So I've had this idea for years now - I keep telling myself I'm going to get a CNC router so I can start making better diffusers, I just really don't have the funds. So I decided to just go ahead and do this idea with an aluminum jig that I'm going to DIY.

My goal, was to make a diffuser in a diffuser, like this design - which I've always thought was interesting, and decently broadband for my needs.




Now, I'd never worked on aluminum like this - so I was hesitant, but willing to give it a try. The stock is 1/4" thick, 4"+ across, and like 24" wide.

I drew out my design, marked and punched the center. I need to remove as much material as I can with the drill to make the next part easier.



I piloted, then started hogging out with the big stepped bit I keep around for punching holes in amp chassis or cars



Since it's a stepped bit on thick material, I flipped it over and continued hogging out on the other side. I did drift a little bit, but only went over one of my many lines *once*. My pencil lines were accurate to the limits of the pencil.  



Then came the scary part...trimming out to the lines...on the router table!! I popped in a cheap bit, and very carefully started nibbling the aluminum to make the round holes square.

Things were going fine, and it turned out to not be so scary! In fact, it was quite satisfying how clean the cuts were, and how easily aluminum got cut away by this cheap bit. Speaking of cheap bit, it was all fun and games till this happened...and it wasn't even under high stress! It pretty much just fell of, snapped clean through!



Anyways, I popped the next sized up, cheap bit and continued on without any issues. These were brand new, I'm pretty sure I only paid like $20 for a box of 6 different sizes.

So, this is what I did *by hand*, and this was before I took a 3/4" file to the holes!!



I'm very proud of my work there. I did tidy it up and square it a hair more with a fine file - I didn't spend more than 10 minutes; then used some abrasive paper to soften the sharp edges.

Then grabbed a 2x4 and my palm router and began to hog out a test run!



My original plan was to use a 1/8" bit with a long shaft that was half smooth and half fluted. I'd run the smooth part up against the jig and just change the depth according to which square I was cutting. Unfortunately in practice this did not work out the way I had hoped. Too much slop in the palm router, in the 1/4 to 1/8" chuck adapter, and in the 1/8" bit itself. All conspired to make cuts that felt barely controlled, and I feared I'd wind up damaging my pretty jig. So I wound up putting a guide bushing (brass collar) on the palm router, which made my 1" square holes now 3/4". But hey, this is a test run/proof of concept.



You can see, even with the collar the cuts were wobbly. Nothing like the beautiful, tightly controlled free hand stuff I was able to do on the router table.



Final 2x4 test piece. The intention was to make mountains of these, as quickly and as accurately as possible, then just glue them to different height (probably hollowed out to save weight) 3.5 x 3.5 blocks to form the diffuser in the first picture; ultimately this would give me a diffuser, within a diffuser.




A few thoughts - making the jig was pretty awesome. I think I'm going to incorporate more aluminum works in my woodshop - though my shop is now all sparkly. I'll probably have to improve my air filtration. LOL. I think I was pushing the limits of what my tools, and especially the 1/8" bit can do. I think I'll just need to bite the bullet, and try again with a 1/4" bit, with the same jig. I'll have more rounded corners, but I'll deal.

Lastly, this was way, way slower than I wanted, to cut out those 8 slots. Changing depth and all that wasn't a big deal, it was really just hogging out that much material, clearing out the dust and chips, then hogging out more, clearing out, then the final clean cutting. I think the deepest I went was only 1.5"...maybe. I'll give this one more chance with a nice 1/4" bit, probably an all carbide spiral upcut, a more stable router platform, and I'll rig up a vacuum hose directly to the router. I bet I could do this in much less time then if this works out. Maybe be able to cut one block every 5 minutes? But then...I need 64 blocks, just for one 28 x 28 diffuser...ugh.

Anyone got a good CNC router for cheap?

Yup, getting a vacuum hooked up some way is worth the effort. You can see better, and I think that there is a bit cooling occurring for the bit as well. Very good job though. I know how frustrating it can with some materials, working them with a machine that can do the job, but isn't specifically made for it.

LR,
I have a line on a good CNC for you.
The table is big enough for any project you could come up with.
3 in X, 4 in Y, And 2.5 in Z. That is in meters lol.
All you would need is around $250K and 440 volt 3 phase, maybe $100K in a foundation, tooling....

LR,
The eBay CNC routers are not too bad. They have their limitations but they are good to learn on. Their limitations mainly is the controller, but that can be replaced later on. Look for CNC3020 or CNC3040 and see if that falls within your budget. But that will not be the final price, you will also need to pay for a real license of the software that runs the machine and then there are the cutters.

Your jig looks real good. I would not have the balls to free hand like that. I know how wood kicks routering out like that so I would never have tried aluminum.

Thanks LFD!

Now that I know I can work aluminum to some small extent, I feel like I have really accurate options open to me for future jigs.

$254 Each? Um, I'm not sure how spending a few thousand on 6" diffusers is saving money!

Besides the fact that I like learning, and experimenting, and problem solving...the truth is, my diffusers are better. They are designed over a broader band (go way deeper especially), have better time delay, and are built around my wants and needs.