Drop Riffle Design

[Duckshot]

I have been screwing around building wooden drop riffle sluices for use to catch fine gold. The riffle design I have found to work best so far is about 3/4" wide and 1/4" deep on the edges with a 1/8" x 1/8" step or rise in the middle. You can see the black sands go over the leading edge of the step and get thrown back and forth over the step while the slice is running. I classify once, about four mesh.

Sorry, no pictures. but I built a 3'6" sluice with twelve of these drops and will be trying it out this week in northwest WI at Nugget Lake. I will try to post up the results.

Anybody else using a drop riffle sluice with a ridge in the middle of the drop?

 

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[KevinInColorado]

Hard to visualize what you've done but go look at the Angus Mackirk website ...your ideas sound similar to some of their compound drop riffles.

 

[Duckshot]

Too much rain at Nugget Lake, the creeks are flooded.

K.C., the standard drop riffle would be a square or rectangular dado crosscut into a board. The riffle I am trying is a series of 1/4" dados all in a row to make one 3/4" wide riffle. The first cut is the middle one, then two deeper dados are cut on each side of the first cut.

Sorry for the carpenter's terms. I am not a photographer. I just make boxes.

Edit, from one end to the other the row of 1/4" dados would be maybe 3/8" deep, then 1/4" deep, then 3/8" again.

 

[goldenIrishman]

I'd suggest making one with different width riffles mixed together in the same box. If one size doesn't catch the fines, then one of the others will. I'm going to have to make me up a new box soon and am thinking of using that "Trex" material instead of regular wood. The wood ones have a tendency to warp over time and I'm thinking that the "Trex" won't. You can still work it with a router too.

Fortunately I speak "Carpenter" and can see what you're talking about in my mind with no problem. My current design starts with a 1ft. section of ribbed mat then goes to a washboard of "VVVVV" routed into the bottom of the box. After that I have a nugget trap formed with a 1/2" box bit and a 1/4" straight bit run down the middle. Then it goes to 1/2" X 1/2" riffles for 18" or so then finishes with 3/4" X 1/2" deep riffles to the end.

When I first started off up in this area, I was using my highbanker recirc system but quickly learned that it clogged up with black sand after about a half buckets worth of materials. This resulted in flat boarding and a loss of gold. The drop riffle design eliminated that problem and I've been getting everything from fines (-100 mesh) to nuggets again. I know there's a difference in materials between Arizona and your location, but physics are physics no matter where you're at.