Building a small dredge
Nov 15, 2008 10:06:09 GMT 12
Post by RKC on Nov 15, 2008 10:06:09 GMT 12
From: RKCNZ Sent: 30/10/2008 12:22 p.m.
G’day Matt ( flapperthermal ),
Its encouraging you have decided on a 4-inch dredge, rather than a 3-inch which would have been mostly useless. And the more I think about it, the use of a well designed 4-inch surface dredge (with a suction nozzle) in some of the small streams of the Lakes District sounds very appealing, and it would be great fun during a hot Otago summer. You will have to increase your pace however if you want to get into the water this coming summer. I know a fantastic small stream in the Shotover catchment that would well suit a dredge such as the one you are intending to make. I unfortunately only become aware of the stream in recent years after coming across it by chance (I could kick myself that I did not find it in the 90s when I was dredging in the same general area). It’s a stream that was most likely hit hard in the late 80s and early 90s, by dredgers using Suitcase dredges … however, that only means ‘some’ of the chunky gold is gone, but there would be plenty of fines left.
I have found that when making a suction nozzle the hard part is to source a length of tube that is bent at a correct angle of ... about 45 degrees. If anyone knows anywhere in New Zealand to source 4” diameter and 5” diameter lite-gauge tube, that is bent at the right angle, I would like to know myself so I could buy some. I have seen some bent tube that produces ridges where it is bent, but such tube is totally unsuitable for use as a suction nozzle as the inside of the tube must be smooth. Also, its difficult for a backyard fabricator, who does not have all the proper tools and a well set up workshop, to fabricate a suction nozzle. So you might like to consider purchasing one from a mining supply store.
The alternative to using bent tube is to cut and weld some tube … like Dan did on one of his suction nozzles.
img.photobucket.com/albums/v172/Coochee/nozzlegold2.jpg?t=1225313697
Which would work OK if a good precision job was done and the angle was no more than 45 degrees. You would also have to be careful how its welded as you need the inside smooth, with not even a minute amount of weld protruding inside the tube.
These suction nozzles
img.photobucket.com/albums/v172/Coochee/P1010001_3inchA.jpg?t=1225313934
are made by Hose and Hydraulic Centre, Greymouth. They have the “machined reducer” in them that Dan referred to in a post above … which may, or may not, be a good thing. They don’t have any in stock at present, and I’m not sure if they are particularly interested in making any more. Miners Den in Melbourne might have some Keene suction nozzles in stock and you could easily find out by ringing them (ask for Geoff). Miners Den might also have some second hand suction nozzles, however if any of the second hand suction nozzles they have are home made, it would be much too big a risk to purchase one and have it shipped all the way to New Zealand, just to find out it won’t work. Miners Den will sell 'anything' even remotely do with fossicking, and when dealing with Miners Den its unfortunately entirely up to the buyer to make himself aware of the suitability of the part being offered for sale before any money is exchanged.
When making a suction nozzle you need to be aware that the length of the nozzle
img.photobucket.com/albums/v172/Coochee/7f6nozzleXXXDDDD.jpg?t=1225315734
should not be too long, as using a long nozzle can be difficult to use in the water, especially in shallow streams such as you intend to dredge in. The length of the suction nozzles made by Hose and hydraulic are about perfect. This is an Australian 3-inch suction nozzle
img.photobucket.com/albums/v172/Coochee/144a.jpg?t=1224988912
I have at present and its way too long in length. If I get around to having a use for it, I will just cut it so its shorter. And I will also change the poorly designed reducer thats presently on it.
The correct design of a reducer is very important. The best example of a reducer I've seen, that is perfect, is on this Keene swivel nozzle
img.photobucket.com/albums/v521/NZGOLD/Equipment/NZGOLD043.jpg?t=1225316706
, and the exact same design can be applied to a suction nozzle. ( BTW: The design of the Keene swivel nozzle is as perfect as I've seen on any nozzle, and anyone who wants to build a nozzle could do no better than to exactly copy this nozzle.). But never ever design a reducer for any nozzle like this.
img.photobucket.com/albums/v172/Coochee/OKOKOK7f6ozzleD.jpg?t=1225317346
You might just get away with powering your 4-inch dredge with a single 5 hp motor because you are using a 'dredge' pump … and one which is one of the best dredge pumps available! Also, you may nevertheless still have to make some design considerations to get sufficient suction. You should be sure to only use a suction hose with a smooth bore so there will be as little friction resistance as possible.
img.photobucket.com/albums/v172/Coochee/NewImagefrictionloss.jpg?t=1225320640
And it would probably pay to run the suction hose as short as possible. In the small shallow streams you will be going into you will not need a long hose in most situations and you could probably significantly reduce the length of a conventional suction hose that is about 4 meters in length on most dredges.
That’s all I have time for now, but I might think of more to add later. Feel free to ask anything more as there are probably a number of men presently building a dredge such as you intend to build. I’d be interested to know what you decide about a suction nozzle. And anyone building a small dredge may like to have a look at this thread
groups.msn.com/golddredgingforum/general.msnw?action=get_message&mview=0&ID_Message=71&LastModified=4675663264626226944
Regards,
Rob (RKC)
G’day Matt ( flapperthermal ),
Its encouraging you have decided on a 4-inch dredge, rather than a 3-inch which would have been mostly useless. And the more I think about it, the use of a well designed 4-inch surface dredge (with a suction nozzle) in some of the small streams of the Lakes District sounds very appealing, and it would be great fun during a hot Otago summer. You will have to increase your pace however if you want to get into the water this coming summer. I know a fantastic small stream in the Shotover catchment that would well suit a dredge such as the one you are intending to make. I unfortunately only become aware of the stream in recent years after coming across it by chance (I could kick myself that I did not find it in the 90s when I was dredging in the same general area). It’s a stream that was most likely hit hard in the late 80s and early 90s, by dredgers using Suitcase dredges … however, that only means ‘some’ of the chunky gold is gone, but there would be plenty of fines left.
I have found that when making a suction nozzle the hard part is to source a length of tube that is bent at a correct angle of ... about 45 degrees. If anyone knows anywhere in New Zealand to source 4” diameter and 5” diameter lite-gauge tube, that is bent at the right angle, I would like to know myself so I could buy some. I have seen some bent tube that produces ridges where it is bent, but such tube is totally unsuitable for use as a suction nozzle as the inside of the tube must be smooth. Also, its difficult for a backyard fabricator, who does not have all the proper tools and a well set up workshop, to fabricate a suction nozzle. So you might like to consider purchasing one from a mining supply store.
The alternative to using bent tube is to cut and weld some tube … like Dan did on one of his suction nozzles.
img.photobucket.com/albums/v172/Coochee/nozzlegold2.jpg?t=1225313697
Which would work OK if a good precision job was done and the angle was no more than 45 degrees. You would also have to be careful how its welded as you need the inside smooth, with not even a minute amount of weld protruding inside the tube.
These suction nozzles
img.photobucket.com/albums/v172/Coochee/P1010001_3inchA.jpg?t=1225313934
are made by Hose and Hydraulic Centre, Greymouth. They have the “machined reducer” in them that Dan referred to in a post above … which may, or may not, be a good thing. They don’t have any in stock at present, and I’m not sure if they are particularly interested in making any more. Miners Den in Melbourne might have some Keene suction nozzles in stock and you could easily find out by ringing them (ask for Geoff). Miners Den might also have some second hand suction nozzles, however if any of the second hand suction nozzles they have are home made, it would be much too big a risk to purchase one and have it shipped all the way to New Zealand, just to find out it won’t work. Miners Den will sell 'anything' even remotely do with fossicking, and when dealing with Miners Den its unfortunately entirely up to the buyer to make himself aware of the suitability of the part being offered for sale before any money is exchanged.
When making a suction nozzle you need to be aware that the length of the nozzle
img.photobucket.com/albums/v172/Coochee/7f6nozzleXXXDDDD.jpg?t=1225315734
should not be too long, as using a long nozzle can be difficult to use in the water, especially in shallow streams such as you intend to dredge in. The length of the suction nozzles made by Hose and hydraulic are about perfect. This is an Australian 3-inch suction nozzle
img.photobucket.com/albums/v172/Coochee/144a.jpg?t=1224988912
I have at present and its way too long in length. If I get around to having a use for it, I will just cut it so its shorter. And I will also change the poorly designed reducer thats presently on it.
The correct design of a reducer is very important. The best example of a reducer I've seen, that is perfect, is on this Keene swivel nozzle
img.photobucket.com/albums/v521/NZGOLD/Equipment/NZGOLD043.jpg?t=1225316706
, and the exact same design can be applied to a suction nozzle. ( BTW: The design of the Keene swivel nozzle is as perfect as I've seen on any nozzle, and anyone who wants to build a nozzle could do no better than to exactly copy this nozzle.). But never ever design a reducer for any nozzle like this.
img.photobucket.com/albums/v172/Coochee/OKOKOK7f6ozzleD.jpg?t=1225317346
You might just get away with powering your 4-inch dredge with a single 5 hp motor because you are using a 'dredge' pump … and one which is one of the best dredge pumps available! Also, you may nevertheless still have to make some design considerations to get sufficient suction. You should be sure to only use a suction hose with a smooth bore so there will be as little friction resistance as possible.
img.photobucket.com/albums/v172/Coochee/NewImagefrictionloss.jpg?t=1225320640
And it would probably pay to run the suction hose as short as possible. In the small shallow streams you will be going into you will not need a long hose in most situations and you could probably significantly reduce the length of a conventional suction hose that is about 4 meters in length on most dredges.
That’s all I have time for now, but I might think of more to add later. Feel free to ask anything more as there are probably a number of men presently building a dredge such as you intend to build. I’d be interested to know what you decide about a suction nozzle. And anyone building a small dredge may like to have a look at this thread
groups.msn.com/golddredgingforum/general.msnw?action=get_message&mview=0&ID_Message=71&LastModified=4675663264626226944
Regards,
Rob (RKC)