Well, the stiffening brackets took me a couple of extra days to complete, but you’ll see why below…
I started with 2" x 2" x 1/4" aluminum angle brackets that were 48" long. I determined that I wanted my stiffening brackets to be 39" long (the distance between the Y rail end plates is just a little bit more, something like 39.5", so I had to cut them down (I used my miter saw, and just went nice and slow). I ordered three brackets just in case I messed one up…
A quick note on why I went with the angle brackets rather than one of the many perfectly valid stiffening plate options that are advertised around the forum (which usually are flat, connect to the inside of the Y rails at the top and the outside of the extrusion underneath the wasteboard at the bottom, and are WAY easier to install)… Those plates do a superb job of stiffening the Y rails in the vertical direction, however I don’t think they do as great a job of stiffening in the horizontal direction. The angle bracket, however, provides resistance to deflection in both directions.
As with the stiffening plates, I wanted to attach my stiffening brackets to the inside of the Y rails at the top/sides, but I wanted to attach to the top (rather than the side) of the extrusion underneath the wasteboard at the bottom of the bracket. I’ve seen at least one other person who also used angle brackets to make stiffeners, but they just used wood screws to attach their brackets to the wasteboard at the bottom. I wasn’t crazy about this method, since MDF doesn’t hold threads well at all, and I could see those screws working themselves loose over a not very long period of time.
For making all the connections, I ordered hardware from Inventables - post-assembly T-slot nuts, button head cap screws, and washers (all M5). I did some mathification based on the thickness of my brackets (1/4"), the thickness of the aluminum extrusion rails (20 mm), and the thickness of the wasteboard (3/4"), and determined that 12 mm screws would be appropriate for the sides, and 30 mm screws for the bottoms, including the washers (about 1 mm thick).
I knew that I wanted to make slots in the rails for my screws, since the likelihood of me getting holes drilled in perfect locations was pretty small. I figured this was also a perfect opportunity to get my feet wet milling aluminum on the X-Carve, so I clamped down one of the angle off-cuts, and…
I had to use a single-flute bit for length in order for the bottom of the router to clear the other side of the angle. I started with the recommended settings in Easel (5 IPM feed, 3 IPM plunge, 0.003" DPP), and it turned out pretty good, although the plunge seemed a little quick to me. My hole size was 0.205" wide and 0.410" long with fully rounded corners (the M5 screws have a diameter of about 0.193"). I did a test fit with my hardware, and it was perfect!
I did have a small problem though… I had to stay a certain distance away from the other side of the angle when milling in order to avoid colliding with the collet nut. I did another test to see how close to the angle I could mill a hole…
…and it wasn’t going to be close enough for where I needed the screw to go to thread into a nut in the extrusion under the wasteboard. I also wasn’t going to be able to mill from the other side of the angle, since I didn’t have any great way to clamp the material down in that orientation. So, I had to resort to the manual method - drill a small hole at either end of where I wanted my larger hole to be, and widen it with successively larger bits - extra fun in my case since I don’t have a drill press, and had to do it by hand. Again, using an off-cut as a test platform…
It didn’t turn out too bad! I used a 1/4" bit for my final hole size (a little on the large side, 0.25" compared to the 0.205" holes I was able to mill). For clearing the material between my initial drills, I basically wiggled the drill bits between the holes and they slowly chewed out the “bridge” in the middle. I DO NOT recommend this method to anyone else attempting the same thing, as it’s terrible for your drill bits (totally not designed for lateral cutting or loading), and not super great for your drill. However, if you are going to be as dumb as me, make sure you wear your requisite protective gear. In fact, even if you’re NOT going to be as dumb as me, make sure you wear your requisite protective gear.
Having proven to myself that I could put a satisfactory hole in the angle bracket where I wanted, I moved on to the “real” pieces. I clamped them to a 2x4 suspended between work horses and marked my hole locations…
I used a nail to put “pilot dents” where I wanted to drill.
…and then I started drilling! I stepped up through four bit sizes for the initial holes (I think I began with a 1/16" bit), then started back with the smallest bit to remove the material in the middle. I made the “real” holes slightly longer than the test one, so there was more aluminum in the middle to remove, and I had to resort to using a small metal file on a few of them.
…but, I finally got there! I used a sander with some 220 grit as a final step to knock down the burrs.
For the second piece, I started with three holes, and the whole experience went much smoother.
Unfortunately, as I was anticipating would happen from my egregious misuse of my drill bits, I suffered a casualty…
However, both angles now had all the bottom holes drilled, and were ready to have the side holes milled using the X-Carve itself.
Now here’s where I got off on a bit of a tangent, and why this effort took four days instead of two. Feeling a bit like I had a new superpower, I wanted to see what all I was capable of achieving in aluminum…
Pretty neat, right? Lest I draw your attention to the bottom of that hunk of aluminum, where you’ll see the gnarled mess of a way over-ambitious carve that resulted in some aluminum welded to the bit. For the record, 25 IPM feed and 0.02" DPP with a single-flute 1/8" bit on the X-Carve is officially too demanding. However, I was able to settle on 20 IPM feed, 0.5 IPM plunge, and 0.005" DPP with very favorable results.
At this point my supervisor turned up, and told me, in his own way, to get back to the task at hand.
I had spaced the holes in the brackets in order to avoid the screws holding the wasteboard down at the sides. Double-checking…
Good! I then measured, marked, and checked where I needed the holes for the sides…
…but I was just a little bit low. So, adjusting…
Perfect!
I designed my hole pattern in Easel - it’s great for simple cuts like that. I split it into two jobs, one for each half of the angle bracket, since the working area of the X-Carve wouldn’t quite cover the whole thing. This meant I had a total of four jobs to get all of the holes milled in both brackets.
After getting the first half of holes milled on the first bracket, I set it up again to triple-check…
For the record, I was off my mark because I was a little off on my zero position, not because my cal is off. 
Awesome! Good to finish off the rest!
Now, again getting a little off on a tanget… Since I had a tested and working pattern, I decided to add a little flare to my stiffening brackets…
Alright, brackets satisfactorily fabricated, it was time to cut channels in the wasteboard to accommodate the screws that would go through the bottom of the brackets into nuts in the extrusions beneath the wasteboard. So, out came the wasteboard…
This didn’t really come as a surprise, but it was neat to see. There were small piles of wood and aluminum dust underneath where all of the threaded inserts were located.
I used a 1/4" straight router bit to cut the channels in the wasteboard. It was just a hair bigger than the slots already in the board for holding it down to the extrusions.
I used the freshly drilled-and-milled brackets themselves as guides for marking where the channels needed to go. I used a square to translate these marks to the edge of the wasteboard, then, as is my modus operandi, double-checked the marks were where they needed to be.
I then measured the distance from the center of my router to the edge of the base (about 1/32" under 3" for my DeWalt DW618), and made guide marks from all my cut marks, offset by that distance.
I used a large ruler as a depth gauge, and and a speed square as a guide. The wasteboard was clamped to the 2x4s underneath, and the ruler and square were clamped to the wasteboard.
I brought the bracket back to check my cuts before moving on to the other side…
Beautiful!
Moving things back to the X-Carve, I again used the brackets as guides for inserting the post-assembly T-slot nuts in the lower extrusions before replacing the wasteboard.
Things had been going so well up to this point, I knew that I must have made a mistake somewhere, and here’s where it finally creeped up on me. While I had made sure to locate my screws so that they avoided the wasteboard screws, I had positioned the end screw holes too far out, and there wasn’t enough extrusion underneath to properly insert a nut (the extrusion I wanted to screw into butted up against the front/back perpendicular extrusion). At this point, I wasn’t going to go through the effort of putting another set of holes into the brackets and another set of channels in the wasteboard, plus these holes were so close to the Y rail end plates that their mechanical contribution could be said to be marginal. I was still able to use the matching holes on the sides of the brackets, as the Y rails themselves run the full length of the wasteboard.
After re-installing the wasteboard, I again checked the positioning of the T-slot nuts…
Still good! Using the brackets as guides one final time, I inserted T-slot nuts into the Y rails.
At long last, I was ready to screw it all down. I first installed all the screws just to finger tightness, then, starting with the bottom screws, tightened everything down firmly in an alternating pattern. I ended up ditching the washers on the lower screws, as they were riding up on the fillet in the angle bend just a little bit, and I wasn’t getting as much threading into the T-slot nuts as I would have liked with the washers left in. I went over all the screws a third time just to make sure they were nice and snug, and finally called the project complete!
As far as results go, I’m going to be a little spoiled. I’ve only got about 100 hours on my machine, so I’m not exactly going to know what I was living without. I can say that, before, I was fairly easily capable of deflecting the Y-rails a few millimeters, especially horizontally. Now, they’re at least solid enough that I can’t move them with all my weight.
Also, some of my lessons learned on aluminum…
Set your Z = 0 position high, by 0.015" or 0.020" or so. Your first few passes will be in air, but this ensures that your first pass in material is no deeper than you want it to be. That first pass is CRITICAL - if insufficient material is cleared out, the bit will be deflected on subsequent passes, leading to all kinds of issues. The below video shows this tactic being utilized - note that the first pass in material isn’t uniform (around the 1:40 mark)!
WARNING: LOUD!! TURN DOWN THE VOLUME!!
In setting your Z = 0 high, set your depth of cut in your CAD model a little deeper to compensate. Say you wanted to cut a 0.05" pocket, and you plan on setting your Z = 0 point 0.015" high - make your pocket in your model 0.065" to adjust.
I highly recommend setting your Z = 0 point without using a probe. Just go slow, and jog by smaller and smaller increments - I go down to 0.001" when I get close to my material. I also like to use a small piece of thin printer paper - when the bit grabs the paper to where I can’t slide it around anymore, I know I’m effectively right at the top of my material.
If you’re wanting to cut a hole completely through your material, set your material thickness in your model just a little bit over what it actually is. For instance, the slots I milled in my brackets only needed to be 0.25" deep to go completely through, but I set my material thickness (and cut depth) to 0.3". Since I also started 0.015" high, it actually only punched an extra 0.035" through the other side of the bracket (I used some 1/4" plywood underneath the bracket to keep from digging into my wasteboard).
All of those tips above are actually good to follow no matter what you’re milling, but especially with aluminum since it’s likely to be the least forgiving thing most people will attempt milling on their X-Carve.
I also wanted to show the condition of my bit. I used one bit to mill all the holes in my brackets, plus all four of the logos, plus four other test patterns roughly the same size as the logo, all of them performed without any kind of cooling (other than the downdraft from the router) or lubrication. The picture below shows both the used bit, and a brand new one. Can you tell which is which?
The new bit is on the left, and the used one is on the right. As you can see, the used one is actually still in pretty good shape! Point being, look for that sweet spot (and use all the advice here on the forum to help you get there) - your bits will actually last quite awhile if you’re using them appropriately.
Next upgrade on the list is the 3GT pulleys and belt for the Z axis. The belts are supposed to arrive tomorrow, so that should be a quick one…