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  1. #1
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    Default Electric motor experts

    Hello all

    Here is the situation. I have purchased a Kondia mill with a variable speed head (FV-1) The 3 phase motor is unserviceable. I have had some quotes and am looking at about $800+ to get this rewound and then I will still need a VFD to run it . These motors have a 25 mm diameter, 160 mm long shaft, so not off the shelf.

    I have seen reasonable priced single phase motors for sale on gumtree. Is it possible to press the motor shaft out of one armature and press in a new shaft? This way I could make up a motor that would work. I would then have a 1.5 Kw single phase mill.

    I have some other ideas but I thought I would rule them out one at a time.

    PS If you have a Kondia mill motor dead or alive I may be interested.

    Thanks

    Steve

  2. #2
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    I recall a discussion on another forum (probably Practical Machinist) about changing a motor shaft. The opinion was that it is doable, but with the warning that the laminations each have a slight burr which means that the shaft can only be pressed through in one direction. Other direction the burrs bite into the shaft and stop it moving.
    Not sure how to decide which way!

  3. #3
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    Quote Originally Posted by Neil317 View Post
    I recall a discussion on another forum (probably Practical Machinist) about changing a motor shaft. The opinion was that it is doable, but with the warning that the laminations each have a slight burr which means that the shaft can only be pressed through in one direction. Other direction the burrs bite into the shaft and stop in moving.
    Not sure how to decide which way!
    I considered replacing a bent shaft for a bench grinder once. Took it to a mechanic with a press not knowing this and neither did he. Result was is was pressed the wrong way and armature was damaged. Even now I don't know which way is correct.
    Nev.

  4. #4
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    I was under the (possibly incorrect) impression that Kondia FV-1's had 2Hp motors on the step pulley variant and 3Hp on the variable version, so you may be dropping 50% over stock.
    I take it that the 3 phase motor is properly fried as in unrepairable? If possible, a repair may be the easiest option. If that's not an option, have you considered using another flange mount motor and extending the shaft? If properly done, I can't see too many dramas emanating from such a modification.
    If using a single phase motor, you will need to change your switch gear so as to maintain the reversability of the motor, (not sure if a 3 phase with VFD has the inbuilt capability of not).

  5. #5
    BobL is offline Member: Blue and white apron brigade
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    If its geared correctly you won't need the variable speed head so just replace it with a pulley directly driven from the motor pulley and then use the VFD to vary the speed.
    You should be able to GET way with <$400 for a new motor and a VFD.

  6. #6
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    Agree with Karl. Buy a comparable flange mount 3 phase motor with say a 16mm shaft and machine a stub shaft to fit over the motor shaft. Could do same to a single phase motor if that is way you want to go but probable cheaper to go 3 phase if you have the supply.

  7. #7
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    Quote Originally Posted by BobL View Post
    If its geared correctly you won't need the variable speed head so just replace it with a pulley directly driven from the motor pulley and then use the VFD to vary the speed.
    You should be able to GET way with <$400 for a new motor and a VFD.

    Thanks for all of the replies so far. I have not disassembled the head any further than pulling the motor out. I would be keen to hear if anyone has gone down the path BobL suggested and how they found it.

    Steve

  8. #8
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    Quote Originally Posted by BobL View Post
    If its geared correctly you won't need the variable speed head so just replace it with a pulley directly driven from the motor pulley and then use the VFD to vary the speed.
    You should be able to GET way with <$400 for a new motor and a VFD.
    I'm not saying you're wrong as you generally have your ducks well and truly in a neat row, but would a VFD offer the required speed range? I don't know as I have never played with them, being lucky enough to have 3 phase at my disposal. Without engaging the back gear, my King Rich has a speed range from 500 to 3600 RPM which by my is a 7:1 ratio range. If I understand the theory correctly, without entering the realm of 2 speed motors, that would necessitate a frequency range from say 15Hz on the low side up to 100Hz on the high which I thought was outside the parameters where most electric motors would be happy and also present cooling issues.

  9. #9
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    I worked in a place that made motors once, and the answer to whether you can press the shaft out is 'it depends...'

    If it were mine I would get the motor repaired, keep the speed change and use a VFD for single to 3 phase conversion and perhaps minor speed adjustment. The range of speeds that you will likely need will far exceed the speed range you can get from a VFD by itself, so you will need some form of speed change on the machine anyway.

    Michael

  10. #10
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by Karl Robbers View Post
    I'm not saying you're wrong as you generally have your ducks well and truly in a neat row, but would a VFD offer the required speed range? I don't know as I have never played with them, being lucky enough to have 3 phase at my disposal. Without engaging the back gear, my King Rich has a speed range from 500 to 3600 RPM which by my is a 7:1 ratio range. If I understand the theory correctly, without entering the realm of 2 speed motors, that would necessitate a frequency range from say 15Hz on the low side up to 100Hz on the high which I thought was outside the parameters where most electric motors would be happy and also present cooling issues.
    It depends on how long you run things for and under what load.

    Under lighter loads most newer 4 pole motors can do 15 to 125 Hz without too many problems.
    If you were to use a newish 3HP motor and a vector drive VFD you would then have 2 HP from about 20 to 120 Hz but if you were heavily loading for extended periods at low frequencies then a separate fan motor would be needed.

  11. #11
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    Quote Originally Posted by Michael G View Post
    …….keep the speed change and use a VFD for single to 3 phase conversion and perhaps minor speed adjustment. The range of speeds that you will likely need will far exceed the speed range you can get from a VFD by itself, so you will need some form of speed change on the machine anyway.

    Michael
    ^ This
    Gear for close to minimum required speed and use the VFD to accelerate the motor, this is generally much kinder on the motor than running it slow with low frequency. This will mean swapping pulleys at some point. Putting a 3kW motor on a machine and using so you only get 2kW out of it is just an exercise in wasting money both in initial outlay an ongoing running costs. Just because you can doesn’t mean you should.

  12. #12
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by racingtadpole View Post
    Putting a 3kW motor on a machine and using so you only get 2kW out of it is just an exercise in wasting money both in initial outlay an ongoing running costs. Just because you can doesn’t mean you should.
    Apart from things like compressors and fans, most machinery motors operate at well under their maximum power for most of their lives. Over a 10 year period the 30% purchase price difference (even less if a used motor is involved) between the price of a 2 and 3 kW motor and running costs, compared to what else is spent in things like tooling is trivial. It's not like were running a factory full of these things for 40 hours a week and 48 weeks of the year.

  13. #13
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    Firstly a big thank you for all the information so far. It has certainly got me thinking about options.

    I have never owned or used a mill of this size, and also have very limited experience with mills.
    A couple of questions have come to mind. This mill appears to have a speed range of 60 to 4000 RPM.
    For home use is lower than 60 or greater than 4000 rpm ever likely to be required?

    Also the mill currently has a 1.5 Kw motor fitted. Is it likely that any more power is desirable for home use where production time is not a concern?

    My plan is to decide what to do, do it once and do it right. I am not looking to do this cheaply, but I want to do this as economical as practical. This includes long term running and maintenance costs.

    In some ways an off the shelf motor, pulley and belts make a lot of sense. Te other side of the coin is just keep to the original design intent.

    Thanks

    Steve

  14. #14
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    Quote Originally Posted by Reidy41 View Post
    Firstly a big thank you for all the information so far. It has certainly got me thinking about options.

    I have never owned or used a mill of this size, and also have very limited experience with mills.
    A couple of questions have come to mind. This mill appears to have a speed range of 60 to 4000 RPM.
    For home use is lower than 60 or greater than 4000 rpm ever likely to be required?
    My thoughts would be that it is highly unlikely that less than 60 RPM will be needed and that 4000 RPM will see you right on the top end unless you plan on a lot of work with really small carbide end mills and want to run them at their theoretical top speed.

    Also the mill currently has a 1.5 Kw motor fitted. Is it likely that any more power is desirable for home use where production time is not a concern?
    According to FS wizard, a 65mm face mill with 5 inserts running full width at 1mm depth of cut in medium carbon steel will drag 1.47Kw at the recommended speed and feed rates, so that is your upper limit based upon available power. End mills and slot drills should not tax your 1.5Kw too greatly.

    My plan is to decide what to do, do it once and do it right. I am not looking to do this cheaply, but I want to do this as economical as practical. This includes long term running and maintenance costs.

    In some ways an off the shelf motor, pulley and belts make a lot of sense. Te other side of the coin is just keep to the original design intent.

    Thanks

    Steve
    My choice would be rewinding the motor you have and using a VFD I think. Second choice would be to source a flange mount 3 phase motor, possibly a 3Hp unit and extend the shaft as required and then run a VFD.
    Based on BobL's earlier post, I'm getting the impression that running on 240V from a VFD may only give 2/3rd of the rated power, (using a 3Hp motor for 2Hp output), which would make for quite an anaemic performance from the standard 1.5Kw motor if that were the case, giving weight to increasing the motor size as a viable option.

  15. #15
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    Quote Originally Posted by Reidy41 View Post
    For home use is lower than 60 or greater than 4000 rpm ever likely to be required?

    Also the mill currently has a 1.5 Kw motor fitted. Is it likely that any more power is desirable for home use where production time is not a concern?
    In terms of cutting speeds, at one end 60rpm represents a 75mm HSS fly cutter on Cast Iron (probably also a useful speed if using a tapping head or larger hole saws), at the other 4000rpm is the speed that a drill in aluminium around 6mm could run at. I certainly would not be tempted to trim the bottom speed; if I had to I'd loose some at the top end, but would still want to keep at least 2000rpm, preferably 3000rpm.

    Power is trickier. You could cut down on power if you needed to but for industrial class machined that is probably low anyway. (my mill, which is not big is around 3kW from memory) Depending on your belt/ pulley combinations, you may not even be getting that power at the spindle at low speed (which is where it is most needed). I would try to hang onto that power, because if you get into stainless steel for example, dropping your feed rate because you have not got the power at the rpm you need is one good way to ruin cutters, as for SS they need to bite.

    Michael

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