The answer to the abrasive and dangerous metal dust and particles produced from plasma cutting and grinding steel is to suck the air, complete with all particles, smoke, fumes etc. away from your workpiece! Items purchased for this project were the filter at $65, the reverse pulse valve at $100 from Ebay, door seal rubber at $30, flat steel bar at $170 and three sheets of steel at $180 This is a high volume (300 CFM) downdraft table designed for all day use with a full 1220 x 2400mm sheet capacity.
Step 1: The First Problem - Warping Steel
If you are familiar with manual plasma cutting of steel sheets, then you are familiar with the pieces warping and moving during cutting. This causes inaccurate cuts and can also mess up the orifice in the plasma cutting tip which in turn causes an angled plasma stream and rubbish cuts. A table with an evenly supporting surface for the job to be laid on is a must.
Step 2: The Second Problem - Metal Dust, Grit, Small Splinters
This stuff gets into your mobile phone, clothing and into your lungs, not good for you. When the small magnet in your phone earpiece attracts these particles, it starts buzzing and consequently stops working as a result, then it's time to make one of these dust extractor tables.
Step 3: Make the Table
Plasma cut 1.6mm steel sheet and tack weld together, then to the frame. Two sheets of 1220 x 2400mm sheets are required for this hopper and some of the offcuts are used later. Getting the four pieces of the hopper together was fiddly and the method of using a pipe offcut to support the centre worked the best because you can adjust the angle of the pipe by bending where it's tacked to the sheet to slightly move the hopper up or down when doing the final tack weld assembly of this part. All through this stage it was impossible not to think of crudely manufactured, Mexican drug running submarines :-)
Step 4: Fabricate the Dust Collector Housing
The main part is folded from a single sheet of steel trimmed down to 1220mm x 2060mm
While the press brake is set for the door opening folds, also fold the 1220 x 340 offcut which is later notched and used for the top and bottom as shown positioned in the second pic
First cut the small circle from the cutout on the top, then the large one. This piece is used at the step down before where the dust extractor fan hose is fitted.
The attachment for the filter is just an M12 cap screw welded to some rod. The crosspiece is bent up the top to prevent it pulling in the sides of the tube. The tube is extended through the main housing to locate the filter underneath.
Step 5: Add the Reverse Pulse Cleaning System
This is a piece of heavy wall linepipe with a 1/4 inch BSP fitting welded into the base and a piece of 1 inch pipe welded out the top. The tank is removable as the pulse valve uses compression fittings and the tank is removed for fitting the valve. After the pipe enters the large tube on the top of the housing, there is a 90 degree steam pipe bend welded to direct the air pulse down into the center of the air filter. Pressure in this tank is straight from the compressor at about 100 psi
Step 6: Make and Fit the Housing Door
The door is made with the same size folds as on the housing opening which allows you to see what the gap is between the housing flange and the inside of the door. This means you can tell how much the rubber seal is being compressed. The hinges use simple steel lugs with rounded ends with 13mm holes in them and have a 12mm steel rod running through them. The hinge side works excellent but really the other rod jams when trying to push it trough to close the door. Might replace this with something.
Step 7: Mount the Extraction Motor
This is an old three phase unit still in good nick and found in the mud next to a timber manufacturing place. The owner didn't want anything for it. The switch was jammed full of sawdust and a bit of rust but cleaned out well. The four mounts are welded to the housing near the corners for rigidity as any vibration will eventually tear the sheet metal.
Step 8: The Extraction Unit Assembled and Fitted to the Table
This is the easy part, fitting the door seal rubber (pinchweld) and pressure testing the reverse pulse cleaning tank. Getting the polyurethane flexible tube onto the painted steel tube required some water for lubrication and is clamped on with hose clamps.
Note where the dirty air enters the housing is below to filter as there is some abrasive blasting here which will very quickly destroy the filter media.
Paint is left over Paperbark and Emerald Green spray enamel mixed together to give a sort of hospital green colour.
Next steps to come soon will show how the 50x3mm flat steel bar is cut, notched and fitted into the table to provide the flat surface necessary for plasma cutting sheet steel. These slats are easily replaced without tools and you get four at 1395 mm out of a 6 metre length which is a fairly efficient use of steel.
Step 9: Wiring the Step Down Transformer and Switch for the Pulse Cleaning System.
Waiting on the transformer from Germany, purchased on Ebay and a momentary switch from China, also purchased onEbay
This will step down the voltage from two of the actives in the three phase from 400 volts to 230 volts which is required to power the small solenoid on the pulse valve. If you have a neutral link in your three phase power supply, then by taking one active and the neutral, you will get your 230 volts.