Myford ML7 faster speed

I am going to agree with Andrew Moyes, when I had my own business I purchased a Myford trileva for a particular job, it was fitted with a two speed motor and we were running it at 1500 revs for 40 hours per week, we had this particular job for eight years until the customer went bust and we moved the machine on through the trade. When I purchased the machine I done the usual adjustments including having a look at the spindle bearings, they were adjusted and new belts fitted and the machine put to work. During its time with us it was oiled daily but no maintenance work was done at all, we just flogged the life out of it. After the eight years it had no discernible play in the spindle or the slides, if I hadn’t needed the space I would have kept it. It was used for first and second operations on acetal blocks which ended up in syringe drivers.

Daren't comment on top speeds I use in case I get a visit from the 1000rpm Police.

However, this what Myford sold.

My lathe has a double row ball raced front and a single ball raced rear bearing.

Top speed is 1500rpm, not 3000 rpm - only wood lathes need to go that fast.

If you don't have flood coolant then red hot chips = fire hazard and I can get those with carbide at 50rpm on a 10" wheel rim.

You can use the new alu inserts on steel at model engineer feeds and speeds, even the give away price ones work OK.

So as Steve says in post 4 "why would you?"

No direct relevance, but permit me to reminisce ...

When I worked in the vibration test lab, we had a ‘slip table’ for applying lateral vibration.

A four foot square Magnesium alloy plate which ‘floated’ on a film of oil on a granite block.

On the axis was a substantial hydrostatic bearing.

Woe betide anyone who set the thing in motion before the oil had insinuated itself everywhere !!

Someone did ... and we were unable to get a new bearing from the manufacturer in time for an important job.

So I arranged to have one made by a local workshop.

Can’t remember the detailed dimension or the material spec. but the shaft was perhaps 3” diameter.

The plain bearing was machined from a block of hard Aluminium alloy and the central section relieved by 0.0004” to avoid bell-mouthing [and to provide a little reservoir for oil]. ... The oil feed was at 3,000psi and it just wept away slowly at the edges of the table.

That’s a nicely configured Hydrostatic bearing.

MichaelG.

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

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