Drop riffle sluice (updated with video at the bottom).

[Astrobouncer]

I posted this in a more local gold prospecting forum I use, but thought I would re-post it here since this is a good DIY project, easy to make, and cost effective.

So the new big thing (besides that newfangled sidewinder sluice) seems to be the drop riffle design. Some sluices that use this design: Le Trap Sluice, California sluice box, and the Angus Mackirk Sluices use a variation on this as well. I'm sure there's more but that's all I could think of off the top of my head.

I ran out of V matting and carpeting from my last couple sluices but it just so happened that I still had a three foot piece of hardwood that would serve as a decent base board for a drop riffle design.

The pros of this design:

You don't have to classify supposedly cause the small riffles don't let big rocks drop in them.

Less water flow is needed because the water doesn't have to flow over riffles and other obstructions.

Looks like its capable of some very fine gold recovery in the shallow riffles.

Easy to clean up, just tilt it sideways and pour water in.

Not as much black sand to go through.

The cons:

Might have to cleanup sooner then a conventional sluice due to less gold holding area. This is offset by how easy it is to do a cleanup.

No inspection mat to see if your in the pay streak. However if you know an area has decent gold, I guess this doesn't matter so much.

Not as much black sand to go through, which means you might recover less gold/black sand mix.


I started with a 1/16 inch groove for fine recovery and gradually increased the depth till it goes to a full 1/4 inch depth on the back riffles. I also gradually made each second riffle wider, while keeping some 1/16 inch grooves for fine recovery between them.

The board I had wasn't perfect, it had scratches and blemishes on it from using it to bear down on, but its good enough for this project.



Here's the grooves from the side.



Here it is with all the grooves cut in it ready to start waterproofing.



Here's after the first urethane coating.



Another pic of it drying.




Since all I had to do was cut some grooves in the board to make a drop riffle sluice, this is an easy project and cost effective. I already had polyurethane and gutter sealer to make the sluice waterproof and seal the crevices between the boards.

The dimensions are 9 1/2 inch by 33 inches, which is just wide enough once I put the sides on it, to use it in a 5 gallon bucket for a cleanup. And its short enough to be back-packable.

Total cost for the sluice: 7.03$ for the can of Truck Bed Liner textured paint I used on it. Might put a couple reinforcement bars on it once the paint (fully) drys, a couple places for rocks to hold it down in the river.

Oh and I tested it already yesterday (when it was unpainted) on some of my cons from Saturday, and gold didn't make it past the first riffle. I used a couple different drop angles for the preliminary test, but I cant wait to try it out on the river.

Does anyone know the proper angle to setup these drop riffle sluices? I figure its similar to the 12 inch length = 1 inch drop that regular sluices use?

Here's the drop riffle sluice pictures.















Here it is next to some of my other homemade sluices.









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[maui]

another good looking and gold catching idea. astro, man you sure do come up with some pretty good idea's i wish i had the fortitude like you. take care and be carefull out there. ron

 

[SCBUZZ]

Looks good.

 

[Astrobouncer]

Added some structural support to it, and a shoulder strap for ease of carrying.



This sluice next to some of my other homemade sluices.

 

[maui]

looks like it is easy to carry to your spot. nice.
take care and be safe out there. ron

 

[greydigger]

Great looking job.
I was thinking about that myself.
Now you have shown me how to do it.
Thank you

Grey

 

[Astrobouncer]

I did some testing on this sluice after I finished a test for my criminal law class the other day. The tests made me decide to make some changes.

I decided to re-do my drop riffle sluice and make the drops bigger and deeper. The drop riffle sluice wasn't catching the fine gold because the fast movement of the water over the short riffles allowed the small stuff to just float on by on the top.

With the new wider and deeper riffles, as long as I keep the angle decent, the water will be forced to fall into each lowered riffle and will create a nice swirl/vortex motion, dropping the heavy stuff.

Basically, the sluice was too straight before in how the water flowed, it didn't agitate the water well. Also the smaller riffles weren't wide enough or deep enough to get that 'dancing' action going inside them, but the new ones should be perfect, because the last riffles of my old design did swirl and dance. Its not so much that the riffles have to be super deep, its more they need width with a little drop so the water will fall into them and create that vortex/swirl. The deeper the riffle (coupled with a good angle or drop) the greater the swirl effect though.

The new waterproofing, black rough coating, and the yellow weatherstripping material I used to seal the sides are all drying today, tomorrow I can test it out and hopefully the changes worked.

 

[nottinon]

Astrobouncer
Nice job on the sluices....Thai look great......Looks like you spent lots of time on them.
Is that dry material that your running true the sluice,in the video??
Don't know why,I prefer running all my materials wet.....When I classified the material,I allway's trow a bucket of water on the screen.
It seemes to work better on the Angus sluice.....Perhaps I will have a chance to run dry sand true it,in a few weeks....
N

 

[Astrobouncer]

It wasn't dry, those were some cons from my carpet sluice and it had the consistency of mud. Usually I run my cons wet also. It does appear dry from the video, but I think that's just from the blond sand that was mixed in there with the heavier black sand.

 

[russau]

i like your concept on this! i think you may want to add a rubber dampner to the head of your sluice. notice the cheveron shape of the water at the head of your box. you need to get rid of that disturbance and flaten the water to make the small stuff drop out of suspension faster. and makeing yourself a autofeeder will save you a lot of effort/time to do other things as the cons get fed into your sluice. i originally made one but it was to small.(it didnt hold enough screened cons) i made another to hold about 10/20 pounds of cons and i think it maybe to small also. i hate spooning cons into a peice of cleanup equipment. you just cant beat someone that likes to tinker!

 

[Astrobouncer]

Thanks for the idea russau, I will try that. It does need an auto feeder, but it was kind of fun feeding 3 sluices today when I was at the river. This thing feeds so well that I barely have to wait for it to clean off like my other 2 sluices.

I was super impressed with this sluice today, it performed like a champ with the new changes. I had 3 layers of cons in every riffle, the monzanite/titanium colored sand first, then black sand, then the garnets that were dancing. Occasionally a piece of gold would sink in one of the riffles and disappear under the dancing stuff, but when I did a clean up the gold was there at the bottom of the riffle. And the cleanup was so easy. I wish I had made this thing last year!

 

[greydigger]

How deep/wide are the new slots?

Grey

 

[Astrobouncer]

I believe some of the shallower riffles are half an inch and the wider ones, up to an inch. Depth is anywhere from 1/2 an inch to 3/4ths of an inch. You can see in my video how fast this thing can be fed and you can also see the riffles dancing toward the middle there. You can also make out the three stratified layers that the riffles did to themselves as I fed the material through (actually 4 layers if you count the gold on the bottom). The heavy stuff would sink and push out the lighter material, which would then get caught in the next riffle and repeat the process. Leaving only the heavies in each riffle.

My camera work was pretty bad because I couldnt see the LCD screen due to glare, so the video turned out worse then I was hoping. Next week I am bringing the tripod so the video will be better.



Edit: I made some changes to the sluice.

Here's some pics of the changes. This thing looks less like a drop riffle sluice now and more like some kind of hybrid.

Here's the 45 degree cuts to the back riffles to help flow.



Here's the new front section that helps break up clay with its turbulence. I needed this since the pay dirt I been working is found on the top of a clay layer that acts like a false bedrock. There's also an eight inch skid plate between the turbulent area and the v matting to further break up the clay.






And then just random pictures of the sluice from different angles. You can see I added a couple deep V grooves further down the sluice just to help catch heavies.







I will test it this weekend, hopefully the new changes will help it. 45 degree cuts is the limit of what my table saw can do, I really need one that can do much wider angles so I can replicate the Le Trap and Angus Mckirck sluices.

 

[Astrobouncer]

New video is up here:



Sluice worked good, especially for the price.

 

[Shake n Flake]

So, what did you capture that you hadn't before fixing it?

 

[Astrobouncer]

The changes on this one were more to help get rid of some of the lighter material and they worked well. This thing will capture superfine gold, provided you have the angle right and dont hit it with as much velocity as you would say a keene a 52. This is actually an older design compared with my new ones but it works fine. With a drop riffle system, the riffles will upgrade as heavier material comes along. So the material in the first riffles is constantly getting heavier as you add more material. I rarely find any gold past the fourth riffle, and when I do it means i'm running too much angle or velocity.

 

[63bkpkr]

Astrobouncer,
Once again you've provided us with another feast of DIY glory. The finished product with all the mods looks similar to some of your more aggressively cut drop sluices, that's with deep grooves, angled grooves. The location of the matting is different as it is down the sluice and not near the top. I will need to watch the video to see how it all worked out and to check if my memory of where the mat was at was correct.

I checked out the CaliforniaSluice site yesterday and found it interesting though I thought the depth they used on the riffles was shallow, I think you mods to yours shows that they need to be deeper. They do have nice looking equipment that is lighter in weight IF one needs to carry the sluice in a long ways with a lot of other equipment then I'd have to opt for their ABS plastic sluice and give up the ability to modify the sluice as needed.

Again, nice post with a great deal of information. 63bkpkr

 

[greydigger]

Astro -
Do you have a width VS depth formula for the slots?
I think you went with a back angle on the following edge (down-stream) for turbulence.
Also mentioned table saw not more than 45 degree cuts.
Try smaller angles on small stock and glue/screwing them on backwards.
Get the same results.

More AU to you.

Grey

 

[FiresEye]

Brilliant work Astrobouncer... I've been following your posts for some time, thanks for all the info, videos and pictures you post!
You inspired my to build my own sluice and boy I'm glad I did, it works wonders in the river. Your sluices are truely works of art... You could set up a little shop, maybe online or by word of mouth to turn a profit on the side selling wooden hand built sluices... the catch being they catch as much gold or more as more expensive " store bought ones"

Anyways, that shot of you in the river with double damn sluice set up, is sick.... just perfection, man.. keep it up!

 

[Caminochaos]

Astro,

You had mentioned that the drop riffles were mad with your table saw. My question to you is did you make the cuts and then chisel them out?

Also you mentioned that you didn't have to classify due to the larger material rolling over the drop riffles. I noticed on your first sluice you went with smaller riffles and gradually got bigger. I think that is a good theory due to the fact the size of the rock is only going to effect the the same size riffle.

I am very intrigued by this idea. I'm sure I speak for all of us in saying I HATE CLASSIFYING. It is a waste of time. With that being said I may have access to a 6"x14"x10' piece of lumber. I was thinking of shaving it to about 3/4" thick and have multiple drop riffles in it sizing from 1/8" wide at the beginning to 3/4"-1" wide at the end. I believe if you shovel straight into it wouldn't be a problem because if a 2" rock gets in there it won't effect even the biggest riffle. Do you think this theory is sound?