I've just completed a little mod on the UTA2 - or as my wires called it, "The UTA Slasher".
I'm very pleased with the result - it's turned it from one of my worst wire cutters to one of my best, most secure through-post atomizers. I also think the static resistance has been noticeably reduced, improving TC accuracy. I haven't yet measured a before and after resistance to be sure, but I will test this when I get my second UTA2 in a week or two.
Quick TLDR explanation and solution:
The problem is caused by the hollow posts with no 'floor' for the wire to sit on.
The general solution in most atomizers is to fill in that floor, which can be done by cutting small bits of wire (copper, silver, nickel) and packing the holes, or, where there is enough thread, threading a small section of screw down to the bottom to act as the floor.
The UTA2 however is fairly unusual in that the posts are held in by screws from the underneath. This blocks the latter method of fixing, but enables another: screw in the floor from the bottom.
Below, the lurid details, in case anyone else should want to try this or a similar fix.
Apologies in advance for blurry photos, my camera can't do macro to save its life.
The Problem
The UTA2 has posts which are hollow all the way down, with the wire holes in the middle. When the wire goes in and the screw is fastened down, there is nothing underneath the wire to support it.
The screw thus presses the wire down, bending it in the middle into the gap below. This puts lots of pressure on the wire at the edges of the screw hole, causing it to break very easily. It is also not a particularly solid or low resistance connection.
This is a particular problem with Titanium, which is heavily annealed and therefore very soft and easily broken. I even had 22G Titanium cut off in the UTA2.
The Solution
Give the wire a floor on which to rest its weary body!
UTA2's posts
The post holes are double-threaded M2.5. There is a section of thread at the top for the post screws, and then another section of reversed thread coming up from the bottom. This is for two further screws that screw in from the underside. In the case of the positive, this is the path to the 510 and the mod. For the negative, the screw secures the post in place as it's not welded, only press-fit. The negative screw also improves the negative connectivity to the base.
Here's the underside of the UTA2, visible once you unscrew the base cap (held in with 2 x Philips countersunk screws)
The two underside screws are M2.5. In the clones they are brass, but I have been told that these are stainless steel in the original.
The screws fit over/into a thin sheet of plastic insulator with three holes:
In this insulator:
- Large hole, top right: for the negative screw
- Slightly larger than the screw head, such that the negative screw goes through the insulator directly touching the underside of the base.
- Smallest hole, top left: for the positive
- Has a flattened section in the middle of the hole, possibly not visible in this poor photo.
- The positive screw attaches through this hole such that the screw head presses against the insulator and does not conduct with the base.
- The thickness of the insulator also ensures that the positive sticks out a bit higher than the negative, pressing against the brass positive ring/510 pin.
- Third hole, bottom: for the airhole
Building a Floor
My plan was to put in longer brass M2.5 screws in the underside, that would screw in far enough so that their end would be a floor for the wire. I purchased a packet of M2.5 x 12mm brass screws, double the length of the original underside screws.
The first issue I encountered is that the thread for the underside does not go up nearly high enough - the posts are threaded such that the post screws are able to screw down well below the floor of the wire holes, so the underside cannot reach the floor from below.
To fix this, I ground down the end of the M2.5 screws such that they were no longer threaded for roughly the last 6mm. They became in effect 6mm brass tubes attached to the end of 6mm M2.5 brass screws:
I did this with a Dremel metal grinding attachment, holding each screw in a clamp and running the Dremel end against one edge of the screw thread, then rotating it 90° and repeating.
Once this was done I was able to screw the new screws in fully. They were a little too long, coming up to the roof of the screw holes, so I then used a hacksaw to cut about 1mm off the end until they came to just above the bottom of the screw hole. On one I also needed to grind down the end a little more, as a result of not hacking off quite enough.
I wanted the floor just above the base of the screw hole so that the wire wouldn't touch the outside edge of the post hole. I figured this would be most reliable, avoiding any potentially sharp edges.
The next issue I had was with my choice of replacement screws. Unfortunately I couldn't get quite the right heads. I could only get "cheese head" screws, which have a larger diameter head. Had I found screws with heads matching the originals, the rest of this section might have been avoided . However I am not sure what the right head type is called, or even whether it would be available in M2.5 x 12mm; I found that 12mm is already relatively unusual for brass M2.5s, at least on eBay, and I seem to recall only cheese head was available in that size. There are probably more head types available for stainless screws, but I prefer brass because of the much lower resistance for maximally accurate TC.
As my screw heads were too large, they would touch and short when both positive and negative underside screws were in place.
I fixed this by heavily Dremeling and filing down the head of the negative screw, and also a small amount on the positive:
The next, related problem was that even after I cut down the heads, the negative still didn't quite fit through the insulator. The solution to this was as simple as it was crude:
With all that done, the replacement screws were able to screw into the underside with the negative touching the base, the positive not touching the base, the positive pressing firmly against the 510 pin, and with a small but definite gap between them:
The Result
I now had the two original brass underside screws left over, so I decided to re-purpose them as my new post screws. I much prefer these to the tiny grub screws that the clone comes with, and this also had the benefit that the brass screws had a perfectly flat bottom where the grub screws have a little indent.
I made one small alteration to the new post screws: using my hacksaw, I cut a deeper central slot to make it easier to turn them, and enabling use of larger screwdrivers to do so.
Here, the final result - in which you can hopefully just see the brass floor. Also, a 24G Titanium coil that went in first time and extremely securely:
My negative post is now completely loose, held in only by the underside screw. I had to hold it very tightly with pliers while tightening the new underside screw, and while attaching the coil and trying to tighten the screw very hard I found the post still had a tendency to want to turn. In the event I still got the wire tightened in place securely, without needing to use pliers to hold the post, but there is now a risk of this.
I am not quite sure whether the negative post was originally secured in any way or if it was just a press fit plus the underside screw. I know that the first couple of times I removed and replaced the original underside screws, the negative post stayed in place. But some time after it started moving when I touched the underside screw, and became completely loose shortly after that.
It's not a huge deal that it moves, but if anyone does this mod for themselves they might want to take care with the negative post when removing and replacing the underside screws. If you can do this quickly and cleanly without the negative moving, life will be easier thereafter.
In my case I am thinking of maybe adding a tiny blob of solder to the head of the negative underside screw head to lock it in place, which hopefully will also lock the post in place. But it's not a big deal, once the underside screw is in as tight as possible the post only moves if you really crank hard on the post screw - which is no longer necessary for a tight wire connection.
