Host Bart Hull
August 26th 2006
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Bart Hull, Tom Davis, Steve Koerner, Louis Wiley, David Butterfield, Neil Butterfield, Larry Carter, Tim Coppage and John Lea
Bart got his
first exposure to media blasting working in his parents motorcycle shop. They
serviced several special European made bikes and had need to clean parts for
use. Their first media blasting system was purchased used not functional and
Bart rebuilt it and learned the tricks of keeping it operational.
The media blast cabinet Bart now has is a modified Harbor Freight free standing unit. The most recent HF catalog lists this cabinet at $299. It is their item number 47603-1CGH.
How do you get the media back to the bottom of the cabinet? A "No-Tell-Mo-Tell" bed vibrator! They can be found on Ebay
When building an aircraft at home you need to be prepared to knock down a few walls to make it fit.
Bart discussing media blasting while a member tries his hand at the cabinet blaster.
Members crowd around the aircraft for the meeting.
Bart is building an
expiramental aircraft in his garage. We got a guided tour of it before the
meeting. The engine he is using is a Subaru 4 cylinder horizontally opposed car
engine. As configured for the plane it will develop over 200 horsepower.
The engine will be water cooled with the radiator placed behind the engine against the firewall. Bart has the entire engine mounting carriage built and the engine mounted in place ready to mount on the plane body. He has taken special care to duct the cooling air down and out between the firewall and the radiator.
The wing structure is built around a special I section beam. The top and bottom cord of the beam is Kevlar and the center web is fiberglass. Kevlar works best in tension and the top and bottom cords are tension members.
Bart has progress photos on the net at www.inficad.com/~bdhull.
The Subaru powerplant on the firewall mount and firewall mockup
Bart shared several tips and tricks to make the media blasting operation work well, be reliable, and safe.
1. The compressed air supply must be moisture free. Bart uses an air separator at the compressor and a second one at the connection point to the machine. Moisture will cause the media to clump and clog. Keep the air dry.
2. The first item to fix on the HF unit is the blasting gun. Bart uses a TP Equipment gun. They are normally available on Ebay. They have replacement parts available when needed. They also have a variety of nozzle sizes to match to the media being used. The power head of the gun is the part that wears the most. Bart uses carbide tips in his gun for all media types except carbide media. Then he uses a ceramic nozzle.
3. The orifice size used in the gun will drive the air compressor size needed. Bart has a 5 hp horizontal tank 2 stage compressor that has max pressure of 135 PSI. The operating pressure for blasting was set at 100 PSI out at the compressor. The hose connecting the compressor to the cabinet is 3/8" diameter hose.
4. Bart has installed a shaker on the side of the lower portion of the cabinet to insure the media moves down to the recovery zone in the bottom of the cabinet. This insures media does not get trapped on the sides and starve the supply hose. The vibrator used is an ebay purchase Magic Fingers unit like those used on hotel beds. A search on ebay for magic fingers vibrator will show several of these units available.
5. Bart replaced the media siphon hose on the gun media inlet port with a larger diameter tube. The larger tube size does not impact the siphon action of the gun, and is more tolerant of small clumps in the media.
6. You know you have the system set up right if the gun continues to discharge a small amount of media for a second or 2 after releasing the trigger.
7. Be sure to have a ground wire connected from the cabinet to a ground wire like the one for the cabinet light. Blasting builds up significant static charges and can really zap you if you don't ground the system.
8. Bart uses plain window glass in the view port for the blast cabinet. He has replacement glass cut at the local ACE hardware store for a reasonable price. The soft vinyl window protectors HF sells do not have very much useful life. With proper blasting care,(Don't blast the cabinet window) and wipe down only with dry cotton towel and the window has reasonable life.
9. Be sure to vent the blast cabinet. Bart uses a shop vac for this purpose. A serious note here. If using glass beads media, be sure to use a special toner filter to contain the fine glass dust. This glass dust can give silicosis if ingested. This is a major caution when blasting. The toner type filter for a Craftsman shop vac is available as an ultra fine particle filter.
10. If during operation the gun jams, a first corrective step is to place the gun nozzle on the cabinet glove and pull the trigger. This pushes the siphon air down the siphon tube and often will clear a blockage.
11. Keep media stores in dry sealed containers. Moisture will cause the media to clump and feed poorly.
12. Bart has 3 types of media available. All are stored in 5 gallon plastic buckets. When changing media types in the cabinet, the bucket is placed below the bottom cabinet hatch and the media released. Bart uses a common kitchen strainer to clean the media as it dumps out. This is a good way to remove clumps.
13. Walnut shell the softest media will only remove loose contamination and surface rust. It does not change dimensions of the work piece. Bart had a cooking pan with burned spaghetti stuck to the bottom. He blasted it clean and did not even disturb the swirl pattern made in the pan manufacture. Walnut shell is also good for removing grease.
14. Bart also has glass bead and carbide media on hand. The cabinet uses about 2.5 gallons of media for a charge. A common error is to use too much media in the cabinet. You only need enough to cover the end of the feed pipe. The vibrator on the cabinet helps keep the media moving down so the pipe has a good supply
15. If glass beads spill outside the cabinet, remember they are very slippery. Think of a pig on ice if you must walk over glass beads.
16. Larry Carter offered the idea of using a rare earth magnet in the bottom of the cabinet to attract the ferrous metal that may be removed in blasting. This helps keep the media clean, and reduces wear in the gun nozzle system.
We got a chance to try our hand on a dutch oven Bart had. The blast worked very well and quickly to get the rust off.
Bart also showed us a powder coat job he did with only the blasting as surface prep. It sure looked great. He demonstrated coating strength with a hammer blow.
Bart got a used kitchen range to use as his powder coat bake oven. He has it hooked up outside the house and has very good luck with it. Caution do not bake powder coat in your cooking stove. It is very dangerous to health.
Thanks Bart for all your great guidance and knowledge. Also thanks for stepping up on short notice with a great subject.