April 9

DIY Vapor Blaster Build

If you're reading this article you know what a vapour blaster is and you probably want to build one. For Google's benefit (so other people can find this information), I'm going to use "vapor" and "vapour" spelling interchangeably.

There are a few resources around that give some hints on construction, and a few people selling plans or fully built cabinets.

This article is for Australian and New Zealander builders as the parts are sourced from vendors down under or, over the dutch. If that sentence makes no sense to you, sorry, its an Aussie/Kiwi joke.

My parts list is linked here (Excel, PDF), and is free to download and copy. Just "Save As" if you're using Excel, and just save the PDF to your local device. I don't even want your email address. My interest is building and modifying motorcycles, so if you come from another field that's cool, just grab my parts list and get cracking.

I also have a Facebook Group here for builders to interact, because the existing ones I am in are shit. They're either people showing off their results - and not sharing how to replicate, or, people trying to sell you something. If you actually want to build a blaster and get it working right, join my group.

Where there are other resources that cover a topic well, I'm not going to repeat their content. I'll just link to it and you can go down the rabbit hole when and if it suits you.

DISCLAIMER: dry and wet blast media can cause damage to seals, bearings and soft materials like aluminium. If you blast parts going into engines or other machines, you need to ensure they are perfectly clean of media before reassembly. Don't say I didn't warn you.

Lets get into the build.

Cabinet

These tools are based on off-the-shelf sandblasting cabinets. Down under you'd typically buy one from Hare and Forbes like this one. if you can score one second hand and cheap, go for it. That's what I did.

I have a H&F cabinet for sandblasting, but the one I found on Marketplace is slightly different construction and unknown supplier, but it does the job.

Most builders recommend stripping the cabinet and sealing all the joints with some sort of silicone sealer. I concur. Even after working hard to seal the cabinet, mine still leaks around the arm portals and screen, because I didn’t add silicone here, and it would be problematic at a joint that needs to be removeable. I'd hate to see how bad it would be if I made no attempt to seal it.

Silicone applied to hopper right before reassembly

Electrical and lighting

The supplied lighting in a dry blast cabinet is rubbish. I've upgraded the lighting in my cabinets. In the vapour blast cabinet, I used a pair of cheap LED outdoor floodlights. I figure they're suitable for wet conditions, but if the environment kills them, I'll just replace them.

I stuck with 240V lights, as the cabinet needs this to run the pump. Using a low voltage light and an associated transformer seemed to add more complexity than I wanted. 

NOTE: This shit is dangerous. Have a competent electricial person wire up your pump and lights. 

If you want a low-voltage lighting alternative or have easy access to 12 Volts, Armoury have a video showing their design.

Blasting gun

I've put this next, as the gun will dictate your air and slurry line sizes inside your cabinet, so make a decision here before going too much further.

DIY blast gun

If you have a lathe, you can build your own gun:

DIY mixing gun made from Armoury Enterprises instructions

DIY mixing gun made from Armoury Enterprises instructions

I purchased this booklet from Armory Enterprises and built it for a few bucks in brass plumbing fittings. His YouTube channel is also very helpful. Go through his back catalog to bone up on the topic.

If you have a 3D printer, you could try this design:

3D printed mixing gun from a free file on Thingiverse

3D printed mixing gun from a free file on Thingiverse

I have printed one but not tested it as my brass one works fine. Armoury Enterprises also have a 3D-printed design available here ($).

If you have neither, you will need to purchase one. I have absolutely no experience with the following but you can check out the links and do your own research.

Armoury Enterprises

Armoury have them shown in their store, since you're buying the same design as I built from his instructions I feel this is a pretty safe bet. 

How To Motorcycle Repairs 

Matt from HTMR YouTube Channel has some great videos on vapour blasting, but he keeps the secrets, well, secret and you have to buy his plans to find out. His blast gun seems highly rated but the price is eye-watering, especially with shithouse exchange rates Down Under. I barely spent this much on the entire cabinet. But hey, if you have cash to spare, throw him some support, I'm sure his design is very well dialled in.

eBay

Search for "vapour blasting gun". You should turn up a few options, including 3D printed versions. This style seems to be popular, but I have no experience with it. 

Air supply

Compressor preamble

There is a lot of discussion around air supply and if you need to buy or upgrade a compressor this will easily be the single biggest expense.

It comes down to a simple factor, that is difficult to determine in practice, and that is "what volume of air can my compressor deliver". The air nozzle in the vapour blasting gun 'consumes' air. You need to feed it.

Compressors are often sold in stores with a measure of "free air delivery". This is a measure of the volume they can provide, BUT, its free air, meaning no resistance to its delivery.If you pump air into the tank, as the tank gets fuller, the compressor has to work harder to continue to pump up the tank. The pressure switch (usually pre-set by the factory) will cut out the pump at the predetermined tank pressure.

Then you connect a whole bunch of hoses and regulators and fittings and these add more "resistance" to the air flow from your compressor tank to your blasting gun, so you have a pressure drop in the lines from the supply point (compressor) to the delivery point (blasting gun).

The compressor pump has to overcome all these resistances to deliver the air you need at the blasting gun. Then, it has to do so continously, because blasting can take minutes or hours.

Most electrical equipment is not rated to run 100% of the time. This is called "duty cycle". If the equipment is rated at 50% duty cycle, in theory it can run 30 minutes in one hour. Now, you can run it continuously, but eventually it'll overheat, and while it might be fine today, you're likely going to have it fail prematurely. Cheaper compressors are cheaper becasue they use components rated for lower duty cycles. This information is likely buried deep in the manual or specification sheet, if at all.

My vapour blaster works well with 60 psi pressure at the cabinet. This tends to be the maximum, and I dial it down for better surface finish. To achieve this, I have mounted a regulator right next to my cabinet. This regulator feeds both a dry blast and my vapour blasting cabinets. Dry blasting I run the regulator wide open. Vapour blasting is done at 60, 40 or even 20 psi.

The first parts where I started getting some decent results.

To generate higher pressures requires more grunt (horsepower) in the compressor motor and/or motors, and to generate more air flow (volume of air) you need a larger compressor pump and/or pumps. And the bigger the tank, the longer it will take before the pressure drops and the compressor restarts to pump it up again.

Down under you might be limited by your electrical power supply.

On a standard 10 amp circuit, you won't be able to run anything bigger than 3 horsepower. I was running an old 2hp unit which I switched out for a larger silent compressor. Its simple math:

240V x 10 amps = 2400 watts/2.4kW, divided by 0.75hp/kW = 3.2hp

So strictly, 3 horsepower will be drawing about 9.4 amps which won't trip your 10 amp circuit breaker (assuming nothing else is on the circuit drawing more current).

On a 15 amp circuit, you’ll be able to find a 4.5 horsepower compressor. If you have a 15A circuit for welding, you can use it to run a bigger compressor. This is what I bought. There are similar units at Total Tools or Sydney Tools, albeit more expensive.

Silent compressors are great, you can run them at night without pissing off the neighbors and keep blasting after hours. They are not actually silent, but light years ahead of reciprocating compressors.

If you are stuck with 10A, consider the bigger silent compressors from either Total Tools or Sydney Tools.

You can get away with a smaller compressor, but it will be running flat out trying to keep up, and you may not achieve 60 psi at your cabinet which will slow you down and/or affect the finish.

Once you have a compressor and a blasting gun, you can start sizing your lines and buying appropriate fittings.

Three vintage mower engines stripped and blasted. Note the difference appearance of various materials and manufacturing methods

Connecting the air supply

If you plan a set up like mine, mount a regulator on or very near the cabinet.

Between the regulator and the compressor, install an air line. I installed a tee on my tank outlet and tapped it directly (rather than going through the regulator right next to my compressor, but ten metres from my cabinet). If you can, or are plumbing a hard line, install something bigger, like 16mm or 19mm lines. This will reduce the frictional losses between the tank and regulator, but don't overhink it. Mine is crappy 10mm air hose all the way and it works fine.

Footswitch

Next you'll need to connect a foot switch to supply air to the blasting gun on demand. I honestly can't remember where I got my foot switch a few years back but here are a couple of examples from Amazon and eBay that would suit. 1/4 BSPT fittings (or "G1/4" as they are called on Amazon) are common for garage air and are what I used through out, including on the footswitch.

Run an airline from the regulator outlet to the footswitch inlet. Do stuff with air hose and barbed fittings and hose clamps to make it work. Thats up to you.

From the footswitch, you need to run a line to the cabinet.

Cabinet air supply

A re-purposed sandblasting cabinet will have a fitting on the outside to connect to the air supply. I plumbed a line direct from the footswitch to the inlet.

On the inside of the cabinet, if it floats your boat, switch out the existing fitting for a tee if you want to install a separate air duster in the cabinet. I did, but I haven’t found it useful and wouldn’t bother with it on another build.

Now you’ll need to provide a line from this fitting to the gun. As mentioned above, the gun inlet will dictate the line size which will determine the combination of fittings needed to hook it all up. Aim to match the hose barbs to the line size, as undersize barbs will be hard to seal and the lines will blow off at high pressure (ask me how I know).

The hose from the sandblasting cabinet might be the right size, otherwise the “food grade” reinforced hoses at Bunnings are available in a range of diameters, so pick the one that matches the gun. Mine is ½” or 12mm diameter, and it works fine. Don’t forget you can always change the fitting in the gun to allow a bigger or smaller diameter hose to be used.

Total Tools have a good selection of fittings, but the prices are pretty high, so order online from Valves Warehouse Australia if you’re organised and can wait for delivery.

I used a check valve in my air line close to the gun, but you could argue it’s unnecessary. The air pressure in operation is much higher than the pump water pressure so its unlikely to draw any water back, but if you cover the nozzle with the pump running and no air, it’ll back feed slurry into the footswitch, which will plug it up. Better to be safe than sorry.

Slurry supply

Pump and reservoir

I get good results out of the Ozito 350W sump pump. Is more power/flow better? Maybe, but this works fine. I dropped the pump into a standard Bunnings 20 litre bucket.

The pump comes with a combination outlet with a barbed hose fitting and 25mm BSP screwed fitting. I just cut off the barb and ran 25mm throughout.

On the pump outlet, I connected a check valve. This is not shown in the build photos below as I added it after initial testing. Probably not essential, but if you cover or restrict the slurry outlet and hit the air footswitch, the air pressure will back feed down the slurry line and restrict the flow.

A 25mm checkvalve is not cheap, but I scored one for five bucks brand new on Marketplace. I’ve added a link in the build instructions. If you don’t want to cough for one, add it later if its necessary.

From the check valve, I’ve got a 25mm tee to draw off some flow to circulate the slurry.

On the circulation line, I connected a gate valve right next to the tee. The logic is, I only want to draw off enough flow to circulate the slurry, but not so much that affects flow to the gun. The slurry will take the path of least resistance. I also messed with a couple of line sizes to get this to work. I ended up using some 19mm line from the 2m piece I bought for the slurry supply line to the cabinet.

Finally getting some high quality surface finish

Slurry supply to the blasting gun

On the supply side, I added a quick disconnect fitting so I can remove the pump quickly for cleaning and media changes. Above this is a 25mm (1“) BSP to 19mm hose barb, then the 19mm hose to the cabinet, another barb to screw fitting, a 90 degree elbow, then the cabinet connection. For this, I used a poly water tank outlet - designed for you to drill a hole through the tank, install a threaded tube through with a seal on either side. These are ridiculously cheap and effective. Since all the fittings from the pump outlet were 25mm, I used a 25mm tank outlet as well.

To install this, I used a step drill to punch out the right size hole in the cabinet wall. Make sure you locate this far enough above the grate inside the cabinet to screw on fittings on the inside.

The tank outlet has a female thread at one end, so I placed this inside the cabinet and just used an appropriate threaded hose barb to suit the ?” (16mm) hose I used to my blasting gun.

Media

99% of my blasting has been done with the regular glass bead from Hare and Forbes. This bag will last a lifetime.

The other 1% is some experimentation with Aluminium Oxide from eBay. I’ve used this both straight, and in a blend (appromximately 50-50) with my existing glass bead. For this, I have two other Bunnings 20 litre buckets, so the media is contained to that single bucket.

Aluminium Oxide is very effective removing heavy corrosion from aluminium parts. The resulting finish is very smooth and matte, so following with straight glass bead improves the surface finish and increased the surface shine.

Consider dry blasting the parts before attempting wet blasting. I've gotten much better results on parts I have dry blasted. Dry blasting cleans paint and other crud off the part quicker and evens out the surface prior to following up with wet blasting. 

Initial system settings

To get started with your cabinet, set it up like this:

  1. Put about 30mm of media in the bottom of the bucket.
  2. Drop the pump in, and top up the bucket at least 3/4 full with clean water. This will evaporate over time, so keep an eye on it and keep it topped up. As the water level increases, the pump will sink into the media.
  3. Close the circulation line valve on the pump outlet (all pump flow to the blasting gun).
  4. Set air pressure on the regulator to 60 psi, and allow the compressor to fill the tank and shut off.

Good quality results in my home shop are straightforward now

Tuning and troubleshooting

Media concentration

Put a jar or small container into the cabinet and fill it with slurry from the gun (no air needed). Within a few seconds, the media will sink to the bottom and the water will sit on top. Remove the container from the cabinet and measure the total water height and the media height. Something around 20% media in the slurry is the target.

If your media level is less than this, try opening the circulation value 50% to direct some pump flow into the bucket to swirl the mixture. Retest the media concentration with the jar or container. Note any difference in slurry flow at the gun with the valve open. Retest at both 25% valve opening and 75% valve opening, just so you learn the effect of the valve (if any).

If you still can’t get enough media concentration by varying the circulation valve, add another 500 ml of media to the bucket. Retest for 20% media concentration.

If the slurry is visibly opaque (not clear like water), there is definitely media in the slurry and it’s worth hitting the air footswitch to do some test blasting.

Surface finish

Preliminary dry blasting for smoothing and cleaning works well for me, however I generally won’t dry blast engine parts and risk having abrasives left in the galleries.

Higher air pressures (say 60psi) do a better job of cleaning the surface. Lower pressures (around 20psi) seem to bring out more shine in the part. Note, this is 100% totally dependent on the material and manufacturing process. Some parts look like they've been painted with high gloss paint. Others are simply very clean and smooth and not really shiny at all.

Die cast parts don't seem to respond as well as sand cast parts. Even though 70s Harley Davidsons have a reputation for terrible quality, the aluminium used in their castings comes up beautifully. 

It'll vary and further testing with different pressures might help improve surface finish with your specific cabinet.

Don't forget to join the Facebook Group for one-on-one assistance.

Good luck with your build!

About the author 

Matt McLeod

I teach people how to build custom motorcycles by helping them build skills and confidence with my coaching, articles and training videos.
I provide better technical information for custom motorcycle builders. And I shorten the learning curve getting you there.

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