DIY Power Air Blaster

[oilshale]

In “Steinkern.de” - the German speaking equivalent of TFF - Eckhard Petersen wrote an article about his high end DIY power air blaster. At that time, I only had a rather unreliable old dental sandblaster from Micron and a small Paasche Air Eraser, both not really suited to prep fossils on a larger scale.
So I decided it’s time to build a new and better air blaster.

As you can imagine, building an air blaster is not an easy task – you will need basic knowledge how to run a lathe (or a good friend who knows how to).
By profession, I am a chemist, and not a lathe operator. But one of my other hobbies is scale model making, I own a small mini-lathe and I am not born with two left hands.

Eckhard was so kind to give me his ok to publish his drawings (actually, these excellent drawings were made by another Steinkern colleague, by Steffl).

It’s not my invention and my design – the credit has to go to Eckhard and Steffl!

So here you go.

This is Eckhard’s original design:

Overall construction costs can be less than 200 US $ if you already have a sufficiently powerful compressor at hand (air consumption will be around 120 l/min, depending on nozzle size), search the internet and from time to time sift through local junkyards….

The most expensive part is the sandblasting-nozzle.
In the beginning, I used blasting nozzles from Renfert – you can get them in different sizes from 0.4mm up to 2.0mm. Good quality and quite durable, but unfortunately also quite expensive (around 80US $). Now, I build my own blasting nozzles – that’s not particularly difficult. All you need is a tungsten carbide tube (you will need them for the construction of this sand blaster anyway) and a brass rod. I will describe the construction of a blasting nozzle in a later post.

Renfert handpiece

The pressure vessel in my blaster is a stainless steel 2 liter air reservoir from Festo (order code CRVZS-2, you can get them in different sizes starting from .1 l and going up up to 20 l). This was the second most expensive part to buy. I was very lucky and found mine in the internet for less than 40 US $. Allowed operating pressure (with a lot of safety margin) is up to 16 bars / 230 psi – this is more than needed.



There might be also other solutions, from gas bottles to seamless pipes with reducing sockets. Working pressure will be only 2 to 6 bars, but under unfavorable conditions, the pressure can reach up to 10 bars / 150 psi – no fun if the reservoir bursts. This happened in Germany several times with a commercial sandblasting unit built with plastic reservoir. Please, please stay on the safe side and add sufficient safety margins! No flimsy constructions – plastic is completely unsuited.

These are the brass fittings you will need to buy:

No 1: Quick connector with cap nut, ¼“ male thread, nipple and cap nut for 6mm O.D./4mm I.D tubing


No 2: Sealing ring, ¼”, soft

No 3: Reducing fitting, ½” OD > ¼” ID


No 4: Threaded double nipple, ¼” male, detachable


No 5: T-shape fitting, 3x ¼” male thread


No 6: Sealing ring, ¼” hard (PTFE or similar stuff)

No 7: Elbow, ¼” male thread, ¼” female thread


No 8: Push-in threaded L-fitting, ¼” male thread > 8mm push-in tubing

First comes the connecting piece to the air reservoir. It’s an adapter nipple (No 3, ½” male thread – ¼” female thread) and a ¼” threaded double nipple (No 4, detachable type).

Solder the two parts together (No 3 and upper part of No 4) and bore the upper thread out to a cone.


Now shorten the thread of the lower part of No 4, so that it will not protrude into the T-shape fitting (No 5).


On the right side, you can see the shortened thread of the detachable double nipple.

Solder the lower part of No. 4 and the T-shape fitting No 5 together (alternatively, you could also glue them together with epoxy resin).

The mixing chamber is the most important part. That’s where the lathe is really needed. The mixing chamber is made out of a PTFE- or POM-rod. When it comes to toughness and ductility, plastic is much better than let’s say stainless steel or brass. Stainless steel will be abraded in no time - holding time for PTFE or POM will be much better. PTFE is a little bit more expensive compared to POM, but in my opinion easier to turn.

The mixing chamber is a sort of Venturi tube. The Venturi effect is the reduction in fluid pressure that results when a fluid flows through a constricted section of pipe.

"Venturifixed2" by User: HappyApple - Own work. Licensed under Public Domain via Wikimedia Commons


The pressure in the first measuring tube (1) is higher than at the second (2), and the fluid speed at "1" is lower than at "2", because the cross-sectional area at "1" is greater than at "2".

Underpressure will be generated in the midsection of the tube where the cross-sectional area is reduced and particles will be sucked in.

This is the mixing chamber (made out of PTFE) and the suction nozzle (made out of brass) attached and detached

See Second Part

Edited September 11, 2023 by oilshale

[Raggedy Man]

Fascinating

[oilshale]

Second Part:

And here are the dimensions of the mixing chamber (sorry, in millimeters and not inch!):

I am not sure if you really need these two additional 1.2mm bores. The original intention was to use them as “air accelerators”, but at least for me it turned out that they are difficult to make (I ruined two mixing chambers). So I just increased the diameter of the bore on the left side from 1.6mm to 2mm and left the diameter of the other bore unchanged (2.5mm).

At least it worked for me – but no guarantee!

Here are the dimensions of the suction nozzle:

The suction nozzle “Ansaugdüse” is made out of brass. Normally I use an 8mm O.D., 6mm I.D. brass tube, cut off a small slice (length ~ 4 to 6mm) and hard-solder this ring unto a 6mm O.D., 5mm I.D. brass tube with the correct length (29,6mm). Then I turn down the hard-soldered ring to the right dimensions.

The nozzle itself on the left end of the brass part is made out of tungsten carbide (where it’s said: “Hartmetallbuchse - hartgeloetet”). Tungsten carbide tubes are offered in different sizes by Saturn Industries at Amazon (or you can buy them directly from Saturn Industries http://www.graphitesupplies.com/Tube_c_178.html ). But I am sure there are other suppliers as well.

The tungsten carbide tube has to be cut with a small diamond wheel and hard-soldered into the brass tube. This is a bit tricky – you have to use a high-silver containing brazing alloy and a good soldering flux (not every soldering flux works – might have to try out several).
If you want to use a wide 1.2 mm nozzle for coarse and fast abrasion, the suction nozzle must have the same diameter or should be slightly smaller (let’s say 1.0 mm I.D.)

If the nozzle in the handpiece has a smaller diameter than that of the suction nozzle, clogging at the handpiece will happen.

If you want to prep some fine details with a 0.6mm nozzle in your handpiece, use a tungsten carbide tube with same size or a slightly smaller one (0.5 mm I.D.) in your suction nozzle.

The size of the suction nozzle and the size of the nozzle at the handpiece have to fit - otherwise, there is the risk of clogging. Useful nozzle range is from 0.6mm I.D. up to 1.2mm I.D.

So you will need several pairs of blasting and suction nozzles.

Attach the two rubber O-seals (5.1 X 1.6mm).

Again the picture of the mixing chamber:

The mixing chamber will go into the T-shape fitting (No 5) and the suction nozzle with the tungsten carbide end into the lower part of the detachable double nipple (No 4).

No 1 is a quick connector with a cap nut (¼” male thread, nipple for a 6/4mm tube). The opening of the cap nut has to be bored out (widened to 7.3mm) to fit the outer diameter of the thick-walled tubing which goes to the handpiece. A fabric-reinforced hose from a flexible fuel line has a very long service life, is sufficiently flexible, rather inexpensive and will do the job.

The other side (where the ¼” male thread is) has to be widened too. This side will accommodate the small end of the mixing chamber (bore out first to 6mm diameter, 16.5mm deep and then to 8mm diameter, 10.5mm deep).

screw in the elbow (¼“ male and ¼“ female thread, No 7) and the push-in threaded L-fitting (air inlet, ¼“ male thread to 8mm push-in tubing, No 8).

You are almost done – screw the mixing chamber into the pressure vessel, add the pressure tubing and attach the handpiece.

Here is how it looks if everything is put together

Of course, that’s not all - you will need a compressor with sufficient capacity. For failure free operation, supply with dry and clean air is a must. One cubic meter of compressed air cannot hold more water vapor than 1 cubic meter of air under atmospheric conditions. If, for example, 7 m³ of atmospheric air is compressed to 1 m³ at 6 bar, for a constant temperature of atmospheric and compressed air there are 6 parts of water vapor too many – this condenses out. If you compress air, a lot of water will be precipitated as drops (dew) and must be drawn off so that it cannot cause any malfunctions. Without several water traps, the dew will clog your abrasive! And of course you will also want to adjust the pressure – a pressure regulator is needed: High air pressure for fast prepping and low pressure for sensitive and difficult to prep fossils.

I’ve mounted everything together on a support:

From right to left: Quick lock coupling, shut-off valve, adjustable pressure regulator with integrated water trap (40µm), branching module with manifold (goes to my air scribe; I need oil free air), two additional water traps (5µm), adjustable pressure regulator, on-off valve / decompression valve with silencer and a manifold with push in connectors.

If it looks differently, then it might be due to my awkward English. I just hope you can still understand what I tried to explain. It’s already difficult to explain technical terms in your mother language, but to do this in a foreign language…

Feel free to ask questions, to improve my description and to add new ideas.

And now – have fun!

Thomas

PS: Part 3 with a couple of improvements will follow.

Edited September 16, 2015 by oilshale

[JohnJ]

Thomas, I've combined the second topic with the first to maintain continuity. Looking forward to the third installment.

[oilshale]

Great - Thanks for combining these two posts

Thomas

[dsalles]

Wow - this blaster really looks great. Hope I can built one. Doesn't seem to be so complicated.

Daniel

[ZiggieCie]

THX. Thomas, you did a fantastic job putting this description together. I think that anyone that has the ability to build this will have no problem understand your description and diagrams.

[oilshale]

There are several small improvements which can be added:

The DIY power air blaster is not prone to clogging, but very fine crushed calcite or dolomite doesn’t flow very well and can cause some problems. An automatic vibrating unit helps to get an even and steady flow of the abrading medium.

I simply screwed a pneumatic rotary vibrator equipped with a silencer (from NetterVibrations, NCT15) to the 2 liter air reservoir and used rubber block supports to mount the reservoir to the frame. I can activate the vibrator for a couple of seconds either automatically by an electronic timer and a magnetic valve (every minute or so) or manually by a pneumatic non-detenting foot-lever.

​

Rotary vibrator

Side view

Magnetic valve​ and timer

Foot​-lever

Part 4 to follow


​

Edited September 20, 2015 by oilshale

[Malcolmt]

A most excellent article.. not something my skills will be allowing me to build any time soon.

[oilshale]

Thanks Malcolm, but as I said: it is Eckhard Petersen who developed this design and Steffl who made the drawings. I just used their know-how to built my own blaster.

It was a lot of fun and sometimes also a lot of frustration. I am not a lathe operator - this were more or less my first trials with a lathe.

Thomas

[Auspex]

I will never, ever, take air blasters for granted again!

[oilshale]

Part 4:

If you want to stop sand blasting a fossil and you simply shut off the compressor, the 2 liter air reservoir needs quite a time to depressurize and the abrasive won’t stop flowing immediately. So what to do?

I bought a short stroke (20mm or so) pneumatic cylinder

with a threaded piston and a 40x40x40mm cubic aluminum block in the internet, added a T-bar to the piston, milled two 8mm grooves into the aluminum block (just wide enough to support the fabric-reinforced hose from a flexible fuel line which goes to the handpiece and the T-bar from the piston) and screwed everything together.

Ok, it’s not a beauty but it works very well. I don’t have a mill - had to do it with a milling adaptor for my lathe. This is how it looks​:

Here it is taken apart: You can see the piston with the T-bar and the aluminum block with the two grooves.

With a foot-lever, I can now pneumatically activate the cylinder, the piston extends and squeezes the hose together; the air flow with the abrasive will stop immediately.

Edited September 29, 2015 by oilshale

[dsalles]

Yippee- Yippee - I made it - I made it - I just completed my DIY sand blaster!

Wasn't that difficult to build - just took me a couple of hours. The most difficult part was to get a suitable air reservoir. I was lucky to find a junk yard for trucks where you can get air reservoirs for a couple of bucks. A friend of mine did the lathe work for me - took me a few beers.

I do have a Paasche air eraser, but I wasn't happy with it at all! It is ok if you don't do a lot of sand blasting, but it will drive you crazy if you have to prep larger chunks and it is not really precise. The Paasche air eraser is designed for model makers to remove varnish or rust and to clean metal parts but it is not designed for prepping fossils. So I decided that I will need a real professional device and not a toy anymore.

Right now I am running comparison tests. A friend of mine has an old Comco unit so I could compare both. Smooth operation, high abrasion, very precise jet and no clogging with very, very fine calcite and baking soda even at low pressures where the Comco unit already gave up.

I am very happy with the result!

Thomas, please say thanks to Eckhard and Steffl and of course also thanks to you for making this construction guidance available!

[JohnBrewer]

Well done! Not a project I'd take on and I raise a glass of ale to you.

Edited May 11, 2016 by JohnBrewer