Thread: Something different? Ducting a SHOP VAC – one happy chappy

The mini cyclone arrived from Mini yesterday, and was pressed straight into action. No noticable drop in suck (although I'm sure there must be some). Only takes about 5-10 minutes to assemble for use.

Happily, the adaptor is identical to the vac input, so no fooling around. I've tied the bucket in place so that when I'm using the green hose (for floor work or sanding etc) it won't pull the bucket out of place. You can see it lying slack at the top of the cyclone, ready to be swapped with the grey ducted vac hose that is currently plugged in (at the "do not pick up here" sticker).


I say, that 40mm angled pipe on the wall make an excellent power lead holder-in-place.


This more or less completes the system for now, until i branch out and go across the room to the router table. I'm pondering a bench design atm, and would very much like to incorporate an outlet strapped to one of the legs or similar.

Originally Posted by FenceFurniture

Thanks Pete and Paul. There's still a bit of life left in the current cap.


Arrr, could you run that past me again Pete? I didn't quite catch the middle bit (or either side).

I must that having used this for a few days now the convenience factor is fantastic. I rigged up the Clearview Mini Cyclone last night, and will put up a picture when I've housed it in place.

You were wanting to use two hoses on the DP, so I was thinking that just like on the mini cyclone the system hose inlet attaches at a tangent to the outer cylinder, so I was wondering if you made up a small cylinder say 60 to 80mm and about the same height(perspex would be ideal) (to see what is going on) with the two hoses attached at a tangent 180° to each other, my thinking being that then promotes a swirling motion that assists the sweeping up of chips, the cylinder has to be positioned around the drill bit, not sure how practical that would be tho

On making adapters to hoses and fittings and such I have used the hot air gun to heat up the end of the pvc pipe and either shrunk or expanded as required, there was a few other good ideas in a thread a while back re shrinking expanding pvc

Pete

Using two hoses to draw air from the same space can be counterproductive to overall air flow as one air flow will often end up slowing the other. The same thing happens when two hoses are used to vent one chamber on a machine. Unless dead air spaces can be clearly identified it's probably better to use a one directional flow.

Right, now I'm with you Pete. I have given consideration to using the really large Festool Flat nozzle (goes on a 50mm fitting). The idea was to drill a large hole through the flat and surround the hole entry, and block off the normal intake slot in the nozzle. It might actually work very well for most hole sizes, but would be better if the flat had a bend in it otherwise it could be hard to get it in position.

Bob has just pointed out what I was initially concerned about, hence why I rigged the DP diverter to be able to vary the flow between the two hoses. What I have found in practice is that this is very easily overcome by hand holding the second hose so that if this appears to be happening then I can just back off or increase the position of the hand held hose, and also shift it around to catch the strays. I can also vary the height instantly (and briefly) to achieve same.

Originally Posted by BobL

....In both cases the air flow should stay above the 4000 cfm limit needed to keep sawdust in suspension by moving air.

Hi Bob

The CTM has a switch so you can tell it what dia pipe you're using, and an alarm will go off if the suck velocity goes below 20 metres per sec. I had the switch on 27 when it should have been on 36, and the alarm went off after I introduced the cyclone. Set the switch to 36, and all is good.

This got me to a bit of thinking, and I've done some calcs.

Givens:
Radius of pipe is 18mm (36mm ID)
Area of Xsection is 10.18 sq.cm
A one metre length holds 1.018 litres
1 cu.metre = 35.3 cu. feet

Workings:
20 metres of pipe is 20.36 litres of air
....which means 1221.6 litres per min (or 1.221 cu metres)
...which means 43.12 cubic feet per minute


That means I'm out by a factor ~100 on your 4000 cfm.

Eh? How can that work?

Originally Posted by FenceFurniture

Hi Bob

The CTM has a switch so you can tell it what dia pipe you're using, and an alarm will go off if the suck velocity goes below 20 metres per sec. I had the switch on 27 when it should have been on 36, and the alarm went off after I introduced the cyclone. Set the switch to 36, and all is good.

This got me to a bit of thinking, and I've done some calcs.

Givens:
Radius of pipe is 18mm (36mm ID)
Area of Xsection is 10.18 sq.cm
A one metre length holds 1.018 litres
1 cu.metre = 35.3 cu. feet

Workings:
20 metres of pipe is 20.36 litres of air
....which means 1221.6 litres per min (or 1.221 cu metres)
...which means 43.12 cubic feet per minute


That means I'm out by a factor ~100 on your 4000 cfm.

Eh? How can that work?

You have done the minutes but have you done the seconds part of the calc?

43.12 x 60 = 2587.2 cfm

Regards

Peter

Originally Posted by FenceFurniture

Hi Bob

The CTM has a switch so you can tell it what dia pipe you're using, and an alarm will go off if the suck velocity goes below 20 metres per sec. I had the switch on 27 when it should have been on 36, and the alarm went off after I introduced the cyclone. Set the switch to 36, and all is good.

This got me to a bit of thinking, and I've done some calcs.

Givens:
Radius of pipe is 18mm (36mm ID)
Area of Xsection is 10.18 sq.cm
A one metre length holds 1.018 litres
1 cu.metre = 35.3 cu. feet

Workings:
20 metres of pipe is 20.36 litres of air
....which means 1221.6 litres per min (or 1.221 cu metres)
...which means 43.12 cubic feet per minute


That means I'm out by a factor ~100 on your 4000 cfm.

Eh? How can that work?

Sorry - I got CFM mixed up with FPM.
It's 4000 FPM or ~20 m/s to maintain sawdust in suspension.

You got the 43 cfm right - maximum is 79 cfm.

800 - 1000 cfm is considered the requirement for invisible dust capture from a diffuse source like turning.

If the dust source is very, very localised even 10 m/s will catch the dust but it will end up clogging the ducting

Phwoah! Thank gawd for that!! I was going to ask which one of us was wrong, but didn't wish to appear rude! So, it would appear that I've maintained the minimum to keep the dust afloat, but bear in mind that the velocity is measured at the vac, and therefore doesn't account for any leakages along the way of course. I should rig up some kind of Man-O-Meter to see what is really going on. Should be able to find something with Google I reckon.

Originally Posted by The Hun

You have done the minutes but have you done the seconds part of the calc?

Yes I did Peter, that's what gave me 20.36 litres / sec * 60 = 1221.6 litres / min.

Originally Posted by The Hun

You have done the minutes but have you done the seconds part of the calc?

43.12 x 60 = 2587.2 cfm

The air speed through a 40 mm diam pipe at this flow rate would be 939 m/sapproaching Mach 3 and the noise would be deafening. It would also probably melt plastic pipe.

lol could just imagine the sonic boom as it got up to air speed

Funny you should mention that - I was kinda getting towards that conclusion meself with the 4000cfm - you know, like "keerist, where's the Barn gawn?" Answer - "it's all in the CTM - we did tell you it's a good vac"

Originally Posted by BobL

The air speed through a 40 mm diam pipe at this flow rate would be 939 m/sapproaching Mach 3 and the noise would be deafening. It would also probably melt plastic pipe.

I knew those Festo vacuum cleaners were good!

Originally Posted by BobL

The air speed through a 40 mm diam pipe at this flow rate would be 939 m/sapproaching Mach 3 and the noise would be deafening. It would also probably melt plastic pipe.

And when the gasflow hit the first elbow.........

Regards
Paul

Originally Posted by FenceFurniture

Funny you should mention that - I was kinda getting towards that conclusion meself with the 4000cfm - you know, like "keerist, where's the Barn gawn?" Answer - "it's all in the CTM - we did tell you it's a good vac"

"Black hole in blue mountains, German engineering to blame?"

If sydney survived i'm sure the headlines would read something like that......