A dry washer is a piece of equipment that is used to separate gold from sand with pulsations of air coming up through a porous cloth medium. This allows the gold to settle downward and get caught. It is the gold prospecting equipment of choice in dry desert areas. The vibrations and flow of air replace the function of water in the normal sluice, allowing the gold to settle downward. Screened gravel passes down an inclined riffle box with cross riffles. The bottom of the box consists of a thin, light weave canvas or some other fabric through which moving air passes upward.
There is question that dry washers are a type of gold prospecting equipment that you just have to have if you're working in the desert, but the prices are really high. In addition, at least for the bellows type dry washer, they are not that hard to make. It really has only been in the last 40 years that you could buy pre-made dry washers quite easily. For a hundred years before that generally most dry washers were home made affairs designed and built in the gold prospector himself. If you'd like to be a part of that great tradition of prospectors, read on.
First, the bulk of what homemade dry washers are made of is wood, so standard home wood working tools are sufficient for all but the riffle tray. I prepared some general plans for an average puffer type homemade dry washer, and they can be seen on my website (see below). You can adopt and use these plans, or use them as a starting point and design your own dry washer. To build one, you need to think about how you will build your particular unit, and what design ideas you want to use on your own homemade dry washer. There are also commercial units on the market, and it can be helpful to take a look at them when thinking about your own design.
The first design concept you need to think about is the air source. Do you want to build a bellows puffer, or a powered blower type of unit. Both work well, but the puffer type is plainly easier to build. Because of this, I recommend a Puffer type dry washer if this is the first one you are building. Remember that dry washers are built such that you could always modify it in the future to switch from a Puffer type to a blower type if that's what you eventually decide you really want to do.
No mater your design, you will need the following construction materials: wood, metal, cloth, screws, screen. I suggest 3/8 inch weave for the material screen - half inch would probably be OK, but I suggest 3/8 inch as best. Too large a size and those larger rocks will help push gold out of your sluice, and if too small and you may loose a nice nugget if you dig one up.
You will need standard working tools. See my web page about obtaining the tools you will need. I have done up a page on hand tools for this type of project, you can check it out on my website.
My best suggestion if you want to start fabricating mining equipment (and keep the stuff you have in good repair) is to purchase a small welder. In fact, I so strongly recommend that you consider buying one of these welders that I have done up a whole web page on it. If you are seriously considering building your own dry washer, you check it out on my web page.
A dry washer consists basically of two connected boxes, and upper box and a lower one. The upper box is really just a hopper you can feed gravel into. The material too large for the screen falls off the screen as "oversize". The exact dimensions of the upper box are not that critical, but you don't want it to be too big or too small. The lower box contains the bellows or blower as well as the riffle set up.
You shovel onto the screen until the upper box is full, then with a puffer type, you step to an upwind location and pull the cord to make the bellows puff. The material then works its way down through the hopper, and across the sluice riffles. When the hopper is empty, you start shoveling again until it's full.
Make sure the screen you purchase for the upper box is durable and that on the hopper it is well supported from underneath. If you toss too many big rocks onto a poorly supported screen it will simply bend and break. That is something that can be fixed, but when you are out in the field, it can be very inconvenient. A couple quarter inch diameter steel rods can be very helpful support for the screen.
The gold catching riffles in the lower box of a dry washer are different than those on a water sluice. The design on a water sluice box is that the gold is retained downstream of the riffle. On a dry washer, the gold is designed to be held on the upstream side of the riffle. The riffle tray is one of the things that really need to be put together by welding. I suppose small bolts would be a possibility, but welding would be much superior. Welding up the removable tray does not take that much work. On the underside of the riffles is a light weave muslin cloth that allows the air to pass upward through it. The riffles need to be a movable tray, so that periodically (usually every hour or two of run time) the riffles and the concentrates can be removed and put in a bucket for later processing. In addition, with the puffer type, dust gets sucked into this lower air box and it needs to be cleaned out from time to time. Check out the welding page noted above for more details.
On the underside of the lower box is where the air comes in. If you use a blower, this is where the duct enters. If you are making a puffer / bellows type dry washer, this is where the bellows will go. Good heavy canvas makes a good bellows. Material that has been rubberized or made waterproof is best. You also need a flapper so that air can go in and go out only through the riffles. The one way flow flapper is usually just a piece of 1/8 inch rubber covering a hole about 4 inches in diameter. The bellows are hinged on one side and a pull cord is attached to the end opposite the hinge. Pulling on the cord puffs the air through the riffle cloth. See the photos on my website for further detail. Its helpful if the support legs on the lower blocks are adjustable in some way, as the ground surface in the gold fields is often very uneven.
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