Mini lathe 3 phase AC conversion

I don't think the motor was the problem, having broken the motor your original plan would have broken the next weakest link in the drive. I would replace the drive with something appropriate, a brushless setup or a VFD in an appropriate size for the machine if you want a mild upgrade. A rethink on your feed and speed rates should get the job done within the capabilities of the machine. Many jobs have been done on home workshop lathes that are too big for the machine but a bit of mechanical sympathy will usually get the job done without breaking anything.

Mike

If it were me, I would not get the higher RPM motor, but would prefer to get the lower 1400 or so rpm motor. With the VFD the 1400 rpm motor can be over driven to 2800 rpm or so. But as the RPM increase so does the power needed to spin at that rpm range. But the 1400 rpm motor has a bunch of torque. But at partial RPM it is not so good. The only issue is at slow RPM's. Some motors do not like running below 15 hz for any length of time, as they can over heat. Although you can get to like 4 to 5 hz, based on a 3k motor, that;'s like 300 rpm. For me I use the 200-300 rpm for tapping etc and it really does need torque to tap successfully. But the 1400 rpm motor would be in the 10 z range.

As others have mentioned, the total power can be limited on the vfd to the motor, same as peak current draw. A 2 kw motor can emulate that of a 1kw motor.

A friend of mine was always asking how i was getting better surface finishes yet I was not running anywhere near the rpm he was. It was sharp tools. A sharp tool at 600 rpm will give a better finish than 1600 rpm with not so sharp tool.

Neil

Posted by Mark Muller 1 on 30/05/2018 20:23:51:
So... not sure if all my replies were read, but you know what, I'm going to shop for 500W motor. I'll use the 3hp for a table saw or something... don't lecture me, I know about table saws!!
I'm upgrading to tapered roller bearings anyway (and "slippable" belts), but to keep the peace, I'll go for a lower wattage motor. I still think it would've been fine (yes, I'm a newbie, but I'm also not daft!), but life's too short and I'll just get the darned little motor. Thanks again everyone. M

Hi Mark,

Now that everyone understands what you have got, along with an idea of your ability, do consider the various options proposed.

If you are considering Neils route, then do consider a higher wattage motor around 1hp+ route, with appropriate VFD, rather than the 500W motor route, especially as it is not clear if the 500W is 'input' or 'output'. This is relevant because thereafter, you have to consider the torque issues - VFD programing. If you have more power to work with, this can be de-rated via the combination of programming as well as mechanical. If you start with 500W, you may get issues with 'not enough torque' at various points in the speed range. This will be a process of experimentation. I don't know if your original 3hp/2.2Kw idea will or will not be appropriate/suitable for de-rating, or if Neils/Steves routes are the directions. This is up to you to consider, based on your abilities, now that we know what we are dealing with.

For the bearings, in your case, do consider angular contact (AC) bearings in place of taper roller bearings (TRB), as the mechanical torque on the TRB will result in transfer of a slightly higher load onto the motor, i.e. the motor will need to work slightly harder to turn/drive the spindle. Reason: Based on the pre-load on bearings, in AC bearings (7206B-2RS) the balls have a two point contact on the insides of the inner and outer race, where as for TRB - 30206 (for example), the rollers insider the TRB have full contact with the insides of the inner and outer race. The difference in accuracy between the two types of bearings is so marginal when used in a mini-lathe that it is not necessary to consider a TRB, and the use of AC bearings can deliver marginally higher speeds, which is great for getting better finish with the right tools, on non-ferrus material.

Ketan at ARC.

Fitting the same type of motor again may not be a good idea because your machine doesn't have any reduction gears in the headstock - it stands a good chance of going the same way as the first one when the going gets tough.

You could do what I did and get yourself one of the new technology BLDC sewing machine motors, which I've seen range in power from around 400w / 750w and are available in various places on the internet at very reasonable prices. Bear in mind they come complete with a suitable controller too.

The advantage of them is they have superb low speed torque - which is what your lathe will need and they have a large speed range making them suitable for small diameter work.

Take a look in my album for some pics of the setup.

Martin.

Hi

Many and varied replies to this thread read through with great interest as an owner of several re powered and modified machines.

Running any motor fitted with a cooling fan at way below it's rated speed will run hotter fit an auxiliary fan if this is a problem.

Blowlamp has an excellent suggestion for a re power for the average home workshop machines.

Eric

I'm just gonna be unhelpful and butt in here with a semi relevant question, anyone have a wild shot at the upper bound for safe maximum motor power on the lathe? Was wondering of a ballpark of 1000w/1.5 hp to have some -e n h a n c e d- metal removing speed which is a bit above other users of 1 hp. 3 hp seems a bit wild, though I have the benefit of hi lo gears.

Hi Sorry for the intrusion this is my slant on Rainbows question

"I'm just gonna be unhelpful and butt in here with a semi relevant question, anyone have a wild shot at the upper bound for safe maximum motor power on the lathe?"

It Depends on the size of the lathe. Pure Guess on my part that you have a far eastern lathe with a Hi-Low ratio gears that are adequate for the motor the manufacturer fitted.

Be prepared for breakages of the gears with a bigger motor fitted.

X2 mill Drill has the same head stock here is a link to the conversion I did six years ago and has run without any problems just a few more alterations.

.**LINK**

Eric

It's the low speed you have to consider. True, the output speed is proportional to the frequency produced in the vdf, so when going for a low speed it is possible that the motor will not be able to cool itself when the speed setting is low. This however is balanced by the overkill motor, which will have a higher mass. You will need to calculate from the lowest normal speed needed. My S7 has an inverter drive, but I still occasionally change the belt position to the smallest spindle pulley so that the motor runs faster in order to get the cooling. I'm not happy on running it below 20 hz for long periods. Perhaps others would like to comment on this. The overkill of the motor power I think is a red herring, it will cost more to run but won't make any difference to the lathe unless somthing jams up! The limiting factor here will be belt slip, which could be left a bit on the loose side to allow intentional slip in emergency