Large Epoxy Granite Vmc Project

gt40

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Exceeding the performance envelope in every way of my Rf45 clone is the base line goal while being on a budget.

I have been accumulating components over the past year. I have come to hate dovetails and am going with linear guides:

THK SHS30 for X axis 18”/700mm travel
THK SHS 20 for Y&Z axis 20”/780mm travel
I am going to be using either THK or NSK -32mm ground ballscrews
Epoxy granite for all major components and use of precision ground steel plates cast in place for the linear rails, servos, ballscrews etc.

Here is the basic design. I am using simple straight forward forms for the molds and incorporating plumbing in the casting to provide for lubrication and cabling:

mill%20frame%20sketch.jpg


THK Linear Guides-

thk-shs.jpg

more to follow...
 
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sgisler

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Interesting......watching


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gt40

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A key point to the design is using 2 steel bars ground to .001" on all sides and 1/2"x3"x36". Each bar weighs a lot. I am aligning the bars and bolting them to each other with the cross members embedded in the epoxy for strength. That way I can pre drill the holes and fix them precisely by bolting them through the mold using coupling nuts which will serve as anchors for them. They will form a coplanar mounting platform for both the linear rails and the mill column.

steel-log.jpg



I am aligning the two 3x36x1/2 precision ground bars parallel using a 12" granite surface plate. Then I will align them on the same plane by cross bolting 1 x 1 precision ground bars to fix them in place aligned.. Once cast into the epoxy base this assembly forms the basis for both the y axis and the vertical column for the z axis which will also use 2 ground steel bars aligned the same manner as the base.

Finally, I am going to cast in place a 15x15 ground plate "frame" on the bottom of the z axis. After reading about using grouting for alignment, I will use this method and have jack screws to do the final adjustments and then grout.

All the ground bars are being drilled and will be through bolted in the mold using coupling nuts to hold them in place.when I cast the epoxy granite. This should provide a precision ground and aligned surface to do final indicating of the rails.

I managed to drill the steel bars for the 30mm linear rails. I was worried about the prospect of drilling 18 holes through tool steel all aligned but it worked. I had to do 3 different setups on my rf45 clone for each rod. I bolted one of the linear rails direct to the table and indicated it straight and then used that as a straight edge for steel bars. Really made me wish I had a bigger mill! At the end, every single hole witnesses the linear rail holes.
drilled%20steel.jpg

As far as the size of the linear rails, they were selected on the basis of the largest I could afford and fit in the design. I got all of them on Ebayand they were new stock. I averaged 200 per axis for rails and guide blocks.

The Y axis has the most forces on it because it has the x on top so I went with the extended version THK SHS30. They are going to be 15" for maximum rigidity. I can get a decent amount of deflection cutting steel on the RF45 and this is one area I wanted to really improve.

The X and Z have less force and going with the 20mm THK SHS to provide more range of motion.

To get an idea of the footprint of the machine, The base is 22"x42" x 9" and will weigh over 800 lbs by itself before adding linear rails, ballscrews and servos.

I expect the whole machine to come in around 2700-3300 lbs(1225-1360 kg)

Envelope for each axis is:

X: 22-24"/560-600mm

Y: 15"/380mm

Z: 18"/460mm

Trying to find a 7-8 hp spindle.

I got a 40mm THK ground screw and another ground ballscew for Harding that is a double nut. Both are larger than my original design so everything got supersized.
 
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gt40

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Here are some more pics:

Length of mold:
length.jpg

width of base:

THK 40mm ballscrew- this thing is really heavy, new old surplus-. It must weigh 30 lbs/14kilos:
thk%2040mm%20ballscrew.jpg
Harding 36mm ballscrew for the y axis:
harding%20ballscrew.jpg
Here is a pic of the layout for the mold base. It is almost ready to go- I will be radiusing all corners in the mold with grout. The pipes are going to be cast in place lift points- stick a pipe or lift strap through them. Keep in mind all of these pics are from the perspective of the bottom of the base looking up or upside down:
layout%20with%20tubes.jpg
Final shot showing the x axis linear rails laid over the mold to gauge foot print- The wider base will support the x axis better.
x%20axis%20rails.jpg

I will post more but would also like to ask for help- I should have the mold finished and be ready to pour the base by next weekend. If anyone local to Santa Monica would like to come down, I could use the help. Mixing 7 gallons of epoxy and 700lbs of aggregate should be interesting.
 
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gt40

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Update:

I have the mold for the base almost finished and the ground steel bases for the linear rails aligned and bolted to the mold. The two 1/2" thick 3" wide bars also have the benefit of supporting and keeping the mold really flat. Pic of the mold with the ground steel bars bolted and aligned:

ry%3D400
My epoxy just arrived and I should have the "flour" portion of the aggregate mix tomorrow.

FYI, the "flour" is from a pottery supply house and is Custer Feldspar, so names because it is a type of mineral mined in Custer, SD, is made up of silica and alumina combined with sodium and potassium oxides, It is finer than their 320 grit stuff they had and the price was right at 50 bucks shipped for 55lbs. There are studies showing adding an extremely fine flour like mix of powdered quartz/aluminum oxide to the blend of aggregates can increase strength by as much as 30%.

I have 3 size sands, decomposed granite to pea sized gravel also.

I plan on casting next week now that I have everything together.

Anyone not familiar with "epoxy granite" may find this link of interest:

http://en.wikipedia.org/wiki/Epoxy_granite

There is also a 4000 post thread on the zone but basically you gain as much as 10 times the vibration dampening capability of cast iron and other benefits:
  • Flexibility: custom linear ways, hydraulic fluid tanks, threaded inserts, cutting fluid, and conduit piping can all be integrated into the polymer base.
  • Inclusion of inserts etc. allows greatly reduced machining of the finished casting.
  • Assembly time is reduced by incorporating multiple components into one casting.
  • Does not require a uniform wall thickness, allowing for greater design flexibility of your base.
  • Chemical resistance to most common solvents, acids, alkalis, and cutting fluids.
  • Does not require painting.
  • Composite has a density approximately the same as aluminum (but pieces are thicker to achieve equivalent strength).
  • The composite polymer concrete casting process uses much less energy than metallic castings. Polymer cast resins use very little energy to produce, and the casting process is done at room temperature.
The idea is to mix various size hard quartz, granite etc aggregates in a mix that minimizes the space between them and 8-15% epoxy as a binder only. you ram it into a mold and if possible vibrate it to further compact things. The material will take accurate impressions of the mold and can cast flat to .001" if done correctly.

While I have worked with concrete and composites a bit, this is my first effort with this material besides casting a sample.

Should be interesting....
 
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jbolt

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Great project!

Just out of curiosity, are you going to add additional support around the perimeter of the mold?

Jay
 

gt40

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Great project!

Just out of curiosity, are you going to add additional support around the perimeter of the mold?

Jay
I going to use strap clamps around the mold and bar clamps + the 2 pipes will be through bolted to prevent 800 lbs of mix from finding a way out hopefully. I have screws every 6" on the mold seams + construction adhesive.

Part of the reason I want some other people around is in case it gets interesting :p
 

Cobra

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With mold walls that thin I would be tempted to run "edge-on" rings around the mold to keep the sides from flexing outwards.
 

MikeWi

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More work and expense, but it seems like embedding the whole mold in a larger box with tamped sand would offer complete support to the mold walls and keep everything where you want it. That's a lot of weight pushing on that wood, and the packing process will want to push it out as well.
 

gt40

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Thanks for the suggestions- I think you are both right about reinforcing the perimeter. I haven't seen any builds this size so better safe than sorry. Any other suggestions are appreciated...
 

rwm

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This is awesome! What do you use for mold release? Is the melonite enough?
I agree about reinforcing those sides some more. They may bulge and become convex. How about a perimeter of angle iron?
R
 

gt40

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This is awesome! What do you use for mold release? Is the melonite enough?
I agree about reinforcing those sides some more. They may bulge and become convex. How about a perimeter of angle iron?
R
I will be reinforcing all castings with re-bar. As far as mold release, carnauba wax works with the melamine coating pretty well.
 

jumps4

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this is a kewl project
I was interested in a build like this years ago but never did it
thanks for posting your build
Steve
 

H8deadW8

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Neat project! I formulate epoxy resins professionally, and I enjoy seeing new uses for my favorite polymer!

What epoxy are you using? I would suggest you have a plan in case the resin exotherms. I have personally had a 1L batch of resin with a quoted potlife of 4 hours exotherm in a half hour. The worst case scenario for exotherm is mixing a big batch of resin in an insulating container. Using a metal mixing container should help, as will adding the filler. If it does run away, there won't be much you could do to stop it-- a garden hose might be the best option.

We generally use 5mil nitrile gloves and safety glasses as the minimum personal protective equipment in our polymer lab. The amine curatives (B-side) can burn skin and eyes. The actual epoxy (A-side) tends to be more benign, however you can become sensitized to it with repeated exposure. If you get any resin on your skin by accident, wash with soap and water-- never acetone, as this allows the chemicals to penetrate your skin.

The A-side and B-side really should be weighed out on a scale prior to mixing to make sure you get the proper mix ratio. This ensures that you get the best cured properties. Also, thorough mixing is critical.

Sometimes we have filled samples that settle during cure. Essentially, the particles fall to the bottom of the sample, producing a resin rich layer on top and a filler rich layer on the bottom. Since epoxy shrinks on cure (though less than almost all other polymers), the resin rich layer contracts more than the filler rich layer, and the sample bows. You are shooting for a very high filler loading, which should prevent that, but if the resin does pool on the surface of the casting, it may be worth removing before it fully cures.

Hopefully the resin manufacturer provides a recommendation for cure time. Most ambient cure systems I have come across continue to gain strength over the first week or 2. Heated post cure improves the properties of most epoxy formulations, but you have to make sure the heat is applied slowly and evenly to prevent the possibility of warping.

I wish I could come help out with this project, but I'm on the other coast. Please let me know if I can be of help remotely.

Nic
 

gt40

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Thanks for your interest. I have made a few things as a hobby and some boat projects with composites but nothing on this scale. I have had the exotherm experience and am concerned about it. I will have to mix about 7 gallons worth of epoxy and then put that into a premixed aggregate mix of around 600 or so lbs. I am shooting for 12% epoxy to aggregate ratio by weight. From what I have been researching, the aggregate will slow down the curing and limit/prevent exotherm.

I bought us composites 635 with the slow hardener, based upon successful application in a few builds on cnczone and the price wasn't as expensive as some. http://www.uscomposites.com/epoxy.html

I have spoken to the manufacturer and to someone who used it in this application and this setup offers low viscosity and long curing time. from US composites website:
"Our slow hardener should only be used at temperatures above 80 degrees unless an extremely long curing time is desired. Temperatures below 70F during the cure can result in a 2-3 day drying time."

My plan is to pre mix the aggregate with a 6 cf polymer barrel concrete mixer, mix the epoxy and add to the rotating mixer as fast as I can mix each gallon of epoxy. Alternatively, I could put the epoxy in a large container mix it at once and then add to the aggregate. I will use a large rotary mixer and properly mix the a&b portions. after it is the right consistency, I will pour into the mold and pack it + attach a bench grinder motor with eccentric weights to vibrate it bolted to the base of the mold.

If you have any suggestions, or concerns about how best to do this, I would welcome any input.
 

dracozny

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normally I would suggest a vacuum Chamber instead of a vibrating table on such a thing but due to it's size that may prove difficult. It would remove any air trapped in the epoxy in extremely short order.
 

brav65

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Would a vacuum bag work? You can buy bag material on a roll then just seal the ends and apply the vacuum with a pump.
 

gt40

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I have a pretty serious vacuum pump and have done some infusion composite stuff but consensus on the cnc zone monster thread is that the thickness of the piece and viscosity prevent large epoxy granite stuff from vacuum. I am going to pack the mold and vibrate. The mix should only be 12-14% epoxy
 

dracozny

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I have a pretty serious vacuum pump and have done some infusion composite stuff but consensus on the cnc zone monster thread is that the thickness of the piece and viscosity prevent large epoxy granite stuff from vacuum. I am going to pack the mold and vibrate. The mix should only be 12-14% epoxy
I haven't seen such a thread but they make large rigid boat hulls under vacuum. over at this vid they are using a vacuum to degas before the pour of a granite sink.
the main thing I have seen from some people making test videos of such a thing is failure to apply a proper release agent to the mold itself. A combination of vacuum chamber and vibrating table is not a bad idea either. The vacuum is going to remove all of the trapped air. The vibrating table will help settle any clumped aggregate.
 

gt40

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I haven't seen such a thread but they make large rigid boat hulls under vacuum. over at this vid they are using a vacuum to degas before the pour of a granite sink.
the main thing I have seen from some people making test videos of such a thing is failure to apply a proper release agent to the mold itself. A combination of vacuum chamber and vibrating table is not a bad idea either. The vacuum is going to remove all of the trapped air. The vibrating table will help settle any clumped aggregate.
I saw that video- the viscosity for the mix I am using is a lot thicker and has different aggregates.

Here is a good commercial example of the process. They show the mixed aggregate being packed into molds:

 

dracozny

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that is some thick stuff. tempted to experiment myself on the matter. too many projects as is though.
 

H8deadW8

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I like the idea of adding gallon batches of resin to the aggregate. The aggregate acts as a thermal sink to reduce exotherm, which is limited by the specific heat capacity of the filler. If I was going to try this and had to use commercially available resins, I would look at RTM (resin transfer molding) resins-- these also go by names like VARTM and vacuum infusion resin, but the resin is essentially the same. RTM resins have low viscosity like the US Composites material (600cps = 0.6Pa.s), but often have very long gel times. Adtech, PTM&W, and Resin Services would be the first places I looked. It would be really fun to formulate a resin for this application-- we could get pretty tricky and increase the working life to 12 hours, add air release agents to help it degas on its own, and pigment it for aesthetics. If anyone has a commercial interest in this, let me know-- I work for an emerging technologies group that can do contract research.

Development of a filler system to achieve maximum filler loading is nontrivial. You can get nerdy and try to calculate it, but you generally have to make the assumption that all of the filler consists of spheres that are consistent in size. A direct approach would be to fill a container of known volume with your largest size filler. Then you add water to fill the void spaces. So you might take a 1 liter container and find that the water required to fill the void spaces is 400mL, hence your system is 60 volume% filled. Next, assume your second largest filler could take up a maximum of 400mL, but if packing efficiency is 60vol% again, then you would end up placing 240mL of small filler in the voids left by the large filler. The problem is that the second filler will likely have a different packing efficiency than the first-- so perhaps you perform 3 experiments at different ratios, maybe 65,60, and 55vol%. Do the water displacement on these to determine the best amount of the second filler to use. Assuming 60vol% turns out to be the ideal ratio again, the void space you would measure would be 160mL, so your system is 84 volume% filled. Note that if the small filler is only 1/2 the size of the big filler, it will not fit into the voids between the big filler, and the packing efficiency will be poor. Ideally, the second filler should be 1/10 to 1/20 the size of the first. You could repeat the testing procedure to add a third filler, though at some point I am sure you would have trouble getting air bubbles out of the filler/water test container. A little soap might help with that. Anyway, moving down to smaller and smaller fillers is a game of diminishing marginal returns, and smaller fillers have a larger effect on the viscosity of the final system due to their high surface area. If anyone decides to go down this rabbit hole, remember that to get from the weight of the filler to its volume, you need to divide by the filler's density. So 84vol% filled will not be 84 weight% filled, unless your filler has the same density as the water (or resin). Sorry about the nerd out!

Best of luck with this project, and please keep us updated.

Nic
 

gt40

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I like the idea of adding gallon batches of resin to the aggregate. The aggregate acts as a thermal sink to reduce exotherm, which is limited by the specific heat capacity of the filler. If I was going to try this and had to use commercially available resins, I would look at RTM (resin transfer molding) resins-- these also go by names like VARTM and vacuum infusion resin, but the resin is essentially the same. RTM resins have low viscosity like the US Composites material (600cps = 0.6Pa.s), but often have very long gel times. Adtech, PTM&W, and Resin Services would be the first places I looked. It would be really fun to formulate a resin for this application-- we could get pretty tricky and increase the working life to 12 hours, add air release agents to help it degas on its own, and pigment it for aesthetics. If anyone has a commercial interest in this, let me know-- I work for an emerging technologies group that can do contract research.

Development of a filler system to achieve maximum filler loading is nontrivial. You can get nerdy and try to calculate it, but you generally have to make the assumption that all of the filler consists of spheres that are consistent in size. A direct approach would be to fill a container of known volume with your largest size filler. Then you add water to fill the void spaces. So you might take a 1 liter container and find that the water required to fill the void spaces is 400mL, hence your system is 60 volume% filled. Next, assume your second largest filler could take up a maximum of 400mL, but if packing efficiency is 60vol% again, then you would end up placing 240mL of small filler in the voids left by the large filler. The problem is that the second filler will likely have a different packing efficiency than the first-- so perhaps you perform 3 experiments at different ratios, maybe 65,60, and 55vol%. Do the water displacement on these to determine the best amount of the second filler to use. Assuming 60vol% turns out to be the ideal ratio again, the void space you would measure would be 160mL, so your system is 84 volume% filled. Note that if the small filler is only 1/2 the size of the big filler, it will not fit into the voids between the big filler, and the packing efficiency will be poor. Ideally, the second filler should be 1/10 to 1/20 the size of the first. You could repeat the testing procedure to add a third filler, though at some point I am sure you would have trouble getting air bubbles out of the filler/water test container. A little soap might help with that. Anyway, moving down to smaller and smaller fillers is a game of diminishing marginal returns, and smaller fillers have a larger effect on the viscosity of the final system due to their high surface area. If anyone decides to go down this rabbit hole, remember that to get from the weight of the filler to its volume, you need to divide by the filler's density. So 84vol% filled will not be 84 weight% filled, unless your filler has the same density as the water (or resin). Sorry about the nerd out!

Best of luck with this project, and please keep us updated.

Nic
Thanks for all the info. I am nearly done with the mold and have been busy radiusing all the inside corners and completed alignment and test fit of the rails - better to do this before you pour epoxy.

I have a couple of questions:

1. What would you suggest for air release agents for the US composites epoxy I already have?

2. What would you suggest as a cost effective means of mixing all of this? I leaning towards the polymer tub gas powered cement mixer from home depot- It is a fall type basically a big plastic barrel with fins inside.

3. If I went the cement mixer route, how do you clean it?

Thanks, in advance for any ideas
 

Eddyde

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As far as cleaning a mixer, Xylene is usually a good solvent for epoxy but it would still be a real mess to deal with and you would have the issue of sludge disposal. Are you planning to rent a mixer of buy one? If you buy you only need to scrape off the bulk of the residue, subsequent mixes will slowly build till the drum is useless, but I suppose you would get quite a few batches before that happens. Also why a gas mixer? an electric will do the job albeit in smaller batches, they are way cheaper too. I have an electric that will easily mix about 250lb batches of regular concrete.
 

gt40

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Thanks for the suggestion on Xylene- it is banned here in the peoples republic of ca. I ended up finding a 90 gallon giagantic 90 gallon mixing tub.
I also picked up a 1000 lbs of aggregates and sand and rinsed about 300lbs of the larger size.

I was able source everything local to avoid shipping costs but the "flour" portion made up of powdered quartz and alumina- I got that online from the big ceramic store 50lbs for 50 bucks including shipping. FYI, it really does feel and look like fine flour. Everything else came from Home Depot and the local West LA Building Supply store.

On top of that, the epoxy came:

epoxy.JPG


Supplies:

Decomposed granite, 60 grit sand, small pebbles and a giant 90 gallon mixing tray:

750lbs.jpg


Unloaded:

Each sand bag is 100 lbs and the rest are 50 or 75lbs + more in the garage

WP_20150316_16_52_45_Raw.jpg

I am easily amused but the mixing tub really is awesome- you can mix the whole batch in one shot.

WP_20150316_17_43_44_Raw.jpg

Here are the different aggregates:


aggregatetypes.jpg


To promote adhesion, you need to wash them and let them dry properly. The decomposed granite was really dirty:


washing.jpg


Here is a close up of the 2 types of large stones from Home Depot:

hd%20stones.jpg


smaller grades:

WP_20150316_17_26_50_Raw.jpg

30 and 60 grit sand also- I didn't have to wash that because you can buy graded washed and kiln dried fairly cheap in 100 lb bags.


Here is a close of the mineral "flour"

WP_20150316_17_26_38_Raw.jpg

I used epoxy tile grout with a large radius form to creat a 3/4" radius on all inside corners of the mold:

WP_20150315_18_47_54_Raw.jpg

Radiusing the corners makes it easier for the mold to release and the final base won't have sharp edges...

grouted2.jpg


Well, my arms are sore but I hope to be able to pour the mold this Saturday- forecast is 59/74. FYI, anyone local to Santa Monica who wants to hang out and see me make a mess, I could sure use the help! Pm if you can make it

Thanks,

epoxy.JPG

750lbs.jpg

WP_20150316_16_52_45_Raw.jpg

WP_20150316_17_43_44_Raw.jpg

aggregatetypes.jpg

washing.jpg

hd%20stones.jpg

WP_20150316_17_26_50_Raw.jpg

WP_20150316_17_26_38_Raw.jpg

WP_20150315_18_47_54_Raw.jpg

grouted2.jpg
 
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sgisler

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Wish I were closer, would be interesting to see it come together and would be glad to pitch in (quite a drive from Dallas though).


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Boswell

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Looking forward to seeing your progress each day. Thanks for sharing. Good luck this weekend.
 

gt40

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FYI, here is the mix I have come up with. I really wanted to use local aggregates wherever possible to save shipping and reduce overall cost. Empirical observation and practical considerations are the basis for the mix:
epoxy%20mix.jpg

epoxy%20mix.jpg
 

gt40

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Update:

I have washed all of the aggregate and have it drying spread out on tarps. For anyone wanting to work with epoxy granite, it is important to wash, clean and dry the aggregate. I washed it by filling 5 gallon buckets with material and then stuck a hose into it and washed it until the water cleared. The larger stones weren't bad but the decomposed granite is really dirty. Afterwards, you spread it out on something to dry. Tarps make it easy. This step is important for proper bonding with the epoxy as the fine dirt and any moisture will mess things up when you go to mix. It is taking about 3 days for things to dry - I have raked it out to rotate stuff each day when I come home from work. Looking forward to casting the base this Sunday...
washed-aggregate.jpg
 

chrisf

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Awesome build so far!! Where did you get your flat stock? Msc had it for 202.00 each.
 
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