Introduction
Accurate bushing work is essential for restoring power and reliability in mechanical clocks. A KWM reamer is one of the most widely used tools for resizing pivot holes before installing new bushings. When used correctly, it produces clean, centered holes that maintain proper depthing. When used incorrectly, it can chatter, wander, or enlarge the hole off-center. This guide explains how to use a KWM reamer properly, how to support the movement on a movement stand, and how to avoid common mistakes that lead to poor bushing fit.
Understanding the KWM Reamer
What the reamer does
A KWM reamer enlarges a worn pivot hole to a precise diameter so a matching KWM bushing can be pressed into place.
Why centering matters
Maintaining the original pivot center ensures correct depthing between wheels and pinions.
Why reamer chatter occurs
Chatter happens when the reamer is not supported, not perpendicular to the plate, or rotated unevenly.
Why plate support is essential
Thin plates flex easily. Without support, the reamer can dig in or wander.
Why a movement stand helps
A movement stand stabilizes the plates and keeps both hands free for controlled reaming.
Preparing the Movement for Reaming
Secure the movement on a stand
Mount the movement on a movement stand so the plate is stable and accessible.
Mark the worn pivot hole
Use a sharp scribe to mark the center of the original hole if needed.
Support the plate
Place a hardwood block or brass plate behind the pivot hole to prevent flexing.
Select the correct reamer size
Match the reamer to the bushing size you plan to install.
Clean the area
Remove dirt, oil, and burrs so the reamer cuts smoothly.
How to Use the KWM Reamer Correctly
Step 1: Keep the reamer perpendicular
Hold the reamer perfectly square to the plate. Any tilt will enlarge the hole off-center.
Step 2: Turn slowly and evenly
Rotate the reamer with steady, gentle pressure. Fast turning increases chatter.
Step 3: Let the reamer cut
Do not force the tool. Allow the cutting edges to remove material gradually.
Step 4: Clear chips frequently
Back the reamer out periodically to remove brass chips and prevent binding.
Step 5: Stop as soon as the bushing fits
Test-fit the bushing often. Over-reaming leads to loose bushings and poor alignment.
Installing the Bushing
Check the fit
The bushing should press in firmly without wobble or excessive force.
Press the bushing squarely
Use a staking set, hand press, or smooth punch to seat the bushing flush with the plate.
Burnish the inside
After installation, burnish the pivot hole to smooth the surface and size it correctly.
Check depthing
Reinstall the wheel and verify proper mesh with its mating pinion.
Verify endshake
Ensure the arbor has free but controlled endshake after bushing installation.
Troubleshooting Flowcharts
If the reamer chatters
Support plate → Slow rotation → Check perpendicular angle → Reduce pressure
If the hole enlarges off-center
Recheck plate support → Verify reamer alignment → Use scribed center → Ream slowly
If the bushing is loose
Hole over-reamed → Use next-size bushing → Ream carefully → Press squarely
Common Mistakes to Avoid
Reaming without plate support
This causes flexing and off-center holes.
Turning the reamer too fast
Fast rotation increases chatter and uneven cutting.
Forcing the reamer
Excess pressure causes grabbing and plate distortion.
Over-reaming the hole
Oversized holes lead to loose bushings and poor depthing.
Skipping test fits
Frequent test-fitting prevents accidental oversizing.
Checklist for Final Verification
• Hole centered and clean
• Bushing fits snugly
• Bushing pressed square
• Pivot burnished and smooth
• Wheel depthing correct
• Movement stable on movement stand
FAQs
Why does the KWM reamer chatter?
Usually from lack of plate support or uneven rotation.
Why use KWM bushings?
They offer consistent sizing and reliable press-fit performance.
Why mount the movement on a stand?
A movement stand stabilizes the plates and keeps both hands free for precise reaming.
Can I ream by hand without a stand?
It’s possible but increases the risk of off-center holes.
Do I need to burnish after installing a bushing?
Yes. Burnishing smooths the pivot hole and improves long-term wear.
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