A sandblaster is not exactly a common shop tool for those of us who consider ourselves to be woodworkers. Nevertheless, many of us also do other types of DIY projects, where owning a sandblaster would be extremely convenient. There’s no better way of removing rust from old tools that are being refurbished or to clean up engine castings when rebuilding a car.
For the woodworker, a sandblaster can be used, with care, to strip paint off of old furnishings, especially where the underlying surface is carved. While that might seem a bit extreme, it all depends on the blasting media used. Some are much more aggressive than others. That’s how sandblasters can be used to etch glass, a nice accent for use on glass doors. The right blasting medium will even allow wood to be artificially “aged,” looking like it has been worn down by the effects of the wind over years.
Looking at this, it’s clear that there is plenty of good reason for a woodworker to have a sandblaster in their shop. But most of us have a longer wish list of tools, than we have money in our tool budget. So, while the sandblaster may remain on our wish list, that’s about as far as it usually gets.
But the sandblaster itself really isn’t all that expensive. Small units, with a built-in hopper go for as little as $20. A pressurized pot can even be bought for about $100. The expensive part ends up being the sandblasting cabinet, especially if one is needed which will allow for sandblasting good sized articles. It’s easy to spend over $1,000 when that’s what’s needed.
Sandblaster cabinets are usually sized by the door opening, as that’s the critical dimension. If the part won’t fit through the door, then it really doesn’t matter how big the cabinet is. But since the door is usually the width of the cabinet, the door size and the cabinet size are pretty much the same.
For those of us who can see the need to have a sandblaster in our shop, but don’t really want to spend a lot of money, there’s another option; building the cabinet ourselves. This is a great plywood project, which can be made in an afternoon.
Requirements for a Sandblast Cabinet
The major purpose of any sandblasting cabinet is to capture the blast media, so that it doesn’t get blown all over the place, making a mess. Some sandblasting is done with the media suspended in water; making a requirement for the sandblasting cabinet to be waterproof as well. However, the majority of sandblasting is done with dry medium, making this requirement unnecessary.
While a sandblast cabinet should ideally be airtight, most are not. At least, they’re not once they’ve been in use for a while. So, as long as the cabinet is built somewhat airtight, so that it will capture almost all of the blast media, it’s acceptable. Of course, the more airtight the cabinet can be; the better.
What makes it hard to make a sandblast cabinet airtight is that it needs to have several openings in it, to make it useful. These include:
- Window to see the work through
- Gloves for the user’s hands
- An air hose inlet
- Someplace to empty the blast media out of the cabinet
- A filtered exhaust vent for the air to escape the cabinet
Typically, commercially manufactured sandblast cabinets have a sloped bottom, with all four sides sloping steeply to the center. This is done to make collecting the media easier. However, it’s considerably harder to make a cabinet like this. We’ll look at a simple alternative.
Instead of a filtered exhaust vent, an air outlet can be installed, connected to a dust collection system. This helps reduce the dust getting out of the cabinet and into the air. However, it requires having a dust collecting system. We’ll also look at an alternative, modifying a common shop-vac to work as a dust collector, without clogging up from the blast media; and while allowing the blast media to remain clean for reusing.
Building the Cabinet
For the sake of simplicity, we’re going to build a flat-bottomed sandblast cabinet, rather than one with a sloping bottom. Designing and cutting the compound angles needed for the normal sloped bottom, leading to a collection port, adds a lot of complexity to the project. If the sandblaster is being used all the time, I suppose that would be worthwhile. But in the case of one that may be used occasionally, it’s a lot of extra work.
The main design criteria are the overall size needed, in order to fit the parts to be blasted. This is somewhat limited by the reach of the operator, while using the cabinet. Having a cabinet that is four feet deep doesn’t help much if the person using the cabinet can only reach in about 18 inches.
Generally speaking, if more than 18” of space is needed, due to the size of the parts to be sandblasted, the cabinet is made wide, rather than deep. Rarely is extra height added, unless it is an automatic sandblaster, of the type which might be used in an engine rebuilding facility.
The other criteria to think of is the window. The larger a window that can be put in the cabinet, the more that can be seen while sandblast. Typically, pretty much the entire sloped front of the cabinet is turned into a window, leaving only a frame. This needs to be positioned at a height which is comfortable for the operator.
In order to locate everything at a comfortable height, the height of the cabinet above the ground needs to be taken into consideration. Whether it is set on a table or mounted on a stand, the height is an important design criteria. For most people, setting it on a stand makes more sense, leaving workbench space available for other things. Moving a sandblast cabinet which is partially full of blast media is extremely difficult.
While a sandblaster cabinet can be made literally any size, the dimensions below are for a 3’ x 3’ cross-section, with a cabinet that is 4’ long. That allows it to be cut from a single width of plywood and will be big enough for most projects. But the main purpose of the drawing is to show the dimensions above the floor level. The dimensions shown for the bottom of the cabinet, the glove and the center of the window are considered ideal for an average sized man.
For the sake of the diagram above, the angled panel is both the window, allowing the user to see the part they are sandblast, and the door for putting parts into the sandblaster cabinet. However, there are two other options for doors:
- Cut a door into one end of the cabinet, hinging it on the back side for access
- Turning the panel with the window in it and the one with the gloves in it into a double-hinged door
It is possible to make the sandblaster cabinet out of plywood as thin as 1/2”. However, that wouldn’t be all that stable. For a stronger cabinet, it is better to use 5/8” or even ¾” plywood. It is not necessary to use high-grade plywood, as common CDX construction grade plywood will work. Anything more expensive would be a bit like gilding a lily.
The easiest way to assemble the cabinet is to use butt L joints, gluing and screwing them together. Be sure to clamp the corners together, drill pilot holes and countersink them to prevent the plywood from splitting when the screws are installed and ensure that the screw heads are below flush. Do not attach the panel with the glass, that will also be used as the door.
In the case where a double-hinged door is being installed, rather than just hinging the section that contains the glazing, then a strip of plywood or 1”x 4” should be attached across the bottom of the opening, to catch the blasting media and prevent it from spilling out when the door is opened.
Seal all the joints on the inside with silicone caulking to help make the cabinet as airtight as possible. It is not necessary to paint the cabinet and sandblast would probably be detrimental to the painted finish anyway.
Installing the Glazing
Before cutting the glazing material, it’s a good idea to first cut out the window in the piece of plywood that is going to form the door. Leave at least three inches of plywood all the way around to ensure structural stability. Cut the window out by first cutting the corners with a hole saw or forstner bit and then cutting the lines between the holes with either a jigsaw or a Rotozip. If a Rotozip is not available, the bits can be used with a small cordless router, inserting a 1/8” collet into the ¼” collet that is normally in the router.
There are several options available for glazing the window in the cabinet. Glass, tempered glass, Plexiglas or other plastic glazing materials can be used. Since this is going to be in a workshop, it is probably best to use a plastic glazing material, as that will be less prone to breakage, even though it will be more prone to scratching.
Plexiglas, or acrylic plastic is the lower cost option for this. The only problem when working with acrylic plastics is that they are brittle; so they can crack when drilling hole and may not cut cleanly. Nor does it always cut cleanly with many types of saws. However, it can be easily cut by scoring the cut line several times (6 to 12) and then placing that cut line on the edge of the workbench to push down and snap the line clean, breaking the piece to size.
It’s a good idea to install the window with a hold-down strip, as just screw through it, into the plywood door, will add strength, reduce the chance of the plastic cracking and help seal the edges tightly, reducing dust leakage.
Attach the door/window to the cabinet at the top, with a piano hinge. Add self-adhesive foam weatherstripping around the edge of the door, to help prevent dust leakage. A latch is not required, but it’s a good idea to install one anyway, as that will put more pressure on the foam weatherstripping, helping it to seal better.
Attaching the Gloves
The purpose of the gloves is to allow the user to stick their hands in the sandblast cabinet, without allowing any of the blasting media to escape. Therefore, the connection needs to be airtight.
Start out with a pair of heavy-duty rubber gloves. They must have a long sleeve, or they will limit movement and reach inside the cabinet too much. These are available from industrial supply houses and from Amazon.com.
The other thing that’s needed is flanges to go into the side of the cabinet, in the vertical panel located below the window. How big these flanges are depends on the diameter of the glove’s sleeve. In most cases, a four inch diameter flange will be sufficient. That can most easily be found by buying 4” toilet flanges in the plumbing department of the local home-improvement center.
However, a 5” flange might be too narrow for some people’s hands. Five inch and six inch flanges are also available, but will need to be purchased from an industrial supply house, like grainger’s. Since they are not as common, the price will also be higher.
Cut a round hole to fit the flanges, either using a jigsaw or the aforementioned Rotozip. The flange should fit inside the hole, and be attached from the outside. Once installed, the gloves can be attached to the flange with duct tape.
Running the Air Hose In
There needs to be an access for the air hose to run into the cabinet as well. There are two basic ways to do this. The first and easiest is to drill a hole in the side of the cabinet, large enough for the hose and coupling to fit through. However, this leaves a gap around the hose, where dust and blasting media can escape. A better option is to install a bulkhead fitting into the side of the cabinet.
Brass bulkhead fittings are available from industrial supply hoses for the side of the cabinet, which are sized appropriately for the ¼” NPT thread that is used for air hoses. This should be installed roughly half way up the side of the cabinet, giving the most flexibility for movement of the sandblaster gun inside the cabinet. A short, but very flexible air hose will be needed (3 to 4 ft.), to go from the bulkhead fitting to the gun.
Adding a Cleanout
Earlier on in this article, I mentioned that we were building a flat-bottomed cabinet, rather than one with a sloped bottom to catch the blasting media. However, it is still necessary to be able to clean out the blasting media, both to keep the cabinet from filling up and to be able to reuse the media.
The easiest way to do this is to install another 4” toilet flange in the middle of the bottom of the sandblaster cabinet. Attach the flange from the outside, so that it will not cause a ridge in the bottom of the cabinet. Extend the flange slightly with a piece of 4” PVC pipe and then put a threaded cap on the end, being sure to leave enough room below the threaded cap to put a five-gallon bucket under it.
One precaution here is to clean the sandblast cabinet out frequently, rather than allowing it to fill up. If too much blasting media is in the cabinet, when the cap is removed, it will probably overflow the bucket and spill all over.
Air Filtration and Dust Collection
Since air is being pumped into the sandblast cabinet, air will also need to come out of the cabinet. The easiest way to accomplish this is to install a rectangular air filter from a car into the back wall of the sandblaster cabinet. Cut out a hole which will allow the silicone gasket that’s integral with the filter to fit snug, without the filter deforming. Then install the filter into the hole.
Ideally, the filter should be installed from the inside, not the outside, as air movement will be from inside the cabinet to the outside. Placing the filter near the top of the cabinet will reduce the chances for it to become damaged by items inside, as well as helping ensure that it is dust, not blasting media, which is hitting the filter.
To hold the filter in place, cut out a rectangle of plywood to act as a clamp flange. The inside of this rectangle should be the size of the filter area, while the silicone edges are captured by the plywood flange. The sides of the flange should be at least 2” wide to give it strength. As the filter doesn’t need to be changed often, but can just be blown out with air, the flange can be installed with screw.
Going a Step Further
Professional shops which use sandblasters regularly attach their sandblasting cabinet to a dedicated dust collection system. However, even if the woodworking shop in question has a dust collection system, it would be ill advised to attach the sandblaster to it. Not only would it tend to fill up the dust collection system rapidly, but it would mix sawdust with the blasting media, making it more or less impossible to reuse the blasting media.
However, a simple dust collector can be made from a Shop-vac and a couple of five-gallon buckets. The main reason to use both is so that the Shop-vac doesn’t fill up with blasting media, which would, once again, end up mixed up with the blasting media. The two five-gallon buckets can act as a dust catcher, with the Shop-vac providing the suction.
In order to make the two buckets fit together, the top couple of inches of one of them will need to be cut off and the handle removed. These buckets typically have four rings of plastic around the top. Simply cut off the top two rings, cutting through the side of the bucket just below the second ring. Once deburred, this should fit snugly inside the open mouth of the other bucket, forming a seal.
This same bucket will need the intake and outlet vents cut into it. The outlet should be right in the center of the bottom of the bucket and is where the hose from the Shop-vac will attach. Install the appropriate sized PVC fitting through the bottom of the bucket here, with a rubber collar that the Shop-vac hose can attach to. It will probably be necessary to start out with a rubber cap and cut a hole in it that will fit snugly around the hose.
For the input into the bucket, the outside needs the same sort of fitting as the connection for the Shop-vac, with a rubber seal. On the inside of the bucket, it will be necessary to attach a couple of elbows together in such a way as to ensure that the stream of media coming into the bucket is directed around the inside of the bucket, rather than going straight down. If it goes straight down, it will stir up whatever is sitting there. By making it go around the outside, it will lose its velocity before falling to the bottom. That will ensure that the media settles to the bottom of the bucket, where it can then be collected.
This same sort of system can be used for collecting sawdust in the workshop, but in that case, a second one should be built. That way, the sawdust and blasting media will be in separate dust collectors, even though both can be powered by the same Shop-Vac.