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I’ve read a lot about how to set the angle on a riffle tray of a drywasher for getting good results, but recently watched some videos of people setting it to a angle that almost looked flat and the material was only very slowly moving along on it.  So slow in fact that it looked like it would take the material as long as 30 seconds or so to move off the riffle tray.  I realize that in terms of production, moving material through faster by using a steep angle is necessary, but for better recovery does anyone else here do that and is it better than using a steeper angle?

Edited by GotAU?
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Watch this video...these two guys are masters at drywashing.

Tom

 

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Your angle depends a lot on your material and how much vibration/air you have. A puffer has a rhythm and a blower has a steady dance. Each one makes the material move differently.

A general rule of thumb is you want the material to be pretty thin across the table as it moves across. Damper material has a steeper angle of repose and piles higher so it requires a bit more angle to move than dry. The same with rougher gravel particles. Smooth weathered sand runs at a flatter angle.

If you can see the top of the riffles on a blower machine you are getting it done. The material is thin enough the gold is getting to the bottom. Above each riffle is a "pool" of material held in suspension by vibration and air. As long as the material going over the riffles is no deeper than about 1/4" your recovery will be fine. If it is deeper than that or too deep above the riffles for your blower to lift then you need to increase the angle a little or get a blower with a higher static pressure.

If your angle is too steep on a blower you will have big bare spots below the riffle. All the air will go through the bare cloth and not through the material. You need to flatten the angle a bit to keep the cloth covered in an even layer of material.

On a puffer it is the opposite. You always want to see a little cloth below the riffle. It is just like exposed bedrock. As the material comes over the riffle the gold is going to find the bottom and slide down it until it gets caught behind the next riffle. As long as the layer of gravel is thin coming over the riffle the gold drops right down to the bottom.

So the angle is how you control the depth of the material as it runs across the table. You want to run it as fast as you can without getting it too deep as it goes over the riffle into the next cell. And you want to keep it deep enough to cover the cloth on a blower but leave a little cloth showing on a puffer.

Leastwise that is how I do it.

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You have got to balance recovery rate against amount if material moved.

I used to work a claim where we recovered the gold using a trommel where we recirculated the water.  The recovery rate was excellent, maybe 95%.  We also drywashed the claim, and decided against dry washing because the recovery rate dropped to maybe 80%.  

Using the recirculating trommel with the better recovery rate was the worst decision we could have made to work the claim.  We could have moved so much more material with the drywasher we had than using the recirculating trommel, and ended up with more gold recovered.  It's embarrassing on that one we never learned out lesson.  We were so caught up with the gold we lost and not the gold we could have made.

The two guys in that video are who you can learn from.  They have done better than I can ever dream of.  Their YouTube Channel, "I brake for Bedrock" has 20 videos in their playlist on drywashing alone.

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Thanks for the references you guys, I appreciate it. I have a Thompson that I’ve used a few times and I think I am doing that one right (it has a set angle so I chock the legs to adjust it) it seems to have good recovery though (I ran the tailings through twice and even more to check it).  I recently purchased a Royal blower type drywasher to get more production, and will be using it for the first time in a couple days. Based on what you guys are all saying, running it flat like it was in the video I saw is not the way to go! The guy was burying the ruffles and had a big mass of material moving like a slow motion mud slide down the tray. it looked like it was a very unproductive way to do it with a lot of loss. I’ll definitely try out your suggestions and those from the video as well, appreciate the help!

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You can take some dirt and toss some lead shot or some lead fishing weights in a bucket of dirt and get a percentage.  That’s about all you can do until you find gold bearing dirt and run it through the Drywasher, and then pan the tailings to see what is left.  Keep doing this until you find the right angle.

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Cut a lead bar with a crosscut saw. It gives you some cool little shapes to test with. Weigh out a gram and see how much you can get back.

A drywasher will miss a lot of really fine flour gold in some circumstances. But if the gold is fairly good sized color it should get it all.

In my experience you will leave more gold on the bedrock than you will miss with a drywasher. In other words your time is best spent doing a better job mining than trying to be super efficient in your concentration.

If you are getting 50% you are going to know if your spot is any good. If it is good you can run it twice. If it isn't there is no use worrying about what you missed anyway.

In nice dry material and sugar sized gold a drywasher should get at least 75% of the gold. I have ran really rich material and then re-ran the tailings to find only a few tiny specks. I think I was well over 90% recovery.

On the other hand I have ran slightly damp gravel that I didn't think was worth running. Only to find out it was really rich after it dried out and ran it again. I was not getting 10% on the first run. If I had not ran a couple buckets of tailings and tested it again I may have lost a good payday.

So efficiency may vary widely depending on a whole lot of factors. But when all the stars come into alignment you should be able to trap everything that is worth fooling with.

 

 

 

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Posted (edited)
11 hours ago, Bedrock Bob said:

Cut a lead bar with a crosscut saw. It gives you some cool little shapes to test with. Weigh out a gram and see how much you can get back.

A drywasher will miss a lot of really fine flour gold in some circumstances. But if the gold is fairly good sized color it should get it all.

In my experience you will leave more gold on the bedrock than you will miss with a drywasher. In other words your time is best spent doing a better job mining than trying to be super efficient in your concentration.

If you are getting 50% you are going to know if your spot is any good. If it is good you can run it twice. If it isn't there is no use worrying about what you missed anyway.

In nice dry material and sugar sized gold a drywasher should get at least 75% of the gold. I have ran really rich material and then re-ran the tailings to find only a few tiny specks. I think I was well over 90% recovery.

On the other hand I have ran slightly damp gravel that I didn't think was worth running. Only to find out it was really rich after it dried out and ran it again. I was not getting 10% on the first run. If I had not ran a couple buckets of tailings and tested it again I may have lost a good payday.

So efficiency may vary widely depending on a whole lot of factors. But when all the stars come into alignment you should be able to trap everything that is worth fooling with.

 

 

 

:idea:  I have a pile of dry landscaping DG I have been needing to move to the backyard.  I now know a perfect way to do it without having to pick up anything and at the same time do a drywasher riffle tray angle test. Thanks for the great idea of using the lead.  I’ll have to see if I can get some birdshot and spray paint it gold. I will also put in smaller lead shavings too. Then I’ll get the neighbor kids to drywash and move the DG pile for me, and I’ll let them keep the ‘gold’ they get after I weigh it for the test. Who knows, maybe they will also get some real stuff out of it depending on the source of the DG. This  will be a fun way to move that pile!  :yesss:

Edited by GotAU?
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