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Harrison M300 single phase from new

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Lee Reynolds 126/05/2020 17:02:42
6 forum posts
2 photos


Has anyone had any experience with a single phase M300?

I am considering buying one that has had an easy life by the looks of things.

The motor is only 1.1kw, half the usual and the speeds halved as a result.

I am guessing the only difference is a slower motor (960 on the plate) and different belt pulleys, the headstock being standard.

A new motor and VFD should give me back the normal speeds.

Have I missed something ?



old mart26/05/2020 17:25:34
3316 forum posts
203 photos

The outlay on the lathe is much greater than what upgrading the motor in the future would cost, and the lathe is usable in the meantime.

Try looking up Inverter Drive Supermarket, they have masses of stuff including these for example:

WEG CFW300 IP20 2.2Kw @£161.  IDS have a quick start guide which makes setting it up understandable and is worth its weight in gold.

TEC IE2 2.2Kw 4 pole 1440rpm motor @ £154


Edited By old mart on 26/05/2020 17:34:30

old mart26/05/2020 19:05:58
3316 forum posts
203 photos

I did notice that the input current for an inverter of this size is 22A. This means that a dedicated spur of 4mm minimum wire with the associated connections would have to be factored into the cost.

Clive Foster26/05/2020 19:07:14
2817 forum posts
101 photos


+1 for Inverter Drive Supermarket.

Quite a few options when it comes to re-powering with a VFD controlled motor. Talk to folk and get a range of views.

My thruppence ha'penny worth.

As the M300 has a decent range of gearbox selected speeds I'm unconvinced as to the practical value of "proper" VFD control using the variable speed capability. I'd find it confusing to translate the frequency display into spindle speeds for each gear. YMMD. Generally I think a rotary switch or calibrated dial easier to work with than the standard display.

The easiest way to go about things is to mate a motor of standard power and RPM to an Eaton DE1 "displayless" VFD drive. No setting up needed, no external controls, basically just hide it round the back, connect power and use the old switchgear to operate the box. Motor runs at standard speed, takes about 3 seconds to run up or slow down. About as simple as can be. Cost about same as the WEG suggested by old mart.

Consider going one step further and exploit the Eaton drives ability to run at two switched speeds to give an electronic "backgear" range. Usually quieter than the standard gear selected method and can give a smoother finish as there are less vibrating gears involved. Not as powerful as proper back gear tho'. I'd futz around with a 6 pole motor running at faster than nameplate for the higher speeds so as to get more oomph in electronic back gear. A nice benefit with electronic backgear is that it gives you some really low speeds when used in conjunction with normal backgear.

When hooking things up make provision to connect a bedstop with microswitch into the control circuit. Just the job for cutting to shoulders. Although the machine will over-run a little as the motor slows down this is generally very predictable. Best to have a run out groove to accommodate over-run when threading. Takes the terror out of blind holes!

The IDS guides make setting up a normal inverter almost as easy as the DE1 so can easily use one of those in the same manner.


Edited By Clive Foster on 26/05/2020 19:08:20

old mart26/05/2020 20:25:01
3316 forum posts
203 photos

Just in case you have not heard of Lathes UK, here's the page for the M300, it mentions the single phase powered versions and the 1.6Kw of the standard version. The nearest equivalent VFD's and motors would be in the 1.5 Kw power (2 hp) which would be lower cost than my 2.2 Kw price estimate. The power for this size would be 16A which would simplify the connections, needing only a permanent switched wall connection from a radial. If you were looking at the IDS inverters in that range, be aware that not all of their products have the Quick Start Guide included, and avoid the one's that don't.


Edited By old mart on 26/05/2020 20:29:11

Edited By old mart on 26/05/2020 20:29:57

Edited By old mart on 26/05/2020 20:30:25

Edited By old mart on 26/05/2020 20:31:05

Edited By old mart on 26/05/2020 20:31:42

Lee Reynolds 126/05/2020 21:42:25
6 forum posts
2 photos

Thanks Gentlemen, very quick replys.

I did originally think it was a one off until I read the post by Tony on lathes UK fully, then realised it was, maybe, a desire by Harisson to make a lathe that could be plugged straight in to a normal (in the old days) 15A spur.

My question should have been phrased more towards the headstock than the power supplying it. I have done three VFD conversions so am happy with that it is more "are all M300 headstocks created equal".

Was it reasonable to assume that it would make no sense for them to build a more fragile gearbox for a limited run 1ph machine. Can I safely double the power I put in. I guess the designers are no longer with us so we can only make an educated guess. The slower motor and a slightly smaller drive pulley would halve the input speed, and therefore spindle speed, without having to change anything in the headstock.

Clive, I will look into your drive suggestion with the "backgear", that maybe is all I need. I bought the M300 manual and noticed the 110v switching system that I could well do without. Give me a VFD control circuit with 24v @ 50ma any day.

Thanks again all,


old mart27/05/2020 15:08:19
3316 forum posts
203 photos

My interpretation is that Harrison chose a single phase motor running at a lower speed to directly replace the standard three phase one. Even the pulley size was unchanged. They may have chosen a slower single phase motor to retain most of the torque, but at lower spindle speeds to sell their products to people with only a domestic single phase power supply. 1.5 kW (2hp) single phase motors of 4 pole running at 1360rpm run at 9.3A full load with a start current of 32A. As mentioned by Clive, the lathe has a full range of mechanical speeds and it might be better to run the lathe on single phase having a suitable dedicated spur.

Vic27/05/2020 15:14:22
2895 forum posts
8 photos

I must be missing something but why not just run the lathe as it was made? I’ve used an M300 at my old job and are a lovely machine.

old mart27/05/2020 15:28:44
3316 forum posts
203 photos

It will indeed run ok as it is, but the spindle speeds are halved from its original design.

KWIL27/05/2020 15:44:50
3413 forum posts
66 photos

Regarding Clive's comment regarding converting frequency into rev in each gear.

Not a problem, used a 10 turn wire 10K potentiometer for the frequency control, fitted with a 0-100 counter dial. Control is almost linear so its just a simple % mental calculation.

My M300 is an original 3 phase machine, VFD fitted, Harrison controls look the same but are rewired to properly use the VFD facilities. Subject of a MEW article some time ago. (MEW154)

Clive Foster27/05/2020 16:57:43
2817 forum posts
101 photos


I think its very much a personal thing.

I've always been a little unsure as to the desirability of infinitely variable speed settings. Since getting my Smart & Brown 1024 VSL which is, by it very nature infinitely variable having just Reeves drive to the spindle and back gear, I'm convinced. Pushing a button and watching the setting counter needle has no fundamental benefits over shifting the levers on my P&B model B gearbox. Its just a different way of going about things.

Mental maths I can do just fine but its another thing to bother with. Divide by 2 switch for a quieter backgear substitute and extra low speeds makes sense, maybe make it three position for some intermediate speeds but beyond that is not for me.

Different if you are having to switch belts of course.

My old square column bench mill had two belt speeds and a displayless VFD hidden in the head to controll the motor. A 12 number skirt on the control pot and a three column table stuck to the machine correlating skirt number with speed in each belt position worked a treat for me.

My P&W got a similar stuck on table to give the appropriate spindle speeds using British 50 Hz two speed motor as the original cast plates are for the single speed American 60 hz motor version. Wartime built, motor fitted in the UK.

But of course a major benefit of a forum like this is to see other folks views on what works for them and how they do things rather than just being blindly stuck on your way. Sometimes its the electronic equivalent of having your favourite corns jumpninked on with size 15 hobnailed boots. Sometimes its "D'oh, why didn't I think of that.". Most times its mash half a dozen ideas up together, strain out the "what I think are good" bits and use them for something completely different!


Edited By Clive Foster on 27/05/2020 17:05:29

KWIL27/05/2020 17:49:26
3413 forum posts
66 photos


I tend to agree with you.

In a way too much is made of actual speed, having a tacho to display it etc. Speeds are only a guide to settings, how it cuts is what it really all about.

old mart27/05/2020 18:47:59
3316 forum posts
203 photos

When I converted the Tom Senior light vertical to R8 from MT2, I changed the single phase 1/2hp motor for a 1hp three phase one. The mill has only four speeds by belt, so I have programmed the VFD running it for 25-75 Hz which gives a total speed range of 7.5. We always make the effort to change the belt positions to take advantage of the best torque available, as I felt that 1hp was in the sweet spot for the machine.

Increasing the M300 to its higher design speed will make smaller diameter work easier, but still having a low backgear speed of 40rpm.

Philip D29/05/2020 09:41:27
30 forum posts

600 Group are still going and if you supply the serial number they will be able to confirm if there was any difference in the headstock type. Great lathes, just be aware any parts are 'Pricey' but hopefully you wont need any.

Len Morris 212/07/2020 19:10:37
54 forum posts
29 photos

Hi Everybody,

Acquired a 3 phase Harrison M300. Needed it to run on 1 phase.

Options? Change motor to 1 phase. Buy a VFD. Make rotary converter.

First 2 options very expensive. Chose the rotary converter option.

Converter made from junk parts. Slave motor was an old Gryphon 1 hp 3 phase wired for Delta. Start capacitors were 2x20uf. Timer switches capacitance to single 1x20uf for run. Output on each phase 235/238/242 volts.

Jumpers on lathe motor set to 220 volt 3 phase operation. Transformer on lathe circuit board changed from 415/110 to 240/110 maintain control circuit..

Job done. Lathe runs a treat on a single 13 amp plug. All speeds available (max measured at 2300 rpm) and all the standard controls are unchanged.

Cost? £25 for new transformer.

Hope this might help anybody with the old problem of buying 3 phase industrial machines.


Bob Worsley15/07/2020 16:43:22
103 forum posts

Really not a good idea to run a three phase motor with a static converter in delta. Endless comments all over the web but principally because of circulating currents in the motor, excess heat.

Joseph Noci 115/07/2020 17:05:26
987 forum posts
1247 photos
Posted by Bob Worsley on 15/07/2020 16:43:22:

Really not a good idea to run a three phase motor with a static converter in delta. Endless comments all over the web but principally because of circulating currents in the motor, excess heat.


Valid, if the machine is running for hours rather that the very intermittent hobby use..

  Mmm, all currents have to circulate in the windings to do any work, I would have thought...

The issue is maybe more one of imbalance of 3 phase currents due to the capacitors attached, and resulting phase imbalances - if this does bother you, for what is anyway intermittent use, you could balance them by selecting your capacitor values..

Rotary converters do work well, are very reliable, no electronics that let smoke out - no variable speeds, etc. Perhaps a little less green in power usage, but maybe greener when considering the total mnfr chain?.

Edited By Joseph Noci 1 on 15/07/2020 17:11:36

Len Morris 216/07/2020 13:41:53
54 forum posts
29 photos

Hi Joseph and Bob, you are both very correct. Static converters obviously work very well if properly matched but many people report initial problems. If I could have afforded one it's a route I might have probably followed.

My rotary converter did not appear overnight. The circuit is relatively simple, but he trick (as you point out) is to match the capacitors to balance the voltage and current in each output phase. In the early days of its development the slave motor would get very warm within 5 minutes. After a bit of work with a volt meter and clamp meter progressively changing the capacitor values, I managed a very pleasant balance. The slave motor will now run all day at 20 degrees C. When running the lathe it's never gone beyond 25 degrees and this is a measured value with a Fluke thermocouple meter. No smoke or RIP moments!.

The capacitance values I mentioned worked for me but might not be right other setups with different motors. They are a good starting point but measurement and some experimentation should be expected. Interesting and very satisfying when it all comes together and works, particularly, as they say in Lancashire, it cost "nout".

Something I didn't expect was the ability to "slug" the motor. Good practice is to allow a motor to stop before reversing it. There is no choice on my single phase Myford where you have to wait for the centrifugal switch to click. In industry there's no time to wait and we would go full forward to full reverse instantly. With curled toes and finger crossed tried it on my set up expecting smoke, blown fuses etc. It worked perfectly! I will still follow good practice but it's nice to know the setup will slug the motor if needed.

Charl Tintinger18/02/2021 18:49:06
5 forum posts

The Ecogoo 9000/9100 series VFD take 1P 220V and make 3P 380V. I use them for a number of machines in my workshop.

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