What you are encountering is one of the reasons I don't usually bother with Dubro horns. Plus they have a tendency to rotate on the shaft while they are in use. Counter that problem with the application of green Locktite on the threads after installation.

You've got the good servo arms to make an excellent installation, but a change for the linkage hardware could be made to either the JR 4-40 ball links and horn or the Nelson Hobbies RCL 70 linkage. I prefer the Nelson and have stayed with it for a long time now.

For a very positive 3D installation, using the equipment noted above, install a ball link on the servo arm at a distance of 1-1/8" from the servo output shaft. Next install the clevis for the aileron or elevator screw a distance of 1-1/8" or more from the center of the hinge line. Installing the clevis at a distance less than the distance from that used at the servo gives a leverage advantage to the flight surface, which is a bad thing.

Another option, using what you already have, would be to shorten the length of the plastic tab coming from the aileron or elevator, and adjust the travels the same as you would with the Nelson or JR linkage, with the transmitter. It will do no harm.

Pat

I forgot to put the next part in.

The angle of the rod will be closest to perpendicular when the servo arm will be at full 3D deflection. That's not a bad thing at all. I have had five planes set up that way using the Nelson linkage and haven't worn one out yet. They DO get flown very hard.