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iowa hill

A Reciprocating Sluice Box for a Trommel

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We have an 80-acre placer operation in an ancient Tertiary channel with cemented gravels. Since I completed major rework of our old trommel, we needed a far more efficient sluice arrangement than the 20+ feet of 12" wide metal conduit trays and old carpeting that was used by the prior owners of our claim. This new reciprocating sluice is made of 14 gage steel 18" wide, 10 feet in length, and is mounted in an angle steel frame with adjustable sluice box angle provided by the chain supports at the discharge end. It is currently (no pun intneded!) powered with a 120-volt two-speed 1/2 HP washing machine motor, and the throw of the box is 3/4" by means of an offset shaft supported in pillow blocks at the feed end. Speed of motion can be selected with one of two switches mounted in a water-proof box (the other switch is ON/OFF). We can fine tune the optimal speed(s) additionally with pulley diameter changes, but I believe I have an optimum range figured out. We'll see in the next couple of weeks.

My design came from inspiration and efficiencies gained from our portable trommel which has a similar setup, but shorter length. Riffle material is #3 raised steel grating laid on ribbed outdoor carpeting (like corduroy), and cinched tight to the carpeting with 8 foot lengths of 2 x 4 pressure-treated lumber wedged tight with wood wedges against angle steel bolsters welded to the sides of the box. Length of each carpet and grating section is 4 feet to make cleanup easier and more convenient. The carpeting is waterfalled in an overlapping fashion so that no concentrates are lost.

Our portable trommel was recovering over 80% of the gold from gravels washed earlier this year in the first four feet of the box. The remainder was found primarily in first 1 1/2 feet of the lower section with very little black sands. What was especially interesting was the large amount of minus 500 mesh gold found in the first section. I believe the present choice of riffle and carpeting arrangement is the best I've ever seen. Our recovery is at least as good, if not better than our neighbor's claim where they're using a trommel, jig, and table (no sluice box). We should be able to handle around 50-60 yards per day with the new box; probably more if we screen the infeed with a grizzly and minus 2" shaker deck (this will be my next design project!).

I'm looking at building a smaller version for sampling and portable use. Stay tuned!

Here are some photos:

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Not a trommel, but on a double deck screening plant.

We built a 12 ft sluice box, with an eccentric cam bushing on the header box end.

Bushing shaft was turned by a variable speed electric motor, much like yours.

18 inch width & 6 inch side walls (half 4X8 sheets).

Expanded metal sections were held down with 1 inch angle iron bolted at the side walls.

Riffle section was held down with metal wedges, via an angled slat, to pound wedges against.

We covered the sluice box floor & side walls with conveyor belting.

Gold particles will gain traction, slow & stop on rubberized conveyor belting.

Where, nonmalleable rock will bounce along, without skidding & stopping.

Same principle as wearing basketball shoes on a basketball court, better traction.

Sometimes, if you are lucky, you can find big used rolls of conveyor belt cheap.

Or, sometimes new rolls that are excess, never used.

We had expended metal in the 4 ft header box section,

Then, 4 ft of ¾ inch angle iron riffles, set like this < < < < < < canted 15 degrees tilt to the rear

Then, last 4ft was more expanded metal.

Sluice was very self cleaning & easy to pull sections for clean up.

We would pull first 2 sections daily, to get the big stuff (with a snow shovel)..

As 1st & 2nd sections caught all the course gold & 3rd section caught the fines.

About every 3rd shift we would pull all 3 sections, for a complete clean up.

We found water volume, direction & velocity was a major factor in how efficient sluice box recovery was.

With a screening plant, with spray bars, water & feed gravel came into the sluice box from the top.

After initial testing, we altered the design to improve & increase water flow direction, volume & velocity.

We altered the upper end of the header box face plate to include a ½ inch slit, the width of the header bow.

Which we pumped water through, that by design ran directly down the box.

We used a valve, so we could adjust the flow, to fine tune that waters velocity.

Adding that adjustable & increased flow, directed straight down the box, increased the efficiency of the system to around 97% recovery.

Which, we were more than happy with.

You might ponder adding a vent type water flow director, to the head end of your box.

Which (IMHO) will improve efficiency & recovery.

Because it gives you more water volume, flowing in a effective direction, which increases the velocity of the water going down the box.

Ponder, water directed into the box from above has to change direction, to flow down the box.

Water directed straight down the box does not, hence you get better velocity & more volume in the direction you wanted.

EDIT TO ADD: Quick 5 second sketch of what I'm talking about.

316047533_o.jpg

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Nice design iowa hill :thumbsupanim

I want to have a trommel build like that for my operation.

Edited by Geo2

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I remeber I v'e had read about vibrating your sluice might not be a good idea for gold recovery because it makes the gold especialley the flakey fines to get up and run down the tailings with the shaking action. Don't remember the source now but I think that's the opinion of some the prospectors'.

Anyhow I like your trommel !

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Nice !!

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