Myford MLsuper7

Hi all, I have a Myford Super7 with the 3 phase motor converted with speed control usual fittings. When I am drilling the whole this comes to a stop it sounds as if the motor is still turning. I dont feel I am puuting the lathe under overdue pressure plenty of lube , only 3/8" drill with pilot drilled first . any help would be most welcombe .

I have had a similar problem - I had assumed it was an inverter problem but it turned out that the primary (motor) drive belt was slipping.

HTH,

Rod

As Rod says, sounds like the primary belt is slipping. It only relies on the weight of the motor to tension it, so is a good overload protection.

Have had this on my ML7 and on the larger successor, (With VFD ) but this time was the secondary belt tensioning arrangements that needed attention..

Maybe the belt is due for replacement?

Oil on the pulleys, won't help either grip, or belt life.

Howard

As a quick rule of thumb, belt tension is about right when you can with your fingers, rotate belt 1/4 turn, midway between the pulleys.

If it slows down when drilling, on the Super 7 it can also mean the adjustment of the front taper bearing is not correct. It could be that the front bearing is taking the end thrust which it's not intended to do. The thrust should be taken on the back (ball) bearing. The manual describes the adjustment procedure.

When I am drilling the whole this comes to a stop it sounds as if the motor is still turning.

I assume this means "when I am drilling a hole the lathe stops, the motor sounds like it's turning, but it isn't moving"

So the motor stalls.

There's a vfd setting that can limit the current to the motor, though more likely the drill may be very blunt or the motor has gone bad and can't deliver it's rated power.

Read Andrew Moyes explanation. Gets my vote for problem you have.

Hi there, Howard,

With respect, I think you're mistaken about the weight of the motor - have a look at item 50 on the illustrated parts list for the Motorising Assembly on the Myford web-site.

Best regards,

Swarf, Mostly!

I would be looking at the belts 1st & if not that check the clutch is not slipping. Depends on age as to which clutch it has installed.

Of course you could do the job again & watch the motor pulley to make sure it has not stalled.

Steve.

Swarf Mostly,

NO. On my ML7, the primary belt was tensioned purely by the weight of the motor and the support plate pivotting. No tensioner.

My more modern Taiwanese lathe, 2003 vintage, also relies on the motor weight to tension the primary belt.

The horror story would be if the motor pulley was loose on the shaft, and both has suffered damage.

Howard.

Sounds like clutch to me.

Probably, the speed control potentiometer sets the speed of the motor.

If you have a readout, it should indicate Mandrel speed, rather than motor speed..

Changing which pulley combination is in use will only change the speed and torque available at the Mandrel..

Lower speed, belt / pulley set up will give higher torque at the Mandrel

If the problem persists, you need to start looking to see where in the drive train the rotation ceases when the motor is running. That is the point at which you need to investigate..

Just be careful with rotating parts when the belt cover is open!

Howard