Sandblasting Cabinet Design
Author: Bob Pickard
Published: September 24, 2002
Revised: August 03, 2005
There are four basic elements to a sandblasting system:
This article will deal with the fourth part of the system, the blasting cabinet. Links to manufacturers of blast cabinets can be found under resources here.
Blasting cabinets come in all sizes and shapes, depending on the particular application of the user. There are top load, front load and end load designs. There are cabinets with vertical, horizontal and 45 degree viewing windows. Some cabinets have flat bottoms, designed to sit on table tops, while "V" bottom cabinets are self supporting with legs.
Small cabinets are ideal for blasting coffee cups, wedding glasses and trophies. Medium sized cabinets can blast larger glass, rocks, and vases. Large cabinets are used for shower doors, plate glass windows, transoms and door inserts. There are cabinets with pass through capabilities of blasting glass larger than the size of the cabinet. Some cabinets even have blasting units built into them. Some cabinets even have built in dust collection systems.
With all these options, how does one decide what to buy? This article will cover what to look for to fit your particular need.
Blasting cabinets are constructed from wood, plastic or sheet metal. I have even built a temporary blasting cabinet using a cardboard box. If you are going to construct your own cabinet, plywood is the preferred material unless you have sheet metal working experience. To build a cabinet from plywood, all you need is a keyhole saw, table saw, and hand drill.
Most cabinets on the market today are constructed from sheet metal or plastic. Plastic cabinets are smaller and lighter and ideal for blasting coffee cups, glasses and trophies. There are three advantages to a plastic cabinet: light weight, will not shock you when blasting with aluminum oxide, and less chance of glass breakage when you bang the glass against the side.
Metal cabinets are larger, however, and can build a static charge when blasting with Aluminum Oxide. Constantly getting shocked can be quite annoying.
A lot of cabinets have a slanted front for the viewing glass. I think this is a carry over from cabinets generally used for blasting items like auto parts, where you don't need the precision you do in glass carving. I would say that roughly 75% of cabinets used in blasting glass still use this type of cabinet. This forces you to look down at the what you are blasting, and may cause back and neck strain in some people. Since you will be spending many hours at your blast station, make sure the design and ergonomics of your station will be comfortable for YOU over the long haul.
The glass is usually 1/4 inch tempered or safety glass, required by some insurance companies. In my own shop, I don't feel the need for safety glass, because if broken, the glass would only fall into the cabinet, and with protected gloves and sleeves, the chances for injury are greatly reduced. I've gone this direction, because replacing tempered and safety glass can get quite expensive, especially if you change glass once a week while doing heavy blasting. The frosting of the viewing glass is the result of abrasive bouncing back from the glass you are blasting, and hitting the window. The window will get frosted more quickly when blasting at higher pressures.
Some cabinet suppliers have plastic material you can place on the inside of the glass to keep the glass itself from getting frosted. If the plastic cover is not completely taped on all edges, abrasive will collect between it and the glass, greatly reducing visibility. A static charge will also build up on the plastic cover, causing dust to cling.
Each time the dust is wiped off the plastic, it will leave scratches, causing it to be changed more often. I find it more cost effective to replace the viewing window with single strength window glass, rather than using plastic.
Because you will be changing the viewing glass quite often, you should consider how easy or difficult the change out operation will be.
Some times, it is very important to get as close to the glass you are blasting as possible. I find this is important when I am doing delicate blasting on a face; the glass may be no more than 12 inches from my face. For me, this means a cabinet with a straight front, specially designed for glass carving. Unless you build your own, these cabinets can cost more, but can be well worth the price differential, since cabinets with a 45 degree front design may not let you get close enough for delicate work.
Being able to have free movement on the hands and arms is very critical when artistic blasting. Most cabinets come with rubber sleeves and gloves attached to keep from accidentally blasting yourself. These sleeves and gloves will restrict your movement in the cabinet. An ideal cabinet will allow you to blast anywhere in the cabinet with ease. Seventy percent of my blasting is done without sleeves and gloves. I only use gloves when I am blasting with pressure over 50 PSI to protect my hands from abrasive bouncing off the glass. Accidentally blasting yourself usually happens once. It's like using a cigarette lighter; only once you burn yourself, you respect the damage it can do.
I have some cabinets with just plastic strips covering the hand slot across the front of them. This type of cabinet allows total movement of hands and arms when doing airbrush technique blasting. This type of hand slot is messier, because it will let some abrasive out on the floor. This is the trade off I live with so I can have total free movement of hands and arms. I find it very difficult to artistic blast using attached rubber gloves.
Jim Yount uses gel-filled mouse pads to soften the hard edges on the hand holes in his cabinets. He finds that in long days of blasting, he tends to lean on the holes, and this can get really painful after a day or two.
The bottom design of a cabinet must be considered when choosing a cabinet. Can you sit down with your legs underneath the cabinet, or will you have to stand all the time you are blasting? Blasting on a project for 6 hours gets very tiring on the legs and feet, especially when you get "more mature", like me! A flat bottomed cabinet that I can set on a table works best for me. The disadvantage of the flat bottom cabinet is removing the abrasive. I use a dust pan to scoop it up and shift it through a strainer to remove foreign particles. Another disadvantage of the flat bottom, the blasting air causes the abrasive on the bottom to get blown up while blasting, producing more dust.
The V bottom cabinets are the most common on the market. In these cabinets, the abrasive will fall to the bottom, where it can be removed through a trap door. Because the abrasive is away from the blasting area, less dust will be produced in the cabinet. The disadvantage of V bottom cabinets is the inability to sit down and put your legs underneath the cabinet while blasting.
There is a cabinet on the market that incorporates both flat and V bottom. The front part is flat, and the back part is V shaped. The cabinet allows your knees to go under the cabinet while sitting and the abrasive falls down away from the blasting area. Jim Yount also uses this design in his shop built second generation cabinet. You can see photos of his unit on http://www.graydog.org/Equipment.htm. Note that he's going back to the straight V for his third generation unit. Jim has also incorporated a vibrating screen in his new unit, so that the abrasive has been pre-filtered inside the cabinet, before it is removed in a sealed container. If he ever gets the time, he claims he'll write an article on this new system. We'll see.
The height of the cabinet is another item you have to look at when choosing a cabinet. You want a cabinet so that your forearms will fit straight through the sleeve holes. If you are blessed with being short, you can always adjust the height by standing on a box. For tall people, it's a different story; you have to extend the cabinet's legs, or build a box to raise the cabinet to the correct height. If people of different heights are using the same cabinet, the height should be adjusted for the tallest person. It is easier to change the box you stand on than change the box the cabinet stands on.
Proper lighting is a must in any blasting cabinet, and I have used all types. If you use a florescent light, you need to make sure it is sealed to keep the abrasive out of the connections. It's very hard to change the bulb when the connections are full of abrasive. If a single incandescent bulb is used, it must be placed to give light where you need it. Some cabinets will have two lights to reduce shadow on what you are blasting. My cabinet has an angle iron across the inside top so I can use a clip on light. I can clip the light anywhere from the left to the right side of the cabinet. The light can be tilted in any direction to focus on the light anywhere in the cabinet I want. When you are doing artistic blasting, the angle of the light is very important. I use a small spot light bulb, 75 to 100w. The back side of the bulb is covered to keep the light from shining in my eyes. Warning: abrasive will collect on the bulb and get very hot. You do not want to knock the abrasive onto your hands or arms because it will produce a serious burn.
Jim uses two swiveling spots that are dimmable inside the cabinet, and a florescent fixture outside the cabinet (shining in through an overhead window) to achieve much the same effect as Bob's cabinet. In addition, Jim also uses an LED edge light fixture, attached to the glass during blasting, since most of his work is small multistage carved pieces.
Slide and Pass Through
When you are shopping for a cabinet you need to size it adequately for the work you expect to do. Many people start with blasting glasses, coffee cups, trophies and small items, so they start based on this workflow. As their business or hobby grows, they start getting requests for larger flat glass items that won't fit into their cabinet. Now it's time to consider a slide or pass through cabinet. I have seen three types of these cabinets: one has a slot in one end of the cabinet so you can put one end of the glass in. After you have blasted one half of the glass, you remove it and insert the other end and blast it. A second type has slots in both ends of the cabinet. As you blast you keep sliding the glass thought he cabinet. The height of glass you can blast in these two types of cabinets will be limited to the size of slot in the cabinet. The third type has a slot in both end and top. The only limitation you have is twice the end slot height. When you are blasting long pieces of glass, you will need some type of support to hold the glass sticking out the end of the cabinet. Some cabinets come with these supports and others don't. When you are shopping for slide through cabinets you need one that will accept 1/2 inch minimum thick glass. The material used to seal the slot against the glass must be a type that won't allow the abrasive scratch the glass. The slot must seal itself up so no dust escapes out when no glass is in it.
Custom Blasting Cabinets
Open Back Cabinet
"What If" the plate glass you are sandcarving was the back of the sandblasting cabinet? You wouldn't have to remove the glass each time you wanted to see how your carving is proceeding. If the glass was the back of the cabinet, I could simply go around the back and see the blasted effect.
This was the thought running through my head as I removed a large, deep carved piece of plate glass from the cabinet for the fifth time. The glass only weighed 30 pounds when I started, but by the time I finished, it must have increased to 70 pounds. One would think the glass would get lighter because of all the glass I had removed, not true.
Carving glass deep has always been a challenge to me, because I am not sure how it will come out. When I am working with a 30 inch by 48 inch piece, removing it each time I want to look at the back side is not practical.
One way to get around removing the glass so many times is to make the glass I am blasting the back of the cabinet. Now it's just a simple matter of walking around to the back of the cabinet and look at the glass. With the light in the cabinet shining through the carving I can see what it is going to look like hanging in a window.
The big problem is how to seal around the glass to keep the dust from escaping. This would be a large problem if I always blasted glass larger than my cabinet. It the glass stuck out on both ends and the top of my slide through cabinet, it would be sealed except for the bottom. In my flat bottom cabinet I could place some foam on the bottom for the glass to set on.
With glass smaller than the cabinet, I have to add spacers to make up the space difference. The spacers are made from 1/4 inch tempered Masonite with an aluminum H channel that fits over the edge of the glass. To take up the space for the top of the glass, one large spacer will work. For the ends of the glass different sizes will have to be used depending on the size of glass I am blasting.
Blasting small flat glass and non-flat glass in the backless cabinet, I installed a door to cover the back. With the door closed on the back, it looks like a regular blasting cabinet.
I have just added a video camera at the back of the cabinet connected to a monitor so I don't have to keep running around the back. It's not that I'm lazy, but with the camera, I can zoom in on the area I am blasting and watch as the glass is being removed. I had to get used to watching the monitor instead of watching the glass. With some practice, I should get this down. The open back cabinet and video camera has increased the quality of my sandcarving.
These are some ways I have changed my blasting cabinet to increase the quality of my sandcarving. You may want to consider the open back cabinet and video camera and how it will improve your sandcarving.
Dust Removal Ports
The cabinet must have two ports for dust remove - inlet and outlet. There must be air flowing through the cabinet; the inlet port must be adjustable to regulate the amount of air going into the cabinet. Tom Eddleman and Jim Yount both duct the air flow to opposite sides of the window, so that clean air enters the cabinet on one side, and is pulled across the window during blasting. This way, the viewing area is constantly cleaned.
In conclusion, my ideal cabinet would be 24 inches wide, 30 inches tall, and 18 inches deep with a 20 inch by 12 inch vertical viewing glass. The arm slots would be large enough for me to blast anywhere in the cabinet with ease. It would have a V bottom with trap door to remove the abrasive. The cabinet would be designed so I can put my knees under it when I am blasting sitting down. The height would be adjustable to allow people of different heights to blast in a comfortable position. The slide through slots on the ends and top could be adjusted to the glass could be moved closer to me when I am doing delicate blasting. It should have an adjustable shelf to set small items on while blasting. It would use a movable spotlight that could point at any place in the cabinet. A door in the back would be nice, so I wouldn't have to remove the glass to see the effect I am obtaining when blasting deep. If the glass I am blasting was the back of the cabinet, that would be even better. I could place a video camera in the back, and see the effect as I am blasting it.
It may be impossible to get all these features in one cabinet, but you should get as many as you can afford.
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