Converting dusty to cyclone

**gingerbeer86** · 19th March 2012, 01:35 PM

Hi Bob, The cabinet saw does not lend itself to be modified very easily. It has a zero clearance insert and a complex enclosure around the blade and motor inside the cabinet. Its design means that a 100mm inlet provides enough air movement to catch the dust as it is contained in a relatively small area compared to saws that need to air decent airflow in a large open area to collect the dust. It would be better if it was 150mm but it is probably designed to work with the most common connection it would see, which is 100mm. I persisted with the 150mm for the main duct work because while the minimum cross section is the major influence on air flow, pipe losses still count for something. More importantly it allows for 150mm to be terminated at multiple branches. 150mm is over twice the area of 100mm duct. Similar to the custom built junction at your bandsaw, multiple paths for air to come together into a 150mm cross section is important and allows for appropriate fpm in each entering duct.

I have finished the box to hold a plastic bag inside the main cabinet to collect the dust. The box it sized to just allow a bin liner from a 240l rubbish bin to stretch over it (had to round the corners to stop it tearing) . The box is then a tight fit in the cabinet, tight enough to not allow dust to fall down the outside of the bag.

The attached photo is with the door open and the box inside. I have no idea what percentage of dust is collected in the separator, but certainly of the easily visible dust it must be close to 100%. I was surprised to see the amount of relatively fine dust it was also collecting, evident by the fact that this fine dust actually sticks the smooth walls of the inside of the box. You can see the patterns of this dust which is sticking where the velocity is a bit slower.

Even when shoveling large handfuls of dust quickly into the inlet there is nothing visible at the exit pipe outside. No doubt the very fine and the invisible dust particles do not have enough mass to be effectively removed by the cyclone but they are now going out of the back wall of the shed to be carried away by the most common prevailing wind.

While it is not exactly light as a feather, the box and bag full of saw dust slides out of the cabinet relatively easily, then it is straight forward to tie up the bag and throw it in the bin. The bin liner bags are not expensive and it is nice to be able to keep the disposal of the saw dust straight forward as it is easy to be enveloped in clouds of dust if you have to double handle dust when disposing of it.

**gingerbeer86** · 19th March 2012, 02:02 PM

Loaded the video into you tube. This shows the air movement around the blade guard with the dusty connected. Hope this video works.....

Table saw guard.mov - YouTube

While it is designed with a 40mm connection for shop vacs, the dusty is moving enough air that nothing noticeable escapes when it is running. Next step is potentially to find a way to position the 100mm flex above the work when using just the riving knife and no guard.

**BobL** · 19th March 2012, 02:29 PM

The cabinet for the dust catcher box seems like it is nice and tidy indeed.

Originally Posted by gingerbeer86

. . . . I persisted with the 150mm for the main duct work because while the minimum cross section is the major influence on air flow, pipe losses still count for something.

Yep I agree It's better to have 150 mm than not, and you can always upgrade the ports later.

. . . . . No doubt the very fine and the invisible dust particles do not have enough mass to be effectively removed by the cyclone but they are now going out of the back wall of the shed to be carried away by the most common prevailing wind.

Excellent.

I don't know if you have seen this graph but here it is again.

Converting dusty to cyclone-pressdrop2-jpg

My guess is the 2 x 90º bends either side of the impeller and the two other 90º bends means you will end up with around 8" of pressure at the point where you take off the 100 mm for the TS.
This means the 100 mm or 4" pipe will pull around 400 cfm (pink dot) and the 40 mm or 1.5" pipe for the guard will only pull about 30 cfm (green dot), whereas the 150 mm ducting is capable of pulling about 1100 -1200 cfm (orange dot). In terms of fine dust collection it would make some sense to place a extra100 mm flexy somewhere near the saw, even if you gaffer taped it to the top of the guard. Be careful not to use 150 mm for the extra flexy otherwise the other two other ducts will not draw so well. That way you would have about 800 cfm being collected from near the TS.

Failing that, having a 150 mm port on the ducting that you could open immediately after saw use and leave it running for 15 mins after major dust generation would clear the shed very quickly.

**BobL** · 19th March 2012, 02:40 PM

Originally Posted by gingerbeer86

. . . . Next step is potentially to find a way to position the 100mm flex above the work when using just the riving knife and no guard.

I didn't realize you were doing that.

**gingerbeer86** · 21st March 2012, 03:23 PM

Thanks Bob, I have not seen a chart like that for many years and would have to dust off the old text books again. It is a good reminder of the relative sensitivity between variables.

I have loaded up a video clip on to you-tube. It shows the external vent while a few litres of dust is sucked into the separator inside. Actually not much to see, which is I guess the point of the separator. I would have liked to have the tools to measure the airflow, anyone got a graph of movement of ferns in the garden as an indicator of airspeed?? The video was taken of the airflow with the two saw connections open.

[ame=http://www.youtube.com/watch?v=BJOo24VpyXM&context=C47ea077ADvjVQa1PpcFPervBwNYTqV5MRlXubJzXigw4lqgGwnxY=]external vent for dust extractor - YouTube[/ame]

**BobL** · 21st March 2012, 06:11 PM

Originally Posted by gingerbeer86

I have loaded up a video clip on to you-tube. It shows the external vent while a few litres of dust is sucked into the separator inside. Actually not much to see, which is I guess the point of the separator. I would have liked to have the tools to measure the airflow, anyone got a graph of movement of ferns in the garden as an indicator of airspeed?? The video was taken of the airflow with the two saw connections open.

It sounds like it still emits a fair bit of noise and also ruffles the ferns up a bit - I'm not sure the ferns are going to like it for any length of time, maybe that is part of your plan

If you want to reduce both noise and air speed then venting into a foam lined box with some foam lined baffles will make a significant difference.

**Christos** · 21st March 2012, 07:51 PM

Great work on the dusty convert.

**veloaficionado** · 27th March 2012, 08:08 PM

The problem is, as Bill Pentz has pointed out, that the tooth tips are launching dust at about 160km/h, and 1000 cfm at 4000 fpm (whatever the metric equiv. is) can only move air at 100km/h. So if you can't get the bubble of air right next to the saw blade to capture that fast-moving dust, then it'll fly out into the workshop and get sucked into your airways, maybe.

**BobL** · 30th March 2012, 04:44 PM

Originally Posted by veloaficionado

The problem is, as Bill Pentz has pointed out, that the tooth tips are launching dust at about 160km/h, and 1000 cfm at 4000 fpm (whatever the metric equiv. is) can only move air at 100km/h. So if you can't get the bubble of air right next to the saw blade to capture that fast-moving dust, then it'll fly out into the workshop and get sucked into your airways, maybe.

4000 fpm is actually only 45 km/hr.
However, while all chips come off a saw blade at the speed of the blade, within cm the big chip speeds drops off significantly. The invisible chips behave like air molecules and within mm drop to the same speed as the air coming away from the blade which, while significant is not 160 km/hr. I will measure it tonight and if my home PC is up and running I will report back as to what it is.

Thread: Converting dusty to cyclone

Thread Tools

Search Thread

Similar Threads

Converting to LPG and CO2

Converting to a cut off saw

converting vhs to cd

converting Flv to view on tv

Tags for this Thread

Posting Permissions