Countersunk holes in magnets

[frackers]

Just got some magnets from CMS Magnetics with countersunk holes but the countersink appears to be on the same pole for all of them. Is this what you'd expect as they were sold as a set of 24 for use in a wind turbine that of course requires alternate poles...

Cheers

[TomW]

Oops.

Seems this is not unheard of.

Someone had posted about this all one pole bit a few years ago?  Maybe it was those curved magnets [with holes] since you can flip the blocks over and have an opposite pole. Oh countersunk? then it won't work.

Tom

[Hilltopgrange]

it`s actually pretty easy to machine the countersink with a glass cutting bit, the trick is keeping it cool, I used white spirit as a coolant. I placed an aluminium foil tray filled with white spirit on the table of a vertical drill, no need for a vice as the magnet holds itself to the table. Just take it slowly with the machine on its slowest speed and set the depth limit to keep them all the same. After machining just clean them with surgical spirit and coat the exposed magnet with epoxy.
I tried all sorts of bits and the only ones that worked where cheap glass and tile cutters similar to these: http://cgi.ebay.co.uk/6-5mm-Glass-Tile-Ceramics-Cutting-Drill-Bit-Silver-Tone-/150547711437?pt=UK_Home_Garden_PowerTools_SM&hash=item230d57c5cd

for more info http://fieldlines.com/board/index.php/topic,138389.0.html

Russell

[bj]

   Frackers--I have used Tungsten carbide burrs, the kind used in die grinders.  Same thing, slow speed in drill press
and lots of cooling fluid.  Submerged seems best.  Anyway, worked well for me, and didn't seem to dull the burr at all.

[windy]

Frackers,
 I had the same thing happen to me when I ordered my magnets. All I did was called CMS back and see if you can return 12 magnets and tell them to send 12 magnets with the opposite poles. That would be easier than drilling. I know they make them with north and south poles on the countersunk side.
windy

[frackers]

Frackers,
 I had the same thing happen to me when I ordered my magnets. All I did was called CMS back and see if you can return 12 magnets and tell them to send 12 magnets with the opposite poles. That would be easier than drilling. I know they make them with north and south poles on the countersunk side.
windy

I've emailed their support address with this in mind exactly. Since the freight from the US to NZ was so much I'll get another 24 of the opposite type and sell one set locally I think rather than spend out even more on freight to return half of them. Just have to work out whether I have countersunk north or south - the sensor in my new smartphone might tell me I suppose - would be nice to have a reference though.

I do have a drill press and I have tungsten masonry drill bits but no burrs. I quite like the idea of having a go with the magnet immersed in a plastic tray of diesel or similar, it will hold itself onto the bed of the drillpress OK anyways

Thanks for the ideas - I'll wait for CMS feedback and drill only if I have to...

Cheers

[ChrisOlson]

Just got some magnets from CMS Magnetics with countersunk holes but the countersink appears to be on the same pole for all of them. Is this what you'd expect as they were sold as a set of 24 for use in a wind turbine that of course requires alternate poles...

Frackers, every one of them I've ever gotten is always on the same pole.  I just pin them and don't use the countersink, putting them on like this:



Never had one fly off yet with them pinned, including in my 12G turbines where the generator is spinning at 640 rpm
--
Chris

[frackers]

Frackers, every one of them I've ever gotten is always on the same pole.  I just pin them and don't use the countersink, putting them on like this:
Never had one fly off yet with them pinned, including in my 12G turbines where the generator is spinning at 640 rpm
--
Chris

Now there's an idea - thanks Chris, I hadn't thought of using roll pins. I'll check out what sizes are available tomorrow (the hole appears to be 3.5mm). Do you get them the correct length or do you have to grind off the backs a bit...

Cheers

[ChrisOlson]

Now there's an idea - thanks Chris, I hadn't thought of using roll pins. I'll check out what sizes are available tomorrow (the hole appears to be 3.5mm). Do you get them the correct length or do you have to grind off the backs a bit...

Those magnets have a 1/8" hole in them, which I believe is like 3.175 mm.  I use 1/8" x 3/4" roll pins.  I got a tool made to drive them into the rotors with that leaves .400" of pin exposed where the magnet goes on, then I grind the excess pin off on the back side of the rotor.

Usually, from driving the pin into the rotor it expands the top part of the pin a bit and you have to tap the magnet down over the pin with a wooden dowel.  Once you put them on those pins you can't get them off again without driving the pin out.

Here's a photo of a rotor I built a week ago for a 12G with all the pins in it.  It's pretty simple, really, and it works good.


--
Chris

[Flux]

I agree with the roll pin, you only need to restrain them in the radial direction. In the perfect world you would use stainless roll pins ( if they exist) but in real life you will never notice any lost flux with steel pins.

I just can't see it being worth the trouble countersinking the things and even if you did I suspect the loss of magnet material would more than offset any loss from steel pins even if you use stainless screws.

Flux

[gsw999]

Chris , do you build all your rotors with these pins or is it just the ones your using with your gearboxes ( higher rpm etc )

Thanks


Gavin

[bob golding]

I agree with the roll pin, you only need to restrain them in the radial direction. In the perfect world you would use stainless roll pins ( if they exist) but in real life you will never notice any lost flux with steel pins.

I just can't see it being worth the trouble countersinking the things and even if you did I suspect the loss of magnet material would more than offset any loss from steel pins even if you use stainless screws.

Flux

stainless roll pins do indeed exist. plenty on ebay at the desired sizes. rather than drilling holes in the magnets just fitting the roll pins on the outside edges of the magnet would be a bit easier. seem to remember someone on here doing that. that is my plan when i redo my rotors in the summer. one down each side so the magnets don't slide into each other and one across the outside edge for radial stability. giving up on the adhesive approach. will coat them with vinyl ester as waterproofing though.

[ChrisOlson]

Chris , do you build all your rotors with these pins or is it just the ones your using with your gearboxes ( higher rpm etc )

I've been pinning all of them, both direct drive and geared.  With wedge magnets I tried machining a lip into the rotor so the magnets had an outside edge to take the centrifugal force but I've had those come loose too.  They'll typically take 750-800 rpm on 10" rotors and they come loose.  With the pins I've run them up 2,000 rpm with no problems on my geared machines.

I wish the wedge magnets would come with pin holes.  I'm not too keen on drilling magnets because it opens the nickel coating on the magnet.

I've seen absolutely no difference in the flux using steel pins vs no pins.  I really don't think stainless pins are necessary when you're putting the magnets on a low carbon steel rotor.  That little 1/8" diameter pin does nothing, that I can tell, as far as the flux strength.
--
Chris

[Hilltopgrange]

The magnets I had at the time were plain without holes and I was using 2 per pole forced to sit in repulsion forming a capital T, I didn't want to depend on glue alone holding them. Pining them around their outer edges to hold them in the T shape would have meant accurately drilling maybe 6 holes or more per pole, with 64 magnets that would be a lot of machining.

The drilling of the magnets was really very easy, but doing 64 of them did take some time. The counter sinking was even easier and literally only took a few seconds per magnet. In your case only half of your magnets have the csk on the wrong side, it would take no more than 10 mins to do them, certainly much quicker than returning them. I tried every type of bit I could lay hands on inc quality masonry bits and they were useless it takes the glass cutting bit, they go through them like a hot knife through butter. It maybe the shape of the bit that makes the difference, they are similar to a spoon type cutter.


This machine has withstood all that our extremely wet and windy weather has thrown at them.
The exposed magnet from drilling was treated with epoxy and shows no sign of corrosion. I didn't pot them, just give them a couple of coats of agricultural paint and they look as good today as when they where fitted.

I have had magnets rust badly in the past when potted, I have even seen the plating on new magnets flake off just from handling them, I paint the magnets on all my machines now and corrosion is no longer an issue.

I used stainless screws as I was worried steel screws would rust and grow in diameter in our wet climate and possibly crack the magnet. I dint think the drilling has hurt them in any way, they have been flying now for about a 1 1/2 years without any problems. I am located in Northern Ireland near the coast and our climate is extremely wet and salty if they were going to corrode they would have done so by now.

At the time I got a good deal on the magnets they where less than half the price of pre-drilled ones so I got twice the amount of magnet for the price.
 
I will be building an 18 footer this summer and I will do it the same way again it has worked well for me.

Regards Russell

[bob golding]

The drilling of the magnets was really very easy, but doing 64 of them did take some time. The counter sinking was even easier and literally only took a few seconds per magnet. In your case only half of your magnets have the csk on the wrong side, it would take no more than 10 mins to do them, certainly much quicker than returning them. I tried every type of bit I could lay hands on inc quality masonry bits and they were useless it takes the glass cutting bit, they go through them like a hot knife through butter. It maybe the shape of the bit that makes the difference, they are similar to a spoon type cutter.

/quote]
hi Russell
been looking on ebay for suitable cutters. have you got a link to the cutter you used. what speed did you use? i am planning on using cutting fluid mixed with water. suds oil i have always called it. i would use stainless pins as they are cheap enough and  shouldn't corrode hopefully.

bob

[Hilltopgrange]

Hi bob these are the ones I used you can get better more expensive ones but these worked for me http://cgi.ebay.co.uk/6-PC-PIECE-GLASS-AND-TILE-DRILL-BIT-SET-KIT-/170509262074?pt=UK_Home_Garden_PowerTools_SM&hash=item27b324dcfa

I wouldn't use any mix that contains water as that might be asking for trouble with corrosion. Al I used was a bath of white spirit in a aluminium food tray like you get from a take away. If you cover the magnet with masking tape it makes the magnetic mud easier to clean off. Finish of by washing them with surgical spirit or thinners before applying the epoxy. I'm not sure of the exact speed of my vertical drill just put it to its slowest speed and try it on a spare magnet if you have one. Regards Russell

[gsw999]

Chris , do you build all your rotors with these pins or is it just the ones your using with your gearboxes ( higher rpm etc )

I've been pinning all of them, both direct drive and geared.  With wedge magnets I tried machining a lip into the rotor so the magnets had an outside edge to take the centrifugal force but I've had those come loose too.  They'll typically take 750-800 rpm on 10" rotors and they come loose.  With the pins I've run them up 2,000 rpm with no problems on my geared machines.

I wish the wedge magnets would come with pin holes.  I'm not too keen on drilling magnets because it opens the nickel coating on the magnet.

I've seen absolutely no difference in the flux using steel pins vs no pins.  I really don't think stainless pins are necessary when you're putting the magnets on a low carbon steel rotor.  That little 1/8" diameter pin does nothing, that I can tell, as far as the flux strength.
--
Chris

Cool , I watched some of your youtube videos , how are your 12g turbines doing?  have you noticed more power using the gearbox or does there need to be a high wind to get the most out of it.

Thanks

Gavin

[Flux]

In Russell's case I agree that screws were probably needed, magnets in repulsion try to flip, it's not the same with single magnets that tend to just move radially. In that case a simple roll pin should do without any screws or the need to countersink.

I am also encouraged by Russell's success with paint rather than potting, I have not really had any luck with potting magnets, it seemed on the face of things to be the logical way but experience has not born this out.  It seems as though the resin breaks away from the steel and invites capillary attraction to keep the whole thing wet.

Flux

[bob golding]

 i am still using the same set of magnets after 5 years. the plating has long gone, i have a test magnet stuck to the side of the bus which seems fine. what i did was dip them in  jenolite washed them off as per the instructions,then dipped them in galvafriod a zinc primer. i gave them 2 coats of this and so far the test magnet seems to be fine. that is 18 months in a coastal environment. if i manage to drill my magnets  without breaking them this is what i will use. i will get the rotors powder coated as well. thanks for the link Russell will order some and try it on my spare. i will use white spirits as a coolant then.

[frackers]

Status update...

Emails to CMS are either bounced or no reply. Does anyone have a working email address for them?

One of the magnets is broken The second one on the stack where you can't see it until starting to unpack to use.

Got some 1/8 inch roll pins and they fall through the magnet holes without touching the sides so the hole is not made to very high tolerance!

Getting a bit despondent - suffering mill withdrawal symptoms...

[zvizdic]

Epoxy painted afterwords

[ChrisOlson]

Emails to CMS are either bounced or no reply. Does anyone have a working email address for them?

I have never been able to get a reply by email from that outfit.  If you call them on the phone they'll usually talk to you.

One of the magnets is broken The second one on the stack where you can't see it until starting to unpack to use.

I've never received any magnets that were busted.  That's not good.

Got some 1/8 inch roll pins and they fall through the magnet holes without touching the sides so the hole is not made to very high tolerance!

I've never seen 1/8" fall thru without touching. They'll slide thru before you expand the pin by pounding it into the rotor hole, though.
--
Chris

[kenl]

Hi bob these are the ones I used you can get better more expensive ones but these worked for me http://cgi.ebay.co.uk/6-PC-PIECE-GLASS-AND-TILE-DRILL-BIT-SET-KIT-/170509262074?pt=UK_Home_Garden_PowerTools_SM&hash=item27b324dcfa

I wouldn't use any mix that contains water as that might be asking for trouble with corrosion. Al I used was a bath of white spirit in a aluminium food tray like you get from a take away. If you cover the magnet with masking tape it makes the magnetic mud easier to clean off. Finish of by washing them with surgical spirit or thinners before applying the epoxy. I'm not sure of the exact speed of my vertical drill just put it to its slowest speed and try it on a spare magnet if you have one. Regards Russell

UHHH (hand raised in the air) what is white spirit?

[Hilltopgrange]

White spirit is a paint solvent used as a substitute for turpentine.

Russell

[Ungrounded Lightning Rod]

Just have to work out whether I have countersunk north or south - the sensor in my new smartphone might tell me I suppose - would be nice to have a reference though.

Hang one by a thread, wait until it stops spinning, and see which direction the countersunk sides of the holes are on.

The magnet will align with the local horizontal component of the Earth's field with the north (= "north seeking") pole pointed toward the Earth's northern-hemisphere magnetic pole and vice-versa for the magnet's south pole.

If you're not too close to the area between a magnetic and the corresponding rotational pole your magnet will also be pointed roughly along the geometric north/south line also.  (You're not over a polar ice cap, are you?  B-) )

[Hilltopgrange]

I just hold a small magnet in my hand and go around the rotor, you should feel it alternate  push and pull your hand  as you go around.

[Ungrounded Lightning Rod]

I just hold a small magnet in my hand and go around the rotor, you should feel it alternate  push and pull your hand  as you go around.

Frackers' problem is not to identify relative polarity of various magnets, but to determine whether it's N or S on the countersink side, so he can order the correct polarity for the other half of his magnets.

You have to know the polarity of your small probe magnet to determine that, reducing it to the previously UNsolved problem.

[frackers]

Rather than screwing the magnets which would make use of the countersink I'll be using pins. Should have the rotors back from powder coating by the end of the week and I'll set the pins and do a trial run with a magnet or two. I think I'll use some slow cure epoxy under the magnets as well (belt and braces never hurts!!)

I'm still waiting on the replacement magnet, its not critical which pole the countersink is on now but if it is the same as the rest then at least I'll have a matching set!! According to the compass in my phone, the countersink attracts the south pole of the compass which I guess means it must be a north seeking pole on the countersink side. If nothing turns up I'll drill one of the surviving magnets with a glass cutting bit and use that.

The leading faces of all the new blades has now been cut, next is thicknessing and then the back profile. It sure is easier the second time round!!

Should all happen at the end of the week - new roof will be on the house, earthquake aftershock total will be up around 4600 (its 4549 tonight) and the 13 tons of concrete roof tiles should all be palletized and ready to sell. Might even get to finish the western red cedar blades