Classification Over Riffles Question

Yukon99669

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Jul 30, 2020
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Alaska and Colorado
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Quick question about position of screen over riffles.
I searched forever to get these two Super Heavy Duty Chunks of Woven Mesh to put over my dredge riffles.

I’m hung up on the amount of gap is needed between the mesh and top of the riffles. The smaller mesh has .130 openings (a bit over 1/8”) and is going over the shorter set of riffles at the top of the sluice. The short riffles sit below the frame edge by about 1/2 inch and to me look fine to rest the mesh on the frame w/ no additional gap…. But I’m not totally sure???

The bigger mesh has .365 openings (between 1/4 and 1/2 inch) and it goes over the lower half of the sluice. There is no gap between the riffles and the riffle frame on this set. Am I ok just going right on top of the frame here, or do I need to create a gap in between?

This is all in a 10” wide by 4’ sluice for my 2 inch dredge running about 9,000 gph. The riffles sit on miners moss w/ expanded metal between the moss and riffles.

Here are some pics to give a better visual.


C9FF7731-59F4-4B42-A0DC-A781045B0266.jpeg
BCF4F89A-BCB8-4836-ACDB-E4BDCFDCF432.jpeg
F47963F6-9D63-428E-9053-F0CAAD5D68D3.jpeg
4062D3B0-3248-478F-89D0-80647A67DFA6.jpeg
EB8D8DB9-1E10-41B3-A470-39ACEB9833E3.jpeg
 
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Reed Lukens

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I say the opposite... those riffles are useless under an 1/8" screen... keep the expanded and toss the riffles. Then go 3 to 4 times the heigth of the opening for enough water flow. The idea is to slow the water under the screen for such a drastically small screen size.
 
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Yukon99669

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I debated ditching the riffles, but I ran a somewhat similar setup w/ some odd-ball, flimsy, 1/4” hexagon mesh that sat about 3/4” above the riffles (due to the frame it needed for support). It performed well, but I sure didn’t think it was optimum. It wasn’t necessarily over-filled, but I considered the amount of cons to be quite excessive.
For me to run my dredges here in Colorado I have to get the classification way down. So I’m trying to find the right balance.
 

Reed Lukens

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You can run hex bolts and nuts thru the mesh for heigth adjustment wherever needed. Use the hex side down.. I forgot that you were in Colorado, make it into an over under for the best recovery using the 1/8" as the screen into the lower/ slower sluice.

 

ratled

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I say the opposite... those riffles are useless under an 1/8" screen... keep the expanded and toss the riffles. Then go 3 to 4 times the heigth of the opening for enough water flow. The idea is to slow the water under the screen for such a drastically small screen size.
Being its a 2" Reed's answer will serve you better. Keep us posted.
 

RTR

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Quick question about position of screen over riffles.
I searched forever to get these two Super Heavy Duty Chunks of Woven Mesh to put over my dredge riffles.

I’m hung up on the amount of gap is needed between the mesh and top of the riffles. The smaller mesh has .130 openings (a bit over 1/8”) and is going over the shorter set of riffles at the top of the sluice. The short riffles sit below the frame edge by about 1/2 inch and to me look fine to rest the mesh on the frame w/ no additional gap…. But I’m not totally sure???

The bigger mesh has .365 openings (between 1/4 and 1/2 inch) and it goes over the lower half of the sluice. There is no gap between the riffles and the riffle frame on this set. Am I ok just going right on top of the frame here, or do I need to create a gap in between?

This is all in a 10” wide by 4’ sluice for my 2 inch dredge running about 9,000 gph. The riffles sit on miners moss w/ expanded metal between the moss and riffles.

Here are some pics to give a better visual.


View attachment 2046723 View attachment 2046724 View attachment 2046725 View attachment 2046726 View attachment 2046727
How about 'Salting' some of your material (with a known amount/weight of gold) and run it every which way on your system and see what combo works best .
Also, I would make the "salted" gold of different sizes,from pickers to fine. And have a catch bucket at the end of your sluice to recoup any gold that made it that far...Good luck .
 
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Yukon99669

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Thanks for all the advice on this guys!!
I’m gonna ditch the riffles and try to run this with the thickest/heaviest raised expanded that I can find.

Anyone have a link to a source for that?

I’ll check McMaster since they had all the options on the heavy woven mesh. If anyone has a different source I’d love to see it!
 

N-Lionberger

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With that fine mesh the expanded you have should work just fine on that fine Colorado gold. You can cut the excess riffles from the ladder and use the riffle frame to hold the expanded down. I use nuts and bolts as a riser for the woven wire like Reed suggested. I have had way better luck with the woven mesh instead of punch plate, I feel the texture creates drag that slows the slurry down helps the heavies drop out, in places where I still have the punch plate I zip tied raised expanded metal on top of the punch plate to create more drag. The big heavy expanded works well, I use it in my river sluice that I shovel feed unclassified and in my 4 and 5 inch dredges under half inch classification, disadvantage it’s super heavy compared to the relatively thin bent Hungarians and for fine gold recovery I am concerned about the corners of the diamond on the heavy expanded that do not make contact with the carpet could scour out. In my 4 which is an undercurrent setup based on Reeds video and recommendations from Hoser John. In my 4 I use a 3/16 inch screen feeding a combination of 1/2 Inch expanded over unbanked veranda RV carpet over fine ribbed rubber and 1 inch expanded over deep V rubber mat, no carpet based on a ProMak dredge sluice video, it works great. Under your screens the expanded looks like it will work fine. I have some heavy gauge expanded aluminum I picked up recently at my local scrap yard it’s about the size of 5 or 6 pound steel expanded but much much lighter, I can mail you a piece if you strike out locally.
 
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Yukon99669

Jr. Member
Jul 30, 2020
53
81
Alaska and Colorado
Primary Interest:
Prospecting
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  • #11
With that fine mesh the expanded you have should work just fine on that fine Colorado gold. You can cut the excess riffles from the ladder and use the riffle frame to hold the expanded down. I use nuts and bolts as a riser for the woven wire like Reed suggested. I have had way better luck with the woven mesh instead of punch plate, I feel the texture creates drag that slows the slurry down helps the heavies drop out, in places where I still have the punch plate I zip tied raised expanded metal on top of the punch plate to create more drag. The big heavy expanded works well, I use it in my river sluice that I shovel feed unclassified and in my 4 and 5 inch dredges under half inch classification, disadvantage it’s super heavy compared to the relatively thin bent Hungarians and for fine gold recovery I am concerned about the corners of the diamond on the heavy expanded that do not make contact with the carpet could scour out. In my 4 which is an undercurrent setup based on Reeds video and recommendations from Hoser John. In my 4 I use a 3/16 inch screen feeding a combination of 1/2 Inch expanded over unbanked veranda RV carpet over fine ribbed rubber and 1 inch expanded over deep V rubber mat, no carpet based on a ProMak dredge sluice video, it works great. Under your screens the expanded looks like it will work fine. I have some heavy gauge expanded aluminum I picked up recently at my local scrap yard it’s about the size of 5 or 6 pound steel expanded but much much lighter, I can mail you a piece if you strike out locally.

Thanks for the info, insight, and input! …and thanks for the offer on the expanded aluminum! I think I got it covered. I was trying to find 3# or 4# grating, but though it might be too tall. I went w/ #6 (which somehow equates to about 2.4#). Definitely a step up from the standard stuff I always used.

In the pic the #6 is laying flat and the standard stuff is leaning above.

…I really wanted it as 1 piece, but the cut is oriented wrong…so now I have to chop it into a few chunks.

AC8724FA-3FDF-4AD2-80E6-711B072B1F16.jpeg
 

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