We got our first noise complaint from the neighbors across the street last night, so we need to find a way to make our CNC router quieter. I was thinking we make an enclosure made of 2 layers of plywood with thick foam panels in the middle and one side with a clearish door for loading material. The router is about 3x4ft. Anyone have suggestions on how to make the machine quieter and mby make less of a mess?
Having had to do this with a 300 horsepower electric hydraulic pump, the #1 step is fully enclosing it with -anything-. You are likely dealing with high frequency noise, so foam type stuff will help you, as will some mass loading (if you used sheet metal or plastic for the enclosure). Low frequency is much harder to deal with! I would use a faced foam to minimize the mess. You might get some more noise reduction from having foam inside and out, but the inside facing foam is the first big win. Spend some time adding weather strip foam to the doors and sealing up the corners!
Plywood is not crazy, and its easy to implement. You are likely to get better attenuation from that than a metal enclosure, but it will be heavier. Make sure you stiffen the large panels a bit so they don’t end up flapping or buzzing; the foam will help that too. Sneaky on the stiffening side would be to avoid dividing your big panels into identical rectangles; offset the brace some from the center 
I doubt that a ply-foam-ply sandwich will work much better than ply-foam. Foam is more effective if you expose it to the noise source.
Put a LOT of light in there!!! Those 150W work lights on Amazon are nice and sealed and put out a lotta light! One of them did a spectacular job on the bead blaster at work. Be sneaky and put in two to four lights in the corners shining in to minimize your shadows. Or run strip light most of the way around.
You might feel the surfaces of the unit while its working hard. You may find areas that vibrate! If you find them, damp them with adhesive rubber sheet (ideally stuff designed for damping), or trowel on a mixture of asphalt roofing compound and sand; only use this on non-moving stuff and things you don’t mind looking ugly! I used to use that mix on the inside of the loudspeakers I built back in college.
Another semi-crazy idea: buy a bunch of sound absorbing blankets and use them to make a tent around the CNC… It can be bigger and you can just push through an over-lapping section. There was a team at worlds that had 5 sides of their pit done this way; it made a HUGE difference in the pit!
Oh, and on the window: either go somewhat thick (1/4"?), or use two layers of thin with some space between.
I’ll stop now! Don’t hesitate to bounce ideas! And show pictures!
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I used some window and door flashing tape and Duct seal putty to damp the steel and plastic door panels in my SUV after installing aftermarket speakers. I rolled the putty into 1/4" diameter “ropes” and stuck them down at intervals on the surfaces to add mass and then applied the flashing tape over it all to hold it in place and add more mass and damping. The sound was dramatically deadened when one knocks on it. It was a lot less expensive than buying the Dynamat sound deadening mats.
Check local/applicable noise level and other nuisance requirements. In the interim at least, you can continue machining without really caring about the neighbors, unless you like them for some reason.
CNC router and 2.5HP compressor in my garage with the door closed (vented out an old water heater chimney) are barely louder than most cars, and certainly quieter than the cars in the garage.
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Interesting ideas, thanks for the response. The thinking behind the plywood sandwich is more abrasion resistance for the foam rather than noise suppression. Also, something I should mention is that the CNC is on a rolling cart which we roll outside when it is used since there isn’t really space in the garage for the machine and multiple people. Basically, weight is a consideration so it could be problematic to add a large amount of sand or something similarly dense.
Yup, the issue is that what we’re doing is definitely illegal to some extent so as I see it we’re at the mercy of the neighbors… obviously if this wasn’t the case, I wouldn’t be spending valuable build season time trying to make them hate us less, but idk what my other options are since not machining past 8pm is not really an option for us…
The issue is that our CNC router and 2.5hp compressor are both outside while being used since we can’t really have the CNC and multiple people in our garage at once since its quite small
Buy some noise cancelling headphones for the neighbors.
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To what extent can you work around this? I don’t know anything about when your team meets, but if you machined just Saturdays and Sundays from 8 AM - 8 PM, that’s still 24 hours of cutting a week. Some teams go entire build seasons with less than 24 hours of CNC time.
That said - you’re machining with a CNC router outside, in the middle of the night. Nobody is going to be happy about that. I would do anything you can to get that CNC running inside your space, where it is far less likely to bother anyone. Most of the advice here assumes you are indoors and there’s really not a lot you can do outside to reduce noise like that. Even if just the compressor is inside that would be a big help… but really the solution is that you have to machine indoors if you are unable to machine at other times.
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Honestly, I’d start with the simplest thing first: a basic 2x4 and plywood enclosure. Remember that human hearing is roughly logarithmic, so a moderate decrease in actual sound energy can make a huge difference in perceived loudness.
if that’s not enough, I’d add sound deadening insulation behind it (e.g. rockwool), and if that still isnt enough, maybe some butyl rubber or mass loaded vinyl sound deadening mat. that stuff tends to be a lot more expensive though
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Another angle to add to this: is it one neighbor or several? If the former, can you put someone’s van/SUV/other-car-I-guess in between the router and their living room? It’s not a substitute for the above recommendations, but it’s free and easy to spam down fast.
I’d also take heed of @CIM’s suggestions; teeing up the router the night before so you can mash start early and be done early would go a long way.
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This is what we did when I worked for Kohler’s generator division --we used sheet metal instead of plywood but the interior was just foam to suppress the noise.
Maybe you can put some foam on your garage door itself too to absorb some of the noise. I guess it depends on if you’re actually breaking any noise laws and how much you like the neighbor(s) for how much effort to put into it.
Machining outside is going to make some noise. I’m not sure where you’re located temperature-wise, but can you leave the machines inside and move your work outside? Honestly, with how much a good CNC weighs, I’d rather not move it around all that much…
For reference, we got our Omio last spring. Over the summer, it was on our main build table in the middle of the shop, and the noise was terrible - hearing protection recommended for anyone in the shop while it was running. Once we got a dedicated table built for it and moved it into the corner, the sound became much more bearable (probably related to reflections off the walls and previously just being in a terrible acoustic location). We have short polycarb walls on all sides (about 18" tall) to help contain debris, but otherwise it’s open. My Apple Watch only registered noise warnings (>80 decibels) when the compressor sitting below it kicked on. So, loud enough to be noticeable, quiet enough that you can hold a conversation right next to it - aka better than most FRC events! We are planning on enclosing the area below it, to try to contain the compressor noise a bit.
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