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Thread: Ducting advice
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7th June 2013, 05:40 PM #1SENIOR MEMBER
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Ducting advice
I am just starting on the ducting and was hoping that the dust experts will cast their eyes over the diagram before I get too far and have to redo some of the work. The picture is of the right hand branch to the lathe and saw. One question I have is should I have a blast gate at the position I have marked with an asterisk?
Thanks for the help.
Safari
Workshop plan.jpgducting.jpg
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7th June 2013, 06:07 PM #2.
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Short answer is Yes
Ideally you should have blast gates just past all junctions so you should consider adding two more at the lines marked in Purple @ 1 & 2.
If you don't do this then the dust going past a non-operational duct will back flow into that duct.
An example of this is the dust path ( purple arrow) from the bandsaw.
If there is no blast gate at 1, dust from the BS will flow back down towards the thicknesser and jointer lines.
The extent to which this happens depends on machine use. It is generally worst when a dust flow passes a duct junction (without a blast gate) to a machine that is not used very often. The dust build up takes time but eventually it can even block the duct so that when you go to use that machine the suck may not be enough to unblock the duct.
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7th June 2013, 06:43 PM #3SENIOR MEMBER
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thanks for the reply Bob. I will include those into the system.
I will add to the post how I ended up cutting the tubing because I have not come across any posts on getting a good cut. after some pretty rough cuts I found that the best way for me was to tighten a hose clamp onto the pipe then run around this with a pencil, take the clamp off and start the cut with an old panel saw and cut a small hole through the pipe large enough to insert a metal cutting blade on the jigsaw. Then follow the pencil line around and the result is a pretty straight cut.
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7th June 2013, 07:20 PM #4.
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On intermediate length pipes (ie up to ~2 m long) that need up to 450mm docked off them I use the bandsaw directly.
I made up a 150 mm high MDF fence for the BS mitre slide and it cuts nice and square and very clean.
When I have to cut in the middle of a long pipe I cut it 10 mm or so longer and then recut to exact size using the BS.
At more than about 2m long it gets unwieldy manoeuvring 6" pipe through the BS and so I mark the length on 4 opposite sides of the pipe and run masking tape around the line and cut to the line with a panel saw. I find it cuts cleaner than my jigsaw which tended to melt some of the PVC.
I also made up a chuck and tailstock holder for my lathe that holds short lengths (ie up to 900 mm) of 6" and 4" pipe and then I simply use a parting tool. The lathe is really good for cleaning up the edges of these short pipes so that the pipes slide into the junctions with minimal effort. By slowly running the lathe and and applying heat with a heat gun, and stopping and expanding the chuck every now and then to a 150 mm long bit of pipe I made a number of useful short couplers or added coupling ends to short lengths of pipe.
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8th June 2013, 11:32 AM #5
I have also found it better to cut with a panel saw than a jig-saw. For one thing you do not have to turn the ducting as you cut it. In my case I find it difficult to turn a full length of 6" ducting with one hand while holding a jigsaw in the other hand because of an injury I sustained in my left hand a couple of years ago while disarming a knife-wielding maniac.
As for measuring, I measure and mark at one point and then bend the tape around the pipe and mark the line with a pencil. It usually finishes up straight enough for the purpose.
DougI got sick of sitting around doing nothing - so I took up meditation.
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8th June 2013, 02:19 PM #6SENIOR MEMBER
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I made an oversize mitre box out of chipboard and a panel saw to do mine followed by a deburring tool
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9th June 2013, 12:42 AM #7GOLD MEMBER
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I haven't found any issues with dust build up in branches that are not being used or heard of anyone who has.
CHRIS
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9th June 2013, 01:36 PM #8... and this too shall pass away ...
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I made most of my cuts on the table saw. Slide the pipe up to the blade, and as soon as it cuts through the pipe stop pushing and start rolling the pipe into the saw. When cutting shorter lengths, I used the fence as a stop. Worked for me.
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9th June 2013, 10:42 PM #9.
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That's either because users have a powerful enough systems and/or use all of their machines and ducting on a regular basis. There was one post I recall on this forum a few months back with photos showing the degree of build up that can take place. In my travels to various peoples sheds I have seen several of these and none of the shed owners even knew they had a problem.
The build up issue is taken very serious in industrial situations where large (ie >12") ducting and large (20"+) impellers are used. Many kgs of dust can build up in an unused line but then when it is use still be picked up by the air flow. This then slams into the impeller and can cause considerable damage. Large dust loads striking an impeller is not a problem for cyclone users of course . A simple alternative to adding more gates is of course to open all BGs on regular basis and clear all lines.
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10th June 2013, 12:10 AM #10
I had considered doing that but I ruled it out for a few reasons, which you obviously found ways to work around, John.
Firstly, cutting a 6m length of anything in crosscut mode requires a great deal of room and setup of outrigger supports and freedom of movement through the blade. Not so bad if its 3m each side but it might be a bit tricky if you are docking one metre off one end and have 5 metres the other and trying to push the workpiece through the cut without skewing it and getting a kickback.
Secondly maintaining a constant length while rotating the piece, which you successfully did with the fence on short pieces, which makes sense. I take it that you had the blade wound down to the minimum height to cut through the wall of the pipe to minimise the severity of any kickback that may have occurred.
Thirdly, I would have thought that the speed may be e bit too high and cause some melting issues.
In my own case, the reduced capacity of my left hand as mentioned above may have been the deciding factor in recent times to go with cutting it by hand with a panel saw, but I certainly considered doing it with the table saw even before the knife attack and decided that there were better ways, at least for me. to do it. Also for some situations you need cut on a 45 degree angle across the pipe. You cant do that on a tablesaw unless you have the depth of cut to go right through the pipe in one go.
How did you work around these issues, John?
Cheers
DougI got sick of sitting around doing nothing - so I took up meditation.
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10th June 2013, 11:48 AM #11... and this too shall pass away ...
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Doug,
Sometimes, I used a panel saw to make the first cut (to cut the 6M lengths into 4M or smaller lengths) after which time they became manageable over the table saw (my saw has a table that is 1,600mm wide)
Yes ... the blade was wound down to minimum height. Encountered no problems at all with kick back. For longer lengths I drew a line around the pipe and fed/rotated that line into the blade ... worked just fine.
No melting issues were encountered ... I reckon a sharp blade prevents that. Cuts were clean.
I never had a need to cut a 45 degree angle in the pipe ... so can't comment.
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10th June 2013, 11:57 AM #12... and this too shall pass away ...
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I had a few issues, particularly when I was using the thicknesser. Forgot to crack the line to the sander (right of pic) and dust accumulated in the line circled in blue. When I did open the line to the sander, a great slug of shavings banged into the cyclone. Moving the blast gates (see pic) all but solved the problem.
Blast Gates moved.jpg
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11th June 2013, 07:04 PM #13SENIOR MEMBER
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11th June 2013, 08:03 PM #14.
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11th June 2013, 08:37 PM #15I got sick of sitting around doing nothing - so I took up meditation.
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