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Myford MLsuper7

stops inder load

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ALAN HEATH29/05/2021 12:48:56
9 forum posts

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 .

Roderick Jenkins29/05/2021 13:02:46
avatar
2129 forum posts
586 photos

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

Howard Lewis29/05/2021 13:22:58
5540 forum posts
13 photos

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

KWIL29/05/2021 14:28:40
3444 forum posts
66 photos

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.

Andrew Moyes 129/05/2021 14:45:32
142 forum posts
23 photos

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.

Dave Halford29/05/2021 14:47:55
1818 forum posts
19 photos

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.

J Hancock29/05/2021 16:38:28
776 forum posts

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

Swarf, Mostly!29/05/2021 17:02:59
615 forum posts
65 photos
Posted by Howard Lewis on 29/05/2021 13:22:58:

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.

SNIP!

Howard

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!

Steviegtr29/05/2021 19:49:26
avatar
2269 forum posts
313 photos

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.

Howard Lewis30/05/2021 10:44:41
5540 forum posts
13 photos

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.

ALAN HEATH30/05/2021 12:00:20
9 forum posts
Posted by ALAN HEATH on 29/05/2021 12:48:56:

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

Hi All , Firstly thank you for all your hep. I have checked all that was suggested. I am a novice all be it an old one. I have been drilling brass at 250/300 RPM according to the read out and still had the same problem. I changed the belt to a lower speed pully and tried again seems a little better. When you change the belt to different pulleys does the RPM readout give a correct reading using the speed control switch.

John Haine30/05/2021 12:12:14
4272 forum posts
251 photos

Sounds like clutch to me.

Howard Lewis30/05/2021 15:38:54
5540 forum posts
13 photos

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

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