A new Milling Machine

[Martin Johnson 1Participant @martinjohnson1]

Hello,

I have just taken delivery of an Elliott Omnimill 00 3 phase machine.  Very pleased with my purchase, but now considering just how to run it off single phase.  Details of the beast here: https://www.lathes.co.uk/elliott-omnimil-00/  https://www.lathes.co.uk/elliott-omnimil-00/

Initial thoughts are that a Steinmetz connection will do for the 1/4 HP coolant pump (easy starting and speaking as a pump designer, 1/4 hp is way OTT for suds).  A VFD inverter would be a nice luxury on the 1/10 hp table feed but I am thinking that Steinmetz might also suffice here, although the starting load would be a lot less favourable.

I have mixed feelings about the two drives for the horizontal (1.25 HP) and vertical (0.75HP) spindles.  If I am interpreting the circuit diagram correctly, the control knobs (off/forward/off/reverse) have an extra way which is used to interlock everything so that only one spindle can run and the “off” setting will drop out the incoming MEM starter, thus killing everything.  If that is the case, will one inverter suffice for both?  I will try and post the diagram shortly.

I am not too bothered about using variable speed on these drives, so wonder if one (or two) of these will do the trick:

https://www.ebay.co.uk/itm/397704177733?var=0&mkrid=710-53481-19255-0&campid=5338590836&toolid=10044&loc_physical_ms=132913&customid=2be61522fd191ff2ac837f6d40449e5d

https://www.ebay.co.uk/itm/397704177733?var=0&mkrid=710-53481-19255-0&campid=5338590836&toolid=10044&loc_physical_ms=132913&customid=2be61522fd191ff2ac837f6d40449e5d

Presumably they are basically an inverter inside configured to start up as the single phase powers up with suitable ramp up times and delays programmed in?

I am hoping to have room in the machine base to lose a couple of inverters or converters, allowing me to use IP 20 units.  Is it possible to configure the average single phase to 3 phase VFD to do the same thing as a conveter?  I ask this because the cost of a stop,start, fwd rev & speed control unit looks to be extortionate for what is actually supplied.  That would also give me the problem of where to put extra auxilary controls.  There is another problem if I go down the cheap chinky (AKA gibberish instructions) route which is finding where to wire such things into the inverter.

Whatever happens, I have four motors that need the star point to be discovered.  I have had a look in one main drive and there are only three terminals in the box.  Does anybody have advice for finding the star point?  At the ends of the stator windings?  Tucked between two poles?  None of the above?  How much insulation and taping am I likely to have to dig out to discover said star point?

The back stop is to single phase the two main drives as I already have a suitable motor for the vertical head but have you seen the price of 1.1kW 4 pole motors????

In due course, there will be a vertical / horizontal Tom Senoir M1 going in the for sale ads, located in DL14 if anybody is interested.

Has anybody adapted the Tom Senoir slotting head to fit an Elliott?  It looks like it should be possible with an adapter block.  I feel a bit of pattern making coming on………….

Collective thoughts on the way forward will be much appreciated.

Martin

[BazyleParticipant @bazyle]

You obviously noted it is only 240v output. One wonders if it is actually just a Steinmetz packaged with maybe a filter. No warning in the blurb about needing a delta wound motor. Do you have an ‘air switch’ (sic) as recommended?

[Robert Atkinson 2Participant @robertatkinson2]

As you say Steinmetz connection will do for the 1/4 HP coolant pump.
Need to see the circuit for the table feed. Are you sure it’s a 3 phase motor? Often these use a universal motor to provide variable speed.

Edit. I see this mill use change gears for table speed.

I’d be vary wary of the ebay units. Probably an expensive capacitor.

Yes you can run a VFD as a fixed con verter, you can almost certainly use the existing control switches. Only one VFD needed for the two motors as only one is run at a time.
VFD adds motor protection, “soft” start and other benefits in addition to variable speed.

Robert.

[Clive FosterParticipant @clivefoster55965]

Martin

I fear Robert may be a bit too cynical.

Back in the day I built a number of Steinmetz starter boxes with proper protection and automatic starter capacitor control so I know you can do a proper “expensive capacitor” job. But frankly these days a simple “single speed VFD” innards will be cheaper and simpler than an expensive capacitor box. Besides being much more likely to work well. After tens of Steinmetz boxes I’ve no illusions as to how much of pest they can be if a motor lays back its ears and decides not to play.

I think  the drive boxes in your E-Bay links do essentially the same job as the Eaton DE-1 “smart starter” units.

Those DE-1 series are simple VFD power units, with no built in controls or display, configured to work as drop in replacements for old style contactor controls. Basically connect and go for simple soft start single speed operation but with a full voltage/frequency VFD inside so they can also be configured as a full on VFD to run via external controls. Book shows that multi speed forward & reverse set ups are easy. There is a set-up widget, which I have, to do more clever things.

I have set up Eaton DE-1 devices to work the way your E-Bay units are intended to and found they work very well indeed in that simple configuration. Just a short, few seconds, delay as the capacitors charge before the motor starts ramping up.

Actually I have a DE-1 in stock ready to do a job that one of the ones you linked to will do just fine. I’m temped to leave the DE-1 on the shelf and go get one off your link!

Although a Steinmetz connection can work just fine I’d not bother with getting the coolant pump running. In my view flood coolant is too messy in the home shop and we never need to run hard enough to properly exploit it. If you have low-pressure air and some sort of low pressure rated oil container available I think one of the cheap E-Bay mist coolant units could be made to work just fine for your purposes. Not bro professional standards may be but a bit of lubricant and bit of air to blow the chips away serves for mots home shop jobs.

All my machines have coolant pumps. All have Bijur Spraymist units, modified to minimise dispersion, too. The Bijurs get used. I know I haven’t turned flood on this decade. Possibly a time or two last decade!

Clive

[Wade BeattyParticipant @wadebeatty78296]

I have used this converter that came with my Omnimill, it works just fine. No drop-outs. I replaced the  .75hp motor with a 1hp motor on the vertical drive.

Regards

Wade

[Martin Johnson 1Participant @martinjohnson1]

Thanks for the replies.  In the interim I have been working on the conversion of my mill.

An auction site is due to provide an unused inverter for one of the main drives at a price under £40.  I wait with bated breath for the postie.

I was expecting the two main drive motors to be fairly simple to convert to 220V Delta configuration.  They are not and there only 3 wires brought out of the windings with the star point being buried in the windings at the terminal box end.  I think I have identified them but can see that inexperienced hands excavating the star point have the potential to trash two perfectly good motors .  Fortunately, we have two rewind establishments in town and one that is willing to take on the internal mods, so I will farm that work out.

I was expecting the pump and table traverse motors to be a S*D.  They are easy with traverse drive having soft soldered connections to all 6 ends visible at the non drive end of the stator.

https://www.model-engineer.co.uk/members/martinjohnson1/mediapress/bits-n-pieces/pump-motor-in-star/

The incoming phases are red, blue and white (plus green PE).  The three sets of windings are connected to a star point, see the black wire bottom right.  An easy job to unsolder the black link wire, identify which winding is which with the AVO and then reconnect in delta.  The incoming connections were undisturbed, so no problem knowing the polarity for each winding.

My modification is shown here:

https://www.model-engineer.co.uk/members/martinjohnson1/mediapress/bits-n-pieces/pump-motor-in-star/

You can see the delta connections in brown with one connection still labelled “B” which is the “other end” of the blue phase winding, connecting to the white phase winding.  So for anybody following this drivel, the key is identify the windings and which end is “in” and which end is “out” – simple enough with some tape and sharpie.  Otherwise it is quite possible to have one phase going in the opposite direction to the other two – not a great idea.

The pump motor was even simpler.

https://www.model-engineer.co.uk/members/martinjohnson1/mediapress/bits-n-pieces/pump-motor-in-star/

Shows what I found, with the incoming phases being red, green and black.  The motor windings are 3 blacks and 3 reds, you can see the reds taken to a common star point on the terminal post top left.  So that was easy enough to use the AVO to identify the red and black pairs for the 3 sets of windings.  Then simply wire red to black in turn.  Reading off the plate (not the manual) the rating is 1/40 HP, rather than the 1/4 HP I had picked up from the manual.  So working on 1/40 HP I fitted a 1.5 mu Farad 450 V rated capacitor (the auction site has them as motor start or run capacitors) for a Steinmetz circuit.1.3 mu Farad would be appropriate on the 70 muF per kilowatt power.

That was not a complete success.  It will not start, but with a flick on the impeller it will pick up and run fine.  Now, I wonder with a motor that small whether the capacitor needs to be bigger.  My reasoning is that the motor efficiency must be pretty poor (being so tiny), that being so, the windings will be larger than the motor rating suggests and in that case I would need a bigger capacitor to tune to the bigger winding.

Any thoughts from the team on the reluctant pump drive please?

Martin

[VicParticipant @vic]

This is how the main motor was rewired on my Omnimill if it’s of interest. I didn’t bother with anything else as a house move meant I only had the machine for about a year and sold it on. Good luck with the conversion, they are a fantastic machine for home use. I did a lot of good work on the machine for the time I had it and had no issues with the motor at all running on 240V single phase.

 

[noel shelleyParticipant @noelshelley55608]

Because I have one, I would use a transwave or Motorun. I know it’s sort of an expensive cap, but it outputs 415v so almost plug and play. Since vari speed is not needed that’s fine.  Noel.

[Martin Johnson 1Participant @martinjohnson1]

Vic,

I still have to break into the star point to replicate your wiring diagrams.  I am not yet committed to inverter drives on both spindles – it depends a bit on what inerters are around at what price but Mr Steinmetz is always an option.  However, on the basis of the pump the starting torque is clearly an issue.  I agree the Omnimill looks to be a great tool and can’t wait to cut metal and find out.

Noel,

The static converter is attractively simple but repulsively expensive (even second hand).  I also had experience of one in a friend’s workshop and was less than impressed.  I guess there is the hybrid option of running a slave 3 phase motor from mains and capacitor bank to make a crude rotary converter.

Thank you both for your input.

Looming large on the hoizon next is rewiring the Omnimill as currents on 220V will be roughly double what they were on 440V, hence uprated cables needed throughout.  I also need to decide if the incoming Memota motor relay box is to be kept or ditched.

I will report back in due course.

Martin

[VicParticipant @vic]

Martin, it may not be the best solution but I was on a very tight budget when I bought the machine so £12 for a large capacitor was a no brainer. I did some good work on it and sold it for what I paid for it when I moved house. For such a small foot print it’s an incredibly versatile machine. I’m sure you’ll really enjoy using the machine once it’s set up the way you want it!

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