Stand for the blasting cabinet

I also made a stand for the blasting cabinet to get a comfortable working position. This is the reason for the elbow connector in the air line, so that it doesn't take room but goes down, as my workspace is very limited and getting pretty crowded with all the various stuff.

I welded the stand from 25 x 25 x 2 square steel tube, better known as "furniture tube" in here. I used a MIG welder because that was available and it is quick to use. I got the material from Rautasoini and it cost me about 20 EUR for the 9.6 meters of material and a cutting fee of 1.7 EUR, so quite cheap.

For welding the frame nice and square I bought a magnetic square from Biltema for 5.49 €. It provides 30 kg of magnetic pull and the 105 mm side length provides accuracy. I tested this little gadgets accuracy with a 400 mm machinist square and the magnetic square was truly a square. In retrospect I should have bought two or three of these to make the setups even more easy, but even with only one I could free my hands and got rid off of using clamps and got everything square in one go.

Once I had welded the frame I checked the diagonal lengths and found that there was 1 mm difference in 900 mm distance, so it was really good. The frame was a little bit twisted, as it rocked on the floor a little, but I fixed this by grinding about 0.5-1 mm off from one of the legs. This way the blasting cabinet sits on the stand without rocking during use. The floor side of the frame doesn't matter as the stand will have adjustable feet.

I used an air powered angle grinder to smooth the welds in all corners and then an angle sander on all surfaces to break the shiny metal so the paint sticks better. I wiped all the grinding dust with a rag and then used a clean rag and solvent to go through all surfaces to remove the last bits of dust and all the oil.

I had bought red oxide primer and black matte spray cans from Biltema for a total cost of about 10 EUR. I sprayed the primer on the frame in thin layers and with a help of a flashlight I inspected every surface that there were no metal to see and that the primer was smooth. I let the primer dry for half an hour and wiped the surfaces with a clean rag to remove the primer dust. I applied the black paint also in thin layers to get an even result, but run out of paint once I had the first layer, so I went and bought a second can of paint. This got me approximately two layers of paint and even surface, so good enough for me. I let the paint dry for two hours.

To give the stand good stability and finish I bought four plastic caps that were intended for this type of tube and had M10 nuts molded in them, so I could screw in the adjustable legs. The upper ends of the tubes I sealed off with similar end caps. All the caps I just whacked in with a rubber mallet and they fit snugly.

Once I got the stand home, I moved it to the correct place, adjusted the feet for level and stability and lifted the blasting cabinet on top of the stand. Fit as it should, with about 2 mm of free space from the tubes to the corners of the blasting cabinet.

Last bit to get this stand finished is to buy a piece of film faced plywood, cut the corners and install it on the supports I welded halfway up the stand to act as a storage space.

Blasting cabinet mods

Here is my blasting cabinet in operational condition albeit still on the floor in this picture. The small rectangular box contains about a litre of pantyhose filtered glass beads ready for use in the small blasting pen. The blasting pen is the one with the long and colorful hose in the middle and it has a small cup that holds the blasting media.

The original blasting gun was supposed to be installed with a small female connector in the right hand side panel so that there would be a G 1/4" female thread for a pipe connector. But as I'm not going to use the original gun but the blasting pen and I want a small air gun in there also for cleaning, I made a small splitter block from aluminum. The splitter block has two female quick connectors to attach the pen and the gun. The splitter has G 1/4" threads for the quick connectors and one cross drilling that I plugged from the end with an R 1/4" plug and pipe connection glue.

The air gun is from Biltema and provides very good adjustability as the trigger lever is long. It also happened to have the dangling hook in an otimal place just by coincidence, as I found out that it fits perfectly loose to the M4 screw that holds the air filter in the cabinet and is in reach of my hand while working. The hose for this air gun I liberated from the original blasting gun as it is quite thin walled and very flexible, so it is easy to maneuver inside the cabinet.

The inlet to the splitter block comes from the compressor with a hose that has a female quick connector in the end that fits a male quick connector. This is attached to an elbow joint that is going through the cabinet wall to the splitter block and keeping it also in place. The elbow connection saves me some lateral room as it comes out only about 30 mm from the side of the cabinet versus about 100 mm that it would take with the quick connector & hose coming in horizontally.

Blasting cabinet

I bought a blasting cabinet from Biltema (article #15-377) for 159 EUR. The cabinet is quite small so it fits my workshop well, as it is more than enough in size for my parts. My intention is to use this with the silent air compressor I built earlier, but I'm going to use a small blasting pen with this cabinet to keep the air consumption low. My blasting media will be fine glass beads as I want to have a nice finished surface on my parts and one lock related project needs this also.

And as with all things that I carry home, it happened once again. I get the box inside, close the door and turn around and the Quality Inspection Team is all over the place. Yup, that's my other cat, enjoying a new toy. Well, at least they get the box afterwards as they love to play and sleep in them :)

The box contained all the parts neatly packed and properly shielded with lots of bubble wrap. I pulled all the essential small parts out front to take this picture. In here you'll see the V-bottom of the cabinet, the gloves, the supplied blasting gun and four nozzles, the lamp and a power source for it, instructions manual and a bag full of nuts & bolts. Notice the grey foam around the V-bottom, this was preinstalled but I was not thrilled of it and the next pictures shows why.

Here I'm applying very liberal amounts of butyl sealant with a caulking gun. The sealant was a 300 ml tube from Biltema for 3.99 EUR and the gun also from Biltema for 2.99 EUR. The butyl sealant is good as it remains elastic and kind of rubbery when it hardens fully (around 1-3 weeks). Downside is the enourmous force needed to squeeze it out of the tube, as it is very thick.

The sealent begans to surfaceharden after about 20 minutes so there is plenty of time to install the parts and screw everything down. In the picture I'm just installing one of the sides to the V-bottom after applying the sealant. You can notice that I removed the original foam seal from the V-bottom. The reason is that I didn't like it and I had a tube full of this butyl sealant that I could install instead. I wanted a blasting cabinet that would not blow the blasting media all over my room from the small holes that would have been left in the corners and joints where the bolts are. Applying this sealant to all mating surfaces provides me an "airtight" blasting cabinet and helps to keep noise level and cleaning down.

The only difficulty I found installing all the parts was with the gloves. I couldn't keep them in place with only one hand while trying to fit the compression ring around them with the other. Finally I figured out that I could put the ring ready on the glove, fold the gloves edge around the ring and then install it in the cabinet. Worked well and got everything assembled. In the picture you see the original gun and its nozzles and the small 12 V transformer for the interior light. This is a nice safety feature as there isn't 230 VAC inside the cabinet. On the right hand side in the upper back corner there is a small yellow air filter that lets out the air but keeps the blasting media inside and also drops down the noise somewhat.

Although the cabinet has its own feet, I'm not putting it on a table but will make feet for it instead and write about them and one other mod I have in my mind.

Silent air compressor

For a long time I have wanted to have pressurised air available, especially for glass bead blasting of machined parts. The main reason I haven't just bought an air compressor is that they are loud as a jet engine, usually in the order of 85-95 dB and that just doesn't cut it in an apartment complex.

About a year ago I stumbled upon articles in the internet of how to use a freezer or fridge compressor to produce compressed air silently. The only drawback is low air output volume, but my need is occasional and very little, so this fits for me.

A week ago I was able to obtain a working compressor out of an old freezer. This was an old ZEM compressor with 110 W of power and it runs from 230 VAC 50 Hz supply. The best thing is that it was from a freezer, as these are usually more powerful than compressors from fridges. The compressor had its original oil still in it, so I poured it in to a junk oil container and replaced it with a regular oil meant for automatic transmissions. The only requirements are low viscosity and that the oil is of mineral variety.

These freezer compressors are able to produce enormous pressures and also vacuums, so care must be taken that the system is able to withstand the pressure. This usually means a pressure switch that cuts of the compressor when the pressure reaches a set upper limit and starts the compressor when the pressure drops below a set lower limit. Also an overpressure valve is needed, as it vents if the pressure switch doesn't switch off the compressor.

To have a big supply of air for some time the compressor needs a pressure tank after it. This can be an old carbon dioxide extinguisher bottle or gas bottle that is rated for the intended pressure. There is also a need for the pressure switch, pressure regulator, connectors, piping, oil/water catcher and air drier. If you have to buy everything as new, the total will cost probably around 100-200 EUR plus all the work needed to assemble everything.

This is the reason I thought of buying a brand new compressor unit and just replacing the compressor unit with the freezer compressor. So I spent 89 EUR to buy a Herkules brand compressor from Bauhaus, as it was the cheapest I found that had a 24 liter pressure tank. The original compressor unit fills the tank in about 2 minutes from 0 to 10 bar, but produces an ear breaking noise of 97 dB at the same time. Not good.

So I started disassembling the unit to get the original compressor out and to take measurements of the pipe size used so I can make or buy a proper sized fitting between the pressure container and my freezer compressor. It was quite easy to just unscrew the plastic cover to reveal the compressor unit, but the Abiko connectors to the power switch didn't want to come off so they got a quick treatment from pliers.

After removing everything not needed, I was left with a tank, a one way valve, a pressure switch, overpressure vent and pressure gauge with an adjustment valve. The output is a 1/4" female quick connector and the input to the tank is from the end of the one way valve that has G 3/8" male thread.


The freezer compressor had a 1/4" OD copper tube as its output, so I bought a hose connector that had a 1/4" hole through it. From this I hacksawed the hose connection part off and after cleaning everything, I soldered this to the compressor output tube. To the one way valve I rolled few turns of PTFE tape and screwed on a G 3/8" -> 10 mm hose connector. This way I can attach the compressor to the tank with a small length of hose and avoid induced vibrations to the tank and also avoid messing with rigid tubing and bending.

The pressure switch was factory set to have 10 bar upper limit and 8 bar lower limit. I plugged the modded compressor to the wall for a quick test and started a timer to see how long it takes to fill the 24 liter tank from 0 to 10 bar. The pressure rise was slow but steady and finally after 24 minutes the pressure switch turned the compressor off. This means that the compressor can provide about 10 litres per minute. The 0-5 bar rise time was exactly 10 minutes.

I was a little bit doubtful if the freezer compressor could start against pressure, so I blead the tank slowly until I heard the pressure switch click on at the 8 bar marker. The compressor immediately started to purr and building more pressure to the tank. I timed how long it took to see how much the air output volume would change from the first run as this was against pressure. It took 4 minutes 50 seconds until the compressor shut off, so against pressure the compressor can provide about 9.93 litres per minute, which doesn't differ from the 0-10 bar rise time.

The compressor temperature climbed to quite warm during the half hour test, meaning I could not keep my hand on it for long. I'm quite sure my air need is so small that this will not be a problem as I can switch the compressor off when I have pressure in the tank, but I could add a small 230 VAC fan to blow cooling air over it.

Of course mounting the freezer compressor meant that I had to fabricate some sort of plate that attaches to the tank mounting holes and that has mounting holes for the freezer compressor. I used a proper sized piece of aluminum plate that I countoured with a CNC mill and drilled and threaded for M6 screws. I used the freezer compressors own rubber feets to isolate vibrations from the unit to the rest of the system. In the rear end I also installed a small water separator unit that is screwed to the plate and inside the plate is an 8 mm passage for the air. On the back side there is one electrical connection to the pressure switch, which is wired in series with the fridge compressor and shuts it off when there is 10 bar in the tank.

So how silent is my silent compressor? Well, I can just hear it running, sounds like a fridge humming its things. Yep, beats the so called "silent" compressors they advertise in hardware stores with about 68-70 dB sound output.

Added 06.01.2011: I bought a small Simota brand air filter that had a connection for a 9 mm diameter tube. This was probably meant for some RC car or something, but works wonders in this application and totally eliminates the small intake sound of the compressor.

I also had an idea for a decal to replace the original "Herkules" tape and so I used 5 minutes with KolourPaint and printed off a nice new decal and attached it (poorly) with a piece of tape meant for covering books. The word "Perkules" is a kind of twist from a Finnish curse word "perkele" and the original brand "Herkules". The word below it is my own drunk misspelling of the word "kompressori", which is Finnish for a compressor.