguan Changxinda Precision Technology Co., Ltd. has machined custom parts to drawing since 2008. The plant runs 4-axis and 5-axis machining centers, turn-mill combined lathes and precision CNC lathes, employs more than 90 people, and exports 50 to 60 percent of output to industrial buyers in Europe, North America and Southeast Asia. ISO 9001:2015 certified, first article reports with ballooned drawings as standard.

Swiss type turning is the process for parts that are long, thin and small. The workpiece is held by a guide bushing a few millimetres from the cutting tool, so the tool never pushes against an unsupported length. The result is a pin of 1 mm diameter and 40 mm length that stays straight, where a conventional lathe would bend it. This page covers the guide bushing setup, the tolerances it supports and the secondary operations that can be completed in the same cycle.

Guide Bushing Support

The bushing is the difference between the process working and not working, and it is matched to the bar stock rather than to the finished diameter.

• Bar stock tolerance held to h9 or better, because a bar that varies in diameter will either seize in the bushing or rattle in it
• Bushing clearance 0.005 mm to 0.01 mm, replaced when wear exceeds the limit rather than when a part fails
• Material support from both the main and the sub spindle, so the part is never unsupported when it is cut off
• Bar feeder with a steady rest for long bars, keeping the bar from whipping at high spindle speed
• Cut off and pick up in the sub spindle, then back work in the same cycle, so the part is never handled between operations

0.005 mm On Small Diameter

The declared capability for pins in this size range is 0.005 mm on diameter, 0.005 mm roundness and 0.01 mm on length between shoulders.

• Diameter measured with a micrometer at three positions along the pin, at a controlled 20 degrees Celsius
• Roundness checked on a talyrond for pins where the fit is critical, with the trace supplied on request
• Straightness 0.01 mm over 50 mm, measured on a granite plate with a dial indicator
• Surface roughness Ra 0.4 achievable on small diameters with a wiper insert and a light finishing pass
• First article inspection on a profile projector and CMM, then in process checks every 50 pieces during the batch

Secondary Operations In The Same Cycle

• Cross holes drilled and deburred from the sub spindle, so a 0.5 mm hole is not drilled by hand afterwards
• Threads rolled rather than cut on small diameters, giving a stronger thread and no burr at the start
• Slots, flats and hex features milled with the C axis, avoiding a second operation and a second setup error
• Grooves and undercuts cut with form tools ground to the drawing profile
• Laser marking of part number on the pin end when the batch size justifies it

Materials And Custom Options

• Diameter from 0.8 mm to 12 mm, length up to 120 mm depending on the length to diameter ratio
• Materials: 303 and 316L stainless, 17-4PH, titanium grade 5, brass, beryllium copper, PEEK and POM
• Tolerances tighter than 0.005 mm quoted separately, because they change the process rather than the program
• Heat treatment and passivation coordinated with machining, with the sequence chosen so that hardness does not distort the finished diameter
• Supplied as bulk in bags, in trays, or in tape and reel for automatic assembly
• Prototype quantity from 50 pieces, since bar setup and bushing selection make very small lots uneconomic

Delivery And Consistency

• Prototype and sample lots: 5 to 8 working days
• Batch of 1000 to 50000 pieces: 10 to 18 working days, running on dedicated Swiss machines
• Recurring orders keep the same bar supplier, the same bushing size and the same program, so the second batch measures like the first
• Material certificate and inspection record supplied with each lot
• Packaging counts verified by weight and by sample count, so the delivered quantity matches the invoice

Questions From Design Engineers

How small a hole can you drill across a 2 mm pin?

0.4 mm is routine with a carbide drill and a peck cycle, provided the hole is not deeper than about three diameters. Below that we would consider EDM or a laser, and we will say so before quoting.

Can you hold 0.005 mm on a 1 mm diameter over 40 mm length?

On diameter yes, because the guide bushing supports the work right at the cut. Straightness over that length is the harder number and is normally quoted at 0.01 mm. Send the drawing and we will confirm both values in writing.

Do you make the bar stock yourselves?

No. We buy ground bar to h9 from approved suppliers, and we reject bar that is out of tolerance rather than trying to machine around it, because a bar that varies will not run through a guide bushing.