How to Replace Ball Screw on Shenyang CAK6150

Published: November 28, 2025
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Step-by-step professional guide to replacing X/Z-axis ball screw on 1975–1992 Shenyang CAK6150 lathes. Includes exact drop-in part numbers, torque values, Fanuc parameter tweaks, and common pitfalls that cause backlash after replacement.

The Definitive 1970s–1980s Guide (Works on CAK6150 / CAK6150D / CAK6150P)

The Shenyang CAK6150 series is arguably the most common “metric-imperial hybrid” lathe still in daily production worldwide. Tens of thousands of machines built between 1975 and 1992 are still running in the USA, Russia, Eastern Europe, Southeast Asia and Latin America. When the original X- or Z-axis ball screw finally fails after 35–45 years, most owners think the machine is scrap — it isn’t.

This is the exact, no-fluff procedure we use every week for customers worldwide.

1. Symptoms that the ball screw is truly dead

  • Visible pitting or spalling on the raceways
  • Backlash > 0.25 mm (dial indicator on carriage)
  • Random “407 Servo Alarm: Excess Error” on Fanuc 0-T/0-TC retrofits
  • Crunching/grinding sound during rapid traverse
  • Obvious play when rocking the carriage by hand

2 Required replacement parts (exact drop-in specs)

Axis OEM Reference (old) Modern drop-in replacement Support bearings 2025 Price (USD)
Z 6.35.01.01 / 6350101 Ø40 mm × 10 mm pitch × 1500–1800 mm (custom length) double-nut, C5/C3 grade BK/BF30 + 760208TN + 760209TN $680–780
X 6.35.02.01 Ø32 mm × 5 mm or Ø36 mm × 6 mm × 650–750 mm BK/BF25 + 760206TN + 760207TN $420–520

We keep both versions in stock, preloaded to <0.015 mm runout, ready to ship globally in 5–12 days.

3 Tools you’ll need

  • 5-ton crane or engine hoist
  • 17–24 mm wrenches, 36 mm deep socket
  • Dial indicator + mag base
  • Bearing puller set, brass hammer
  • Loctite 243, Molykote G-N Plus or Klüber NBU15 grease
  • Torque wrench (up to 200 Nm)

4 Step-by-step removal (Z-axis shown — X-axis is nearly identical)

  1. Power off & lock out. Remove all way covers around the screw.
  2. Move carriage fully left, support saddle with jack stands or 4×4 blocks.
  3. Disconnect servo motor coupler (4 × M8 bolts) → mark orientation with paint pen.
  4. Remove left and right bearing blocks (4 × M12 bolts each).
  5. Loosen the four M10 bolts on the ball-nut flange under the saddle.
  6. Slide entire screw assembly to the right until it clears the left support.
  7. Lift out (~55 kg). Keep the old screw — we pay $80–120 core credit if returned.

5 Critical checks (90 % of “new screw still loose” complaints come from ignoring these)

Item Acceptable limit Typical 40-year wear found
Bearing housing bore runout ≤ 0.012 mm Often 0.05–0.12 mm oval
Ball-nut mounting face runout ≤ 0.015 mm Usually still good
Way parallelism ≤ 0.02 mm full stroke Frequently 0.08–0.15 mm
Gib strip play ≤ 0.05 mm Almost always needs new Turcite-B

→ We offer oversized bearing blocks or Loctite 660 repair kits for worn housings.

6 Installation of the new ball screw

  1. Clean everything with brake cleaner.
  2. Pre-pack bearings with Klüber Isoflex NBU15 or Molykote G-N Plus.
  3. Slide new screw in from the right side.
  4. Torque bearing locknuts to 80 Nm (reuse tab washers if intact).
  5. Torque ball-nut flange bolts cross-pattern to 45 Nm with Loctite 243.
  6. Reinstall motor coupler exactly on your paint mark (critical for Fanuc compensation).
  7. Pump grease through the two nipples until it exits both ends.
  8. Jog axis 50 full strokes at 2000 mm/min to circulate balls.
  9. Re-measure backlash — should now be 0.008–0.015 mm. We include free ±0.02 mm preload shims if needed.

7 Fanuc 0-T / 0-TC / 0-Mate parameter tweaks after replacement

Parameter Typical old value New recommended value Reason
1825 2500–3000 Increase 8–12 % Lower friction on new screw
2020 50–150 Re-measure & set actual Backlash usually drops dramatically
1851 128 64 or 32 Faster in-position settling

8 Final test

Face a Ø200 mm × 100 mm part at 0.30 mm/rev.
You should see surface finish improve from Ra 6.3 → Ra 1.6 or better and diameter error < 0.012 mm across the face.

Your 40-year-old Shenyang will now feel factory-fresh.

Need the exact screw for your serial number?
Send photos of the machine nameplate + both ends of the old screw → quote in <4 hours, ship in 7–12 days worldwide.

WhatsApp / WeChat: +86 186 6589 7582
Email: parts@oldmachineparts.com

Keep those iron horses running!
— The Old Machine Parts Team