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Showing results for tags 'abrasive blaster'.
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Preferably to the friends from UK: What is the best preparation method for a Pterichthyodes milleri from the Devonian of Achanarras? Carbide tipped graver, air scribe or abrasive blaster? And if you can use an abrasive blaster, which abrasive is best? The fish is still almost completely covered and lies in a devilishly hard and thick slab. I want to prep the fish from the other side. What you see here should be the ventral side. What do you think? @Terry Dactyll, @Kosmoceras, @James_R_V
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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
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