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kaveman
02:18:14 Mon
Apr 2 2012

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Building a 6" dredge sluice.

I need to run into town tomorrow to buy materials for a 6" dredge sluice and powerjet, so I'd like to hear a few last minute thoughts and suggestions tonight(and even early in the week while I'm building). It's going to be fabricated quick and dirty and doesn't need to be the greatest design, but I'd like it to be as good as I can make it(in keeping with the quick and dirty scheme).

It's not actually for use on a dredge,.........it's going to be bank mounted, but I'm going to be suctioning up material off of bedrock. It's going to be steel(so I can weld it)and it's going to be heavy(same reason). Thinking right now of building it primrily from 1/8" sheet steel. Weight isn't much of a factor. I'll be moving it around with the excavator or the boomtruck. Either way; 500# or so won't be a problem. I'm thinking(at least at this point)of building it as one complete unit with about 7' of jet tube feeding into a crashbox, feeding into about 8' of sluice. Just working out dimensions in my head right now.

I want the crashbox because it's simpler to build and more foolproof. Also shorter overall and more forgiving on the HP requirements. The churning action of the box also outweighs the smoother feed of the flared designs in this case(I'm expecting mostly cemented gravels).

I envision the whole rig sitting on a gravel dike between the dredge pond and what I'll call the 'tailings' pond. One point to be considered is that due to the suction intake, no rock over about 2" will be allowed up the hose, but a fair amount of the material dredged will probably be sharply angular. I'm also going to run it with tremendous suction, so there's going to be more water running through the sluice than on a typical 6" dredge. It's all mechanized; no diver. Bedrock will be broken up and processed. All this has got me guessing on the sluicebox dimensions. I'm finding examples of factory 6" dredges with sluiceboxes from 20" to 26" wide. With all the extra water and no large rocks to move, I'm considering widening out the box to somewhere around 30". Pretty sure I'm going to flare the sluice and run primarily expanded metal riffles, maybe with some angle iron at the head. Maybe 24" wide at the crashbox and widening out to 30" at the discharge just to be safe. If it wasn't for all the angular rock I'm expecting to tear up I wouldn't be so worried about going too wide.

Any thoughts?

  
AK_Au_diver
04:25:51 Mon
Apr 2 2012

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Re: Building a 6" dredge sluice.


Sounds good. Go wider, you can always put in 2x4 or 2x6 on the inside side walls to effectively narrow it, if you need to later.

30" should be fine, this is a single box right? Those 24" ones are "triples" with two stages stacked on the second half.

I'd shy away from the angle iron, it causes lots of turbidity, negating some of the settling that happens in the flare. Try larger raised expanded metal for the first 6" to 12" if you are looking for trapping larger gold.

  
kaveman
16:45:16 Tue
Apr 3 2012

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Re: Building a 6" dredge sluice.

Yep, wider it will be. The trip to the scrapyard was fairly productive. They had very little in 1/8" but a very nice supply of new sheet steel in 3/16", so tht's what I went with. I was considering 1/4" for the sluice, but 3/16" should be plenty heavy enough to maintain a flatbottom without any reinforcement. Kinda heavy for the crashbox, but better too heavy than too light.

I just hope my fabrication plan works out, or else I'll be welding bead forever. I bought two sheets, 47" x 84" x 3/16. The first will become the flared sluicebox. I'm going to lay it face-down and score two lines with the Makita/cutting blade,........30" wide at the upper and 36" wide at the lower end,.........and attempt to break along the scored lines by hand. That should create a flared sluice with sides 8.5" high at the upper and 5.5" high at the lower end. I'm thinking(hoping)that a 1/16" deep scored line will allow the fold and still leave plenty of strength at the break. I'll probably reinforce with some scrap angle tacked in.

The second sheet for the crashbox gets a little bit more complicated. I'll cut 30" off of one end, leaving the sheet at 47" x 54". I'll rip that one in two and have two sheets 23.5" x 54". Both of those will be scored to break 90 degrees at the 24"/30" point. By flipping them around, I can create the 30" wide floor and one 24" side with one; the 30" back and the opposite 24" side with the other. That's gonna require 78" of weld bead to create the outer portion of the 'box'. The leftover 30" piece will get scored and wrapped to become the inner crashbox itself. All outer corners will get wrapped with angle iron reinforcement.

I have something I may try with the expanded riffles. Since they're flared same as the sluice, I'm considering tipping the sluice sidewalls in 30 degrees from vertical, something like this,........

/_______________\ looking up from the discharge end.


/-----------------------\ with the expanded in.


The expanded will drop right down into the sluice above the carpet, but with the flare of the sluice, driving the expanded upstream will force it tight along the sides and tight to the bottom due to the tipped in sidewalls,.............in theory. There may be a tendancy to pucker up the center of the expanded tho. Should easily pop loose with a smack in the downstream direction. Not sure whether to try to lever it tightly into place from th bottom or maybe pull it forward with a boat winch from the top. I'll try to get some pics during assembly that will make it all easier to explain.

And it's getting heavy already. About 650# yesterday with the sheet and expanded and that's not including any part of the jet. Probably gonna be 800# before it's done.
[4 edits; Last edit by kaveman at 16:49:39 Tue Apr 3 2012]

  
overtheedge
22:17:59 Tue
Apr 3 2012

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Re: Building a 6" dredge sluice.

Before you weld the sides with a tilt inward rather than vertical, you might want to grab another tapered sluice and cut some 2x4 into the same side angles, i.e. cross corner cut across the 4" width, and run some material.

It doesn't have to be gold bearing, just small gravel and sand from a gravel pit. I think you will find that the increased friction loss will result in moderate to severe loading-up along the sides.

I am a fan of tapered sluices, but the design isn't a cure-all and presents some problems of its own.

What a tapered sluice does do is:
Twists the lateral currents caused by friction against the side walls towards downstream rather than across the sluice.

It lowers the water level a bit and promotes laminar currents in the lower portion of the sluice. This enhances the sluice's ability to recover small/flour gold.

But this same taper can create some problems too:
The slope MUST be increased to clear light fines from the lower portion of the sluice. The increased current is counter-productive to recovery of small gold.

Because of the water level drops as it goes down the sluice, there is an increase in loading up of larger material in the lower portion of the sluice. The water depth must be higher than the material you want flushed from the sluice. Again this is counter-productive in increasing the laminar flow in the lower portion of the sluice.

How do I know? Been there, done that. I have mixed feelings about tapered sluices for general purposes. Where they shine is when you classify tight and practice good water depth discipline. If you attempt to put a tapered sluice on a float system, you must grossly over-size the flotation platform. This is due to the slurry shifting the weight and balance of the sluice and altering the slope.

I still have and use tapered sluices, but NOT on a floating platform. I also classify to 1/4". Actually the screening is 1/4", but there is very little that gets through the screen larger than 3/16" and most is 1/8" and smaller. See Taggart, "Handbook of Mineral Dressing" also quoted in Wills, "Mineral Processing Technology".
eric

  
RUSTY_HAPPY_CAM
22:39:24 Tue
Apr 3 2012

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Re: Building a 6" dredge sluice.

Still got those 2 8" sluice boxes setting here. One is even galv. steel with a flair made on.

  
kaveman
00:28:42 Wed
Apr 4 2012

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Re: Building a 6" dredge sluice.

I know Rusty. Matter of fact, I happened upon a link to your photobucket account again just last week while searching for a ready-built sluice. I had another look at them, but at the time I was stuck on 6". Only over the last day or so did I eventually arrive at the same dimensions as your 8" boxes,.............so I get to go back and rethink. It would definitely be easier to fab up some riffles for one of your boxes rather than scratch build the entire thing, even if I have to adapt to the 8" feed. I really don't want or need all the complications of a sump, but the Keene box looks to be pretty easy to patch over. Whatcha askin' for that one?


  
RUSTY_HAPPY_CAM
03:10:38 Wed
Apr 4 2012

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Re: Building a 6" dredge sluice.

I think you will like the sump when you use it. In your area the 1/8"+ nuggets are getting scarce but there is pounds of -30 gold around if you can catch it. With the high flow that you used with your operation it is hard to do a good job on small gold when you are dealing with larger rocks in the same box. Keene is yours for $300. I also have a lot of riffles and riffle parts that you can use to quicken the conversion process.

  
kaveman
03:32:09 Wed
Apr 4 2012

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Re: Building a 6" dredge sluice.

Thanks Rusty. We may go this route. I'm not overly worried about the fines because the tailings from this operation will be reworked. We just need some type of recovery in the circuit so we'll know when we're done clawing blindly at the bedrock. When gold quits showing up in the sluice we're done, but the tails will be tested for loss and if it's richer than the unworked overburden it'll get washed again.


Heading down Sacto way tomorrow to pick up my pop. We'll discuss the options on the way back and try to decide whether we really want to waste another week cutting and welding. You can probably expect to hear from us later in the week.

  
thegoldgopher
03:02:31 Mon
Apr 23 2012

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Re: Building a 6" dredge sluice.

Keep it simple. 80% of the gold will be caught in the first 20% of the riffles. If the angles of the riffles are correct, and the angle of the whole sluice is correct, you will be "pretty close". Remember those old sourdoughs used rough sawn lumber, with actual moss in the bottom, and they did pretty good.

Level manufacturers make levels that have like four level bubbles in them, used by electricians and ironworkers for the most common angles they use when bending conduit and rebar. They can be custom ordered, or bought at regular stores, and prices are very reasonable.

If you want to have a x degree riffle, and an x degree angle to your sluice, just order it, and it will be set in epoxy on a 6" level, and you can strap that on to whatever you're working with at the time. Down and dirty.

HTH

thegoldgopher

  

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