Myford Super 7 and 3-phase Motor

I had a posting elsewhere re powered cross-slide issue which gradually changed to a motor problem with a Super 7. I had a single phase motor which had possibly been used on the lathe but when fitted and powered up ran very very slowly when a load was put on it. The general concensus was to change to 3-phase and use a VFD.

Now I happen to have 3-phase supply but obviously will have more flexibility with the VFD. I fitted the 3-phase motor to test it and wired it directly (via Red 3-phase plug-in connector) to the isolator on my distribution board. Initially the motor ran sluggishly but once I had the tension correct on the belt it appeared to run okay. I then tested the clutch, gearbox and powered cross-slide etc. to check all was okay with these functions. They were perfectly okay. I now began to notice the lathe was running slower and slower and the motor was getting significantly hotter. Is this an issue because of not using a proper 3-phase starter switch, i.e just having direct cable. The motor is currently star wound but can be changed to delta.

I had hoped to use this resiliently mounted motor with the VFD, but if motor is no good then will need a new motor to go with the VFD components. I notice that the kits sold by Transwave use standard foot mount motors, not resilient mount. Is this a problem and is more noise and/or vibration apparent.

Thanks,

Colin

My understanding is that single phase motors are, by their design, more inclined to vibration than 3 phase motors. This is why Myford specified a resilient mount for 1ph.

My S7 now has a VFD 3 phase set up with a rigidly mounted motor and it is fine, definitely smoother than before.

HTH,

Rod

Sounds as if it's possibly knackered. If it struggles even to move the slides without any metal being cut, it's clearly not up to the job. What power rating is it - and what do you know of its provenance?

If this is running "normal" domestic 3-phase (ie 415V phase-to-phase, 230V phase to neutral), it should be in star as you have it. Connecting it in delta would not be recommended unless you are running a VFD on single phase.

If it's a half decent motor you shouldn't need resilient mounts for 3-phase but they shouldn't affect its operation either way.

Edited By Muzzer on 09/10/2016 12:10:05

Newton Tesla supply resilient mounted motors as a direct replacement for the original Myford supplied motor in their single - 3 phase conversions.

Well pleased with mine which has been in use for about 8 years.

Dave
The Emerald Isle

Interesting. I bought one of the Newton Tesla Myford kits to fit to my Milling Machine in 2007 and that came with a rigid foot mounting motor. When I fitted a VFD to the lathe I went for the cheaper Transwave option and, as I said, that is a rigid motor as well.

Cheers,

Rod

What would be the recommend HP of a suitable 3-phase motor, 1/2 or 3/4 or whatever the equivalent in Watts is.

Is there any advantage in the Newton Tesla offerings compared to the Transwave offerings.

Colin

My 3-phase motor is solid mount and at speed I just hear the whirr of the headstock bearings.

Neil

3/4 hp for a S7 should be adequate.

I've got 3 VFDs from NT and their service and help has been excellent. I can't speak for Transwave, but I would imagine their service would be just as good. In the end it's your money.

Dave
The Emerald Isle

I bought one of the Newton Tesla fully wired up, enclosed and programmed sets. Works fine. Transwave offer a kit of parts to wire up yourself, hence the cost saving.

3/4 hp is fine and I can now wind the maximum speed up to 3000rpm, However, I don't use this speed and just leave the belt on the highest speed mandrel pulley and never use the high speed pulley on the motor - 1600 rpm is fast enough for me. I do occasionally run out of torque so sometimes have to move the belt at low speed. A bigger motor will give you more torque and therefore more flexibility.

Rod

Before doing any thing more get your 3 phase motor sorted out. Having proper starter won't make any difference to your motor running and resilient mounting will make your motor run slightly quieter. First, have you got access to an insulation tester and multimeter ? if not, seek an electrician who has, then carry out insulation test on all three winding to earth, which is the motor frame, then between each winding. To do this your need to disconnect the Star point, it will have three connections on one terminal post. Whilst the Star point is available, check the resistance of each of the three windings, using a multi meter, set on the lowest ohms range,all should be almost the same resistance. Don't use the Insulation tester on the insulation resistance range, as that should be 500 Volts DC and will confuse the issue. If all those test are OK you don't need a motor, Check your wiring. It doesn't really matter from whom you buy your inverter they are much the same, programming is easier on some that is about all. There is a man, on, dare I say here, Home Workshop who often has ones for sale and also look on the net. I've fitted a few of this make "Huanyang " for my Model Engineering friends, bought via ebay and they are all OK, one was £90. 40. Should you decide to buy one.I have made a simplifier program which you could have a copy of. I hope that is of some help.John

Colin what parts do you have and were from. I had a similar problem with my tec motor and drive from a supermarket firm this did something very similar and had to go back to single phase. Are you sure you are not over cooking bearings . Are the earths good . Check for anything live or arcing.

I would go much more than the HP you are trying to use . Just my experiance of getting one of these delightful machines going my problems were on a Drummond .

M

Edited By Martin Newbold on 09/10/2016 18:21:28

Martin,

The two motors I have came with the lathe, but the person I brought it off had not used, he had bought it from a watchmaker colleague intending to swap it out for his non-gearbox Super 7 but had not got round to it. The lathe and motors have possibly not been run or at least five years if not longer.

The first motor is a Brook Crompton Parkinson motor no VMB5341D136BG, 370W, 1425RPM, Star 380/440 (1.2A), Delta 220/250 (2.1A) 3 Phase

The second motor I have is a Brook Motors CUB, .33Hp, 1420RPM, 230V

This second motor was bench tried a few times, the majority of which it turned over only at a few rpm, although once it did run at full speed, I decided not to use this as it was such low power and try the 3-phase motor only

I initially had run the motor on the bench, but only for a couple of minutes to check that it ran okay, was quiet (no whine from the bearings and not tight) and reversed when two of the phases were swapped over. I then fitted it to the lathe. I initially I found that I had the drive belt to tight as the motor struggled. After a few seconds of this switched off and then re-tensioned the drive belt a lot looser. The lathe now ran okay and I check the functionality of the clutch, gearbox, forward and reverse drive to the leadscrew, half nut function and power cross-feed function. All this worked satisfactorily. I then noticed that the lathe motor was getting significantly slower. I found that the motor casing was extremely hot. There was no arcing that I could see or hear.

I do have insulation tester and multimeter but time is a problem at present due to work.

This may have to wait a few weeks.

Colin

Run the motor without belt for half and hour and it should not be more than warm - comfortable to touch. but don't walk away when doing this, stop every few minutes to check that the bearings are not hot and it isn't stiffening up. Check the countershaft and spindle each spin freely without belts on.

Then if all ok above connect up and run again checking the temperature of all bearings every so often and if it seems to slow down whip the belts off and manually check which item no longer spins freely.

Half a horsepower is easily enough to run a Myford off load all day long. So I think something is getting hot and tightening up.

One advantage of the resilient mounts is that they reduce the thump when you turn on, and the motor tries to get up to speed instantly. This is not needed with a VFD which has 'soft start'. Even, with some, soft start which you can adjust to be more or less gentle.

Cheers, Tim

I agree with Bazyle, it sounds as if something on the lathe is tightening up, possibly countershaft or headstock. Try the motor again, if it begins to labour, release the clutch, if the motor comes up to speed, release the belt tension lever. This could be the headstock front bearing, check it's got oil in it.

Just run the motor for around 15 minutes. It is now getting to the point of being too hot to touch. Is has not started to slow as yet. Have switched off and checked headstock and countershaft and these are both running freely. Have found a pair of flip-top oil receptacles on the motor and have topped these up. Loathe to run it much more due to the amount of heat it is generating. I have an electrician colleague hopefully paying a visit tomorrow and he will run some insulation checks etc. on the motor for me. It feels to me as though the section of the motor casing nearest to the lathe is getting hotter before the opposite side.

Colin

It's just possible that one of the windings on the motor is connected in the wrong sense. I didn't use to think this mattered, but because of the mutual coupling between the windings it does. There is a thread somewhere here about this with a method of checking.

It sounds it me as if your motor might be past it. An insulation test will only tell you if the winding has broken down to the frame. It will not detect shorted turns within a winding, which would cause overheating like you describe. There used to be a thing called a growler to test for this, but I'm not sure if they are still used. It is hard to detect shorted turns since they don't make a lot of difference to anything you can easily measure. Anyway, the best test is usually to run the motor with no load for a while and see if it gets hot.

John