Dust collection for a 48x96 CNC router table

Greetings to all of you at Carbide 3D.

I stumbled into this community because I am trying to determine the best way to add dust collection for a new CNC router table that should arrive in my classroom/lab in the next month.

I teach a robotics engineering program at a high school near Pittsburgh, PA. For my program, and also for a FIRST Robotics Competition team, a corner of the room will soon be home to a new Avid CNC 48" x 96" router table. Here’s a link to the table: Avid CNC Pro 48 x 96 cnc router table

The following spindle will be mounted for this unit: Spindle

I expect that the materials used on this table will be approximately:
40-50% aluminum
30-40% wood
15-25% plastic (Delrin, Lexan)

I was already concerned about safe dust collection before I came across this thread: Potential Health Effects of CNC and Machining

Now I’m REALLY concerned, and appropriately so, because I want to protect not just myself but the health of every student in my program.

I have seen very knowledgeable discussions by a number of members of this forum, and so I come to you for help with my situation. In particular, I am hoping that @mbellon can evaluate if a Festool CT unit could be used in my situation. I am confused about the comparatively low CFM listed on the Festool units. I wish I could have the CFM of a 2HP dust collector with the 0.5 micron HEPA filtration offered by the Festool.

One final note on the system I have spec’d out with the help of the Avid CNC staff: A 79 mm shoe has been recommended to me from Kent CNC. Supposedly, this standard shoe fits the equipment I will be acquiring. Here’s the link: Standard Split Shoe Note that the 79mm must be selected from the drop-down box.

I thank all of you for helping to keep me and my students safe to the best of my ability. I knew next to nothing about dust collection when I started looking into this situation. Feel free to talk to me like the newbie I am.

Many thanks in advance!
Mike

You may have noticed that in my air safety discussions I mention the Festool CT only in the context of the Nomad. This is because I’m fighting a losing battle… people just don’t believe there is a problem or don’t have the budget to be properly safe. Since anything is better than nothing - it’s all about risk management - I elected to do what you see.

A Nomad plus Festool CT is “pretty good” for frangible materials (e.g. wood, MDF, carbon composite) … provided that the enclosure doesn’t leak air and the vacuum is left running a a few minutes after the end of the job.

The principals I publish are true for any CNC machine working with frangible materials. A larger CNC machine, like the one you’re discussing, requires A HUGE AMOUNT MORE AIR than a Festool CT can draw.

With larger CNC machines one requires 4 inch (100mm) tubing with several horsepower of air extraction to be properly safe… assuming the machine is in an enclosure. Most shops are willing to take some risks so they forgo the enclosure and up the vacuum… or just live with the risks.

A HEPA filter is a requirement only if the air is returned to work area. A cheaper solution, if available, is to dump the air outside. All that is necessary is a 5 micron filter to prevent “snow”. Can you dump the air outside such that it doesn’t easily come back in? Can the output be placed such that the noise doesn’t bother a neighbor?

A proper cyclone (dust separator), vacuum (dust collector), and HEPA filter to deal with a machine of this size is $$$$. One can often build a unit that is cheaper than a commercial unit but the simplicity of a “canned solution” is often hard to refuse (just be done with it; buy your way out).

Yes, you need serious air volume but you also need serious air velocity. This requires big tubing, lots of HP, and proper set up.

The best thing I can advocate is call me and we’ll talk it out. We can work out a solution that is the best given your budget and circumstances. I live in the SF area (west coast). Call me @ 650-714-2693 and let’s get you set up.

KentCNC: AWESOME! I use them myself and in all my consulting

mark

P.S.

Some materials may be VERY DANGEROUS to CNC. MDF is one of the worst. FR4 (PCB material) and carbon composite are two others. NEVER, NEVER let anyone machine “Copper” unless they can prove that is is Beryllium free.

No Plutonium either. :slight_smile:

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The physics for lofting - dust pick up - is complex but in the end one can greatly simplify (the approximations are more than good enough). For “perfect” collection one needs smooth 5 inch tubing, all the way to the dust head. Since there are losses along the way due to friction - non-laminar flow - and turbulence - bends and turns - man shops have 6 or 8 inch piping for distribution.

The infrastructure for 5 and 6 inch CNC dust collection is expensive. The alternative - widely used - is 4 inches. Why? Because a 4 inch system, properly designed and implemented, is very close to the efficiency of a 5 or 6 inch system… with much lower cost.

Dust collection is not simply a matter of using a vacuum - pressure - it is also a function of the air speed. Both are only possible using large diameter piping/tubing. The bigger the better.

Under no circumstances is 2.5 inch tubing satisfactory for larger CNC machines. For small CNC machines (e.g. Nomad 883 Pro) a properly designed 50 mm or 2.5 inch vacuum system is “pretty good”. The spindle or router tend to be smaller, generating less dust, and with a proper enclosure design one can be safe.

Large machines (e.g. 48 x 96) are often installed without an enclosure, due to the cost and need for accessibility (large sheets need to be fed). This means that there is more of a chance for dust to escape - particularly the very small, lung dangerous particles. This is why it is critical to have a high quality, properly designed vacuum system. One must ensure that as much dust as possible is collected.

Other downsides of having an “open” CNC machine are noise and safety. The noise - which can go on for hours - is very damaging for hearing. One must wear high quality hearing protection… which isn’t a lot of fun. The safety aspect touches on two areas: things going flying and hands going where they shouldn’t.

A dust separator - typically a cyclone - is necessary to reduce the amount of dust sent to the dust collector. The dust separator introduces friction - reduces the pressure and air speed - and so has to properly calculated into the system.

The same losses occur with a HEPA filter. Everything in the system matters. Also, keep in mind that HEPA filters are expensive… especially for large scale systems. They become “full” after a while and have to be replaced. Some can be cleaned and reused a few times…but there are even more expensive.

In factory scale CNC, the air is often dumped outside without a HEPA filter - just a 5 micron filter… which creates quite a noise issue for those nearby. One can solve this… again at cost.

There is no simple solution nor is there a trivial cost solution. The good news is that with a good understanding of the layout of the large scale CNC machine and the room it is in, it is possible to implement a “more than good enough” vacuum system at a reasonable cost. It’s all about risk management - air, ear, and mechanical safety.

Again and again I see a rush to get a CNC machine, only then to discover that the true cost involves a vacuum system… and the vacuum system is compromised. Better to get a smaller CNC machine with a proper, safe vacuum system, than a larger one with an inadequate vacuum system.

The noise from a vacuum system is often LOUDER than the CNC machine itself. The same principals that apply to CNC machines apply here as well plus a few additional issues. A bit of care and this can be solved easily.

Again and again, I see little concern given to the noise. This is a HUGE issue, affecting the safety and performance of all those in the vicinity of a CNC machine.

A cautionary note about CNC vacuum systems and especially about HEPA filters - virtually all vendor LIE. There are no testing standards; they are all testing under different conditions. Many only work as advertised when the filter is near the end of its life. Caveat Emptor!

For cost reasons I’m a big advocate of dumping the air outside whenever possible - no HEPA filter. Dumping the air inside - often the only practical way of doing things - requires a great deal of thought… and don’t forget that the HEPA filters have to replaced (often if the machining volume is high).

I use and highly recommend the KentCNC dust heads.

I’m always willing to talk to people and help out. Far too few people are concerned, exposing themselves and those around them to preventable dangers. Solving these issues isn’t rocket science.

mark

P.S. I do not work for any of the companies whose products I recommend.

On machining Aluminum (commonly 6061). I strongly recommend a Minimum Lubrication Quantity (MLQ) system. While “do it yourself” systems work, quality commercial system work infinitely better.

No, WD40 is not a good cutting fluid. It does work (sort of), but it also exposes the user to toxic fumes. Modern MLQ systems and cutting fluids are non-toxic and safe to dispose down the drain. Properly used, an MLQ system with destroy/use 95% of the cutting fluid in the cutting process… virtually nothing to clean up.

Conventional cutting fluids require EPA mandated disposal methods (they are toxic to some extent). They are usually diluted with water (1 part in 16 to 20 is not uncommon) and make quite the mess. The atomization process often sends the liquid into the air, exposing the lungs to nasty stuff.

A well designed MLQ system can be designed at a minimal additional cost to be able to switch better two cutting fluids - one for aluminum and one for plastics. Yes, using a cutting fluid for plastics is worth it - the finish is much improved over dry machining… even when using Onsrud’s amazing plastic cutting machine tools.

Air blast is an “ok” solution but it has to be properly designed so as to no send particles into the CNC machine. Too often I see machines requiring repair due to improperly design air blast systems. If using air blast, USE A DUST HEAD, EVEN FOR ALUMINUM!

For those interested in obtaining the very best and safest aluminum and plastic cutting techniques, let me know and I can explain. They aren’t cheap but the results are AWESOME. Can’t afford some such? We can still work out an acceptable, cost effective solution.

I’m more than happy to help those who ask. I only charge is you want me to build and deliver it.

mark