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

Originally Posted by Groggy

Sounds like this feller, CTM 26.

Now that's one sexy vacuum cleaner



Regards

Every time I see one of those festool jobbies I half keep expecting it to chirp up, "How can I be of service O master?" In some ways guess this is not that far away?

Originally Posted by BobL

Every time I see one of those festool jobbies I half keep expecting it to chirp up, "How can I be of service O master?" In some ways guess this is not that far away?

Actually Bob, that feature is already on it, but I got sick of it (the accent was terrible), and dialled it out.

Nice work Brett. You will be needing a new thinking cap soon. I'm sure the old one must be very near worn out.

Regards
Brett.

Nice work Brett, not to steal your thunder but that sort of vac ducting system has been on my mind also, good for all those smaller tools and cleaning up,.

On the twin hose for the DP I wonder how if you set each hose up so that they intersected a small diameter short cylinder (in perspex would be ideal) tangent to the outside of the cylinder which then surrounded the job, sort of like a mini mini mini cyclone in reverse with 2 outlets both sucking, probably offset to each other at 180°, due consideration to allowing air in would be needed. I'd draw something but



Pete

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

Originally Posted by pjt

On the twin hose for the DP I wonder how if you set each hose up so that they intersected a small diameter short cylinder (in perspex would be ideal) tangent to the outside of the cylinder which then surrounded the job, sort of like a mini mini mini cyclone in reverse with 2 outlets both sucking, probably offset to each other at 180°, due consideration to allowing air in would be needed. I'd draw something but Pete

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.

Hi FF - what size PVC ducting did you use?

Hi Brett,
Love the idea, i was slightly worried about loss of suction reading your posts but it looks like its not a problem at all. I like the idea of the flexible spout, but just to throw another idea at you, i have a cheap magnetic dial indicator stand that is pretty well useless as it is not rigid enough. However it works very well as an arm for the vac hose (held on with a couple of cable ties currently) . The big bonus is being magnetic you can stick it anywhere.

40mm Bob

Originally Posted by FenceFurniture

40mm Bob

Thanks Brett. I wasn't sure if it was 40 or 50 mm.

I put 10 m of straight smooth wall 40 mm PVC pipe into a pipe pressure calculator and found it consume ~40% of the max vacuum (24000 Pa) that a CTM 26 can generate. By way of comparion, typical values for dust extraction systems for this parameter are ~10% of the max suck. In your case this could have been reduced by a factor of 4 by just going to 50 mm pipe and by a factor 10 by going to 60 mm pipe. In both cases the air flow should stay above the 4000 cfm limit needed to keep sawdust in suspension by moving air. In practice it would probably be safer to stay with 50 mm because every system is one way or another blocked and the sawdust falls out of suspension and it is not always picked up again once the air begins to flow. I note you have also used PVC glue on the junctions, this is not a good idea because it becomes a PITA to clear when ducting gets blocked..

Adding corrugated hose, 90º bends, T junctions, chip collectors, tool/machine ports, dirty filters, and the not very flow friendly diverters will further reduce the suck. In practice these systems do not completely run out of suck but as back pressure builds the flow rates must be reduced. If the criteria for success is that it continues to pick up sawdust that is one thing, but it is impossible to just look at an air stream sucking up sawdust and say if it is working to it's optimum capacity.

Please note I am not saying not to do this but just be aware of the issues. Fortunately the CTM26 is such a gutsy performer, but especially using 40 mm pipe with a cheap vacuum cleaner might not be so impressive

For anyone else thinking of centrally ducting a vacuum cleaner consider the following.
- use an optimized pipe diameter,
- instead of 90º bends use 2 x 45º bends. 40/50 mm fittings are quite cheap so you might want to think of even using 6 x 15º bends.
- Replace T- junction with y junctions and a 45º bend
- Avoid using those diverters and use a Y- junction and either a blast gate, or a no obstruction tap.
- Minimize the length of corrugated hose being used and consider replacing it with smooth walled flexy.
- If your machine is stationary plump the fixed ducting as close as possible to the machine.
- avoid gluing fittings.

G'day Ewan

In the very early days of developing the DE on a DP system (about a year ago) I had played around with a Rare Earth Magnot, but quickly realise that it could only go where i had some steel, and that was not always the case. I have nil cast iron or steel tops (it's not a regular DP, or table saw, or router table). Many of the clamps are timber/stainless/brass so that won't do either.

However, for someone who does have CI/Steel tops your solution would work admirably well.

I've been doing some further development of my Drill Deck over the last few days, and am reasonably happy with the solution for the vac hose support (at this stage). I'll be posting all that in a separate thread when I've got a "close to final" result.

Cheers
Brett

Hi Bob, yes you've got a lot of very good input there, some of which i had considered (and was partially stymied on because of a lack of a decent hardware store). Other parts are (or were) beyond my knowledge. I'll pick them out in the quote:

Originally Posted by BobL

In your case this could have been reduced by a factor of 4 by just going to 50 mm pipe and by a factor 10 by going to 60 mm pipe. If only I could have gone 50. There was no (or not enough 50mm pipe, but a better range of 50mm fittings available, except for some of the vital ones.

In both cases the air flow should stay above the 4000 cfm limit needed to keep sawdust in suspension by moving air. In practice it would probably be safer to stay with 50 mm because every system is one way or another blocked and the sawdust falls out of suspension and it is not always picked up again once the air begins to flow. Yeah, I was concerned about this, and that's why I wanted the elbows with inspection caps, so I could shoot in some compressed air every now an then, to shift things along. I'd really have preferred clear pipe, but I guess that doesn't exist (not up here anyway).

I note you have also used PVC glue on the junctions, this is not a good idea because it becomes a PITA to clear when ducting gets blocked.. Yes, again I did give that some (little) consideration, but the dry joints couldn't be pushed home, without fear of fracture or cracking.

Adding corrugated hose, 90º bends, T junctions, chip collectors, tool/machine ports, dirty filters, and the not very flow friendly diverters will further reduce the suck. In practice these systems do not completely run out of suck but as back pressure builds the flow rates must be reduced. If the criteria for success is that it continues to pick up sawdust that is one thing, but it is impossible to just look at an air stream sucking up sawdust and say if it is working to it's optimum capacity. Yes, dead on I reckon, but as you say, it still picks up dust. I was fully aware that I was losing some suck but.....(next para)

Please note I am not saying not to do this but just be aware of the issues. Fortunately the CTM26 is such a gutsy performer, This is what I was counting on

but especially using 40 mm pipe with a cheap vacuum cleaner might not be so impressive Reckon that's dead right too.

For anyone else thinking of centrally ducting a vacuum cleaner consider the following.
- use an optimized pipe diameter,
- instead of 90º bends use 2 x 45º bends. That's actually what I wanted to do....but not enough available. 40/50 mm fittings are quite cheap so you might want to think of even using 6 x 15º bends.
- Replace T- junction with y junctions and a 45º bend
- Avoid using those diverters and use a Y- junction and either a blast gate, or a no obstruction tap.
- Minimize the length of flexy/corrugated hose being used. Absolutely
- If your machine is stationary plump the fixed ducting as close as possible to the machine. Yep, mine's about a metre away.
- avoid gluing fittings.

Unfortunately I was heavily limited by the fittings available, but I won't pretend that I thought of all that you mentioned there

As you say, the secret to getting the best flow when it comes to corners is to make them as large a radius (of the curve) as possible, and avoid sharp edges corners such as in 90 deg bends and T's.

O'course, after I had finished it all, I was told by a neighbour that there is a Reece Plumbing supply closer to me than the crap Hardware Store.

I think the saving grace of the system (in my case) is the power of the CTM 26 behind it all.

I was trying to figure out how to construct a blast gate for this out of timber and perhaps a piece of perspex, but didn't get too far when I discovered those diverters. A blast gate would be quicker to change, and I could have a couple more of them. Any ideas on the design (the homemade type)?

Hey Bob, the other thing that has been rolling around in my head is a "spark bong" to use behind anything that produces sparks (Worksharp or other grinders). So far i have envisioned a small version of a "Big Gulp" probably made from MDF with a short hose going to the spark bong and then onto the ducting system. Just something to put the sparks out basically. Any thoughts? I have read your posts before about using water as filter for a catchment of dust, and i agree that it would be a sludgy waste of time, but in this case...

Originally Posted by FenceFurniture

Hey Bob, the other thing that has been rolling around in my head is a "spark bong" to use behind anything that produces sparks (Worksharp or other grinders). So far i have envisioned a small version of a "Big Gulp" probably made from MDF with a short hose going to the spark bong and then onto the ducting system. Just something to put the sparks out basically. Any thoughts? I have read your posts before about using water as filter for a catchment of dust, and i agree that it would be a sludgy waste of time, but in this case...

A simple stainless or ally insect screen mesh can act as a very effective spark arrestor but it could also be quite restrictive on a narrow opening so I would only suggest using one where you are really worried about the sparks rather than flow. One possibility is to use a bigger opening like a 60 mm to 40 mm reducer and put the screen in front of the 60 mm opening and connect your hose to the 40 mm end.

Sparks are usually not a problem for hobby level DC and vacuum systems - I had my Makita belt sander upside down on a stand hooked up to a DC via 2" transparent flexy and sanded steel and ally on it for years. At night with the lights out I could sand steel and observe how far down the flexy the sparks would travel before going out and it was never more than about 12". The flexy would eventually collect metal dust for about 1 m from the sander and start to restrict flow and have to be emptied out. The same will happen with a vacuum cleaner so make sure the ducting or hose can be easily removed for at least a couple of metres from the pick up point.

I was trying to figure out how to construct a blast gate for this out of timber and perhaps a piece of perspex, but didn't get too far when I discovered those diverters. A blast gate would be quicker to change, and I could have a couple more of them. Any ideas on the design (the homemade type)?

There are many designs on the web including a very nice rocker model.
One simple design is - lets assume 40 mm ducting
- purchase a female coupler for the size of ducting you are using and cut it in half lengthwise.
- cut two squares of 6 mm thick MDF that are about 40 mm larger than the ID diam of the ducting ie ~80 x 80 mm.
- cut holes in the middle of the squares that make a tight fit for the half female couplers and glue the half couplers into the holes. A ww lathe is the ideal way to get a nice tight fit - also to cut the coupler in half and tidy up the cut edges..
- Cut two 15 mm wide strips of 6 mm MDF the same length as the sides of the squares (ie 20 x 80 mm).
- sandwich/glue and screw the strips between the squares along opposite edges. This should leave a 6 mm gap on the other opposite sides for the gate.
- Cut a strip of 6 mm tick MDF wide enough to fit neatly through the gap and long enough to make a gate ( eg ~50 mm wide x 180 mm long) and cut a hole on one side leaving enough blank on the other to block the hole.
- add some handles to make it easier to slide the gate in and out.
That's it.