Mullen Bent Cross Rods

[Erv Niehaus]

Bob,
I'm sure Dell turns the ends of the cross shafts to the proper diameter before he bends them. Once the cross shafts are bent the ends will not be parallel with the lines you drew. The ends with have to be positioned in some sort of self aligning bearing in order not to bind up when rotated.

[Chris Lang]

b0b says:

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.

What???. b0b are you serious??


There are not two axis of rotation when using the bent crossbar..

But there are two different axis!! That's why the "bent" approach is flawed!
As Erv points out:

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

And again:

Bob,
I'm sure Dell turns the ends of the cross shafts to the proper diameter before he bends them. Once the cross shafts are bent the ends will not be parallel with the lines you drew. The ends with have to be positioned in some sort of self aligning bearing in order not to bind up when rotated.

Sorry b0b, your wrong on this. Pure and simple. For the life of me, I cannot understand how you cannot see this! Seriously. Did you read Richards explaination:

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.

I can understand why some folks do not want to acknowledge the "bent" crossrod issue. Mullen has made some fantastic guitars in the past, and they are extremely nice people.

HOWEVER!
As brought out throughout this post:
The bent crossrods are not physically correct!


If your goal is to build the most precise guitar, using a bent crossrod is one of the last things you would want to do, as it is NOT physically correct. It is in fact a design flaw.


Sorry if that hurts, but it is the truth! You guys can say what you will, but I have yet to see anyone provide any evidence showing that the bent crossrods are physically correct! They are not!

Now, bring on the science, and leave the opinions, and faulty excuses behind!

[Bill Moran]

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.

Bill, I was wondering about multi. pulls on both necks. I thought if there were ever to be a problem the multi. pulls would be it. You answered my question !! I really didn't have a question but that did run through my mind.

[Lee Baucum]

It appears as though Del has a whole new research and development team working on fixing something that isn't broken!

[Earnest Bovine]

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.

Right, b0b, of course there can be only one axis of rotation.
The red lines that you added to the photo show where it is.
I think Chris's confusion is about the meaning of the term "axis of rotation." He was talking about lines that run thru the middle of the shafts, not its axis of rotation.

[Danny Bates]

Chris, for the record, I deleted my post 20 minutes before you quoted me... so will you delete your remarks now?

[Travis Hillis]

Out of curiosity, do you think you could build a better steel then the Mullen guys, Chris?? It seems you think you could...

PS: I heard a Mullen on TV last night. Sounded dang good.

[Tony Glassman]

That's all well and fine, but the laws of physics are still around, being applied today! (except in the case of the mysterious bent rods)

Chris, It sure seems you are stating that the "laws of physics" don't apply to the "bent" cross-shafts in this response .

[Chris Lang]

Tony:

Chris Lang wrote:
That's all well and fine, but the laws of physics are still around, being applied today! (except in the case of the mysterious bent rods)
Chris, It sure seems you are stating that the "laws of physics" don't apply to the "bent" cross-shafts in this response .

Well, Tony, at least you are reading the posts, before responding.

However it should be quite obvious the meaning of that statement is: The laws of physics are still in play, but not in the case of the Mullen "bent" crossrod.

Mullen crossrods are not physically sound!

Keyword in the quote: except

[Chris Lang]

b0b, you still there?

Have you tried the "hanger" experiment?

[Richard Damron]

Rick Collins -

You are absolutely correct.

"Unconventional design" it is - and shall be.

Respectfully,

Richard

[J D Sauser]

There is only ONE way this can work:
If you please go back to Bob's (b0b) post on page 5 where he outlined in RED a common axis, THEN the bearings or collars/bushings holding MUST be inserted into the rails at a 90Deg. angle to THAT (average inclined) RED line (IN Axis with that line)... in other words NOT "flat" relative to the rails. BUT, BOTH tips which insert into the bearings or collars/bushings would have to be bent IN LINE with that (Bob's) RED average axis!



If the bearings holding these bent cross shafts are inserted "flat" (axis at 90Deg) into the rails, TWO parallel axis will result. IF one or the other would "win" the result would be that the other section would NOT ROTATE but MOVE back and forth following a RADIUS which center is the axis which would "win". Obviously, both axis seek to win which, if there is not a substantial (mechanically inappropriate) amount of play in between the cross bar's shaft and the bearings or bushings/collars it is logged logged in would result in them being locked (or only able to turn as far as "play" would allow).


Another option would be -if we assume that the level difference between the two decks may be around 1/4"- to drill the rods off-center by an 1/8" so that both meet at a common horizontal axis and used pins to connect the shafts to the rails.


Physics is physics. There is no such thing as "bad" physics, you can't prove physics wrong or disregard it just because it's a steel guitar. Physics lead to mechanical results or, if not followed to bad mechanics.

Given the fact that I hope that I may assume that the good folks at Mullen Steel Guitars are dedicated to produce a mechanically sound instrument, I am inclined to suspect that they have indeed aligned their cross shaft's bearings or bushings IN LINE with the average slanted axis as suggested by Bob (b0b).

Self aligning bearings as suggested by Erv on page 5 too, MAY be able to meet that average axis. However, let me tell you this: In mechanics, self aligning bearings, just like universal joints (cardan) are not regarded as an adequate tool to transpose the axis of rotations at different angles, but merely meant to help adapt/compensate for minor, usually tolerance induced misalignment of an axis to be at 90Deg to the bearing's radius.

I find the Mullen approach "interesting" as long as it does not thrive on excessive "play" or on the premises that the shaft needs not to be able to fully rotate freely (which evidently would be "bungle").

... J-D.

[Earnest Bovine]

The laws of physics are still in play, but not in the case of the Mullen "bent" crossrod.

I thought Chris didn't mean to say that before, because there was no response to my question about which laws of physics are being broken in this case.
As someone else already posted, when an observation of reality disagrees with a law of physics, then one of them is wrong.
If Chris's logic is correct, then I hope we get a response soon, because kids are going back to school soon, and we have to rewrite all those textbooks!

[Earnest Bovine]

Have you tried the "hanger" experiment?

A coat hanger may not be ideal for this experiment because it is not rigid.

What would it prove if it were rigid? Any rigid object would rotate the same as any other.

[Chris Lang]

Earnest says:

I thought Chris didn't mean to say that before, because there was no response to my question about which laws of physics are being broken in this case.

Earnest, that means Mullen is trying to make their "bent" rods work, without regard to physics.

[Chris Lang]

J-D shows:

There is only ONE way this can work:
If you please go back to Bob's (b0b) post on page 5 where he outlined in RED a common axis, THEN the bearings or collars/bushings holding MUST be inserted into the rails at a 90Deg. angle to THAT (average inclined) RED line (IN Axis with that line)... in other words NOT "flat" relative to the rails. BUT, BOTH tips which insert into the bearings or collars/bushings would have to be bent IN LINE with that (Bob's) RED average axis!



If the bearings holding these bent cross shafts are inserted "flat" (axis at 90Deg) into the rails, TWO parallel axis will result. IF one or the other would "win" the result would be that the other section would NOT ROTATE but MOVE back and forth following a RADIUS which center is the axis which would "win". Obviously, both axis seek to win which, if there is not a substantial (mechanically inappropriate) amount of play in between the cross bar's shaft and the bearings or bushings/collars it is logged logged in would result in them being locked (or only able to turn as far as "play" would allow).


Another option would be -if we assume that the level difference between the two decks may be around 1/4"- to drill the rods off-center by an 1/8" so that both meet at a common horizontal axis and used pins to connect the shafts to the rails.


Physics is physics. There is no such thing as "bad" physics, you can't prove physics wrong or disregard it just because it's a steel guitar. Physics lead to mechanical results or, if not followed to bad mechanics.

Given the fact that I hope that I may assume that the good folks at Mullen Steel Guitars are dedicated to produce a mechanically sound instrument, I am inclined to suspect that they have indeed aligned their cross shaft's bearings or bushings IN LINE with the average slanted axis as suggested by Bob (b0b).

Self aligning bearings as suggested by Erv on page 5 too, MAY be able to meet that average axis. However, let me tell you this: In mechanics, self aligning bearings, just like universal joints (cardan) are not regarded as an adequate tool to transpose the axis of rotations at different angles, but merely meant to help adapt/compensate for minor, usually tolerance induced misalignment of an axis to be at 90Deg to the bearing's radius.

I find the Mullen approach "interesting" as long as it does not thrive on excessive "play" or on the premises that the shaft needs not to be able to fully rotate freely (which evidently would be "bungle").

... J-D

Most excellent explaination, J-D!

I like the use of your word, "interesting"


Why not just use the physically correct "straight" crossrods, like every other builder???

[Bent Romnes]

Richard Damron,
Thanks for your response to my remarks, inquiries earlier. Your well thought-out remarks and facts are just that, and I agree with your statements.

As you, I have a great amount of respect for the Mullen people and their obvious innovative designs.

As I follow this thread without too many more posts of my own, I arrive at the one fact that I stated at the outset: The design is innovative, and pleasing to the eye. It works - that's obvious. Something that works as intended, repeatedly, is a good design. Therefor, if something works as intended, it is not flawed.
with respect
Bent

[richard burton]

A simpler device than a double-universal joint would be an Oldham Coupling

http://en.wikipedia.org/wiki/Oldham_coupling

[Chris Lang]

[Earnest Bovine]

Mullen is trying to make their "bent" rods work, without regard to physics.

I have no idea what that statement means, but I think you mean that Mullen is only "trying" to violate physical laws as currently understood, but have not actually done that. That's good news because it means we can still use last year's textbooks. Have you seen how much new textbooks cost these days? It's an outrage.
BTW I have the greatest respect for people who try to break the laws of physics. It's very difficult, but when you succeed, future generations of school children will read your name in the history books (if they can afford them.)

[Elton Smith]

I have a question.I assume the 6th neck is on one level of the bend and the 9th on the other.Does that mean we are playing both necks at the same time?

[Richard Damron]

J.D. Sauser -

Gotta call ya out on a generalized statement that you made regarding universal joints.

"are not an adequate tool to transpose the axis of rotations at different angles."

Many moons ago, I owned a 1961 Jaguar XKE (E-type). At the rear end were two half-shafts connected to the differential and the short wheel axles by universal joints. Granted, they were not of the "constant velocity" variety which overcomes a nonlinearity attendent to garden-variety U-joints but they, nonetheless, DID "transpose the axis of rotations" - and very well, indeed. They can't be all THAT bad since Jaguar, other sports car manufacturers, Formula One, Formula Ford etc., etc., etc. all used them - and on the fly, no less!

As I think I stated earlier, the Mullen "bent crossrods" need not "rotate freely" but, rather, only through a few degrees +/- around a centered location. The tolerances given apparently allow this minimal movement.

Respectfully,

Richard

[Jaclyn Jones]

The point that seems most important, at least me, is that it does work. Every day for the last 2 years. In bars, clubs and my living room. I love my G2. If the universe imploded because it fractures the laws of physics, it was fun while it lasted. You guys need to lighten up. Truth is, playing steel in high heels is way more dangerous than bent cross shafts!

[Richard Damron]

Bent Romnes -

Thanks much for the nod.

We are in total agreement.

Seems that we are odd-balls in this thread.

Respectfully,

Richard

[Richard Damron]

Jaclyn Jones -

Thank you, Darlin' - right about now I needed a smile.

Respectfully,

Richard