Oberg Die Grinder

[Alexander Smith 1Participant @alexandersmith1]

My friendly scrap man recently handed me a nice wooden box which he thought might be "interesting". Inside was a beautifully made, high speed Oberg die grinder (VM17 Nr 202) with collets and cable but, unfortunately, no power supply. Not a problem you might think – however, it's 38V, 400W and 900Hz to give a top speed of 54,000 rpm.

Oberg were a Swedish engineering company who made high quality files but I can find very little about the die grinder or its power supply. Has anyone ever used one of these or have a manual or circuit diagram or can anyone suggest what I might need. The plug has 3 pins (I presume the casing is earth) and I wondered whether it is low voltage 3 phase which I might be able to supply from an inverter somehow?

Any suggestions welcome

Put some pictures in an album but can't get them in the query.

thanks

[Alexander Smith 1Participant @alexandersmith1]

[John McNamaraParticipant @johnmcnamara74883]

Hi Alexander

Fein make high frequency power tools for industrial use from memory 300 cycle. Maybe if you spoke to one of their agents you may find a source. I have seen a rotary converter set up for driving an entire sheet metal factory, there was a special and separate bus system. to drive the tools. They are very robust.

Regards
John

[Anonymous]

It'll be a low voltage 3-phase 2-pole motor. Taking the 'synchronous' speed of a 2-pole induction motor at 50Hz of 3000rpm and multiplying by 900/50 you get 54000rpm. I think most standard VFDs go to 400Hz; no idea if you can get ones that go higher.

Andrew

[frank brownParticipant @frankbrown22225]

If you want to use a VFD then you need to use transformers to get from 230V to 38V. Each rated at 200W.

Your motor has a "resistance" of 38^2/ 133 = 11 ohms which is not a million miles from 8 ohms of a loudspeaker. So what I am suggesting that a pair of 200W audio amplifiers driven by a variable oscillator which has the phases of its output correct could be another way to go.

Or if you are really clever you build your own VFD

Frank

[Ingemar SchroderParticipant @ingemarschroder26824]

Hi Alexander

I think this high speed spindels ar sold under the name SPINTEC nowadays.

Check this links.

http://www.ptsintl.com/pdfs/SPVSpintec.pdf

http://shop.spvspintec.se/

Ingemar

[MWParticipant @mw27036]

I would keep hold of it and see if you can find a use to get it working because if it's anything like the Hi-speed spindles sold by Arc they are quite expensive to replace.

Michael W

[AjohnwParticipant @ajohnw51620]

This might sound crazy but at that voltage they probably drove it via something a little akin to a 400w RMS audio amplifier although I doubt if it was a hi fi one. It was probably powered from a 110v supply. 38v RMS sounds about right for that as the peak voltage with a sine wave would 2 root(2)*38 which comes out at about 106v . I'd guess it would be driven with something more like a square wave in practice. That way the usual sort of speed control used to keep speed stable under load could be used

John

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[russellParticipant @russell]

i agree with Frank and John – an old audio amp driven from a simple frequency generator should give you enough power at that frequency.

possibly doesnt need to be that big – depends on what you are grinding i guess, but an old 100 w amp should be pretty cheap, you may be able to parallel the channels.

-russell

[Neil WyattModerator @neilwyatt]

If it has three windings, you should be able to run it of a BLDC motor controller – simples.

**LINK**

This will knock you back the thick end of a tenner though.

Neil

[AjohnwParticipant @ajohnw51620]

I'd guess it's 38v RMS AC Niel not DC.

If some one wanted to try an audio amp the simplest solution would be to drive the channels in anti phase and connect the motor across the outputs of the 2 channels. Trouble is though I'd guess it was driven with a pretty simple switched DC square wave drive and inductance effects might blow an audio amp up.

If it was driven with a switched square wave the arrangement may be similar to the speed controllers used on universal motors. In that case the motor might be 180v and the speed controller has a limited a range of "speeds". The mark space ration is never 50 – 50 it's always less to control the power into the motor. The back emf duration when the drive is off is used to detect that the motor is under load which would normally cause the speed to drop. That's prevented by increasing the mark to space ratio over a limited range. I understand electric model loco's use a similar arrangement and via a DC supply.

John

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[AjohnwParticipant @ajohnw51620]

Having said all that I'd guess it would be fine with a 900Hz switched 50v DC supply or somewhat lees so wonder what they did do. I am assuming it's "pre brushless" but if not Neils idea may work out but I suspect it would really need one that will take a higher voltage.

John

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[Alexander Smith 1Participant @alexandersmith1]

Apologies for the delay in responding to all the helpful advice. Unfortunately, we had a leak in the kitchen on Friday (at least I became aware of the effect of a long term slow weep from a joint under the sink when the parquet under the lino started to swell and buckle up). You wouldn't believe how far water can spread!

Anyway, many thanks for all the comments – I am always amazed by the breadth of knowledge on this site. Ingemar (I'm guessing from Sweden) identified that Oberg are now Spintec and the site gave lots of information. They still make a VM17 spindle which fits all my information on mine so the die grinder is a 3 phase induction motor powered from a converter. I'm guessing that the power packs they supply will be well out of my price range so I was very interested to read Neil's comment that it may be possible to power it using a BLDC motor controller designed for a brushless DC motor – I can certainly go for a £10 solution (long Scottish heritage). I knew nothing about the technology of brushless motor control but when you read a bit about it, they do appear to be pretty similar to a low volt 3 phase motor although I certainly don't understand all the stuff about different waveforms etc. I did see that brushless motors appear to have Hall effect sensors to feed back motor performance data – will that be a problem here since presumably there won't be any on my spindle. I will probably contact Spintec to see if they can provide any more information but thanks again for all the help.

[Neil WyattModerator @neilwyatt]

Posted by Alexander Smith 1 on 27/06/2016 20:01:59:

Apologies for the delay in responding to all the helpful advice. Unfortunately, we had a leak in the kitchen on Friday (at least I became aware of the effect of a long term slow weep from a joint under the sink when the parquet under the lino started to swell and buckle up). You wouldn't believe how far water can spread!

Anyway, many thanks for all the comments – I am always amazed by the breadth of knowledge on this site. Ingemar (I'm guessing from Sweden) identified that Oberg are now Spintec and the site gave lots of information. They still make a VM17 spindle which fits all my information on mine so the die grinder is a 3 phase induction motor powered from a converter. I'm guessing that the power packs they supply will be well out of my price range so I was very interested to read Neil's comment that it may be possible to power it using a BLDC motor controller designed for a brushless DC motor – I can certainly go for a £10 solution (long Scottish heritage). I knew nothing about the technology of brushless motor control but when you read a bit about it, they do appear to be pretty similar to a low volt 3 phase motor although I certainly don't understand all the stuff about different waveforms etc. I did see that brushless motors appear to have Hall effect sensors to feed back motor performance data – will that be a problem here since presumably there won't be any on my spindle. I will probably contact Spintec to see if they can provide any more information but thanks again for all the help.

Might not work with a BLDC controller – these days most don't have hall sensors they use back-emf sensing, but they do normally have permanent magnets so might not work if yours is an induction type. It would probably run once its started, but I doubt it would start.

[Thor LindParticipant @thorlind27354]

I have some hard time finding the right startup frequency and acc and dec time for my Oberg wm17. I have a vdf type sunfar E300-2s0015 (b) with rated capacity 2.9Kva rated output current 7.5A and Applied motor power 1.5KW
Can anyone help me with the settings of this parameters?

[Neil WyattModerator @neilwyatt]

Hello Thor,

Welcome to the forum. the above posts suggest the WM17 needs a 38V supply so make sure this is programmed into the VFD (it seems that the minimum may be 25V chastotnii-preobrazovatel-sunfar-e300-manual-en.pdf )

Neil

[Thor LindParticipant @thorlind27354]

Thank you for your reply Neal.
It looks like the minimum speed for wn17 is 15000rpm.Therfor i have set the lower freq to 250 Hz
upper freq to 900Hz
acc time to 10sec and dec time 10sec
Modulate mode is set to synchronization?
Basic running freq is set to 900Hz
Max output volt to 38v
Min setting freq 250Hz
Max setting freq 900Hz

But i have not test the spindle with the aboue parameters yet because im not sure if this actually would work.
I would be very grateful if you can help me to set it up right.
Thor

[Neil WyattModerator @neilwyatt]

Thor, I have set up my VFD for a conventional 3-phase motor, but I am no expert on high speed motors.

Your do seem right to me but I am no expert.

I would guess a quick try to see if it works should be OK if you have the voltage limited to 38V, but you may want to set a current limit as well?

Good luck – you might want to wait and see if an 'expert' turns up in a bit!

Neil

[Thor LindParticipant @thorlind27354]

Thanks Neil, to me you look like an great expert
I been told that the most important parameters that I have to set is:

1.V/Hz 0.042 (38 Volt at 900 Hz)

2.Maxfrequency 900Hz

3.I-trip 6-8A

4.acc and dec time

The only problem is that I don’t know witch off the parameters who look very similar to each outer on my vfd to correspondence with the settings mentioned above.
Eks I-trip is not a parameter on my vdf, and what is the difference of basic running frequency max frequency, AO frequency,digital frequency and sett frequency?
Acc and dec time set to 10sec was just a wild ges.
Thor

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