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How to modify a rocker for different Latitude

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Larry Myers the maker of the MI-250 only had one size of rocker assembly cast.  It was for 35° to 45° centered at 40°. He had to mill them to make ones for other Latitudes.
asked May 20, 2016 by tom_hilton (220 points)

1 Answer

0 votes


"If a rocker needed to be changed for a different Latitude, then one end of it had to be milled off. This had to be done in a flat, level, straight line from the south end to the north end of the rocker.  If going to a lower Latitude, then more would be milled of the North end, not touching the South end.  If going to a higher Latitude, then the metal would have to come off the South end.  This has to be done in a mill, so that the medal removed is in a smooth flat line. 

If I understood Larry's instructions, this is how he changed a stock 35°-45° rocker assembly to a
25°-35° rocker assembly.

This metal would come off in a straight line from the south to the north side.  It would come off
of the black RA rocker.  No metal would be removed from the South end, but from the south end
gradually more and more towards the north end.  This has to be done in a mill, by a machine shop.
You determine how much this way, if I understand Larry correctly.

1. Remove the Rocker assembly from the RA Assembly.
2. Take the rocker and cradle it in the mid point of the Rocker Slot and sung it down.
3. Take the RA assembly and set it onto the male Rocker.  You will want to use two people.
4. Put a Magnetic based Protractor  on the face of the RA. Most likely it will read the
complement of the Current Angle. (Probably 50°,  which is 90°- 40°)
5. Leave the south end in contact and lift the north end reading the protractor, until
it says 60°.  (Again the complement of the desired angle which is 30°, 90°-60°=30°)
6. While holding it at this position, measure how much you lifted it off the north end.
7. Just for discussion sake, say it was 1/2".   You would mark a straight line from the South end (start even with the south end) to the North end, but 1/2" down on the north end.  This is how much a machine shop would have to mill off the black rocker assembly top.  This is assuming you have the newer colored
mount, where the rocker assembly is black and the rest of the mount is white.
8.  This is going to mess up the screw holes where the Rocker assemble mounts to the RA Assembly.
They will no longer be perpendicular to the RA Assembly.  You will have to correct this, to be able
to reassemble them.
9. These instruction are assuming you want to lower the angle, IE move the mount closer to the
equator."  To go the other way, then reverse the north and south in the above instructions.


answered May 20, 2016 by tom_hilton (220 points)