Draw Angle

Alvin Douglas · Post by **Alvin Douglas** » 9 Feb 2014 12:16 pm

Looking at the underside of my MSA Classic, I notice that some of the rod levers are canted towards the changer, some are at a rt. angle and some are canted away from the changer. I do not know the proper name for these short levers but they have several holes that holds a small roller that tightens onto the aluminum pull rod with a grub screw. I think the proper or ideal position for this lever should be just past the rt. angle position so the total swing of the lever is split evenly with 1/2 either side of the rt. angle position. Is this true? In setting up the guitar, should I be changing the angle of these levers to this position?
Thanks in advance for your comments.
Alvin

chris ivey · Post by **chris ivey** » 9 Feb 2014 12:49 pm

bellcranks.

Tom Gorr · Post by **Tom Gorr** » 9 Feb 2014 1:02 pm

The differing angles help time the pulls to start and end at the same time. The 'acting' radius on the crank is changed by the different angles giving you virtual infinesimal refinement of the pulls. What you see could be the hack work of an amateur, or the master work of an experienced technician...you'll have to gauge it by how the guitar plays and the pulls work together.

Riley Hart · Post by **Riley Hart** » 9 Feb 2014 4:00 pm

I saw this earlier googling around forum. References stiffness vs. travel in terms of lowest angle of tuning nut leaving changer into imaginary space. Sri, can't seem to find the specific link in my history...

Mike Wheeler · Post by **Mike Wheeler** » 9 Feb 2014 5:13 pm

IMHO, what you are seeing with the angles of the bellcranks is an adjustment that makes the pedal, or lever, stopping point "feel" solid without having to press hard to keep it there. It's all about leverages.

If you don't know how to set these leverages, you'd best get a good steel mechanic to take a look at it for you. There's more involved in setting one up than just the hole positions the rods are in.

Some people hate these round cross-shafts in the older MSAs, but the pedals and levers can be set up to feel incredibly fast and accurate when done right.

Richard Damron · Post by **Richard Damron** » 11 Feb 2014 1:03 pm

Alvin -

You are entirely correct. Tom Gorr has added a useful bit of information.

Ideally, any pull should be "linear", that is, in the same direction as the rod. However, everything in a PSG is rotational - a circular motion. In order to reduce the effort required to pull a changer finger, the most "linear" configuration is to be found where the direction of the pull is tangential to the arc formed by the radius of the rotating bellcrank, + and - about the center point of the arc. Some may quibble about how much energy is saved by adhering to this fact but the reasoning is sound, nonetheless. The same reasoning should be applied to the connection between the pedal rod and the actuating lever attached to the crossrod.

Richard

Alvin Douglas · Post by **Alvin Douglas** » 11 Feb 2014 1:24 pm

Thanks All. Yes, after looking at the underside photos of guitars on this forum, it appears as though the bell cranks are adjusted so they are at a right angle to the pull direction. Mine are all over the place so I think I will try to make some adjustments. I have learned about the ergonomics of the pedals and levers. Adjusting the relative height of the pedals and position of the levers so as to make it natural to push the A pedal while operating the LL lever (for example) has taken a while but I'm getting there. Thanks to everyone who commented. Your help is invaluable.
Alvin

Donny Hinson · Post by **Donny Hinson** » 11 Feb 2014 4:57 pm

Tom gives great advice! Unless there is a problem with how the pedals feel, or how the guitar is playing, I wouldn't go changing things "for looks".

Larry Bell · Post by **Larry Bell** » 11 Feb 2014 6:28 pm

My first 4 guitars were MSA Classics. The bellcranks only had 4 positions to adjust the leverage (i.e., stiffness and amount of travel/pull) AND the TIMING. Some other guitars have 14 or more positions on the bellcrank, allowing very precise timing (when a pull starts). The MSA Classic design had round cross-shafts which would allow setting, e.g., a full step raise on the 5th and 10th strings so that each started at the same time and pulled to the stop, by moving the bellcrank a bit shy of or a bit past perpendicular. I WHOLEHEARTEDLY agree with the advice NOT TO MESS WITH THE SETUP until you completely understand what you're doing and how to un-do it.

Just my take on it.

Oh, and I'll add, BE SURE TO TIGHTEN THE BELLCRANKS VERY FIRMLY, especially if they are not perpendicular. They can slip if not really firmly tightened. Just a word to the wise. I've had 'em slip on gigs and it sometimes takes a minute to figure out that's what the problem is.

Lane Gray · Post by **Lane Gray** » 11 Feb 2014 8:12 pm

Larry, by having the round cross shafts, the MSA has much more flexibility than even the 14 hole Emmons cranks. If it's near TDC, it pulls its fastest, but when they lean over, they're pulling slower.

Dustin Rigsby · Post by **Dustin Rigsby** » 12 Feb 2014 5:27 am

interesting stuff I didn't know about my MSA ! Quite honestly I wish someone would start an MSA tech thread with this type of subject matter. They are interesting creatures.

Erv Niehaus · Post by **Erv Niehaus** » 12 Feb 2014 8:28 am

I'm rebuilding an old ZB and putting in a conventional cross shaft and bellcrank setup.
I looked around at the various systems and decided on the MSA Classic setup with the round cross shafts and associated bellcranks. It's much more adaptable to what I'm doing with the ZB.

Tony Glassman · Post by **Tony Glassman** » 12 Feb 2014 8:37 am

Lane Gray wrote:Larry, by having the round cross shafts, the MSA has much more flexibility than even the 14 hole Emmons cranks. If it's near TDC, it pulls its fastest, but when they lean over, they're pulling slower.

Lane is right. When the bell crank is tilted away from the perpendicular, the arc through which it moves is a motion of combined (or resultant) force consisting of both horizontal and vertical motion (vectors).

With the bell-crank set just behind TDC, there is less vertical (wasted motion) and more horizontal (pulling) motion acting at the changer.

Richard Damron · Post by **Richard Damron** » 12 Feb 2014 11:27 am

Georg -

I think that I've gotta correct your assessment.

When the bellcrank is leaning towards the changer, the horizontal component of the motion is greater than the vertical moment. As it is rotated further, the moment is almost vertical, resulting in little movement from the changer. Hence, the movement of the changer is faster at the beginning.

Lane Gray · Post by **Lane Gray** » 12 Feb 2014 11:35 am

Tony, I think instead of calling it "wasted" motion, it might be better to call it "bled off," since you do it to pulls you WANT to slow down. "Wasted" carries a negative connotation, but you WANT unequal outcomes from an equal input.

Tony Glassman · Post by **Tony Glassman** » 12 Feb 2014 12:41 pm

Lane, no negative connotation was implied. I meant, â€œwastedâ€ as in motion that is not capable to do work (linear changer movement). From timing standpoint, that may desirable to get two changes to end simultaneously

Richard, Please feel free to correct me. To my understating of physics, movement at TDC is the closest youâ€™re going to get to pure horizontal (or linear) movement at a bellcrank-pull rod couple traveling in an arc. The farther one moves away from that point, will result in greater vertical displacement (positive toward Top Dead Center or negative away from it). A tangent drawn across any point in the arc will show the resultant motion as compared to the horizontal cabinet floor. I'd tilt the bell cranks slightly aft, so the vertical motion is similar both at the start and finish of the pedal excursion.

Russ Wever · Post by **Russ Wever** » 12 Feb 2014 7:20 pm

Another 'angle' (pardon the pun) on all this is that with the cranks mounted
on round cross-shafts, you can opt to cant the crank towards the changer
(at idle) and as the pull progresses, the force necessary to 'mash' the pedal
thru its range will increase, whereas, if conversely you opt to cant the crank
away from the changer, the force required to 'mash' the pedal thru its range
will decrease.
Of course, the 'rate of leverage' changes accordingly in each case,
but this option is one that can be taken into consideration.
~Rw

Mike Wheeler · Post by **Mike Wheeler** » 13 Feb 2014 5:50 am

Well said Russ. That's what I was alluding to in my previous post. The bellcrank angles can be used to great advantage because they're infinitely variable. And by the same logic, can make for terrible pedal action if set wrong. Learned that lesson long ago.

Richard Damron · Post by **Richard Damron** » 13 Feb 2014 8:17 am

My Bad -

I misread the post.

Richard Damron · Post by **Richard Damron** » 13 Feb 2014 8:22 am

Tony Glassman -

You're right, of course, but, if the pullrod is at an angle to the changer, then "top-dead-center" is shifted such that the rod is tangential to the arc formed by the bellcrank. This is nit-picky, I know, but it's nonetheless accurate.

Richard