[walter]

Could you share what formulation you used to make the table you describe in post #2052? What you are describing is good enough for me. I want to get casting and building my first cnc machine, pronto! As you guys perfect the formula, and find cheap and easy ways to find most of the materials, hopefully I will be on to an e/g cnc lathe or a larger mill, where I can benefit from the new formulas.

That is good thinking; Cameron's grading works and there's no need to waste time.

Please read this first: http://www.cnczone.com/forums/showpo...postcount=1942

This one has the info on doing your own aggregate sizing:
http://www.cnczone.com/forums/showpo...postcount=1824
I was impressed by it, but I wasn't able to learn it.

The formula I'm using is based on Cameron's trial formula: http://www.cnczone.com/forums/showpo...postcount=1753
in which I substituted G850 Zeeospheres for G200.

1 part #6 Agsco Brown Aluminum Oxide
1 part #4 Agsco Quartz
1 part #2 Agsco Quartz
1 part #2/0 Agsco Quartz
1 part G850 Zeeospheres
2 parts G800 Zeeospheres

Agsco is the supplier, #6 Brown Aluminum Oxide is 3070microns or 0.120" - I really like this stuff.
http://agsco.thomasnet.com/item/all-...=prod&filter=0

The formula is said to be able to fill up to 88%, how much epoxy is up to you. Less is better and don't forget about vibrating. BYK sends free samples, I got mine in 6 days. Get the large one, it's good for over 500lbs. G200 Zeeospheres are better, don't use G850. Total cost of the formula with resin ~$0.90/lb

Good luck!

[walter]

Can anyone help me decipher these properties?

Hardness Shore D1/D15 84/83
Tensile modulus of elasticity MPa 3,000
Tensile strength MPa 69
Flexural modulus of elasticity MPa 2,600
Flexural strength MPa 100
Compressive strength MPa 85
Elongation at break 7.5%
Temperature of glass transition 71 C
Coefficient of thermal expansion 77 x 10-6.K-1

I would really appreciate it.

[lgalla]

Dave,I agree on the pre carbon black and the first layer.This is mandatory any way as TT is done in more than one pour.First coat is a seal coat.US Composites has a detailed How to do it.Read it.
Like the side plate idea.
Me too want not to scratch ESP.Since I am a wood guy,I will build a vacuum box over the platen and many holes and scraficial MDF top sheet.Milling the scraficial MDF top is done religiously by wood shops to maintain parallelism to the gantry.
Charcoal I understand is for bar-b-q(flame2) Not plates.Art supply houses have carbon black or lamp black which is soot like from a candle.Try to get a free sample of Monarch 800 from Cabot.
Larry

[jhudler]

Hardness Shore D1/D15 84/83 – See http://en.wikipedia.org/wiki/Durometer or http://www.machinist-materials.com/hardness.htm.

Tensile modulus of elasticity MPa 3,000 = 435,113 PSI
Tensile strength MPa 69 = 10,007 PSI
Flexural modulus of elasticity MPa 2,600 = 377,098 PSI
Flexural strength MPa 100 = 14,503 PSI
Compressive strength MPa 85 = 12,328 PSI
See http://www.megaconverter.com/mega2/

Temperature of glass transition 71C ... I dunno Scotty; using the euclidian metrization of a K-fold contravarient Riemannian tensor field, it could be the temperature that Dilithium crystals fail to undergo crystali restructer. In other words; got me!

Elongation at break 7.5% means the elongated 7.5% just before it broke.

The CTE is throwing me because it's incomplete... probably a test standard from Mettler.

[dfro]

The formula I'm using is based on Cameron's trial formula: http://www.cnczone.com/forums/showpo...postcount=1753
in which I substituted G850 Zeeospheres for G200.

1 part #6 Agsco Brown Aluminum Oxide
1 part #4 Agsco Quartz
1 part #2 Agsco Quartz
1 part #2/0 Agsco Quartz
1 part G850 Zeeospheres
2 parts G800 Zeeospheres

Agsco is the supplier, #6 Brown Aluminum Oxide is 3070microns or 0.120" - I really like this stuff.
http://agsco.thomasnet.com/item/all-...=prod&filter=0

Walter,

Thank you for the summary - very enlightening.
A few more questions, if I may?

Where are you getting the Zeeospheres? Are you getting them from The Cary Company? It looks like they are close to Agsco in Illinois. I will do a road trip and pick up all of this rock, if both companies will sell to an individual. Are Zeeospheres sold in 50 lb. bags?

Also, once you mix all of the aggregate together my volume, do you then add in the epoxy 10 to 20% by weight or is it by volume?

I have a hunch about how vaccuum bagging will help the casting (maybe somebody has already speculated on this). I remember reading in this thread that vibrating the epoxy/aggregate mixture in the mold will cause the aggregate to compact more tightly and extra epoxy will pool on the top. I have noticed, while vaccuum bagging, that any extra epoxy gets sucked out the seams of whatever I am gluing together. In fact the extra epoxy seeps out all over the part and the glue table. This property could be used to suck out of the e/g casting the extra epoxy that pools at the top and make it stronger - help it approach the 10% ideal. Because the epoxy will seeps into every nook, it will probably be necessary to destroy the mold to remove the e/g casting.

The extra epoxy will help in saturating the aggregate, de-airing/vibrating, and flowing into the mold. Then it will be sucked out of the top of the mold when it is vacuum bagged. Thoughts?

Larry,

I was looking at your gantry mill design. I like the idea of the raised rails to provide less torque on the gantry and its bearings. I have been considering that design also for a long time. I could not figure out how to easily make the raised rails stable and accurate using weldments, though. How about casting two raised walls into the mill table along the 'x' axis? You could cast 1/8" ridges into the top of the walls (just like I propose doing on the table) and pour leveling epoxy for the guide rails at the same time you pour the leveling epoxy for the table - that way everything is aligned the same in one easy step. Also, everything is one solid, stable piece. What do you think?

I know what I am thinking: I need to buy a 1 or 2 ton hoist, tomorrow.

Thanks,
Dave

[jhudler]

Walter, where did you purchase your Zeeospheres (3M Ceramic Microspheres) from?
What did you pay for them?

Thanks,
Jack

[walter]

Thanks for your help.

Zeeospheres are from the Cary Co (Agsco for everything else).

Total cost of the formula with 635 resin about $0.90/lb.

Zeeospheres are sold in 50lb bags at $25/bag for G800/G850 and I think twice as much for G200.
$50 min order at Cary- very friendly people

[lgalla]

Dave I don't think you are talking about my design.My design is a large table router.The concrete should read polyconcrete or E/G
Larry

[dfro]

Larry,

I was talking about the gantry mill pics you posted in post #963. I like your surface plate/table design - very elegant. My feeling is that the larger the table, the more one should consider just casting it into the concrete floor of one's shop. Steel rails for attaching guide rails and motor mount plates can be imbeded in the casting (or part of the outer frame, like you have designed). Then you cover them in a 1/8" inch thick epoxy surface plate. Since I rent my shop space, I don't think I will go for this approach. A person would have to do a lot of stooping over to attach work pieces to the table, also. Maybe a raised bed of steel reenforced concrete could raise up the bed 12" or more.

I am working on some cad sketches of the raised wall mill table design.

Thanks,
Dave

[Coogrrr]

Can this stuff be CNC milled after it is formed? with a stone bit?

Can we make a mold to create this table (see picture) I think the whole machine and solidifying the base etc is a huge endeavor and I think you guys can beat it but I was looking at building a nice table for my CNC with leveling bolts built in and tslots and vacuum channels too!

with E/P i think this table could be made or I could be daft as one poster put it.

Coog

[Coogrrr]

Dave I don't think you are talking about my design.My design is a large table router.The concrete should read polyconcrete or E/G
Larry

How would you hold down your materials to be milled? I would suggest placing bolts every so many inches and then twisting them out afterward??? I thought I read on an earlier post that stud holes can be cast into this stuff...

I posted a suggested table top that is t-slotted to handle this.

Thoughts?

Coog

[dfro]

How would you hold down your materials to be milled? I would suggest placing bolts every so many inches and then twisting them out afterward??? I thought I read on an earlier post that stud holes can be cast into this stuff...

Coog,

My feeling is that all of the bolts (with release agent on them) sticking up when I cast the leveling epoxy will create manisci everywhere. This will very much mess up the flatness of the epoxy surface plate when it is poured. I also don't want to worry about alignment of bolt holes when casting the table. I want to use the machine when it is operational to drill holes into steel bars embeded in the table.

Dave

[greybeard]

Coog - I'd be interested in the answer to your question about milling the E/G.
While I have no doubts about my spin casting method, retaining the resin in the mold, and the mold on the bench, I am worried about retaining the relative positions of channel formers. Being able to clean up the section after casting would be a useful insurance.

My gut feeling re milling it is that whatever cutter material you choose to cope with the aggregate particle - steel, carbide or diamond - it will become gummed up by the resin, even with an appropriate coolant flooding it.
I'd be glad to be shown to be wrong.
John

[walter]

Also, once you mix all of the aggregate together my volume, do you then add in the epoxy 10 to 20% by weight or is it by volume?

I've had everything in plastic cups and did not premix the aggregate. Initial batch was done by volume then carefully weighted. I used that to prepare 120 cups of material, resin and hardener. Aggregates went one by one into the mixer, starting with the largest -which is probably the wrong way around..
20% epoxy is by volume but I tried to lower that number.

And, I'm very interested in seeing your results with vacuum bagging.

Cheers!

[Coogrrr]

Coog - I'd be interested in the answer to your question about milling the E/G.
While I have no doubts about my spin casting method, retaining the resin in the mold, and the mold on the bench, I am worried about retaining the relative positions of channel formers. Being able to clean up the section after casting would be a useful insurance.

My gut feeling re milling it is that whatever cutter material you choose to cope with the aggregate particle - steel, carbide or diamond - it will become gummed up by the resin, even with an appropriate coolant flooding it.
I'd be glad to be shown to be wrong.
John

I thought this stuff could be resurfaced with some kind ofr paste like substance and a buffing wheel like device??? I dont know but I am sure it would be helpful if someone knows how this could be done... Do we mill it like stone since there is little plastic in it or do we mill it like plastic and ....

[ckelloug]

Can anyone help me decipher these properties?

Hardness Shore D1/D15 84/83
Tensile modulus of elasticity MPa 3,000 =435,000psi
Tensile strength MPa 69 = 10,000 psi
Flexural modulus of elasticity MPa 2,600
Flexural strength MPa 100=14500psi
Compressive strength MPa 85= 12325 psi
Elongation at break 7.5%
Temperature of glass transition 71 C =127F
Coefficient of thermal expansion 77 x 10-6.K-1 =4.3e-5 inches/inch degree F would really appreciate it.

The Glass transition temperature is the temperature at which the epoxy goes from a hard brittle solid to a floppy flexible solid like rubber. The coefficient of thermal expansion was given in meters/meter degree Kelevin where the meters cancel out and you are left with 1/K. I translated this to inches/inch degree Farenheit.

Jack got it right otherwise.

--Cameron (in Menlo Park CA this week)

[ckelloug]

coogrrr,

You could probably grind this E/G material with diamond grinding equipment but if you're aiming for metalworking precision, I would not want to do so as you can cast epoxy to within a few tenthousandths over a foot if done carefully whereas grinding will only be as good as you can hold alignment on the grinder.

I would not want to use standard screw threads bearing directly in the material, generally, in commercial products threaded inserts are placed into the material to provide for bolts. Also, you could probably cast a teflon rod into the part if you just wanted a hole.

[dfro]

I thought I would share some pics of a vibrator I cast in aluminum for use in my small foundry. I followed a design in 'Metal Casting: A Sand Casting Manual For the Small Foundry Vol. 1', by Stephen D. Chastain. I made some slight changes to the base, compared to his design. He made the vibrator to help him release board mounted patterns from the sand after ramming a sand mold.







Compressed air drives a ball bearing around in a circle and escapes out of small holes in the top of the casing. A piece of thick walled steel tube is cast into the part to make sure that the casting does not crack and explode under the pressure of the ball spinning. I imaginge that these could be cast in e/g instead of aluminum. You could cast four of these in one go, easily. The force of a 5/8" ball is not very great, so I would make the ball bigger. by changing the air pressure you can change the force and frequency of the vibration. You might be able to get a higher frequency than the $40 concrete vibrator. I am sure you won't match the force, though. But maybe frequency is more important than force. And the direction of vibration is horizontal with the air vibrator, wheras the electric one seems to vibrate on the vertical plane. This could make a difference in compacting and de-airing the e/g mixture, who knows? Might be worth a try.

Dave

[svenakela]

Darn! That was a really nice KISS design! I have a an engine running a unbalanced wheel with a belt, but this one was a lot better. I'm going to copy your design, count with that!

[daviddecker]

I imaginge that these could be cast in e/g instead of aluminum. You could cast four of these in one go, easily.
Dave

Thank you for the great post. Brilliant! Do you have any idea of how much air it consumes while running?

If we cast the housing in E/G wouldn't that act to dampen the vibration and thus defeat the purpose? The aluminum design as you have it would seem to be a suitable means of transmitting the vibration.