Air Tool Silencer

**Blu_Rock** · 26th August 2012, 10:52 PM

I picked up a used ABAC 3hp, 340 ltr/min compressor a few weeks ago for $450. Not a bad price as it had only seen a bit of use and they go for about $1100 new. I rushed down to Masters and picked up a die grinder for $30 and hooked it up and let it rip. To my surprise, it was loud, and I mean very loud. I've got a sound level meter and it was pushing out 115db, way too loud for use in the burbs... if you want to keep the neighbors at bay.

A bit of a Google revealed that silencers are available to quieten air tools to acceptable levels. However, I'm cheap and also enjoy making stuff so I thought I'd give it a go making my own.

The materials I used were a compressor hose fitting, a bit of brass rod, some round stock, a bit of round of tube that came off an old tread mill and a couple of green scourers for the stuffing. I cut the tube to about 60mm long, made two end caps from the round stock, cut the fitting in half and joined the two halves together with brass rod. I drilled six vent holes in one of the end caps to allow the spent air to escape. I cut the scourer down so that it would fit inside the tube when rolled up and then assembled the silencer.

Now running the die grinder only produces about 90db, a massive 25db reduction in noise. It was getting a bit late so I did not try it out but will later in the week. I'm not sure whether the quietening has come at cost of reduced power, that I suppose is related to RMP? I will remove the silencer and clock the speed of the tool without the silencer fitted and then check it again with the silencer fitted. If there is too much difference and the grinder lacks adequate power, I will add some more vent holes and/or remove some of the stuffing.

**QC Inspector** · 27th August 2012, 10:31 AM

I applaude your effort to silence the beast. Checking the rpm alone may not be enough as the tool may still come up to speed but when loaded, bog down. Any way of applying some friction to it while checking the speed?

Pete

**Blu_Rock** · 27th August 2012, 10:12 PM

Hi Pete. Thanks for the suggestion, I will also load it up while checking the speed.

**nearnexus** · 28th August 2012, 10:56 AM

Nice looking machining, however I would have done it differently.

I wouldn't use that green packing as it will slow down air flow.

Instead I would replace it with about 5 thin drilled discs (baffles) much the same style as for your muffler outlet.

Place these about 5 mm apart down the full length of the centre tube.

You can also alternate the style (eg. move the venting holes /use a notched edge)

This is basically how a silencer on a rifle works.

Doing it this way you can reduce the length and maintain full air flow.

My similar looking die grinder gets by with just a simple plastic finned muffler on the air outlet. Works OK, but still a bit noisy.

Rob

**jack620** · 28th August 2012, 12:07 PM

What you have made is very similar to what the Brits use for silencing their air guns (air gun silencers are legal in the UK). They use the scotch brite pads that you have used, perforated discs as mentioned above or a combination of the two.

Having said that, an airgun silencer has to deal with one big shockwave whereas your muffler has to deal with a continuous flow if air. From what I've read on the subject a LOT of tuning is required to get optimum silencing. For your application, near enough is probably good enough.

Personally I think you are on the right track. If you decide to add perforated baffles as suggested, you can separate them with cymbal felts. Make the spacing between each baffle different so that each chamber muffles a different frequency. A search of "airgun silencer internals" on Google Images will throw up a million designs.

Chris

**Blu_Rock** · 3rd September 2012, 09:01 AM

Thanks for the suggestions Rob and Chris. I will probably eventually get around to trying a metal disc setup because I'm thinking that the air tool oil will eventually clog up the scourer whereas a baffle system will be maintenance free.

**seafurymike** · 3rd September 2012, 09:11 AM

That's a great idea, but I also wanted to make a silencer for the compressor inlet. On my machine the thing makes so much noise. I'll be interested to see what you come up with and I'll apply the basics to my compressor.

Keep up the good work

**Blu_Rock** · 3rd September 2012, 09:44 PM

Thanks Mike. I am also thinking about an intake silencer for the compressor (compressor now runs at 95db), but that one is a fair way down the list

**Gerbilsquasher** · 4th September 2012, 06:51 PM

Just make sure that you use the full title "compressed air silencer" in future conversation because firearm silencers are illegal in this country and some over-zealous busybody will have the SOG raiding your house at 3am

LOL!

**Blu_Rock** · 4th September 2012, 08:27 PM

Thanks for the advice, I'll have to take to wearing PJs again... don't want to shock them if they come storming into my bedroom at 3am

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