Designing a new PSG: Nomenclature: Steel for shafts and axle

[J D Sauser]

I am in the process of drawing the final concept plans to prototype a new PSG.
I WILL discuss the base concept later.

I will be posting questions and ask for help now and then.

I am looking for the NAME for the steel type usually used for shafts and axles.
Back in Europe, the material of choice was called Silberstahl [DE] or Acier Argent [FR], while, contrary to what it's name may suggest, it has nothing to do with silver.
It's a nasty to work on material, very hard and causes cutting tools to overheat quickly. It comes in precise dimensioned standard diameters. Usually it is only cut to length and used as a shaft or axle or custom length pin.
The finish is almost like polished. I would guess that this would be what most builders use for their changer shafts.

What's the correct name in the US for it?


Thanks! ... J-D.

[Scott Harbison]

Some call it "A2 drill rod". You can purchase it in the rough oiled form or polished.

[J D Sauser]

I found some info on the material I used to know back in Europe:

http://www.ibl-raimund.de/shop/silberst ... -2486.html

It's a Chrome-Vanadium alloy now called "115CrV3"

Some call it "A2 drill rod". You can purchase it in the rough oiled form or polished.

Thanks Scott.
I am googling it "as we speak. Interestingly two things come up here.

1-One supplier lists the material as "good machinability" (the material I alluded to was anything but) (?).
2-A2 drill rod (precision ground) is often offered with the option of "O1". What is the difference between A2 and O1?

One more question:
Does the term "Drill Rod" itself automatically imply that the material is precision ground?


Thanks! ... J-D.

[Bent Romnes]

JD
Drill rod is precision ground. In its raw state,it is rather soft and not the best to use if you want as hard an axle as feasible (to avoid the slightest bending)Drill rod needs to be soft for shaping and is hardened afterward.

I have run this changer axle question across to my engineer friend and off the top of his head he thought something hardened to Rockwell 60 would be best. I need to speak with him again for final assessment on this.

He turned a tone bar for me to try. I am very happy with it and thought that maybe this steel would be great for axles as well it is stainless and has the description of 17 PH 4 for those of you who know your steel.

[richard burton]

I would use something like a 9/16" (14 mm) diameter stainless steel (grade 316) for the changer axle.

No need to harden it if the fingers are made from aluminium, and the large diameter means that that sucker ain't going to flex, even if the guitar is a twelve string

[Joe Babb]

O1 means oil hardening, versus water hardening.

This is an interesting question about the steel to use. In working on older guitars I have found galling of the aluminum on the steel shaft in the changer. After a long enough time the residue builds up and scores the steel and the aluminum fingers don't move freely as they ought to. I've thought about bushing the fingers with brass but that's a big job seems like. What am I missing? Hope I'm not hijacking the thread. But if you are designing from scratch it is something to be aware of.

[Bent Romnes]

Richard, I think 1/2" is sufficient.And with the extra hardness, 1/2" aint gonna bend either! That leaves a bit more material for the radius on the finger.

Joe, wear by the aluminum on the drill-rod axle is definitely a concern. I saw an Emmons PP where there were actually deep tracks in the axle from the fingers.
Your idea of a bushing works well. I built my first steel using oilite bushings in the finger. One other builder I know of who uses this is Fulawka, and it has certainly stood the test of time

[J D Sauser]

Most suppliers' data sheet on precision ground A2 Drill Rod suggest that it is heat treated to 60 Rockwell.
That would make it seem quite similar to it's European analogue "Siverstahl [DE]" now 115CrV3 specifications.



One thing I do remember well from my studies at tech college was the classes on APPLIED metal properties. In other words, what each metal is good and not good for.
We all know the advantages of aluminum but some if not all PSG builder seem not to know some of it's disadvantages, the foremost being; "thou shall not use aluminum in any application which involves FRICTION!"
This comes as an exception to the common rule which tell us, that we want a soft material (typically brass, bronze or even iron or non-hardened steel) "running" on a hard material (typically heat treated).
Aluminum however, still BEING a soft material, does not behave favorably in ANY friction material. And surprisingly enough, it can even deteriorate the harder material.

Well, razor blades do get worn on skin and in the ol' days, men would sharpen them back up on... a piece of leather.

Just like Bent shared, I too recently had been asked to look at a PSG which behaved "lazy".
A high quality pro steel made by a builder I have nothing but respect for. The guitar is 10 years old, a well cared for bedroom instrument but plaid diligently for 2 hours a day. So, about 7200 hrs of noodling time... the bulk of it on E9th, of course...
I checked from the pedals and levers up and ended up at the changer. I came to believe that the changer must have been gummed up with mixture of residue and maybe a history of inadequate lubrication accumulated IN BETWEEN the scissors and the fingers.
After disassembling the changer, I was surprised to find relatively clean and freely moving scissors but that the fingers alone were very sticky.
The shaft came out black from what I first thought would be ALUMINUM and oil residue... but after cleaning it all, I could see and FEEL the wear on the pressure/contact side of the STEEL changer SHAFT... and ONLY on the with of the aluminum fingers, NOT on the thin contact line of the steel scissors (well, they are also not pulled into the shaft by the strings' tension as the fingers are).
For the lack of a new shaft, I had not other choice to clean and lube and assemble it all back, only making sure that I left the shaft turned 180 deg. so that the worn surface would face towards the nut and the unworn surface the fingers' contact/pressure point (from the string pressure). We'll have to install an new shaft next time, but bin the meantime they guitar is playing like new.

The truth is, that while the movement and speed of the fingers of a PSG's changer is fairly minimal the pressure at which the fingers are pulled into the shaft by the string may be underestimated. That paired with the fact that aluminum does not behave well under friction is cause for concern.

Yes, in my opinion, changer fingers should either not be made of aluminum or have a pressure fit bronze or brass insert.



Bent, in your first answer to me on A2 Drill Rod... you got me confused:
Am I right to assume that finished A2 Drill Rod I buy IS always precision ground and thus HAS been heat treated?


... J-D.

[Bent Romnes]

JD, first off I am no metallurgist or machinist. I only learn from people I ask and who presumably know more than me.

This to me makes sense: Drill rod, by it's very nature, has to be on the soft side in order for the machinist to put the "twist" in it. I understand this is a machining procedure and can only be done before hardening. The only thing that separates drill rod from other rod is that fact that it is precision ground down to a thou or so
After machining, the hardening process is done. I may be mistaken, but I think the hardness of a drill bit is in the neighborhood of Rockwell 50.

I'll try and do some research on this and if I find anything I will post it.

[Bent Romnes]

This should be good for study. A2 tool steel, including drill rod.
From what I understand it is un-hardened in it's normal state and is hardenable after machining. It is also approx .015 to .035 oversized.
http://www.speedymetals.com/information ... plications

[Bent Romnes]

Here are the properties for 17-4PH That I wrote about earlier. My friend turned a 15/16" bar for me to try.
He believes this is the right steel for a bar, in that it has a very high tolerance for abrasion i.e rubbing the bar against the strings a million times.
Of this holds true, I can see where this would be a great steel for changer axles as well
http://www.onlinemetals.com/alloycat.cfm?alloy=17-4

Fairly pricey, but well worth it if it performs.

[Martin Weenick]

J.D., I have been useing 1/2 inch 7075 precision ground aluminum shafting that has been anodized. (McMaster/Carr). The anodize is very hard and very slick against aluminum fingers. The anodized shaft actually sparks when I cut it on the bandsaw. Martin.

[Peter den Hartogh]

J.D., does the changer HAVE to have an axle?

Did you consider the system of the Fender Artist series (built by Sho~Bud in 1976) which was based on a knife-edge system? It was also used on the Fender 1000 series...the later models.

[J D Sauser]

No Peter, I did not (consider).
And here is why. "Knife" or blade designs can be cheap and sturdy (in ONE direction) but to work as friction free as possible, the blade needs to be as thin as possible and when it is, it tends to act as a knife... cutting into the changer finger. Wear may become an accelerated issue.
In any event, the choice of materials remains of importance.

I think that for that time it was an interesting study, but I do not understand what really they patented. After all the scissor changer had been invented long ago.


Thanks! ... J-D.

[John Roche]

Silver Steel

[Bent Romnes]

After reading the suggestions, I still come back to my earlier suggestions: Drill rod hardened to Rockwell 50 or 17-4PH stainless

[Pat Comeau]

I use small motor and transmision shaft from home appliance machine, as my father repaired appliances all his life and still has a bunch of old parts left , these shaft are hard as rock and hard to cut and grind, i don't know what kind of metal it is but it's hard ,as for cross shaft you don't really need anything special...just stainless or aluminum is strong enough, when everything is smooth there's hardly any pressure on cross shaft and that;s why alot of today builders use aluminum compared to steel years ago, i think the newer changer design makes it alot easyer to play with less pressure to push the levers and pedals.

[Paul Redmond]

Most air-hardened tool steels must be "cooked" up to temp in an endothermic furnace to prevent de-carburization (loss of carbon content). They are usually quenched in open air. Some very thick sections are initially quenched in hot oil, then immediately put in an airstream to bring them down the rest of the way. O-1 is an oil-hardened tool steel which used to be the mainstay of the mold-making trade before the advent of the now-common S-7. O-1 is still used for punches in punch press dies as is its mate, O-6 which is a graphitic version of the same steel...it hardens to a higher Rockwell C reading.
S-7 is a shock-resisting steel and a good all around general-purpose tool steel. All S-series tool steels are air hardened and are usually "cooked" in endothermic furnaces to keep the oxygen/carbon thing in balance.
NONE of these steels is rust resistant. I wouldn't recommend the use of any of them for cross-shafts in a steel guitar unless a secondary plating or anodizing process follows. If heat-treated, the rust problem becomes worse.
In the Whitney guitars, I used S-7 shafts, but then had them flash-chrome-plated with Tibon hard chrome after heat-treating (and an emery satin finish).
I have been using 316 stainless recently. It doesn't require heat treatment to prevent galling with aluminum if a drop of oil is used periodically. ALL friction points should be lubed once in a while. I would avoid 304 stainless because of its poor machining qualities unless you can buy it in a fully-annealed state.
Drill rod usually implies that the rounds are cylindrically ground to a standard size and not an oversize condition as is the case with some "MF" tool steels...that BTW means machine-finished. These steels are usually milled or sawn to an oversize dimension ranging from 1/64" to as much as 1/16" on larger sized billets 3 inches or larger.
PRR

[J D Sauser]

Thanks Paul!

... J-D.

[Ron Randall]

JD

Maybe this has been covered.
My 2c. For cross shafts...
The strength of all the materials discussed is far beyond what is needed and that is fine. The most important attributes are the "modulus of elasticity" (stiffness), corrosion resistance, machinability, shape, and cost.

You need stiff metals to preclude "cabinet" deflection. In round numbers, steel and its alloys are 3X the stiffness of aluminum alloys. Stronger does not mean stiffer.

Check out the term "modulus of elasticity".
I won't go into more detail here, Because the truth is usually slammed in public.
I have the college and graduate school credentials. My last professional job was designing and manufacturing guided missiles. (they work really good)

R2

[Ron Randall]

JD

Maybe this has been covered.
My 2c. For cross shafts...
The strength of all the materials discussed is far beyond what is needed and that is fine. The most important attributes are the "modulus of elasticity" (stiffness), corrosion resistance, machinability, shape, and cost.

You need stiff metals to preclude "cabinet" deflection. In round numbers, steel and its alloys are 3X the stiffness of aluminum alloys. Stronger does not mean stiffer.

Check out the term "modulus of elasticity".
I won't go into more detail here, Because the truth is usually slammed in public.
I have the college and graduate school credentials. My last professional job was designing and manufacturing guided missiles. (they work really good)

R2