Myford ML7 faster speed

[Mike PooleParticipant @mikepoole82104]

Myford seem to have baulked at using the high speed pulley with the two speed motor, perhaps the 35rpm slow speed was thought to be more useful than a 1740rpm top speed or maybe they thought that was a bit too fast for the bearings. The super7 had a completely redesigned headstock to cope with the 2400rpm top speed or even a bit more on 60Hz machines, they may have had other reasons apart from speed but I suspect speed was the main driver for the redesign. Maybe the ML7 original 650rpm was ultra conservative as the reports of users who have doubled this and more would seem to indicate, and indeed they pushed it to 1280rpm on the trileva themselves. For anyone planning to work with small diameter brass and aluminium they may be happier with a machine with a higher top speed than the ML7. As diameters reduce the speeds required climb way beyond what most general purpose lathes can achieve but the job still gets done, just takes a bit longer.

Mike

[Mark RandParticipant @markrand96270]

Just a few notes:-

Pressurised oil feed is not needed for high speed, it's needed for low speed. The load carrying capacity of a hydrodynamic bearing increases as the speed increases.

A hydrodynamic bearing has zero load carrying capacity for loads that occur at approximately half per rev. Hence the danger of oil whirl in lightly loaded bearings. This tendency is reduced by using lemon shaped bearing bores. In internal combustion engines, half speed loads are intrinsic in the four stroke cycle.

If the bearings aren't running warm and there is a reasonable rate of oil feed, then just jack the speed up…

The counter shaft bearings will fail well before the mandrel bearings do, they are smaller, more heavily loaded.and less reliably lubricated.

 

Edited By Mark Rand on 18/11/2020 20:24:10

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