Here's a few thoughts on these two
rda's:
https://www.fasttech.com/product/1353408
https://www.fasttech.com/product/1391101
A pic of the bases and caps of these two rda's (after drilling for bottom feed)
Both bases are pretty well identical, 12.8mm diameter where the o-rings are fitted, around 14.5mm total outside diameter, with a slight dish in the floor, and the top caps are interchangeable. Both have brass center posts making it easy to drill compared to stainless. Or you could slot the center pin or center pin insulator, I haven't tried those methods. I use a 3/64" drill to drill the center pin, last time I did it I drilled from above, and then from below, meeting in the middle, not sure if this is the best method but it ensures a nice neat hole in the center of the bottom of the post, and less chance of wandering off-center too far. I fit a 510-510 adapter to center the drill bit on the bottom of the post to drill it, and use a block of wood which has 2 holes, one for the 510 connector and one for the whole base to hold it all straight and level. The same piece of wood is also used to press out and refit the center pin using the drill press as a manual press. There is also a 1/8" hole in the wood to hold the center pin while the actual feed hole/s is drilled, the holes that let the liquid onto the floor of the atty.
These two rba's vape well and there is no leakage if the o-rings are good, they have a smaller chamber than an RM2. To me they are somewhere between a RM2 and an Igo-S. Sometimes the o-rings are chopped up a bit on assembly at the factory. The o-rings do swell a bit with eliquid over time. I have a selection of 1mm thickness o-rings in case. A 10mm diameter o-ring will stretch and be thinner than a 12mm diameter for example, so you can fine tune the fit of the cap. If the cap is too tight, an alternative method is to put the base in the drill press and use a triangular file to deepen the grooves for the o-rings. I have a special bolt for this, the diameter of the bolt fits the drip tip hole snugly, I rounded off the head of the bolt on a bench grinder to fit inside the cap, and put a washer and nut down over the bolt where the drip tip normally goes. Then the long threaded end of the bolt is coming out the top of the cap and this can be put in the drill press for polishing or shaping of the cap. I have shaped a couple of caps using files with the cap spinning in the drill press, then polished them. Slow work compared to brass, but not that tedious.
The order I do it in:
1. Drill the center post vertically from top and bottom.
2. Press out the center pin and drill the side feed hole or holes.
3. Press the center pin back in making sure you have the coil wire holes lined up properly.
You want the center pin to sit about 0.170" from the bottom surface of the atty. If you vape heavy VG liquid in a cold climate you might want to use a 1/16" drill bit for drilling the center post. Be careful of the threads if doing this from the top of the post.
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