Resiliant or standard metric foot mounted motor?

Hi guys,

Just a quick couple of questions, I am currently looking at converting my Myford S7, which has the original resiliant "imperial" single phase motor, to the popular 3 phase invertor route via Newton Tesla or Transwave for example.

The main issue is deciding on the type of motor. I can get in one package a resiliant "imperial" motor that dimensionally is the same as the old one, or I can choose a slightly different motor this being a "metric" foot mounted (non resiliant?) motor which is slightly cheaper. Chosing the metric motor option will mean some"iron fighting" as the existing pulley will need machining to suit the new metric motor shaft and also some packing (effectively large shims) will need to be made as the centre line of the motor is different to the imperial motor.

So imperial straight swap or metric option?....by the way the metric motor has a fan whereas my current old single phase motor has no fan....is this an issue following the conversion as the motor may not always be running at its "normal" speed so the fan may become less effective?

What are your experiences on this?

Regards to all

Derek

Is there a reason (maybe price?) not to get the complete motor/ inverter package from Newton Tesla?

Comes fully wired as a bolt on package. £469.20

regards Martin

I fitted a foot mounted motor as I felt the resilient mounting would be unnecessary withe the superior smoothness of a three phase motor. I am happy with my decision.

Mike

Edited By AJW on 03/12/2018 13:34:53

Edited By AJW on 03/12/2018 13:35:40

Resilient or solid mount is more a factor with single phase motors which are inherently a bit more vibratory than single phase ones. Resilient may still be a bit smoother but can't see it mattering here.

Unless the price differential is significant straight swap imperial is the best option. In my experience "just" jobs as in "just machine out the pulley bore" and "just fit some shims" come with whole platoons of gremlins in tow with big sharp teeth waiting to bite you on the bum.

Fan speed is pretty much a non issue with modern name brand vector drive inverters. They are very good at supplying just enough power to the motor so heating is much less than the old style, simple frequency variation, drives which tend to have significant internal circulating currents warming things up but doing no real work. Power output at very slow speeds is inevitably low so you probably won't do it much. Old fashioned though the ± 1/3 rd name plate speed range for normal operation is it still remains very much the sweet spot where things just work as you expect them to.

Clive

The 3-phase motor I just fitted to my Unimat is mounted hard down to the baseplate, not a trace of vibration. Resilient mount not necessary IMO.

A couple of years back I converted my S7 to a 3phase conversion courtesy of Transwave. Being lazy I stayed with an imperial motor to save the problem of shaft diameter and I have not regretted it, in fact the only problem was the annoyance with myself for not having done the conversion years ago. A long afternoon's job or a short day and it was complete and that included making mounting plates for the remote and the inverter. When I first switched it on to test it, I initially thought that it wasn't working as the control pot was set at about half way and there was no noise or vibration whatsoever. It was only when I spotted the pulley rotating that I realised that indeed it did work.

Phil

Hi Derek

Converted my S7 last year using the Transwave package with metric motor, non resilient mount. As Phil said, wish I had done it years ago. It's very quiet, which means I can use the Lathe late a night without waking the wife up. I only had to make three changes.

1) New pulley to fit metric shaft. I do not know if you can modify the existing pulley. I did not, as I did not have facilities to bore it out to size. RDG sell one with the correct bore size.

2) I had to modify the Myford mounting plate by slotting the holes by a few mm. I used M8 coach bolts.

3) Turned the motor connection box around by 180deg so the cables exited facing down. Also fitted the cable to the temp sensor if required in future, the lathe is in a awkward position to do this in situ. You may not need to do this it depends on the Lathes location.

Other than that it was plain sailing. It's a good idea to set it up on a bench first to check it all works (make sure the motor is fixed down first). I would suggest before you start you make a support structure to hold the motor mounting assembly when fitting.

If you pm me I can sent some photos .

Hugh

Edited By HughE on 03/12/2018 18:37:48

??

Something needs editing, methinks.

Brian

Just add batteries !!!!!

Ooops! Edit induced error. Should read "nherently a bit more vibratory than three phase ones".

Clive

My Harrison M250 was a factory 240Volt motor with twin link belt and a weighted flywheel and resilient feet, which shows how much they thought a 240V motor needs damping. I fitted a 3 phase motor no resilience as per Harrison 3 phase spec and matched v belts and the difference was not just noticeable but remarkable. The machine is smooth and quiet. I would have no hesitation in hard mounting the motor if you are going 3 phase VFD. That said if it is the easier option I see no harm in fitting a resilient type of motor.

Alan

Edited By Norfolk Boy on 03/12/2018 20:22:43

Edited By Norfolk Boy on 03/12/2018 20:23:12

AJW re absent £ sign, Check you've not got an American keyboard. Happens to me everytime windows 10 updates.

Roy

ps To change it back if it is. Prsss Windows key + Space

Thanks all of you for your responses.

What a great forum this is. Someone somewhere has the answer!

General consus seems to suggest that the conversion is a "no brainer" anyway...

Regards to all

Derek