Saturday, March 31, 2012

A Mini Sandblaster -- Princess Auto Cat. No. 8059966

Princess Auto had this item on for $12.99 -- I couldn't resist. I just have to install an air connector, and I can try it out.

My instincts tell me that I've wasted $12.99 on a toy, but if this works out I'll be happy as a clam. My sandblasting needs are not large; this may do what I need it to. Here's a view of what I'll be trying it out on.

It's an ornamental, cast iron bird bath bowl, about six inches in diameter. I've emptied and vacuumed the sawdust bin from under my table saw to use as a 'containment' area for working in. We'll see how it goes. (And by the way, I'm entirely new to this -- I know virtually nothing about sandblasting. I'll share what I learn as I go along.)

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Here it is after about 2/3 of the tank's supply of abrasive.

It does work, after a fashion, but I've learned one lesson already; you can't fake a sandblast cabinet with an open box. The particles bounce and ricochet and fly about everywhere. I'll have to do this outside, and be resigned to losing the abrasive as I use it.

Anyway, the tool shows some limited promise of doing what I need it to. Tomorrow, I'll arrange to work outside and at least get this item paint-ready. To be continued.

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It turned out that I didn't get back to it 'tomorrow'; I got back to it today.

Anyway, here's the bowl after nearly two tankfuls of abrasive.

The tool did do what little I needed it to. The edges and the underside I can get at easily with wire brush wheels. I'll likely be reserving use of the sandblaster strictly for those situations that defy wire wheel brushing.

The Tool's Behaviour

For what I paid for the thing, I really can't complain, but I can't say that I'm really impressed by it, either. The trigger can be difficult to pull at times, and abrasive delivery is inconsistent -- it stops at times until you shake the thing.

I partially disassembled the tool to get a look at its innards; there's not much to it.

Abrasive just leaks down from the tank by gravity, and falls into the airstream to be hurled out the nozzle. It doesn't look to me like the design employs any Venturi effect to coax the abrasive into the airstream -- it's strictly gravity fed. (I imagine that the air rushing by has some tendency to draw down particles, but I don't see that there's what I think of as a 'venturi'.) I guess the abrasive tends to pack in its feed orifice at times; that would explain the interruptions in delivery I experienced. (The small hole behind the abrasive delivery hole is for a fastening screw.)

Air Consumption

Air consumption is considerable -- the nozzle's inside diameter is 5.2 mm. What that tells us is that to a compressor, a sandblaster is just an open-ended pipe. The tool's consumption specs are:
  • 4 CFM @ 90 PSI average.
  • 15 CFM @ 90 PSI continuous.
They don't explain what's meant by 'average'.

My 11 U.S. gallon, 115V compressor claims to deliver 6.1 CFM @ 90 PSI, and it seemed to be able to supply the sandblaster adequately for my purpose. Permit me a brief digression here, concerning compressor specifications.

Air compressor manufacturers have a well-deserved reputation for playing fast and loose with specifications, especially with 'horsepower'. On the side of the motor on my Campbell-Hausfeld machine, there's a big decal that says "3.5 HP". That figure is all but meaningless; it's a 'peak air power' figure that's based on what the machine's full tank of compressed air can momentarily deliver. My compressor runs off a standard household 115V, 15 Amp circuit. On a good day with a favourable tail wind, such a circuit can deliver a continuous 2 HP. 3.5 HP can never be realized from a 15 Amp household circuit. There's an interesting article here that tells a good deal more about the subject.

Should you be shopping for an air compressor, choosing one is easy -- get the biggest machine you can afford and have space for. If I had the wherewithal, I'd have a compressor the size of a small vehicle.


Here's the abrasive I bought along with the sandblaster.

Here's what a little heap of the stuff on the workbench looks like.

It's a remarkably 'clean' material; using it doesn't result in clouds of noxious dust.

There's quite a variety of abrasives available; crushed glass appears to be the cheapest -- that 50 lb. bag in the photo was $9.99. Aluminum oxide is probably more effective, but it's almost five times the price.

The manufacturer, Opta Minerals Inc., has a fine website with lots of information. This page summarizes all the types of abrasive. As with everything, one could make a career of learning all there is to know.

Before I wrap this up, I should mention safety considerations. Take a look at the photograph of the bag of abrasive above. Note how the guy with a sandblaster is suited up. I can understand the outfit. The bounce-back you get of abrasive particles is wicked. Eye protection is essential; a full face shield would be better. Add leather work gloves, and a hat to keep the stuff out of your hair. I didn't feel like I needed a respirator for what I was doing, but it wouldn't hurt to use one. Depending on the abrasive being used, and the type of work being done, a respirator might be essential at times.

Anyway, there's my introduction to sandblasting. The $12.99 tool is useful as a 'spot' sandblaster. One can do some useful work with it. Don't expect more of it than it can deliver. For serious sandblasting, I'd want to acquire that vehicle-sized compressor I mentioned, and a fully-grown sandblaster to match.

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Addendum -- FRIDAY, JULY 11, 2014

Be careful where and how you store an opened bag of abrasive. I made the mistake of leaving a bag open near my drill press, and that's an invitation to contaminants such as this.

That little curlycue of aluminum swarf found its way directly into the sandblaster's abrasive feed orifice, and clogged it. I had to take apart the tool to extract the curlycue.

Keep bags of abrasive closed, and away from where you do machining work.

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Service Note: Valve Stuck Part Way Open -- SUNDAY, August 14, 2016

I had an incident today where the sandblaster's valve stuck part way open -- it would not close. I think I've found the cause.

To gain access to the valve, first remove the blue rear cover on the handle. It's held in place by two claws that are just visible inside two small, rectangular openings.

You'll encounter a hexagonal plug at the upper rear of the handle. Unscrew that with a 5/8" socket wrench. 'Careful -- there's a spring inside.

Now you can unscrew the valve from the trigger with a plain slot screwdriver.

With the trigger unfastened from the valve stem, you can extract the valve stem with its spring and two o-rings.

Note the larger o-ring. If that o-ring escapes from its groove, you'll get a valve that sticks part way open. Reseat the o-ring and reassemble the sandblaster. (Note: When reinstalling the plug, do not use a wrench; use only the socket itself and your fingers.)

Princess Auto doesn't appear to make the o-ring available as a service replacement part. They really ought to.

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