Just the start of a fresh school year and I am already set to undertake an exciting design opportunity at Larsen Motorsports. I was paired up with another intern to design and build a custom downdraft table that could be used in the composites lab or fabrication bay in the shop. We immediately set out to do some research and understand the operating mechanisms of such a table. They are meant for eliminating dust from a work area by sucking in the dust from tasks such as welding, sanding, plasma cutting etc. We looked at various tables available in the market and how much these tables cost (usually between $5000 – $12000 if you want a heavy-duty, industrial down draft table). Our goal was to build one that could fit within the budget allocated to us and use the raw materials that are readily available, either in the shop’s scrap metal collection, or material that could be purchased at the local home depot. We wanted to use steel for manufacturing because it is durable and can handle practically all metalworking, woodworking, and composites tasks.
I went home that day thinking of different funnel designs for the interior of the table. I was thinking of a way to optimize the space we had within the dimensions we had to work with. The table needed to be 4 ft by 2ft by 3 ft and had to be portable. Based on the dimensions, we calculated the interior space we had to work with. The next difficult part was to figure out what the interior needed to have. We definitely wanted a blower and a motor along with it to act as the vacuum that would suck the dust down. We also wanted a funnel-like structure to be able to direct the dust and form a closed hollow body so that every single dust particle was drafted into the table. However, the shape of the funnel was the tricky part. We needed to have enough space to fit in the dust drawer which collects larger dust particles, the filters which filter fine particles, and finally the blower.
So we decided to go with the following design shown below:
Funnel Design for the interior of the table
A chicken gage was to be placed in the rectangular cut-out and replaceable filters were to be inserted right behind it. The blower was to be mounted aft of the chicken gage. Once this design was created and approved by our supervisor, Mr. Tocci, we set-out to find the right blower to be used. We needed to perform CFM (cubic feet per minute) analysis to know how efficient the blower we purchase needs to be in order to function well with the internal size of the table and surface area of the table top. Eventually, a value of 2000 CFM was settled upon after a number of calculations and online research. This was also a good value because a lot of the industrial blowers available offered this mode.
Next, we needed to figure out what to use for the top surface of the table. It obviously needed patterned holes so that there was an opening for the dust to be sucked in. But what was the best material to use, and what was the best way to make the holes? We agreed upon steel once again for the heavy shop work, and decided to use a rubber mat with holes cut into it to be used alongside the steel surface for composite work. A rubber mat was purchased from Lowe’s that had the perfect dimensions for the table. However, we were still contemplating how to pattern the steel top.
Mr. Chris has purchased a decently large workshop table and we were going to use a third of the table as the exterior body of the table. Therefore, we decided to mark up the table to the dimensions needed, and chose to manually sketch the holes onto the table which we would later drill. Using a chalk-line and a sharpie, Muhannad and I spent most of a Wednesday afternoon drawing, erasing and re-drawing the pattern for the holes. We were simply unable to get them to be precise and follow vertical lines. Drilling through the table was going to be even harder because accurately drawing something is one matter, but accurately machining it is a whole new ball game.
The only work around to this was to either use a laser cutter, or to cut out the top surface and replace it with a ready-made steel that has holes cut into it. The latter seemed to be easier to attain. Expanded metal was the replacement we thought was best suited. So I spent about 3 hours and plasma cut the surface of the table one Friday afternoon. It was a totally new experience for me that I thoroughly enjoyed.
The next step was to build the funnel based on our design. However, taking a second look at the design we created, it seemed like a much more difficult way of building the funnel since it wasn’t a symmetrical shape and only had once slanted side. This would also case problems with placing the blower and filters and lower the efficiency of the blower because only one side of the interior was doing the whole task. So, we went back to Solidworks and re-designed the funnel shape so as to make it a symmetrical frustum. Now the lowest part of the funnel was going to have a slot for the filter in such a way that it was placed directly perpendicular to the flow of dust being sucked in. The dust drawer would then be directly below the filter, maximizing the use of the interior space.