Saturday, December 15, 2007

Sawing Pork

What do you do when you have a 6lb pork iceberg and really need 2, 3lb blocks? How about when you find that your razor sharp you can shave with it hatchet is not enough to go through some hunk of flesh? How do you make a fine, powdery swine snow that will make your rottie puppy think she’s in heaven? What is the correct blade for cutting frozen blocks of meat? How do you supply your neighbors with plenty of reasons to say “what the heck is he doing now?” How do you send your wife running for hot mits while covered in pork?

Well, for these and other questions that you don't dare to ask your mother…

A Super Sawzall + 10” Craftsman, rough cut pruning blade will saw through that 6lb porksicle like buttah…

BTW, the hatchet probably would have worked but after a few swings I came to the conclusion that the swing that it would take to go through cleanly would have probably broken the counter. I wonder why they didn’t build that thing right in the first place…

Now where is that free-loading cat?

Friday, December 14, 2007

Making a Non-AC Heater Box for 3rd Gen F-Bodies


You guys have my attention.  

There are at least 3 threads out there now with “where did your non AC heater box pics go” since the server that was hosting them crashed and burned… honestly I never expected anyone to miss them.

Anyway, lets discuss this for a second, put up some info on how I made it and some pics.  I’ll have to apologize ahead of time: the whole thing might be a bit disjointed, especially the pictures, since I’m taking it from 3 different places. I’m also sadly missing the pictures of the actual fiber glassing since between the resin that sticks to everything and the very abrasive dust generated cutting and sanding ‘glass I probably would have destroyed a camera.

For those of you that aren't coming from the assorted forums looking for this- some quick background. Basically, for a whole slew of reasons the 3rd gen f-body guys have been getting rid of their air conditioning style heater boxes, “my AC doesn't work and I don’t feel like converting to a new refrigerant,” just to clean up the engine bay to get rid of some clutter, make room for modifications or because it’s more of a race car and what does a race car need AC for? For those of you asking why does a race car need heat either I’ll say for a consistent drag car you need consistent engine temps, with a heater you have a ready built, small radiator and fan assembly to use for just that; that and to keep your hands warm on those mineshaft, incredible conditions "this thing will run the best times ever," nights- ask my brother, he removed his and now drives to the track with a little electric heater and his hands between his knees looking like he's doing something he shouldn't at stop lights.

In my case I originally did it because:
  1. It didn’t work
  2. It was extra weight in a car that I owned for no better reason than to go faster
  3. It took up tons of space in a place that I could use for a turbo down pipe.
To give you some idea, here are a few pics of my “new” project car with it’s complete AC box.  Not only is it impressively large (it’s really about 2x what you see in the pictures, you can’t see the bottom half that extends almost all the way down to the frame rail, hell, you can’t see the frame rail, the firewall, and you can’t get to a large part of the engine on that side), but all the stuff around it is actually connected to it.

In contrast, here is my older car which has now become a parts car that has my box in it. There is actually more wiring harness around it because this car has been converted to use a different ECM, programming and 2 barr MAP sensor (mounted on the firewall above the air box with the green plug), and you can see what an enormous difference it makes, you can see all of that side of the engine, the firewall, frame rail…

Now there is another solution. A few f-bodies came from the factory without AC, but this has it’s problems also. The non AC boxes were borrowed from the S10’s and were steel, unlike the FRP (Fiber Reinforced Plastic) AC ones, and the steel ones just didn’t look right, they stuck out like a sore thumb. They also had a smaller fan housing, which used a smaller fan and motor which were setup for 3 speeds as opposed to the 4 that the rest of the setups have, meaning different wiring and dash pieces that you have to dig up somewhere. Lastly, this is the big one, they’re not that rare, but people have gone insane with their prices. You can find them pretty readily on ebay or assorted message board sale boards, but I’ve seen dented and rusted out ones going for $150-300.

So there’s a perfect reason to waste a bunch of my non-existent free time stinking up the house and killing a few of my dangerously lacking brain cells with fiberglass resin. Lets get dirty!

Actually, first a quick note about the design (sorry for the false start). This thing would have been much easier to make with some pleasant curves and nice lines and usually somewhere in that universe you hit an elegant state of “form follows function,” but that was not one of the goals here. I wanted something hard and angular, with the occasional awkward curve, like the original box it was replacing. The idea was that it should fit in. I’ve had guys very familiar with these cars closely inspect around under the hood trying to figure out how I made so much space on that side never even noticing the “different” heater box. This is a case of “form follows GM.”

So here is what I started with:

There’s 2 significant things here that you might not immediately realize. First is that the AC fan box is the right size and fits the 4 speed fan that we want and has the shape that we want, so lets use part of it… I found a convenient place to cut it from the rest of the box. Second, I took a piece of cardboard and made a pattern for the base plate. One that covered all the necessary holes in the firewall…. Once I had a shape I liked the fan box got taped to the top of it (you might be able to see it better from this angle:
At this point I had to work out the rest of the shape, and cardboard was the perfect medium. I took a piece and scored it to make the hard, square corners, glued/taped it down to the cardboard base plate and added whatever shapes I needed to make the thing up. At this point I took and blended/sanded/ground the fan box edges so it’s shape flowed smoothly into the rest of it.

Now to use the whole thing as a plug mold, as you can see in the pictures it needed a shiny surface, it got wrapped in duct tape. Without a shiny surface the fiberglass would have never released from it. The whole assembly then got stapled to a big sheet of plywood which was wrapped in plastic wrap (again, the resin won’t stick to shiny smooth surfaces). If I really intended this thing to be reusable for multiple uses I would have given it a heavy coat of shiny paint or gel coat to make it shinier and less sticky to the resin.
Next the whole deal got slathered with a few heavy coats of car wax to act as a mold release. You can use proper mold release, but anything that gets a good layer of wax where you don’t want things to stick will work.

Now this is where the fun part started, basically I put on layers of resin and ‘glass cloth, carefully pressing them down to squeeze all the excess resin out and to make sure that the cloth was tightly following the lines. Since this thing had all these different shapes and cloth doesn't stretch like mat does I used it in strips, kind of like paper mache.

The 2 layers of glass gave me a light, thin, and adequately strong part to work with. The more layers I’d put on top of the plug mold the more it would cover/obscure the shape of the part, so at this point I popped it off the mold… well, more accurately, since the mold was not totally smooth I pulled up on it and the mold came up with it, pulling the staples out of the wood. The mold stuck where the edges of the tape was, but I wasn't really stressed about it, and broke it up and pulled it out (again, if I meant it to be reusable I would have given it a heavy coat of shiny paint).

At this point I went to turning it into a useful part. 

The base plate put a ridge around the lower inside of the part which was easy to follow to cut out and sand to shape. From there I gave the part it’s structure by applying multiple additional layers off ‘glass mat (it’s easier to form into intricate shapes) mixed with cloth (stronger, lighter, really not necessary for this, I ended up with a part that was super light but strong enough for me to stand on) to the INSIDE of the part.
I didn't care at all about the finish on the inside of the part, but the outside I did. I gave the outside a single, thin layer of mat/resin since mat has a random pattern to it and doesn't have the same tendency to “print through,” as cloth. Then I did what I consider “cheating” the final finish, saving me a good deal of the sanding and other finishing that I would need otherwise by taking some bondo body filler, mixing it with some ‘glass resin (both are polyester based products) and spreading that thinned out goop across the top surface of the part, letting it smooth itself out.

What was left was sanding, sanding and more sanding, some paint and finally cutting out and drilling the holes for the motor/fan assembly and the coil assembly (plate that screws to the top of the duct to cool the coils used for fan speed control).  Slap it together and you’re ready to go.

This is what it ended up looking like (before cutting out the hole for the fan speed coils):

Here is a view from the inside assembled:

And finally, a view from the top assembled, with the motor cooling hose installed, all screwed up, ahem, together:

Wednesday, December 12, 2007

Dayton SA240 240W Subwoofer Amplifier Bass Boost Modification

Well, it was time, I got tired of using a test rig to power a subwoofer I built years ago so I decided to go with something better.

For a lot of people Parts Express is pretty much the standard for DIY speaker building supplies and their Dayton subwoofer amps have become pretty much the standard for powering home built subs. I decided the biggest of their old school, original series amps, the SA240, 240W one was the way to go. It helped that it was on sale for $99.

Anyway, the amp is available in a couple of different versions, one that supposedly has a flat response curve and the more popular version that has a 6 dB bass boost at 30Hz. I probably would have just ordered the one with the bass boost considering I’m using a sub that has what amounts to a tiny driver (8”) in a huge room (if I remember right it’s something like 19’ x almost 30’), but as luck would have it, they were out of stock. What do you know, I plug it in and decide “Yup, I think I’ll need to play with the bass boost settings.”

Interestingly, Parts Express is quite willing to provide information about choosing component values to change settings, but at the same time a lot of people tend to complain that they are too difficult to modify. For those of you out there debating about the thing, I decided to take a few pictures and put up a quick description so you can decide yourself if this is something you want to get into. Since I’ve build a few speakers and am always changing things and “voicing” different combinations of driver, enclosure, source… combinations, that of course means that I need to over complicate the solution so I don’t have to rip the whole amp apart every time I want to change something.

So here’s a chart of the documented settings for the amp:

Simple enough, change 2 resistors and it does something different, so let’s have at it.

The resistors are located at the center of the pre amp board, the board that has the crossover frequency and gain knobs on it as well as the RCA jacks. To get it out you need to remove the 4 main case screws, disconnect 2 jumpers, one going to the line level jacks and the second going to the main amp board, and then remove the screw that holds it to the back of the face plate, a second screw that comes in through the front of the face plate in the middle of the RCA jacks, the 2 knobs and the nuts and washers holding the pots to the front face. This is all pretty straight forward and if you’re worried about that part than don’t even consider doing the rest. The worst part is that the output wire is glued to its hole in the back of the case limiting the amount of room you have to work around inside.

So once you have it out it looks like this:

I realized that I don’t really have anything that gives you a good sense of scale with these things, well to give you some idea the big monster looking resistors on the bottom left are your typical ½ watt resistors, usually you don’t see them much smaller than this unless you’re talking about surface mounts.

So here are the buggers we’re after, they’re almost right in the middle of the board:

And no, I don’t know who the rocket scientist was that decided to put the capacitor lead right over the top of one of them, and yea, it’s at least as much in the way as it looks in that picture, probably more.

Here is my solution to only having to disassemble this thing once and still be able to tinker with it. Instead of desoldering the resistors and replacing them with the new ones, instead I replaced them with sockets making them easily removable.

Actually, I should give credit to my brother, these were his idea. These are pins used to make IC sockets. I was originally going to use the pins that you use to make computer cable “DB” style ends, which are very similar but taller.

People will give you all sorts of suggestions about the best/neatest way to desolder stuff like this, and I’ll admit, I tried some desoldering braid to start with but got nowhere with it. Not being much of an electronics freak, I didn’t have the typical desoldering irons or even a proper soldering station, so I ended up just flipping the board over in a Tupperware (to give the board that sticks out off of it somewhere to go), grabbing a generic 30watt Weller soldering iron and just heating the pins and pushing them through their holes till the resistors fell out.

To put the pin sockets in I put the socket in the hole and while holding the board in my hand and using my forefinger to push a toothpick up against the socket holding it in position on the board and feeding in solder and the iron with whatever limbs I had left over.

The end result looked sort of like this from the back:

(look towards the center of the board and you’ll see a few solder joints with dark flux around them, the flux was eventually cleaned off before the board was put back in the amp).

From the top you can see the sockets, and you can also see the R35 and R36 labels on the board where the resistors have been removed. You can also see the lead from the previously motioned capacitor carefully bent around the bottom right socket:

And finally a picture with some 1/4watt, radio shack resistors installed (if you know what a normal, small resistor looks like this picture might give you some sense of scale, one set of the pins had to be bent back under the resistor to fit in the socket spacing. I purposely left the leads on the resistors a little longer to allow for easier insertion/removal during testing, and when I finally decide on what values I like I’ll probably put little tape over them or a dab of glue if I have any indication that they might vibrate out (I really doubt it).