Sandblaster, Part 2

This is Part 2 of my sandblaster project.  Continue reading below, or Click here to go back to Part 1.

The Doors

Wait, no, not those Doors.  We're still working on the sandblaster.   Well, you've kinda seen this show before, so let's do the short version.  Here's the steel pieces, after much cutting/grinding/drilling:

And here's the finished doors, one for each end of the cabinet:

As with the glove flanges, I cut oversized pieces of wood, bolted them to the door frames, and then used a router to trim the wood exactly flush with the steel frames.  The result was a much better fit (and a much easier process) than if I had tried to measure/mark the wood and cut it on a table saw.

The Air Supply

Wait, not that air supply, we're still working on the sandblaster.  (Sorry, that was just too easy.)

Before starting this project I bought a book, "Build Your Own Cabinet." Ironically, it contained plans for building a cabinet roughly as big as my tiny Harbor Freight unit.  I knew this when I bought it, but thought it might have some useful ideas for me anyway. 

As it turned out, yes, it did.  The blasting gun sucks sand up from the collection funnel via a venturi device inside the gun.  You would think a simple suction tube jammed into the sand pile would work, but the reality is a bit more tricky.  First of all, you need two tubes:

These two tubes get welded together, and the right end is positioned in the sand.  The suction hose (which brings the sand to the gun) connects to the left end of the long tube.   The shorter tube provides a way for fresh air to get down to the bottom end of the pickup tube; the pickup tube needs to get a pretty good draft going to entrain a useful amount of sand, and the shorter tube provides this air.

Wait, there's more:

Near the bottom end of the pickup tube assembly (seen in photo above), there's a 5/16" hole drilled in the side of each tube.  Those holes get aligned and held in place by a short piece of 5/16" bolt shank, which you can just make out in that picture.  This crossover hole is where air from the supply tube enters the pickup tube. 

Once the two tubes are welded together, that short piece of bolt shank is removed, the crossover holes get covered by silicone-RTV, and the bottom end of the air supply tube gets peened shut:

Presto, the sand pickup assembly is ready to mount inside the sand collection funnel.

Next, I made an unusual air supply manifold for the cabinet.  Before:

After:

What's so unusual?  The simple way would be a couple of barbed fittings welded to a plate, to bring compressed air into the cabinet and supply the gun.  But I wanted to try something extra.  The compressed air enters at top left, and the bottom left fitting feeds the gun.  But the valve and copper tube will supply a trickle of air to the bottom of the sand pickup tube.  Instead of relying on simple suction, I wanted to provide a little "kick" to encourage a bit more sand up into the pickup tube, resulting in faster blasting.  Further down (see Final Assembly) you'll see how it's supposed to work.

Oh yeah, installing the air supply manifold in the side of the sand collection funnel.  Well, this was my first misstep, trying to just "eyeball" the installation:

Two pass-thru holes for the fittings, and six bolt holes, and you can see they're more than a little off-plumb.  It wouldn't have been a big deal, except one of the bolt holes came too close to the steel frame inside the sand collection funnel:

Solution?  A "custom" washer:

If it weren't for me blabbing about it on the web, no one would ever know about it.  :-)

The Lens

The lens glass and two-piece plastic frame were purchased from TP Tools; all I had to do was cut and drill my plywood panel to receive those pieces. 

I had learned from previous projects that a circular saw used with a straightedge can give a very nice straight cut.  And so I set about cutting out the window hole:

After drilling a few bolt holes, the panel got installed for another test fit.  Now it's really starting to look like a blast cabinet:

What's left?  Waddya mean what's left?  You didn't think I was going to leave all that bare metal and wood unfinished, didja?  ;-)

The Paint

Yep, it needed paint.  Lots of it.  And here's where I made one of my biggest mistakes, opting for SPRAY paint instead of a gallon of plain old brush-on/roll-on house paint.  Spray paint is expensive, noxious, and extremely messy.  Here's a piece of the cabinet frame, on the floor of my garage:

I laid down cardboard to protect the floor, but not enough of it; some overspray managed to stick to the floor.  And overspray went even further, leaving paint dust all over the entire floor of the garage.  That distant overspray didn't particularly stick to anything, but it sure made a mess; the painting took a while, and I had to sweep up the overspray dust several times to keep the mess under control. 

I painted the interior of the panels white to make best use of the available lighting, but you can see from the pic that I painted the frame blue.  The panel exteriors were also done in blue, and you'll see below that I added some yellow (maize, actually).  Hey, this is Michigan, the only other plausible option was do the whole thing up in green and white.  ;-)

The Wiring

With the paint work done, it was time to wire up the light box.  A switch, two E27 lamp sockets, and a small 120Vac fan for ventilation, and a dedicated power cord:

Browsing at Home Depot, I had found the mother of all CFL's, a "300-watt-equivalent" lamp that required just 65 watts of power.  So I bought two of 'em:

Anybody who has used CFL's knows that "X-watt-equivalent" is a bit of an overstatement.  There's no way these giant CFL's put out the same amount of light as a true 300-watt incandescent bulb, but they certainly put out enough light for this project, and the fact that they ran very cool was a big bonus as well.

The Final Assembly

At last, after a long winter of measuring, cutting, drilling, welding, and painting, it was time to put this beast together, piece by piece.

Assembly begins upside down, with the top of the cabinet:

Then the bottom of the cabinet, with its tabs for attachment of the legs:

The sand collection funnel "spider":

Panels installed on the funnel:

Funnel subassembly in place:

Legs and stiffener/shelf (I didn't bother painting the underside of the shelf):

The whole thing, flipped rightside up:

Cabinet main panels installed:

Lightbox and doors (with latches) installed:

The door open, showing the sealing gasket and the sand-shedding wedge at the bottom of the door (this prevents an avalanche of sand every time you open the door):

The interior, nice and clean (for the last time ever):

A visor above the window blocks lightbox glare from hitting the window directly.  Note also the ground wires on each glove flange, connecting them both to the frame.  The frame was ultimately connected to the ground line on the power cord.  Sandblasting in the old cabinet has, at times, created static electricity strong enough to make my arms twitch involuntarily; I was determined to make sure static discharge would not be a problem in this one.

Before installing the expanded-metal floor panel, I covered the top of the floor frame with strips of silicone rubber (in red here):

This prevents the floor from rattling, metal-against-metal, when parts are placed or moved in the cabinet.  Note also the red air hose attached near the bottom of the sand collection funnel, and the black hose that brings sand from the pickup tube.   If we zoom in and reorient a bit, just below the air hose fitting at the bottom of the funnel you can see a small copper tube.  that's part of my experimental air supply system:

Here you can see that the copper tube blasts directly up into the bottom of the sand pickup tube, helping to drive extra sand up to the gun.

The Replacement

Since 2005, my Harbor Freight cabinet has blasted about 1300 Mojolevers.  Blasting in the exact same way every time, I had actually worn a hole in the side of the cabinet, allowing sand to leak out.  Not that you'd notice, since there were myriad other leaks in the cabinet to begin with.  The sand was piled at least an inch deep behind it:

You can see from that photo how I had propped the cabinet up on bricks to get it to a useful height.  With the bricks gone and the old cabinet placed next to the new one, you can also see how absurdly small it really was:

For comparison's sake, here's how one single Mojolever fit into the old cabinet:

The Mojolever had to lay corner to corner, with very little room to spare.  Now you can see how I managed to blast through the cabinet wall over time. 

In sharp contrast, the new cabinet can hold 10 Mojolevers comfortably, leaving plenty of room to position things for optimal viewing and blasting:

Epilogue

I finished the cabinet in March 2010.  In fairly short order I discovered that the hoses had an annoying tendency to flop over and get tangled in my work.  In fact, the previous photo shows that tendency.  That was fixed with a single bracket: 

By forcing the hoses to stand up a bit, it made it much easier to keep the hoses clear of the work space:

I've had a few months to work with it now, and I can say it's much, much better than the old one:

So, mission accomplished, partly.  I've got a nice big blasting cabinet, and it can be broken down and removed from the basement if the need ever arises.  So what about the money-saving part?  Er, FAIL. Turns out all those parts and pieces (especially the paint!!!) added up pretty fast.  My grand total for this project was a whopping $921.  That is indeed less than the $1100 I would have paid for a comparably-sized commercial-grade cabinet, but it's way, way more than I thought I would be investing.   

Still, no regrets; I'm very happy with the results.  :-)

Click here to go to Part 1 of the sandblaster project

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