Pores/holes in Strat pup. magnets ?

[the great waldo]

I was just doing some work on a strat and noticed small holes in the bottoms of the magnets. I have noticed this quite often over the last 30 years. Does anybody have any ideas as to what causes this or could this be the difference optically between cast and sintered magnets ?

Cheers all

Andrew

[David King]

From what I know, which isn't very much, this is just typical of sand cast alnico. I'm not sure magnets are sand cast anymore, they might be cast into graphite molds. I still see the pits or voids on new magnets from time to time so perhaps it's more a matter of QC, someone pulls the ugly magnets off the assembly line these days?

Someone should do an examination of the crystalline structure of old magnets so see if there are any differences there. To do this one would polish the outside or a cross section and then etch the surface with nitric acid or similar and examine under a microscope. The grain structure will be fine or coarse depending on the cooling conditions in the mold. One would expect to see finer grain towards the inside of the magnet where cooling was slowed down.

Modern magnets might be significantly different if cooling was better controlled at one period or another.

[Down Time]

I have noticed the same thing. I ordered 500 magnets and maybe 50 had some pitting. I think it is just the luck of the draw. I don't it is anything more than a cosmetic issue. I think a slight pit in a magnet would not affect its performance.

[the great waldo]

I wasīnt really worried about the performance effect, I was curios if Fender used a different type of alnico, I have seen over the years quite a few strat pickups with fairly large chips knocked of the magnets.

Cheers all

Andrew

[Down Time]

Fender used to tumble the magnets to smooth the edges before assembly. In using this process chipping can occur. I have seen this on many vintage Fender pickups.

[the great waldo]

Fender used to tumble the magnets to smooth the edges before assembly. In using this process chipping can occur. I have seen this on many vintage Fender pickups.

Hi Down time

I did notice that, mainly on the bottom side of the pupīs, the sharp edges were deffinitely missing. I actually bought a stone tumbler to do the same thing, but thought again as there seemsīno point.

Cheers

Andrew

[Down Time]

I take a new uncharged magnet put in a drill press and slightly round the edge over with a honing stone. This makes the magnet easier to install into the flat work. I takes about 10 minutes to do six magnets. If you look on You Tube you can see a video of the Seymour Duncan factory using a grinding wheel to round over the rod magnets. I feel this can be a little to aggressive. I like a very slight round over on the magnets. If you look at some of the new Fender RI pickups it looks as if someone put them in a pencil sharpener. I don't like the look of that kind of severe bevel. I try to make my pickups look like a 50's and 60's Fender pickup without the chips.

[David King]

Vibratory finishing or tumbling should never cause any chipping. I think the chipping was caused by something else, perhaps rough handling or just the grinding to length.

[Electricdaveyboy]

I have rough sandcast rods wich chip verry fast wehn I tumble and some have those holes on the polished end and one I had was hollow.
Those magnets can look ugly but they sound good in my pickups.

[Down Time]

I have rough sandcast rods wich chip verry fast wehn I tumble and some have those holes on the polished end and one I had was hollow.
Those magnets can look ugly but they sound good in my pickups.

I agree, I was told by a major pickup manufacturer many years ago that the tumbling method Fender used is what caused the magnets to chip.

[David King]

Yes, in a big tumbler I can see that happening. Those have been mostly replaced with vibratory finishers for that reason.