sandblasting

Sandblasting gives bright-as-new lookBy MANLY BANISTER

There are many uses for this versatile sandblastingunit—from cleaning corroded metal to etching glass

Scarred and rust-caked ladle, nippers and hammer were transformed by a sand shower andlight emery cloth rub. Projects shown at top of page were made by using the sand-blasterpictured. Turn page for plans

turn the page

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YOU'VE PROBABLY come up against a dozenjobs when you wished you had access to a sand-blaster—to clean rust and paint off steel, put amatte finish on metals, etch frosted designs onglass and metal, clean sparkplugs—or even totexture wood for picture frames, lamp bases andwhatnots.

If you've been stumped by such jobs in thepast, then wish no more. With the plans presentedon these pages, you can build your own sand-blaster gun—plus a reach-in cabinet for handlingall but the biggest items. And once you've caughtup on your backlog of sandblasting jobs, you'llthink of many more—such as producing noveleffects in jewelry-making, ceramics, or copper,brass and aluminum crafting.

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Cut openings with a saber saw (above),gripping coupled tubs between your knees.Stand unit upright to cut holes in top

The easiest way to lay out cutting linesfor viewing windows and armholes is to cutpaper to dimensions, tape cutouts in placeand trace around edges, as shown at left

If you already own an air compressor for paintspraying, your outlay for materials shouldn'tstrain the shop budget. You use stock 3/8-in. pipefittings to build the nozzle unit around a lever-type blowgun that you can buy new for less than$5. For delicate work, it operates on 15 lbs. ofair, or less; but for rugged duty, such as blast-ing steel, you up the pressure to 100 lbs. or more.The higher the pressure, the faster the cut.

You can use any sand that will pass throughthe siphon tube—including river sand. However,if there's an industrial supply house near, youcan get much better results with the professionalsands available. Those intended for nonrecovery

are very cheap; extremely hard grits such asgarnet, emery and carborundum are higher ininitial cost, but can be used over and over almostindefinitely. For general use on a recovery basis,No. 60 garnet is a good choice. A hundredweightcosts $5 or so and should last years with inter-mittent use. For special jobs, you may want toswitch to other grits. A textured effect on firplywood is best achieved when No. 36-meshgarnet grit is used to erode the fibers between thehard annual rings. For such work, you need anair pressure of over 80 pounds per sq. in. Ideally,your compressor should supply at least 5 or 6cu. ft. of air per minute at a constant pressure

Solder the window frame outside and in after seating it in hole and bending the straight tabsagainst inside of tub. Then stick weatherstrip around window

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SUIT AIR PRESSURE TO JOBPounds-per-square-inch settings for No. 60-grit garnet

GLASS Etching with stencil: smallareas (such as cutout letters),30 p.s.i.; larger areas, 40 p.s.i.Though glass can be etched atpressures as low as 15 p.s.i.the higher the pressure, thefaster the cut. Paper stencilwill wear away before glassetches at pressures over 30p.s.i.

ALUMINUM Etching surface, 40 to 50 p.s.i.COPPER Etching surface, 50 to 75 p.s.i.BRASS Etching or cleaning, 60 to 80

p.s.i.STEEL Cleaning rust or paint, 90 to

100 p.s.i. Etching surface,same (or higher with morepowerful compressor)Steel can also be worked, moreslowly, at pressures under 90lbs.

Inside view shows the gun ready for action,laid on the screen table that's soldered attop rim of the cone. Note 1/4-in. i.d. hosethat connects the gun to the siphon tube

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Clam-shell construction makes it easy to insert work pieces that are too big to pass througharmhole. It also hastens cleaning of cabinet when you change grits. With trunk latchesclamped, the unit is ready for blast-off (right). Air hose is connected to gun inside; exhausthose carries off the dust

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Sandblast gun consists of long-nozzle blow gun andstandard pipe fittings. Only machining required is

for added sand nozzle made of drill rod. Center-bore from both ends, machine to fit nipple, thenheat .nozzle cherry red and quench in water.Tap-and-die tool for threading sand-hose connection

costs about $2—plumbers use it to installcopper overflow pipe in toilets. To substitutereservoir, unscrew connector from tapped plug

sandblasting

sandblaster, continued

of 100 lbs. or more. With smaller-capacity com-pressors, you'd probably be able to do onlyabout 5 sec. of blasting out of 25—the bulk ofyour time being spent pumping the pressure backtoward 100 p.s.i.

Sandblasting is often used on driftwood lampbases. Real cutting is done with No. 36-grit attop pressure. Then, at pressures under 100 p.s.i.,the gun is backed 1 ft. away from the surface tosmooth and semipolish the wood, using one ofthe finer grits, such as No. 60.

The hardening treatment for the nozzle, de-scribed, leaves the drill rod so brittle it couldshatter if you dropped it. So some of the tempershould be drawn by placing the nozzle in a 300-deg. kitchen oven for a half hour and quenchingagain.

If you don't have access to a metal-turninglathe to do the simple machining called for, acommercial machine shop can do it for you ina few minutes.

Even with tempering, the nozzle will wear out.When the opening wears nearly through, makea new nozzle. And when the blowgun nozzlewears out, replace it with one of hardened steel—or buy a new blow gun; they're cheap enough.

metal cabinetThere's a double reason for using a cabinet

with the gun wherever possible. Not only does itprovide for recirculation of the sand; it keeps theair clear and protects the operator from flyinggrit. The sand issues from the nozzle with con-siderable force and in doing its work generates alot of dust, which must be drawn off by means ofa shop vacuum or similar suction device.

Because of the wearing effect of the sandblast,.the cabinet must be metal. Two No. 2 (15-gal-lon) washtubs simplify construction, but areless expensive than an equivalent amount of sheetmetal of suitable gauge.

To avoid the sheet-metal construction shownin the hinging detail you could substitute a gate-size strap hinge. The sloping hopper is providedin the bottom tub so the sand can slide down andreplace that drawn up from the center by thesiphon tube. A pipe-reducer drain is soldered inthe bottom hole to facilitate emptying the hopperwhen you want to change to another grit size.

When formed into a cone, the hopper shouldfit snugly enough so that it must be driven downwith light mallet blows. But don't put it in placeuntil you make the cutouts for the armholes and

air line, as shown. Bend a ring of heavy wire, tryit for size inside the tub, then cut the ends squareand braze them together. Solder a square ofhardware cloth to the ring and trim away theexcess with diagonal wire clippers.

Now you're ready to tackle the top tub. Thelight sockets are the two-piece type that unscrew,leaving a shoulder and throat of porcelain. Themetal of the cabinet must not come in contactwith the metal screw of the socket. Wire thesockets with No. 18 light cord and install a lineswitch in the cord. Make a sheet-metal cover asdetailed and solder it over the exposed connec-tions.

Your soldering is done when you've addedthe sheet-metal tube (to fit the hose of your shopvacuum) and the frame for holding the 6 x 12-in.double-strength glass of the viewing window.When soldering this frame into the cabinet, besure to seal all the gaps to prevent sand leaks.

use a plastic screenIf you plan to use any coarse grits, such as

No. 36, it's a good idea to stretch a piece ofplastic window screen across the frame, about% in. inside the window. Without this screen tokeep rebounding grit from reaching the glass,you'll have an etched window in short order. Thescreen (which must be plastic, since a metal meshwould quickly wear out) cuts down on visibility—but far less than a frosted window would.

You can either set the cabinet on top yourworkbench or build a special stand, as detailed,bronze-brazing the sections of conduit with anair-acetylene torch. The stand's platform has acenter hole for easy drainage of the hopper.

When work is too large to fit inside the cabi-net, you need a separate sand reservoir, as shownin the photo and sketch. If a very large supplyof sand is needed, a tubful can be set by the workwith the gun connected to the rubber feed tube,as in cabinet use. Don't try outside-the-cabinetblasting indoors unless you have a special roomwith a vacuum exhaust system.

Whether inside or out of the cabinet, handsshould be protected with heavy industrial-typerubber gloves. Outside the cabinet you'll alsoneed goggles or—better still—a face shield.

The air line should be equipped with both aregulator and a filter—the latter to trap moisturewhich could clog the flow of sand if it gets intothe gun. This is especially likely in a cold room,or outdoors.

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