4gal Shopvac Cartridge Filter Mod

Description:

The 4 gallon Craftsman shopvac comes with a sock filter and no provisions for installing a cartridge style cylindrical (cannister) pleated filter. My local hardware store had a large HEPA filter in stock so I decided to make it fit.  

I modelled a lugged adapter that inserts into the slot in the bottom of the filter cage. You insert it and turn it to lock it in. The lug accepts a 10mm nut in the bottom - it's a tight fit so I had to use a mallet to insert it all the way. I printed it in PETG-CF but PLA would probably also work.

There is also an adapter for the other end of the filter that centers it on the base and seals it. I forgot to take a photo of it but I included a photo of a failed print of a TPU version I experimented with. Turns out since the filter gasket is soft rubber it's better to print this adapter in hard plastic - again I used PETG-CF. I gave it a wrap of a single layer of electrical tape, overlapping onto the filter base to help prevent air/dust leaking under any tiny gaps between the adapter and the base. The adapter fits very tightly so it may be tough to slide down to the bottom, but you just have to kind of shimmy it down - after filing off any elephant foot over extrusion on internal diameter of the first layer.

Installation Steps:

1. Install the 10mm nut in the lug, then insert it into the filter cage and twist it to lock it in.  You'll need to trim the lip on the bottom of the filter cage off as shown in the photo, or else the filter cap will not seat deep enough into the filter. I just used the close cutters that came with my Ender 3 and snipped it away one piece at a time.
    
2. Slide the filter adapter over the base as shown in the photo. Slide the filter on next, it should be a tight fit against the adapter (especially with the extra friction from the electrical tape against the rubber gasket on the filter) but again, shimmy it down - it should slide all the way down to the shoulder on the base. 
    
3. Then you must modify the cap that comes with the filter as shown in the photos - drill out the center to let a bolt reach through to the nut in the lug. You'll need to use an appropriate length bolt since if it's too long it'll bottom out against the filter cage before tightening the filter down. I happened to have a bolt I removed from an old eSun filament spool, which is also where I got the nut. 
    
4. You'll also need to cut away some of the ribbing around the hole to make room for a washer - the washer is necessary to distribute the force on the cap so that it doesn't just warp the small section of plastic around the hole, since the point is to transfer that force to the filter and press it down so it seals well. I had to use two sizes of washers just due to the larger washers I had on hand having too large of a hole for the head of the bolt I was using - but if you buy the right washer this is unnecessary. I also added two extra washers due to my bolt being a bit too long, but again the right sized bolt won't require this.
    
5. Then push the cap into the bottom of the filter, put the bolt/washers in and tighten it down. You're good to go!

Notes: 

The large filter I used reduces the capacity of the little 4 gallon collection tank - it takes up a lot of space inside. So I'll have to empty it more often. But I figure since the vac was made for a sock filter and the HEPA probably has more resistance per unit of surface area, the extra surface area of the larger filter may help counter that. Plus it was the only size HEPA they had at my local hardware store. You can likely use the lug model for similarly adapting a smaller filter as well, you'll just need to adjust the scale of the filter adapter. The vacuums internal base for the filter has a stepped shoulder design so it looks like it can accommodate multiple filter diameters - but you might need to use a different length bolt or make other modifications since I'm not sure how the cage and lug will line up with the end of the filter.