[greybeard]

Here's a simple method for sieve making based on having plastic buckets/large flower pots available.
I hope the photo is self explanatory, but for clarity, starting from the left, first cut the top 3" or so of the bucket, making as smooth a cut as possible.
Glue the sieve material across the top of the bottom section of the bucket. In my case it was cotton mesh for these three, but it will be stainless steel for the finer ones. The glue I used was a flexible transparent one designed to have fast "grab" and work with most materials. It dries in a matter of minutes, but remains flexible. When it's dry, trim round it, leaving about ½"(15mm) sticking out, then glue this down the outside of the bucket. You may have to cut into the margin every 2" or so, to avoid wrinkles and to get it to lay down properly.
Next, the clever bit.
Take the original top of the bucket, and drop the bottom piece down through it, till it jambs. How far it drops is a function of the taper and thickness of the wall, but mine dropped about 1.5" down, hence my original choice of cutting a 3" deep section.
Push the sieve covered section as far down as it will go, keeping it as level as possible, then fix it in place with a sealant of your choice. I've got one that's designed as a nail substitute, called, originally enough "Hard as Nails"(there's another one called No more Nails).This dries hard fairly quickly, but I left it overnight to be sure it was solid.
Then, turning the assembly on its side, cut round the bottom edge of the outer wall, and you have a 3" deep sieve, which if you've been lucky enough to choose a stacking set as I did, then give you stacking sieves. One lid for the top, and a spare bucket for the bottom, and there's your set.
The actual source of my buckets were onion seed containers on the farm where I live, and they come with a snap on lid, but I've seen the same type in many places from catering jam containers, to 5 litre paint buckets.
I haven't decided what to do with the 5 bottom pieces yet, though one possibility might be a large anemometer for the wind turbine, but that's another project.....
John

[probinson]

Hello everyone,

Graybeard had mentioned this thread so I stopped by for a peek. Now that I see what he was up to I would like to suggest another method for sorting your particulate.

You can use two rollers with a gradually expanding gap similar to the drawing below. The gap in the drawing is greatly exaggerated so that it shows up but here is how it works.

You would start with a very small gap for the first pass. You feed your aggregate in a slow stream at the closed end with the rollers turning upward so the grains keep moving and roll down hill. The particles will fall through when the gap exceeds the grain size so you can place multiple bins below it and sort to any desired size. The wipers on each roller keep grains from just going over the side and the large gap at the bottom collects anything bigger than your current maximum sorting gap. The first pass collects the finest materials then you increase the gap and run whats left again repeating the process until it's all sorted.

The best part is that any Do-It-Yourselfer can make this cheaply and to any scale you like for adequate throughput. To make this work with extremely fine materials, however, everything must conduct electricity. If you use rubber, paper, plastic, wood, etc. static electricity will build up and fine particles will not drop through the rollers.

You could, of course, use a static charge to draw out the really fine particles first but that's another project.

Pete

[greybeard]

Hi Pete - and welcome. I like the roller idea especially the simplicity of the concept.
I wonder if you could go one step further, and use a pair of plain shafts, readily available from scrapped photocopiers, in order to avoid the necessity of accurately concentric axles ?
Or put it another way, I can't turn metal but have polished ground shafts in my scrap bin
Could you drive the shafts in a 'centerless' setup with a friction roller(s) at the top end ?
John

[Pakou]

Hello,
This is my first post, and hope you to answer my questions.
First, all I have read in this forum about polymer concrete for machine-tool basement is focused on epoxy/granite. Epoxy is expensive and difficult to process although it gives the best performance. My questions are:

- What about to use a vinyl-ester resin? Has anyone tried? Do you think it suitable?

- Referring to an epoxy (or vinyl-ester), what about the creep resistance? A high precision machine-tool demands time stability and polymers tend to this long term behaviour movements.

- Is postcured necessary? In both vinyl and epoxy?

- The exothermic reaction of an epoxy, wouldn't make it problematic for high thickness parts due to high temperature generation?

these questions are made from a machine-tool basement builder point of view, so hope the answers go in the same way.

that's all for the moment guys.
thanks in advance.

[greybeard]

Welcome Pakou.
The reason this thread has concentrated on epoxy is that, if you choose the right grade, it can produce the most accurate dimensional castings, and far better than any other system.
With regards creep over the long term, this is part of the ongoing search for the recipe that we are all seeking. Not only getting sufficient stiffness into the frame, but its long term stability is equally important.
I think others will give you better guidance than I regarding the exotherm problems, but it certainly is necessary that the castings go through some high temperature cycle in order that all the cross-linking at the molecular level takes place at an early stage in the reaction of the components. Otherwise, the cross linking may never take place, and the material not realise its full strength.
Regards
John

[probinson]

I wonder if you could go one step further, and use a pair of plain shafts, readily available from scrapped photocopiers, in order to avoid the necessity of accurately concentric axles ?
Or put it another way, I can't turn metal but have polished ground shafts in my scrap bin
Could you drive the shafts in a 'centerless' setup with a friction roller(s) at the top end ?

It could be even simpler that that. All you need is to slip a rubber band or an O-ring over one of the rollers and it will drive the other one and provide the tapered gap. A thin O-ring for a small gap, thick O-ring for a bigger gap.

You don't need a center shaft but it would make things easier. If you have a center shaft that is considerably smaller than the roller then you wont need any bearings.

Let's say, for example, that you have two 1" diameter rollers with 1/4 shafts. You could use two pieces of 2x4 as the end supports.

For the narrow end, drill two 1/4" holes, roughly 1/2" deep, and 1" apart. Wallow out the holes just a little so the shafts will spin freely in the holes. Do the same for the other end except make the holes 1 1/8 inches apart and a little lower so the gap end will be down hill. Put your rubber ring on one of the shafts and roll it up toward the narrow end until it makes good contact with the second roller. Turn either roller and it will drive the other in the opposite direction.

If you are working with really fine material then you will need a more elaborate setup but this will work for the stuff you can see.

Pete

[greybeard]

Nice one Pete.
John

[roach]

pakou
the exothermic reation when casting should'nt really get above 70 no matter the size of the casting the granite and depending what wmould you use should retard this
last week we did 7 ton one in a wooden mould didnt get above 70'c
vinly ester tends to shrink when casting due to the more rapid curing times

[ckelloug]

Is anybody reading this thread from somewhere near Lexington ,VA or does anyone know anyone? If so, I have need of a small E/G related favor involving picking up and shipping a couple items for which I would be happy to reward the volunteer. I would need a response in the next few days for this to work well.

Regards all,

Cameron

P.S. I've been very busy and the message notifier for this thread hasn't notified me of all the activity lately. Also, I will be in the California Bay Area this week if anybody wants to do lunch etc.

[roach]

is that anywhere near leicester :P

[ckelloug]

John,

I got the sample set you set from your side of the pond.
It was about as fast as mailing things domestically! I see
you gave it a valuation of $1. My thoughts are usually only worth $.02 so you must have put a lot of work into those samples! I'm on travel this coming week so It will be a week or two before I get results posted. They look good!

Regards all,

Cameron

[greybeard]

Great. I'm going to produce a set with just 'silver sand' as a filler, to give a base line agaist which we can judge the improvements. I should have done that first I suppose, but I'll give it the same spin cycle for comparison.
Regards
John

[greybeard]

Health and Safety Issue.
I didn't check the mounting of the B&D drill in the lathe headstock, so after about 10 minutes it worked loose and must have flung the spinning molds across the workshop.(chair)
Fortunately I was in the house, but I heard the commotion. No damage done to persons or property, but a valuable lesson learnt.
The molds remained intact with no leaks, so a restart was in order.
No problem since then, and they continue for the rest of the three hour spin.

This mix is 1 part playsand, 1 part silver sand, and 1 part flint powder, all mixed with 20% resin as before.
The flint powder is courtesy of SWMBO, retired pottery teacher. I measured its density to be 2.65, so it's the same as the sand, and I hope will not stratify in the spinning. If it 's ok then I shall use that as my smallest size component.

I'm now collecting quite a lot of meshes, the latest being a steal at the local auction - a set of five Endecott sieves for £11.

A bit battered, but in good working order, the sieves, not me. I'm due to become radioactive in about three weeks, so if I glow in the dark, I'll post a pic. He he he.
John

[greybeard]

Herewith todays results, saved from yesterday's debacle.

The smallest particles, the flint powder, once again seems to have stratified, but I have a theory

The powder did have a tendency to cake, so if I assume that it was damp, this would lower its density relative to the dry sand, and at 200G the difference might be enough to cause the observed effect.

If anyone has a better explanation, I'd be pleased to read it, as I can already see a flaw in the theory.(chair)

I'm not sure if the flint is still surrounding the larger particles of sand, it's difficult to see.
If anyone has the expertise and equipment to examine a section could they give me a shout. My stereo microscope only does x20, and I can't really see it well enough to know what's there.

The breakout of particles in the middle area, white because they're full of polishing compond, might be caused by my using a bandsaw to slice the ends off. Not the best tool, but the only one to hand.

John

[ckelloug]

I'm still on travel and thus not getting anything E/G related done.

Jack,
Can you help out John on the microscopy?

--Cameron

[probinson]

John,

Once you have a polished surface, acid etching will make your aggregate pop up so you can get a good look at it.

I don't know off hand which acid is appropriate, perhaps some else here does. I expect that any high strength acid would yield good results, but I do know that paint stripper will work and it's readily available.

Brush on some paint stripper, let it sit for 30 seconds (adjust as needed for the strength of the stripper used), then rinse it thoroughly while scrubbing with a soft bristle brush. The stripper will soften the surface of the epoxy but won't touch your fillers. Scrubbing away some of the softened epoxy will make your aggregate stand out so you can get a good look at it.

Pete

[greybeard]

Thanks Pete, I'll give that a try.
My main concern is just not being able to get enough magnification to see the fine particles of flint.
I've done a check on the powder by cooking it for half an hour at 160 C, but found no weight change, so my idea of adsorbed water was wrong. This leaves me wondering if air is trapped on the surface of the particles, and might be seen at high magnification.
This would give it just that extra bouyancy to produce the stratification, but I don't see why it didn't affect my earlier density measurement.
Possibly Cameron has it right when he suggested to me that the excess resin I'm using to improve the flow into my narrow test molds, is allowing this separation to occur.
I'm now thinking of using a refilled sealant gun to inject a thicker paste into the molds.
John

[probinson]

John,

I wouldn't expect you to be able to measure the moisture and other volatiles unless your scale can differentiate down to the micro-gram.

When epoxy is used for high strength applications it is almost always either put under deep vacuum before curing or under pressure during the cure. Having built ultrasonic imaging transducers, I know from experience, that it is nearly impossible to get a perfect casting from a straight pour.

If you would like to send a small amount of the materials you're using I'd be glad to cast them under different conditions and post the results. I have vacuum chambers and curing ovens and can test the yield strength, density, particle uniformity, and take some micro-photographs. I work at the Medical Collage of Virginia so any equipment I don't own myself I probably have access to. Just let me know if you'd like some help.

BTW, is your mix targeted at yield strength or reducing the epoxy content?

Pete

[greybeard]

Pete, I may have given you the wrong impression of what I'm doing.
I thought I might have >5% moisture in the flint powder before mixing. As I can weigh to +/-10 mgms, I assumed I could detect a weight change after drying, but on my 10gm sample I couldn't find any change at all, so I've ruled that out as a prime reason for the appearance of the casting.

Re the strength/resin reduction question, I'm now trying to establish a base line figure via Cameron's testing equipment for my spin casting method using a single fill, then moving on the more complex recipes.
Bear in mind that the path I am following differs in casting technique, so my "best" recipe is going to finish up somewhat different to most other peoples, even though what we all learn may be of mutual benefit in the process.
Unfortunately, I've started backwards by sending him a multiple aggregate casting to start with, instead of the simple one.
I got a bit distracted by seeing the separation that occurred in it. By trying to guess what caused it, namely the variation in density of the components, I tried to solve it by using all "quartz"(sand and flint), and found the problem remained.
Finally come to my senses and can see that I must go with a single fill, make it as high a concentration as I can, and use that as a benchmark to judge the improvement I can obtain by introducing more components along the line of de Larrard's work.
All fascinating stuff, and many thanks for your offer, as I am sure I'm going to need it, sooner rather than later.
Regards
John

[probinson]

Hey John,

I hope you don’t mind the intrusion but, I’d just like to help if I can.

This thread is rather massive so I only read a few pages at the beginning and a few more at the end, which didn't give me the full picture. Now that I have more insight into your method, I'd like to offer my analysis of the problem and some possible modifications to your procedure.

Your epoxy looks clear or translucent which puts the specific gravity pretty close to 1, in which case, almost any filler you choose, that isn't hollow, will sink. The relative density between particles makes no difference and I don’t believe your problem has anything to do with buoyancy but rather with how particulate settles in a viscous mixture.

Think of it like this. Spinning the mix has the same affect as increasing gravity. This increases the pressure so bubbles become more buoyant and pop to the surface easier but, except for speeding up the settling process, it doesn't change how the particles settle.

I imagine that you pour in your mixture and probably stir a little or tamp it down to help it distribute evenly. At this point, your mixture is nicely uniform but is not yet compacted so it then goes to the centrifuge to force the aggregate to pack down as tight as possible. As the mixture compacts, the large aggregate quickly settles out. It packs down evenly just as planned but displaces some of the mixture in the process. The fine particles are easily carried to the surface by the epoxy flowing out of the decreasing space between the larger particles but these fine particles can’t settle back down around this fixed matrix. The fine particles migrate to the surface simply because their small size keeps them in suspension longer, not because they are more buoyant.

As I see it, there are two basic options. Either you force the aggregate to settle evenly or you use a thick mixture that doesn’t need to settle.

Vibrating the mold is probably the simplest method to force even settling. This works best if you are using a low viscosity epoxy. If your epoxy is thick then inserting a vibrating rod or paddle will be more effective than simply vibrating the mold. After vibrating you can spin the mixture to encourage any trapped bubbles to escape and force epoxy into any minute irregularities in the aggregate.

The other option is to make your mixture either with a very thick epoxy or make the mixture very dry, like cookie dough. A dry mixture will use less epoxy and produce a much denser material but it should be cured either under pressure or in a vacuum bag to eliminate voids. In any case, your material must be mixed thoroughly so you need a very slow or thermal cure epoxy for this.

Using a dough-like material does have the advantage of being able to easily produce partially self-supporting features. You could, for example, press it onto the inside of your mold to make a hollow structure. Form a few ribs for added support and you have close to strength of a solid pour but with substantially less material and weight.

Pete