ML 7 spindle speed

[AJWParticipant @ajw]

[AJWParticipant @ajw]

I am in the process of installing a Bosch Rexroth inverter and 3 phase Brooks Crompton motor to my ML 7.
I have kept the original pulley size so when the inverter is running at 50Hz the spindle speeds will be as designed. The motor is designed with inverter use in mind and is capable of running at twice it’s rated rpm without problems.
I have never had bearing troubles on the Myford, keeping lubrication on the ‘generous’ side but what might the safe maximum spindle rpm be?
The spindle uses the early shell type (lead, indium?) bearings.

Alan

[not done it yetParticipant @notdoneityet]

I would be quite sure that the designers of the machine took into account the speed attainable, commensurate with extended bearing life. Any speeds excessive to the design are likely to reduce the life of the bearings, but a safety factor will/should have been used in the design.

That means any increase will initially eat into the ‘safety net’ included in the design. Likely 20-50%, but after that bearings may either a) wear significantly faster or b) risk failing.

So, I would guess you might get away with 20%. Increase, but then with no safety margin – and that would depend on how loaded the bearings might be, in use, and their initial condition.

There may be other parts of the machine which could fail if excessive speeds are used. Like doubling the rotational speed of a chuck might put it beyond its design safety factor (although most chucks will be rated above 2000rpm, I expect).

Motors are often capable of much higher speeds, but they are likely well balanced and have high speed ball bearings fitted, which are easly replaced, as service items.

[HopperParticipant @hopper]

I wouldn't stretch it much over 1,000 rpm with white-metal bearings and drip lube. I had my Drummond geared for 1100 rpm with white-metal bearings for quite some time and it did OK.

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