Riffle Design, Height & Spacings??

[kiwi jw]

Riffle Design, Height & Spacings??

Hi guys,
What do you consider to be the best angle off verticle for the face of a riffle to be? Also what spacing between riffles relevant to there height for a box around 36" in length x 9" wide ?? I know there are all sorts of other things that come in to play like water velocity & size of gold & material etc. I generaly pre classify material down to about 5/16ths (10mm) through a sieve bucket set up. I like to keep bigger material out of the box as I often work in a creek that has very little water flow & find this size pre classified material goes through with no problems & not having to attend to the box for jamb ups. Also the gentle flow of water is very good for fine gold recovery. This box is 44" X 10" the riffles are about 2.5" apart, about 5/8ths high & the angle of the face of the riffle about 25 degrees off vertical with a 1/8th lip off the top at 45 degree to the riffle face. This box got flogged from where I had it stached in the bush along with all my crevicing gear, hand gravel suction pumps, sieve buckets etc. WANKERS!!

Sieve buckets for pre classifying

I am in the process of making another box & had these riffles bent up for me by a fabricator.I went for an elongated 45 degree 'Z' riffle. I spaced these at about 3.25" & the riffles are about 1" high.

The mistake I made was not to kick the top lip up about 18 degree from flat & hence the riffles hold too much material unless the water flow is quite aggressive, not good for fine gold recovery. I feel they are too big in height for the smaller box & I dont know about the 45 degree angle either. I am now looking at going back to the type of hungerian riffle in the first box & no bottom lip. What is the purpose of that bottom lip on the elongated 'Z' riffle design. Is it just to seal off the underside of the riffle if the riffles are sitting on top of an expanded mesh??

I am making my next box shorter & just interested in you humble advise & experiance in what your thoughts are on riffle design, angle & spacings relevant to there height.

Many thanks & happy golding

Kiwi JW

 

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[blindpig]

Re: Riffle Design, Height & Spacings??

G'day Kiwi JW , Yaeh I think the best angle for the face of the riffles is 45' . This morning I whent down to my shop [ formerlly a garage] and gave some boxes a look over , there doesn't seem to be any "formula" for the size / spacing of the riffles . other then the dredge sets are taller and closer , i.e. 14in. box for 3 in. dredge riffles where 3/4in. tall and 2 1/2in. set apart, and there "faces" where closer to 60' than 45' , these where older boxes as well ? Now I have two sets of "factory" riffles for the hand sluices , one had 1/4in. riffles set at 4in. apart , the other had1/2in. riffles set at 4in. apart. The set's I made have two riffles at 3/8 high , followed up with 1/2 , 5/8 , 3/4[?] 10 in total , set at 3in. apart . As you did,.. I took that job of bending the riffles to a shop , as to get nice "sharp" parallel bends , I believe the idea was to do two at 3/8in. followed up by 5/8in. , but in the end I graded them out , 1/2 , 5/8, 3/4[?] .

As I looked at your sluice set in the creek ,. I thought that the angle was a bit steep . I would try to get more water velocity going into my box by lowering the front of the box which my give you a little more "head-pressure" . Maybe , just maybe even lose the expanded -metal at the front of the box [maybe ??] . Looking at the water flow there and the size of the gold you speak of , I think I would try a set of riffles about 1/2 in. high set at 3-4 in. apart . Another idea would be to build a box say 6 in. wide and a set of riffles a bit taller [5/8in. ?] , a well set 6 in. box can run alot of materal . One last thing , in your pic it looks as if your expanded -metal is welded to your riffles or ?? , anyway if so I think that would make clean-up a bit of a job ?? Anyway your on the right trak , make'n your own , to fit YOUR need's , can be better then any factory stuff , and if you enjoy doing it ,... well even better !!
Good luck mate ! Joel

 

[kiwi jw]

Re: Riffle Design, Height & Spacings??

G'day Joel & thanks for your reply & info. It is appreciated.
You know..... I think at the end of the day it isnt all that important as to the type of riffle used or the spacings. Any thing is better than nothing. My very first box I made years ago was 4' long X 10" wide with 6" high sides. I made a set of 'step ladder' riffles out of 1" X 1" timber spaced at 1" appart nailed to 1" X 24" side rails. These seemed to work just as well as any thing else I have made since. Here is a pic of that first box.

Now that I see that box I realise that in that photo I had made a new set of riffles & spaced them at 2".

The expanded 'Z' riffles that I made for the box in my first post are 3/4" high, 45 degree, 1/2" bottom lip & 1/4" top lip. Spaced at 3.25". The action between them wasnt very great unless you had fast water going down & with a short box that isnt good for fine gold recovery. As I said in my first post I should have had a bit of a kick up on the top lip & not had it parallel. Like you said I could have had the box set with more slope but then I felt it would have been boiling fine gold out. I did use the same riffles in a little highbanker at the same spot that I had the sluice box set up in. I was running a 2" suction nozzle through it & as you can see in the pics the water action is very fast. But then there wasnt any fine gold as I had a gold pan catching the tailings & when I panned that out there was nothing in it. The high banker is actually made from the sluice box in the above pic. I cut the box in half & used the two halves to fabricate the top hopper & bottom sluice box.

The gold I recovered for a couple of hours sucking out this bed rock

I feel that if your riffles are spaced further apart then it is very important not to have too much water pressure going down your box as the only action you are going to get from the riffles is the inital tumble of the water over the riffle & then the water flatens off in the bigger gap before the next riffle. If your water pressure isnt too great then the gold has a chance to drop into the carpet or behind the mesh if it doesnt get in behind the riffle. Like you said the dredge box riffles are a lot closer together & I have always based my riffle spacings along this ideal. I have a 3" dredge box & a 4" dredge box. The riffles in both boxs are 1" high & spaced at 3.25" but the 3" box they are 45 degree & the 4" box they are greater probably 60 degree like you said.

The other day I made different sets of riffles to try in my 36" X 9" box. First set was at 18 degree from vertical with a .25" top lip that had an 18 degree kick up from horizontal. The riffle had no bottom lip so I guess you could call it a hungerian riffle, They were 5/8th high. I tried this riffle at 3.5" spacings, 3" spacings & 2.25" spacings. Next I tried the same riffle at 28 degree with the same spacings as before. I tried fast water & slower water. Conclusion was..... they all worked. Some needed a bit of box slope adjustment. The 2.25" spacing took more time to clear. The 3" spacing not so long to clear & the 3.25 even quicker to clear. I found gold on every clean up. The material I was putting through was pre classified through my sieve buckets in my first post above & I put a bucket full through for each test I did. At the end of the day I feel the 3.25" spacing with a slow water speed is better for finer gold recovery as there is more flat area between the riffles for the fine gold to get into the carpet & not agitated out.
The point you made about dredge box riffles being closer together is that they are a fast water riffle set up. They have to be for a dredge to get rid of the bigger material that goes down them. With the riffles closer together you get the water bouncing back off the next riffle down to really create that churning, vibrating, sorting action betwwen the riffles. Not so much when the riffles are spaced firther apart With a stream sluice & classification you can have a gentler flow of water & you are more in control of what is happening. Like I said at the start of this post, I dont think the riffles you use & there spacing is a as important as the control of the water velocity & the amount & size of the material you put down your box. It comes down to the size & the state of the material you are working & the size of the gold you are saving or hope to save. Each stream is different & may require different set ups. To cover more options you can use the same box but have different riffle set ups along with different mattings. Adjust water flow & veocity & angle of your box.

Here are some pics of my finished box. I oppted for the 28 degree X 3.25" spacings.

Also made some crevice snipping suction pumps

Happy golding

Kiwi JW

 

[russau]

Re: Riffle Design, Height & Spacings??

you may want to veiw this video on a version of a Miller Table . this is this mans small version of a Miller Table. all it is is a sluice with slate paint(black board paint) on it and controll the flow. maybe another idea for you.

 

[kiwi jw]

Re: Riffle Design, Height & Spacings??

Thanks for that. Yes a great little set up for running your concentrates. Great water control for the finer gold clean up. A bigger version would be good for sea beach gold.
My local river has pretty fine gold & I have used my little high banker with good results shoveling in to it. The water pressure from the pump is on start up idle only so the water flow is pretty gentle. I was suprised at how well the ribbed rubber mat held on to the gold as that area was probably the most aggresive with the water & classified material droping down on to it from above. The box was set at a steeper angle to get the right action between the riffles. Steeper than I would normaly be happier with in a river sluice. This reflects the type of riffle I made which I am not overly happy with. I may have put these pics up before on another post but here goes any way.

Water action over the riffles

Gold recovered after a few shovels of black sands that were left high & dry after a major flood. Pretty fine.

I have also used a large expanded mesh as a riffle system on its own. This reduced the size of material left to pan off. I also added the mesh riffle set up in another box on to the end of the larger riffle box of the highbanker & at a flater angle. It did trap more finr gold that had escaped the top box riffles.

Black sand deposited behind the mesh on water shut down

I re run my concentrates through a blue bowl after panning off but the above table may be quicker for an inital run & I can use the same bilge pump recirculating system as I do for the blue bowl.

It is all good fun. Thanks for the link

Happy golding

Kiwi JW

 

[Jack Hamilton]

Re: Riffle Design, Height & Spacings??

Thanks for the video russau. Thats a nice fine gold recovery system. I think I will make one myself. I have an extra water pump that is about 100 gph that should do the trick. I'm a noob to prospecting, but have been doing my homework. Pretty soon Imma come up on some yellow

 

[russau]

Re: Riffle Design, Height & Spacings??

a word of caution: when using expanded or riffels, if you can see light under/between the riffels and expanded, you will loss fine gold! but in the picture, you sure do have some of what im talking about! but another guys picture of his expanded, i could see light under it.