# variable speed lathe conversion?



## wildewood (24 Sep 2016)

Hiya

I'm hoping to get a Union bowl lathe this week (finally fingers crossed) It's a single speed - I believe I have read that people have converted there's into a variable speed lathe, does anyone know how/what I would need to do this please?
Many thanx shaun (hammer)


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## marcros (24 Sep 2016)

I suspect that the conversion is a 3phase motor version fitted with an inverter to allow it to run on 240v


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## flh801978 (24 Sep 2016)

If it's a union graduate bowl lathe then it should be 4 speed as standard
If it's 3 phase then just put a VFD on it after changing it to 240v (delta)
If it's single phase then you need a new 3 phase motor and a vfd
It's the best modification to make to a graduate
I have 3 at the moment all modded as above
If you need any more help let me know
Ian


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## graduate_owner (24 Sep 2016)

Agree. The way to variable speed is a 3 phase motor which can be connected in delta mode ( not all can so check before buying) and a 3 phase inverter. Save yourself grief and get a British made one. I have posted about this several times before, as have others. Take notice of issues such as possible motor overheating at very slow speed, enclosure of inverter being suitable for the workshop environment etc. Also note that you will not be able to use the existing switchgear and microswitches. The inverter must be connected directly to the motor. Buy one with suitable HP to run whatever other machines you think you might acquire.
My inverter powers my lathes, milling machine and surface grinder giving me variable speed on all of them.

I love my graduate bowl lathe - solid and well built. I bought an Axminster chuck with left and right thread so fits both sides of headstock. I was so pleased when I got my graduate that I called myself G.O. when I joined the forum. (I only joined to find information on the graduate, but have been a regular visitor since).

Finally, make sure you get all the bits you need such a faceplates, rests etc - they are very expensive to buy. There is a graduate handbook online. Also visit lathes.co for more information on it.

K

K


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## TFrench (25 Sep 2016)

Sorry to go off topic slightly, but how do you switch your inverter between machines, G.O? I wondered about doing it with mine but I thought if the motor has to be direct to the inverter putting a plug in there might upset it?


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## J-G (25 Sep 2016)

TFrench":s5nr03de said:


> Sorry to go off topic slightly, but how do you switch your inverter between machines, G.O? I wondered about doing it with mine but I thought if the motor has to be direct to the inverter putting a plug in there might upset it?



I do the same with my two lathes - My inverter feeds a 10amp power out socket into which I plug the feed to whichever lathe I need 'live'. You must power down the inverter first because it 'reads' parameters from the motor at start-up but I find that a small price to pay for the advantage of variable speed. 

I understand that it is either not possible or against IEEE regulations to have two inverters on one ring main.


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## graduate_owner (25 Sep 2016)

That is what I do JG. I can plug whichever machine I want into the 3 phase socket on the inverter. When I wrote the motor must be connected directly to the inverter, I meant that you must not interrupt the inverter output to the motor by having switchgear which can open the circuit. Using a plug and socket keeps them connected, so no issues there, but you must switch off before removing the 3 phase plug.
To control the motor you either use the switchpad on the inverter, or control remotely by wiring a switch and variable resistor into the control circuit of the inverter (not into the mains input or into the 3 phase output - there are separate control connections specifically for this. These are low voltage connections.)

K


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## flh801978 (25 Sep 2016)

I don't know why GO said you can't use the existing switchgear and microswitches ?
The only thing to get rid of is the contactor a quick rewiring into the inverter and you are good to go
Using existing on/off buttons and the 2 microswitches on the access doors

Ian

The switchgear as fitted needs rewiring to suit an inverter..its not just a case of plugging an inverter direct into a 3 phase input on any machine

but theres nothing wrong with the switchgear as long as its rewired to suit


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## graduate_owner (25 Sep 2016)

Hi Ian,
I may be wrong here and apologise if so, but I was assuming that any switchgear which disconnects the motor from the inverter whilst running would be a bad thing for the inverter. The safety microswitches would do just that if operated accidentally while the motor was running, and if operated after stopping the motor correctly then they would serve no purpose anyway. 

On mine I have a remote switch and variable resistor housed in a plastic box. I glued magnets to the base so I can locate it easily on most of my kit. The motor is connected directly to a 3 phase plug - no possibility of open circuiting via any switchgear.
I suppose H and S requirements would include safety microswitches, but I don't need to be involved with those issues, thankfully.

K

Ian - did you mean connect the 3 phase output to the motor via the microswitches? If so then my comments above apply as the motor would not connect directly to the inverter, but on re-reading your posting I thought you might mean connecting the low voltage control wiring through the microswitches, in which case I think your comments are fine - good idea in fact.


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## J-G (26 Sep 2016)

graduate_owner":t04qterv said:


> To control the motor you either use the switchpad on the inverter, or control remotely by wiring a switch and variable resistor into the control circuit of the inverter (not into the mains input or into the 3 phase output - there are separate control connections specifically for this. These are low voltage connections.)
> 
> K



Likewise, I built my own remote control box with a potentiometer and switches for [Forward] [Reverse] [Jog] etc. (though I've never fathomed out how the [Jog] works  and never really had need of it). It seems to me that all inverter manuals are written with the object of confusing the user ! (hammer) This is connected to the Inverter via a 6m long 9 core cable, each core being about 0.5mm Ø - we're talking 5V logic rather than power of course - so I can move it about the workshop as needed.


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## flh801978 (26 Sep 2016)

The proper way to convert any machine to variable speed ( i realise i'm going to upset people here ) is to

Use one inverter for each machine that you need VS on
Use switches that are properly placed for easy operation and most importantly easy to stop in a panic
That means no inverters mounted above spinning parts that you have to reach over for a small off button (most inverters built in buttons are so small)

Wire in the inverter with properly sized cable DIRECT to the motor 3 core and earth
wire in the input with again properly sized mains cable and most importantly via an isolator so if you unplug the input theres no chance of electrocution (slight but theoretical)
wire in the signals start stop variable speed with suitable screened cable...place the switches where the designer of the machine wanted them....they are generally the best and safest place
Most importantly wire in any safety interlock guards to the stop circuit
Set the inverters parameters to suit the machine you have fitted it for 
1.accelaration up and down
2. motor max current
3.max and min speeds
plus all the other settings which I admit will be similar for any other motor running on 240v 3 phase

with inverters so cheap now it makes sense to wire one inverter into each machine with proper safety considerations for that machines operation
Ian

see I said i'd upset people


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## graduate_owner (26 Sep 2016)

I have no doubt this is the correct procedure, but obviously more expensive. I use my inverter to control 4 separate machines, all of which have 1 HP motors. I have not set any parameters and I find the default values seem to work fine as they are, although I suppose if I bothered to digest the manual then there could be some advantages. Having the control box moveable means I can place it in any convenient (and safe) position. 

Finally, I don't see why anyone should get upset by being given good advice.

K


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## J-G (26 Sep 2016)

flh801978":213lwee7 said:


> The proper way to convert any machine to variable speed ( i realise i'm going to upset people here ) is to
> 
> Use one inverter for each machine that you need VS on
> 
> see I said i'd upset people


Not upset in any way, but I am curious.

As I said in my first post, it is my understanding that you may not have more than one inverter on a ring main. I don't know whether this is due to IEEE regulations or something more fundamental. I would appreciate a definitive ruling on this and it seems that you (Ian) might have the knowledge required.

As far as having the control switches ' _where the designer of the machine wanted them_' the whole point of a remote control box - often available from the original manufacturer - is to have them in the most convenient position. In my case at the front of the machine (no reaching over anything). Using screened cable is common sense but I appreciate that that is often 'un-common', so pointing it out is useful.

Whilst the price has dropped over the past 10 years I don't consider £150 - £200 'cheap'.


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## flh801978 (26 Sep 2016)

I must confess I've never considered how many inverters on a ring main at once or seen any regulations regarding that.
In my home workshop I have 18 machines currently all with inverters on
Obviously not using them all at once
But sometimes I may be using 3 at once...on the same RM whilst CNC is in use
I have power factor meter permanently installed and it looks ok.

I go to businesses who are running loads of single phase inverters all at once on one RM and 3 phase inverters at the same time...maybe as many as 12 at once ( this is in the print trade)
Checking PF there all seems good

Whilst years ago a inverter was 150-200 I can't say I have paid more than £50 for a used inverter on eBay
Even a new Chinese 3kw one is only £100
And all new brands seem to be made in PRC

I've never bought a faulty one...even ones that have looked awful worked after setting parameters back to default and reprogramming for its new application
And I've only had one fail in use in my workshop

I must have fitted upwards of 100 inverters to people's machines usually as retrofits to give VS rather than single phase capability


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## Doug B (26 Sep 2016)

From a practical point of view I've found if you have two inverters on the same feed controlled by a RCD you can only have 1 connected to the mains at a time as even though neither may be working just the two being connected will cause the RCD to trip.

It doesn't have to be on the same ring, my two inverters are on separate 16amp feeds from one fuse box but as that fuse box is protected by a RCD I have to keep one of the inverters isolated at all times, it's a bit of a pain having to remember to check one is isolated before powering up the other but it gives me use of my 3 phase machinery so I can't grumble too much.


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## flh801978 (26 Sep 2016)

Doug
Many inverters have a switchable filter on the input supply that will cause your Rcd's to trip
Are yours switched in?


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## Doug B (26 Sep 2016)

flh801978":q75ul96a said:


> Doug
> Many inverters have a switchable filter on the input supply that will cause your Rcd's to trip
> Are yours switched in?



Not sure, both of mine are IMO idrives, I simply put live, neutral & earth in & connected the 3 lives & earth to the motor as well as wiring in the remote, don't remember mention of a switchable filter though it was a couple of years ago


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## wildewood (30 Sep 2016)

wow great stuff people many thanx lots to think about - much appreciated.


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