Mullen Bent Cross Rods

[Chris Lang]

Oh Pete, I guess I forgot to answer your question.

I play in a small to medium church on Wednesdays, and Sundays.

As far as brand of guitar, I play a GFI SD-10 3x5. Keyless of course!

(I bet you saw that one coming!)

[Richard Damron]

Tony Glassman -

I lied. My "permanent rest" is not so permanent after all since I'm forced to reply to your latest post.

I think that you should have emphasized the word "mechanics", which you placed in parentheses, as opposed to the word "physics" which, in this case, is much, much less apropos. It's purely "mechanics" and not "physics" per se.

The use of the word "crankshaft" is also misleading, if not in error, since any true crankshaft will have the main bearings on a single, concentric axis. To reiterate, the bearings of the bent crossrod DO NOT share a common concentric axis. There is NO "pure shaft rotation". None at all.

Richard Burton -

The use of miniature universal joints is an excellent - if not expensive - idea. HOWEVER - since there are TWO distinct axes of rotation, I believe that it necessitates the use of TWO such joints in series. The implementation of only one such joint will provide angular rotation of the two "half-shafts" (F1 technology, anyone?). A second joint would have to be used in order to bring the second "half-shaft" on an axis PARALLEL to the first. F1 technology does just that. OOOOppppppppppssssss! Just noticed!!!!! The lower - double - universal in your post would work, however, the center section would always be at an angle to the two shaft axes. This makes the use of a centre brace necessary but almost impossible unless the center of the joint can be ground so as to supply a smooth bearing surface and the brace, itself, mounted at the appropriate angle. My bad. Hope I vindicated myself.

I must admit that, since I am enamored with "elegant" solutions, this would be the approach that I would take. DAMN the expense and complexity, this is BEAUTIFUL!

Respectfully,

Richard

[Chris Lang]

Richard said:

This makes the use of a centre brace necessary but almost impossible unless the center of the joint can be ground so as to supply a smooth bearing surface and the brace, itself, mounted at the appropriate angle.

That is true Richard.

You might be able to machine a groove on each side of the double U-joint, to allow for upright mounted bearing assemblies(mounted on their respective platforms). Either way would work.

As far as the expense goes, you are already spending around 4000.00 for a SD-10, so what is a little more? It really couldn't be that much more, could it?

It would definately be a whole lot better design than the "bent" approach, IMHO.

[Richard Damron]

Chris -

Excellent point. It'll woik!

However - and I'm gonna hate myself for saying this - one should "Keep It Simple, Stupid" if at all possible. In the above post I've just indulged myself the luxury of expressing a love for fine mechanics.

[Erv Niehaus]

We're getting waaaaay to fancy here.
Something like this would be easier and less complicated. It would allow for some deviation in the axis of rotation.:

[Chris Lang]

Erv says:

We're getting waaaaay to fancy here.
Something like this would be easier and less complicated. It would allow for some deviation in the axis of rotation.:

You would still have the added "rise and fall" problem though, would you not?

I like your second illustraion. It shows the crux of the "bent" crossrod problem very well.



Richard says:

However - and I'm gonna hate myself for saying this - one should "Keep It Simple, Stupid" if at all possible. In the above post I've just indulged myself the luxury of expressing a love for fine mechanics.

It's ok to indulge yourself, I love fine mechanics as well! The love of fine mechanics, is what defines a truly fine, mechanically correct, work of art!

These latest ideas are really good ones, IMHO. Ones that I believe should be taken to heart!

[Richard Damron]

Erv -

You're right. That would satisfy my picky mechanical sensibilities. Thought of it much earlier but discarded it as being expensive and cumbersome. But - what the hell - as long as I'm gonna "design" an "elegant" PSG then why not?

I consider the "rise and fall" problem to be minimal. I'm surprised that no one has mentioned the fact that the center of rotation of the bellcrank moves in an arc and longitudinally to the instrument.

Since both of these dilemmas seem to be factored out in the overall setup then, once again, I cannot argue with success.

Respectfully,

Richard

[b0b]

Tony:
I said:

BTW, if anyone has any scientific supporting evidence that will show that the "bent" crossrods do not violate basic physical laws, then by all means, please come forward!

Watch the keyword here: scientific!....

You have presented no scientific evidence to support your thought.

That's absolutely silly, Chris. A steel guitar can't violate the laws of physics. We don't need "scientific evidence" to prove that. Nobody is claiming magic.

Now, if I may, I'd like to address the issue of "two distinct axis of rotation". There are not two axis of rotation when using the bent crossbar. The axis is a line between the endpoints. Each puller intersects that line at a different point, so each has its own axis. That axis is above the crossbar on the E9th neck and below the crossbar on the C6th neck.

The net result is that there is slightly less vertical movement of pull rods on the E9th (since the center of rotation is above the crossbar), and slightly more vertical movement of pull rods on the C6th. I honestly don't know whether this is an advantage to the player or not. I'm just pointing out that there are not "two axis of rotation" as has been claimed. The axis is vertically different for each rod puller, depending on its distance from the end points of the crossbar. The axis are points on a diagonal line.

The double-U-joint solution would create two level axis.

[Joseph Carlson]

I have no dog in this fight either way, but I thought this might help people understand what the discussion was about:

[Rick Collins]

Chris Lang, contextually your phrase "design flaw" doesn't fit here. Use of the term design flaw implies that it was not intentional __ it was.
Mullen knows this, I know this, most who have responded know this; but you keep using it as if it were an accusation of someone not knowing the true classical physics and mechanics of the design.

"Design flaw" _ improper here; I know it, you know it, everyone at Mullen knows it, we all know it!

[b0b]

I've drawn straight red lines on the photo to illustrate how the center of rotation changes along the bent crossbar.

[Pete Burak]

I think if you hold a Quarter in your hands like a steering wheel, and put your thumbnails at "10 and 2" you'll see approx the amount of angular rotation it takes to make a pedal or lever raise/lower.
Given the slack requiered in an all-pull system, this basically becomes a straight line pull (I recall a diagram of circle sitting on a line... ie. a small enough portion of a circle is basicaly a straight line).
I personally love the look of those rods in that pic!
I have no reason to doubt that it works perfectly.
Funn Stuff!
Lets hear that GFI, Chris!

[Erv Niehaus]

The trouble is, Bob, the ends of the shafts and the correspoding bearings are not in align with the line you drew.

[Richard Damron]

b0b -

Thanks for your support.

In an IDEAL situation, one would prefer two distinct and PARALLEL axes of rotation. The bent rod concept does not support this. The two universal joint solution does. Erv's "pillow block" solution allows for the nonlinearity in the bent rod scheme.

As to "scientific" evidence, I can only refer to Ross Shafer's computer expertise in showing the fallacy in the bent rod design - the tendency for such an arrangement to bind up under rotation.

Re: My post above. As long as the cumulative nonlinearities are effectively "zeroed out" when assembling the instrument then all of this analyzing is for naught as the technique WORKS!

Kudos to Del Mullen for a PRACTICAL approach to the crossbar dilemma.

Respectfully,

Richard

[b0b]

The trouble is, Bob, the ends of the shafts and the correspoding bearings are not in align with the line you drew.

Not exactly, no, but the lines illustrate my point. The center of rotation does not go through the center of the crossbar. It is different at each point along the length of the bar.

I've never seen the bushings and bearings. Perhaps they are more complex than I imagine.

[Bill Moore]

I haven't seen one of these guitars. But, it seems to me, all that would be needed for the shaft to rotate freely would be a slight taper on the ends of the cross shaft. It does look different, but I'm sure it functions as it should.

[Richard Damron]

Rick Collins -

When I use the term "design flaw" it is with regards classical mechanical design - the necessity of having distinct axes of rotation. This is an IDEAL quest for correctness and nothing else. No one - not you, not Del Mullen nor anyone can dispute this.

If you've read my posts then there is no way that you can misconstrue anything that I've stated which even alludes to an accusation that Del Mullen is an incompetant designer. To the contrary, I've applauded him for his ingenuity as a designer of a fine instrument.

I know, you were dumping a little bit upon Chris, but, since I, too, have used the term I feel it is necessary to defend my quite distinct position regarding the use of the phrase.

No offence, my friend, just clearing the air a tad.

Respectfully,

Richard

[Danny Bates]

deleted to make people happy. Peace

[Erv Niehaus]

Bob,
Dell would have to use self-aligning bushings or bearings to get in alignment with the lines you drew. To my knowledge, he does not incorporate this type of cross shaft suspension.

[Erv Niehaus]

Danny,
Why a personal attack on Chris?
He's entitled to his opinion like everyone else.

[Richard Damron]

Danny -

You obviously have not read - really read - the above posts. I would invite you to do so as they just might prompt you to edit - delete - your second and third statements; those statements having been proved either unnecessary or lacking in background knowledge.

Respectfully,

Richard

[b0b]

Bob,
Dell would have to use self-aligning bushings or bearings to get in alignment with the lines you drew. To my knowledge, he does not incorporate this type of cross shaft suspension.

I guess I don't understand your point, Erv. Where are the actual centers of rotation for each puller, if they are not (approximately) along the diagonal lines that I've drawn between the endpoints of the crossbars?

[Danny Bates]

Deleted to keep people happy. Peace

[Rick Collins]

Rick Collins -

When I use the term "design flaw" it is with regards classical mechanical design - the necessity of having distinct axes of rotation. This is an IDEAL quest for correctness and nothing else. No one - not you, not Del Mullen nor anyone can dispute this.

Your further clarification is fine and acceptable, Richard.

No offence, my friend, just clearing the air a tad.

I'm breathing a little better, Richard.

My personal choice of words would have been "unconventional design".

[Bill Stroud]

Let me tell you, I've got one of the most Pulls on a Steel that you would ever want, 10 Floor pedals 7 Knees that raises and lower strings on both the E9th & C6th neck at the same time. Mike & Del built this G2 Model for me last year and it plays as well as any Steel that you would want to play nice job Mike, and if anyone wants to play this Steel in the Mullen room I will bring it to St Louis for you to try out and see how well it plays and the action is second to none.
The offset that everyone is talking about is no big deal, a self aligning bearings would take care of any of that, but I don't see where you need to do anything but play it, there's no issues.
Last year when I first got the Steel David Hartley sit down and played it with no complaint, and it was setup different than what he is use to having and I might add played it well.
Let me know if you want to try this Steel out.
Mike thanks for a good job and making a good playing Steel to be proud of.