Fletty's new shed WIP ....or is it a retrospective??

**fletty** · 17th February 2016, 10:10 PM

Originally Posted by BobL

It sounds like you are still working on duct area ratios which is incorrect - it takes 3 x100 mm ducts to carry the same amount of air as 1 x 150 mm duct at most DC pressures.

It would be useful if you quoted some actual flow numbers but what I also wanted to know were things like
What sort of anemometer was it? i.e. propellor based or hot wire anemometer?
What sort of air speeds were you measuring and what was the maximum air speed it could measure?
These questions are important because most hot wire anemometers can only measure up to 30m/s and in a 100 mm duct the air speeds might be greater than this.

Did you
- use a smooth wall test duct at least 1m long with a test port in the side of the test duct at the 500 mm into which the anemometer was inserted
- measure the air speed as function of radius across the test duct
- determine the air flow at each elemental radius
- integrate the air flow at each radial annulus.
If this is not done it will not give an accurate measurement of the flow.
Placing the anemometer in the end and in the middle of the duct and multiplying the resultant air speed by the area of the duct will give results that are incorrect by as much as 40% which is far greater than would be observed between different types of ducting.

Checking for radial variations of air speed is also important to detect turbulence.

Regarding the rockler flexy - I'm struggling to see how it can maintain a straight smooth bore once it is stretched even a small amount. Unless the material between the wire rings actually stretches it must fold creating wrinkles in the wall. If it stretches it must constrict slightly between the wire rings. A close up side on photo of it slightly stretched and fully stretched would be interesting to see.

Good grief Bob! I will try to answer your questions, concerns and doubts BUT please note that am claiming no particular insight nor knowledge of dust collection particularly with reference to woodwork. I regard dust collection, like sharpening and sanding, as necessary evils to achieve sustainable craftsmanship in woodwork. Dust collection, sharpening and sanding are not goals, they are means. However, there is so much misinformation and grandstanding included in the sources available to us that I decided to do what has always stood me in good stead through a long industrial career and that is to find out for myself. A lot of it is only minor detail and assumptions but, to me, the greatest folly that is being chased, the Holy Grail of Dust, is that some nominal 1000cfm of airflow "MIGHT" remove sub-micron dust? My knowledge of airflow and contaminants is that ONLY laminar flow can remove sub-micron contaminants and l doubt that any of us achieve laminar flow in any part of our extraction systems at ANY flow rates.
I purchased this anemometer ........

image.jpg

.... and used it to measure all flows at all current pick up points. My target was to 'at least' double what I already had, NOT to chase some numeric goal in which l had little confidence.
My then current extraction rate was 'adequate' ..... so twice that rate must be better? At some of my pick-ups, I was operating as low as 167cfm!
Your questions and comments re my working on incorrect duct area ratios misses the point that I am not designing a theoretical nor ideal system, I am trying to use what is already available and get back to woodwork. Simple area maths without any reference to skin friction nor surface area ratios shows that the area ratios of 100/125/150 mm diam are 1.0/1.56/2.25. So, in terms of base area, 2 X 100mm ducts are better than 1 X 125 but not as big as 1 X 150. Clearvue make a 150/2x100 adaptor so, in some parts of my network, I will be using 2 X 100.
Now to the Rockler 100 mm flexi. I will be using twin lengths of this where I am increasing my machine outlets from 1 X 100mm to 2 X 100 mm and yes, I am aware that this is not as big nor efficient as a single 150.
This is standard 100 mm flexi (s100f) static

image.jpg

....and compressed....

image.jpg

...both demonstrating a very corrugated surface.

This however is the Rockler 100 mm flexi (r100f) (externally) compressed showing the internal surface...

image.jpg

..... whereas this is r100f stretched by about 200% of the maximum 700% available showing the small degree of separation of the inner corrugations and the relative smoothness when compared to s100f in any state.

image.jpg

HOWEVER, the magic happens IF you cut the r100f to the right length. When the vacuum is applied, the Flexi (internally) compresses such that, in a straight line, both the inner and outer surface are smooth and the Flexi becomes rigid.

image.jpg

My interim system, probably in service next week, will have mostly 150mm backbone, some 1 X 100 r100f and some 2 X 100 r100f machine attachments but still with the 125mm choke point at the impeller face. Within the month it will be all 2 X r100f machine attachment.

Fletty

**BobL** · 18th February 2016, 10:19 AM

Thanks for the detailed reply and the pictures.

I won't clutter this thread with OT detail suffice to say that measurements of air speeds in narrow ducts made with a propellor based anemometers will not give correct results.
Any conclusions including that of the Rockler ducting arrived at about ducting with these instruments are likely to be invalid.
As I hate to see members wandering off on the wrong path I recommend members wishing to make, even relative, air flow measurements read Bill Pentz website about what instruments to use and how to perform the measurements.
I will write something a little more concise for one of the stickies in the dust forum.

**Chris Parks** · 18th February 2016, 10:24 AM

Fletty, I made my own 2 into 1 units without blast gates before my CV days. You can have a lend to copy it if you want, PM me your phone number and I will arrange it.

**fletty** · 19th February 2016, 01:21 PM

I'm making sawdust again ........

........ but you really can't tell!

My deprivation is over. After far too many weeks, l can finally woodwork again. I haven't finished the DC soundproof enclosure and my machine connections are still 1 X 100mm flexies, but I can run some machines to help with the shed fit out.
As I noted before, the idea is to have all of my 'prep' machinery on wheels and moved into place under the boom only when in use.

image.jpg image.jpg

The first cab off the rank today was the drum sander which l need to finish a new hardwood bench top for the shed. The sander will soon be converted to a 150mm diam pick up and so the 100mm in the pic above is only a temporary arrangement to keep me going. Even so, it worked very well. As an extreme test, I sanded a length of NSW scented rosewood which would normally send me spiralling into an asthma attack but, today ...... nothing!
Harking back to my old shed, the tardis, this is also the first time I have had the room to be able to completely unfold the sander base and use it as I had intended.

It's a good day, Fletty

**Bushmiller** · 19th February 2016, 01:32 PM

Alan

Looks good.

I have a question regarding drum sander as I have never had anything to do with them. Is it's prime purpose rapid finishing or is it/can it be used for light thicknessing?

Regards
Paul

**fletty** · 19th February 2016, 02:15 PM

Originally Posted by Bushmiller

Alan

Looks good.

I have a question regarding drum sander as I have never had anything to do with them. Is it's prime purpose rapid finishing or is it/can it be used for light thicknessing?

Regards
Paul

Hi Paul, that comes under the heading of 'bl**dy good question' !
I originally bought it to do light thicknessing on gnarly grained timbers that had a lot of break out on my normal thicknesser. After I fitted the segmented head to the thicknesser, that problem virtually disappeared overnight? I then found l was using it for light thicknessing/flattening of workpieces and assemblies that were too wide to fit into the thicknesser or too short to be safe in the thicknesser.
The job lm building up to today, is the flattening of a loose benchtop which is made up of strips of hardwood glued to an MDF substrate and will be about 600mm wide.
Also, as it 'abrades' rather than 'cuts', l can use it to thickness ACROSS grain. Although that sounds just plain wrong, it is really handy for instance if some clutz

had messed up the domino settings and the pieces that made up a face frame didn't line up in thickness? That person, whoever they may be, could then run the whole face frame (750 X 1200) through the drum sander so that it long grain sanded or cross grain sanded all of the pieces giving a perfectly flat face frame.
The infeed and outfeed rollers that I added to it were particularly to help me do long double passes which l now do on all face and door frames.
I certainly use it as a flattener and thicknesser but the process seems to be too brutal to be regarded as a 'finisher'.

fletty

**ian** · 19th February 2016, 02:21 PM

High Paul

the primary purpose of a drum sander is to remove the milling marks (small scallops) left by a thicknesser.

Then it can be used to come close to final sanding of flat pieces.

then it can thickness sand thin work pieces.

and thickness highly figured wood.

in an ideal world, the wood machining process would go
1st joint and thickness, plus any sawing to width
2nd through the drum sander to remove the milling (and saw) marks
3rd ROS to refine the surface

just be aware that the abrasive covered drum is probably as dangerous as the cutter head on a thicknesser, but much more accessible.

**Bushmiller** · 19th February 2016, 04:03 PM

Thanks Alan ( and Ian). Luckily I don't have anywhere to put one nor the funds necessary. I may have to look up some of those plans for homemade drum sanders, but I wonder if they are sufficiently robust as I imagine there is a fair amount of pressure involved in the process.

Then there is still the problem of where to put one. May have to give it a miss for now.

I am making a mental note of all the dust collection antics and storing them away to be regurgitated at a suitable time. In fact I recently purchased a simple cyclone for my two bag system, but cannot find the time to install it.

Regards
paul

**wheelinround** · 19th February 2016, 05:49 PM

Looking good BUT no sawdust/shavings no sign of work

Carefull of following that sign up on the wall unless your doing it by eye of course.

**Sawdust Maker** · 19th February 2016, 10:02 PM

I'm interested in seeing how you go about the 6" conversion on the sander

**ian** · 20th February 2016, 04:13 AM

so am I.

perhaps it's time to break out (interpretation: find if I still have) my old hydraulics texts and revise boundary effects.

looking at the construction of the Jet [drum sander] dust shroud, expanding the 100mm outlet to 150mm will probably mean building a new taller rectangular to round transition to replace the existing shroud. The new shroud will need to flare from 100mm wide at the drum to 150mm wide where the round extractor duct connects.
I'm not sure that such a modification is warranted, unlike the cabinet of a table saw where you're trying to evacuate a poorly ventilated enclosed space, the shroud of a drum sander functions very much like the floor sweep on a vacuum cleaner.
and perhaps the higher velocity is not a bad thing.

**fletty** · 20th February 2016, 09:04 AM

Originally Posted by Sawdust Maker

I'm interested in seeing how you go about the 6" conversion on the sander

Originally Posted by ian

so am I.

perhaps it's time to break out (interpretation: find if I still have) my old hydraulics texts and revise boundary effects.

looking at the construction of the Jet [drum sander] dust shroud, expanding the 100mm outlet to 150mm will probably mean building a new taller rectangular to round transition to replace the existing shroud. The new shroud will need to flare from 100mm wide at the drum to 150mm wide where the round extractor duct connects.
I'm not sure that such a modification is warranted, unlike the cabinet of a table saw where you're trying to evacuate a poorly ventilated enclosed space, the shroud of a drum sander functions very much like the floor sweep on a vacuum cleaner.
and perhaps the higher velocity is not a bad thing.

Im really enjoying setting up my shed and doing what I love the most ....... trying something new and different. My concept of wheeling in the machines and 'plugging in' to both overhead power and dust extraction is driven largely by my space available but also to see if it works as a practical solution. I am most comfortable with a suck-it-and-see trial even though I know this will often cross over boundaries and limits defined by physics and other people having already tried things that may well also fail for me?
Another experiment last night after the heat had gone, the mozzie coils had driven the ravenous little bustards away and the Shiraz had softened showed that I have a fatal flaw in my 150mm DC outlet plan!
I WAS planning on using the Clearvue 150mm/2 X 100mm adaptors to be permanently 'moulded' into the shrouds on (particularly) the drum sander and thicknesser to provide the 150mm diam outlet and the rectangular transition to be the internal dust and dwarf pickup. I had made cardboard templates and was about to embark on surgery, cutting the shrouds, merging the 2 pieces, 2 pack putty etc etc but.....
As the night went on, the plan (and Shiraz) slowly melted away. The problem is that:

the heads of both the drum sander and thicknesser rise and fall to do their jobs
l have a high wall line but l lose some of that height in bracing the boom
the only 150mm Flexi that I can find is quite rigid and decidedly NOT flexible
ALL of which means that it will be too cramped and too much load will be put on the new shroud/s during installation and any operating adjustments.

I have pretty much decided to dump the 1 X 150mm outlets and settle on 2 X 100mm outlets on all of my machinery. Now, I know that 2 X 100's isn't the same capacity as 1 X 150 but for some of my machines (especially router table and disc sander) , 2 'lesser' outlets has many benefits.
So, a slight delay while I regather my thoughts and bits and pieces to continue.
fletty

**FenceFurniture** · 20th February 2016, 09:34 AM

Fletty, what about using 125mm flexy (available from Felder in Emu Plains)? It's very flexible. I know that brings in a new set of linkage problems, but probably no more than you were facing. The flow will restricted by the smallest choke point which would be at the machine - possibly even before the dust outlet. The cross sectional area is slightly less than half way between 4" and 6", so should yield an improvement.

**fletty** · 20th February 2016, 09:52 AM

Originally Posted by FenceFurniture

Fletty, what about using 125mm flexy (available from Felder in Emu Plains)? It's very flexible. I know that brings in a new set of linkage problems, but probably no more than you were facing. The flow will restricted by the smallest choke point which would be at the machine - possibly even before the dust outlet. The cross sectional area is slightly less than half way between 4" and 6", so should yield an improvement.

AND, there are already 2 pieces of 125mm flex in the circuit. Both the 'hinge' for the boom and the connection to the impeller are also 125mm flex and therefore already provide the lowest common denominator?

fletty

**Bushmiller** · 20th February 2016, 10:34 AM

I am just musing about the loss in flow rates for the smaller diameter fittings.

My understanding is that flow rate is lost by frictional resistance. This can come about by size and smoothness of the inner surfaces of the pipe. Consequently that resistance is also dictated by the length of pipe. If the initial restriction of, say, two 100mm outlets quickly transitions to a 150mm pipe is there very much loss? It must be minimised at the very least and I think this is what you are trying to achieve.

This assumes that the outlet from the machine is an optimum shape. If this were a fluid there is a simple formula P1 V1 = P2 V2. We see this relationship with our garden hose and a spray/jet nozzle.

Having said that, we are talking about a gas laden with solid particles and it does behave a little differently.

Of course it would be preferable to have 150mm outlets starting at the machine, but we are not in a perfect world with infinite time

.

Regards
Paul

Thread: Fletty's new shed WIP ....or is it a retrospective??

Thread Tools

Search Thread

Similar Threads

Mrs Blackie & Fletty

Container Of Memories Retrospective Exhibition

For Fletty

Retrospective

Workbench build diary (retrospective)

Posting Permissions