ShopBot Dust Skirt assembly

[harryball]

I've got my bot up and running. Right now the dust skirt is giving me some trouble and I'm wondering if you guys see the same thing. When I start my DC (3HP Oneida) the suction pulls the plastic flaps back up into the housing and actually closes off most of the inlet. I reduced the suction by opening more ports, but I have to open 3 or 4 more 4" ports before the flaps don't clog it up and then the machine begins to throw a little dust.

Do you guys see the same thing? Is there a stiffner or some other part that might be missing?

I used a laser pointer to illuminate dust particles. When I taped the flaps back and resurfaced the table with the DC pulling on that one port... I didn't find a speck of dust that got past.

Robert

[paco]

I've noticed that too (not at a such degree that it clog my dust skirt though) and I guess that I have a much less powerful DC than yours... no missing stiffener; you'll have to design your own. Unless you don't like performance, you shouldn't release any pull form your DC; most of us are probably at envy from yours... you probably can get a good hold on those flaps with some added rubber; nothing too stiff to keep thing flexible under there. Maybe completely remove those end flaps could do the trick...?

[pete]

Robert

I have seen some dust pickups with shortened vinyl flaps. Maybe try cutting .5" off each flap - it sounds like with that much vacuum you should still have plenty of dust pick-up. You might have to experiment with the length of cuts to get a happy balance between good dust pick-up and airflow. You might also experiment with replacement material for the vinyl, such as the brush type. If you end up cutting off too much vinyl, you can buy vinyl sheet material in a hardware store and cut another one to the length you need. Just a suggestion.
Pete

[ed_lang]

I found that my 5HP Cyclone running 6" duct to the CNC and then reducing to 4" flex hose to the skirt did the same thing. I removed the screws holding the flaps and am happy with it. I was going to keep working on finding the right length but have never gotten back to that project since the restriction is now the mashed flex pipe at the end of the dust skirt.

I cut a few sheets of .75" MDF with a .375" straight bit and the cyclone pulls all of the dust out of the kerf so those missing flaps are not hurting me too much.

[harryball]

Ed, I think you are right. With such high volume of air flow the skirts can come off without too much loss of suction. I also have to be careful, with the skirts on this thing will suck small but sizeable parts right off the table.

I'm running 6" to a 4" flex hose as well.

I'm considering now trying to pull the vac table with the collector as well. Have you, or anyone else, tried this? Does it work well enough to bother with trying?

Robert

[davidp]

Robert,

Your dust extractor does not have the suction ie pressure usually measured in inches of mercury (" Hg) to efficiently hold down parts. Most vacuum hold downs have high vacuum ("Hg) but low airflow (Cubic Feet per minute, CFM). A dust extractor on the other hand can create high air flow (CFM) but at very low pressure ("Hg). A Dust extractor also relies upon the air flow to create its suction. In a vacuum hold down air flow can some times be minimal.

There have been several discussions over the years on this topic on the forum by people who are much cleverer than I, search for them and you will find more detailed reasons why you should not do what you suggest.

Regards,
David

[evan]

A simple way to illustrate what David is saying is to put a reducer on one of your 4" ducts and attatch a 2" hose and see how little suction you get.

[evan]

I should have said how little air flow, not suction.

[ed_lang]

Robert,
The 5Hp Cyclone in my shop will not hold a full sheet of ply to the CNC. I am much better off using one Fein Turbo III for that. I do use two of them so I get more air flow. I am very happy with this setup. Since I have been cutting vacuum masks and using the AllStar gasket material around the masks, my parts have been help much tighter and this is the direction I will continue. It is fun to watch visitors in the shop when I show them how I can hold something on the table. They keep looking around the machine, looking at me and then they go back to the part and have to pull, shake or push on it again.

I know it is hard to find time in the shop to experiment, but that was the bottom line for me. Read here what others are doing and then go try things in your shop, with your equipment and report back. Sometimes it the little things that make the most improvements. Gasketing for me was one of them. Moving from .25" to .375" cutters was another example. Put both improvements together and my feed speed went up as well as cut quality.

My parts now are not spending so much time at the sanding station!

They are now CNC! "Cut N Carry" :-)

[harryball]

FYI, I added some industrial doubleback tape between the skirt rear layers to bond them. Still flexes and I can still see the bit in the front. The suction is fantastic, just spent 15 minutes carving a sign in MDF with very little dust escaping. It was 10 minutes before I started even smelling that MDF smell in the air and even then it was faint.

Robert