Thread: Scion xB '06, in-dash Atom 330, Lilliput 889GL; details, pictures, links. Index: pg 1

Originally Posted by roflcopter

what about aluminum? its easy to bend and its non-corrosive. with the amount of metal actually needed, i cant imagine a sheet being too expensive. especially if purchased from a home depot or lowes.

I agree -- aluminum is very nice to work with. The finished product doesn't "rust", and, even if I were going to paint, aluminum would be great, because it takes very little preparation. Galvanized steel has to be washed well with phosphate. Aluminum is more expensive than steel, because we have to use a heavier gauge to get the same strength.

I happened onto a panel from a discarded computer, this time from a big server, and it doesn't appear to be galvanized steel, but rather "aluminized" steel. That means it's been hot-dip coated with aluminum-silicon alloy, and it has the no-rust benefits of aluminum with the strength benefits of steel. It's the best of both worlds.

There's enough steel for the head unit brackets and a bunch of other stuff in just one piece. Hidden or not, these parts won't need paint.

Steel Panels

Here's a picture of that steel cover panel I'll use for the head unit mounting system. It's painted dark gray on the outside (the streaks you see on the inside appear to be overspray from the powder coating operation). It needs to be cleaned, but I'll happily trade some cleanup time for the zero-cost price tag.

Along with the cover panel was a panel of perforated aluminized steel, also free. It was formerly the cover to a huge power supply. It would be terrific for the ends of my computer case, but I'm not going to take the completed case apart and redo it. It might be interesting to build a whole case out of this material. I hate to think what I'd pay for a perforated panel like this if I went to buy it. We'll need it for something . . . it can go into storage until then.

Click image to enlarge.

Revised Head Unit Mounting

As is typical of new designs, the head unit mounting has changed again. As I began to cut cardboard pieces to make these bracket mockups, I noticed that the left bracket would be pretty easy, so I decided to make that one first. I mocked up a cardboard piece to attach to the left side of the HU and go down to that big Phillips-head screw. That's when it dawned on me that a shift in the design would result in a better system. "Ahhhh!", I said out loud, "how 'bout a deck and rail system?"

That's what I'm building: a bolt-in system that will support the head unit separately from holding it in. The HU slides onto a support deck that holds it in position laterally and vertically. and tabs on the back of the HU bracket are fastened to the deck so it's held in place fore-and-aft. If the mount is solid, the heavy head unit will be, too.

The huge advantage to this system is that I can build the whole thing without the head unit in place, so the workspace is much roomier. It also means I only have to fasten one time to the Phillips and Torx fasteners, which are at odd angles and are hard to reach. Then the HU can be removed and reinstalled easily.

Cardboard Version

Cardboard is easy enough to work with, and it's a lot faster than metal when I'm just trying things to get some concept of fit. For most of this work, I'm not using corrugated cardboard, like boxes are made from. This is posterboard, about 1/16" -- 1.5mm -- thick. It only takes scissors or a knife for cutting and a Phillips-head screwdriver to make holes. I can do all that kind of work in the car, because the only mess is cardboard bits, so it's easy cleanup. If I need to extend a part, I can trim and try new pieces of cardboard until I get the fit I want, and then make a new one from a single piece. The biggest problem with cardboard is that it's just too flexible to provide very good accuracy. Still, it gets me into the ballpark, and lets me try things out until I get a concept that looks like it will work. The parts look rough in the pictures; I didn't try to make them pretty -- just functional.

Step one was to make a mock head unit for positioning, so I could see how high the deck should be and what angle to use for it. The cardboard mount can't support the actual HU, and it's no fun to try and support that heavy weight in position while I do fit checks, so this is a good substitute. I chopped down a Woot shipping box to the exact dimensions of the head unit. This the one place I used corrugated material, because it was handy. There's no top, and I cut one end open so I can see how it mates to other surfaces:

Click images to enlarge.

Then I made a cardboard deck to go under the HU, and added a cardboard leg to connect it to the Phillips-head screw. I bent the back edge up; that will provide strength, and the HU will slide back against it. I also extended the tab out under the deck to provide stiffness. I put temporary corners in the back to keep the back bend in position (they won't be necessary in the metal versions), and cut a hole for cooling to match the holes in the HU. Cutting the hole -- rather than just marking it -- lets me make sure everything will work together. In doing the fitting, I used the actual HU, not the mockup; the mockup is just for the in-dash fit checks.

Here are two views of the cardboard deck and its left leg. They're inverted in these shots:



Here's how the top of it looks:



Next I needed to support the deck on the right side, so I built a leg running up from those Torx T40 socket-head bolts. The bottom of the leg has tabs that the Torx fasteners go through. Next, I added a piece on the top where it would meet the deck; it took several tries to get the piece just the right shape. Finally, I added an extension to support the deck and provide more stiffness. Here's the original part, inverted so you can see the tabs more clearly:

Click images to enlarge.

Here's the opening in the dash with nothing in it, and then with the deck on its two legs. You can just barely see the legs sticking down from the front lip.



The pink area at the top of the left picture is apparently my finger. Oops.

That's it so far. Next I'll mock up the HU brackets.

Head Unit Brackets

The brackets that connect the HU to the deck bolt into the sides of the head unit, and each has a flange that extends under the HU. There's enough gap between the flange and the HU that the deck can just slide between them. The flanges lock the HU in place both laterally and vertically. Here are the brackets, then the brackets mounted on the HU (the HU is inverted here):

Click images to enlarge.

Making sure there's just the right gap between the flanges and the HU will be critical in making this system fit, so it will be one place I take plenty of time to make it exact. The gap should be very slightly larger than the thickness of the deck, for a nice, tight fit. The light metal version will be a bit loose because the deck material is thinner.

I'll put some tabs at the back of these brackets, then build tabs on the sides of the deck to match. After drilling matching holes in them, I'll put speednuts on the deck flanges. After installing the head unit, I'll attach the brackets with short sheet metal screws, and they'll hold the HU in position fore-and-aft.

Next I'll clean up the right leg design, and then I'll start on the light sheet metal version

Revising the Right Leg

This is a development process, and sometimes sleeping on an idea makes it come up cleaner. I wasn't very happy with the right leg design two posts above; it had too many bends and notches, the bottom tabs weren't big enough, and it looked weak. I had to live with the middle notch, but I cleaned it up and added some extra depth. Here's the progression of that leg (it's inverted in these shots):

Click images to enlarge.

The first picture shows the leg after a bunch of fitting and making something that worked from several pieces. I cut the second part after tracing the cobbled-up piece, so it would retain its shape -- the tape has too much "give" in it to stay aligned properly. In the last picture, I added some small pieces to it to make it stronger and add width at the bottom for the mounting tabs. I didn't make a new part. The additions were cut to fit and taped on because they aren't structural. The part is still a single thickness of cardboard, and easy to trace, so there's no need to make a "final" cardboard sample.

I'm still a little concerned about its strength at that thin section in the middle, but I'll build it as is and see how strong it feels.

Now it's time to start cutting sheet metal.

Making Metal Parts

The head unit is relatively heavy, and it's cantilevered out from the mount points, so these support parts have to be strong. In making them, I have to consider not just the normal load of the head unit sitting on them, but vertical acceleration loads -- such as the load I impose by going over a big unexpected bump (where I grew up, that was called a "Whoop-Dee-Do", unless it was really rough, when it was "Holy $#!^!").

The cardboard version of these parts gets me a pretty good fit, and it also lets me see where there may be weak areas. The steel I'm using -- both the light galvanized duct material and the final 22-gauge steel -- is still relatively thin, so I add strengthening flanges to keep the parts from deforming under load. Although the flanges may not always be necessary, a little extra metal is cheap insurance and it adds very little weight. It's better to over-engineer than get an unpleasant surprise. If I can make these parts strong in light sheet metal, they should work fine in the heavier steel.

I lay out the metal parts one of two ways: by tracing the cardboard shapes, or from a relatively formal sketch with all the dimensions. I trace the odd-shaped cardboard parts -- like the right leg -- and add material where I need flanges. I start at 1/2" flange width, but can reduce that amount if there's a fit problem. Where parts have very specific dimensions I have to maintain -- like the deck -- I do drawings. The deck has to fit precisely under the head unit, so, rather than tracing the cardboard deck, I simply make a drawing with all the necessary dimensions, and lay the part out from that, scratching the design into the metal, keeping it aligned with a steel ruler and a square.

The light sheet metal test parts can be cut with sheet metal shears, whereas the heavy sheet metal final parts get cut in the band saw because the material stays flatter; the shears tend to bend the parts. Both types of parts get bent on the little sheet metal bender and drilled on the drill press. I do a little edge finishing on the light parts, mostly to keep from cutting my hands up while I'm using them. For the final parts, I edge-finish several ways: on the grinder/buffer, with a rotary tool, and with hand files.

I do all the manufacturing work on the metal parts -- including trimming and filing -- outside the car to keep chips out of the carpet.

Radiusing Corners

One of the good tricks in working with sheet metal is to avoid cutting a hard inside corner. When two cuts come together, it's a good idea to drill a small hole at the meeting point before starting the cuts. The outside edge of the hole should be right at the cutting line. The result is a radiused corner, which is much less prone to fatigue cracking. If drilling isn't possible, then careful filing to produce the radius works well. Although outside corners don't develop fatigue cracks, I round off them off, too, but that's more to protect my skin and make the parts look OEM.

Choosing Fasteners

One extra concern in building these parts is the fastening process. Pop rivets are fine for most of the fastening I'll do here. But I don't want the rivets to be "bumps" on the deck where the head unit slides onto it, so I have some choices:

(1) find a way to place them so they don't get in the way
(2) countersink the holes and use "pop" rivets
(3) countersink the holes and use solid rivets
(4) countersink the holes and use short countersunk head bolts and either locking nuts or regular nuts with lock washers.

The countersunk solid rivets give the smoothest finish, but they're a pain to install. Real rivets take practice, and this is just a hidden part, so I'll do some testing with countersunk pop rivets. Where the parts will later be disassembled -- like the junction between the right leg and the deck -- I'll use bolts.

The fastening of the leg to the deck won't ever be permanent, even in the finished part. I made the leg as wide as possible for strength, and it takes some work just to get the leg alone up into the dash. If I assembled the leg to the deck before installation, I couldn't get it in. Since one of the goals in this installation is to be able to go back to stock, I'll use removable fasteners -- the countersunk head bolts -- at that joint.

Do I Really Need a Built-in DVD Unit?

I've been considering whether I should put a DVD unit in the dash. It would have to go on top of the head unit, because putting it below might create a conflict between the DVD tray and the shifter. While it would be simple to build a sheet metal case for it that attaches to the HU brackets, it would also mean redesigning the HU support system, because the HU would be about 3/8" lower. I'll have an audio DVD player in the HU, so it all came down to deciding whether I could imagine needing a PC DVD unit in the car so often that a portable unit wouldn't be sufficient.

Decision: no built-in unit.

I'd prefer to run a DVD unit -- even a portable one -- on IEEE 1394 (Firewire), because it's more reliable for high-power-draw devices. That means I need to get a portable case for the DVD unit. It also means I need to add a Firewire port to the PC, but there's space to do that using a low-profile PCI card. The card will require two more holes in the PC case, though, so Firewire and the DVD get added to the list of future enhancements.

That means I can keep right on going with the HU mount as planned.

Building the Deck

The first metal part I made is the deck. This is a part that's unlikely to change in the design, so I decided to go directly to the finished part, instead of doing the light metal part first. I've added a strengthening flange at the front, and I also added the mounting tabs I mentioned. Here's the drawing of the part, produced in Google Sketchup:

Click images to enlarge.

I normally use pencil sketches for the parts, not Sketchup drawings, but the output from a quick Sketchup drawing is a lot easier for you to read in this worklog.

The material for this part was previously the bottom paper tray panel from a dead fax machine. It's my favorite material -- stainless steel. Here are the cardboard mockup and the new metal deck:



I cut the cooling hole in the middle of the deck by drilling some holes and using a saber saw to cut the rough opening (it was a really rough opening -- the saber saw blade didn't like being asked to cut the stainless steel). Then I put the grinding bit on the Ryobi rotary tool, which is an 18V-battery-powered version of the Dremel. That got the opening pretty close to finished size. I did the final work with a hand file.

Where there are multiple bends to make on a part, as there were on this deck, I have to plan the order of the bending, or I may get the part to a point where it won't fit into the bender and I need to go to the vise. For small bends, that's okay, but the vise doesn't produce the clean, finished quality I like. For long bends, the bender is indispensable. On this piece, I bent the tab legs first, using the metal bender, and then I bent the tabs themselves in the vise. That gave me just enough room to bend the long back flange in the bender, and I finished with plenty of room to do the front flange the same way.

The brackets are next.