downdraft table design

[karossii]

Hi all!

I am eagerly awaiting the shipment of my new carvewright, and thought I might go ahead and get started on a project in the mean time to help pass the long hours I am counting off until it arrives;

I have seen several ingenious downdraft setups, and am wondering if anyone (or hopefully, a few of you) might be able to post general dimensions needed for the table, the slot, etc., so that I can draft up a decent design which will work?

I plan on making it a somewhat portable unit, as I will probably be using the CW in at least 2 if not 3 locations...I have a few ideas in mind but haven't started drawing out anything solid just yet, since I need some dimensions.

Also, I am looking at several systems, I assume ~ 2.5 microns or less is a requirement; what CFM should I be going for at a minimum, about 1,000? I have found that very few DC systems list decibel ratings, any suggestions on powerful but relatively quiet performers? At least, nothing louder tan the carvewright would be, that is . . .

Thanks for any input you may have,

- Ken


(P.S. I have done several searches and replied to a few threads about DD systems already; noone yet has given dimensions that I have found, and I didn't feel like hijacking any other threads.)

[MikeMcCoy]

I'm not home so I can't be real specific with answers but you wan't your slot just big enough to accomodate the slot on the CW. Use weather strip to keep from sucking dust all across the electronics. I have a 1 1/2 HP DC for my shop but I just use the Fein Turbo vacuum for the CW. It works fine and is a whole lot quieter than the DC or a regular vacuum.

[Jeff_Birt]

Thought I had noted the dimensions down in the thread I had started on the subject, but I guess not. Here are the specs on the dust collection unit I purchased.

I picked up a 2hp Grizzly G1029 dust collection unit yesterday and got it put in today. I read many reviews of different DC systems and looked at several yesterday. I choose the Grizzly as it offered the biggest bang for the buck: 2.5 micron filter bag, free pre-separator (trash can separator), 2 HP motor, 1600 CFM and static pressure of 11", for $279 ($20 off). It is largish for my 1 car garage/workshop but it will probably last me forever.

It is my opinion that the 2.5 micron or smaller filtration is a must. Otherwise your just blowing out the really small, really harmful to your lungs, particles back out into the air. From what I read before buying a DC you need about 600~700 CFM per tool. The 1600 CFM my unit is rated for seems OK for leaving the floor sweep (another must) open a bit while having the other hose on the CW. My next step will be to create a 'filter box' to mount up near the ceiling. The second DC hose will run up to it and Pull air through a 3M filtrete air filter to catch any of the stuff that gets out into the air. It's just a poor man's replacement for the commercial units with a built in fan. I figured I can keep the filter box running along with any other tool that uses the DC and let it run for 15 minutes of so afterwords.

Ha! Just found a post where Doc Wheeler listed the 'slot size' (I searched for 'slot size': http://forum.carvewright.com/showpos...59&postcount=5. One other tip is to keep the collection box/tube under the machine as small as possible. You want to keep the air moving through it. I made a 'U' shaped tubular piece: http://forum.carvewright.com/showthr...atic+air+blast, other have cut the top off a large piece of PVC pipe.

[wasacop75]

What size does one need to mount on a portable unit?
One that can be moved around the garage or shop?
I hope to get my machine ordered soon and will need a DD system
so that mother will let me play in the garage till i get the shop built.

Thanks.

Mike

[Kenm810]

Mine is a bit on the large size, (36" tall x 40" long x 30" deep)
It's mobile and has a self contained DD System built in.
I've seen a few larger and several smaller,
it depends a lot on how much room you have.

[karossii]

Jeff,

Thanks for a lot of good info, and a great job on that search for the slot size! Now I just need to know where that slot is to be positioned on the tabletop in relation to the carvewright, lol.

From what I have read up on DC systems, the actual CFM pulled through any ducting is roughly half (in some setups as little as a third) of the advertised CFM of the machine, which is assuming an open fan with no filters or duct work. So your ~ 1,600 CFM is actually down to about 800 CFM due to your setup... possibly even just over 500 CFM (especially considering you leave your floor sweep open a bit.

That's why I was assuming 1,000+ CFM as a minimum.

I've also found some great info on the ESD + Dust Cloud phenomenons, particularly regarding PVC ducting. From what I can see, and I actually have gone and pulled a few books to verify/back up what I read online, there is no cause for concern there...it is a myth that metal ducting or 'grounded' pvc (its impossible to ground pvc) ducting is needed. Here's a link to the best article I have seen, even if it is very old; http://home.comcast.net/~rodec/woodw.../DC_myths.html

Mine is a bit on the large size, (36" tall x 40" long x 30" deep)
It's mobile and has a self contained DD System built in.
I've seen a few larger and several smaller,
it depends a lot on how much room you have.

I like the self-contained DC unit you have there Ken, it would be great for portability... where is the dust collected, and what level of filtration do you have? Are you using standard DC dust bags in the base of the unit?

[Jeff_Birt]

Yes, I think the real possibility of causing an explosion in the home shop due to static build up via a DC system is about nill. The most probable issue is getting a nasty shock or having a static discharge damage a piece of electronic equipment.

And yes, you cant 'ground' a plastic pipe. What you can do however is prevent a static charge from building up by providing for a conductive path between the inner and outer walls of the pipe. Usually this is done by using a really shirt self tapping screws inserted through the pipe every 12"~24". All the screws are tied together with a copper wire with is grounded.

For my flex tubing I do not run copper wire inside it as everyone always suggest, that just causes clogs. Instead I lace the wire around a rib every 18" or so. Doing so around a rib gives you a nice mechanical connection inside and out and will not allow the tubing to tear. You can dab a bit of silicone over the penetration to seal them up.

Edit: I 'think' the slot is centered L-R (front is keypad side), but it is not centered F-R.

[Ike]

Yes, I think the real possibility of causing an explosion in the home shop due to static build up via a DC system is about nill. The most probable issue is getting a nasty shock or having a static discharge damage a piece of electronic equipment.

And yes, you cant 'ground' a plastic pipe. What you can do however is prevent a static charge from building up by providing for a conductive path between the inner and outer walls of the pipe. Usually this is done by using a really shirt self tapping screws inserted through the pipe every 12"~24". All the screws are tied together with a copper wire with is grounded.

For my flex tubing I do not run copper wire inside it as everyone always suggest, that just causes clogs. Instead I lace the wire around a rib every 18" or so. Doing so around a rib gives you a nice mechanical connection inside and out and will not allow the tubing to tear. You can dab a bit of silicone over the penetration to seal them up.

Edit: I 'think' the slot is centered L-R (front is keypad side), but it is not centered F-R.

Jeff, that is a brilliant idea! I have heard of running a straight copper wire through the pipe, but using screws is just brilliant! Thanks for sharing that!

Ike

[karossii]

Yes, if you follow that link, it is an old page about ESD and DC systems, but it seems all accurate and up to date per my independent research recently; and it mentions the screws as being the best possible form of static discharge reduction... but it also mentions it really isn't necessary to have them, as the chances of anything occurring within the ducts is as near to 0% as is possible for anything (there's always the exception to prove any rule). It is a very long read, but it is worth it if you like to keep yourself informed about the whys and hows, in addition to the how-to's.

[Jeff_Birt]

Yes, I read that guys info too. Let me repeat what I said earlier though for clarification. The real danger of an ungrounded DC system is a static discharge damaging your CarveWright. A few folks have manged to do this with their shop-vacs. Proper grounding prevents the static build up.