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

[Astrobouncer]

I made all the basic rough cuts with the saw, and yes I used a wood chisel to smooth them and make some changes. Also used sandpaper to help smooth the riffles. A smooth riffle is better because it allows the vortex action to occur. Too rough of a bottom and the riffle just fills up with material that cannot as easily be spiraled away. This slowing down of the vortex action can also happen if you overload the riffle by feeding it too fast.

It is, and there' something else that affects that which I will attempt to explain.

The velocity of the water in one of these sluices is greater because of the lack of obstructions like those that are in a normal sluice. Thus even if you have 1 inch rocks rolling down the board, the velocity pushing behind them will roll them over a 1 inch wide riffle. And if you have enough velocity they will likewise roll over even a 2 inch opening. Now you might think that's bad, but the heavier sands will definitely settle in the riffle, unlike a lighter stone. When I was out running this sluice last time, I had a nice size flake just slowly creeping its way down the slick plate until it got to the first riffle and buried itself in there. Whereas the lighter stuff just rolled on by and right out of the sluice. I also have been running one of my newer drop riffles emptying into one of my pans on the back, and no specs of gold in there yet.

I have noticed on my unclassified runs that even rocks 1/2 the size of the riffle will just roll on by and not drop in if they are only light gravel. The major problem with out classifying at all is some of the much larger 3+ inch rocks can cause a 'blowout' of material as the roll over a smaller riffle. But this problem can be somewhat mitigated by having some extra deep 1/8 inch groove at a 45 degree angle and below the main one. You can see where I did this on some of the sluices on my latest's one. A deeper simple straight one will work somewhat, but not as well as an angled version. Also if the rock is big enough and heavy enough, it can get hung up in the later part of the sluice with deeper riffles, thus blowing out all the smaller stuff there. Though it is doubtful any gold will have made it back that far, but you might lose garnets and other heavies.

I hate classifying too, and it really slows down an operation. I have some ideas I need to test that I think will allow one to just shovel material in without worry of classifying at all. Also, there is a great video about how to make a trap sluice, where you dont have to classify by Mike. I intend to make one of these to try out soon.

 

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[Caminochaos]

Do you think just simply put a BBQ grill running parallel to the flow of the water about 1/2" or so above the riffles help? That way the larger rocks can roll above the riffles while the smaller stuff just falls through.

Or design your riffles like this:

 

[Astrobouncer]

Camino, I tried a riffle like that, it didn't work too well because it was slow clearing. There's not the right design to create the vortex that is needed to swirl away the lighter stuff fast so as a result it builds up with everything that falls into it and then has no room for the heavies. The lip is too much. You got to have some opening to create the vortex. It will eventually clear the lighter stuff, but the process takes way too long compared to the regular drop riffle. So with a design like that you have to feed it super slow, then wait a good while to clear. One thing I just realized though, is that I tested mine with a normal drop (inch per foot), with excessive drop, a riffle like that might work better.

However, if you put a slight 1/16" or 1/8" inch cut like that in the bottom of a regular drop riffle , then it works great as the vortex inside the main riffle will scour off the lighter stuff, and the heavies will drop down into the groove and protect it from larger material passing over head. You can face it either way and it will work. Light stuff will initially fall into the small groove as well, but it will be displaced by heavier stuff as the vortex does its work. You do have to feed these kind of riffles slower though, as too much material fed at once will plug up the back cut on the drop riffle and cause it not to work. The best is when you feed it and see the material dancing out of the riffles but leaving the black sand behind. If its catching the black sand, then its usually catching the heavier things as well. I have set my pan behind and under my newest sluice as a test to see if I was losing any gold the last two times I was out, and even checking tailings with a loupe I could not find any gold getting out of the sluice. And I overfed the sluice both times just to try and push my luck since i wasnt worried about losing anything with my safety pans behind it.

Also, you can try a grill like you said but you have to design it in a way that it wont impede the flow on a smaller creek. And it wont create too much low pressure to drop everything out like my low attempts did. The problem I had with mine was the creen I used impeded water flow too much and I had excessive buildup of material below it and got little to no riffle action because of the low pressure.

I think the real ticket is just to use very thin metal on the front grill (think wire size) so as not to impede the water coming in, then above that grill (on the top) you can use anything you want to let the rocks roll away but it has to be high enough up (and thin enough) not to create a low pressure zone. I usually work on creeks nowadays instead of rivers and flow is a big issue for me and the main reason I havent done more on this. I have used 4 mesh screening in a similar manner and because I didnt have a removable grizzly it ended up more of a pain to remove the stones then just preclassifying since I had to pick out stones by hand since the water flow up above was not significant enough to allow them to roll out. Now, if I had more flow this would not have been an issue, but I was working on a small creek with 1-2 inches of flow and barely any drop. Nonetheless, I have several ideas and am confident it is only a matter of time before I get this figured out and working,however, even the best no classifying sluice is still going to require shoveling behind it from the buildup of discharging all this material behind it, so its always a tradeoff regardless. Instead of spending time classifying, you will be spending time shoveling material from behind it. Granted its probably much less time to shovel material away but its still time spent. Even if I make a side dumping grizzly that might still create a buildup of material that is a problem for the side which could need to be shoveled away. A highbanker doesnt have this issue with buildup of material behind it because its flow is not dependent on the water flow of the creek or river.

 

[Jason in Enid]

Looks pretty nice. Have you ever considered using a dovetail router bit to make a /_____\ drop riffle?

 

[Caminochaos]

Looks pretty nice. Have you ever considered using a dovetail router bit to make a /_____\ drop riffle?

Funny u said that. I was going to ask the same exact thing.

 

[Astrobouncer]

Yes I tried a riffle like that in one of my prototypes. It didn't work and stayed backed up with material. Drop riffle is the old technology, the better sluice is the fluidized bed system, since its almost impossible to lose gold, and they can move some serious material, at least twice as much as a drop riffle that you have to classify in the same amount of time. See my new thread on making a gold trap sluice it deals with that system in more detail. Now drop riffles do still have a place though, I still use them when the water flow is so small you cant use anything else. I used an Angus McKirk this past weekend cause we were in a spot with low water flow and it worked great. But for any kind of decent flow I would only use a trap sluice now.

 

[russau]

i see 2 potential problems with this design. 1) the pvc in the lower collection box is going with the flow. it should go across the flow to prevent "corn rows" in the concentrats. 2) you dont have enough presure,or adjustment to your water supply to give you enough water column in the collection box, to create a good fluid bed for the fine gold entrapment. but takeing your design to a larger scale would make this a winner.

 

[stilllookin]

Astrobouncer, you have done more to stir my interest in the drop riffle sluice. I made one similar to your earlier designs I believe and now I am very interested in making the drop trap sluice. I'm not willing to put my hard earned gold through the sluice to prove its capabilities but I do enjoy these diy projects. I am enclosing a picture of the drop riffle sluice I built more as a test on how to post a picture than anything. If the snow will ever melt we'll be able to try it out. If you don't see a picture I did something wrong, and I'll try again sometime.

 

[Astrobouncer]

Lookin that looks good, and I bet you can just bank run the material through it without classifying. The width of the drops coupled with the water current should prevent any big rocks from falling in there. Nice job.

 

[riverrunner814]

Great sluices!!!!! Here in CO. theres fine to small nuggets. Which one would work for this?

 

[Astrobouncer]

Any drop riffle would work fine with coarse gold, and with a little slower water they work great for the fines too.

I would make one with at least 20 drops, and vary the sizes. Make some 1/16 inch wide, some 1/8 inch, some 1/4 inch, some 1/2 etc. All the way up to an 3/4 of an inch or so. And make them all about 1/2 inch deep. The more drops the more heavies you will catch and longer you can go between cleanups. Also more drops help act as insurance in case any gold makes its way further in the sluice.

 

[Lookin]

Lookin that looks good, and I bet you can just bank run the material through it without classifying. The width of the drops coupled with the water current should prevent any big rocks from falling in there. Nice job.

Gosh! For a second there, I thought you were talking to me and I hadn't even posted!

Nice looking sluices!

 

[Snarkie]

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.

What is the optimum degree on those angles, AB? I have a 1957 Powermatic table saw that will go past that (back when they made stuff to do the job right).

This is a really cool idea.

 

[rockhound69]

Hey astro just wanted to say thanxs for the inspiration and the testing knowledge on the drop riffle
sluice, just built my third one, second drop riffle and it's sick, grabs every little bit of gold I'll post pics if I can
figure out how!

 

[Goodyguy]

Good work Astrobouncer

You inspired me to try a drop riffle myself. I found some vinyl soffit on the side of the road....guess it fell off a truck, anyway it has 1/2" x 1/2" channels every 3-1/2" and there was enough to cut it to fit my 14" wide sluice and my 10" wide sluice so guess I'll try it out this weekend.



GG~

 

[rockhound69]

Here is my version of your drop riffle, works killer grabs every little bit!

 

[russau]

Astro, just like Good Guy did, but im wanting to use some ABS to form my sluice, and use some 1/4,1/2 inch thick ABS and cut it into strips and glue it down to the ABS sluice. ive been working with this ABS for sometime now and im ready to jump on this. i want to design it to fit into my Beach box/highbanker as a insert or just use it as a sluice. i gotta do something while we are haveing this nasty weather!

 

[TheEquineFencer]

Did you ever try it?

Good work Astrobouncer

You inspired me to try a drop riffle myself. I found some vinyl soffit on the side of the road....guess it fell off a truck, anyway it has 1/2" x 1/2" channels every 3-1/2" and there was enough to cut it to fit my 14" wide sluice and my 10" wide sluice so guess I'll try it out this weekend.

View attachment 563547

GG~