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Old 30th May 2006, 10:15 AM   #1
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Default Steel for DIY driver

What grade steel is best to use for making your own drivers? I have seen grades like 1008 and 1018 and 12L14, but I've no idea of the difference. Also, for anyone who has done such a thing, where can I get steel cut into shapes for top plates / pole pieces/ back plates / etc? If anyone has any links to people's projects like this they would be much appreciated.
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Old 2nd June 2006, 04:46 AM   #2
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for cuts like that a machine shop is where you want to go. To make the magnet you can place it near a big electromagent. ferrite is what the magnet is normally made of. I'm sorry I have seen a few be made but I don't have links. For software Spead would be wonderful if you had access, I think its quite $$ for diy.
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Old 2nd June 2006, 04:59 AM   #3
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Iron is better than steel. Neo (neodymium iron boron) magnets are far more powerful than ferite ones. Depending on which type of magnet you use the design will probably be quite different so that would affect your design options. Iron is better but steel is generally much easier to cut on a lathe than Iron. If you use Neo magnets then you'll probably put the magnet inside a steel/Iron cup or "pot" then put a disc shaped pole piece on top of that. There's not much point to doing any of this unless you have some magnetic flux modeling software to optimize the design. There are some such programs that have a free trial period.

Oh, and about which steel to use, well as long as it's not stainless steel it will probably be ok.

Then you need to worry about the bobbin (voice coil former), voice coil (what kind of wire, how thick, how many layers...) , cone shape, cone material, surround, basket, what kind of glues to use etc etc etc...
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Old 2nd June 2006, 05:07 AM   #4
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I have been using femm 4.0 for the FEA modellign, it seems quite good for a free program (I think it is GPL or some other such public use license). I have also since downloaded the software for eMachineShop, which is a CAD program put out by an online machine shop place. You design your stuff, specify materials, tools, finish, etc and it quotes you a price for what you want done. It's kinda neat.

Re: magnets, I am definitely using NdFeB just because there's no reason not to, the cost of having parts custom machined is well in excess of the magnet costs, I wouldn't save much by going to ferrite. My only problem will be assembling the motor with pre-charged magnets as I read NdFeB is brittle.

Right now I am most worried about where to source the VC from, mine is going to need to be fully custom for what I want. I hope I don't have to order a small run
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Old 2nd June 2006, 05:12 AM   #5
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the one video i seen on tv showed them putting the assembled magnet/motor/frame in a device(electromagnet) to make it a magnet. The cone, spider ect was added later.... Just an idea. For aligning the coil from the inside, removing shims then adding the dustcap.
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Old 2nd June 2006, 06:42 AM   #6
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Quote:
Originally posted by speakerguy79
I have been using femm 4.0 for the FEA modellign, it seems quite good for a free program (I think it is GPL or some other such public use license). I have also since downloaded the software for eMachineShop, which is a CAD program put out by an online machine shop place. You design your stuff, specify materials, tools, finish, etc and it quotes you a price for what you want done. It's kinda neat.

Re: magnets, I am definitely using NdFeB just because there's no reason not to, the cost of having parts custom machined is well in excess of the magnet costs, I wouldn't save much by going to ferrite. My only problem will be assembling the motor with pre-charged magnets as I read NdFeB is brittle.

Right now I am most worried about where to source the VC from, mine is going to need to be fully custom for what I want. I hope I don't have to order a small run

The Neo magnet will SMACK down into the pot, you will have to have a very precise positioning method to keep it from slamming to the side also, while the glue dries. To keep it from smacking down hard when you put it in the pot you could have a hole in the bottom of the pot and say a stainless steel bold that you unscrew to lower it down. That's just one solution, shouldn't be too hard to think of one that works for your particular sitiuation...

You could find out what voice coils are available, find the one close to what you want, then design the rest around that rather than paying a shop to do the setup. The magnet does not need to be precisely the right width, just needs to be narrower than your voice coil with a little extra margin and approximately the right height, you can make the pole piece wider than the magnet without much flux strength loss.
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Old 3rd June 2006, 02:43 PM   #7
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Default reply to original question

hi ,

the grade of steel directly refers to the carbon percentage in the steel ie mild steel runs about .18 to .25 % of carbon quantity
1008 = .08%
1012 = .12%

lower carbon = better gauss - in my openion very driver and
/ use / specific - why explaned later below

diy ing vs 1008 etc :-

low carbon steel is soft requiring good and delicate tooling and finishing on grinding machines after intial lathe cut , 1008 is in my openion often mentioned and used when the plates are forged

which is the norm of the day as 90 % of the plates are oem supply from either China or India , and numbers are large

during forge forming the carbon content raises a bit therefore if a low carbon steel is used intially it is better ( and also soft steel is required for forging - helps the forming process )

for diying in my openion mild steel is fine its normal lathe job for starting intially on making own drivers
ofcourse as you go up on quality operations will increase

I have extensivly measured in professional low frequency drivers that :-

forged motor structures with 1008 steel and a clone motor structure with mild steel there has been no loss in gauss where as tightly machined motor structures have measured to have higher gauss ( this has been my own physical measurements and may be debatable but I am siting what I have measured accurately , though my mild steel selection and machining process is extensive )

this changes in the case for eg professional tweeters where due to other technical reasons - effect on vc inductance during operation in high frequencies with relation to the equal ditribution of a very high gauss motor structure required as a design criteria for these drivers

low carbon steel is essential

for further technicalities on motor structures , magnetic field instabilities and related distortion , sources of distortion due to mechanical properties of a transducer will be a good read for you - all of which I have written about now and then please search the threads

suranjan das gupta

transducer design engineer
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Old 3rd June 2006, 04:10 PM   #8
renfrow is offline renfrow  United States
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One thing you might try is buying bucking magnets to use as your driver magnet. Parts Express has some, here's one: Bucking Magnet.

Good luck on this!

Tom.
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Old 4th June 2006, 12:29 AM   #9
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Well you could use a bucking magnet. But since i'd figure you're trying do make a really nice driver as the costs of it would seem to be quite high. What about a huge neodymium magnet.

http://www.kjmagnetics.com/ This place has many magnets in all shapes and sizes.

This magnet here

http://www.kjmagnetics.com/proddetai...od=MM%2DD%2D60

I guess something like this could work as it already has a rudimentary pole piece but only if your driver was smaller.
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