The AM Forum

The  big air variable in a matching network  I just built has so little friction that the rotor just rotates by gravity until the plates are all the way down. What is supposed to provide the friction so it holds position? Can it be adjusted? I've attached a diagram from the web that closely resembles the one I have. Is it that nut and screw in the back? 

I didn't lube it. It was purchased probably ten years ago, never used.

Yup. Unlock the jamb nut and put a little pre-load on it with the screw adjustment, but go easy, you cont want to damage the bearing surface. Probably a good time to clean and lube the friction points as well.

I contacted the manufacturer who was kind enough to respond immediately.  I was advised not to fool with any of the screws and nuts on the cap. It won't help. This cap is almost always connected to a motor which holds the position for the cap. There just isn't a lot of friction. The engineer suggested either adding a counterweight or friction on the shaft.  He did offer to swap it for something else but I just added a counterweight and all is well.

I had the same challenge and solved it with a 6:1 vernier gear made for 1/4 inch drive shafts. 
The shaft connects to your dial. The internal friction in the 6:1 vernier did the trick.
Chuck                   

Although it's somewhat kludgy, I've used a rubber grommet in a 'unibitted' oversize hole.

Make the hole JUST big enough to give enough friction on the shaft.

If the shaft MUST be insulated, be careful... I've been burned on rubber grommets having a high carbon content and showing measurable resistance.

IE, my 70A supply idles at about 15 amps using rubber grommets as a feed through insulators.  Went to the shoulder washers from an old mirror mount antenna bracket, no more problems!

--Shane
KD6VXI