Page 1 of 5 12345 LastLast
Results 1 to 15 of 62
  1. #1
    Join Date
    Feb 2006
    Location
    Perth
    Posts
    27,757

    Default DRAFT Ducting Recommendations

    DUCTING RECOMMENDATIONS: INTRO

    This DRAFT thread covers recommendations/guidelines for a setting up the ducting for a woodworking dust extraction ducting.
    The emphasis is on ducting, with limited discussion about dust extractors at one end, and machinery at the other. Blast gates are briefly mentioned, but more detail may be added later.

    More comprehensive discussions and recommendations about wood dust collection can be found in these forums, or elsewhere e.g. Dust Collection Research - Home

    Theory and explanations will be to a minimum. If you want to know “why” maybe post a question?

    These recommendations are primarily directed towards DIY fine dust collection which is achieved by maximizing air flow. Commercial operators or those with deep pockets can no doubt find other solutions. For occasional weekend woodwork warriors using mainly power tools, and/or mainly hand tools there are also some alternatives that do not involve fixed ducting but these are not discuss these here.

    There will be many times when due to factors like physical or financial constraints, these recommendations cannot be easily followed and you may have to simply go with less than optimal implementations.

    Table of Contents



    Each topic in the table of contents is posted as a separate post with hyperlinks from the TOC above to that post.
    There is no claim that this recommendations are final and as these posts can be edited by me I am prepared to edit these based on questions and discussions posted in this thread.
    If you have a different opinion please add it to the thread or send it to me via PM. Significant contributions will be acknowledged by member name in the text.

    More links and images will be added over the next few days but feel free to send me comments. questions, suggested links, suggested images etc.
    Maybe PM me these to reduce clutter in the thread and leave the thread for discussions.
    Last edited by BobL; 14th June 2022 at 10:37 PM.

  2. # ADS
    Google Adsense Advertisement
    Join Date
    Always
    Location
    Advertising world
    Posts
    Many





     
  3. #2
    Join Date
    Feb 2006
    Location
    Perth
    Posts
    27,757

    Default

    DUCTING RECOMMENDATIONS: Ducting materials

    Ducting can be made from a wide variety of materials, but ideally it needs to be smooth walled, lightweight, reasonably robust, inexpensive, and easy to assemble and modify.

    Spiral or non-spiral sheet metal pipe is an ideal material (especially in a commercial environment) for ducting but it tends to be expensive and is not always that easy to modify.

    Ducting can also be readily made from timber such as MDF, but this limits construction to square or rectangular cross sections hence has to be made larger than pipes so it may take up more space. There can be a lot of work involved but if you have lots of free or low-cost material, and lots of time this might still suit you. Wooden ducting also tends to be heavier than other forms of ducting so better supports are needed.

    PVC ducting is widely used to for sewage (grey colour, also called - DWV) and storm water (Cream coloured). It’s smooth walled, light weight, easy to install and modify, and relatively inexpensive. Some storm water ducting has a PVC inner/outer shell and foam core making it even lighter without losing much strength and is my preferred ducting material for 150 mm or greater diameter ducting. There is no 100mm stormwater pipe available (closest is 90mm which was too small) so for 100 mm diameter ducting, DWV ducting and fittings are the only choice available. 150mm DWV and Stormwater fittings are fully interchangeable.

    There a several commercially available ducting products such as Black Acrylonitrile Butadiene Styrene (ABS) and rigid transparent PVC pipe, but these are relatively expensive and only available in relatively small sizes so I will not be dealing with these here.

    Corrugated Flexible Hose (Flexy) is regularly used for a wide variety of reasons in dust ducting systems. Flexy can be made of many materials such as Polyurethane (PU), PVC, and High density polyethylene (HDPE). Whatever lengths or materials are used, the lengths of Flexy should be kept to minimum (ie less that 500 mm).

    In general, softer more flexible materials such as PU and some PVCs are more flexible so suit some applications such as getting around a tight radius of curve bend, but these are also more constrictive to air flow under high air speed conditions. To maximize flow, reduce the lengths of flex used, and where possible choose stiffer flexy materials.

    There are also some semi rigid aluminium ducting that could be useful for high heat applications such was metal work fume extraction.

    Back to TOC.
    Last edited by BobL; 4th May 2020 at 11:52 AM.

  4. #3
    Join Date
    Feb 2006
    Location
    Perth
    Posts
    27,757

    Default

    DUCTING RECOMMENDATIONS: Ducting sizes.

    PVC storm water ducting is only available in a limited range of sizes.
    NOM Size (mm) Mean OD (mm) Wall Thickness (mm)
    75 75.10 1.50
    90 90.10 1.80
    150 160.30 2.90
    225 250.35 4.50
    300 315.10 6.00
    Using the basic principle that large ducting moves more air, then the larger the ducting used the better. The limit to using very large diameter ducting is that it reduces the speed of the air in the duct which can lead to sawdust settling out of suspension. Once settled it becomes even harder for a slow air stream to pick up the deposited duct which narrows the effective pipe diameter. Dust deposition may continue until the duct diameter is restricted to the point where the air speed becomes fast enough to maintain that smaller duct diameter but it will not normally completely clean out the sawdust in the duct.

    For “off the shelf” DCs of 2HP or less, using 150 mm ducting generates too low an air speed in the duct so smaller ducting is needed. BUT 90 mm storm water is very restrictive to flow so this is why 100 mm ducting is about the best at can be used with these systems.

    NB 100mm size ducting is unlikely to move enough air to enable fine dust to be captured at the source of the4 dust which is why larger DCs that can utilize larger ducting are preferred. It is possible to modify a conventional 2HP DC to utilize 150 mm ducting although the result is still very much a compromise and should be restricted to short duct runs so small sheds. The way to modify these DCs is described in this sticky in this forum.

    3HP and larger DCs can usually utilize 150 mm ducting, while some 4HP DCs can utilise 225 mm ducting, while it normally requires a > 6 HP DC to utilize 300 mm ducting. The final size used sometimes also depends on depends on having the necessary space around machinery and elsewhere in the workshop.

    Back to TOC.

  5. #4
    Join Date
    Feb 2006
    Location
    Perth
    Posts
    27,757

    Default

    DUCTING RECOMMENDATIONS: Junctions

    Although it is possible to make junctions from materials like MDF, PVC pipe works best with PVC junctions. However, there are a number of pitfalls involved that can significantly restrict air flow.

    Generally;

    • Avoid using any “Tee” junctions, instead use 45º “Y” junctions (see "Stormwater Junction" below plus a 45º bend

    Tconnect.JPG

    • Use as large a radius 90º bend as possible (see pics below)
    • Two standard 45º bends are more restrictive than a large radius 90º bend.
    • Standard PVC reducers (also known as “Level Inverts”) are very handy to up or downsize ducting but are not optimized for air flow as the transition is from one size to the other is too rapid. If maximum air flow is needed then a less rapid transition (maybe DIY) is required.


    Screen Shot 2020-02-13 at 8.11.16 pm.pngScreen Shot 2020-02-13 at 8.11.00 pm.png

    Large radius 90º bends can be achieved using multiple 15º junctions but this can be expensive. Storm water 90º bends have a very tight radius and are hence also restrictive but the standard DWV 90º bend has twice the radius of curvature and although is more expensive has a much lower flow resistance. This about the only DWV junction needed for 150mm and larger ducting.
    Screen Shot 2020-02-13 at 8.08.45 pm.pngScreen Shot 2020-02-13 at 8.08.30 pm.png

    Joining ducting to flexy is not always easy eg 150 mm flexy will not go over 150 mm ducting. It is better to avoid trying to squish flexy inside the ducting as this restricts airflow. If the connection is permanent then it is worth considering larger and more expensive flexy eg 160 mm ducting will fit over 150mm ducting.


    If you wish to be easily able to connect and disconnect the flexy then a “Threaded coupling” (TC) junction plus a “Threaded cap” fitting is one way to do this. A hole that is a tight fit for the flexy is cut out of it the centre of the cap and fitted as follows. The female junction on the other side of the TC can be used as a push fit to ducting.

    flexyjunction.jpg IMG_1922.jpg

    A additional detailed post regarding optimisations of ducting and junctions is available here at DRAFT: FAQ - Dust Extraction (Practical Aspects)

    Back to TOC.
    Last edited by BobL; 5th March 2020 at 01:40 PM.

  6. #5
    Join Date
    Feb 2006
    Location
    Perth
    Posts
    27,757

    Default

    DUCTING RECOMMENDATIONS: Static

    The risk of static produced inside PVC ducting causing a wood dust explosion/fire is extremely low.

    To reduce the effects of the static inside the pipe causing discharging from operators and other equipment to the outside of the PVC ducting, wrapping a grounded wire around the PVC will assist with this problem. NB this does not remove the static from inside the duct. If you read the FAQ you will see why this particular form of wording has been used.

    It is recommended that any metal ducting and metal junctions and the metal wires in flexible hoses be grounded.

    To further expand on the topic of static, the following FAQ has been prepared by dmorse - thanks Dave - much appreciated

    Where does the charge come from?

    The charge comes from the friction between the moving wood dust and the walls of the duct stripping electrical charge off the internal wall of the dust leaving it with an opposite charge It's the same process that causes charges to appear on clothing in the clothes dryer or when you rub your hair with a toy balloon in dry weather.

    StaticPVC1.png

    How does the charge get to the outside of the pipe?
    The charge cannot transfer to the outside of the pipe. PVC is an insulator. The internal charge eventually leaks off via charged particles that ordinarily exist in the air and conductive contamination of the surface of PVC, but it is unable to move through the PVC so sits on the inside surface of the duct.


    I get a shock when I touch the outside of the pipe. Where does that charge come from?
    It comes from you. The charges on the inside of the pipe exert a force on other nearby charges, repelling charges of the same polarity and attracting charges of opposite polarity.

    When you (See A in diagram below), a big bag of salty water containing positive and negative charges, move closes to the charges inside a pipe the charges in your body temporarily redistribute (see B). Charges in your body of the same polarity as those inside the pipe move inside your body as far away from the pipe as possible while those of opposite polarity move closer to it.

    StaticPVC2.jpg
    If you get close enough to the pipe a spark forms and transfers charge from you to the outside surface of the pipe (see C). Even if you move away from the pipe such as in D, a corresponding small spot of charge from you remains behind on the outside of the duct (F) bound there by its attraction to the charge on the inside.
    StaticPVCdischarge.png StaticPVCinduction2.png


    Can you ground a PVC duct by wrapping a wire around the outside?
    No, you can't ground out or remove the charge from the inside of the duct, but you can shield the charge that's already inside the pipe. When a grounded wire is wrapped around the pipe the charge inside the pipe attracts an equal and opposite charge into the wire. That charge is supplied by the Earth (see G). With the internal charge balanced by the outer charge the net charge is zero and there's no attraction for more charges ands no zap from touching the outside of the pipe. Most of the attractive force is within the wall of the pipe, acting between the inner surface charge and the charge in the wire.

    StaticSheildedPVC.png

    Note that there is no need for a bare wire touching the PVC. An insulated wire works just as well. The more wraps of wire used the greater the shielding but increases the installation difficulty.

    The following photo shows the "ineffectiveness" of wire wrap grounding.
    Note how most of the ducting is covered by static attracted dust and only a small area close to the wire is free of dust.
    GroundedPVC.jpg


    Some claim they can “ground” a PVC pipe and eliminate the charge by running a wire inside the pipe and grounding it. How does that work?
    It works the same way as wrapping a grounded wire around the outside. The wire pulls a balancing charge from the Earth and effectively “shields” the charge on the pipe inner surface. All of the attractive forces between the opposite but equal charges are now confined to the inside of the duct.

    It looks better than wrapping the outside, but there are some disadvantages. For a start the wire interferes with air flow and if you produce stringy wood dust the internal wire can cause some of it to hang up, possibly blocking the duct. If it's a bare wire there may be some sparking where it comes close to the inner wall. The sparks will be small, with low energy, so not likely to cause any problems, but, you will be adding sparks where they wouldn't otherwise be found.

    The outfeed table of my planer (thicknesser) sometimes shocks me. Why does that happen and how do I fix it?
    As before, when you are close to a internally charged duct that charge attracts an opposite charge in the part of your body close to the duct. At the same time, it repels like charges in your body so that charge is pushed to the opposite side of your body. If that part of your body is close to or touching an exposed metal part of a machine that repelled charge can discharge to the grounded outfeed.

    That shock can also be much greater than the one you may get directly from touching the outside of a PVC pipe. The amount of charge transferred to the outer surface of a pipe is limited by the area on the pipe that is reached by the ionized air of the spark. Transferring charge to grounded metal moves all of the induced charged in your body to ground. More charge means higher current and so more pain.

    To eliminate this problem, shield the charge inside the duct by wrapping a wire around the pipe or hose and ground it to the machine. Just be absolutely sure the machine is grounded. The wire doesn't have to cover all of the duct, just the length nearest you. If you're using hose and it has a spiral wire just ground that.

    Do I need to ground metal duct and spiral wire in flex hose?
    Yes, all metal parts in or near the dust path should be grounded. This especially includes things like sheet metal fittings used between PVC sections.

    The spiral wire wraps the whole hose. That exposes it to the entire charged inner surface of the hose. This induces a large charge imbalance in the wire that, if not drained, can cause large sparks. These sparks can be painful and even dangerous to people, especially those with pacemakers or other life support electronics. They can also interfere with CNC equipment.

    So, what is the overall fire/explosion risk
    There are plenty of examples of “spark initiated” dust explosions and fires in industrial situations caused by charge build up on ungrounded metal surfaces. Metal is conductive so a spark will utilize the entire charge that was on the metal object. PVC is non-conductive so sparks only discharge a small area of the duct and therefore produce much smaller sparks. dust/air ratio. The bigger the spark the more likely it is to produce an explosion. The other issue is that wood dust explosions will only occur when a large enough discharge occurs inside a duct with a specific wood dust/air ratio range. Given that the dust/air ratio inside ducting is highly variable in space and time the likelihood of this occurring is very low and there are many other greater risks in a DIY workshop that you should worry about and attend to..

    Although there is a requirement that dust collection systems be grounded in their entirety, PVC is an insulator and can't be grounded.

    PVC ducting is not used to extract wood dust in industry due to a number of factors eg the greater robustness of metal ducting, cost being less of a factor, lack of a range of duct sizes and fittings, and the requirement for mixed installation skillset. Hence there is no incentive to test it's safety.

    If static discharges from plastic hoses caused explosions there would be lots of exploding vacs and social media would have spread that information very quickly.


    Back to TOC.
    Last edited by BobL; 28th July 2020 at 10:28 AM.

  7. #6
    Join Date
    Feb 2006
    Location
    Perth
    Posts
    27,757

    Default

    DUCTING RECOMMENDATIONS: Terminations/Dust Ports.

    By this I mean almost any junction, hood or means of attaching anything to ducting. Terminations are poorly understood and contribute significantly to restricting air flow.

    Terminations/Ports can be divided into two types.
    “Naked” such as those used to collect air from the near vicinity of a machine like a lathe, or “Fixed” such as those attached to the cabinet of a machine.

    Naked terminations consisting of just the open end of a duct or flexy can highly restrictive to flow. To reduce this restriction, some form of hood is usually employed. Wide hoods work better than no hood for fine dust but not so goo for chips. By far the most optimal shape for fine dust and chop collection is the flared Bell mouth hood (BMH). This collects more air, and from further directly out in front of the BMH, than other hoods. The optimal shape of the BMH is “trombone like” but the length of this shape is almost always too impractical for wood working. Instead a simple formula that uses the radius of curvature of the flare is half the radius of curvature of the duct is in terms of air flow performance surprisingly close to the trombone.

    BSandernew.jpg 16inchfront.jpg

    The most important factor regarding dust ports on a machine is they should be matched to the size of the ducting. It is almost pointless to run 150mm ducting to a machine and plumb that to a 100mm port on the machine. I know it is not easy to cut a 150 mm hole in a new machine but it may not necessary to do this. Some machine ports are located on removal plates or segments of a machine which can be removed. Then it’s just a matter of replacing the plate with a larger port cut into the replacement.

    Fixed terminations are usually performed by fitting a simple PVC flange to a machine but can also benefit from using a BMH. A BMH can also be used to connect ducting to a DC, through to connections to a machine cabinet. Sometimes there is not enough room for a BHM but even a partial BHM connection will help.

    Here is an example of a fixed BMH extracting dust from a cabinet (image from this post by arniew)
    Improving machine cabinet dust ports
    BHMcabinet.jpg

    Here is an example of a naked BMH used on a lathe


    BMHs can be turned from blocks of timber or MDF or molded or pressed from short segments of PVC ducting. The ultimate performance of BMH is very much dependent on the flow – if there is very little flow to begin with a BMH will not make much of a difference. OTOH if there is very little flow then every little extra bit helps.
    Some info on how to make them is here Improving machine cabinet dust ports

    Back to TOC.

  8. #7
    Join Date
    Feb 2006
    Location
    Perth
    Posts
    27,757

    Default

    DUCTING RECOMMENDATIONS:Design layouts

    This is potentially a complex topic requiring many considerations so all I will describe here are some general principles some of which will be quite obvious or have been repeated before but are included for completeness.

    • The shorter the path length and the fewer junctions used between a machine and the DC the better.
    • Locate the dustiest machines (drum/belt sanders, thicknessers, table saws) as close as possible to the DC. These should all be serviced by 150mm ducting
    • Less dusty machines like drill presses and power tools can be further away from the DC and may even be serviced by 100 mm diameter ducting.
    • Bnds saws are a special case and need at least two and possibly 3 X 100mm ducts.
    • The simplest system layout has one “trunk” line from the DC across a shed which uses Y junctions to connect to ducting “branches” to connect to individual machines.
    • Sometimes a branched trunk line (two trunk lines) is required – if so, it is worth adding blast gates at the branch junction to block off the unused trunk branch. But then you have to remember to open/close them as required.
    • Where possible, a layout that has only one machine per branch is best. More than one machine on a branch will ideally requires the use of more blast gates.
    • For safety reasons avoid where possible ducting laying across the floor.
    • If planning a shed from scratch, consider under floor ducting to a few likely places in the shed floor where machines may be used. ‘In floor” duct openings should be fitted as recessed so when unused can be covered over to leave a smooth floor.
    • A stated earlier, Y’s are the preferred junction to use on a trunk line, then adding a 45º bend to the side offtake converts that into an easy to use 90º bend.
    • For future use, consider adding additional Y’s right from the start into the ducting every 3 or so metres of trunk line ducting even if you are not using them.
    • Minimize the use of flexy.
    • Planning onto a shed map showing the locations of machinery helps determine how many metres of ducting and what junctions are is needed


    This is an example of a basic initial plan shown thae lay out with most of the machine locations and junctions needed. Significant components not shown was flexy and gates.
    APMSPlan.jpg

    Back to TOC.
    Last edited by BobL; 2nd March 2020 at 01:31 PM.

  9. #8
    Join Date
    Feb 2006
    Location
    Perth
    Posts
    27,757

    Default

    DUCTING RECOMMENDATIONS: Construction tips and Ducting Suppliers

    There are many ways to install/suspend/hang PVC ducting from ceilings and walls. The easiest way if available is to lay ducting across ceiling rafters.

    If suspension is required, 1mm thick by 25mm wide galvanized steel sheet or strip, cut to the required length so that it wraps around ducting and is bolted to itself with 6mm gutter bolts can be used. At the ceiling or wall, the strip can be Tek screwed in place or wrapped around a rafter and bolted together with the same 6mm bolts. Drilling a few extra holes in the straps allows for some height adjustment during installation. To enable the ducting to be as level as possible, suspension of ducting using all thread rod can provide for fine adjustment of levels after installation.

    12 mm thick rods with threaded ends every 2m to support 225mm stormwater ducting
    Ductinsuspension.jpg
    All thread rod and simple hook support for 150 mm duct
    clamp.jpg

    If the ducting and junctions are all fitted square and lightly hammered home with a rubber or wooden mallet they will not leak so glue, or tape is not essential. I would definitely not glue any joint because sooner or later you will change your mind or move houses or . . . . A short Tek screw or two will easily hold the junctions and ducting together. If you are concerned about leaks a thin bead of silicone around the exterior of the join will be all that is needed and has the added benefit of easily being removed.

    If a duct or junction needs to be removed but is stuck then, while pulling the joint apart and side to side, firmly tap on the side of the duct or junction with a wooden or rubber mallet will eventually unstick the tightest joint. Having another person for this task makes it easier. Remember to remove any Tek screws beforehand.

    If you have help, sometimes it is easier to lay out and fit together (Tek screw) a linear segment of ducting and any required junctions on the floor. Just take care to line up the Y’s in the correct orientation before lifting the segment into place although it's usually no drama even when the ducting is in place to remove the Tek screws and make final adjustments to any fitting’s rotational orientation.

    If you have to fit ducting (in)to an awkward situation/orientation ie go up/down over/under something to remember is that 45, 30 and 15º bends can in combination with short lengths of duct produce a wide variety of ducting Construction tips curves, offsets and diagonals. While not always ideal they can often get around most things. If all else fails a short segment of flexy can be used.

    The most expensive places to purchase duct and fittings are big hardware stores which usually also have a restricted range of junctions but may be useful for an emergency purchase eg over a long weekend. Plumbing suppliers vary widely in price but can also be expensive.

    The cheapest places to purchase are usually dedicated PVC pipe and fittings specialists as they have very high turnover. An example of this in WA are https://www.pipeonline.com.au – they also will ship and although shipping is expensive you may find it's overall cheaper that local hardware or plumbing suppliers. They also my have a deal going with suppliers in other states on 6m lengths of pipe which is worth investigating. If 6m lengths of 150mm pipe seem like overkill don't worry, you will eventually use it up even if it its just to make a vertical garden,

    Back to TOC.

  10. #9
    Join Date
    Feb 2006
    Location
    Perth
    Posts
    27,757

    Default

    DUCTING RECOMMENDATIONS: FAQs

    Q: I have heaps of 100mm ducting. Can I run two 100mm ducts instead of using 150mm ducting as they are about the same in cross sectional area.
    A: They are indeed about the same area, but it requires 3 x 100mm ducts to carry the same amount of air as one 150mm duct. The complications of running 3 lots of ducting are just not worth it.

    Q: I can’t afford too many large junctions what about if I make up MDF/Perspex boxes that have 3 duct sized holes in 3 of the sides?
    A: In the situation where two of the holes are opposite each other this becomes effectively a T-junction which creates considerable added turbulence which will significantly restrict flow. If the holes are on 3 adjacent side thwat will be even more restrictive. It is possible to make up Y shaped junctions out of MDF but they won’t be as effective as the PVC Y’s see below.

    Q: I want to make up some of my ducting square or rectangular out of MDF, what size should I use to obtain equivalent flow to 150 mm round ducting?
    A: A 150 x 150 mm square cross section duct will have about the same flow as 150 mm round duct. The square duct will have a slightly greater flow but this will be counteracted by a greater restriction of any transition from “square to round” or VV unless smooth gradual transitions are used.

    Q: Can I use corrugated black poly irrigation pipe in place of flexy?
    Besides being very stiff so it doesn’t bend all the easily, the shape of the corrugations on black poly flex are more restrictive to flow than conventional flexy. It will often make a very annoying whistling noise at high air flows. If you wish to use this material it needs to be considerably larger than the regular size flexy, but then you risk dust falling out of suspension inside the flex.

    Q: What is the best/easiest/safe square st way to cut large diameter ducting?
    A: Safe very square cuts can be made using a medium TPI hand saw with the ducting held inside a custom MDF mitre box that is clamped down onto a bench. Shorter cuts can be made slowly on a bandsaw and holding the ducting up firmly against the mitre slide. Freehand cutting on a Bandsaw is not recommended as the blade can make the ducting rotate and veer off square. It is also possible to cut shortish lengths safely with a TS, see method here. Another safer useful tool to cut plastic with if you have it is Renovator/Multitool .

    Q: How do I connect a 150 mm diameter PVC duct to a square/rectangular dust port?
    A: It is not that difficult to make a square/rectangular to round transitions. Ideally transitions should be about 5 ducting diameters long but this is often impractical in woodworking situations so whatever you can manage is better than a box like transition. In some cases it may be possible to heat the end of the PVC and force it over a custom made wooden former to force the round into a rectangular/square shape. A flange end may then need to be fitted. This can be cut from MDF or PVC sheet and screwed to the rectangular/square end of the PVC duct.

    Back to TOC.
    Last edited by BobL; 28th February 2020 at 06:05 PM.

  11. #10
    Join Date
    Apr 2019
    Location
    NSW
    Age
    37
    Posts
    1,126

    Default

    very nice effort, and thanks for a concise, easy to read and easy to understand info.

    my only tiny suggesting would be to avoid using internet/forum acronyms, saves me having to google what they mean.

    look forward to reading the final product

  12. #11
    Join Date
    Apr 2019
    Location
    NSW
    Age
    37
    Posts
    1,126

    Default

    hi Bobl, as a question Re: materials is there any benefit/down side to using the semi rigid ducting available. one big thing will be price its probably close to double the price of foam core PVC but it seems to be readily available.

    being slightly spiral wound it obviously isn't going to be as turbulent free as PVC but i think it would be better then fully flexible. I don't personally have the gear to test the difference between using it though.

    only other concern might be if the tubing might collapse on it self if there was a blockage

    Pacific Air 3m x 150mm Semi Rigid Duct | Bunnings Warehouse

    duct.jpg

  13. #12
    Join Date
    Feb 2006
    Location
    Perth
    Posts
    27,757

    Default

    Quote Originally Posted by havabeer69 View Post
    hi Bobl, as a question Re: materials is there any benefit/down side to using the semi rigid ducting available. one big thing will be price its probably close to double the price of foam core PVC but it seems to be readily available.

    being slightly spiral wound it obviously isn't going to be as turbulent free as PVC but i think it would be better then fully flexible. I don't personally have the gear to test the difference between using it though.

    only other concern might be if the tubing might collapse on it self if there was a blockage

    Pacific Air 3m x 150mm Semi Rigid Duct | Bunnings Warehouse

    duct.jpg
    Thanks for the info and I will add it to the list of materials
    I'll also put it on my list of things to test when I next get around to it.
    The shape of the corrugations seems to play a role of how how restrictive flexy is but I have not really tested this out in detail.

    For some Wood working applications I don't think it would stand up to constant flexing but could be useful in semi permanent situations.
    I'd say its definitely worth using to vent hot gasses in metal working applications. In fact I can see an application for it right now as one of my bros has bought a new house with an underground workshop which he will use as a metal shop and will need an exhaust setup to vent welding gasses etc.

  14. #13
    Join Date
    Apr 2019
    Location
    NSW
    Age
    37
    Posts
    1,126

    Default

    yep i agree i wouldn't think it would be usable in a constant flexing situation as a replacement for say flex between a mobile thicknesser and wall mounted PVC. that to me would need to stay as proper plastic flex line.

    Thinking about using it as you said as semi permanent ducting on the wall as trying to track down some local foam core isn't as easy as i thought.

  15. #14
    Join Date
    Jun 2009
    Location
    Elizabeth Bay / Oberon NSW
    Age
    76
    Posts
    934

    Default

    Quote Originally Posted by BobL View Post
    DUCTING RECOMMENDATIONS: FAQs

    Thanks for a very informative sticky, Bob.

    Q: What is the best/easiest/safe square st way to cut large diameter ducting?
    A: Safe very square cuts can be made using a medium TPI hand saw with the ducting held inside a custom MDF mitre box that is clamped down onto a bench. Shorter cuts can be made slowly on a bandsaw and holding the ducting up firmly against the mitre slide. Freehand cutting on a Bandsaw is not recommended as the blade can make the ducting rotate and veer off square.
    For very long lengths I used an thin disc angle grinder guided by a sheet of newspaper taped around the perimeter. For shorter, more manageable lengths, I set my table saw about 2mm above a sled and slowly rotated the pipe using the fence to steady the pipe. Each subsequent cut was about 2mm deeper than the previous one. This method creates a lovely clean finish and often I cleaned up an angle grinder cut on the table saw.

    mick

  16. #15
    Join Date
    Feb 2006
    Location
    Perth
    Posts
    27,757

    Default

    Quote Originally Posted by Glider View Post
    For very long lengths I used an thin disc angle grinder guided by a sheet of newspaper taped around the perimeter. For shorter, more manageable lengths, I set my table saw about 2mm above a sled and slowly rotated the pipe using the fence to steady the pipe. Each subsequent cut was about 2mm deeper than the previous one. This method creates a lovely clean finish and often I cleaned up an angle grinder cut on the table saw.

    mick
    Lots of methods can be used. I just recommended what I considered safe methods especially for newbies.

    Angle grinders are one of the most common power tools resulting in a DIY hospital emergency attendance and I always worry about balancing long lengths of any material on a TS especially when trying to cut a short length from a 6m length of duct. Not that many DIY will have 6m to play with either side of their TS. If a TS is used a high TPI composite or negatively raked toothed blade is the safest blade to cut material like plastics as this prevents the blade from grabbing the workpiece. These blades will also cut all plastics, Al and composites very cleanly and safely even with the full blade exposed so any money invested on these will not be wasted.

    Your method of only exposing a small amount of blade is a good one for short pieces and is probably even safer than my suggestion to use a Bandsaw.
    A medium fine toothed hand saw and mitre box is I think still the safest and will often usually be the quickest.

    Most of the 150mm ducting at the mens shed was cut by a younger member with some "issues". I felt quite comfortable leaving him to cut the lengths with a handsaw and to sand the edges with some sandpaper. I gave him the lengths and he cut them as specified and didn't get one wrong.

Page 1 of 5 12345 LastLast

Similar Threads

  1. Help with down draft table
    By Dez Built in forum DUST EXTRACTION
    Replies: 1
    Last Post: 6th September 2016, 12:49 AM
  2. Balance lug draft
    By BradLH in forum Michael Storer Wooden Boat Plans
    Replies: 13
    Last Post: 13th October 2010, 10:21 PM
  3. Dovetail Markers (first draft)
    By kevjed in forum HAND TOOLS - UNPOWERED
    Replies: 8
    Last Post: 18th September 2009, 10:54 AM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •