Yet Another Dust Skirt

[joel_schuman]

In the previous episode, I presented a shop-made fiberglass connector between the Alpha skirt and 4" hose to replace that unspeakable squashed 3"hose kluge. But while it solved a few problems, the connector did not address the most annoying issues. Sigh. Time for a clean-sheet redesign, making this the most expensive skirt I'll ever own; probably worth more than my wife's wispy Prada skirt, although slightly less stunning. Here are the design requirements I started with:

1. Skirt height is relative to table, not spindle, as was the old pre-Alpha ShopBot skirt. I find it impossible to make dados and thru cuts in 1" or 2" MDF with the Alpha skirt in place. Cutting any easily marred material with the Alpha skirt is risky - scratches seem inevitable.

2. Curtain is stiff enough to resist folding under when sucked by a 3HP dust collector.

3. Curtain lets little air thru. My dust collector pulls enough that if the curtain is within 3/8" of the workpiece, it stays clean as a whistle and all chips and dust go up the chute.

4. Curtain is easily replacable and is made of cheap, locally available material that won't mar work and won't hold sharp chips.

5. No tools required for use and adjustment. Ever. Period. Full stop.

6. One-handed adjustment.

7. Skirt stays in alignment. No pitch, no roll, no yaw.

8. Skirt holds height on its own while being tightened.

9. Air flow has no bottlenecks, restrictions, or sharp bends to reduce draw.

10. Large chips and splinters unlikely to cause jam. In case of jam, easy access to all airways without ANY disassembly.

11. Bit change does not require removal of skirt when cutting materials up to 4" thick.

12. Skirt can positioned away from cutting area without removal and without interfering with tool operation, travel or limits in any direction.

13. See-thru skirt plate can be easily replaced with cheap, locally available material. No molding or complex machining required - just a single SB part file.

14. No special parts or hardware. Small parts are cheap, locally available.

15. Strong, durable, can take a hit from flying workpiece or broken bit without exposing operator.

Here's the prototype. It meets all the requirements. I'm looking for suggestions for improvement before I do it in 1/8" Al. As they say on eBay, "Thanks for looking!"


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[mzettl]

Joel,

I've only had my Bot for a couple of months, so I've spent most of my time learning the software, and how to get it to do what I want it to do. Recently, I have become interested in improving the dust collection, and have studied the recent threads carefully. I have done some experimentation on my own, but you are light years ahead of me.

Nonetheless, I have a few observations which may prove helpful. I have an Oneida 3 HP collector with a 4" hose going to the bot, although I could easily increase that to 5". In my discussions with Oneida before I purchased my system a couple of years ago, they made it quite clear that the key to successful dust collection was air flow, not "suction." As you have so dutifully pointed out, any constrictions or sharp bends in the ducting will lessen effectiveness.

My only concern about your skirt is the solid gasket material. If that is touching the workpiece, or very close to it, wouldn't airflow become restricted? Perhaps that is why it works so well when it is 3/8 inch above the workpiece. I wonder if a brush type of skirt wouldn't provide better airflow. In fact, if the back of the skirt around the hose inlet were solid gasket as you have shown, and the front around the spindle were more "porous" the net effect might be to concentrate the true pickup area closer to the bit, with more flow where it will do the most good.

I really like your idea though. Much of my cutting will be in 2" thick material, and I agree that the skirt that comes with the alpha is worthless in such a situation. Would you be willing to share your plans? I would be glad to be one of your "Beta Testers!!"

Thanks for the photos and the great ideas.

Matt

[joel_schuman]

Matt,

Thanks for the feedback.

I've been testing various curtain materials since I got my 'Bot 3 years ago. I've tried brushes of various length, thickness, and stiffness. A short (<1.5") stiff brush works well enough most of the time. But a solid curtain concentrates the air flow close to the work surface and seems to work better in most situations and is never worse, even with materials with static problems. The strip brush that works best is a special order for me and is expensive.

The 3/8" height above the workpiece is a win for me. I determined the optimum height by observing the catenary my 4" lightweight flex hose (from PSI) makes between the 'Bot's bow and the metal pipe - it appears to be a reasonably sensitive indicator of air flow. But even when the curtain is set too low, close to or touching the work surface, the dc's draw flexes the solid curtain along its length and enough air passes under to do a better job than the original did.

I don't seem to need more air flow than I have now - it just about sucks the gloves off my hands when they're near the curtain at the work surface - and as I said it picks up everything. I can't usually see any output chips or dust, either under the skirt plate or in the hose on the bow - it's all just GONE. The biggest unexpected plus for me is that the gap allows the big hanging splinters I sometimes get when roughing oak or other brash wood to pass under the curtain where I can safely peel them away instead of seeing them pile up and block that narrow intake on the stock Alpha skirt.

I'll wait until I've been thru the full range of jobs I normally encounter before I commit to a metal version. When I do, I'll want to work with someone who has an Alpha Y-car (mine's an upgraded pre-Alpha PRT) to make sure it fits both old and new. From the SB pics, it looks like there's less clearance on the Alpha, but when I move to metal, the whole deal can be much smaller and less obtrusive (intrusive?), so it should work. Maybe you can check the fit when I get to that point?

My goal is to make an easy-to-build set of plans available here. I don't plan to sell complete units - don't think I could produce them in small runs at reasonable cost.

Cheers,
Joel

[mzettl]

As is often times the case, experience wins out over theory. I certainly appreciate your thoughtful observations over three years. I also am in full agreement with your desire to use readily available materials and components.

Sounds like you and I work with very similar materials. My work is almost exclusively with hardwoods, including a lot of imported stuff. In my current projects I'm using Jatoba (Brazilian cherry), which is a bit harder and denser than hard maple.

I would be glad to help out in any way that I can, just let me know.

Matt

[beacon14]

Joel,

Great work towards what has been an elusive goal. The biggest down side I see to your setup is how far the open area extends off the table when machining close to Y=0. You probably won't get near the actual dust collection (if any) when the opening is hanging out over the end of the table. I suppose you could add a table extension to solve that problem.

Also, I see from your photos that the spindle mounting differs from the typical router mounting in that the spindle collet and bit hang much lower compared to the bottom of the Z axis mechanism that do a router collet and bit. In order for me to reach the material with most of the bits I use, the opening in the top of the shoe would have to accomodate the entire router motor and Z-axis plate, including the springs. Hmmm, another reason to upgrade to a spindle....

[Brady Watson]

Keep at it Joel...I bet you have some time into that one! Soon you will be like some of us old school PRT guys...with about 4 or 5 different dust foot variations hanging around the shop!

Ah...the pursuit of the perfect foot...It's like a woodworking podiatrist's dream


-B

[joel_schuman]

David,
Machining at Y=0 isn't a problem - the skirt is the same width as the stock Alpha (has to be to clear corner posts). At X>115 draw drops off, but the chips get collected when the skirt comes back fully on the table. I'm not cutting down there all that often.
Thanks for mentioning the router mount difference. I hadn't thought of that and I'll try to accomodate it in my final version.

Brady,
Omigod! Are you suggesting the perfect dust foot is not a goal that can be reached? I'm trying to dig in my heels on what is beginning to feel like a very slippery slope. I'd rather spend my free time on my own work than on 'Bot mods, but I must admit I had as much fun with this simple project as on any sculpture I've done. Whenever I get the urge I come here and cruise this area, hoping vicarious satisfaction will do it. God forbid I should end up like some of you more advanced Bot hackers! I got a family - bad enough I should sneak off to the shop and spend a whole Saturday, albeit a rainy one, on this. K
Joel

[Brady Watson]

Joel,
You're right...projects like these are fun! Especially when they help you every time you use them.

Making the ultimate dust foot is a process...Everyone has their own ideas of what it should be and how it should function. It only really has to be good enough for you!

-B

[patricktoomey]

Joel,

That looks really good, I would love to give it a try since I've been having serious jamming issues with my existing foot. I cut lots of prefinished Chinese birch ply and it leaves strings and long slivers all over the place. They get jammed up in my 2 1/2" vac hose which I currently use through a reducer to my dust collector. Moving to 4" has been something I've wanted to try but just haven't had time to design a new foot. Do you have a SB cut file for your parts? If so, would you be willing to share it?

[joel_schuman]

Patrick,
I don't have an SB cut file, sorry. I fitted this prototype a piece at a time the old fashioned way. My intention is to tune it and then make the final one out of 1/8 inch aluminum plate. I'll do plans for that one and post them.
I do a lot of Baltic birch ply, too. 4" hose helps a lot, but only if you get rid of all the other restrictions at the same time, hence this effort.
Joel

[hespj]

That certainly looks like it'll give better airflow , which I would welcome, but the severe reduction in z axis travel makes it of limited use to me personally. I guess I could swap dust skirts for different applications.