Sessions Clock Bushing for Beginners Hand Tools Guide

Sessions mantel clocks that won't keep running after cleaning reveal the most common problem with these American movements - severe wear in the top four pivot holes of the time train combined with failed clicks on the mainspring barrels. These clocks were built with heavy mainsprings that create substantial power, but decades of operation wear out the escape wheel and third wheel pivot holes causing the movement to stop unpredictably. Making the problem worse is previous amateur repair where someone punched the pivot holes from inside trying to tighten them up, which only creates deep grooves that damage pivots and accelerate wear without providing lasting improvement.

Proper correction requires installing brass bushings in the worn holes, but beginners face the challenge of centering bushings accurately without expensive equipment. This guide covers everything from diagnosing Sessions-specific wear patterns to choosing between hand tools and machine methods for bushing installation. You'll learn why Sessions clocks need bushings more than many other movements, how to tell which holes actually need bushing versus which can be left alone, and what tools represent the minimum investment for acceptable results versus professional-quality work.

Understanding Sessions Clock Wear Patterns

Why Sessions Clocks Wear Severely

Sessions manufactured affordable shelf clocks using heavy mainsprings providing substantial power. Original mainsprings often measure 0.018 inches thick - considerably heavier than many comparable movements. This aggressive power delivery creates strong torque driving the train but also accelerates bearing wear particularly in high-speed pivots experiencing greatest rotational stress. Escape wheel spinning fastest in train shows most severe wear. Third wheel also wears substantially from combined high speed and gear mesh loading transmitting power to escapement.

Design choices also contribute to wear problems. Sessions used relatively soft brass plates without hardening or special bearing treatments. Pivot holes wear progressively from steel pivots rotating against soft brass creating egg-shaped openings with material displaced rather than removed. Additionally, many Sessions movements have thin plates providing limited bearing surface depth. Shallow bearing combined with heavy power loading concentrates stress creating accelerated degradation compared to movements with thicker plates distributing bearing loads over greater surface area.

However, not all Sessions clocks show equal wear. Movement operated continuously for 80-100 years without service develops severe degradation. Clock operated intermittently or serviced periodically shows less wear. Additionally, movement kept properly lubricated throughout life experiences reduced friction minimizing wear rate. Assessing individual movement condition requires systematic inspection rather than assuming all Sessions clocks need identical bushing work. Some movements surprise with relatively good condition while others show destruction requiring extensive correction.

Common Click Mechanism Failures

Sessions click mechanisms securing mainspring power fail frequently from material fatigue and improper design. Click spring providing tension holding click engaged against click wheel loses temper over decades becoming weak. Weak spring allows click to slip under load creating sudden spring release potentially causing injury or movement damage. Additionally, click rivets securing click to great wheel arbor wear allowing excessive play. Loose click doesn't engage click wheel teeth reliably creating intermittent power delivery or complete failure.

Click failure symptoms include clicking or rattling sounds during operation, sudden spring unwinding when winding key is released, or complete inability to wind movement because click won't hold power. However, diagnosing click problems requires movement disassembly and careful inspection. External symptoms may be ambiguous suggesting multiple possible causes. Systematic evaluation during cleaning and service identifies click problems definitively enabling appropriate correction through click replacement or spring tension adjustment.

Replacement clicks and springs are available from parts suppliers. However, installation requires careful fitting ensuring proper engagement geometry and adequate spring tension. Improperly installed click may engage too deeply causing excessive friction or may engage inadequately allowing slipping under load. Professional installation or careful following of established procedures ensures reliable long-term click operation preventing future failures that compromise movement function or create safety hazards from sudden spring release.

Identifying Punched Pivot Holes

Amateur repair attempts often involve punching pivot holes from inside plate using center punch creating raised material around hole periphery reducing effective hole diameter. This crude technique appears to restore proper pivot fit temporarily but creates severe long-term problems. Punching distorts plate material creating irregular bearing surface. Raised metal doesn't extend through plate thickness - it only deforms material at interior surface leaving exterior surface unchanged creating stepped bearing that concentrates wear at specific points.

Punched holes are easily identified through careful visual inspection. Interior plate surface shows ring of raised metal surrounding pivot hole creating volcano-like appearance. Multiple punch marks may be visible around hole circumference where repairer struck plate repeatedly attempting adequate tightening. Exterior plate surface appears normal without punch marks because punching is performed from interior side. However, pivot running in punched hole develops deep grooves at plate surfaces where raised metal creates concentrated contact areas.

Critically, punched holes always require bushing regardless of apparent current condition. Punching work-hardens brass making further punching increasingly difficult while creating brittle material prone to cracking. Additionally, pivots running in punched holes are invariably damaged showing grooves or scoring from irregular bearing surfaces. These damaged pivots require burnishing or replacement before movement can provide reliable long-term operation. Simply installing bushing without addressing pivot damage creates premature bushing failure as damaged pivot continues wearing new bearing surface.

Choosing Bushing Tools and Methods

Hand Tools Versus Machine Methods

Bushing installation using only hand tools represents economical approach for hobbyist with limited budget. Method involves broaching hole to appropriate diameter, pressing bushing into hole using arbor press or improvised pressing tool, then broaching bushing interior to fit pivot. This approach requires minimal investment - set of broaches, reamers with handles, bushings, and simple pressing tool total perhaps $200-300. For individual repairing single clock or exploring whether clock repair will become long-term interest, hand tool approach provides entry without substantial financial commitment.

However, hand tool method has significant limitations. Achieving proper centering requires exceptional care and experience. Reamer held by hand wanders easily creating off-center bushing installation that increases gear mesh friction reducing efficiency. Even experienced clockmaker struggles maintaining perfect perpendicularity during hand reaming. Additionally, hand broaching bushing interior after installation risks cocking bushing or creating tapered hole rather than straight parallel bore providing optimal pivot bearing.

Machine methods using drill press with proper fixtures, dedicated bushing machine, or small milling machine provide superior centering accuracy and perpendicularity. Drill press adapted for bushing work costs approximately $300-500 including quality drill press and necessary fixtures. Dedicated bushing machine costs $800-1200 providing purpose-built tool for this specific operation. Small milling machine costs similar to bushing machine but enables many other precision operations beyond just bushing making it versatile shop tool justifying investment for serious hobbyist.

Minimum Hand Tool Kit

Beginner attempting first bushing project using hand tools needs specific essential items. Broach set containing 6-12 graduated sizes enables progressive hole enlargement and final bushing bore sizing. Twelve-piece set provides better size coverage than six-piece economy set. However, six-piece set suffices for basic work if budget is limited. Cutting broaches remove material aggressively. Smoothing broaches create final surface finish. Both types are useful though cutting broaches are essential minimum.

Reamer with handle creates hole in plate accepting bushing. KWM system uses smaller bushings suitable for shelf clock work. Number 3 reamer with D cutter creates 2.7mm hole accommodating KWM bushings. Bergeon system uses larger bushings providing more material around bushing circumference potentially improving retention in worn or damaged plates. Choose system based on application and existing bushing inventory if replacing previous work. Handle must fit selected reamer shank - KWM and Bergeon use different mounting systems requiring specific handles.

Bushing assortment provides range of bore sizes accommodating various pivot diameters. Rather than buying individual bushings for specific known sizes, assortment ensures appropriate bushing is available as pivot diameters are measured during service. However, smallest bore bushing can be broached to larger size if needed making buying bushings slightly oversized acceptable compromise reducing inventory requirements. Pin vise or similar holding tool enables controlled broach operation. Small diamond file assists deburring and cleanup operations maintaining clean professional appearance.

Alternative: Fitz-All and Similar Tools

Fitz-All bushing tool represents intermediate option between pure hand tools and professional machines. This American-made tool from past decades occasionally appears on used market at reasonable prices. Design provides mechanical advantage and improved alignment compared to pure hand reaming while costing substantially less than bushing machine or mill. Tool holds plate and guides reamer maintaining better perpendicularity than freehand operation achieving results closer to machine methods than pure hand tools.

However, Fitz-All tools are no longer manufactured making acquisition dependent on finding used examples. Condition varies widely. Well-maintained example provides excellent service. Worn or damaged tool may create more problems than it solves through poor alignment or inadequate clamping. Careful inspection before purchase determines whether specific tool is worthwhile investment or should be avoided. Additionally, learning curve exists - tool isn't automatically foolproof requiring practice developing proper technique achieving optimal results.

Modern alternatives include imported tools from various manufacturers offering similar functionality at varying price points and quality levels. Research and recommendations from experienced clockmakers guide selection avoiding poor-quality tools that create frustration without delivering promised benefits. However, even marginal improvement in centering and perpendicularity over pure hand methods justifies modest tool investment for hobbyist planning multiple bushing projects developing skills progressively rather than attempting perfection on first project.

Bushing Installation Procedures

Determining Which Holes Need Bushing

Not every pivot hole in worn movement requires bushing. Selective bushing of only severely worn locations reduces work scope while achieving functional improvement enabling reliable operation. Checking for wear involves systematic inspection of each pivot hole assessing dimensional change and shape distortion. Hole appearing round and properly sized with minimal clearance may not need bushing even in older movement. Hole showing obvious egg shape, excessive clearance, or visual wear patterns requires correction.

Practical test involves observing pivot behavior during trial assembly. With mainsprings let down completely, rotate each arbor by hand feeling for binding or roughness. Arbor should rotate smoothly without hesitation. Lift arbor upward testing endshake. Proper endshake shows slight movement - approximately 0.005-0.010 inches - providing clearance preventing binding. Excessive endshake indicating substantial wear requires bushing. Additionally, check pivot lean. Arbor should remain relatively perpendicular to plates. Excessive lean approximately five degrees off perpendicular indicates adequate endshake though gross lean suggests severe wear.

For Sessions movements specifically, escape wheel and third wheel pivot holes in time train almost always require bushing. These high-speed pivots show most severe wear. Second wheel may or may not need bushing depending on individual movement condition. First wheel and great wheel rarely require bushing having lower rotational speeds creating reduced wear rates. Strike train follows similar pattern with faster wheels requiring attention while slower wheels often remain serviceable. However, any punched holes require bushing regardless of apparent current condition because punching creates damage necessitating correction.

Achieving Proper Centering

Centering represents most critical and challenging aspect of bushing installation. Off-center bushing creates misalignment between pivot and bearing causing increased friction, accelerated wear, and potential stopping problems. Proper centering requires bushing hole to be drilled or reamed concentrically with original pivot hole position maintaining correct gear mesh relationships throughout train. Hand tool methods struggle with centering because maintaining exact position during reaming or drilling requires extraordinary care and experience.

One hand tool approach uses initial small pilot hole drilled carefully at center of worn hole. Progressive reaming enlarges hole maintaining original center point. However, this assumes original hole center is still identifiable after severe wear creating egg-shaped opening. Alternative approach uses assembled plates with front plate acting as guide during reaming. Pilot extending through both plates maintains alignment though technique still requires careful execution preventing reamer wandering. Practice on scrap plates develops skills before attempting valuable movement.

Machine methods inherently provide better centering. Drill press or mill centers work precisely over marked position using crosshairs or indicator. Bushing machine uses plate holder and adjustable centering mechanism positioning plate accurately relative to fixed reamer path. These mechanical aids eliminate human error maintaining consistent centering across all bushing installations. For movement requiring eight to fourteen bushings as typical severely worn Sessions, cumulative improvement from machine centering versus hand centering becomes substantial affecting overall movement performance and longevity.

Bushing Retention Methods

Bushings stay in plates through interference fit created by press-fitting bushing into slightly undersized hole. Properly sized hole requires substantial force for bushing insertion but doesn't distort bushing during installation. After installation, skin friction between bushing exterior and plate hole interior prevents bushing rotation or migration during operation. This simple elegant retention method requires no adhesives or mechanical fasteners maintaining clean professional installation easily reversed for future service if necessary.

However, severely worn or punched plates may not provide adequate hole material for reliable interference fit. Deep punch marks create voids around hole circumference reducing contact area between bushing and plate. In these situations, additional retention may be necessary. Some clockmakers use bushing expanding technique where small ball bearing or broach is forced through bushing after installation creating slight expansion locking bushing in place. However, this distorts bushing requiring additional broaching restoring proper bore dimension and may create stress concentrations risking bushing failure.

Better approach for problematic retention situations uses larger Bergeon bushing providing more circumferential material improving grip even with damaged plates. Alternatively, adhesive retention using small amount of Loctite or similar product supplements interference fit providing additional security. However, adhesive complicates future service requiring heating for bushing removal. Balance immediate retention concerns against long-term serviceability selecting appropriate retention method for specific situation considering plate condition, bushing size, and expected service life before next overhaul.

Broaching Bushing Bore

After bushing installation, interior bore must be sized to accept pivot with proper running clearance. Bushings are supplied with pre-drilled bore typically slightly smaller than final desired dimension requiring broaching to final size. Start with smallest broach fitting bushing bore. Assemble both plates before broaching using opposite plate as guide maintaining straight broach path through both bushings simultaneously. This ensures perpendicularity and alignment between front and rear bearings critical for proper arbor operation.

Progress through successively larger broaches approaching final dimension gradually. Don't attempt removing all material in single broaching operation. Multiple light passes produce smoother finish and better dimensional control than single aggressive pass risking oversize bore or rough surface. Test fit pivot frequently during broaching checking for proper clearance. Pivot should enter bore easily under light pressure without binding but shouldn't have excessive play creating sloppy fit.

Final clearance should allow pivot to lean approximately five degrees from perpendicular when arbor is assembled in movement. This provides adequate clearance preventing binding while maintaining reasonable tolerance ensuring proper gear mesh and minimizing power loss through excessive clearance. However, slightly loose is better than slightly tight. Tight bushing creates binding stopping movement immediately. Loose bushing creates inefficiency but movement still runs allowing future correction if problems develop. Conservative broaching leaving slightly loose fit prevents over-correction requiring bushing replacement from excessive bore enlargement.

Pivot Inspection and Correction

Burnishing Worn Pivots

Pivots running in worn holes often show damage requiring correction before bushing installation. Damaged pivot continues wearing new bushing creating premature failure. Proper service addresses both bearing and pivot ensuring optimal bearing surface pairing. Pivot damage appears as grooves, scoring, or rough texture visible under magnification. Severe damage shows stepped profile where contact area shows reduced diameter compared to unworn sections. Even minor roughness accelerates bushing wear requiring correction achieving smooth polished surface.

Burnishing removes minor damage polishing pivot to smooth finish. Pivot burnisher - smooth hardened tool - is pressed against rotating pivot under light pressure. Friction creates localized heating causing slight material flow smoothing surface irregularities. Multiple passes with progressive pressure produces increasingly smooth finish. However, burnishing has limitations. Deep grooves or substantial material loss can't be corrected through burnishing alone requiring pivot replacement if damage exceeds burnishing capabilities.

After burnishing, inspect pivot under magnification verifying smooth uniform surface without visible defects. Test pivot in new bushing checking for smooth rotation without catching or roughness. Properly burnished pivot in correct-size bushing creates barely perceptible resistance - just enough friction for controlled rotation without excess drag indicating binding or roughness. If pivot feels rough after burnishing or shows persistent grooves, replacement is necessary preventing bushing damage and ensuring reliable long-term operation.

When Pivot Replacement Is Necessary

Severely damaged pivots beyond burnishing correction require replacement. This advanced operation involves removing damaged pivot and installing new properly-sized replacement maintaining correct arbor dimensions and relationships. For beginners, pivot replacement represents substantial challenge requiring lathe and specialized skills beyond basic bushing work. Movement requiring extensive repivoting may justify professional service rather than amateur attempt risking irreversible damage to valuable arbors.

However, some pivot damage allows interim approaches. If pivot is scored but maintains reasonable diameter, operating in oversized bushing providing adequate clearance may provide acceptable temporary service. This isn't ideal long-term solution but enables functional operation while skills and equipment for proper repivoting are developed. Additionally, for inexpensive common movements like Sessions shelf clocks, accepting marginally damaged pivot may be reasonable compromise balancing repair perfection against economic reality and hobbyist skill level.

For valuable movements or situations where long-term reliability is essential, proper pivot replacement is necessary. This involves securing arbor in lathe, removing damaged pivot through drilling or turning, installing new pivot through soft solder or silver solder, and finishing to proper dimension. Professional service ensures correct execution preventing damage while amateur attempt creates risk of destroyed arbor requiring expensive replacement. Honest assessment of skills and equipment guides appropriate decision about DIY pivot work versus professional service.

Fast Run Test for Bent Pivots

Bent pivots create wobbling during rotation causing erratic operation, increased friction, and accelerated wear. Fast run test identifies bent pivots before final assembly preventing wasted effort installing bushings only to discover fundamental arbor problems. Perform test by removing pallet arbor completely letting down both mainsprings first for safety. Wind time train several turns creating powered rotation. Observe each pivot as wheels spin watching for wobbling or eccentric motion indicating bent pivot.

Bent pivot appears to move in circular path rather than rotating around fixed axis. Wobble amplitude varies with bend severity. Slight bend creates subtle wobble barely visible requiring careful observation under magnification. Severe bend creates obvious eccentric motion visible without magnification. Any visible wobble indicates problem requiring correction before proceeding with service. Attempting to install bushings with bent pivot wastes effort because movement won't run reliably regardless of bushing quality.

Straightening bent pivots requires specialized skills and tools. Amateur attempts often worsen problem or break pivot completely. Professional service straightens pivots correctly using proper techniques and equipment. However, for inexpensive movements, arbor replacement may be more economical than straightening. Additionally, determining why pivot bent is important. Manufacturing defects, excessive force during disassembly, or prior service mishaps create bending. Understanding cause prevents repeating same mistakes during current service creating additional problems.

Economic Considerations and Expectations

Tool Investment Versus Clock Value

Spending $1000 on tools to repair $30 clock seems economically irrational. However, tool investment isn't justified by single clock value but by future use across multiple projects. Clockmaker repairing single clock should pay professional for proper service rather than buying tools used once then abandoned. However, hobbyist planning ongoing clock repair developing skills across many projects justifies tool investment as long-term capability building not just single-clock fix.

Consider total cost of ownership perspective. Professional Sessions service costs approximately $200-300 including cleaning, bushing, adjustment, and testing. Doing work yourself saves service cost but requires tool investment and time. After repairing four or five clocks, tool cost is recovered compared to professional service. Additional clocks represent pure savings plus satisfaction of DIY accomplishment. However, this calculation assumes competent work producing results comparable to professional service not repeated failed attempts creating frustration and damaged movements.

Additionally, tool investment enables other clock repairs beyond just bushing. Broaches, reamers, and measuring tools serve multiple purposes throughout clock service. Skill development through progressive projects builds capabilities extending to increasingly sophisticated work. Initial tool investment provides foundation for long-term hobby or even part-time business if skills develop sufficiently. However, unrealistic expectations about immediate professional-quality results create disappointment. Patient skill development through practice on inexpensive movements builds capabilities reliably.

Starting With Inexpensive Movements

Sessions shelf clocks represent ideal learning vehicles for bushing practice. Movements are inexpensive and readily available making practice affordable. Common design means mistakes don't destroy rare irreplaceable mechanisms. Additionally, Sessions movements typically need bushings creating realistic practice scenarios. Successfully bushing Sessions movement demonstrates capabilities applicable to other shelf clock types while building confidence for advancing to more valuable or complex movements.

However, Sessions movements aren't trivially easy. Thin plates and severe wear create challenges even for experienced clockmakers. Beginner expecting simple learning experience may encounter frustration from accumulated wear and previous amateur repairs creating complicated situations. Alternative approach starts with even simpler time-only movements from alarm clocks or basic shelf clocks learning disassembly, cleaning, and reassembly before attempting bushing work. This progressive skill building reduces overwhelming feeling from confronting too many new challenges simultaneously.

Practice approach involves repeated disassembly and reassembly of same movement developing familiarity with components and relationships. Willie X suggests doing this five or six times thoroughly examining everything, polishing pivots, and understanding mechanism operation before attempting permanent repairs. This investment of time without permanent modifications provides learning without risk. After complete understanding is achieved through repetition, bushing work proceeds with confidence rather than uncertainty creating better results and less frustration.

Recognizing When Professional Help Is Appropriate

Not every repair situation suits DIY approach regardless of enthusiasm or tool availability. Movement with severe damage, complex strike mechanism, or high monetary or sentimental value justifies professional service ensuring proper correction. Additionally, beginner lacking proper tools attempting work requiring precision equipment creates poor results potentially destroying movement beyond economical repair. Honest assessment about capabilities, equipment, and stakes involved guides appropriate decision about DIY attempt versus professional service.

Professional clockmaker has experience diagnosing problems, appropriate tools producing quality results, and knowledge avoiding common mistakes. For valuable family heirloom or rare clock, professional service investment protects irreplaceable mechanism ensuring proper repair for future generations. However, for common inexpensive movements with limited value, DIY attempt represents reasonable learning opportunity even with risk of failure because economic loss is modest while learning experience provides lasting value developing skills.

Middle ground approach involves consulting professional for guidance while performing work yourself. Some clockmakers offer tutorial services teaching bushing techniques using customer's movement under supervision. This combines professional expertise ensuring proper results with hands-on learning building capabilities. Cost exceeds simple DIY but substantially less than full professional service while providing educational value justifying additional expense. Various learning approaches suit different situations and preferences selecting path matching individual circumstances and objectives.

FAQs

Why do Sessions clocks need so much bushing work?

Sessions clocks need extensive bushing because they used heavy mainsprings creating substantial power that accelerates bearing wear particularly in high-speed pivots experiencing greatest rotational stress where escape wheel spinning fastest shows most severe wear while third wheel also wears substantially from combined high speed and gear mesh loading. Design choices including relatively soft brass plates without hardening or special bearing treatments plus thin plates providing limited bearing surface depth concentrate stress creating accelerated degradation compared to movements with thicker plates distributing bearing loads over greater surface area. Movement operated continuously for 80-100 years without service develops severe degradation requiring eight to fourteen bushings as typical for worn Sessions while movements operated intermittently or serviced periodically show less wear. Top four pivot holes in time train almost always require bushing where escape wheel and third wheel show most severe wear while second wheel may or may not need bushing depending on individual condition. Strike train follows similar pattern with faster wheels requiring attention while slower wheels often remain serviceable though any punched holes require bushing regardless of apparent current condition.

Can I bush a Sessions clock using only hand tools?

Yes you can bush Sessions clock using only hand tools though achieving proper centering requires exceptional care and experience where method involves broaching hole to appropriate diameter pressing bushing into hole using arbor press then broaching bushing interior to fit pivot requiring minimal investment of $200-300 for broach set reamers with handles bushings and pressing tool. However hand tool method has significant limitations where achieving proper centering is challenging because reamer held by hand wanders easily creating off-center bushing installation that increases gear mesh friction while maintaining perfect perpendicularity is difficult even for experienced clockmakers. Machine methods using drill press with proper fixtures costing $300-500, dedicated bushing machine costing $800-1200, or small milling machine provide superior centering accuracy and perpendicularity justifying investment for serious hobbyist planning multiple projects. For individual repairing single clock exploring whether clock repair will become long-term interest hand tool approach provides entry without substantial financial commitment though unrealistic expectations about immediate professional-quality results create disappointment where patient skill development through practice on inexpensive movements builds capabilities reliably over time.

Which Sessions pivot holes actually need bushing?

Sessions pivot holes requiring bushing are those showing obvious egg shape excessive clearance or visual wear patterns where escape wheel and third wheel pivot holes in time train almost always require bushing having highest rotational speeds creating most severe wear. Second wheel may or may not need bushing depending on individual movement condition while first wheel and great wheel rarely require bushing having lower rotational speeds. Strike train follows similar pattern with faster wheels requiring attention while slower wheels often remain serviceable. Additionally any punched holes require bushing regardless of apparent current condition because punching creates damage necessitating correction where amateur repair attempts involving center punch create raised material around hole periphery that distorts plate material creating irregular bearing surface and deep grooves damaging pivots. Test for wear by observing pivot behavior during trial assembly with mainsprings let down where arbor should rotate smoothly without hesitation and lifting arbor upward testing endshake should show slight movement approximately 0.005-0.010 inches while excessive endshake indicates substantial wear requiring bushing. Check pivot lean where arbor should remain relatively perpendicular to plates and excessive lean approximately five degrees off perpendicular suggests severe wear requiring correction.

What is proper bushing bore size for Sessions pivots?

Proper bushing bore size for Sessions pivots provides adequate clearance preventing binding while maintaining reasonable tolerance where final clearance should allow pivot to lean approximately five degrees from perpendicular when arbor is assembled in movement. Start with bushing having bore size closest to pivot diameter without being too tight where if 1.4mm bore bushing is too small but 1.5mm fits then use 1.5mm bushing and broach slightly if needed after installation rather than starting with oversized 1.6mm bore. Assemble both plates before broaching using opposite plate as guide maintaining straight broach path through both bushings simultaneously ensuring perpendicularity and alignment between front and rear bearings. Progress through successively larger broaches approaching final dimension gradually testing pivot fit frequently where pivot should enter bore easily under light pressure without binding but shouldn't have excessive play creating sloppy fit. However slightly loose is better than slightly tight where tight bushing creates binding stopping movement immediately while loose bushing creates inefficiency but movement still runs allowing future correction. Conservative broaching leaving slightly loose fit prevents over-correction requiring bushing replacement from excessive bore enlargement.

How do I know if my pivots need burnishing or replacement?

Pivots need burnishing when showing minor damage including grooves scoring or rough texture visible under magnification where even minor roughness accelerates bushing wear requiring correction achieving smooth polished surface. Burnishing removes minor damage polishing pivot to smooth finish using hardened tool pressed against rotating pivot under light pressure where multiple passes produce increasingly smooth finish. However burnishing has limitations where deep grooves or substantial material loss can't be corrected through burnishing alone requiring pivot replacement if damage exceeds burnishing capabilities. After burnishing inspect pivot under magnification verifying smooth uniform surface without visible defects and test pivot in new bushing checking for smooth rotation where properly burnished pivot creates barely perceptible resistance without excess drag indicating binding or roughness. Pivots running in punched holes are invariably damaged showing grooves or scoring from irregular bearing surfaces requiring burnishing or replacement before movement provides reliable operation. Additionally perform fast run test by removing pallet arbor letting down mainsprings then winding time train several turns observing each pivot as wheels spin where bent pivot appears to move in circular path rather than rotating around fixed axis indicating problem requiring correction before proceeding with service.

Should I invest in expensive bushing machines for hobby work?

Investment in expensive bushing machines depends on commitment level and project scope where clockmaker repairing single clock should pay professional for proper service rather than buying tools used once but hobbyist planning ongoing clock repair developing skills across many projects justifies tool investment as long-term capability building. Professional Sessions service costs approximately $200-300 where after repairing four or five clocks tool cost is recovered compared to professional service making subsequent repairs represent pure savings plus satisfaction of DIY accomplishment. Drill press adapted for bushing work costing $300-500 including quality drill press and fixtures provides substantial improvement over hand tools at modest investment suitable for serious hobbyist. Dedicated bushing machine costing $800-1200 provides purpose-built tool but small milling machine costing similar amount enables many other precision operations making it versatile shop tool justifying investment for serious hobbyist performing various clock repairs. However unrealistic expectations about immediate professional-quality results create disappointment where patient skill development through practice on inexpensive movements like Sessions shelf clocks builds capabilities reliably while tools provide foundation for long-term hobby or even part-time business if skills develop sufficiently through progressive learning.

What causes Sessions click mechanisms to fail?

Sessions click mechanisms fail from material fatigue and improper design where click spring providing tension holding click engaged against click wheel loses temper over decades becoming weak allowing click to slip under load creating sudden spring release potentially causing injury or movement damage. Click rivets securing click to great wheel arbor wear allowing excessive play where loose click doesn't engage click wheel teeth reliably creating intermittent power delivery or complete failure. Click failure symptoms include clicking or rattling sounds during operation sudden spring unwinding when winding key is released or complete inability to wind movement because click won't hold power. Replacement clicks and springs are available from parts suppliers requiring careful fitting ensuring proper engagement geometry and adequate spring tension where improperly installed click may engage too deeply causing excessive friction or may engage inadequately allowing slipping under load. Professional installation or careful following of established procedures ensures reliable long-term click operation preventing future failures that compromise movement function or create safety hazards from sudden spring release during normal operation or maintenance.