For students, apprentices and lecturers
We are a working CNC machine shop in the West Midlands, and we built these tools because we needed them on our own shop floor. They are free for anyone to use, and that emphatically includes anyone learning the trade. No sign-up, no email wall, no ads.
Lecturers, trainers and technicians — the short version. You may link to any of this, print the charts, photocopy them, put them on your VLE and drop them into your own handouts and course material. Freely, and without asking us. A credit to dalloways.com is appreciated where it fits naturally, but it is not a condition of use.
If it is easier to have that in writing for a resources committee, the full position is on the page for colleges, along with what else we can offer — placements, talks and drawing reviews for student projects.
Why these are different from most online calculators
Every tool shows its working — the formula, and the numbers substituted into it — so a student can check the answer by hand instead of trusting a black box. Several will tell you when a standard stops being valid rather than returning a plausible number anyway: the hardness converter refuses to give a Brinell value above the range ASTM E10 permits, and refuses the steel table for aluminium entirely. Where published sources genuinely disagree — boring bar length-to-diameter limits, for instance — we show both figures rather than averaging them into false precision.
That habit is the useful lesson, more than any individual number. Knowing where a standard stops applying is most of what separates a technician from someone typing into a website.
Printable reference charts
Five A4 sheets — tap drill sizes, ISO 286 tolerance grades, hardness conversion, GD&T symbols and surface finish. Built to be printed, pinned above a machine and photocopied for a class. Open the charts →
Grouped by what your course actually covers
These headings are the recurring topics across published UK college engineering courses — BTEC Level 3, T Levels, HNC/HND and Level 3 apprenticeships. We have deliberately not labelled them with awarding-body unit numbers: those differ between Pearson, City & Guilds, EAL and the Scottish SCQF framework, and a wrong unit number is worse than none. The topic names are what gets taught.
Engineering mathematics and trigonometry
Taught as "Engineering mathematics" (BTEC/HNC) or "Engineering Maths 1 & 2" (SCQF).
Trigonometry
Right-angle and any triangle with a draggable diagram. Almost every setup calculation reduces to this.
Bolt circle coordinates
Polar to Cartesian, which is trigonometry with a job attached.
Taper and angle
Included angle, per-side angle and taper ratio — three ways of saying the same thing.
Engineering drawing and interpretation
Taught as "Engineering drawing", "Graphical engineering communication" or within CAD units.
GD&T decoder
Build a feature control frame and read what it demands — and whether it is even legal. Most charts omit the legality rules.
ISO 2768 general tolerances
What applies when the drawing does not say — the tolerance students forget exists.
ISO 286 limits and fits
What H7/g6 actually means in millimetres.
Materials and material science
Taught as "Material science", "Engineering materials" or "Materials selection".
Materials database
50 real grades with properties, machinability and achievable tolerance.
Material equivalents
EN, BS, DIN Werkstoff, JIS and AISI/UNS cross-referenced, for when the drawing uses a system you do not.
Material selector
Filter and compare grades against what the part actually has to do.
Hardness conversion
Rockwell, Brinell, Vickers — and an honest refusal where the standard says the conversion is not valid.
Measurement and dimensional control
Taught as "Dimensional control", "Measurement" or "Inspection and testing" — named on almost every course page we checked.
Surface finish converter
Ra, Rz and N-grades, with a confidence column marking which conversions are exact and which are approximate.
True position
Positional error with MMC bonus, drawn on the tolerance circle.
Tolerance stack-up
Worst case against RSS, and why the two disagree.
Thread measurement
Three-wire and pitch-diameter measurement over wires.
Turning, milling and grinding
The practical core: "manual machining progressing to CNC" is the standard progression, at every college we looked at.
Feeds and speeds
RPM, feed and chip load from cutting speed — the calculation apprentices do most and get wrong most.
Cutting power
Whether the spindle can actually carry the cut you planned.
Machining time
Where the cycle time actually goes.
Turned surface finish
Predicting Ra from nose radius and feed, before you cut.
CNC programming and toolpath
Taught as "CNC machining", "CNC technologies" or "CAD/CAM".
Scallop height
Stepover against the finish it leaves — the trade-off behind every finishing pass.
Tool deflection and chatter
Why a long slender tool cannot hold a tolerance, whatever the program says.
Bar stock yield
How much of the bar becomes swarf, and what that costs.
Quality management and statistics
Taught as "Quality management" (HNC) or "Quality control" (L3). Consistently the least-loved unit, and the one with the fewest decent free resources.
Cpk and process capability
Cp, Cpk and PPM with the distribution drawn against the spec limits.
Gauge R&R
Whether the measurement system is trustworthy before you trust any measurement it produced.
Threads, fasteners and assembly
Spread across bench fitting, assembly and design units.
Tap drill sizes
Which drill before which tap, and why the answer is not the thread diameter.
Thread engagement
How much thread you actually need — the shear area uses pitch diameter, not nominal.
Bolt torque
Torque to preload, and the friction assumption everyone forgets is an assumption.
Press and shrink fits
Interference, assembly force and the stress it puts in the hub.
If you are an apprentice
Most people studying engineering at a UK college on day release are employed, and a fair few are working towards the Machining Technician (ST1305) standard. We have written up how these tools map onto that programme and its end-point assessment, from the point of view of a shop that does this work rather than a training provider that assesses it. Read that →
Final-year and apprenticeship projects
If you are designing something that has to be physically made, a look over the drawing by a working shop is genuinely useful — the features that would be expensive, the tolerances tighter than they need to be, the internal corner that cannot be milled because no cutter has a zero radius. It is the difference between a project that could be made and one that only looks like it could, and it is hard feedback to get hold of while you are still studying.
We do offer it, free and with no expectation of an order — but we arrange it through your college rather than directly with students. We are a small shop fitting this around live work, so we agree a small number of drawings and a sensible timeframe with a lecturer or tutor in advance. That way the ones we take on actually get done properly, instead of thirty arriving in the same week and nobody hearing back.
So the ask is: get your lecturer or tutor to contact us. We will tell them straight away what we can take on that term — and sometimes the honest answer will be "not this time". Everything they need is on the page for colleges.
A note on why we do this
There is no catch and no lead magnet. We are a subcontract machine shop; if you end up needing parts machined one day, or you end up running the buying at a firm that does, we would like you to think of us. That is the whole business case, and it only works if the tools are genuinely good — which is why they show their working, cite their sources, and admit what they do not know.
Send Your Drawing for a Same-Day Quote
Talk directly to the engineers who will machine your parts — no account managers, no trading-company markups. Complimentary DFM review with every enquiry.