Project "Groove Scribe"- A DYI stereo 45/45 head.

[emidisc]

Not sure this of any use to you guys busy winding coils! but an old guy in an electronics shop when hearing me enquire about coil winding said back in the day they used to keep the wire taught on the bobbin by passing it through a slit(razor cut) in a piece of sponge as opposed to direct from the reel.

Emidisc

[Fatrecco]

very good discussion

I got two of these ring-magnet 40x23x6mm. This is my plan. Could it work ? Will the steel go in saturation (but not in seen in Femm Simulation)??

coil1.jpg

[Fela Borbone]

Hi Fatrecco,
It seems that you are simulating in planar inzstead of axis simetric (see project settings) .axis simetric is draw using the 0 in the vertical axis for simetry and boundary of the simulation. In commecial devices is usual to work near saturation or t e boss will complain for the waste of material!

[Fela Borbone]

Hi

[Fela Borbone]

Hi Bryan,
This magnet setup loooks weird, did it came in te original design?

[Fela Borbone]

And the shield seems to be doing agood job, but simulations are just a clue, not a statement

[Fela Borbone]

The red line is 1 cm wider than theFB magnet and I made the plot in a different way tbis time shows when te peak is negative or positive. as is closer to the magnet (0.5 mm) peaks are higher

[Fela Borbone]

I can send you te project by mail ,I cant post it here. so you can load femm and change parameters and dimensions in your computer..fun garateed!

[EpicenterBryan]

If you put a magnet near them you will magnetise the cores of the head, which in turn will affect frequency response.

That's a damn good point. The funny thing is I always thought the reason for demagnetizing heads was because they could slightly erase (most noticeably at HF) the source tape with each pass. Damaging the tape by playing it was to be avoided.

Now I have to pull out a book I bought 20 years ago at a library book sale. I thought it was interesting to have but never read it...

IMG_4110[1].JPG

I had a mini tape recorder when I was a kid. When you went into record, it moved a small magnet onto the tape ahead of the one any only record / play head. So there was not an actual erase head, just a magnet to mess up the tape in front of the record head.

I think it had a whopping 5 transistors in it too.

Bryan

[EpicenterBryan]

Angle affects the "usefullness" , as its sine is multiplied to yield the zones of the analized line that will generate signal.
In this plot, the x means the length of the simulated line. The black lines marks were the edges of the ring magnet are.green shows all flux avalaible.red is the sine of the incidence angle( escaled to fit in the graphic) ...
and the black is what really matters, the length of this line where the coil will be producing signal.
Conclusion. the flux density is not impressive but not bad for a"bare magnet".the good news is that the magnetic "fringe" is narrow. So, in my opinion, the coil( or coils,if you use 2 opposite winded ,one on each peak) have to cover the peak plus the expected displacement at each side,to work at its best

OMG, I am so thankful for your inputs Fela. This helps so many of us to take some of the mystery out of why we have experimentally found more signal being generated not in the center, but further to the edge.

So in this simulation, what is the length of the magnet?

Bryan

[EpicenterBryan]

Total curve ball idea regarding the tape heads! Awesome!

I love to throw you curve balls Bennett.
Let us know how this goes. And you have a tape head ready to go! Awesome!!!!

Bryan

[EpicenterBryan]

Hi Bryan,
This magnet setup loooks weird, did it came in te original design?

Yes, that's the original driver many of us are messing with. I did a destruct disassemble on one after messing it up by trying to plate the whole thing in copper. That's when I discovered the opposing magnets and the steel washer...

You can find photos on page 9 of the thread here:
http://www.lathetrolls.com/viewtopic.php?f=15&t=5371&start=160

Bryan

[EpicenterBryan]

This magnet setup loooks weird, did it came in te original design?

Yep, that's how the stock driver is set up. I'm pretty sure I measured things correctly. And I got the data about the polarity of the magnets and stuff from taking one apart...
Here is the link to page 9:
http://lathetrolls.com/viewtopic.php?f=15&t=5371&start=160

Bryan

[EpicenterBryan]

And the shield seems to be doing agood job, but simulations are just a clue, not a statement

Fela, I can't thank you enough for your contributions. I am a guy who learns buy doing - or seeing. I can read about how things work, but unless I can convert it into something I can visualize, many times I don't fully get it. I think there are many people like me out there, and I'm sure I speak for them in that we express our appreciation for your efforts on this project - and helping us to understand invisible things!

Many of us speak different languages. Translating text back and forth can cause confusion. But a picture helps us all understand. Thank you.

Bryan

[Bahndahn]

These simulations are awesome, Fela!

If only the coil could be wound such that it passes through the flux lines on the outside of the magnet where many lines are seen at 90ºs to the vertical. I could machine a little coil overhang device to do it, I imagine, but it would be some tiny work. It might be worth it. Damn I wish there was more time in a day!!

[dimi751]

Bryan,fella,ciuens,Mark and others

You guys are awesome, very interesting to read the
The experiments you are doing even though I have no clue on the technical stuff, it's still interesting.

Dimi

[Fela Borbone]

So in this simulation, what is the length of the magnet?

Bryan

your wellcome, dimensions are (if not mistaken) the same as the draw you published. The grid size in first pic is 1 mm.

[EpicenterBryan]

The red line is 1 cm wider than theFB magnet and I made the plot in a different way tbis time shows when te peak is negative or positive. as is closer to the magnet (0.5 mm) peaks are higher

Let me make sure I understand. The line is 1cm (10mm) longer than the magnet on each end. And there is a peak at 10mm and at 22.5mm (about). The magnet is 12.7mm long so the first peak is at the bottom edge of the magnet, and the next one is 0.2mm before the top edge of the magnet. I think that 0.2mm may be me reading the 22.5mm number off the chart. So there really is a peak efficiency if the split coils do sit right at the edge on both ends.

It does bother me a little bit that there is not a match on the field strength top to bottom. When you send the file I'll look at possibly putting an metal ring on the top and see if that balances the two ends.

0.5mm is darn tight tolerances though for a home made guy. I'm not sure that will be attainable.

Thanks Fela!

Bryan

[opcode66]

You may want to check out my thread...
http://lathetrolls.com/viewtopic.php?f=15&t=5250&p=38347#p38347

[Bahndahn]

To elaborate on a mention previous about accessing the magnetic field outside the magnet, I made an image to show what I mean.

A pushrod with a little disk could be machined [from aluminium] such that a cylindrical section would extend over the top of the magnet. Soldered to the circumfrence [aluminium beverage can thickness] could be a cylinder around which the coil could be wound.

There is certainly way higher flux density out there, which has me thinking it could be worth it.

In the image the orange lines outline the aluminium, the yellow line is the position of the coil, and the other stuff is the same as the FEMM analysis shown previously.

FluxDensityOverhang.png

Just a thought.

On the other hand, this sort of thing isn't found in professional cutterheads, so its probably overkill.