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.RC.
18th Dec 2015, 01:51 PM
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I have purchased a rotary magnetic chuck that was part of a surface grinder. Unfortunately when the seller scrapped the rest of the machine, he also scrapped the controller, leaving just two bare wires.

When I got the chuck home I tested it with 12V DC and it does indeed work and has a 50 ohm resistance. It has stamped on the side 110V 240W which with ohms law gives us the 50 ohms I measured.

I need to be able to power the chuck. I can purchase a controller from Taiwan but at $400 I think I can build something much cheaper, especially as I do not expect to be using this a great deal. So if someone can go give Ray a poke as I am sure this sort of thing is right up his alley.

I think I need a 110V DC variable power supply that has the ability to also inject AC power into the coil to demagnetise everything when the job is finished.

I am suspecting something like a variac 0-110V device, a bridge rectifier plus a capacitor to smooth out the ripples. Then some sort of switch to bypass the bridge rectifier and inject AC for demag mode.

I already have 110V AC on hand as the optical comparator I got has a whopper of a 240-110V transformer in it.

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RayG
18th Dec 2015, 02:18 PM
Hi .RC,

I think you've already got the right idea, just a 110V DC supply @ 2A (or more) is what you need, I'm not so sure about doing demag with 50Hz AC, the one on my SG is fairly low frequency, maybe 1Hz or less.

You could just use a drill speed controller type circuit, ( phase angle fired triac) and rectify the output from that rather than waste an expensive variac.

The thing that will bring you undone is the inductive kickback from the mag chuck coils, you will need to put a decent sized diode across the chuck coil, to absorb the flyback voltage spike.

If you are then reversing the current to demagnetize the chuck, the reversing switch needs to be between the flyback diode and the chuck, other wise the diode will short out your DC supply.

So the demag procedure would be power off, reverse the connections, power on, wait 1 second, power off, reverse, power on... and so on.


I hope that all makes some kind of sense...

Ray

PS .. I had a quick look on line, and seems like lots of demag circuits just feed the AC straight through?

.RC.
18th Dec 2015, 05:05 PM
Thanks Ray. Something like this could be adequate then M012 Power Control 110 - 240 V/AC, 1200 VA (http://www.kemo-electronic.de/en/Light-Sound/Effects/Modules/M012-Power-Control-110-240-V-AC-1200-VA.php)

I wonder do they vary voltage or output an adjustable width square wave (is that what they call pulse width modulation)? I am not sure how electromagnets will work if it just outputs a square wave of varying width turning off every 1/50th of a second. It will not be a pure DC form.

I did some reading over on PM forum and it mentioned there the problem of a voltage spike when turning off and decent diodes were recommended.

RayG
18th Dec 2015, 09:37 PM
Thanks Ray. Something like this could be adequate then M012 Power Control 110 - 240 V/AC, 1200 VA (http://www.kemo-electronic.de/en/Light-Sound/Effects/Modules/M012-Power-Control-110-240-V-AC-1200-VA.php)

I wonder do they vary voltage or output an adjustable width square wave (is that what they call pulse width modulation)? I am not sure how electromagnets will work if it just outputs a square wave of varying width turning off every 1/50th of a second. It will not be a pure DC form.

I did some reading over on PM forum and it mentioned there the problem of a voltage spike when turning off and decent diodes were recommended.

That's a chopper type speed controller, ( phase angle fired triac) should work fine, remember that the output waveform is still AC, that is a chopped sine wave, so, you still need to put a rectifier on the output.

Back to the demag question, rethinking it, I guess that just connecting the 50 Hz chopped waveform to the coils would probably work, the parts will buzz at 50hz and vibrate their way off the chuck. :) That should be a bit of excitement for anyone nearby with a pacemaker.

Ray

.RC.
19th Dec 2015, 04:02 PM
Thanks Ray. I already have one of the Kemo units here. I use it as a speed controller on my Biax. I find it very good.

I see now the phase angle fired system is different from pulse width modulation https://en.wikipedia.org/wiki/Phase-fired_controllers https://en.wikipedia.org/wiki/Pulse-width_modulation

I am currently cleaning up the rotary table portion. Unfortunately the brushes broke when I was disassembling it, but that is not a big deal, they are just bog standard type, 6mmX9mmx25mm carbon.

.RC.
19th Dec 2015, 10:00 PM
A couple of pics of the clean up process which is mostly done.

The table top seems to be very parallel with the ways underneath it.

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.RC.
23rd Dec 2015, 01:42 PM
I have cleaned up the hydraulic motor. I was expecting a gear motor or at the outside a geroller/gerotor style motor.

Instead what I have is an axial piston type motor. It works like this, inside the housing is a series of pistons running parallel with the output shaft. These are fed pressurised oil by a rotating valve in the top of the motor. These pistons act upon a swash plate, which is a plate at an angle to the output shaft. So the pistons push against the plate on an angle forcing it to rotate. Other hydraulic motors operating on the same principle have the swash plate running perpendicular with the output shaft and have the pistons on an angle, the motor will look like a boomerang.

I have seen car air conditioning compressors use the same principle, and no doubt someone has made a working engine on the same principle.

There is some corrosion on the swash plate no doubt from contaminated hydraulic oil and the big angular contact bearing on the end has some minor corrosion on the outer race. As it is a 7212 bearing so not real cheap, I will leave it as is for the time being.

bare housing

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housing with pistons

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swash plate/output shaft assembly

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.RC.
29th Jan 2016, 04:42 PM
I have picked up another tiny electromagnetic chuck. Not sure if this is commercially made or not. it has no markings at all on it.

I have powered it with 5V from a computer PSU and it draws 3 amps and works very well for larger items.

I was thinking of using it for TC grinder duty.

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My big chuck has stalled trying to find a brush supplier, I need 6mm X 9mm X 25mm brushes. Waste of time going to local shops, they stock nothing other then small brushes. They could get them made though. I can do that myself if I can find a suitable larger brush to cut down.

jhovel
29th Jan 2016, 07:23 PM
... I can do that myself if I can find a suitable larger brush to cut down.

You might look for starter motor brushes. You may even be able to get two the size you need out of one of those. ANother advantage is that they have decent sized copper connections.

BaronJ
30th Jan 2016, 11:14 PM
Thanks Ray. Something like this could be adequate then M012 Power Control 110 - 240 V/AC, 1200 VA (http://www.kemo-electronic.de/en/Light-Sound/Effects/Modules/M012-Power-Control-110-240-V-AC-1200-VA.php)


I did some reading over on PM forum and it mentioned there the problem of a voltage spike when turning off and decent diodes were recommended.

A simple way of reducing or even eliminating the inductive spike kick back voltage when feeding DC into an inductor is to place a capacitor across it. The capacitor reduces the speed at which the voltage drops when the supply is removed. This capacitor often will have a resistor in series with it to adsorb some of the energy.

RayG
30th Jan 2016, 11:39 PM
A simple way of reducing or even eliminating the inductive spike kick back voltage when feeding DC into an inductor is to place a capacitor across it. The capacitor reduces the speed at which the voltage drops when the supply is removed. This capacitor often will have a resistor in series with it to adsorb some of the energy.

Yes, exactly right, we use them by the hundred, they are called snubbers. More for AC spike suppression than for DC, DC spike suppression can be MOV's Varistors, or sometimes just a flywheel diode.

Ray

.RC.
23rd Feb 2016, 08:36 PM
Well I ended up buying a US made controller that was on US ebay for a very reasonable price. It has not arrived yet, also it does not have variable controller on it but I might be able to get around that. It does have demag.

I have drilled and tapped three holes on each side into the main housing where the drive chain runs. I am going to put some bolt studs in there so when I want to lock up the table I will be able to. Been looking into alternative ways to drive the table. Hydraulics is just horrendously expensive. Wondering about a 12V motor and worm gearbox. I need about 70rpm. Was looking at those scooter electric motors and make a worm drive for it. The motors seem to be very common and hence cheap.

Another job for the horizontal borer. Just spin the table for each side. :D

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PDW
25th Feb 2016, 08:14 AM
Another job for the horizontal borer. Just spin the table for each side. :D

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Wonderful the jobs that become simple when you have one of those beasts in the shed, isn't it?

I've got a big steering quadrant for a rudder to bore out as soon as it's extracted from the boat. New rudder stock is bigger than the current one. A lot of ways this could be done, but the simplest is on the HBM.

PDW

.RC.
26th Feb 2016, 08:13 PM
The controller turned up today. It has been modified in that someone has installed a small rheostat and cut a track on the circuit board and soldered in some wires. Not yet sure if it does anything as turning the knob makes no difference to the output voltage which is only 50V, although the electromagnet really sticks anything to it with it plugged in. better then by permanent 6X12 magnetic chucks I have.

There is nothing to these electromagnetic controllers, so not sure why they retail for such big $.

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RayG
26th Feb 2016, 11:44 PM
Hi RC,

Check the open circuit voltage, and then re-measure with the chuck connected, If you have a DC clamp meter measure the amps the supply delivers.

You are right about being simple, it's just a glorified DC supply.

Ray

PS. I'm guessing the relay clicks on and off reversing the current when you select demag?

.RC.
27th Feb 2016, 10:34 AM
Hi Ray, The voltages have changed a bit since the initial measurement.

The OCV is around 130V.

Operating voltage is 100V. Amps is 2.3 which is about right as the magnet is a 240W

demag voltage is what the rheostat changes, but it is around 14V and goes lower from there.

RayG
27th Feb 2016, 12:01 PM
That all sounds about right, when you said it was 50V instead of the 100V, I was thinking the power supply might have been underrated for the chuck.

All good.

.RC.
8th Mar 2016, 05:27 PM
In the quest for a motor to drive the table I have settled on one of these

NEW Healthmate 2 Wire 500W 240V Constant Drive Brush Motor Treadmill Belt | eBay (http://www.ebay.com.au/itm/371478174268)

to be controlled by one of these

Kemo M012 Power Control 110 240VAC 1200VA KI8346 | eBay (http://www.ebay.com.au/itm/331553381327)

The I just need a worm drive to gear it down to around 60-70rpm.

jhovel
8th Mar 2016, 06:40 PM
plus a rectifier and maybe some capacitors and a choke, I imagine?

.RC.
8th Mar 2016, 07:02 PM
Possibly Joe. I chose this sort of motor after finding there is a fair bit of info about this style on the internet.

jhovel
8th Mar 2016, 08:39 PM
Possibly Joe. ...
It's a DC motor, isn't it? The controller you linked to is AC in and AC out.

.RC.
9th Mar 2016, 06:30 PM
I see what you mean Joe. I have founds heaps of info on the net about these treadmill type motors, so will see how I go.

.RC.
13th Mar 2016, 11:33 AM
I am always surprised as to what sort of electronic components are out there easily available on ebay.

Have found all these controllers out there with varying voltage outputs, some do 220V, some do 180V some do 90V

1000W AC 220V TO DC 0 220V Adjustable DC Motor Speed Regulator Controller Board | eBay (http://www.ebay.com.au/itm/1000W-AC-220V-to-DC-0-220V-Adjustable-DC-Motor-Speed-Regulator-Controller-Board-/131515023521)

.RC.
14th Mar 2016, 07:11 PM
So the 220V DC 500W Permanent Magnet motor turns up today. Looks pretty good actually. As usual these days the armature has not been varnished or dipped in anything. Is it worthwhile getting it varnished? Or paint it myself?

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jhovel
14th Mar 2016, 08:33 PM
Mmmm - the blue blobs are indicators of dynamic balancing. If you dip it, that will change the balance.... I'd be hesitant, unless you have access to re-balancing. On the other hand, the coils are clearly machine wound and tight. Maybe its not necessary for them to be 'glued' together. The downside of dipping is that there is more mass generating more centrifugal/centripedal force, pulling on the coil strands....
In summary, I'd leave it alone.

.RC.
14th Mar 2016, 09:29 PM
Yes I thought they would be to do with a highly technical balancing technique of putting blue epoxy putty to balance :)

I will leave it alone, and look into the worm gearbox next.

pcx
17th Mar 2016, 09:27 AM
G'Day RC,
In regards to your worm drive quest, I have two worm drives from a Holden electric seat adjusting mechanism. I don't know what model.
They are motor driven and the output shaft has a coarse thread on it. I think you could modify one of these to drive your chuck.
I have been looking at them as I thought that someone who wants to make a power feed for a mill drill X or Y axis would be able to use them.
Just have not gotten around to offering them on this site yet.
Unfortunately I am overseas at the moment and will probably be away for another 3 weeks so I can't post a photo.
You are welcome to them when I return if you want them, or since you probably want to continue with your project you might want to check out some of the wreckers in your area. I think the worm drive of these might be ideal for your project.

.RC.
20th Mar 2016, 10:00 PM
Thanks for the offer pcx. I think I will end up making the gearbox as of yet I am not sure what speed the DC motor I bought will do and am waiting on the controller to arrive from China. Then I can measure the speed and work out the reduction to get about a 60-70rpm output.

.RC.
6th Apr 2016, 04:18 PM
The electric motor speed controller arrived. I connected it to the motor and testes it out and it works very well.

The amount of torque the motor produces at low speeds is impressive, however I think some sort of cooling fan will be required.

Top speed is 4500rpm, which I need to reduce to about 80.

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.RC.
20th May 2016, 07:21 PM
Things have progressed on the theoretical front. I have dug out an old heavy duty drill that had a burnt out armature. It has a double reduction in it and I have worked out it should put out something like 120rpm if connected to the motor.

I have looked at bevel gears on ebay and picked a small 2:1 bevel reduction set from China. Bevel Gear Metal Gear 90° Angle 1 2 1 5M Modulus 15T 30T Teeth Bore 5 6 8 10 12 | eBay (http://www.ebay.com.au/itm/252195197749) I expect quality to not be fantastic but at a slow RPM I hope they are adequate. Who would have thought they call them umbrella gears. I could have cut parallel depth bevels but I only own one single gear cutter and gear cutters are more expensive then the gears.

.RC.
8th Jun 2016, 02:27 PM
The bevel gears have arrived and while they need deburring and not the prettiest gears I have ever seen they are better then I was expecting. They appear to actually be correctly cut on a planer.

I am not sure how to position them relative to each other in the grabbox I have to make.

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.RC.
17th Nov 2016, 04:46 PM
No I have not forgotten about this project. So I have done a bit more to it.

I have mated up the old dead drill gearbox to the motor. I have also devised a way to make the bevel gears fit and mount it all to the rotary table.

There was a bit of fiddling to make the adapter plate and the input gear is just loctited into the motor shaft.

Testing proves it works well. The motor has no cooling as it is a treadmill motor, But I think I will be putting a cooling fan onto the rear, probably a high capacity computer fan or something like it so I still get high air flow when the treadmill motor is doing low RPM's.

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I still have to devise a way to provide lubrication oil to the table ways. It needs a constant flow as it runs on scraped ways.

I also picked up another magnetic chuck controller off ebay. The magnet sticking works OK, but the release does not. It has a few basic electronic components in it like a triac, caps, resistors. I need Ray for a day to trouble shoot it for me ;)

jhovel
17th Nov 2016, 09:34 PM
Hi Richard,
did you find that the DC motor makes a strong humming noise when running on the controller you got? I think I have the same controller but I don't like the 50Hz hum it creates. I worry about the permanent magnets in the motor being 'demagnetised' slowly by the 50Hz DC supply....
I'd be interested in your experience.

BaronJ
18th Nov 2016, 02:48 AM
Hi Joe,

It sounds like the controller you have is a triac phase switched type. The 50 Hz wont harm the motor, but I agree that it is annoying. The sort of controller you really need is a "PWM" Pulse Width Modulation one. These effectivly switch a constant DC supply on and off at frequencies way beyond those that you can hear. By varying the width of the pulses the effective power to the motor is controlled varying its speed.

jhovel
18th Nov 2016, 02:39 PM
I think you are right, Baron. Mine is identical to the one Richard referred to in post #23: 1000W AC 220V to DC 0-220V Adjustable DC Motor Speed Regulator Controller Board | eBay (http://www.ebay.com.au/itm/131515023521)
But the one he showed in post #29 looks different. I wonder if that is a PMW controller.

BaronJ
19th Nov 2016, 01:22 AM
I think you are right, Baron. Mine is identical to the one Richard referred to in post #23: 1000W AC 220V to DC 0-220V Adjustable DC Motor Speed Regulator Controller Board | eBay (http://www.ebay.com.au/itm/131515023521)
But the one he showed in post #29 looks different. I wonder if that is a PMW controller.

Hi Joe,

The one in post 29, uses two TYN412 thyristors. So that is definitly a phase switched controller. Actually it would make a good stage lighting dimmer.

The Ebay picture shows something different, so that could be either, its very hard to tell from those two pictures.
Do you have any paperwork showing a circuit diagram ? If so I could take a look at it and try to determine what yours is.

.RC.
19th Nov 2016, 01:32 PM
My speed controller is the same as this one www.ebay.com.au/itm/Input-AC220V-Output-DC-0-220V-Motor-Speed-Controller-1200W-/262557251130 (http://www.ebay.com.au/itm/Input-AC220V-Output-DC-0-220V-Motor-Speed-Controller-1200W-/262557251130)

It says PWM but who knows. It does work and it hums a bit but it makes no different noise to say a variable speed electric drill.

I have the motor coupled to the rotary table now. I just need to add a support bearing to the shaft that goes into the table drive. I have also added a fan to the motor. I can see now the variable speed is not really going to be that useful. Lets see if I can upload a video. I have never had any luck uploading videos to this site before.

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jhovel
19th Nov 2016, 08:00 PM
Thanks for that info Richard and thanks for the video.
Looksing great. I suspect whe you are machininig something on the RT, you will be glad for the variable speed.

BaronJ
19th Nov 2016, 11:11 PM
Hi Guys,

Richard. Video is just fine. It certainly drives that table at some lick.

Joe. PM sent.

.RC.
15th Dec 2016, 11:39 AM
I got the last majpr piece of the puzzle for this tool a short time ago. It is an auto lubricator to pump oil to the plain bearing the table spins on.

I just need pipe and wires now to finish it off. Of course now I find on ebay a chinese seller selling larger bevel gears which would be more suitable for this. I also picked up an extremely powerful computer fan for cooling of the motor.

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