Relapping Heads

evm1024

New member
I thought to start this thread to serve as a resource for those who are brave enough to give relapping a try.

Nortronics has this guide to head wear and relapping:

http://recordist.com/ampex/docs/repairtips/heads/nortronics.pdf

You might want to get a copy on your hard drive.

This thread could serve as a forum for our success and failures.

----------

Also, my tascam 38 has one good head (sync) and an older worn head on playback. I would like to get a new(er) 38 head to put in the sync position and move the current sync to the playback position. This would free up the worn head for relapping.

Just gotta find that newer head at a price I could afford.

Regards, ethan
 
I've not seen this guide before, but I have lapped a few heads myself, from my Otaro MX5050. I started with 600 grit wet sandpaper on an old bathroom mirror (the glass is for flatness), then moved to 15u and then 5u optical polishing sheets. Here's a few pics of the work... first one is before (of course), second one is after the 600 grit, and the final is all three heads (plus erase head which did not require lapping) mounting in the headstack after polishing.

Any questions, feel free to ask! :D

before.jpg


after.jpg


polished2.jpg


:cool:
 
Nice job!

These are great photos for us all to look at when the question of head come up. On the worn photo you can see the difference between the flat and the unworn head area. Do you recall how much the head was worn away?

The Noritronics guide says that the gap depth on typical heads is between 16 and 22 mils (1/1000") and that one should relap at 5 mils wear and at 10 mils wear.

So not to selves. When asking if your head is good measure the wear depth. Assuming that it has not been relapped before if there is more than 15 mils wear your head is good for relapping practice.

Regards
 
I thought to start this thread to serve as a resource for those who are brave enough to give relapping a try.

Nortronics has this guide to head wear and relapping:

http://recordist.com/ampex/docs/repairtips/heads/nortronics.pdf

You might want to get a copy on your hard drive.

This thread could serve as a forum for our success and failures.

----------

Also, my tascam 38 has one good head (sync) and an older worn head on playback. I would like to get a new(er) 38 head to put in the sync position and move the current sync to the playback position. This would free up the worn head for relapping.

Just gotta find that newer head at a price I could afford.

Regards, ethan

Ethan why not just get the worn head relapped and then reinstall it? The turn around time is only about a day.
 
Prior

The deck appears to have had the current sync head replaced at some point and the (bad) playback head appears to have worn through the gap length. I think that it is too far gone for a relape.

--Ethan
 
Me and a 12 year old Scottish friend...

... Finely got around to trying my hand at lapping a few 8 track, 1/2" heads that I picked up a while ago. Not sure which deck they come from. The headstack base is like that of my 38. All 3 heads are brass based like the rec and repro. The wires go to phenolic PCB rather than a header like the 38. Anyone know?

Here are 2 photos of the rec/sync head. A before and an after. Looks like a usable head. When I get the time I'll open up the 38 and pull those heads. I may build a header and try putting one of these heads in.

OK here goes: I did this on the kitchen counter, rinsing the sand paper and head frequently. Starting with 400 grit wet I followed the Norinco instructions to remove the keystone and establish a nice profile. Once the flat spots were all gone and things looked good I moved on to 600 grit wet paper. This took much less time to remove the 400 grit marks. When I thought there was enough of the 600 (perhaps 10 minutes) I moved on to a 1500 grit paper. I took another 20 minutes or so with this. I took extra care to not mess up the work that I had already done.

One thing tha I did do was to rotate the head 180 degrees at every rinse. THis was to make sure that my hand pressure was equal on both sides and top to bottom. I wanted whatever weirdness I was doing to cancel out.

The last photo shows the side of the heads. You might notice that the brass/epoxy at the head face might show the gap depth. Not sure of the construction inside but it was about 20 mils before I started.

Oh, I did use a caliper to measure the wear depth and came up with about 7 mils. It appears that theblown head on my 38 has a wear depth of 20 mils. This is consistent with the 20 mil gap depth figure that I've heard. wore later when I get it our and try a relap.

Regards, Ethan
 

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Very nice work! Hard to see the contour of the head in the first two pics, but the last one certainly shows off that beautiful curve. :cool: :p
 
I agree...nice work. Too scary for me yet, but I may have some spare heads here depending on what I do with my "parts or repair" 48.

That head reminds me of a Fostex E16 head...no edge slots.
 
I might even tackle that if there were no head slots but my deck has them so I'd be freaked about wrecking it. Nice work tho'.
 
Ethan,

This is good stuff! :)

The head doesn't look like an Otari, and it’s not the 38/48/58/TSR-8 type. It may be from an 80-8 or ATR-60/8, but not sure. SAKI and JRF both made aftermarket heads for Tascam decks. It doesn’t look like the SAKI for the 80-8, but perhaps the one for the 38. Any numbers or markings on it?

:)
 
Ethan,

This is good stuff! :)

The head doesn't look like an Otari, and it’s not the 38/48/58/TSR-8 type. It may be from an 80-8 or ATR-60/8, but not sure. SAKI and JRF both made aftermarket heads for Tascam decks. It doesn’t look like the SAKI for the 80-8, but perhaps the one for the 38. Any numbers or markings on it?

:)

I was quessing the 80-8 or 60/8 as that the headstack baseplate is like but not the same as the 38. The record head has a label but the whole headstack was not treated kindly so it is not readable. It is Teac and looks like the sync/record heads so I expect that these are Teac/tascam heads.

I'll post a photo of the baseplate and erase head later....

--Ethan
 
Edge relief slots are usually put in during lapping by JRF Magnetics to improve performance as the head wears again. They prevent the tape from lifting slightly at the edges.
I was just noting that it looked like a pic of an E16 head I saw in another thread. Many heads come factory with the slots cut too, like the heads on my 48 and 58.
 
Pulled the 38 headstack out

Starrting to look at the 38s headstack. This photo sucks....

However, the sync head is a newer head than the repro and erase head. Looks like I suspected. The sync head appears to have about 5 mils wear and the repro closer to 15. the color of the brass is different as well as the locktite.

the photo does show the pronounced flat spot on the repro head but does not show the places where the gap is blown through. I'll get some better photos later.

I have located a tsr8 headstack that (if the head is good) will replace the repro head and depending on how much wear get relapped.

These heads have edge relief slots but they are deep enough so as to not need any work during the relap.

Regards, Ethan
 

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Repro head test lap

Popped the repro head out. Remember that we know it is toast so this is a learning experience. Once you get the head off the base plate you can push it out of the shell. This head had about 18 to 20 mil wear and a pronounced flat spot. Looks like it has never been relapped.

Here is a photo before starting on it and one after 400 grit shaping. Notice how the already open gap open up more and in more places.... Also, notice how the edge relief slot has gotten smaller due to the amount of metal removed.
 

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When do you know that your heads are worn enough to warrant relapping?

No this is not the start of a disgustingly geeky joke:p
 
Hi

Hi Brian,

Give that noritronics pdf in the first post or 2 a read. It will tell you most everything that you need to know.

They suggest that you relap after 5 mils wear.

I have used a dial indicator to measure wear depth but I DON'T Suggest this as that it can scratch the heads.

You could measure the thickness of some tape and see how many layers just get trapped by a piece of plastic the head. Kinda like using the tape as a feeler guage (ifyou remember them).

Regards, Ethan
 
On to the next step.....

I picked up that TSR-8 headstack the other day. The erase head from it is less worn so I will swap that in place of the original. Wear here is in the plastic. I'll post some side by side later.

The TSR-8 rec/play head shows a little keystone and not much wear. Side by side with the 38 sync head they look to have about the same wear.

The question is to re-lap or not? I cols go either way. The pro for re-lapping is that the heads are not as smooth as I would like. The con is that this is the real thing. Mess up and I'm out $. But then again that is what all this trial and error has been about.

I think that I will get some measurements of wear depth and then decide if I want to re-lap (round the nose to tale out the flat/keystone) or polish with 30u then 9u lapping film. Or just leave them alone....

Let me know if this gets boring.

-Ethan

PS 38 is the first photo
 

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Boldly go....

OK, So I thought why not get rid of the keystone and see what you get. So I did.

There was only 3 to 4 mils wear so I started with the 600 grit rather than the 400. I figure that it would be less metal removed to smooth it out. It only took about 10 gentle minutes to shape the head. Note: this time I reshaped only in the nose area.
This came out very nicely. As you rotate the head looking at a reflection of a light you will see the reflection flatten out in flat spots and in general star a tight line in the curved areas. this tells you when you have the flat spots out. I rotated the head 180 degrees so as to be sure that my hand did not intoduce a bias. First photo shows the results.

Moving on to 1500 grit I again tried to work only in the nose area. 1500 is for removing the 600 grit "scratches". Another 8 to 10 minutes here with lots of washings, rotations and inspections. Won't actually get a mirror finish but it will become reflective with a hazy image. Photo 2 shows. hard to see the improvement but it is quite visible. Feels smooth under a finger.

Next is 12u lapping film (3M yellow). It might have been better to start with 30u lapping film but none here today. Just means more work. In a lapping file the abrasive is bonded to a mylar sheet. You can use quite a lot of downward force. Clean often and move to a new section when it loads up too much. You can feel if it is cutting. Now the head starts to take on a mirror finish. And it gets a silky feel under your finger. Photo 3.

Last is 9u lapping film (3m blue). It really did not take too much more time to put a nice shine on the head. Feels very silky. From the photo you can see that I ended up polishing outside the head. Quite sure that that is not a problem.

Regards, Ethan
 

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