Restoring an X68000 floppy drive with a 3D-printed pulley

A failing floppy drive can make an otherwise healthy Sharp X68000 appear unreliable. The machine may power up, recognise a disk intermittently, or produce a grinding sound while the spindle struggles to reach speed. In many cases, the problem is a small rubber belt that has stretched, split, or turned into sticky residue. A damaged motor pulley can make the repair harder, particularly when the original plastic has cracked or lost its grip.

Replacing the belt is usually straightforward when a suitable spare is available. The difficult part is sourcing a pulley with the correct bore, diameter, groove profile, and position on the motor shaft. A 3D-printed replacement provides a practical solution for preservation work, provided it is measured carefully and printed with suitable material and tolerances.

This repair suits owners who are comfortable removing a floppy mechanism, checking alignment, and testing an old computer gradually. It is especially useful in Australia, where vintage Japanese drive parts can be expensive to import and local listings are inconsistent. The finished result can keep an original X68000 mechanism operating without permanently altering the computer’s case or mainboard.

Identify the mechanism before ordering parts

X68000 models and drive assemblies are not completely uniform. An XVI, Compact, Super, or early tower model may contain a different mechanism from another machine bearing a similar external appearance. Some drives use a belt to transfer motion from the spindle motor, while others use a belt in the eject or loading assembly. Before designing a pulley, identify exactly which motor and belt path are present.

Begin by removing power and disconnecting the mains lead. If the computer has recently been opened, allow time for its power supply capacitors to discharge, but treat the power supply as dangerous regardless. Australian users should remember that the system is connected to a 230–240 V supply, even when the original Japanese computer was designed around a different mains arrangement. Work on the floppy drive only after it has been removed from the powered computer.

Photograph the drive from several angles before touching the belt. Record the motor markings, connector position, pulley height, belt route, and the location of any washers or clips. A photograph with a ruler beside the assembly is valuable when the old belt disintegrates. Repair notes and preservation projects collected by X68K.NET can also help establish whether a particular drive variant has known belt or pulley problems.

Inspect the belt path and pulley damage

A degraded floppy belt often leaves a dark, tar-like coating on the motor pulley and driven wheel. Isopropyl alcohol on lint-free swabs can remove most residue, although several passes may be needed. Avoid flooding the motor or allowing solvent to run into bearings, optical sensors, or the drive’s electronic board. Cotton buds are useful around the groove, but a wooden toothpick can remove soft residue without scratching the pulley.

Measure the original belt if it is still intact, but do not rely on its present length. A stretched belt gives a misleading result, and a broken belt may have lost sections. Measure the distance between pulley centres, the diameter of the driven wheel, and the approximate belt cross-section. A flexible O-ring may work for testing, but a square or flat drive belt with the correct dimensions is generally more stable for long-term use.

Inspect the motor shaft for corrosion, burrs, or a flattened section. Measure the shaft with digital calipers at several points. A nominal 2 mm shaft may be slightly under or over that size, and a pulley bore printed exactly at 2.00 mm may be either too tight or too loose. Check whether the original pulley was secured by a press fit, adhesive, grub screw, or a raised section on the shaft. The attachment method determines the most reliable printed design.

Design a replacement pulley in CAD

The pulley should reproduce the functional dimensions rather than its cosmetic shape alone. Important measurements include the shaft bore, outside diameter, groove width, groove depth, flange diameter, and distance from the motor body to the belt centreline. If the pulley sits too high or low, the belt will climb the flange, rub the mechanism, or work sideways until it comes off.

A simple pulley can be modelled as a revolved profile in FreeCAD, Fusion, OpenSCAD, or similar software. Add a small lead-in chamfer to the bore and outer edges. A shallow V-groove can centre a round belt, while a wider flat or crowned surface suits a flat belt. Avoid sharp internal corners, which are difficult to print and create stress points. If the original belt was square-section, the groove should support it without pinching the belt against the bottom.

Design the bore slightly undersize for the selected printing process. For a common FDM printer, a first test might use a 1.8–1.9 mm bore for a measured 2 mm shaft, then be reamed carefully to fit. The correct allowance depends on printer calibration, layer height, filament, and whether the shaft is smooth or knurled. Printing several inexpensive bore-test rings before the final pulley is usually faster than repeatedly remaking a complete part.

The pulley must also be concentric. A visibly eccentric wheel changes belt tension once per revolution and can cause spindle-speed variation, read errors, or audible pulsing. Use a high-resolution circular profile, print with the pulley axis vertical where possible, and avoid supports inside the bore. A 0.12 or 0.16 mm layer height, three or four walls, and a solid top and bottom can provide adequate precision for a small drive component.

Select material for a long-lasting repair

PLA is easy to print and can produce a precise prototype, but it is not the preferred material for a warm computer interior. It softens at relatively low temperatures and can creep when held under continuous belt tension. A PLA pulley may work for a short diagnostic test, yet it is a poor choice for a restoration intended to last for years.

PETG offers better heat resistance and is widely available, although its tendency to string can affect small grooves and bores. Nylon or a suitable polyamide is mechanically strong and wear-resistant, but it absorbs moisture and may be harder to print accurately. Engineering resins can produce excellent detail, though the finished part must be fully cured and chosen for dimensional stability rather than appearance.

For many hobby repairs, an engineering-grade PETG, ABS, or ASA pulley is a sensible compromise. ASA is useful where heat and ageing matter, but it requires an enclosed or well-controlled printer. Australian owners using a local maker space in Melbourne, Sydney, Brisbane, or Adelaide may be able to order a small part in nylon or resin even without owning a printer. Give the service the exact orientation, material, tolerance, and finish requirements rather than sending only an STL file.

Do not lubricate the belt. Rubber and many printed plastics become contaminated by oil, and the belt can begin slipping under load. Clean the motor shaft and pulley bore before assembly. If the drive mechanism has metal bearings or sliding guides that require lubrication, apply only a tiny amount of suitable plastic-safe lubricant to those points, keeping it away from the belt and pulley surfaces.

Fit the pulley without damaging the motor

Test the printed pulley on the motor shaft before installing the belt. It should press on firmly but should not require enough force to bend the motor bracket or push the shaft into the motor body. If it is too tight, enlarge the bore gradually with a hand reamer or a correctly sized drill turned by hand. Do not force a drill through at high speed, because it can remove material unevenly and leave the pulley eccentric.

A small drop of compatible retaining compound may be appropriate if the shaft fit is slightly loose, but adhesive should not be the first solution to an incorrectly measured bore. Cyanoacrylate can wick into the motor bearing and make future replacement difficult. If the original pulley used a retaining feature, reproduce that feature in the design instead of relying on glue.

Position the pulley so its groove aligns exactly with the driven wheel. Check this with a straightedge or by looking along the belt path. Install the belt without twisting it. The belt should have modest tension: enough to transmit motion, but not so much that the motor stalls, the spindle bearing loads up, or the belt stretches rapidly. A belt that is too tight can create a fault that looks like a bad motor.

Turn the mechanism by hand through several revolutions. Watch for lateral belt movement, pulley wobble, rubbing, and any point at which tension changes. If the belt walks towards a flange, correct the pulley height before applying power. This manual check can prevent a new printed part from damaging an irreplaceable drive belt or loading the motor unnecessarily.

Test the drive in controlled stages

Reconnect the drive while keeping fingers, loose cables, and tools clear of moving parts. Start with the computer’s top cover removed only if safe access is necessary, and never work near an exposed power supply while the system is energised. Listen to the drive during initial spin-up. A smooth, even sound is encouraging; rhythmic surging, squealing, or scraping indicates an alignment or tension problem.

Test the drive with a known-good disk, preferably one that is not the only copy of important software. First check whether the spindle reaches speed consistently. Then try directory reading and a low-risk disk operation. If the X68000 reads one disk but not another, do not immediately blame the pulley: dirty heads, incorrect drive speed, damaged media, and ageing capacitors can produce similar symptoms.

A belt replacement does not correct every floppy fault. The head carriage may need cleaning, the eject mechanism may be stiff, or the spindle motor may have worn bearings. If the drive reads intermittently, inspect the belt after testing for shiny surfaces, frayed edges, or dust accumulation. A belt that slips leaves a polished track on the pulley groove and should be replaced with a better-matched size.

For owners in Perth or regional Australia, sourcing a second compatible drive for comparison may take time and postage. Record the drive model and measured dimensions before ordering another part from Japan or an Australian marketplace. Keeping a diagnostic log avoids repeating expensive imports and makes the repair useful to other X68000 owners.

Compare practical repair options

The best solution depends on whether the original pulley is present, whether the drive must remain visually original, and how quickly the computer needs to return to service. A generic belt can be the least invasive answer when the pulley remains sound. A printed pulley becomes valuable when the original is cracked, swollen, or impossible to source.

Repair approach	Advantages	Limitations	Best use
Replace belt only	Fast, inexpensive, and preserves the original pulley	Fails if the pulley is damaged or contaminated	A clean pulley with a known belt path
Buy a replacement pulley	Usually accurate and ready to install	Availability, postage, and model compatibility can be uncertain	A documented drive with an available part
3D-print a pulley	Reproducible, customisable, and locally manufacturable	Requires accurate measurements and test fitting	Rare mechanisms or damaged original pulleys
Replace the complete drive	Can provide a quick working reference	Reduces originality and may require modification	Severe mechanical or electronic failure
Print a complete belt system	Allows a full redesign around available parts	More complex and less historically faithful	Experimental restoration or unavailable components

A printed pulley is most successful when treated as an engineered replacement rather than a decorative replica. Keep the original part, even if it is damaged, because its profile and dimensions may help future restorers. Save the CAD file with measured dimensions, material notes, printer settings, and the belt specification. A small label inside the computer or in the repair documentation can identify the modification without marking the visible case.

The Australian second-hand market can be unpredictable. eBay Australia may offer belts but list them by generic dimensions, while Gumtree or local retro-computing groups may produce a complete donor drive. Jaycar and similar electronics retailers can supply calipers, cleaning materials, and basic tools, but they are unlikely to stock a purpose-made X68000 pulley. Buying a small quantity of candidate belts together can cost less than repeated international shipping.

Preserve the repair for future owners

Document the original drive number, pulley measurements, belt dimensions, material, and final bore size. Include photographs showing the pulley height and belt route. If the part was printed by a service, record the printer technology and material rather than writing only “3D printed”. FDM, resin, nylon, PETG, and ABS parts can behave very differently after years of heat and tension.

Keep the original pulley and belt fragments in a labelled bag. They may reveal details that are not obvious once the repair is complete, such as a stepped bore, a hidden flange, or a special belt profile. Store the repaired X68000 in a dry environment away from direct sun, and avoid leaving disks inserted during long periods of storage. Heat, dust, and humidity accelerate deterioration of both belts and magnetic media.

A successful repair should leave the drive quiet, centred, and serviceable without placing extra load on the motor. The printed part does not need to be visible or perfectly attractive; it needs to maintain alignment and transmit motion reliably. When measurements and test results are recorded, the same solution can be reproduced for another machine rather than becoming a one-off rescue.

Download the drive photographs, measure the shaft and belt path, and make a simple test pulley before committing to the final print. Share accurate dimensions and observations with the X68000 preservation community so scarce mechanical knowledge remains available to the next Australian owner restoring a machine in Sydney, Melbourne, Perth, or beyond.