We go .020" narrower on the acrylic vs the aluminum, and make sure to round every hard corner. At this size, the rounding is very noticeable. It should be rounded to just over your cutting bit's radius. So for me, that would be a 1/8" bit, so radius is usually .07". For larger stuff we go with a 1/4" bit as the difference is negligible once it's over 12" tall. Going this route, we basically
never have to file the acrylic or the aluminum.
View attachment 181755
Personally, I leave 1/8"-1/4" of lip on the back side, this makes them far more resilient if they get dropped, and we start with 3/4" acrylic, so depending on metal thickness, you have about 3/8-1/2" of exposed letter edge. The lip's width can be as narrow as 1/8"-1/4", the 'smaller' it is, the more resilient it is. Further, instead of gluing the letters in, we span them with a piece of 3/16" lexan, that is bolted to welded studs. This helps minimized the number of studs, diffuses the light more evenly than clear acrylic, and takes all the force off the acrylic if the face gets hit. Apply vinyl before cutting the acrylic for the cleanest look.
We stock basically one module here, principal qwik mod 2 in 24v. It does channel letters and shallow push through cabinets really well with minimal guess work.
I hate this style. The white tends to darken toward all the corners, as the light has to go through that much more substrate, without beveling all of the corners, you'll never get a good even lit letter. The tip of the R in your example is particularly dim.
Usually it's a pocketed out front 'cover' in white acrylic, and a lipped back piece in clear. Line it with those crappy tape in modules, seal it all with a particular silicone (I forget if it's RTV, non vulcanizing, or what. The kind that doesn't leach ammonia as it cures, this is basically potting the electronics.), and you have a non-serviceable waterproof letter. Kinda like this:
View attachment 181759
I'd honestly order something like this rather than fab, as a replacement letter is a bunch of labor for a one off, and since my process are far from set in stone, I'd spend more time pouring over files to figure out what offset I actually used and everything just to make sure the new letter matched the old ones. We've ordered from everylite before, and while I hate the idea of ordering customer made stuff from overseas, their quality was top notch and the price was far below what I could match in house. The ordering process and shipping were not ideal, changes were made once a day since the main contact was in the phillipines, and some stuff got lost in translation that required even more emails to correct. At least the letters 'shipped' out of FL, but it was obvious they just used that as a US mailing address to avoid customs and tariffs. Here's their page for this particular style:
https://everylite.com/products/alpha-letter/acrylica/