Dust collection - CFM for CNC router?


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    Member ddurbs21's Avatar
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    Default Dust collection - CFM for CNC router?

    I've got a 2'x3' machine that spends most of its time on MDF, pine and plywoods. Right now I'm struggling with an old 16g Craftsman vacuum and a Dustopper separator on a 5g bucket. I have a dust shoe with double bristles installed. It maybe picks up half the dust and chips. I also have other typical tools I need dust collection for, but only ever one at a time.

    I know I want a 2-stage system to keep things tidy, so anything I get will need that addition. I've been eyeing everything from the $200 650CFM wall-mount units with single 4" inputs to the $1000 ones capable of around 1250CFM with a 6" input. Until I get 220v down stairs I'll be using 115/120 for everything. Money is a big factor and I don't want to spend any more than I have to in order to get the performance I need. My 'happy medium' seems to lie near the Jet DC-1100VX-5M which can be had for around $500 a few times a year. I have a fairly confined space and it is just a weekend hobby so I don't need the fancy remote controls and all the convenience extras if the dollar difference is significant. But I don't want crap, either.

    Any input and anecdotes are appreciated. Thanks!

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    Default Re: Dust collection - CFM for CNC router?

    I am surprised that it is only getting 50% of your material; I have a home built system, and it gets it all. Could the double-bristle set be preventing a good air-flow near the cutter? As we say in the vacuum business, vacuum systems don't suck (professional humour, sorry). The dust and chips are pushed by the air flow.

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    Default Re: Dust collection - CFM for CNC router?

    I can't rule out that the double bristles might have an impact. But I can perhaps give a better example. My last gift project contained a lot of full depth contour cuts in 3/4" MDF with a 1/4" straight flute bit. I took it conservative and made multiple passes - can't recall but maybe 0.15"-0.20" each, being full WOC. After each pass I hit feed hold and used a narrow flat blade screwdriver to free the dust from the contour lines and vacuum it manually, despite the dust shoe having been active during the operation. Or what typically happens is the bristles of the dust shoe run off the panel being cut and now there's a 3/4" gap to the spoilboard and out comes a wave of fine MDF dust. The Dewalt DW618 router I'm using puts out a good amount of air down toward the collet and happily finds a number of ways to make a mess.

    I assume I need more suction, and I may have room for improvement elsewhere too. But nonetheless I'd like a less noisy centrally located dust collection system for my other tools as well as my CNC table. When I find an elechicken who will grace me with his/her presence in exchange for a thousand bucks I'll have a subpanel installed and some 220v options for a VFD/spindle.



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    Default Re: Dust collection - CFM for CNC router?

    Packing of dust in the cut may be due to the chipload being too small and you are making dust rather than chips.

    You may need to increase your feedrate or lower your rpm.

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    Default Re: Dust collection - CFM for CNC router?

    I have yet to see an extractor that gets all the dust.If you are cutting at any depth the kinetic energy of the particles being ejected at the bottom of the cut is too great for an extractor to deflect upwards with in the boundary of the bristles and the swarf flies out of the region regardless.Maybe a longer and softer bristle would help.There are improvements you can make,regardless of the extractor unit and one of the best is to find a hose that minimises the flow loss.The usual spiral wire reinforced hose makes the flow rate drop by a lot and I have measured it on a 13 foot length of 4 inch hose at 75% less than at the extractor boss and with a 6 inch hose at 50% less.There is a less bad type of hose and it helps a lot.I used a flow meter that hang glider pilots use for measuring windspeed and while I didn't take the figures to be absolutely accurate,I did believe the drop in flow rates.



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    Default Re: Dust collection - CFM for CNC router?

    I think routalot hits it on the head; restriction in the branch circuit is what kills most systems and that starts with the spiral hose pick up. There are some hose types that are smooth inner surfaces and promote higher flow rates. They also tend to be a bit less flexible, an important consideration when fitted to a CNC pick up. In a well designed system, there needs to be a balance between relatively high flow rates (the pros like to see 4000 CFM in the branch) and high static pressure, both of which are necessary to suspend chips in the air stream. Shortening the overall length of the circuit, reducing the number of elbows and generally close coupling system components (cyclone to fan to air filtration) will reduce system losses. Also, keep in mind that a tight seal at the brushed pick up isn't necessarily a good thing; if there isn't sufficient air flow, there won't be good pick up.



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    Default Re: Dust collection - CFM for CNC router?

    Quote Originally Posted by MARV View Post
    Also, keep in mind that a tight seal at the brushed pick up isn't necessarily a good thing; if there isn't sufficient air flow, there won't be good pick up.
    Flow restriction from the brushes should be negligible. Having a good seal with the brushes insures you'll getr all the airborn dust and chips, which is imo the most important thing. You'll never get all the chips out of the cut, without resorting to making extra passes just to pull the chips out.





    Your best chance of getting the chips out of the cut with MDF is to use higher quality MDF, usually called Super Refined. Plum Creek is a brand that we use.

    Even then it will be difficult, and it's much more difficult with cheaper MDF.

    An Upcut bit will help.
    A roughing cut about .03" oversize will give more room for the chips and let them come out a little easier.

    Best bang for the buck is the Harbor Freight 2HP dust collector. I have an old Crafstman 1HP 600 CFM, and the Harbor Freight is far superior for CFM.
    With coupons, they can be purchased for about $175-$200 I think.

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    Default Re: Dust collection - CFM for CNC router?

    Gerry, I agree MDF is miserable stuff to cut. Packs up slots and into corners of pockets, typically more dust than chips. I know of some folks that direct a compressed air stream right at the bit as a means of keeping the dust and chips loose. Its whatever works.



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    Default Re: Dust collection - CFM for CNC router?

    Yes, I forgot to suggest a jet of compressed air will be the best bet.
    The new industrial routers we're looking at have separate air jets for different cutting directions.

    Gerry

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    Default Re: Dust collection - CFM for CNC router?

    Thanks for the replies. The router does exhaust out the front quite a bit but it isn't as directed as it could be to evac dust from slots. I like the approach of cutting a wider contour where space allows and I'll have to add that to my list of things to try. I really dislike cutting MDF but it's where I'm at right now.



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    Quote Originally Posted by PaulRowntree View Post
    I am surprised that it is only getting 50% of your material; I have a home built system, and it gets it all. Could the double-bristle set be preventing a good air-flow near the cutter? As we say in the vacuum business, vacuum systems don't suck (professional humour, sorry). The dust and chips are pushed by the air flow.
    Probably the most accurate statement I’ve seen about dust collection in years. You need air flow for these things to work. To an extent you need the right air velocity which is why the size of the pipe varies in these systems.

    Currently I have one system, a small Jet, that I move from machine to machine. Yes this is a pain in the ass. This includes my bandsaw, planer and jointer. I believe the hose on this unit is 4” which results in decent air flow and velocity.



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    Quote Originally Posted by ddurbs21 View Post
    I can't rule out that the double bristles might have an impact. But I can perhaps give a better example. My last gift project contained a lot of full depth contour cuts in 3/4" MDF with a 1/4" straight flute bit. I took it conservative and made multiple passes - can't recall but maybe 0.15"-0.20" each, being full WOC. After each pass I hit feed hold and used a narrow flat blade screwdriver to free the dust from the contour lines and vacuum it manually, despite the dust shoe having been active during the operation. Or what typically happens is the bristles of the dust shoe run off the panel being cut and now there's a 3/4" gap to the spoilboard and out comes a wave of fine MDF dust. The Dewalt DW618 router I'm using puts out a good amount of air down toward the collet and happily finds a number of ways to make a mess.

    I assume I need more suction, and I may have room for improvement elsewhere too.
    It isn’t suction per say it is air flow that makes the difference. This is why dust collection systems specify performance in CFM’s. Obviously you need a pressure differential to get the air moving but anything that reduces how much air you move will greatly impact performance.

    Remember the air pressure at sea level is only 14psi or so. That means you can’t create much of a differential pressure wise. Air flow on the other hand is a huge component in a successful “”vacuum”” system. Think about it a bit if you pulled a perfect vacuum there would be no air to pull the waste along in. Rather it would be like the videos from NASA of the space walks. No air means nothing gets pushed around.
    But nonetheless I'd like a less noisy centrally located dust collection system for my other tools as well as my CNC table.
    Maybe modern units are better but the reduction in noise from larger systems largely comes from them being in another room or even outside. Moving air tends to be noisy. The more turbulence in the system the more noise. Now compared to a shop vac yeah likely to be much reduced in sound level, but still enough to be bothersome.
    When I find an elechicken who will grace me with his/her presence in exchange for a thousand bucks I'll have a subpanel installed and some 220v options for a VFD/spindle.
    I’ve done much of the electrical in my shop myself. Even then I don’t always have enough branch circuits in all corners of the shop. A dust collector will need to be on a separate branch circuit. It is bad enough tripping a breaker on a band saw in the middle of a cut. On a CNC it can be a huge headache.

    The other problem here is that if you buy a cheap 120VAC dust collector now, you will Be replacing it when you get 220 ran to the shop. I’d suggest that it might make more sense to see if you can improve the current approach.

    So what might work with the current hardware.

    1. Check to see if the current vacuum can handle a larger hose and still give good air flow. Shop vac class machines, of suitable size, should do better with a 2 to 2-1/2” hose.
    2. Minimize the area of your vacuum shoe or shroud with the goal of max air flow around the cutting bit. For a shop vac that means not much more than 4” in diameter.
    3. Minimize vertical clearance of the hard part of the shroud but not so much that you impact air flow or start to hit things. Remember the goal is max air flow around the cutter. Anything that impacts air flow, into the plumbing, kills performance. On the flip side if your vertical clearance is too high you air flow is spread out over a much wider area thus reducing velocity to the point nothing gets picked up.

    4. Speaking of efficiency every bend, joint and surface, impacts the ability of the system to pull material. Frankly it helps to think like an electrician and make use of long radius elbows when needed in hard pipe. Hoses like wise would ideally be smooth inside and not be subjected to sharp bends. Attachments like Cyclone heads can be a mixed blessing with shop vacs due to loss of performance which is sometimes gained back due to cleaner filters. The point here is that every little bit helps when you are already starting out with a minimal system.

    In any event hope the above helps some. At work we have used a variety of Swarf extraction systems over the years. This isn’t wood working but the concepts remain the same. In some locations we have made use of PVC pipe dry fitted together. In this case smaller diameters around 2” pipe. They are dry fitted to facilitate clean out In case of a plug and for general maintenance. The positive here is that the material is readily available, more or less cheap and support hardware readily available. The big negative is static electricity which needs to be mitigated. It is likely more of a problem in the larger pipe sizes simply due to weight. However there is much that is off the shelf so to speak so with a bit of creativity you can put together interesting solutions.

    Lastly you mentioned packed MDF in the slots. This is a bad sign because nothing you do will pull tightly packed material out of those slots. I’d look at mitigating the packing. You may need to switch tools between roughing and finish cuts or consider other options.

    Oh one more thing you don’t want to restrict air flow through the router itself. So make sure any changes made don’t impact the router head itself.



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Dust collection - CFM for CNC router?

Dust collection - CFM for CNC router?

Dust collection - CFM for CNC router?