Magnetic Tensioner (heads up for the Brits)

[the great waldo]

Hi Jimbosticks

What do use to demagnetize the plate ?

Cheers
Andrew

[Stratz]

Maybe I can get a beater MT-100 for small dollars on eBay, for science.

Joe, this seller had 3, sold one MT300 best offer for $100 and has one 300 and one 800 left.

Rob


1 USED TANAKA MT-300 MAGNET TENSION UNIT UNB | eBay

1 USED TANAKA MT-800 MAGNET TENSION UNIT UNB | eBay

[Jimbosticks]

Hi Jimbosticks

What do use to demagnetize the plate ?

Cheers
Andrew

I should say first... I've been calling it a plate, but the part I wanted to demagnetize is actually a round ferrous disk with a center hole. A washer if you will.

I needed a demagnetizer, so I made one from an old 120Vac vibrating air pump from a broken desoldering machine). It's just a laminated core transformer with the "I" portion of the core discarded, and the "E" portion (and winding) remaining. I connected a line cord to the winding, and plugged it into the outlet.

Now the problem was HOW to apply the demag field to the ferrous disk. I found that applying the demagnetizer to the face of the disk did not work. Iron filings still clung to the disk in clumps.

I put a iron nail on the center post of the demagnetizer, and then passed the hole of the disk over the nail, until the disk rested on the demagnetizer core. Then I slowly pulled the disk off the demagneitizer and nail. That did the trick. The manuever couples the alternating magnetic field to the disk, just as if you had wrapped a winding around the washer and energized it with AC.

I think you can probably do the same thing with a commercial demagnetizer.

[the great waldo]

Hi Jimbosticks

Thanks for the info, I should be able to knock something similar up.

Cheers
Andrew

[Joe Gwinn]

Joe, this seller had 3, sold one MT300 best offer for $100 and has one 300 and one 800 left.

Rob


1 USED TANAKA MT-300 MAGNET TENSION UNIT UNB | eBay

1 USED TANAKA MT-800 MAGNET TENSION UNIT UNB | eBay

Thanks for the pointer.

Now he wants $180 for the 300 or the 800. Think I'll wait until a MT-100 comes up.

[Joe Gwinn]

Joe, this seller had 3, sold one MT300 best offer for $100 and has one 300 and one 800 left.

Rob


1 USED TANAKA MT-300 MAGNET TENSION UNIT UNB | eBay

1 USED TANAKA MT-800 MAGNET TENSION UNIT UNB | eBay

Thanks for the pointer.

Now he wants $180 for the 300 or the 800. Think I'll wait until a MT-100 comes up.

[Joe Gwinn]

When you turn the large black knob, that moves a permanent magnet inside the box towards or away from a ferrous metal plate which is connected to the backside of the external pulley. ... The positioning of the permanent magnet relative to the plate controls the tension.

The units DO increase in tension as the plastic threads associated with the adjustment knob wear. These threads are cut into the plastic faceplate. When you replace the plastic faceplate the tension levels for a given setting return to the original values. That is because the magnet no longer tips inward towards the metal plate. I don't know what the cream colored plastic is. Maybe PVC or ABS. Personally, I think the faceplate should be made from aluminum, or the threads should be implemented with an insert made from brass. I have already designed such a faceplate, but do not have the machinery needed to cut the fine, large diameter thread.

Yes, all true, and I do understand how it works. The details are in Tanaka's patent (US 4,526,329), which is very informative.

Patent US4526329 - Magnetic tensioning device - Google Patents

There are two distinct issues being discussed here. First is the lumpiness due to magnetization of the steel plate. The other is wearout of the threads on the tension control knob. This issues have nothing to do with one another. Above, we discuss only the knob. Below, we discuss only the steel plate.

The ferrous plate is not normally magnetized. There is no reason for it to be.

While it is true that the plate is not normally magnetized, it is not true that the plate can be made of a magnetically soft material, as discussed later.

In another posting, you mentioned that it was a washer made of thin steel. What color is the washer? Blue to dark blue?

Look, I don't know if the Tanac MT-100 classifies as a "hysteresis brake", but after 10 years of working with, and repairing them, I know what goes wrong. When the wire doesn't pull through the pulleys smoothly, the problem is spot magnetization of the plate. And the solution is to remove and demagnetize that plate. I've done that on at least 5 units, with great success. That is also why I think a plate made of soft iron or some other material with low retentivity would be advantageous. Actually, I'm not certain if it isn't made from iron already. I just know it gets magnetized. And that makes for "lumpy" wire feeding.

All such tensioners utilize a braked capstan of some kind. The braking can be implemented in various ways, one of which involves magnetic hysteresis. Tanaka uses hysteresis, as his patent makes quite clear.

The drag is generated by the magnetic field from the permanent magnet forcing the metal of the washer to be permanently magnetized this way then that way and back to this way, all of which consumes energy (the washer gets hot). This drag effect does not depend on rpm. As the permanent magnet gets closer to the washer, the field at the washer grows, as does the volume of washer metal whose magnetization is being flipped back and forth on every turn of the capstan.

I can't imagine how feeding some heavy wire through the wire pulleys, OUTSIDE the box, is going to fix what is going on INSIDE the box. Maybe you can explain that to me. Maybe continuous high speed operation will gradually demagnetize the metal plate. However, our machines go idle overnight, and over the weekend. And our operators have to change wire gauges and tension settings all the time. It wears the threads.

If one has been running at a heavy tension, the magnetic field at the washer will be large, and a large permanent magnetization footprint will be impressed on the washer. If one later turns to a lower tension, the field at the washer will be less, and will not (completely) erase (in the sense of a tape recorder) the larger footprint. If one runs with heavy tension and gradually slacks the tension as the capstan turns, one will be able to erase the larger footprint without disassembling the unit. I dimly recall a discussion of this in one of Tanaka's patents.

[Stratz]

Thanks for the pointer.

Now he wants $180 for the 300 or the 800. Think I'll wait until a MT-100 comes up.

It's not what he wants, Isn't what he'll take.
The last MT-300 that he sold was listed for $180 with the "make offer" option. He accepted an offer of $100.

[Joe Gwinn]

It's not what he wants, It's what he'll take.
The last MT-300 that he sold was listed for $180 with the "make offer" option. He accepted an offer of $100.

Ahh.

The other problem is that the MT-300 is a bit oversize for pickups, especially for say #45 wire. I'm assuming I can fix and use it.

I suppose I can offer $75 and see what happens.

One question. What does a replacement plastic tension knob cost from Tanac? This is key. Maybe Jimbosticks knows.

[Jimbosticks]

................ I do understand how it works. The details are in Tanaka's patent (US 4,526,329), which is very informative........
There are two distinct issues being discussed here. First is the lumpiness due to magnetization of the steel plate. The other is wearout of the threads on the tension control knob. This issues have nothing to do with one another. .......While it is true that the plate is not normally magnetized, it is not true that the plate can be made of a magnetically soft material............. you mentioned that it was a washer made of thin steel. What color is the washer? Blue to dark blue?............All such tensioners utilize a braked capstan of some kind. The braking can be implemented in various ways, one of which involves magnetic hysteresis. Tanaka uses hysteresis, as his patent makes quite clear............The drag is generated by the magnetic field from the permanent magnet forcing the metal of the washer to be permanently magnetized this way then that way and back to this way, all of which consumes energy (the washer gets hot). ...............If one has been running at a heavy tension, the magnetic field at the washer will be large, and a large permanent magnetization footprint will be impressed on the washer. If one later turns to a lower tension, the field at the washer will be less, and will not (completely) erase (in the sense of a tape recorder) the larger footprint. If one runs with heavy tension and gradually slacks the tension as the capstan turns, one will be able to erase the larger footprint without disassembling the unit. I dimly recall a discussion of this in one of Tanaka's patents.

Sir:

You said the issues have nothing to do with one another. In my experience they do! The worn threads allow the magnet to come in closer contact with the plate/disk/washer. If the unit is sitting idle, the washer develops a magnetic pole or spot which interferes with the smooth operation of the machine.

It was you said the washer was steel, not me! I said it was a ferrous metal. By asking me if the washer is blue or dark blue, are you suggesting it gets so hot that it acquires the color of a tempered steel? Because it is grey colored on every unit I have ever disassembled, as well as new replacements. I've never observed the disk to get hot - although I suppose it could cool off enough by the time I got the case open, to not be noticed. If it DID get hot enough to discolor the "steel", it would melt the plastic backing. And I have never observed that.

You said this unit utilizes a braked capstan of some kind. I've never head the word "capstan" used to refer to anything but a driven metal drive spindle impressed against a rubber roller, such as in a tape recorder, to regulate speed. There is no such thing happening in the MT-100. The wire being tensioned passes through an externally mounted pulley, which is mechanically coupled to the interior washer. The only linkage from the knob to the washer is the magnetic flux.

You said the washer could not be made of a magnetically soft material - presumably because it is a hysteresis device. However just because Tanaka holds a patent on a hysteresis device, does not mean the principle is coming into play on this machine. Maybe you are correct about this. However, I haven't found any "large permanent magnet footprint" impressed on the washer. Just random spots on old machines. Also, I find that the only way to repair these units is to replace the disk or demagnetize it. Newly purchased disks are NOT magnetized. You can see that by applying some powdered iron filings to the disk.

You suggested the washer could be demagnetized by running the machine at high tension (with a heavy gauge wire), and while running, gradually reduce the tension setting, moving the magnet away from the disk. That's interesting. I will have to try that. Although the process is not readily amenable to our day to day operation. The bobbins we wind have so few turns on them, I doubt I'd have time to gradually turn the tension knob back out. I'll have to make a larger bobbin to use as a takeup reel.

I am no college professor, scientist, or engineer. I have been out of school almost 40 years, and I may be misunderstanding the way this unit operates. If so, I apologize. However, I do know how to fix them. And the main purposes of my original post were to shame Tanac into responding to the problems, and tell people here how they can correct them. There is nothing in the operators manual of the MT-100 which describes the principle of operation. Tanac does not tell owners how to correct problems of this sort. In fact, neither the USA or Japan support staff would even acknowledge that the problems exist! When I emailed my description of the problems and the steps I've taken to fix them, they did not even have the courtesy to respond.

While this is an interesting forum, I'm not going to return to read or respond to any more posts. Nothing personal. It's just that I'm not in the music business or a hobbyist in the field of music. I just stumbled across this forum while looking for the solution to an unrelated problem. Having struggled for so long to figure out how to fix the MT-100, I felt I should pass along my information, in case it helped others. Thanks for listening!

[ken]

Let's say we already own these tensioners, and our tensioners have these issues we mentioned above.
How can we retrofit this unit to make it more useful for us?

ken

[Joe Gwinn]

Sir:

You said the issues have nothing to do with one another. In my experience they do! The worn threads allow the magnet to come in closer contact with the plate/disk/washer. If the unit is sitting idle, the washer develops a magnetic pole or spot which interferes with the smooth operation of the machine.

The point is that entirely different physical causes are simultaneously at work, and each cause must be understood and solved on its own terms.

It was you said the washer was steel, not me! I said it was a ferrous metal. By asking me if the washer is blue or dark blue, are you suggesting it gets so hot that it acquires the color of a tempered steel? Because it is grey colored on every unit I have ever disassembled, as well as new replacements. I've never observed the disk to get hot - although I suppose it could cool off enough by the time I got the case open, to not be noticed. If it DID get hot enough to discolor the "steel", it would melt the plastic backing. And I have never observed that.

Actually the patent implies that the washer is spring-tempered steel. There are two kinds of spring-tempered steel in wide use. One kind is blue to dark blue. The other kind is indeed gray to straw colored. The colors are a result of the tempering process; the metal comes that way, and is not a result of overheating in service. While the washers will get warm in service, to a degree proportional to the product of tension and winding RPM, they will not get nearly hot enough to cause tempering colors to appear. I don't know that a MT-100 ever runs with enough tension for the warming to be noticed.

McMaster-Carr

McMaster-Carr

You said this unit utilizes a braked capstan of some kind. I've never head the word "capstan" used to refer to anything but a driven metal drive spindle impressed against a rubber roller, such as in a tape recorder, to regulate speed. There is no such thing happening in the MT-100. The wire being tensioned passes through an externally mounted pulley, which is mechanically coupled to the interior washer. The only linkage from the knob to the washer is the magnetic flux.

The word "capstan" is commonly used for such things in mechanical engineering, where a string or tape is wound around and driven or retarded by a cylindrical roller of some kind. The term comes from the nautical world.

You said the washer could not be made of a magnetically soft material - presumably because it is a hysteresis device. However just because Tanaka holds a patent on a hysteresis device, does not mean the principle is coming into play on this machine. Maybe you are correct about this. However, I haven't found any "large permanent magnet footprint" impressed on the washer. Just random spots on old machines. Also, I find that the only way to repair these units is to replace the disk or demagnetize it. Newly purchased disks are NOT magnetized. You can see that by applying some powdered iron filings to the disk.

This confuses the current state of magnetization with the ability to be magnetized.

Consider a slug pole made of 1008 mild steel and a cylindrical magnet made of alnico but not yet magnetized. They are both cylinders of a ferrous alloy, of approximately the same physical dimensions. Put them side by side in an industrial magnetizer and push the big red button. What will happen? The alnico will become permanently magnetized, while the slug will not. Yet both were initially unmagnetized.

The alnico exhibits large magnetic hysteresis, while the 1008 steel does not, so alnico can be a hysteresis brake material, while the 1008 cannot.

There is a specialized alnico alloy called Hysterloy that is used for industrial-size hysteresis brakes and couplings: Dexter Magnetics - Magnetic Coupling, Magnet Coupler, Linear Coupling, Rotary Coupling, Eddy Current Coupling, Hysteresis Coupling.

You suggested the washer could be demagnetized by running the machine at high tension (with a heavy gauge wire), and while running, gradually reduce the tension setting, moving the magnet away from the disk. That's interesting. I will have to try that. Although the process is not readily amenable to our day to day operation. The bobbins we wind have so few turns on them, I doubt I'd have time to gradually turn the tension knob back out. I'll have to make a larger bobbin to use as a takeup reel.

Use a loop of wire or fishline. For fishline, use a weaver's knot to prevent snagging. Or melt the ends together to form the loop.

I am no college professor, scientist, or engineer. I have been out of school almost 40 years, and I may be misunderstanding the way this unit operates. If so, I apologize. However, I do know how to fix them. And the main purposes of my original post were to shame Tanac into responding to the problems, and tell people here how they can correct them. There is nothing in the operators manual of the MT-100 which describes the principle of operation. Tanac does not tell owners how to correct problems of this sort. In fact, neither the USA or Japan support staff would even acknowledge that the problems exist! When I emailed my description of the problems and the steps I've taken to fix them, they did not even have the courtesy to respond.

If you wish to know the principles of operation, a good place to start is to read the patent.

Early in your conversation with Tanac, I bet they tried to tell you what they thought was going on. What did they say?

Nor do I understand why one cannot simply replace the worn plastic tension knob.

While this is an interesting forum, I'm not going to return to read or respond to any more posts. Nothing personal. It's just that I'm not in the music business or a hobbyist in the field of music. I just stumbled across this forum while looking for the solution to an unrelated problem. Having struggled for so long to figure out how to fix the MT-100, I felt I should pass along my information, in case it helped others. Thanks for listening!

Thanks for the field report on the Tanac tensioners. Some pickup winders seem to be having the same problems.

[Joe Gwinn]

Let's say we already own these tensioners, and our tensioners have these issues we mentioned above.
How can we retrofit this unit to make it more useful for us?

I'd be tempted to call Tanac and ask. These units are widely used, and I bet there are answers.

[David King]

Why wouldn't a brake that relies on eddy currents in a non-ferrous metal disk like copper or aluminum work here as a retrofit? The permanent magnet on the dial side might need to be considerably stronger to work effectively and the braking action would become more speed-dependent (like a governor). I'm unclear why this hysteresis model Tanaca used isn't speed dependent -I'll need to read the patent for that info I guess.
If someone figures out what the dial threads are I can make a small stack of aluminum or brass threaded inserts or faceplates if there is interest.

[Joe Gwinn]

Why wouldn't a brake that relies on eddy currents in a non-ferrous metal disk like copper or aluminum work here as a retrofit? The permanent magnet on the dial side might need to be considerably stronger to work effectively and the braking action would become more speed-dependent (like a governor). I'm unclear why this hysteresis model Tanaka used isn't speed dependent -I'll need to read the patent for that info I guess.

The problem with eddy current brakes is that their drag effect increases with speed (or the square of speed?), which is precisely the wrong response. Drag should be constant.

If someone figures out what the dial threads are I can make a small stack of aluminum or brass threaded inserts or faceplates if there is interest.

Could be. I bet the threads are non-standard metric of some kind. I think the tensioner body is made of an aluminum or zinc alloy, so aluminum threads on the knob won't work, as they will surely gall. Black delrin could work, and is easily machined.