A custom acrylic window, plus some pointers on a couple other things

I mentioned in the Arcade cabinet thread that I needed to break off and deal with a far more important project. The title of the thread kinda buries the lead, but I managed to cut out a nearly perfect window with a vent hole in it for a portable air conditioner.

This may seem like an odd thing to do, but I live in an odd house where NOTHING is standard. The windows of my room are crank out casement style. On top of that, they’re a non standard size, and for some reason the screen enclosure is even less standard at 48 7/8 inch tall by 17 1/16 wide.

I wouldn’t have even attempted something this custom at this stage (I just finally got my triangulation kit done on saturday and dialed in yesterday), but I have three ferrets and keeping this room below 80F is critical for keeping them alive. Also, I’m a cold weather person and in the Chicago area we’ve been getting temps in the 90f-95f range over the last couple days. It’s murderous to people, not just animals.

I will share the gcode for this project, but it’s SO SPECIFIC to my living situation that it may not be of much use to anyone else. What WILL be useful is me running through how I dealt with staging, testing, then running the final cut on the acrylic (with some pictures sprinkled about).

Everything shown here is done with a .25" bit, non-up flute.

First things first, I had to design the hole I was cutting out of the acrylic. I did this by looking at the vent mount included with my choice of portable air conditioner (LG LP0817WSR 8000 BTU unit, it’s a small room). The mount happened to have an odd oblong oval with three evenly spaced .25" tall by .5" wide tabs cut out on the tops on bottoms. From what I can tell, the oblong shape is so you can put the vent piece into the cover, slide in one directions, and drive a small screw in place to hold the vent assembly in place.

I got to throw the regular options out the window. After designing a few replicas as close as I could to the vent mount, I decided to say screw it to the tabs and just extend the top and bottom of the oval out the full .25" for the distance of all three tabs.

Looks almost like a bad submarine:

Before going much further, I figured I’d better develop a way to mount the piece of acrylic I grabbed. This is a 36" x 72" sheet of .220" thick from Menards, cost $140 before taxes. My solution to this was simple, I set up a box matching those dimensions centered around X/Y zero, and generated some gcode to do an outside profile at .1" deep on the sheet of MDF I have on my unit.

After this, I did a test cut of my submarine surrounded by my measured window opening at .1" (vent hole inside profile, window opening outside profile), and checked measurements to ensure I was as square as possible given what I knew about calibration.

From there, I double checked to make sure the measurements, then drove screws into the MDF inside the already routed cuts, two at the bottom first, placed my acrylic, then put a screw in on each side, then a couple up top to make sure my medium wouldn’t move. Then I reset my gcode to do this:

What’s by FAR the most important thing when you’re dealing with acrylic like this is to turn down the RPM rating on your router. I’m running the default Ridgid and dropped my RPMs down all the way to 11500 (second slowest setting). This will vary depending on the brand and thickness of acrylic you’re cutting, but this is a good work point. The melt I ran into was minimal, and things cut smoothly, except for the bottom right corner in the picture. This was when I found out that the 2"x4" I’m using for my top bar is both bowed AND twisted. It was causing some issues that forced me to keep a bit of extra pressure on the sled as it cut, and my hand slipped off on the first pass.

I had to wait until the temps dropped into the 70f range to actually finish off the work. I got home from a truck unload and disconnected the AC unit to test the vent attachment, and it fit! I just had to ream out the holes on the vent attachment to 1/4" and drill through the acrylic to mount the vent with some bolts then slot it in place.

I overdid it on the bolts a little bit. Could have gone shorter.

The overall sheet didn’t end up being exactly right, there were a couple points where it was off by around a millimeter (mostly around that corner that got goofed up in cutting), but it fits FAR better than the temporary foam I had in place.

I had some adhesive weather stripping laying around, so I use that to seal up the small gaps.

And that’s it. I used my maslow to make a window with a properly sized vent hole. I am now sitting here enjoying the pinnacle of human achievement thanks to having a Maslow.

Oh, and I still have some acrylic left over. I’m probably going to set up a control panel top glass for one of my games in the next day or two, all the corners are blown out on it.


I think about this every time I see a window air conditioner installed with duck tape and foam, I’m glad to know somewhere out there is a better solution :grin: great work!