Aeronautical engineer needed

Re: Aeronautical engineer needed

Don Stephan

Not sure what you want. A divider? And the air flows into the 4" round? Cut a 1/2" or 3/4" piece of plywood, taper both ends, and secure with a couple screws through the metal into the sides of the plywood.

Re: Aeronautical engineer needed

eric

equation for symetric airfoils: https://en.m.wikipedia.org/wiki/NACA_airfoil

probably overkill.

Re: Aeronautical engineer needed

Dennis in Southern Oregon

John, I am an engineer, although not in that specialty. I expect that the purpose of the "wing" is to suppress rotary motion of the air entering the funnel, which would tend to retard airflow. As a practical matter, I do not believe that the profile of the "wing" is significant in this modest application. (It would be in a turbojet engine.) I would just use a thin flat piece of metal mounted edge-on to the airflow. I would guess that the profile used in the Powermatic unit was specified by a marking type rather than an engineer.

not an engineer but here's a picture

Jeff Willaford

John, Maybe this is what you are talking about.

Ask an engineer a question

Dick Coers

and 99% of the time you will be asked a question right back. What do you mean by improving air flow? You want more velocity or more volume? As mentioned about the only thing an air foil will do is a minor flow straightening. Air foils are used to produce lift, it's not a venturi. The only thing to do to improve that thing is throw it away. You are going to need a much longer cone along with a larger diameter exit for any changes to flow characteristics. That design has a ton of dead zones in it with almost a flat bulkhead. It's only designed to adapt to two different size openings, not to provide optimum air flow.

Re: Aeronautical engineer needed

Dave Delo

I think this might be a picture of the old PM dust hood. If you enlarge the photo you'll see the shape (not sure what you call the shape so I'll call it a double tear drop) they put in their offering.

Re: Aeronautical engineer needed

john lucas

Thanks everyone. Quite interesting. I would think that the idea behind the central pillar or wing or whatever you want to call it is to increase the velocity. By increasing the size of the opening you obviously decrease the airflow and maybe velocity as well. I realize there may be much more efficient systems I'm just trying to improve on what I can readily get hold of without making the whole thing from scratch. I need the larger hood for things like platters (I'll swing it vertical for those) and horizontally for spindles. However when you get a larger hood although the area is larger it seems like you pick up less airborne dust. Having to constantly move a 4" hose to get the best pick up is just more than I and probably anyone else wants to do. So I'm looking for a larger more efficient duct. consequently I thought about modifying this one.

Thanks for the photo of the PM hood. I had forgotten the shape of the central pillar.

Just a round piece of dowel would ......

JamieDonaldson

..... be sufficient for holding the mouth of the hood open, and air flow from the opening into a 4" hose will not be significantly affected. I did once take a course in flow dynamics which I have used in several different applications, like trim tabs and bug deflectors.

Re: Just a round piece of dowel would ......

John C Lucas

Its stiff enough to stay open as is. Im just looking for a way to increase how much dust it picks up

Re: Just a round piece of dowel would ......

Dick Coers

If you just want to pick up more dust without changing the dust collector, I'd suggest a more contoured front lip. Something that cradles under and over the work. Consider a C shape to the shroud. Just having an open flat face requires more velocity to take the dust out of it's current direction off the part. If you can interrupt the path of the dust with the shroud, you'll need less air flow. Of course you will have less access to the wood. You might also consider adding a brush strip to the shroud so you can get it right up to the work.

Re: Aeronautical engineer needed

Ron Solfest

John,

My PM came with the dust collector attachment but after a couple uses I haven't used it in years, it was much more cumbersome than just dragging a 4" hose around. As we've discussed at the monthly meeting I just moved here to TN and have now set up a 6" hose (off of a 3hp Oneida). Not sure if I moved the PM dust hood/bracket or not, if I find it I'll bring it for you to next months meeting.

Ron

Re: Aeronautical engineer needed

Jake niedling

John - the concept you mention will have no to very little impact on dust capture efficiency. It's all about capture air velocity at the face of the collector. As you enlarge the collector opening, the capture velocity drops off. If you increase the airflow in the duct or add two separate 4" ducts to the collection hood, then it will work signifactely better in capturing dust. Now adding a wing design to a hand mirror would be interesting. 😃

Re: Aeronautical engineer needed

john lucas

Good responses. I may look at splitting the air hose and have 2 hoses going into one sort of half tube. I would just use the hoses but since my spindles are longer it just makes more sense to have a longer duct. Going to Cookeville today for a Dr's appoitment. May stop by Lowes and see what I can come u with. What I just built will work better below my disc sander and won't need the wing.

Re: Aeronautical engineer needed

Barry Irby

John, about ten years ago I did a lot of work setting up dust collection in my shop. One of many things I learned was about "capture" of the dust. Look on Bill Pentz's site for a ton of information. We are saking the air to deflect the particles into the hose. High velocity air can redirect a slow light particle, but the big heavy ones are very difficult. I tried to put the hood into the path the particles were already traveling. Let the tool or blade fling the particles into the hood.

And, the people that pointed out that the hood reduces the velocity are correct. If your hose has about 13 square inches and the hood at 8 by 12 has 96 square inches the loss in velocity would be dramatic.

I used parts for duct work. Things like boots and end boots as pickups. Put the hose in the bottom and try to let the dust fly into the hood on its own the DC suck it out. The air flow in to the hood will help. I tried some brushes also to extend the hood and they helped. What I wanted was those "hula" brushes you see on tractor trailers. Never found the really long ones. I think they would help to deflect the particles and air into the boot.

Re: Aeronautical engineer needed

philip f Duffy

Why not create a rotary wing system with moving control surfaces, ie, a helicopter, and then I would know exactly what the right answer would be - -but not by some fancy formula~! And, this question could then go on for weeks on end. Philip

Fan blade

John C Lucas

My friend who was a production turner back in the 70s before anyone used dust.collection used a fan. He had one of the old Delta lathes and made a fan blade out of cardboard that fit on his handwheel. It would blow the dust away from his face.

Re: Fan blade

dave Stricker

John, I use a push-pull system to try to control the dust. I have a big gulp collector hood mounted behind the lathe and a small 4" fan mounted on the headstock with magnets directed down and toward the hood. The fan blows the dust into the hood. This is a fairly common industrial practice. It is easier to control air flow by blowing than by sucking.

Re: Fan blade

Dick Hines

It looks to me that everyone is over engineering the dust collector. My simulation was to use a 9 in bowl I blew years ago. I cut the bottom to fit 4 in dust pipe connected to my collected. Since the shape let's it wrap around whatever I am turning it catches MOST of the sanding dust.

If anyone figures out how to catch ALL dust when sanding they will have more money than they can spend.

Z

Re: Aeronautical engineer needed

Mike Mills

Here's one I made about six years ago with a floor register. Once the flange is snipped of it automatically goes oval.

My "shroud" is plastic file folder and can be moved or sized as you desire.

Shown would be for a platter/bowl where the open side is aligned with the front. All air would be pulled across the front as the back side is blocked off.

It rotates in any position so for a spindle it would be turned 90* and the shroud extending would be under the work. For a bowl it may be 45* and turning the entire jig also 45* front to back to follow the shape of a bowl exterior.

Shrouds are attached with Velcro so they can be positioned as needed. There is a wire (coat hanger probably) across the front to keep the shroud from being sucked in. Note hardware cloth in the throat to catch loose sandpaper.

Re: Fan blade

Jeff Smith

John: a couple of years ago, Fine Woodworking tested various dust collection systems. Part of the data they collected was the effect of various shapes of hose terminations had on the velocity of the air at the business end. If memory serves (and thats probably somewhat questionable) they determined that the best airflow into the hose was created with a bell-shaped collector.

I'd guess that the article is still available if you know a subscriber. I'll see if I can find it.

Re: Aeronautical engineer needed

john lucas

For now, at least temporarily I'm going to use the Oval floor vent until I have time to really experiment. I mounted it yesterday and found that simply putting that piece of scrap in there seems to increase the "suction" if that's the proper term. I'm going to make a more wing shape today and give it a try and see if I can tell the difference. I'll drop some shavings a few inches in front and see what it pulls, and then add the wing and do the same experiment.

Seems to me from reading what you all have said the best thing would be to make a cone out of sheet steel. Then flatten it into an Oval and possibly put a wing in the middle. Oh well,it's just playing while I'm waiting for glue, paint or stain to dry on other projects.

sanding dust

John K Jordan

>>>I'll drop some shavings a few inches in front and see what it pulls, and then add the wing and do the same experiment.

I use a pickup I got from Woodcraft for sanding:

I was amazed at how much sanding dust this picks up. With a darkened background and bright light on the wood and sanding while turning in reverse, I watched the dust come off a spindle and travel to the pickup from at least a foot past the end of the pickup. A video of this would be fun.

It will certainly pickup chips if dumped close enough although they don't present much of a health hazard when turning. But to help evaluate any air flow differences with different inlet designs it may be useful to also sprinkle fine sawdust, say from a salt shaker.

JKJ

Here's my wing

john lucas

I threw this together this morning made out of 1" blue foam just as a test. It's hard to tell the difference in pick up by dropping shaving 5" in front. Still not much pick up but then the 4" hose didn't either. Seems a little improvement judging by the amount of shavings left on the bed of the lathe but then who knows if I picked up a callibrated amount of shavings each time.

When you stick you fingers in toward the back there is a noticeable feeling of accelerated air with the wing in place based on how cool your fingers feel. I haven't tried sanding yet but maybe will have time this afternoon. I think it will pick up more than my 4" hose simply because it will be closer to the work on various parts of spindles. The whole thing rotates so I can place it vertical when sanding mirrors and should get most of the dust.

Re: Here's my wing

John K Jordan

My DC is a 5hp cyclone and it would suck up a cat if it got close enough, but although great for sanding dust it is almost worthless at picking up chips coming off the lathe.

JKJ