Invent Design Make

Step 3 – Find New Magnets

This is probably going to be a tricky bit.  I went to elaborate lengths to acquire some neodymiums that were an exact dimensional match to the old ferrite ones.  However I have come to the conclusion that this may not have been strictly necessary.  You could, for example experiment with a number of bar shaped magnets of appropriate proportions, say having 5 or 6 of them replace a single ‘arc segment’ shaped magnet.

For reference here is the dimensions of the arc segment magnets necessary for the Bosch PSB24 VE-2

Remember you will need an opposing pair – so one that is polarised North – South along the arrow shown in the diagram and one that is the other way round (South – North).  This is important! If you have two magnets polarised the same way it will not work.

Other considerations

The material of the magnet is important.  We want rare earth magnets because they are super strong. Neodymium magnets, are a kind of rare earth magnet. Luckily the material used in rare earth magnets really isn’t that rare at all, and with new manufacturing techniques the price has come down quite a lot in recent years (though still not enough to be found on any but the highest quality motors).

So we want Sintered NdFeB (or neodymium) magnets… It will need to be able to withstand a bit of heat, which, neodymium traditionally is not that great at.  There are many types or grades of neodymium though. Being rated by a number (which is roughly equivalent to its strength) and a letter (which denotes its resistance to heat). The ones I opted for, for example, are:

N 40 SH

40 is an indicator of the flux density and SH means it withstands 150 degrees C before it starts to demagnetise. Standard N40 magnets start to demagnetise at just 80 degrees C. This is a link to a useful “table of grades” – sorry this website expired.

A Sintered NdFeB N40SH Arc Segment magnet, coated with Nickle then Copper then Nickel again (Ni-Cu-Ni). Lovely.

Leave a comment to let people know if you attempt this, and how you get on acquiring magnets.  If anyone is interested (in the UK) I have a few left over from the drills I have converted.

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Responses to 3 – Find New Magnets

1. Andy
   November 15th, 2010 at 8:01 pm

   Hi
   interested to read about your fix for the Bosch drill – thanks for posting it.
   Could you tell me where you got your new magnets from – or can you sell me your spare ones pls!
   cheers
   Andy


2. Bongo
   November 16th, 2010 at 9:48 am

   Hi Andy,
   I am afraid I have used them all up now for various projects and more drill fixes.

   I forget the exact place, but I imported a bunch from a Chinese firm. But there was a long wait on the delivery. You may well be better off considering some of the UK distributors like this http://e-magnetsuk.com/ or http://www.first4magnets.com/?gclid=CPaLptH2pKUCFQhO4Qod4Vg1jg – who probably will all have the magnets you want custom made and delivered from China, but they have the contacts and supplier all sorted ready.

   Hope that helps – let us know how it goes.


3. Andy
   November 16th, 2010 at 7:41 pm

   cheers I’ve emailed them


4. Bongo
   November 16th, 2010 at 7:45 pm

   Good stuff, let me know what they say. And feel free to use the diagrams & measurements here / refer them to this page.


5. Andy
   November 16th, 2010 at 8:08 pm

   Thanks again, I did put a link to this page in….my only experience of magnets is with a travel chess set so I’m just following instructions….
   what exactly do these magnets do – make the drill more powerful?
   If so why didn’t Bosch use them in the first place…?
   Also will a stronger motor be too much for the other components in the drill? Someone else posted that they burned the armature out, is it worth just replacing like for like (ferrite)…assuming i can find replacements (one of the originals is cracked).
   By the way, if you know of a way to repair the batteries too then you could be onto a real moneyspinner …..


6. Bongo
   November 17th, 2010 at 9:53 am

   Andy,
   You can expect more power from the neodymium magnets, but in practice you would probably only notice an increase in battery life – because the power is so good already. The reason neodymium magnets are not really found in anything but very expensive machines (stuff like high spec military motors), is cost. But this is changing quite quickly now as manufacturing and processing techniques improve, price of neodymium magnets is becoming less of an issue. The only other consideration is the heat resistance of neodymium, and I talk about that in the article…

   Also will a stronger motor be too much for the other components in the drill?

   I have heard of people going through a few replacement motors on this drill before the drill drive gears or some other part breaks. But I guess it depends how you use it. Personally I never use it without the torque slipper (at least on the strongest setting). That way if the drill bit catches, you don’t end up with a sprained wrist! As the motor with the ferrites has plenty enough power (with a full battery) to make the torque slip, you would technically be putting no extra strain on the gearing. Just go carefully in hammer mode, which has no slipper clutch protection, and don’t go far beyond the official drills drilling specs. (wood 30mm, steel 13mm and concrete 15mm – though sticking below that requires far greater restrain, and a higher level of ‘boring’ than I could ever manage).

   Even if the gears give up on you, the great thing is that there are plenty of these drills knocking about, that have a shot motor but perfectly good gear chain – you can get a replacement for close to £10 on ebay and transplant in your super motor.

   Saying all that, you could just as easily replace them with ferrites, and if you clean it up, grind down the motor can and stick it in right, it should still work fine. But if you are going to all that trouble anyway, why not go for a super motor…

   As for the battery, that is a different kettle of fish – there are ways to ‘re-awaken’ sleeping cells, by ‘zapping’ them with a 12V lead acid battery, but this is a lot of faff, slightly dangerous, and will never give you much more than a handful of extra uses before they stop taking a charge again. Unfortunately with our current technology (as far as I am aware) after a certain number of cycles the NiHi batteries just die a death…


7. Andy
   November 17th, 2010 at 5:29 pm

   Hi Steve
   cheers again for your help. I’m struggling to find these magnets – but still waiting on a couple to get back to me.
   You mentioned about using a series of smaller magnets…would the ones posted below do it….if so would i still need to make the two sides opposite polarity? or could i just fill the motor casing with these…

   Andy

   http://www.magnetukonline.com/products.asp?v06en0tr=EE&v06T4172=FL&v06cntr=D


8. Bongo
   November 17th, 2010 at 5:42 pm

   I don’t think those would be very ideal at all as they are spherical. Rectangular magnets would be better. At just 2mm thickness, you would also have a very big air gap – bad news! The air gap makes a huge difference. Doubling the air gap between the magnets and the rotating armature more than halves the power. The arc magnets I got were 4.5mm thick.

   If you do go that rout, you still want to flip half of them over, though that would not be such an issue if you went with little bar magnets instead of arc, as they could easily be flipped over. Whatever you go for though, you do need to make sure they are magnetised in the correct orientation: not along the length, but through the thickness (as in the diagram).


9. Scott
   January 9th, 2011 at 5:54 pm

   People in the US might try http://www.kjmagnetics.com/custom.asp. They can make custom magnets as well.
   Hope that helps someone! :)


10. daniel
    February 17th, 2013 at 9:19 pm

    Hi, im looking for a Bosch psb AS my old drill was stolen(without the charger…).
    The arc shaped magnets seems habe to be custom made so they are pretty expensive. You wrote hat one could usw 5 To 6 bar shaped ones. I found some but they are 5mm thick, and 10 wide, could they fit into the Motor case? Do you know of some one who has tried it with man bar shaped magnets? Thanks for the documentation.
    Greetings from the blackwoods:P
    Daniel


11. Shaylee Packer
    January 6th, 2021 at 3:37 pm

    It was mentioned that rare earth magnets are super strong. My brother is coming up with a more convenient way to hang his bike in the garage and is wondering if Neodymium magnets will be strong enough to do the trick. He wants to essentially click it into place, then be able to just pull it down when he wants to go riding. I will have to let him know that these type of magnets are very strong.