Bob58
03-26-2007, 12:27 PM
I've been asked about what I did to my Lee Pro 4-20 pot, so that it doesn't drip. Rather than reply individually to those who asked, I wanted to post a description of what I did, so that those more knowledgeable than I could read it, and comment if I did something wrong.
First, it's possible that I just got a Pro 4-20 that wouldn't have dripped anyway, had I done nothing to it. I didn't try the pot prior to lapping the metering rod, so I don't know.
Here's what I did.
1. Remove the screw, near the top of the metering rod. This screw allows adjustment of the flow rate.
2. I didn't clean the fitting at the bottom of the pot, where the metering rod fits, since my pot was brand new and didn't look like it had any use. But for a pot that has seen duty, the metering rod should probably be taken out, and the fitting where the metering rod sits should be cleaned as thoroughly as possible. You want to be lapping the fitting, not crud in the fitting where the metering rod sits.
3. I used lapping compount from Sinclair International's scope ring lapping kit. This is a fairly course abrasive (it's designed to allow rifle scope rings to be lapped into alignment with each other fairly rapidly.) I suspect that valve grinding compount, or something similar, would work also.
4. Place a small amount of lapping compound on the bottom of the metering rod, and drop the metering rod into the fitting where it normally sits.
5. Using a screwdriver, apply downward force on the metering rod, while turning the screwdriver (I turned in only one direction, so as to be sure to lap symmetrically.)
6. When the lap gets dirty and "broken down", clean the lapping compound residue off of the bottom of the metering rod, and out of the fitting where the metering rod sits.
7. Repeat steps 4 thru 7 "until done."
8. Clean all lapping residue, and reassemble (metering rod adjustment screw back in place.)
I lapped for probably 15 minutes total, before I "guessed" (hoped?) that enough lapping had been done. Apparently, thiswas enough, as after several sessions with the pot, it hasn't leaked, even once.
Again, I don't know if what I did, described in the above steps, was responsible for the pot not leaking.
If somebody has a better method, please feel free to post it here.
First, it's possible that I just got a Pro 4-20 that wouldn't have dripped anyway, had I done nothing to it. I didn't try the pot prior to lapping the metering rod, so I don't know.
Here's what I did.
1. Remove the screw, near the top of the metering rod. This screw allows adjustment of the flow rate.
2. I didn't clean the fitting at the bottom of the pot, where the metering rod fits, since my pot was brand new and didn't look like it had any use. But for a pot that has seen duty, the metering rod should probably be taken out, and the fitting where the metering rod sits should be cleaned as thoroughly as possible. You want to be lapping the fitting, not crud in the fitting where the metering rod sits.
3. I used lapping compount from Sinclair International's scope ring lapping kit. This is a fairly course abrasive (it's designed to allow rifle scope rings to be lapped into alignment with each other fairly rapidly.) I suspect that valve grinding compount, or something similar, would work also.
4. Place a small amount of lapping compound on the bottom of the metering rod, and drop the metering rod into the fitting where it normally sits.
5. Using a screwdriver, apply downward force on the metering rod, while turning the screwdriver (I turned in only one direction, so as to be sure to lap symmetrically.)
6. When the lap gets dirty and "broken down", clean the lapping compound residue off of the bottom of the metering rod, and out of the fitting where the metering rod sits.
7. Repeat steps 4 thru 7 "until done."
8. Clean all lapping residue, and reassemble (metering rod adjustment screw back in place.)
I lapped for probably 15 minutes total, before I "guessed" (hoped?) that enough lapping had been done. Apparently, thiswas enough, as after several sessions with the pot, it hasn't leaked, even once.
Again, I don't know if what I did, described in the above steps, was responsible for the pot not leaking.
If somebody has a better method, please feel free to post it here.