The experiments an undergraduate syllabus obliges you to run, why cased kits and floor-standing rigs behave differently in procurement, and how to split the buy across an academic year without stalling a course.
A theory of machines syllabus looks inexpensive on paper. Thirty small mechanisms, most of them hand cranked, hardly any of them needing a power supply. Then the list meets a class of sixty in a three hour slot, and the arithmetic changes shape. The question is rarely which rigs exist. It is how many of each, mounted on what, and bought in which order.
In most Bangladeshi mechanical engineering departments, mechanics and theory of machines share a room, a technician and a budget line. They are not the same purchase, and treating them as one is how departments end up with forty mechanisms and no way to teach vibration.
Basic mechanics is forces, moments, equilibrium, simple harmonic motion and rotational inertia. The apparatus is small, hand operated and often supplied as fitted cases: an integrated set such as the EDIBON LIMEBA, plus stand-alone units like MEMB2 for moments on a two arm lever, MELH for Hooke's law, MSHU for simple harmonic motion, SRI for rotational inertia, MIF for the inertia flywheel and MFCE for centrifugal force. Low unit cost, low power draw, low floor area.
Theory of machines is kinematics and dynamics of mechanisms, and it splits again into three groups that behave very differently once you try to buy them. Linkages and mechanisms (MBD slider crank, MYE Scotch yoke, MBM2 Whitworth quick return, MCA four-bar, MME Geneva stop, MUN Hooke's joint, MEX cam and follower, MDA Ackermann steering) are still small and hand cranked. Power transmission (MGTA gear train assembly, KSGT for the kinematic study of gear trains, DMGT for multistage gear trains, MSDA and MCDA drive assemblies, MTSF worm and wheel) sits in the middle. Balancing, governors and vibration (MES, MED, MBMRC, CGU, MGI, MVL, MVLF, MEVTC, MVCC, MEER) are motorised, need a stiff mounting and are the reason the room has to be planned rather than filled.
Work from the course outline your own university approved, not from a catalogue index. Almost every Bangladeshi undergraduate mechanical programme, and the diploma equivalent, requires the following groups. If a group is missing from your equipment list, a student sits an examination on something they have never seen turn.
Two experiments are worth arguing for even when the budget is tight, because they are the ones industry recruiters notice: dynamic balancing, and whirling of shafts. A graduate who has watched a shaft pass through its first critical speed has a physical memory that no simulation supplies.
The distinction is not really about size. It is about who can move the equipment and what happens when they do.
| Cased and bench kits | Floor-standing and motorised rigs | |
|---|---|---|
| Typical items | Mechanics kits, linkages, gear assemblies | Balancing, whirling of shafts, forced vibration, governors |
| Mounting | Any sound bench, no fixing | Bolted or on a stiff base, away from other benches |
| Services | None, or a single socket | Dedicated socket, and a stabiliser if the supply wanders |
| Storage | Back in the case, in a cupboard | Stays where it is, permanently occupies floor |
| Main loss risk | Components walk off and are never replaced | Bearings and shafts damaged by misuse |
| Buy multiples? | Yes, this is where multiples pay | Rarely, one well-used rig beats two neglected ones |
Cased kits are the better value per experiment and the worse asset to manage. A set of weights with three hangers missing is not a working experiment, and nobody notices until the week it is timetabled. Every case that comes into the laboratory needs a stamped inventory taped inside the lid and a check at the end of each session. That is a technician instruction rather than an equipment specification, but it decides whether the kit is still usable in year three.
Floor rigs have the opposite problem. They survive neglect and then fail expensively. A whirling of shafts unit run without its guard, or with a bent shaft, will damage bearings and put the rig out of service for as long as it takes to import a part. Specify the guard as non-negotiable, and buy spare shafts with the machine.
Departments plan for the class and should plan for the section. Sixty students is usually two sections of thirty, and the room only ever holds one section. That single correction halves most equipment lists.
With thirty students in groups of four you have eight groups in the room. There are two ways to serve them. Either every group does the same experiment, which needs eight copies of that apparatus, or every group does a different experiment and they rotate week by week, which needs eight different rigs and an eight week cycle. Mechanics and theory of machines suit the rotation model almost perfectly, because the experiments are short, independent and do not share a service.
The rotation has one consequence people miss: the cycle length sets the semester. Eight experiments, eight weeks, and no slack for a public holiday, a rig out of service or a makeup session. Plan the rotation at one or two fewer experiments than the number of teaching weeks available, or buy a second copy of the two cheapest rigs so a group can be doubled up when the schedule slips.
Where multiples genuinely pay is the small hand apparatus. Four copies of a Hooke's law unit or a moments lever cost less than one balancing rig and remove the queue at the start of the year, when every section is doing the fundamentals at the same time.
A department that spends its whole allocation in one tender and then waits nine months for a single consignment teaches nothing in the meantime. Where the procurement rules allow it, split the buy into tranches that each leave you with a teachable laboratory.
Order the room in the same sequence. Benches and cupboards first, sockets and a stabiliser before the motorised tranche arrives, floor space cleared and marked before the vibration rigs land. Equipment sitting crated in a corridor because the room is not ready is the most common avoidable delay on university installations, and it starts the warranty clock for no benefit.
Nothing in this laboratory is fragile in the way an analytical instrument is fragile. It fails in small, inexpensive, slow to replace ways.
Humidity is the other quiet failure. Bright steel shafts, ground weights and unpainted linkage pins corrode through a Dhaka monsoon if they live in an open rack. A closed cupboard with a low wattage warming element, or simply a rule that every kit goes back into its case with a wiped film of oil, costs nothing and adds years to the apparatus. Departments that skip this replace weight sets every few years and never work out why.
Finally, write down who owns the laboratory. Not the head of department, who signs, but the technician who checks the cases, the faculty member who sets the rotation and the person who raises the consumables requisition. A mechanics laboratory rarely fails because the equipment was wrong. It fails because nobody was responsible for a missing hanger.