1 HP on an ML7 isn't insanely powerful, just over-the-top for a machine not designed for that much oomph.

The first problem with it is the 'As long as I am careful' statement. Nothing matters when being careful, it's accidents that do the damage! For example, if lubrication fails a big motor will rip more metal off the bearing than a small one. Whatever the accident it does more damage all round simply because there's more energy in the system, whether running the saddle into the chuck or ripping a ring finger off.

Second problem is the slow temptation to use the extra power. Satan whispers every day. Because all seems OK, the operator will gradually start taking faster deeper cuts than the lathe is happy with. It's unlikely to fail spectacularly. Rather a bearing that would have lasted 15 years only lasts 3 whilst the extra stress quietly wears the bed prematurely, twists the frame, and fatigues the keyways etc.

Generally not smart to up the power of machines without considering the whole system. For example, putting a sports engine with Nox into my bog-standard Corsa wouldn't be a good idea unless I also uprated the clutch, brakes, tyres, suspension and cooling system. Plus a roll-bar if I'm driving it!

There are reasons why Myford didn't put huge motors on their lathes. It's not because their engineers lacked imagination or cojones!

Dave

Edited By SillyOldDuffer on 06/07/2020 19:02:50

Not that far over the top – While the instructions suggest 1/3 to 1/2 HP for the ML7, 1/2 to 3/4 for the Super 7 and Tri-Leva ML7s were recommended 3/4 HP so with a VFD it is probably the top end of normal.

I remember buying a new back plate for a 4 jaw chuck to fit my ML7  ,this would not go on all the way.Faceplate, catch plate and 3 jaw chuck all spun on easily by hand.

I bought a tap ,tapped the new back plate and it fitted alright then.

Edited By Maurice Taylor on 06/07/2020 21:41:12

Fastdave

Tracy tools list a tap the same thread as the Myford spindle nose and taps can also be found to fit the Boxford spindle which is 1 1/2 x 8 IIRC.

Dave

You did make sure that both threads were clean?

The other day, one of my chucks stuck before going on all the way. Using an old, cleaned, toothbrush removed one piece of swarf from the chuck thread.

End of problem!

Now, I always check and clean both threads before fitting the chuck.

If the register on the Backplate is undersize, by a little, you could screw it onto the mandrel, with the register facing outwards. If you run the lathe as slowly as possible,and apply some fine emery to the register, you can remove a little metal. You are only looking for a tenth of a thou or so, maybe just removing a burr.

Cover the bed, to prevent abrasive dust falling on to it.

Stop, clean everything, and check the fit frequently, until you get a fit with which you are satisfied, (Tight rather than slack! ).

HTH

Howard

Edited By Howard Lewis on 07/07/2020 12:29:29

About halfway down this post the two speed motor (3 phase) recommended for the tri-leva is mentioned as being in Myford catalogue 733A with the p/n 60/014A

**LINK**

Further to Daves comments on VFDs and motor overheating at low RPM its worth remembering that modern VFD boxes come in two flavours. Old style V/F (voltage/frequency) control devices and modern Vector drives.

Basic V/F control VFDs merely vary the input voltage and frequency to get the motor running at the right speed. The motor sorts out the actual current drawn itself using the same self generated back emf opposing applied voltage mechanism that occurs when it is simply connected to utility power. For all sorts of reasons this works best when the motor is running at the speed its designed to run at. Once you shift significantly from that speed things start to go wrong and you get lots of excess current running round inside the motor that just makes things hot. The going wrong once too far off the design speed issue also affects torque and power output. Hence the old advice of staying within ± 1/3 rd of the design frequency because things are generally well behaved in this range. High quality, expensive, VFD boxes are generally better engineered and have internal programming to mitigate such problems. Economy range ones won't. Motors vary considerably in how the actually behave too so apparently equivalent pairs of motor and VFD of different breeds may behave rather differently. Performance over a wider speed range is something of a lottery when mixing any random pair of affordable v/f drive VFDs and affordable motors. Especially if the motor is old.

Vector drive VFDs attempt to give the motor exactly the power it needs at any given speed and load. So the pair is much better behaved, less prone to overheat and torque tends to hold up better at lower speeds. We are most likely to encounter self tuning vector drives which measure the motor characteristics on set-up and select an appropriate drive characteristic from a pre-programmed set. The sophisticated (aka expensive) breed having feedback from the motor can do pretty spectacular things but are not for the likes of us. Generally vector drives have eliminated overheating worries in sane use and also overspeed / over power worries. If you set the limits properly of course. Ultimately performance with a self tuning drive is limited by how closely the drive it provides matches what the motor wants. As ever better brand and higher price tends to mean better performance. I'd be suspicious of the over cheap imports. Many modern motors have a highest speed rating on the plate. This generally refers to the highest speed at which rated torque is available at standard voltage. Above that speed torque falls off unless voltage is raised to compensate.

Properly engineered VFDs can put out a voltage higher than the nominal line input. Which helps keep torque up. Although the 220 / 320 or similar rated VFDs will run a motor in star (420 V) configuration the actual output voltage is always lower than the motor should have so performance is inevitably limited, especially at higher speeds. Although they do work to run a motor that cannot be rewired into low voltage delta configuration the input rectifier design is severely compromised and power somewhat limited. Best thought of as the VFD equivalent to a static converter. Works but only use when there is no alternative. There are properly engineered ways of making a voltage doubling VFD work but the market seems to have decreed that the price-performance ratio doesn't work.

Clive

Edited By Clive Foster on 08/07/2020 13:25:51

Edited By Clive Foster on 08/07/2020 13:26:26