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kaveman
18:40:54 Thu
Nov 15 2012

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Re: Extruded EPDM Saw-Tooth Mat

You start production of the 8 Riffle Nugget Trap Mat and I'll be in line to buy it. You've put a lot of thought into it and I like how you think.

  
goldfreek1955
13:40:33 Wed
Nov 28 2012

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Re: Saw-Tooth Mat

Hello to make a saw tooth matt take a jointer and shape the knives how ever you would like then run your matt through simple

  
dragline
19:43:44 Fri
Nov 30 2012

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Re: Saw-Tooth Mat

goldfreek1955,

I'm not a wood worker but I like your idea. Theoretically it should work given the right equipment and tooling. My concern is whether a jointer is the right equipment for this job. Three wood working machines come to mind...

Jointer
Planer
Shapper

After reviewing the equipment choices and tooling for those machines my first impression is that the optimal choice would be a 12 inch wood planer with custom ground knive.



Perhaps I'm not thinking this through. Since I know very little about wood working equipment and tooling I could be way off track here.

Planers typically have replaceable knives anyway...


Why not have a tool maker cut a 4-TPI pattern into a stock planer knife to my specifications. I could then purchase stock 3/16 to 3/8 inch thick EPDM sheet and let the black EPDM dust fly! (not too fast lest the smell of burning rubber be a problem)

Please set me back on track if I'm not thinking clearly about this.

  
dickb
21:21:59 Fri
Nov 30 2012

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Re: Saw-Tooth Mat

I'll add to your idea's. What your suggesting create's waste. That means you buy more raw materials than you need and throw away the unused material. Which drives up the cost of the finished product. Extruding the raw rubber and vulcanizing it is cheaper and more efficient to produce the product and the dies once made will produce much more mat before needing replacement. Another problem with your macnine is it cannot create negative space that is under the riffle. Extruding it will. You can even create hollow spaces in the mat if needed.
Not trying to shoot down your ideas, just explain why. Keep on thinking it really helps in design concepts.

Dickb

  
dragline
03:47:16 Sat
Dec 1 2012

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Re: Saw-Tooth Mat

Dickb,

Alright. You make some perfectly valid points. However, having been involved in manufacturing since the mid 1970s I have learned a few things about raw material costs versus manufacturing costs. Extruding a 6 inch wide 4-TPI saw-tooth mat is very costly relative to the raw material costs. In other words, I pay between 15 and 20 times for my extruded mat per ton than my manufacturer pays for his EPDM raw material. That's just the way things work when the total produced extruded material is about 2 or 3 tons relative to the hundreds of tons that my manufacturer purchases per month of the EPDM raw material.

Let's back up and go at this from a different direction for a moment (bear with me while I figure this out). Let's consider our choices of raw materials. If we are contemplating cutting my 4-TPI pattern into a raw material is EPDM optimal? Well, no, as an extruded material sure, nothing comes close to EPDM on a cost to benefit analysis. But as a machined raw material, no, there easier, better, cheaper, or more appropriate materials than EPDM.

What materials are better? High Density Polyethylene (HDPE) Sheeting and/or Ultra High Molecular Weight (UHMW) Polyethylene Sheeting. Of course UHMW is better than HDPE but then again its a lot more costly too. In fact, the abrasion resistance of machined HDPE is four times better than extruded EPDM! In other words, under identical slurry abrasive conditions EPDM will wear away four times more material than HDPE.

Is HDPE sheet expensive? Good question. I haven't found an optimal wholesale supplier yet but I did easily find US Plastic Corp of Lima, Ohio (almost all US plastics manufacturers seem to be located in Ohio).

Since my 4-TPI mat is 3/16 inch thick I figure I could easily cut my 4-TPI teeth into a 12 inch x 96 inch sheet on a 12 inch wood planer after cutting up a 4 x 8 foot sheet into four pieces. What's the cost of a 4 x 8 foot 3/16" thick HDPE sheet? $95.03 (that's just about $3 per square foot plus shipping costs of course).
http://www.usplastic.com/catalog/item.aspx?itemid=23869



Of course this wouldn't solve the problems of under riffle negative space or hollow spaces but for the 4-TPI and 8-TPI mats these would definitely not be problems.

I'll have to look into this further. Perhaps there are issues and problems with my idea of using a wood plane with a custom knife but it probably wouldn't be too costly to set something up and give it a try.

Thanks for the suggestions!

dragline

  
overtheedge
05:43:01 Sat
Dec 1 2012

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Re: Saw-Tooth Mat

Sharpening the knives might be real interesting. Will take an unusual jig. Perhaps something like the Oregon chainsaw filing device for files could be adapted.

Something else to consider, thermo-forming. For this purpose, even LDPE would work.
eric

  
kaveman
15:30:31 Sat
Dec 1 2012

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Re: Saw-Tooth Mat

I've been looking into thermo-forming and have been collecting components for a machine(vacuum pumps and heating coils). I'm interested in making a series of drop sluices for my own operation. From what I've learned, it would be hard if not impossible to form sharp features from any of the thicker plastic panels and the thin sections won't wear as well as you'd like,..............but they'd wear well enough and be fantastically cheap. And forming panels up to 2' x 4' isn't too difficult.

Going back to the planer idea,...........the wood planers have three identical knives that would have to be ground together and indexed properly to cut the pattern. Not too difficult. And they're not expensive. I bought one 15yrs ago for about $100 and have surfaced literally tons of walnut with it and have never done anything other than plug it in and run it.

A trick you may want to try depending on how 'grabby' your selected material is,............often the material will cut easier if it's been frozen. Probably not a problem with the plastics, but if the material is rubbery it may help. It's a trick we use contouring rubber buttpads to gunstocks. Grinds and sands much cleaner.
[1 edits; Last edit by kaveman at 15:32:58 Sat Dec 1 2012]

  
dragline
16:18:13 Sat
Dec 1 2012

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Re: Saw-Tooth Mat

overtheedge,

Yes, I thought about thermo-forming also.

Back in the 1980's I was doing some manufacturing engineering for a web process PVC multi-laminate with thermo-embossing, the sort of thing involved when you impress an embossing roller with a real looking leather pattern onto a PVC and muslin cloth laminate. But we had a surface mylar layer making an optically lenticular integration surface. The nip temperatures I had to deal with were about 420 F but the pressures were also key to getting the deformation needed to establish the desired tensile strength and elastic memory at the surface without liquifying the polymers and sticking them to the rollers.

Of course I was dealing with terrible and complex heat transfer concerns as well and web widths from 36 to 120 inches. The material had to be uniformly heated prior to entering the nip and the embossing cylinder had to be water cooled. But the challenges of getting an optically uniform embossed pattern were beyond the abilities of our development team and the project eventually failed.

In this case with our 4-TPI mat an embossing roller could easily be cut sharply with a lathe, but it'd still need to be water cooled for more than really short prototypical runs. Of course the entire embossing nip could be cooled under a water spray which would be reasonably simple and the post-nip material and embossing roller temperature could be flow controllable.

Pre-heating the HDPE could be done from the top with radiant electric elements and conveyance could be nip driven with passive input and output rollers.

The problem I see with this approach would be the nonlinear embossing stress induced on one side of the sheet. Because the embossing surface would be expanding it would tend to cause the entire sheet to bend downward as it cooled. The embossed sheets would therefore not lay completely flat. One way to fix this problem would be to induce an opposite upward arch in the sheet while cooling. This wouldn't be difficult for a continuous process but it definitely wouldn't work perfectly toward the ends of the 8 ft long by 12 inch wide sheets previously mentioned. Ultimately the optimal embossing width would be 48 inches, the width of a 4 x 8 foot sheet of raw material, but of course the tooling costs go up significantly in going from 12 inches to 48 inches wide.

Thermo-embossing could reduce material costs significantly but manufacturing costs increase significantly also. Ether manufacturing method could be profit optimal depending upon production volume. For more limited production cutting the saw-tooth pattern would be least costly and for larger production runs thermo-embossing would be most cost effective.

When it comes to cutting the 4-TPI pattern in the wood plane knives, I think it'd be best to leave that work to a qualified tool maker. I don't believe the cost would be unreasonable and relative the tooling costs of EPDM extrusion dies I could have 5 or 10 different patterns cut for about the same cost, 16-TPI, 8-TPI, 4-TPI, and perhaps even 2-TPI patterns.

Something to think about.

dragline

  
JOE_S_INDY
16:26:45 Sat
Dec 1 2012

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Re: Saw-Tooth Mat

Kave,

There are 2 ways to thermo form - one with the "mould" ending outside the plastic to be formed and one with the "mould" on the inside of the part to be formed.

Putting the form on the outside of the sluice box means that the soft plastic is pulled (through vacuum) to the outside, leaving the inside (working) surface of the sluice box to mearly follow the general contour of the form. The inside texture then is "pebbly". Much less expensive to construct with pretty good (depending, of course, what you compare it to)recovery. California Sluice Box is one of those manufacturers that seem to use this style.

http://home.comcast.net/~dadababa/pwpimages/Jr.%20Stream%20sluice3.JPG



By going the other (and more problematic) way and pulling the soft plastic to an internal form, all the inside edges and angles are exact and smooth, because they are in full contact with the form. The downside is that it is harder to remove the internal form unless great skill and care are used.

My G-1 made by Joel Farmer is formed this way.

http://www.usprospector.com/index.php/concentrator



For just a "onesie" or "twosie" production it is just simpler, and much less expensive, to use a router to form your drops. :smile:

Realize that crisp, sharp angles on the drops are usually not wanted. :gonetoofar:

Joe





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Wiser Mining Through Endless Personal Mistakes
 
 
dragline
17:47:46 Sat
Dec 1 2012

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Re: Saw-Tooth Mat

kaveman,

Yes, the vacuum thermo-forming systems that you are describing would probably not be able to replicate sharp teeth. But I don't believe that would be a big problem. Just having the teeth present with dull tips would get the job done reasonably well, assuming that the radii of the teeth tips were less than 5% or 10% of the tooth height. Of course that might not be practical with thicker more durable sheet thicknesses.

Vacuum thermo-forming would also allow you to start with thinner sheets thereby reducing material costs. The problem with this approach would be that it probably wouldn't be as strong or abrasion resistant as a cut or embossed thicker sheet.

In regards to the raw-material selection, I don't believe there is a more abrasion resistant and profit optimal choice in this specific application than HDPE. The only non-exotic material that is more abrasion resistant is UHMW-PE which would be 3 to 4 times more costly than HDPE.

Unlike vacuum thermo-embossing, with roller thermo-embossing there is almost no limit to the detail and sharpness of the embossed teeth. And, if material costs are a major concern and one did want to entertain thermo-embossing UHMW-PE one might consider two nesting embossing rollers, one above and one below the nip. This way one could start with a 1/16 inch thick sheet embossing both the top and bottom of the sheet symmetrically. This would eliminate the post-nip warpage and create a reversible surface with twice the life-span.

But I do agree with you regarding the three identically cut and registered wood plane knives not being that big of a deal. One of my concerns would be keeping a thin kerf when cutting the 4 x 8 foot sheets into 12 inch wide strips to fit the 12 inch wood planer. Infinitytools makes an ulta-thin 1/16 kerf 10 inch table saw blade that would probably work well. But at $179.90 each these are a bit pricey...
http://www.youtube.com/watch?v=pD-g9ZOxVM0

But more generic thin kerf carbide blades are available with 0.090 kerf width at a fraction of the cost (less than $20).

I'll be checking the costs for making custom planer knives here shortly.

dragline

  
overtheedge
20:36:00 Sat
Dec 1 2012

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Re: Saw-Tooth Mat

Keep in mind who your customers are. Sure we all want everything we buy to last a lifetime, but that is mostly nonsense.

How long (yards) does the mat have to last? I mean come on, gravel is an abrasive so stuff wears out.

1/16" ABS works well enough for some applications, but 1/8" is so much more durable. Thicker plastic of any variety will last longer, but there is weight issues, cost, formability, etc. LDPE offers a measure of flexibility over HDPE and certainly over UHMWPE and the cost differential is large.

Lindsay Books is going out of business, but they still offer a good book on vacuum thermo-forming:
http://lindsaybks.com/dgjp/djgbk/vacf/index.html

I bought one a few years ago and it covers what Joe Indy was mentioning about positive/negative moulds.
eric

  
kaveman
05:28:29 Sun
Dec 2 2012

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Re: Saw-Tooth Mat

A close approximation of the Protoform machine is what I'm working towards. Already have all the major components and several how-to books, but not the time to build it.

http://www.youtube.com/watch?v=WhA3wrdNFvc

This is a tremendously dull video, but if you can make it to 2:20 it'll be worth your while.

I've got some of DanfromNY's sluice trays that we've been using for the last couple of yrs and I'd like to experiment some, but the main goal is to create a sand sluice of nested plastic trays to run the finest screened material off the washplant. With individual trays of 24" x 48"(with an effective width of maybe 18"), I'm expecting to run four long by four or five levels nested together into a single structure. That'll take 16 to 20 individual sluices, plus at least as many more as spares. I've got a good local supplier of 24" x 48" x 1/8" ABS for about $20 per sheet. For that many trays, I think it's probably worthwhile to build the forming machine. The more I think about it, the more I believe it's a viable method for the saw-tooth.

  
JOE_S_INDY
11:38:45 Sun
Dec 2 2012

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Re: Saw-Tooth Mat

Go for it, Kave!

Shame on you if you don't keep us up to date! :devil:

Joe



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Wiser Mining Through Endless Personal Mistakes
 
 
Au_Seeker
21:12:19 Sun
Dec 2 2012

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Re: Saw-Tooth Mat

Dragline,

I haven't read this entire thread, but most of it so I may have missed some of the input, so excuse the following question if it has been mentioned and found not feasible.

That being said, Have you considered using CNC technology to get the results you're looking for?

Skip

  
dragline
23:05:34 Sun
Dec 2 2012

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Re: Saw-Tooth Mat

Skip,

Sure, but CNC is going to be useful for the fabrication of the extrusion tooling needed to extrude EPDM, or some other polymer, and make the mat that we believe would be most efficient at capturing and retaining fine gold.

I suppose that for limited production runs you could CNC each Saw-Tooth and the step across 1/4 inch to the next tooth and so on until you have an entire 2 x 4 foot rubber mat cut with saw teeth. I imagine, however, that this would take a lot of time on a very expensive tool. If that 2 x 4 foot pattern then served as a mold for Kaveman's vacuum forming system that might be pretty cool.

dragline

  
kaveman
19:28:40 Wed
Feb 6 2013

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Re: Saw-Tooth Mat

Just thought I'd bring this one back up for review.

  
dragline
22:44:46 Wed
Feb 6 2013

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Re: Saw-Tooth Mat

Sure.

I did hit the Douglas County Gold Prospectors Association show this last weekend at the Douglas County Fairgrounds here in Roseburg, Oregon. There were about a dozen or more booths there with the typical Keene straight from the box dredges there for sale but not too many innovators or custom sluice manufacturers and absolutely no washplant people. I found two folks there that were building custom sluices for somewhat specialized recreational applications.

After showing them the samples of the mat I had brought with me they seemed genuinely interested in giving my mat a try. I left both builders with enough samples so they could evaluate the mats performance. I talked to one guy at length about the differences between my saw-tooth mat and the Vortex mat he has been using in his builds and he could easily see how the saw-tooth mat might have advantages when it comes to efficiency over a wider range of flow velocities and conditions. But the proof is always in the pudding, as they say.

But in regards to my current inventory I still have enough material remaining that will get me through the testing and evaluation phase of my efforts. But nailing down my mass production methods are pending additional research and development on alternative manufacturing technologies. The EPDM extrusion manufacturing method is reasonably cost effective although it isn't anywhere near the cost to performance ratio of Vortex mats at the moment.

For recreational prospecting its all about the cost. But for commercial mining its less about cost and more about pushing an increase of efficiency by 1% or 2% and the increased take-home at the end of the day. My saw-tooth mat will definitely do that relative to Vortex mat or any other mat but breaking a product like this saw-tooth mat into the commercial markets takes time and effort and a lot of luck.

I knew going into this project that I didn't want to have to compete with all the BS involved with marketing to recreational miners. So the only avenue remaining for breaking into that market, in my opinion, would be purely based upon the price point. No manufacturing method can possibly compete with Home Depot vinyl runner floor matting and that isn't the problem. Most recreational miners know that stuff isn't worth the effort to install it. Neither do the Gold Hog mats present any real competition based purely on their relatively poor overall performance. The problem is getting the cost of the saw-tooth mat down to or lower than a reasonably good performing mat like Vortex.

I'm still working on that. We'll see.

dragline

  
Fleng
18:59:09 Mon
Jan 6 2014

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Re: Saw-Tooth Mat

As far as a low-tech, low-cost alternative how has a thick rubber outside mat faired as a slick plate?

http://www.walmart.com/ip/Clean-Step-Outdoor-Rubber-Scraper-Mat/24964528

WaL-Mart

This product while NOT designed for gold prospecting is 36 x 60" and weighs 16 pounds. It is far thicker than the Gold Hawg and I'd expect it to last much longer. It does not have the continuous riffles or varying sizes but is cheaper and easier to replace. With a standard size slightly larger than a typical sluice could it be worth a try?

  
JOE_S_INDY
23:42:55 Mon
Jan 6 2014

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Re: Saw-Tooth Mat

I have seen those mats in various restaurant doorways for years - and I firmly believe that is where they belong. I would never consider them for use in any sluice box., ever.

The pattern is designed for a specific application - some place to scrape your shoes. As to retaining Gold in that pattern - no, no, no. There is no continuity along any plane to retain Gold, just as some styles of expanded sheet metal have design channels which allow Gold to zig zag through the lath field. This pattern is even worse.

The only possible use for this mat would be a kind of stripper - to pull small Gold from the slurry at the very top of the sluice - only to allow that Gold to migrate right through that mat pattern. Better stripper designs exist - and they are just as tough as this rubber floor mat.

Good try, not going to work - use them for door mats and use well designed mats (like Hog mats) to retain Gold.

Joe










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Wiser Mining Through Endless Personal Mistakes
 
 
Fleng
18:29:01 Wed
Jan 8 2014

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Re: Saw-Tooth Mat

I wondered about the different styles of expanded sheet metal. How do you identify the "right" style for sluicing. There are multiple sizes as well. Obviously the angle and quantity of water will influence.

As I like to say there are no stupid questions....only stupid people asking questions.

  
JOE_S_INDY
18:48:33 Wed
Jan 8 2014

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Re: Saw-Tooth Mat

Fleng,

On that expanded - look for offsetting rows. Every other row (at least) should be offset so that there is no straight line path through the lath field.

The non-offset expanded tends to be used as louvers or vent screens instead of of the 'usual' expanded.

Joe




---
Wiser Mining Through Endless Personal Mistakes
 
 

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