In 2005 when I started the whole Mojolever enterprise, I wasn't sure if it would all work out, so I tried hard to minimize my investment. Instead of buying a large commercial-grade sandblasting cabinet, I bought this cute little guy from Harbor Freight. Saved about $800, but it was just barely big enough to fit a single Mojolever into it, and it required some mods - better lighting, a better blast gun, a foot-activated air valve - to make it usable over the long haul.
By October 2009 I had blasted a staggering 1300 Mojolevers in that little cabinet; it's fair to say I got my money's worth out of it. But I was tired of working in such tight quarters, tired of cleaning up the sand that leaked out of the many holes and gaps in joints of the cabinet. Still, I was wary of the price for new cabinets: something of appropriate size and quality would cost over $1100. And how would I get such a monstrous thing down into the basement? As it happened, I was itching to take on a new project, and so I hatched a new scheme.
The goal: build a sandblaster of a size comparable to commercial units (floor: 3' x 4'), for considerably less money, and make it so that it can be disassembled and hauled through residential doors and down residential basement stairs.
And to have fun doing it.
In the machine shop where I work (my day job), there is a commercially-made sandblasting cabinet. It's fantastically cavernous, and the positioning of the window and arm holes seems to be ergonomically spot-on. I made a few measurements of that cabinet, and after fiddling around with some CAD software, I came up with a design for a cabinet of roughly the same size, made of plywood panels on a steel frame - something that could be disassembled and moved through doorways if need be.
With the initial planning done (I say "initial" because plans ALWAYS get tweaked along the way), the first step was hauling 12-foot pieces of steel stock home to build the frame. And that's where the miracle of fold-down rear seats in a sedan came in handy, without which I would have had to pay someone to haul it home for me:
After much cutting, grinding, and drilling, I had the frame members for the main part of the cabinet and legs ready to weld:
There was still more cutting/grinding/drilling to do (door frames, shelf frame, sand collection funnel), but this was enough to get started on the welding.
If you plan on welding anything where accurate 90-degree corners matter, a right-angle vise is indispensable:
You can easily clamp two pieces at a 90-degree angle and hold them there until you're done welding. It's fair to say I used this item a lot during this project.
After just ten welds, I had the floor frame done:
The floor dimensions are 35" x 47". The actual floor panel is expanded steel (not shown in this photo), which is somewhat flimsy; the cross braces provide additional support to prevent sagging.
Once the floor frame was done, it was time to go 3-D. Here the angle-iron work for the sides is done:
Don't mind about the cockeyed piece on top, that's just scrap resting there.
The last two left-to-right crossbars (not yet done in the above photo) connected to angle iron joints that weren't at 90 degrees, which meant I couldn't use standard 90-degree angle iron. Instead, I had to get flat steel strapping, and weld two pieces of it together to make custom-angle iron. I clamped scrap angle iron to each piece to hold them flat while I welded them together along their length:
In that picture, you can see about two-thirds of the welds are completed ; the next weld goes in right where the small red C-clamps are located. When done, the whole piece looked like this:
After welding one more pair of flat steel straps together, the cabinet frame was nearly complete:
Along the way through this job I discovered that some weldments are more sensitive to thermal distortion than others. With improper technique (too much heat on cold metal, starting the weld at the wrong end of the joint gap), one of the joints warped pretty badly, and pulled the floor frame way out of alignment. This shot is sighting down the length of one of the floor members:
After reading up on proper welding technique, I ground away the offending weld, and tried again. This time I preheated the joint area, and started the weld at the correct end of the gap. The result much pleased me:
If you've never used a sandblasting cabinet before, the great thing (compared to an open-air sandblasting gun) is that the abrasive gets recycled: the gun fires the sand against your part, it bounces off, and falls down into a big collection funnel under the floor fo the cabinet that brings the sand back to where the gun's pickup can suck it up for another round of abuse.
So with the main cabinet done, my attention turned to the funnel. More cutting, grinding, and drilling:
With a few temporary joiner pieces and nuts and bolts, I done made me some triangles:
Finally, I turned the cabinet frame upside down and laid the triangles up to form a pyramid, which (when turned right-side up) would become the sand collection funnels:
Packing tape (barely visible on the sloped legs) held the triangles together as a pyramid, and the red C-clamps keep the whole pyramid centered on the cabinet frame. The sloped portions got welded together along their lengths and at the top, making a kind of four-legged "spider." The base segments of each triangle got welded to the cabinet frame, but the spider didn't get welded to those base segments; to fit through doorways, it was important that this spider be removable from the cabinet.
Not shown in the above photo: a 2" threaded pipe stub got welded to the apex of the pyramid. The stub accepts a threaded pipe cap, which acts as a stopper: remove the cap, and you can drain out contaminated/shattered sand before pouring new sand in up above.
Like the sand collection funnel, the legs had to be removable if there was gonna be any hope of getting this thing through doors and into the basement. The top of each leg got a 5.5" piece of angle iron welded to it, with 2" of overlap. Here's a leg, with its 5.5" tab, ready to weld:
And with the weld finished:
The 3.5" of protruding tab received a quartet of 1/2" holes; during final assembly, this tab (on each leg) gets bolted to a corresponding tab on the main cabinet frame.
It's pretty much a given that:
a) the basement floor won't be 100% level, and
b) even if it was, there's no way I could possibly weld the cabinet to have four perfectly level feet.
So the bottom of each leg got a small load-bearing plate welded to it, along with a threaded nut that accepted an adjustable-height foot. Here's a finished nut-plate assembly, along with another one clamped and ready to weld:
After welding all four baseplates to their legs, I assembled the legs and the storage shelf frame together, along with the attachment tabs to be welded to the main cabinet. The whole leg assembly then got parked on top of the upside-down cabinet frame, with clamps at each corner to keep things in place:
In the above photo you can just make out the threaded pipe stub and cap at the apex of the sand collection funnel.
Once the attachment tabs were welded to the cabinet frame, I flipped the whole thing upright for a brief inspection:
Not a bad start: a recognizable sandblaster frame.
With a few nuts and bolts, I disassembled the whole frame, moved it piece-by-piece into the basement, and put it back together. If you're wondering how that big main cabinet frame got through the doors, keep reading: at the end, you'll see how it's made in two pieces that bolt together.
With the frame done, it was time to start cutting the plywood panels. I used 5mm utility plywood - thin enough to be lightweight, but reasonably rigid when properly supported.
Having learned lessons in dust management on previous projects, I hung plastic sheeting around my work table, and laid my shop vac hose inside the enclosure to create a negative pressure zone, assuring no dust would escape:
In that photo you can see two of my previous projects, the torsion box work table and the shop vac silencer (links open in new windows).
With a dust containment zone set up, I sliced up the plywood according to plan, and began fitting up panels on the frame with clamps:
Once a panel was clamped into position, the holes I had previously drilled in the frame members acted as drill pilot holes; I didn't have to mark the hole locations on the plywood at all. The panels were then secured to the frame with carriage bolts:
Finally, I had the four main cabinet panels - glove, lens, top, and back - and the funnel panels secured to the frame:
Note the overlap of the rear panel past the left edge of the cabinet frame. All of the panels had a similar amount of overlap, all of which got marked at this point with a pencil, and later on removed with a circular saw.
My old Harbor Freight blasting cabinet came with an anemic 40-watt fluorescent tube for lighting, which was absolutely useless. I ended up buying some cheap lamp sockets and installing 3 "100-watt-equivalent" CFL bulbs. Once the dust got caked on everything, even that much light was barely enough for that tiny cabinet. I knew that I would need a LOT of light to illuminate this monster, and so I set about building a light box to be fastened to the top panel of the cabinet. The light box was to be 12"x24", and about 5" high. This was fairly easy to make out of plywood and some other scrap I had lying around:
Plywood is great for panels, but it doesn't make good corner joints by itself. That's where the 1/2"-square oak sticks (near right side of photo) came in. After some glue work and a bit of sawing/drilling, the final light box structure was done. In this photo you can see where the light switch will go in the front, and there's also an opening in the back for a ventilation fan:
A test-fit of the angle-iron pieces that will fasten the box to the top of the cabinet:
The angle-iron pieces are offset below the bottom plane of the box by 3/8" (you can see this at the bottom of the photo); this way the angle-iron captures a 3/16"-thick pane of glass that is the exact length and width of the light box, and the bottom of the box squeezes the glass against the main cabinet, along with a 1/4" foam sealing gasket.
Sandblasting necessarily creates large amounts of dust, and that dust needs to be removed from the cabinet to maintain visibility and avoid contaminating the blasting sand. My shop vac worked well for this purpose with the old blasting cabinet, so I designed the new cabinet with fittings to accept the vacuum hose.
More plywood, oak planks, and glue:
After assembling the wood pieces to form two small boxes, I used a hole saw to create a 90-degree elbow passage through each box. A soft-rubber fitting attached with screws is what grips/retains the vacuum hose. In addition to the shop-vac fittings, I also bent up some sheet-metal baffles to help disperse the inrush of fresh air through the inlet, and prevent usable airborne sand from being sucked out the exit:
In this pic, you can see one of the baffles installed on the inside of the rear cabinet panel (in the background), along with the hole where the other baffle will go (in the foreground):
On the outside of the same panel, you can see one of the shop-vac fittings:
Rather than buying standard 10" round glove flanges, I decided to make oval flanges. This is what's on the sandblaster at my day job, and they seem to offer the best range of motion for your arms.
First, I laid out the pattern for the bolt ring in CAD software, printed out a template, and glued it to a piece of 1/8" steel sheet. After that, it was down to some drilling, sawing, belt sanding, filing, etc. to make the bolt flange. The half-round segments of the glove attachment ring was made by wrapping 1" strapping around a mandrel; in this case, one of the argon bottles from my welding station happened to be close to the ideal size. The finished pieces for one of the two glove flanges:
After welding the pieces up to make two complete flanges, I located two bolt holes for each flange in cabinet's glove panel, then temporarily bolted the flanges in place:
The flanges served as a template for a pencil line marking the inner edge of each flange. After removing the flanges and then rough-cutting each glove hole with a jig saw, I bolted the flanges in place again, this time with all 8 bolts on each flange. The jig saw leaves an awful rough edge on the wood; not only that, but it would be difficult to line up the cut nicely with the inner edge of each flange. Instead, you can see I left a generous margin with the saw:
With the flanges bolted back in place, I was then able to use a router with a flush-trim bit to cut the remaining wood cleanly away so that it lined up exactly with each flange and left a nice, clean edge:
Back into the cabinet frame for a test fit:
So far, so good. :-)
Next up, building the doors.
Questions? Comments? Email me!
©2010, Mitchell P. Patrie