A Side Thought Regarding The "Lubrication" Question.

[Storm Rosson]

As I mentioned in the axle thread, find some supplier of motor shaft material that has been nitride coated (McMaster-Carr only goes down to 3/4" dia) and you ain't gonna wear the shaft period, not in your lifetime at least...

[azgoatroper]

I believe that the first part of the equation was the application. ATF was designed for hydrolic applications not lubrication. Its design characteristic is to provide just enough lubrication to prevent galling of components but yet allow the friction components in a transmission too 'shed' most of the fluid when they engage. It has filming agents to allow it to cling to and coat the components with a light film. It is engineered to give up its retained heat more readily than heavier oils and it has chemical agents to stabilize these properties.

If you look at the drive train of a vehicle, you will find at least 3 different oil types, engine oil, auto-transmission oil, and gear lube. For those of you that do your own service work, you know that each of them has a different consistency. Each is engineered for a specific purpose. All lubricants have a 'shear' factor. This is the amount of force required to force all film from between two contacting surfaces. ATF has a very low coefficient compared to 90W Gear Lube used in the rear differential and manual transmissions. These two areas see the highest loading of surface contact, which is on the gear teeth. Hence the 90W lube, as it has a very high shear factor.

This is where it comes around.... using ATF as a lubricant is useless. That's not it's design intent. In the finger/axel arrangement you actuall have point contact in a linear fashion for the width of the finger. Even if you have a reamed hole and polished/ground shaft with no more than .0005" running clearance, you still have point contact. Now I believe that I read one thread that gave some calculations about the load that is applied by the strings is around 1200lbs? I'm probably way off on that, requardless, even light machine oil has a higher shear factor than ATF as it was designed as a lubricant.

I used to be into sailing and studied boat building and participated in constructing a 40 footer. I understand about galvanic corrosion and sacrificial anodes. Sea water is a very stong electrolite and corrosion happens rapidly between the bronze thru hull fittings and anything they are in contact with, hence the zinc anodes bolted to the prop shaft and rudder.

It was most likely the additives in the ATF that lead to the corrosion issue. I have seen aluminum tooling worth tens of thousands of dollars, corrode overnight, and be frozen solid with corrosion after sitting for a weekend. The large machine tools, mills, lathes, machining centers, all use coolants to flush chips, lubricate the cutting tools, and dissipate heat. Most are water based and mixed at specific ratios but they are also engineered for a high lubricating shear factor for the force exerted between the cutting tool and material. Here again is application. But sometimes the maintainence folks don't understand and place the wrong coolant in the wrong machine and the chemical reactions cause the corrosion with the alumunum and the problem is compounded twofold.

So, all that said, I don't believe that there is sufficient current flowing through these parts on a PSG to cause this problem and it really doesn't matter that the materials are dissimilar. Aluminum will leave a black residue no matter what lubricant is used. A clean hole (size and finish) and a clean shaft with as close to a line fit as possible, and a good lubricant is always the best senario.

This is all based on my 30+ years experience in the machine trades and wrenching cars, machines, whatever. I've been in the aircraft turbine industry for close to 27 years.

I've been following these threads and have really enjoyed the discussions as I can see that there are some very intelligent individuals here with engineering backgrounds. Sometimes you just have to break it down.

I, in no way, intend to demean or discount anyones theories, nor do I wish to offend anyone, and if I have I offer my apologies. I've seen a lot in my day. I analyse and go through different iterations to arrive at solutions. It's critical when a 3/4 million dollar piece of machinery is stopping production.

We all have our miscalculations and I've had some doozies! Moral-don't use ATF as a lubricant.

I would like to offer my warmest requards to all of you who undertake these projects. You guys do stuff that I would never have dreamed of and the results are sometimes nothing less than stupendious. Some of the artisic expression I see, I only dream about.

[Bent]

That, I must say should be the most reliable "paper" written on the ATF for lube trial. You wrote it so convincingly, backed it up with facts and experience that I for one will say that we know now for a fact that ATF should never be used as a lube in steel guitars.

I would like to solicit your expertise regarding the lube I am currently trying: Mobil jet turbine oil. It did give me the impression that this had to be the ultimate in lubrication and preservation: It lubricates a jet engine and it must also be compatible with steel and aluminum applications - look at all the aluminum in a jet - even 6061 T6, the aircraft metal we use in our steels.
I am using this oil in the two changers I made, one for myself and one for Dave Seddon in England. The only downside to this oil, the way I see it at the moment, is that it is a dust collector like any other oil. Oh...I forgot to say..I am using brass, uncoated , in the fingers of these 2 changers. 304 stainless steel axle.

[Storm Rosson]

I know I sound like a harpee on this but imo dry lubrication is the answer. In addition to the aforementioned nitride coating, the auto racing industry has come up with some very useful practices ,ie: Molybdenum Disulfide (MDS) is now both used to electro-coat many rotating assemblies such as camshafts ,oil pumps etc, and to impregnate it into many other materials. Teflon(Polytetraflouroethylene) is being used to coat piston skirts, pushrods,rocker arms, lifters,etc.In short, although these substances must be incorporated during the design and fabricating phase of a build, in the long run they are far superior to any "wet" lube currently available if for nothing else than to eliminate the "dust magnet" effect inherent in wet lubes.....jmho....Stormy

[richard37066]

Stormy -

Since I started this thread, I may as well add a penny's worth here.

The string calculations were supplied by me with the aid of an online site with an interactive formula for determining string tension. For a basic E9 tuning, the tension - per string - was in the neighborhood of 27 pounds. With a couple of pedals mashed to the floor, the total tension on the axle would be in the vicinity of 300 pounds. This is academic, only, even though the value of 27lbs/string is nothing to sneeze at.

The fact that there is black residue on Bent's axle shaft is indicative of the wearing of the aluminum finger - it being a much softer material than the stainless. What has not been answered is the reason for the ridges that Bent found in the axle, itself. I, among others, have made a hairbrained guess or two but the actual mechanism of wear still eludes.

In my original post, I told of a friend who lubricated his differential with Moly Disulphide. I was into sports cars at the time (MGB, Jaguar E-type) with a passion for Formula 1 and SCCA racing. (No, I didn't race!) Moly was used even then. This was back in the early to mid sixties and is the first basis for my acceptance of Moly as a superior lubricant. I've not seen - in the ensuing years - anything which would surpass its' qualities hence my dedication to it as my lube of choice. Teflon-based lubes are quite good but, as you suggested, I'll stick with assembling things with good old Moly and then not be concerned with wear.

I've searched for any information which might indicate that there's an additive in ATF which might promote corrosion. Came up empty. It's a science unto itself.

Lastly - and there's been disagreement on this - I'll also stick with the much stronger materials for shaft and fingers. Things like stainless and drill rod - if the surfaces are finished to a fair-thee-well - will outlast and outperform the softer materials.

Like you, I admire and marvel at the inventiveness, inquisitiveness and tenacity of the members in their search for the "right" answers and methods. These guys are special and the best thing that I've done in recent times is to join this forum. It makes my day.

Richard

[azgoatroper]

That's very true Stormy. The dry lube coating would be the ideal in this situation. It is also used extensively in the aerospace industry where components are not easily reached for lubrication but absolutely must not sieze. If had to spec it out on numerous parts such as missle release hooks for the F4 Phantom (years ago). Imagine the pilot arming a Sidewinder and firing only to have the missile release hook lock up! Bummer!

The nitriding of the shaft would add tensile strength and wear resistance to the surface of the shaft to a depth of about .025" much like the hard anodize process for aluminum.

The biggest drawback to these processes is the cost. Most companies that do this type of hardening and/or coating usually charge a 'lot' charge averaging around $80 just for setup on each run. Then it's charged by the pound of material. To be cost effective you need to have volume to amortize the cost over say a hundred parts so the that the individual item cost remains reasonable. This holds for almost any process in manufacturing.

Bent, the jet turbine oil is a good candidate as it is a 5W oil that will flow into the crevases between the fingers and axel. The caveat is that it is still a 'wet' lubricant and as such will have a tendency to collect dust. Given the design considerations of any PSG changer, this is going to be an unavoidable issue. Someone needs to design a 'sealed' changer! Another good choice for this application is '3in1' oil. It's readily available and fits the application criteria. It cleans, lubricates, and protects against corrosion. If you can find the '3in1' electric motor oil in the blue can, it seems that this would be the best as it has the same characteristics but a slightly higher viscosity at 20W.

Just as reference, there is almost no aluminum in a turbine engine as the operating tempuratures are far too high. The cold side compressor section is primarily titanium and the hot side is mostly high temp nickle alloys and stainless with the gear cases being magnesium.

Back to the theme of applications, I found an article about live steam model locomotives where the author discussed the use of different lubricants in their realm. I found it interesting as most of what he said can be applied to many applications. here's the link for those interested http://www.southernsteamtrains.com/notes/lubeoil.htm.

3in1 oil is made by the same comany that makes WD40 but 3in1 dates back to 1896. WD40 is a no-no for the PSG. It is a cleaner, penetrant, and water displacement product not intended for lubrication. It then it gums up in time as all the volatile components evaporate.

To sum, yes the jet oil should be good.

We would always want two components that are in contact with each other to be of dissimilar types. One needs to be softer than the other to allow wear to a certain extent. I believe that Richard stated that he would prefer a stainless shaft and fingers. That's really not a good idea due to the fact that stainless is designed for corrosion resistance and has a tendency to be 'gummy'. This may not enter into the equation on a changer due to the lower operation forces but my experience has taught me to never apply two stainless surfaces in a friction situation as you will very quickly have metal transferrence, i.e. galling. The same would hold true with aluminum, brass, titanium, all to varying degrees unless one component had been surface treated to be harder than the other.

Think about all the mechanical mechanisms you've ever seen. How many times have you ever seen similar materials in direct contact with each other in a load bearing/friction situation? Let me qualify that with 'quality' mechanisms.

[richard37066]

Azgoatroper -

In my view, the thrust of this whole discussion concerns the measures to REDUCE friction and wear. To each his own, I suppose, but I rebel at the idea of fabricating a "sacrificial" part and knowing that I'll have to replace it at some point in the future simply because its' wear properties are less than the part with whom it mates. A couple of us have referred to the PSG changer as the only "precision" part of the instrument. Precision parts are designed such that wear is kept to an absolute minimum thus ensuring longevity. I, personally, will spend the time and money in order to achieve the optimum degree of precision so that I can enjoy my creation indefinitely - while others may spend time and energy tearing things apart and rebuilding them. In this old mind, that last scenario just does not compute.

In every research paper that I've read, the number one theme in regards wear and "galling" is the surface finish. As I've stated earlier, even a highly polished surface has a jillion microscopic protuberances. If macroscopic defects are allowed then the wear factor goes through the roof regardless of lubrication. Although I prefer the use of stainless in the fabrication of changer parts, it will do no good if I hog things out with worn drill bits and coarse files. Ditto with any other material. My personal philosophy is that I apply care to those areas which require attention to detail and precision and leave the "good enough" attitude for things which are of little consequence. Those who have done the laboratory research have taught me to mind my p's and q's regarding the above.

Ah - but it's the differences which keep this ol' world goin' round and round.

Richard

[Storm Rosson]

Whatta u guys think about heat fitting a hardended phosphor-bronze bearing into each changer finger, sorta like the bushing inserts on Bemt's new foot pedals?....Stormy errrr that would be Bent not Bemt...lol

[azgoatroper]

Yes Richard, you are absolutely correct in all of your statements. Precision is the key to longevity. You must have concentric bores and diameters with a good surface finish and close fit to keep the wear factor to the absolute minimum, but on the other hand if you achieve these two criteria, then the wear and friction issues are almost mute. At this point there is no sacrificial component. As you stated, there are macro and microscopic ridges and valleys in any surface, in this instance even a good hone job on the bores would be good and still leave those ridges and valleys. These are beneficial in this application as they provide a minute space in which to trap and hold the lubricant.

When I tore my Sho-Bud professional apart I found that the fingers were stamped/punched out of sheet material. Punching and shearing operations only cut the first 20-30% of the material thickness then the rest is virtually torn away. This left approximately .050" of actual bearing surface in contact with the shaft. This guitar is a '72 and I understand that it saw some road time yet there was little wear on the axel shaft but the fingers were shot by my standards.

I'm sure that we have all dissassembled a mechanical device that is 50+ years old (let's say an old motor) and found that although the winding has failed, the bearing (usually oilite) and shaft are still in near perfect condition! The shaft is harder than the bronze and therefore the bronze takes the brunt of the wear but being that the bushing contained minute traces of oil, it kept the wear to almost nothing.

As I stated, the galling of stainless may not apply to this application due to the lower forces involved. I would however recommend using 303SS and not 304SS as the 303 has better machining and finishing characteristics. The 304 tends to be the gummier one. I did not mean it as an attack on your choice of materials although I would also recommend an Oilite bushing in the finger.

Stormy, as far as using a bronze bushing, that's one good way of reducing the friction as it is slightly harder than the aluminum. If you are referring to 'Oilite' material, you would not want to heat it as that would drive the oil from the bushing. Oilite starts as a powder that is pressed and then sintered to bind it. Once that is done, it is interlaced with fine pores. It is then placed in a vacuum and infused with a light oil which is then released very slowly as the bushing warms from the friction of the shaft and provides a constant lubrication barrier. That's why the motor shaft above lasted so long. Oilite was developed by Chrysler in 1930. Oilite bushings are found in the nose of almost every engine starter motor where they are supporting the shaft for the starter pinion.

Richard, it is your attention to details and your analysis of things that makes this forum so interesting. Between you and Georg on this knife edge changer, it's so out of the box, I just love it!

Michael

[Storm Rosson]

I think u could use oil-lite if it were assembled opposite of my initial thought ie: put the oil-lite bearing in the freezer and heat the finger ,a coupla hundred degrees would be plenty and then press the cold contracted oil-lites into said finger....mite work no?....Stormy,,,,,,,,,hmmm somewhere I remember seeing some MSD infused metal bushings too.....gotta remember where duh!!