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DT 2.7
Unfinished
| Question | Answer |
|---|---|
| Marking metal | High carbon steel scriber harder than metal. If hard to see, use ink such as engineer's blue on the surface. If circles or arcs required, use dividers, or beam compasses for larger radii. |
| Marking timber | Marking knife or pencil. Could be carpenter's pencil with thicker lead to avoid breakages |
| Marking polymer sheet | Marker pen, or if the material is to be cut rather than bent a scriber can be used |
| Normal marking out measurement | Steel rule, but measuring tape for more than a metre |
| Large marking out | Laser devices such as cross line levels - projects perfectly horizontal and vertical line onto objects of any shape |
| Tools for accurate measurements and marking out | Obvs free hand isnt precise Surface plates and gauges with digital or dial readouts. Andle plates. V blocks. Necessary for all of these to establish datum surfaces to be referenced from e.g. face edge on timber to ensure squareness |
| Marking guage | Mark a line at a constant distance from an edge of a piece of timber |
| Combination square | Also can mark out a mitre (45 degrees) and has a spirit level to help with checking horizontal and vertical accuracy |
| How to mark weird angles | Protractor. Either a simple one or a highly accurate vernier protractor. |
| Marking out holes for drilling | Normal practice to use a centre punch mark so drill centres correctly and doesn't 'wander' |
| Centre punch marks also used for | Processes involving heat e.g. forging, since scribed lines can be difficult to see when metal heated |
| Digital test guage | Single axis measuring device for precise measurement. Easy to read digital display and potential for providing direct input to computer systems. |
| Graduated dials attached to machine handles | Allow for precise linear movement typically with accuracy of 0.01mm |
| Why accuracy important | Increasingly important as parts need to fit together more precisely with miniaturisation of many devices Also just generally needed e.g. gears, threads on nuts/bolts the same, holes for KD fittings, correct washer |
| GD&T | Geometric Dimensioning and Tolerancing Standardised system of symobls and figures used on CAD model or engineering (aka technical/working) drawings to show dimensions and tolerance following BS ISO 8015 and BS 8888 |
| Convention for decimal points on engineering drawing | Comma |
| Datum surface use | Doing all dimensions from datum surfaces rather than each other reduces chance of cumulative errors. |
| Why lack of accuracy can be good | Seems unique - good for hand-forged gates where people want that handmade, bespoke look |
| Why bottle needs to be high accuracy | Screw top fit without leakage and correct volume to comply with legislation. Mass also checked for capacity checking |
| How thread checked | Profile projector - tolerance of +-0.015mm in suitable equipped QC lab so needs to be regular samples |
| Go/no gauge pros | Very robust, quick, and low-skill |
| Mould accuracy requirements for the glass bottle | Often made using Electrical Discharge Machining (EDM) to tolerance of +-0.002mm Highly trained engineers check moulds and ensure not too worn over time - need equipment like digital micrometer or vernier |
| digital micrometer or vernier accuracy | 0.001mm. Flexible measuring unlike go/no go |
| Jigs, templates, and fixtures importance | Appropriate in large-scale where accuracy, consistency and time are crucial |
| Use of non-contact measuring devices | Employing lasers and other technologies, such as material thickness sensors, laser micrometers and alignment systems is also becoming more common |
| Jigs | Devices to control motion of tool relative to workpiece. Most common is drilling jig, locked onto workpiece using clamps, and replaceable, hardened brushes guide the drill. No need for marking out and low skill level needed. |
| Fixtures | Robust frames with holding points and clamps to hold workpieces firmly while machining/welding/assorted manufacturing operations. Essential every component held in exactly the same position each time to ensure consistency |
| Templates | Usually consists of a rigid shape or pattern, often of thin manufactured board or sheet metal, used to transfer a design onto a workpiece. Held securely while outline traced with appropriate marking tool. Same shape each time ensured. |
| Accuracy definition | The amount of conformity of a measurement to the ***required *** value (not true value) |
| Tolerance definition | The acceptable upper and lower limits of accuracy of a measurement (if outside, generally rejected as part of QC and QA) |
| Measurement definition | The process of using tools to check existing dimensions |
| Marking out definition | The transfer of designs onto pieces of material or parts |
| Datum definition | A surface or edge used as a reference from which measurements are taken to improve accuracy |
| Templates usage | Outdated in industry but used as stencils e.g. laser cut template for one-off project or batch |
| Diameter of drilled hole is 25 +- 0.5 What % uncertainty is acceptable on this dimension | 4% 4% difference in either direction would be accepted - not using the uncertainty rules if you're already given the +- 0.5 |
Created by:
Pyrogearos2