Bronto’s Blind Spot · Case C
The splendid spindle comparison
One brochure leads with speed, the other with power. Do those 2 numbers choose the machine?
- 3 questions
- “I don’t know” is a valid answer
- Nothing is sent
The case
What is on the table.
A fictional buyer is choosing between two machining centres, Machine X and Machine Y.
Machine X’s brochure leads with a higher maximum spindle speed. Machine Y’s leads with a higher spindle power figure. The buyer wants to pick the stronger spindle from those 2 numbers. The part, the material and the tools have not been written down.
Answer 3 questions about what those numbers can and cannot tell you.
The explanation
The 3 issues, and why they matter.
Read the explanation (it gives the answers away)
1Headline maximums are not the conditions you cut at.
Best answer: No. Maximum speed and peak power are measured at different points; what matters is the torque and power available at the speeds your tools will actually run.
A spindle delivers different torque and power at different speeds. A large tool in a hard material needs torque at low speed; a small tool needs speed. The power and torque curve, read at the speeds your tools will run, says more than either maximum.
2Two ratings on different bases cannot be compared directly.
Best answer: They are not directly comparable. Ask both makers for the same basis (continuous and short-time) and the full power and torque curve.
Motor ratings are stated for a duty: continuous running, or a limited period. A short-time figure can be well above what the spindle sustains for a long cut. Compare like with like, and treat a missing basis as missing, not as a match.
3A comparison needs the job it is for.
Best answer: The work: the parts and materials, the largest tools and cutting conditions, and the tool holder interface each spindle takes.
Write down the parts, the materials, the largest tools and how you intend to cut, then estimate the power and torque the cut needs with the tooling maker’s formulas. The tool holder interface decides which tools you can use at all.
Compare the machines on the rows that change that job, with the source of each figure next to it.
Spindle figures only mean something next to the job they are for. Write down the work first, ask for the full power and torque curve on the same rating basis, and compare the machines on the rows that change the job, with a source for each figure.
Sources
Where the explanation comes from.
- IEC 60034-1:2026, Rotating electrical machines, Part 1: Rating and performanceInternational Electrotechnical Commission
- Milling formulas and definitions (net power, torque)Sandvik Coromant
- Compare toolThe Machine Blue Book
- Evidence standardThe Machine Blue Book
Sources and technical copy last reviewed:
Every scenario here is fictional. No real manufacturer, dealer, auction house or financier is described.
Next step
Use it on a real machine.
The comparison shows only the rows where the machines differ, with the source behind each row and the questions to verify.
More cases: The machine arrived. The project did not. · Net to you. After what?
General educational information, not engineering, safety, legal, tax or financial advice. Confirm the requirements of your own machine, site and agreement with qualified people.