Dust Collection / Shopvac

Chris Sedlock

Feb 13, 2024

161

image courtesy of Dust Collector vs Shop Vac (Side by Side Comparison)

What is a "Dust Collector" and which is best for my CNC? Unfortunately, in the CNC/woodworking community this is not very well defined and virtually impossible to answer. Everything from a brush, broom, dustpan, compressed air hose and blower nozzle all the way to a semiprofessional cyclone system and everything in between is called "dust collection". Here we are going to discuss the two types of systems very briefly most used with a small CNC routers and possible ways to maximize the effectiveness of both. Fortunately, 99% of all our CNCs are identical (or close) as far as its matters for dust collection. They are simply a router/spindle motors from 1-3hp using bits with 1/8" to 1/2" shanks that max out with about a 2" cutter diameter but usually use 1" or less. This is just saying occasionally you surface something using a big surfacing bit but most of the time you're using 1/8"-1/2" straight, ball nose and v-bits. Your CNC moves the spindle around at between 0-500 ipm and you need to collect the dust. With this pretty much defined and assuming you don't want to use a broom and dustpan let's discuss dust collection.

There are two types of dust collection available to the hobbyists and small professional CNC/woodworker. One is low volume/high pressure (LVHP)... think shop vacuum. The other is low pressure/high volume (LPHV)... think traditional dust collector with blower and bags. Both move the intake air, which will pick up chips and dust, move them into some kind of collection container and blow clean air out as exhaust.

There are advantages and disadvantages to both HPLV and LPHV systems. There is also a TON of misinformation out there. What will work best and why gets very confusing.... so hopefully we are all on the same page and can try to figure out some solutions that are as simple as possible. The first thing you should never use to judge the performance of any dust collector solely on horsepower. Walk into any big box store and I'm confident you can walk out with a 5 to 6.5hp shop vacuum. If you tried to walk out of the same store carrying just the motor of a 5hp table saw or air compressor you'd probably have a sore back tomorrow. The facts are the advertisers are lying to you. No motor over about 2 hp can run on a household 110v circuit. Traditional dust collector advertising is no better. They inflate the volume of air being moved (CFM) by measuring it directly at the intake with no hose on the intake or filter on the exhaust. Both are a guaranteed way to think your dust collection system is going to work much better than it ever will in the real world.

The best way to think about LVHP and HPLV systems is like water. Low pressure systems are more like a water hose being fed by gravity. The size and shape of the piping effects it much more than a high-pressure system which is more like a water hose being fed off a pressure tank or your towns water system. No matter how much hose you connect or how much it's wrapped around your car it still shoots out hard. Of course, this isn't perfect examples but just a way to visualize it. A low-pressure system can lose 90% or more of its suction with just a couple of mistakes in its plumbing while a high-pressure system can overcome a lot more. A high-pressure system can be rated at much lower CFM and perform much better.

Let look at some recommendations that might make your current or future system work better especially for CNC. First buying a handheld anemometer will help you measure to some degree how much air is being moved. If you are planning to use a traditional dust collector (LPHV) then plumb it in with smooth wall straight piping as much as possible. Use sweeping 22.5° or 45° instead of sharp 90° or "T" fittings. Reduce the amount of flex hose to an absolute minimum. Don't ever reduce hose diameter until you get as close to the point of collection as possible.

On a side note... a LPHV hose reduced at the proper time (usually within 4'-6' of the boot) can improve performance. This is because the reduction in volume of air being moved will increase the velocity of the remaining air being moved. I discovered this accidentally years ago with a shop-built router table. Reduction of the hose attached to the fence from 4' to 2.5" reduced the amount of escaping dust tremendously.

Unless you have a big blower (220v 5hp or larger) that moves a huge amount of air wanting to be able to use multiple tools at once is probably a bad idea. If you want to do other things while your CNC is running, it's probably best to use either a dedicated dust collector or shop vacuum to collect the dust at the CNC and a separate unit for other tools. I personally have looked at and failed to see the advantages of individual units for a long time. The cost of a dust collection system capable of effectively collecting dust from even two machines far exceeds the price of two or three individual unit's dedicated to their own source of dust. A dedicated shop vacuum will often outperform a traditional dust collector that isn't plumbed in correctly. Units known as dust extractors (festool, fein, or bosch for example) look like a shop vacuum but with better suction and filtering to keep a more consistent airflow moving.

Lastly what I said I wasn't going to discuss... filters. All I will say about it is a clogged filter are as bad as incorrectly plumbed system. A filter with too little surface area will clog up very quickly and a clogged filter will rob any system or performance. Flowing air is REQUIRED to keep the system working correctly. What type of filter material and how fine of particles it captures is up to you but keep it clean if you want the best results and wear a respirator.