ML4.. Questions Questions. Pulleys this time

[Togalosh]

Evening Gents,

I cannot get any of my callipers onto the drive shaft to measure it up for a new pulley. Does anyone know for sure what it is please? My best estimate is 18.2mm..which seem close to 3/4" - but it's not.

I really don't want to take anything apart & leave it days /a week before I can get it back together again. I was too busy getting everything else set up in my workshop today to even see how the drive shaft (Mandrel?) comes off/out - any clues??

I have a new 3ph motor & a 230V-in, 415V-out inverter drive & am planning to get a multi groove (6 or 7 rib belt) & pulleys then set it up as per;

http://www.ebay.co.uk/itm/Myford-ml4-b1 ... SwFqJWi6N9

As the speed is controlled by the inverter drive I am unsure as to what size pulleys to get ..but again in the above machine they seem to be 100mm -120mm.

I have timing belts & pulleys off big food mixers but these do not allow for slippage or jamming (according to what I have read, which surprises me as mixers all too often get overloaded & need belt slippage or else something else gives) so am going for multi V.

Can anyone spot any problems with this set up ? I've just realised 1..the back gearing. The pulley needs to be disengaged to run the back gear & the original has a grub screw but the pulley I was looking at is a taper lock which also needs a keyway..so perhaps a standard single V Belt will be needed ? These all seem to be aluminium - are these strong enough?

Then positioning the motor. I see that almost all single belt set-ups site the motors above the lathe so the belt pulls the lathe upwards & that counter shafts are above the lathe too - is this so that the lathe isn't pulled backward & potentially twisted out of true? The seller had the motor mounted at the rear.

Thanks in advance (for your patience too)
Togs

 

[DTR]

So you want to drive the spindle direct from the motor? I would have thought that running the motor slow enough for metal turning would result in very low torque, and possibly the motor overheating. I'm not well versed in these inverter drives though, so I'm open to correction.

 

[dickm]

Speaking from similar level of ignorance to DTR, I can't really see that nearly direct drive like those pictures is a good idea. I know inverters are wonderful things (one day, will get the one sorted to run the Mystro ) but for the range of speeds needed for metal turning, would not be happy with that setup for torque and cooling aspects.
In the OP's position, I'd be inclined either to stick with a conventional countershaft plus flat belts to the lathe, or for a nicer job, convert the flat pulleys to poly-Vee and the same for countershaft.
But there speaks a mechanical luddite!

 

[Togalosh]

I spoke in length to the supplier of the drive (who only deal in drives, motors, DOL starters etc) who are very knowledgeable about all their various products (as you'd expect) & applying them to lathes as they sell a lot to turners.. now, I didn't ask how many were metalworkers but one chap brought his lathe on a trailer all the way from Manchester - a wood lathe wouldn't need to be trailered surly?.. They said they've never had a comeback other than a low IP model failed within 2 days as the customer was grinding right next to it. That drive was very cheap but I went for the high IP model with potentiometer control.

My first questions were about torque & Hz. I have always been told that if you run a 50Hz motor (land based) at 60Hz (marine) it will run hot & fail sooner rather than later but apparently not with these drives.. & perhaps it's more with 1ph motors & compressors not 3ph motors. Also the problems occur when the RPM is increased over that the motor is rated at. This is why I also purchased the motor they recommended instead of using 1 of the many 2nd hand ones I have acquired from big mixers/peelers etc.

As for the torque, it is effected at very lower speeds but this is when less aggressive cuts are being done anyway.. erm, is that right ?? The overheating issue is with the drive itself which must have ample room to dissipate the heat it generates. In will soon find out either way.

I saw on my apple scratter that the taper lock has just 1 grub screw so I can't see any issues with back gear working.

What are you views on motor/belt positioning ? To the rear - ok or bad ? motor above - no difference or a must ?

 

[CHJ]

--My first questions were about torque & Hz. I have always been told that if you run a 50Hz motor (land based) at 60Hz (marine) it will run hot & fail sooner rather than later ..

More likely the other way round, using a 60HZ induction motor on 50HZ results in slower speed and an increase in drawn current (less built in reactance to supplied power)

(50HZ motor on 60HZ higher speed less power consumed)

Most invertors have a current overload cut-off setting, so stalled or overloaded cut results in invertor shutting down until switched off, cooled down and re-set.

To maintain best usable torque from your motor try and select pulleys that allow invertor settings between half and double basic frequency. Using pulleys (as a gearbox) is the most efficient way of maintaining the torque at the cutter.

Beware of running a cheap motor for long periods well below it's basic speed, the built in fan cooling may not be good enough.

 

[graduate_owner]

I agree with CGJ on motor speed, if you run your motor at very slow speed then your cooling fan is also slow with the risk of overheating the motor. I would go for a suitable pulley arrangement that enables you to keep a reasonably fast motor speed, plus you get better torque.

K

 

[Togalosh]

Hello CGJ & G.O thanks for the advice. Can you shed some more light on what you'd recommend please as I am having trouble calculating what I need?

I have read (Amateur's Lathe & lathes.co.uK etc) about which speeds I need & it seems that everyone has their own idea of the important speeds are ..so I got 150, 180, 300, 360, 600, 720 & 800.. then 1400rpm for some brass work & polishing.

I understand (to a degree) the relationship between 2 pulleys & their sizes & have found 2 or 3 online calculators but they don't include the drive motor shaft speed which I thought would be starting point - unless I am being really thick.

Lathe.co.uk have a section on inverter drives & it still recommends a countershaft pulley but gives no details - so I guess a 10" pulley (?). Does that mean they recommend still changing pulleys ?? I bought a drive to avoid doing this... & besides I didn't get a countershaft with the lathe.

My local supplier cannot help me with the calc's - just tech info on the parts themselves. What am I not seeing /understanding please?


Motor:
I got my 60Hz info wrong as you say - 60Hz is no bother. The issue with heating I am told is with low speeds/low Hz but not with 3 phase motors without a neutral. My inverter output is 3 phase no neutral & the motor has been matched accordingly but worryingly the online pic of the data plate shows 3PN.. I will enquire tomorrow. F class windings go to something like 300 degC but would the bearing be up to that heating ? Then the motor has over temp protection & if that does operate then I have plenty of cooling fans I can hook up & then extra heat sinking if that's not enough. - although I am aware that that would be dealing with the syptom & not the cause. I am trying to read Electric Motors & Drives but it's not exactly bedtime reading or something to browse while cooking dinner or conversing with SWMBO.

My Lathe:

I took the mandrel out to measure up & found a skeleton in the cupboard !
The Headstock Casting above the drive bearing has broken & been reapired with a well made strap. It looks & feels sturdy but time will tell if it isn't.

Togs

 

[CHJ]

I would stop concerning yourself about the motor temp, just don't run it for long periods at invertors lowest frequency.

Using a countershaft enable you to double or treble the speed rang with smaller pulley size differentials.
Selecting two speeds for the motor to countershaft and then three speed options for the countershaft to spindle should give you a fair selection.

With your variable speed drive there is nothing critical about the exact ratio of the pulleys as long as the pairs match, you will have more than enough variation,
If you don't want to make a countershaft then work out your three or four stepped pulley pair for motor to spindle to cover the middle of your speed range and use the invertor to reach the extremes.

Doing a few maths you may find that a simple 3 or 4 to 1 ratio between the motor and the spindle will give you a usable speed range without going to the extremes of the invertor.

 

[Togalosh]

Thanks CHJ, that's a great help.

I now see that I have misunderstood the online calculator.. typical. There's nothing like showing everyone just how slow I can be.. perhaps my brain needs a few extra Hz.

I am not worried about the motor temperature - just answering concerns raised. I will be monitoring the temperature just out of curiosity. My brother-in-law was an armature winder & he said not to worry once he knew what the specs were.

Then as you say - just go easy at low Hz.