More fun with the pressure box

When I compared the pressure box to the lid, I discovered that while the lid was almost perfectly square, the main part of the box was slightly out of square. It also rocked slightly when I set it on a flat table. In order to square up the box, I decided that some mechanical fasteners were in order - I didn't want to rely on just gluing & clamping.
So, I put the lid in place and using some hardwood scraps, I clamped the lid and the box together, side to side and end to end, to forcibly square the side/end assembly (with the already square lid):








Then I flipped the arrangement upside-down, and drilled some pilot holes for some small screws so that they would screw into the centerlines of the hardwood reinforcing strips that were glued to the lower edges of the side and end pieces:








Before gluing, I drove all the screws in to the bottom panel so that the points stuck out slightly and would "find" their pilot holes in the side/end assembly:









I then applied glue to all of the bottom-facing edges of the side/end assembly, set the bottom panel in place and tightened down all the screws:









Once the glue had dried overnight, I found that everything was square and flat, and I got a nice square fit with the box and the lid.

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Pressure Box Initial Assembly

I started putting the pressure box and lid pieces together. Getting everything to line up precisely was a bit of a challenge.

One of the first minor problems I noticed was that the shorter side pieces and tracker bar platform pieces were all just slightly too long to allow the longer sides to fit flush with the bottom and the lid top. Since I had cut them all from a single length of ripped 1/4" plywood, they were all exactly the same amount too long. (about 1/32")

The amount I needed to remove was too small to handle with the bandsaw, and I knew from previous mistakes that hand sanding the end of a thin strip of wood to remove a little length often results in an edge that's less than square.

I remedied this problem by clamping all the pieces together so I could run them over my sanding block and gradually reduce their lengths. By clamping all the pieces together I could keep the end cuts square.

 And here's how the ends looked after sanding. (the one piece that looks shorter is actually a reinforcement strip that had already been glued on to one of the plywood strips)

Once all the pieces had been sized more precisely, it was time to glue everything (almost everything) together.

(Since I'm going to be staining and shellacking the pressure box in a multi-step process, I elected to keep from gluing the bottom on at this point.)

Here's a pic of the lid pieces finally glued together:

Here's the pressure box glued together (without the bottom):

Another view of the pressure box, lid and bottom:

And stacked together to check the fit:

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Back at it!

I've been distracted for long enough and figured it was time to get back to the building….

For the last week or so, I've been focusing my attention on the pressure box.

I've been busy cutting out and gluing together all of the reinforcements and various pieces in preparation for assembly, and here are all of the pieces that I've been working on for the pressure box and the lid:

Another view:

Here's the lid put together as a dry fit to see if everything lines up correctly:

And here's a dry fit of the pressure box:

And a detail shot of the tracker bar platform pieces:

I'll still need to drill some holes for the air entry and the take-up spool shaft, as well as for the crankshaft end and the idler shaft.

It feels good to be back building!

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Trackerbar tubing

After getting the trackerbar stained with a "golden pecan" color and 3 coats of shellac, I decided I'd try to put some more brass into the build.

Since I'm planning on having a hinged top panel between the pressure box and the pipes, I thought I'd tidy up the wad of tubing that connects the trackerbar to the pipe nipples. I gathered up the 1/4" rubber tubing I had, and after seeing what 15 pieces of this looked like, and how much space it consumed, I wanted to go for a more streamlined arrangement. I searched the web and YouTube and found all kinds of info on bending brass tubing without flattening it or giving it an oval profile in the bends. After trying a couple of test pieces, I came up with a method that seemed to work fine with the tools that I had.

First off, after calculating and cutting the pieces to length, I annealed the brass - first with my propane torch, then after that ran empty, I used the gas stove.

 The idea is to get the brass tubing just to the point where it's faintly glowing red near the area to be bent. It helps to do this at night, with the kitchen light turned off, so the faint glow is easier to detect. After getting to the desired temperature, I then ran the tubing under the faucet to cool it off so I could handle it and anneal the other end.

Of course this leaves the brass discolored, so after the annealing process, I gave all the tubes a good sanding with some 1000 grit sandpaper. It's much easier to polish them up before they have bends in them.

Next I prepared the tube for bending by crimping one end closed with a pair of vise-grips

Then I filled the tube with table salt, making sure it was well tamped in and filled the entire tube. It's important that there is no moisture in the tube, so it's good to let them dry after their post-annealing quenching.

Once the tube was full of salt, I pinched closed the open end with the vise-grips and wound up with this:

Having calculated the measurements for the length and the reference points for the bend radius, I put the tube in my tubing bender, lined up the mark and put a 90 degree bend in it. The tubing bender I bought was a cheap $9 model from Harbor Freight, and I found that giving the tube and the tool a shot of WD40 helped the bender from dragging on the brass too much.

This left the bends with a nice circular cross section all the way around the bend. I wanted to make sure the air path was not obstructed by kinks or sharp turns.( I'm guessing that the travel through the brass tubing will actually prove a little more efficient than the airflow through the rubber tubing, since the brass is smooth inside and should cause less turbulent interference along the way.)

Here's a view of what it looks like from the bottom of the tracker bar. The 5 larger pipes with their 5/16" nipples and tubing will remain as in the plans.

And here's a view from the top. the array of brass tubes is about 2 1/2" wide at the point where it will exit the pressure box side. At the back of the pipe board, the black rubber tubing will vertically connect the the brass tubes with the pipe nipples.