Archive for mediablasting

Blast it all!

sandblasterOne of the tools I’ve always wanted is a blaster for cleaning metal. A blast cabinet would be nice, for doing small parts in an enclosed area. But I wanted a bigger unit that would also let me work on frames and bigger pieces.

A couple of years ago I bought a 60-gallon, two-cylinder, 12 CFM compressor that was on close-out (about $350, I think) at Lowes. I had an electrician come in and wire a 220 outlet into my garage and hook it up. But I never used it. Not even once. I never even turned it on except to be sure it ran. I didn’t have any piping or anything. So, like most of my projects, it sat for a year and a half while I went on to other things.

Back in the spring I bought a spinner bike that had been in a fire. It’s a nice unit — a Lemond Revmaster — but the paint was pretty badly smoke damaged. I plan to rebuild it and I have all the parts, but I needed to paint the frame. Before I can paint I need to get the burned powder coat off. Sanding it by hand was not getting me anywhere — there are just too many nooks and crannies and odd angles. I needed a sand blaster! At least, that’s what I told myself.

So I went to Tractor Supply and bought one of their 20-gallon pressure pots for $129. It’s made by Clarke Products and is, at best, a piece of Chinese crap. But I knew that going in. Really, it’s not too bad. I mean, a metal tank is pretty much a metal tank. It’s just that the fittings and manifolds and filter/gauge are junk. The pressure gauge was actually broken on the one I bought.

So I bought a better pressure gauge at Sears ($10) and, using some Black Diamond blast media I got at Tractor Supply I tried blasting. It didn’t work at all. Clogged up immediately and wouldn’t blast a wet paper bag. I was unhappy.

So I started reading the stickers on the side and one of them said, “Use only 80-grit or finer media.” I don’t know anything about blasting grit, but it looked to me that the Black Diamond I bought was pretty coarse. It didn’t say anything about grit on the package. So I dug around on the internet and found some info that said it was probably 30-60 grit.

Aha! I thought. I need finer material. So I did more research, talked to a couple of people, and learned that I needed something called Star Blast. It’s about 100-grit, and I bought it locally at a blasting specialty shop downtown for $10/50lb bag.

I came home and tried it again. It worked better. But after a little bit the sun started to set, the temperature went down, and suddenly my blast nozzle was spluttering, spitting, and spewing water. Bad. I Looked at the cheap Chinese filter and thought it was at least part of the problem (I can’t afford an $900 chiller/dryer right now.) The next day I had to go to a plumbing supply house so I stopped by Northern Tool on the way home and bought an Ingersoll-Rand filter for $50. I put that on and tried it again.

Sure enough it worked better. But the unit still didn’t work very well. It just didn’t put out enough volume and the pressure in the tank wouldn’t stay high enough to do the job.

When I hooked it up I used a 3/8″ ID hose, because that was all I had fittings for. I had a 1/2″ ID hose, just no fittings for it. So today I went to the hardware store and bought the necessary fittings and adapters to connect the bigger hose to the unit.

Voila! It works like it should now. 30% more air volume did the trick. The compressor is big enough to keep it full, but the little hose was choking it down. Now the unit will stay at about a constant 70psi, which is enough to do a decent job of blasting. I will eventually replace the fittings with American units of better quality, and maybe look for some way to replace the manifolds — which are threaded with straight 3/8″ threads instead of tapered pipe threads, so they don’t seal well. But as a blaster it works quite well now, much faster than before. At some point I might even try upgrading to an even larger, custom-made 5/8″ ID or 3/4″ ID supply hose.

Still, blasting takes some time, and some technique. Adjusting the amount of material that comes through the hose is important for both efficiency and effectiveness. I have learned there is an art to taking off as much material as possible with each pass of the nozzle. The angle matters a lot. And it is still tedious. Even though I believe I have the unit working at full capacity now, blasting a whole frame is quite the undertaking.

It could easily take 5-6 bags of media, which is $50-$60. I don’t know of any way to recycle media when you’re blasting outside. Not to mention the mess that much media makes in the driveway. I will probably just blast all the welds and hard to reach areas, then sand and feather the flat surfaces into the blasted metal.

The Star Blast does a great job. At 100-grit it doesn’t remove much metal at all, and it leaves pretty much a primer-ready surface — not at all the rough surface you see with commercial aluminum oxide blasting. I could basically wipe it down and prime it once I’m through. That’s nice.

So the bottom line for effective blasting is you need lots of clean, dry air. Getting that in a home shop is not necessarily cheap or easy. But it makes the job a lot easier. I have some old CZ engine cases that aren’t good for much so once I finish the frame I will try blasting those to see what it does to the aluminum. I also have some broken magnesium hubs that I might try it on, too. I will post pictures of the blasted frame before I paint it.