I did some experimenting the other night with pegboard and DC. I was a bit surprised how efficient a cobbled together downdraft table could be. Anyone have some suggestions as I design a permanent sanding/scraping station that will be used with non-shopvac connected tools? I am going to use part of the TS rear outfeed table as a location (23 x 43). I can tap off 4″ and 5″ homerun DC lines giving me a max 32 sq inches of duct area. I am figuring the open area of the pegboard at ~39 sq inches.
Suggestions already received include countersinking the pegboard, routing shallow channels between the pegboard holes, and cutting slots around the outer perimeter.
I need help figuring how deep the box should be; support/baffles for top; and location of DC port/ports. Without any slots around the top’s outside perimeter the ratio of duct area to open table area is 1.2 to 1. Do I need that much?
Many thanks!
-Jerry
Replies
http://billpentz.com//woodworking/cyclone/Downdraft.cfm The best description of the issues that I know of.
dloc,
Thank you. I feel really stupid as I have been to that site many times - twice in the past few days. Never noticed the section on downdraft tables. Anyway, I do appreciate the help!
Best!
-Jerry
Hi jerry,
I'm thinking of making a similar kind of setup as you. I have two of these and am thinking of just building a small box under the table to accomodate them with a center divider. They measure 12¼" x 12¼" and have beveled sides. I'd laminate 2 layers of the pegboard for the top and perhaps bevel the holes?
Connect the two ports underneath via a Y into the main run for my DC, with a blast gate.
Regards,
Bob @ Kidderville Acres
A Woodworkers mind should be the sharpest tool in the shop!
Bob,
I'm still experimenting with hole sizes vs table size vs duct size. The more I fool with it, the less that I think it will be a overwhelming success. I'm running 2 hp of DC at about 1300 cfm and it's not quite enough on paper to make me happy. I'll run some more actual tests later in the week and let you know how it goes.
Best!
-Jerry
I don't have the experimental data to prove it, but I think the basic concept of a downdraft table is fundamentally flawed, because what you need is to entrain the dust particles that are floating around outside the box, which means that your entire shop is the "pipe" that the air is flowing through.
Instead, I think you'd do much better with an enclosed box designed in much the same way that a chem lab fume hood is designed. The air flows into the hood at the front, and out into the ducting at the back. Thus, you have a well-defined stream of air from the front to the back that is entraining all of that dust.
-Steve
That's a good idea, sandblast cabinets can be had relatively cheaply that would be large enough for most jobs that a downdraft table would be used for. They could be easily modified.Giving money and power to government is like giving whiskey and car keys to teenage boys. -- P.J. O'Rourke
Steve,
Methinks you are on to something. I'm going to let the downdraft project rest for awhile.
Best!
-Jerry
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