For students, apprentices and lecturers
We are a working CNC machine shop, and we built these tools because we needed them. They are free for anyone to use — and that emphatically includes anyone learning the trade. No sign-up, no email wall, no ads.
Why these are different from most online calculators
Every tool shows its working — the formula and the numbers substituted into it — so you can check the answer by hand instead of trusting a black box. Several of them 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, we show both figures rather than averaging them into false precision. That habit is the useful lesson, more than any individual result.
Printable reference charts
Five A4 sheets — tap drill sizes, ISO 286 tolerance grades, hardness conversion, GD&T symbols and surface finish. Designed to be printed, pinned up and photocopied. Open the charts →
Starting out — workshop and first-year
Trigonometry
Right-angle and any triangle, with a draggable diagram — the maths behind almost every setup calculation.
Tap drill sizes
Which drill before which tap, and why the answer is not the thread diameter.
Metal weight
What a part weighs before you make it, across 50 real grades.
Drill point & countersink
The geometry hiding at the bottom of every drilled hole.
Drawings, tolerances and inspection
GD&T decoder
Build a feature control frame and read what it demands — and whether it is even legal.
ISO 286 limits & fits
What H7/g6 actually means in millimetres.
ISO 2768 general tolerances
The tolerances that apply when the drawing does not say.
Tolerance stack-up
Worst case against RSS, and why they disagree.
True position
Positional error with MMC bonus, drawn on the tolerance circle.
Quality and statistics
Cpk / 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 the measurements.
Shop floor — cutting and machining
Feeds & speeds
RPM, feed and chip load from cutting speed.
Cutting power
Whether the spindle can carry the cut you planned.
Tool deflection & chatter
Why a long slender tool cannot hold a tolerance.
Machining time
Where the cycle time actually goes.
Bar stock yield
How much of the bar becomes swarf, and what that costs.
Materials
Materials database
50 grades with properties, machinability and achievable tolerance.
Material equivalents
EN, BS, DIN, 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 has to do.
Final-year and apprenticeship projects
If you are designing something that has to be made, we are happy to look over a drawing and tell you what a real machine shop would flag — the features that would be expensive, the tolerances that are tighter than they need to be, the internal corner that cannot be milled. That review is free and there is no expectation of an order attached to it; it is the same DFM check we run on any enquiry. It is genuinely useful feedback to have before a project is submitted, and it is the sort of thing that is hard to get hold of while you are still studying. Send a drawing →
A note on why we do this
There is no catch and no lead magnet. We are a subcontract machine shop in the West Midlands; if you end up needing parts machined one day, 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.