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2 Attachment(s)
Emco Mentor Mill conversion
So after a long time away from anything hobby related I have finally got around to some shed time.
having learned from my drill conversion saga I hopefully have done it properly now and just bought a descent mill to convert to cnc. It is actually an EME mentor mill MM1 base with a Maximat7 mill head. 4 speed gear box and 0.25kW 415V 3 phase motor.
Attachment 8624
The main problem is that the motor is 415v and the plastic gears in the gearbox are shot. In light of this I think the best option is use a DC motor from a treadmill and convert it to belt drive giving full speed control and 2hp.
The existing motor is part of the top plate and also holds the bearing for the final drive cog. To fit a different motor would mean making a new plate. Not having a working mill does pose the problem of how to make this.
Attachment 8632
Any takers for quoting to make this part? subjec to proper dims and drawings etc.
Cheers
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Re: Emco Mentor Mill conversion
Ross
I'm rebuilding the head off my Arboga at the moment where the gearbox sits on top. i had to dump this to build a direct drive. I would just mount the mount up off the top plate you have already and remove all the gubbins from your box. This way you would just need a couple of pieces of Bar to raise the motor in the air to accommodate the pulleys.
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Re: Emco Mentor Mill conversion
Same as Ross.
Saw the top plate off the motor, job done and everything fits and is in line.
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Re: Emco Mentor Mill conversion
Thanks Swarfing and John. I always seem to miss the easy solutions, although I was hoping to make all mods reversible. Didnt want to hack up something that I might be able to sell. Are 415v motors for these machines worth anything?
I'll have another look and see if the end plate will come off without destroying the motor, that would be the best out come.
Thanks again
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Re: Emco Mentor Mill conversion
If it wires 230 - 240v delta then just wack a vfd on it and away you go :-)
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Re: Emco Mentor Mill conversion
Quote:
Originally Posted by
Swarfing
If it wires 230 - 240v delta then just wack a vfd on it and away you go :-)
How can I tell? motor plate says 440v and there isnt the normal terminal box for changing star or dlta configurations. will a 440v motor run on 240v not be half as slow?
Cheers
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Re: Emco Mentor Mill conversion
Nice to see you back Ross, was reading some of your threads the other day and said to myself "i wonder what hes upto these days".
.Me
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Re: Emco Mentor Mill conversion
If there is no obvious opening or cap to reconfigure then maybe not? google mot or details and see what comes up.
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Re: Emco Mentor Mill conversion
Thanks Lee, good to be back. Been converting a barn for the last 3 years and still not quite finished but need some down time to try and keep me sane.
Progress will be slow but I have a lot planned for this mill, essentially it will be full cnc but with a Arduino (or similar micro processor) to monitor speed, axis DRO and act as a standalone controller for quick manual use.
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Re: Emco Mentor Mill conversion
I think you probably can still reconfigure it , but you will need to find the star point on the windings and the rewire as delta. G.
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Re: Emco Mentor Mill conversion
Whether the motor can be altered to run on 240V depends on if it's wired as Star or Delta 440V.
It's a case of carefully dismantling the motor, and seeing where and how the coils are connected. If all the coil wires ultimately end up with 3 going to the power feed, and 3 joined together in at one point, it can be changed to run on 240V. However, if each of the three going in split to two, then it's already in delta and can't be changed.
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Re: Emco Mentor Mill conversion
Absolutely correct m_c, I assumed the motor is probably wired as star which is why I said it can "probably" be reconfigured to delta. If it is already delta then there is no "simple" solution. G.
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Re: Emco Mentor Mill conversion
Thanks I was going to ask Geoffrey to elaborate but it think thats clear enough now. I'll have to check but I think the motor plate has a triangle on it so already delta. I've found a bit more info and it looks like the wiring is all done in the base. I'll have a proper look tomorrow.
A bit more research has also highlighted the weakness of the plastic gears so even if I can find replacements then it looks like a maintainance problem. belt drive might be worth the work.
Thanks for the info. good to know all the options
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Re: Emco Mentor Mill conversion
Quote:
Originally Posted by
GEOFFREY
Absolutely correct m_c, I assumed the motor is probably wired as star which is why I said it can "probably" be reconfigured to delta. If it is already delta then there is no "simple" solution. G.
From my experience, if a motor is 240V capable it will be written/stamped on the plate as being capable of dual voltage. However if it's wound for 415V in delta, it will most likely be marked as 415V only.
However, until you dismantle it and check how the external wiring links to the coil wires, you can only make a guess.
There are a couple options to avoid a motor swap. If you can live with reduced torque at higher speeds, you can run the motor via an inverter on 240V. HowTo: 240V Supply to a 400V AC Motor - Application Detail explains it well.
Or you can get inverters that will step up 240 to 415V - DIGITAL 240 TO 415 INVERTERS | Drives Direct Inverters LTD
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Re: Emco Mentor Mill conversion
As a general rule I think the motors (usually older motors) wired internally were not intended to be run on 240V. Ihave been running 3ph motors on single phase for years as the 3ph machines are cheaper to buy s/hand due to lack of diy 3ph availablity.
I have also never used a proprietry inverter due to cost considerations, but have sacrificed some torque and used capacitors to give "quasi" 3ph. Whilst this may be frowned upon I have found this to be a good solution on motors up to 3HP. As Ross has decided to use a different motor this is academic, but I mention it in case someone else wants to run a 3ph motor on single phase, provided of course the motor is configured as 240v delta. G.
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Re: Emco Mentor Mill conversion
Ok had another look tonight and the plate says 440 star, so might be in luck, bought some smaller gear pullers and got the motor apart without damaging it. Only 3 wires + earth go in to the motor there looks to be more wires joined and pushed down into the casing. not brave enough to dig them out yet, think I had better find a diagram for which wires are which coil.
if it was possible to convert to 240v what size inverter would I need? rated 0.25kW@ 440v so 0.125kW@ 240v? I have an inverter that I bought for the lathe but Its 1.5kW so might fry the small motor.
thanks for the 240>440 info but I think that if the motor cant be rewired to run on 240 then I will do the DC motor swap which looks a bit easier now I know I can use the existing top plate.
Cheers
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Re: Emco Mentor Mill conversion
If it is star, then the first thing you need to do is find the star point. *runs of to find image*
A quick google gave me the lower of the two images on this page - Star Delta Start Up Principles
(ignore the writing/figures, as it's explaining something you really don't need to worry about!)
as you should be able to see, the lefthand is Star configuration. What you need to do, is split the star point, then reconnect the coils in Delta (right hand image), and apply the power inputs to the delta points.
The motor will still be 0.25kw, however it will now require almost twice as much current, which should be around 1-1.2A of the top of my head. You can use a bigger inverter, however you'll need to alter the current limit settings to ensure it limits the amount of current should the motor get overloaded for any reason.
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Re: Emco Mentor Mill conversion
Quote:
I have also never used a proprietry inverter due to cost considerations, but have sacrificed some torque and used capacitors to give "quasi" 3ph. Whilst this may be frowned upon I have found this to be a good solution on motors up to 3HP
As long as its safe and it works for what ever application its in then I dont think it matters, I read that some of the Emco lathes and mills are configured like this from the manufacture.
Thanks Mc, worth a try.
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Re: Emco Mentor Mill conversion
sorry for the short reply, had to go out sooner than I thought. thanks for getting star - delta spec I was hoping to get the wire colours for each coil but the best I can find from emco is brown, blue, black, to the motor. looks like I'm going to have to find them buy trial and error, or testing. as a starting point Ill draw up the existing arrangement and get back back to you if that's ok?
Thanks again for your help. if there is a way to get this working on 240v then I'm keen to sort it out so I can test the machine before I make to many plans.........looks like some gorilla has been pounding on the draw bar with a hammer to release the collet holder and bent the top part of the spindle. arrgg:sorrow:
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Re: Emco Mentor Mill conversion
Stick with it it Ross. I am fairly sure you will be able to run that motor on single phase with with your inverter (or capacitors!).
When you check out the wiring you should be able to find the star point fairly easily, and once the wires are separated can then just do a simple ohms check to identify the three windings. Reconfigure as delta and you will be away. Good luck. G.
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Re: Emco Mentor Mill conversion
I'd highly doubt the coil wiring will have any sort of identification. They're usually just the enammeled copper wiring with a bit extra insulation slid over the top.
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Re: Emco Mentor Mill conversion
I think I have it sorted now! the motor was wired in star and has 6 coils which are interconnected in pairs. Before I cut the star connection I tested the input wires and got 100 ohms across each phase, which in star con fig is 2 coils (4 actually). When I cut the star connection and retested each coil I got continuity from the buzzer and 50 ohms reading.
The question is can I run it using a capacitor in delta configuration to test? or will it only run from the inverter and risk damaging that if I got the rewire wrong? Lastly can I use a cap from another 240v motor or is the capacitance value dependant on the motor?
Thanks again
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Re: Emco Mentor Mill conversion
Thing is you will need a few caps and they will be different sizes for the phases. By the time you have messed around you might as well get an inverter (vfd). If the motor does not work out i would still use another 3 phase motor.
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Re: Emco Mentor Mill conversion
Ah. I thought is was 1 cap in one of the phases or is that for star config?
I was only wanting to try the cap route for initial testing after I rewired the motor as I don't want to damage the VFD. (already got one)
Is there any other way to test a 3 phase motor?
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Re: Emco Mentor Mill conversion
Quote:
Originally Posted by
Ross77
Ah. I thought is was 1 cap in one of the phases or is that for star config?
I was only wanting to try the cap route for initial testing after I rewired the motor as I don't want to damage the VFD. (already got one)
Is there any other way to test a 3 phase motor?
you wont damage the VFD*. if its a half decent one it'll have foldback current limiting and overheat protection.
*but dont blame me if you let out magic smoke :biggrin:
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Re: Emco Mentor Mill conversion
Quote:
*but dont blame me if you let out magic smoke
Ah that old chestnut "It'll be allright but don't blame me if it goes wrong.....":smug:
I'll have to dig out the VFD and see if its 'spanner rewiring motor proof' Got to find the dam thing first, bought it a few years ago for the lathe and never managed to get a 3 phase motor for it.
Looks like a job for tomorrow night after I have finished the tilling
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Re: Emco Mentor Mill conversion
You only effectively need 1 capacitor to run a three phase motor from a single phase, however you normally need to use a few connected in parallel to acheive the required capacitance.
Search for 'static phase convertor' if you want to know more, however you need to check the generated voltages while running to ensure the 'false' phases aren't too high/low, and the voltages will also vary depending on load.
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Re: Emco Mentor Mill conversion
Ross, as m_c said ,you do usually only need one capacitor, connected across one leg of the delta triangle, but to get the correct capacitance you may need a couple in parallel. It is sometimes necessary to have an additional capacitor to increase the capacitance for initial starting, especially if starting under some load. this extra capacitor can be operated with a spring loaded switch, held on until the motor reaches speed (only a second or so) or as I do now using a timer circuit. G.
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Re: Emco Mentor Mill conversion
If you really want to go down that route then have a read of this. It helped me get my cross feed motor going on my BP. I could not swap that out because of the frame of the motor.
phaseconverter
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Re: Emco Mentor Mill conversion
Thanks guys, I think I'll pass on the capacitor route then. Worth mentioning though as it might help someone else.
Out of interest what is the verdict on DC motor vs AC + vfd or is that a question for another thread
?
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Re: Emco Mentor Mill conversion
It's not quite true you only need one cap? i had to use a few to get the balance right on all the phases. Takes a bit of messing but worked well in the end and saved me using a VFD for the job. Ross it is horses for courses, for me i prefer to use AC and VFD because it is easier. Brushless DC would be second choice but expensive (large servo would be even better). How deep are your pockets?
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Re: Emco Mentor Mill conversion
Swarfing, once the correct value cap has been established, apart from the "start" cap you are still only putting "C" across one leg of the delta (or am I missing something?). To give the correct "C" value you may well decide to use a combination of caps to achieve that value, but a single item of the correct value can usually be found. If Ross already has an inverter then obviously that is the best way ahead for him. I only make this point because I would not like to be thought of as misleading anybody. G.
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Re: Emco Mentor Mill conversion
G it was a long time ago when i did mine, you may be right so don't think you are misleading people. Mine would not balance across each phase so had to tweak with various caps to balance. If one phase runs out of balance then it would contribute to a short life of the motor. Bear in mind mine was 69 BP i applied this too. look at the second image up on the link i supplied earlier in this thread and you will see what i mean. That is the way i followed and it works a treat with only slight loss of torque.
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Re: Emco Mentor Mill conversion
Yes, I think its a great way to do it for very little expense and whilst I am aware that it is "quasi" 3 phase, I have never noticed any power losses. Mind you I have never had the real thing, so I wouldn't would I? G.
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Re: Emco Mentor Mill conversion
Quote:
Originally Posted by
Swarfing
It's not quite true you only need one cap? i had to use a few to get the balance right on all the phases. Takes a bit of messing but worked well in the end and saved me using a VFD for the job. Ross it is horses for courses, for me i prefer to use AC and VFD because it is easier. Brushless DC would be second choice but expensive (large servo would be even better). How deep are your pockets?
Cheers, I always thought that ac with vfd was more reliable but restrictive on high rpm also I had heard that torque at low speed can be an issue.
I was more looking at cheap treadmill motors, mainly because I picked one one up on ebay for £1. Not had chance to break it down yet but the specs say 1.75hp continuous and 3hp peak. geared down to 3000 rpm for the mill as it has roller bearings then that would be about 3hp continuous. geared up 1:2 on another spindle it should still achieve 1hp at 12000rpm :cool:
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Re: Emco Mentor Mill conversion
Sounds like your most of the way there then. Just need an appropriate controller and your away :-)
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Re: Emco Mentor Mill conversion
Quote:
Originally Posted by
Ross77
Cheers, I always thought that ac with vfd was more reliable but restrictive on high rpm also I had heard that torque at low speed can be an issue.
You can run a lot of standard induction motors at well over their rated frequency using a VFD and you will still get approximately rated power at the higher speed, however for that to happen clearly the torque drops proportionately. When you reduce the speed with a VFD, ideally the torque remains constant but in reality it drops a little. Even if the torque did remain constant, your power output will reduce with speed as power=torque*angular velocity.
The cheap VFDs from China seem to be good:
http://www.ebay.co.uk/itm/VARIABLE-F...item3cc89d5929
I use one of those to power the 2.2kW motor on my lathe and it works well.
Quote:
Originally Posted by
Ross77
the specs say 1.75hp continuous and 3hp peak. geared down to 3000 rpm for the mill as it has roller bearings then that would be about 3hp continuous. geared up 1:2 on another spindle it should still achieve 1hp at 12000rpm :cool:
Ideal gearing doesn't change the power output - if the input is 1.75hp, then whatever gearing you put in between the output will still be 1.75hp continuous, not 3hp. Clearly in reality you loose a few percent due to the inefficiency of the gearing.
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Re: Emco Mentor Mill conversion
Looking at the size of the machine i think the DC motor will do you fine. Mine will be running with only 1HP motor and that is more than enough for my needs.
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Re: Emco Mentor Mill conversion
Thanks Jonathan, is the torque drop off noticable? or is it dependant on the motor?
With referance to the gearing I was talking about power at the tool cutting tip. obviously the motor will always be the same power. :nevreness: Or have I got that wrong as well?
edit yes I have.....increase in velocity when gearing up and increase in torque when gearing down.