[johnohara]

brunog,

The Zanite video on youtube shows a surface coat being applied to the mold prior to the actual pour of material. The segment starts at 3:24.

1. A view inside the mold shows inserts as the coating is being brushed on.

2. Low viscosity, no large aggregate, black oxide color.

3. Brushing it on.

4. Close-up.

~John

[brunog]

John,
They do this for aesthetic reasons to get a nice outside finish, probably some fine particules in the mix.

Nice find

Bruno

[lgalla]

John it is called a gelcoat.If you use it you will not see the voids and air pockets of your E/G mix.It has been discussed on the thread many posts ago.
Larry

[johnohara]

I read the slurry coat link that brunog posted. Coverage is specified at 1/8" deep. I got the impression from his post that he was suggesting to use it as an outer coat with heavier material then added inside.

~John

[brunog]

John,
My crazy idea was to add larger size aggregate and mix it into the slurry coat to get EG

Best regards

Bruno

[ckelloug]

If we can coax jhudler out of hiding, he has a laser interferometer and could probably help do a creep measurement. For the kinds of numbers we want to measure, this would require tight temperature control as a tiny temperature change is enough to make a bigger difference than the creep.

If the packing density is high enough, essentially all of the aggregate is in contact. Under these circumstances, I believe the aggregate will carry most of the load in compression and that the epoxy won't be too heavily loaded. If I am right, there shouldn't be much creep.

If anybody has a university library and some spare time, figure out which ASTM standard is used in measuring creep in a composite like ours and perhaps we can set up a measurement.



Regards all,

Cameron

[brunog]

Larry,
You forgot to post these 2 photos.

Regards

Bruno

[brunog]

John,
There is extensive information to pick from the Zanite video in regards to the purpose and fonction of all components used and/or required in making machine bases.

We all have a lot to learn by watching the video over and over again.

Regards all

Bruno

[ckelloug]

Hi Oxford,

That slurry coat stuff looks interesting but they mention in the datasheet that the low heat distortion temperature could be a problem in some applications. It sounds like this stuff is very much like the U.S. composites thin epoxy and slow hardener with some sand added: Reichhold 37-127/37-606.

In general, a good aggregate design will get you to a reasonable modulus with almost any epoxy. But, if you pick an epoxy with a heat distortion temperature that is too close to room temperature, leaving the machine in the sun will warp it and it will be a lot less stiff at room temperature than a machine made with an epoxy with a higher heat distortion temperature.

Unless we find out that a normal viscosity epoxy is sufficient, I think that Hexion 813 (which is normal viscosity epoxy reactively diluted with phenyl glycidyl ether) is the best choice I've seen for epoxies.

Because I can handle safely handle the IPDA, I intend to go with Hexion 813 hardened with Degussa IPDA (corrosive with potential for some nasty fumes). I'll throw in some silane or some titanate and some BYK 535 deairing additive. Roach, the guy who showed up that was probably from Granitek hinted that this was the right way to go.

Hexion 813 with Albemarle (ETHACURE 100) DETDA would non-toxic but it would need to be cured at 180C to attain useful physical properties and I haven't tried it. Preston mentioned this back on page 259.

Most of the formulated hardeners have a lot of nonyl phenol and other things which aren't good for the heat distortion temperature and are bad for chemical resistance. Longtime regular lgalla pointed out the woes of nonyl phenol. In a small machine that isn't going to be immersed in flood coolant or stored in the sun, its possible that what I'm saying is not helpful, I just like to cover all the bases. I would check with precision epoxy on the actual value of the heat distortion temperature before committing. You also in principle want to get a good idea of the size of the sand involved so that you can design your aggregate mixture to take advantage of it.

Unlike what Mike from precision epoxy said, deairing agents will help deair the epoxy but they won't pack the aggregate thus an unvibrated part won't have the stiffness of a vibrated part.

I'm not trying to rain on any parades here, it looks like you were on a good track. I've learned an incredible amount reading the things people have shared here and I'm just trying to give back to the community by applying my engineering background and remembering what everybody has posted.

Unfortunately, most of the things I suggest turn out more difficult than what the poster intended and I am sorry for that. E/G is rather complicated when it comes to getting the best performance and bang for the buck. It would be great if the best materials were easily available on the retail market but in my opinion, they're not.

It's likely that most folks here will make something they are satisfied with when they try. I don't want to discourage interest in the subject like my posts often seem to do. My goal is to make commercial quality material and to characterize it well enough to be able to use it in cases where it matters. A small desktop machine with no hard specification may not need this level of care. For folks that don't need to do better than yellow pine for stiffness, almost anything will work. For folks worrying about creep and micron accuracy, material design is critical.


Regards all,
Cameron

[veteq]

Well said Cameron,

Keep up the good works with that helicopter view of yours!!!!!!!!
:banana:

[lgalla]

The slurry coat system and flooring epoxyies in general have the property of being flexable.Elonglation can be way over 10%.Sure would damp well but accuracy would be minimal and creep would be a huge issue.
I do not like typing.Pictures are worth 1K words...
http://opensourcemachine.org/files/G...%20Machine.pdf

[veteq]

Thats a nice machine...
Been reading on the CNCECKE for years and there are more EG machines over there. A lot discussion and test with EG!!!!!!!!!

The spindle looks like this:
It are the CAD pictures of that spindle with manual toolchange...

[RotarySMP]

Shame they painted that beautiful E/G base!

[lgalla]

At the beginning of the thread Walter and I would bug the suppliers of aggregates.Apparently some got the bug in their ear.
http://www.zeeospheres.com/images/Ze...BasedAggre.pdf

[veteq]

Shame they painted that beautiful E/G base!

Thats the trick Mark,
It protect it against moisture and uv-light

[oxford]

I like Zeeosphere's simple common sense approach to finding out how much of their fine aggregate should be added to the mix for best results....add until it changes volume :P

[ckelloug]

Oxford,

I agree that that the process described in the paper at zeeosphere.com is good. Kudos to Larry for posting it. The math model that I developed from de Larrard's book embodies a very similar principle to that idea with the difference being that de Larrard spent a decade turning logic like that into math.

When mixing two aggregate components, it is easy to do what the zeeosphere paper suggests. When mixing a bunch of components, it's hard to know what to adjust. Models are never as good as experiments in terms of accuracy but they do help in knowing what to do.

Regards,

Cameron

[jonpry]

I did some FEM deflection simulations. I know somebody was seeking low deflection on a 4 foot beam supported at the ends. I don't really know what that beam is used for, but seeing as how the specification was only for deflection, I assumed an I-beam would suffice. I started with a structure that is 8" tall and 4" wide. With the flanged being 1.5" thick and the rib being 1". I made the beam 60" long so that it could be supported with 6" of something on the end and have a free span of 48". This assumes a young's modulus of 20 GPa, which may or may not be close.

There is a 200lbs load in the center, which is distributed over a 6"x2" area. The calculation also includes the beams own weight. Which at a volume of 20 liters, is ~100 lbs depending on the density. The first screen shot indicates a deflection of .00136.

It occured to me that while the E/G is a material with statistical properties. Macroscopic reinforcements need not be so random. So I made a model with a 2x.25x48" piece of steel embedded in both flanges. Next shot is of that. This cuts the deflection in half to .000608 including the beams own weight.

Making the steel 4x.25x48, cuts it almost in half again to .000360, but this would probably require making the E/G part of the flange wider as well in order to make it moldable.

I figure .0001 should be the target for any such madness, but how to get there i don't know.

[lgalla]

jonpry,perhaps you could run deflection of a beam for me.The tube,7'8"is A36 4"x12"x.25"
The ends are supported 4"x6"x2"thick cast iron angle.The centre load is 150Lbs.The load is from the front face not the top.
In the other side view the I beams are A36 W6-20 with 900Lbs load.
Thanks
Larry

[jonpry]

Larry,

Perhaps you could make some iges or step models of the parts you want simulated. That would make it much easier. Surface/surface interactions take a lot of time to setup, so i recommend unioning the beam with some structure to support. Like in the files i ran there is a base beam and two columns. The base and columns should be solid to eliminate compression, and the columns should be fairly long to allow them to bend inwards when the beam is under load.

On another note, does anybody have experience with boron triflouride-amine curing agents? For example this one http://www.hansonco.net/Boron%20TDS.pdf Seems to offer unlimited pot life until you bake it. That would give a lot of opportunity for mixing. And my next idea :-)

What about putting some seriously low boiling point solvent in the epoxy. Like dichloromethane, or maybe something less obnoxious, but something like that. Both to decrease the viscosity and increase the volume of the epoxy ensuring good wetting/mixing. Then pumping it down under vacuum to boil out all of the solvent.