By Martin Harris.

DIY Dust Separator: Three Builds for a Shop Vac

The easiest DIY dust separator for a shop vac is a cyclone kit mounted on a 5 gallon bucket. The cheapest is a Thien baffle lid you cut from plywood. The third build, a two-bucket stack, fixes the most common failure of both: a bucket that caves in under suction. All three sit between your tool hose and your shop vac and catch most of the dust before it reaches the vac filter.

A separator pays off quickly on a vac. Fine sanding dust loads a vac filter fast, and suction drops as it loads. With the dust landing in a bucket, the filter stays cleaner and suction holds up longer through a session. Below is how to build each one, the parts you need, and where each one falls short.

What every shop vac separator needs

• An airtight seal. Oneida Air Systems says the container must seal airtight for best performance, and suggests foam gaskets or silicone caulk. A leak pulls in outside air that skips the separator.
• A container that holds its shape. Oneida says a shop vac pulls more than 60 inches of water column (in. w.c.), which is a measure of suction pressure. It says a 5 gallon bucket needs at least a 90 mil wall (0.09 in.) to resist collapse, and that big box store buckets are too thin. A mil is one thousandth of an inch.
• Ports that match your hose. Shop vacs usually come with 2.5 in. cuffed hose ends. Measure yours before you buy fittings.
• Short hoses. Every foot of hose adds resistance, so keep the hose from the separator to the vac as short as it can be.

If you are still shopping for the vac, my picks for the best shop vac for woodworking list the vacs I would pair with a separator.

Build 1: bucket lid cyclone kit

This build uses a store-bought cyclone that you mount on a bucket yourself. You buy the hard part, the molded cyclone, and supply the bucket. A cyclone spins the air so dust hits the wall and falls into the bucket, while cleaner air leaves out the top to the vac. Two common kits:

• The Dust Deputy 2.5 DIY from Oneida. Its ports are 2.25 in. inside diameter and friction fit standard 2.5 in. vac hose cuffs. The kit includes a gasket and mounting hardware, with no bucket. It stands 15.5 in. tall. For vacs with ports of 2 in. or smaller, Oneida recommends the original Dust Deputy DIY instead.
• The Dustopper PRO, a low-profile separator that fits standard 5 gallon buckets. It seals to the bucket rim with a hollow-core EPDM rubber gasket and comes with two sweep elbows and a 36 in. hose for 2.5 in. vac and tool ports.

1. Pick the bucket. Use a 5 gallon bucket with at least a 90 mil wall, or build the two-bucket stack described below.
2. Mount the cyclone. For the Dust Deputy, cut a hole in a bucket lid to fit the cyclone base and attach it with the included gasket and hardware. The Dustopper goes on the bucket in place of a lid.
3. Seal it. Run silicone caulk around any gap you can see at the mounting screws or the lid edge.
4. Hook it up. The vac hose goes on the top outlet. The tool hose goes on the side inlet.
5. Check for leaks. Run the vac and listen for hissing at the lid and ports.

Pros

• The quickest of the three builds, with only a few cuts.
• A molded cyclone with published performance. Oneida says the Dust Deputy 2.5 stops 99% of dust from reaching the vac filter. On my separator page, the Dust Deputy Deluxe caught 96.5% of fine dust and the Dustopper PRO caught 92.5% on a 2.5 in. shop vac setup.
• Catches more fine dust than the Thien baffle lid in Build 2.

Cons

• Costs the most of the three.
• The Dust Deputy adds 15.5 in. of height on top of the bucket.
• Still needs a thick bucket, or a stack, to hold up under vac suction.

If you would rather skip the DIY part, the Oneida Dust Deputy Deluxe comes with the bucket. And if you are unsure whether you need the shop vac size or the collector size, my Dust Deputy vs Super Dust Deputy guide sorts that out.

Build 2: Thien baffle lid

A Thien baffle lid is a plywood lid with a slotted disc hung a few inches below it. Air spins in the space between the lid and the disc, and dust drops through the slot into the container. The disc keeps the spinning air off the dust that has already settled. Phil Thien designed it for his own shop vac and posted the numbers on jpthien.com. These are the ones to copy for a vac build:

• 2.5 in. inlet and outlet ports, with the outlet at the dead center of the lid.
• An inlet elbow about 3/4 in. from the container wall, blowing along the wall.
• A baffle cut to the container's inside diameter about 3 in. below the rim, and hung at that depth.
• 120 degrees of the baffle left at full size, and 240 degrees trimmed 2.25 in. smaller in diameter, which leaves a 1-1/8 in. drop slot along the wall.
• Spacers cut from 1/2 in. ABS pipe to hold the baffle under the lid.

A builder named dbhost, who posted plans on Thien's forum, runs the outlet tube 1.5 in. below the lid on his shop vac unit. My guide on how to build a Thien baffle walks through the layout, the cuts, and a full materials list, step by step.

Pros

• The cheapest of the three. It uses plywood or MDF and plumbing fittings.
• Low profile. Only the lid and fittings sit above the container.
• Thien says you can fill to within 3 in. of the top, the bottom of the baffle, without losing separation.
• It scales. The same layout works on a steel trash can or a drum if you move up in size later.

Cons

• Takes an afternoon of careful layout, cutting, and sealing.
• How well it works depends on how well you seal it.
• Holds back less fine dust than a cyclone. In the collector-size versions on my separator page, the Thien baffle caught 94.5% against 98.0% for the Super Dust Deputy.
• In a 5 gallon bucket, the 3 in. under the lid goes to the baffle, which is a real share of a small bucket.

On a shop vac, use a steel can or a thick bucket for this build. Suction that crushes a thin bucket under a cyclone will crush it under a baffle lid too.

Build 3: two-bucket stack

Bucket collapse is one of the most common complaints about shop vac separators. The bucket sucks in and deforms under suction. The Wood Whisperer ran into it in his cyclone separator shootout, where one unit's collection bucket collapsed under suction. When a bucket caves in, the seal at the rim can open up and separation suffers.

Oneida's fix works with any lid: nest two thin buckets together. To collapse, the inner bucket has to push outward somewhere as it bends, and the outer bucket stops that from happening, so the inner one keeps its shape. That lets you use cheap big box store buckets that would fail on their own.

1. Buy two matching buckets. Get two of the same 5 gallon bucket so they nest tight all the way down.
2. Inspect them. Oneida says to avoid old, damaged, or thin-walled buckets. Skip any with cracks or dents.
3. Nest them. Press the inner bucket fully into the outer one.
4. Add your lid. Put the cyclone lid from Build 1 or the Thien baffle lid from Build 2 on top, and seal the rim.
5. Empty it. Lift the inner bucket out to dump it, then press it back in all the way before you run the vac again.

Pros

• The cheapest fix for bucket collapse.
• Uses common buckets you may already have.
• Works with either lid.

Cons

• It is only the container. You still need a lid from Build 1 or Build 2 to separate anything.
• A single bucket with a 90 mil wall does the same job with one bucket to handle.
• Worn or cracked buckets can still fail, so check them when you empty.

For more on bucket wall thickness, liners, and drums for bigger separators, see my guide to dust collector bins, buckets, and liners.

Which build to choose

Sources: Oneida Air Systems product pages and FAQs; Dustopper product listing; J. Phil Thien, jpthien.com; The Wood Whisperer cyclone separator shootout.

My pick for most small shops is a combination. If you sand a lot, put a Dust Deputy 2.5 DIY on a two-bucket stack, since sanding makes the fine dust that clogs vac filters. If you mostly clean up chips from sawing and routing, a Thien baffle lid on a two-bucket stack costs the least.

Using a shop vac separator day to day

• Empty early. Keep the pile below the baffle or well below the bottom of the cyclone, or the spinning air picks dust back up and sends it to the vac.
• Look in the vac now and then. A lot of dust in the vac means a leak or an overfull bucket.
• Protect your lungs when you dump it. Fine dust puffs up as it pours. Wear a fitted respirator and dump the bucket outside when you can.
• Watch for static. Oneida sells anti-static Dust Deputy versions, which it says carry static charge away to prevent shocks.

For every separator I recommend, including ready-made units, see my best dust separator roundup. For the whole picture, from tools to filters, read my complete guide to small shop dust collection.

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