[ckelloug]

I have spoken with lazlo on the homeshopmachinist board who has looked into this and says that Harlow is using accures castings.

[ckelloug]

In general, I have to agree with Andrew that the E/G that's been made here on the thread is way less than the 2e6 psi modulus that I've been using in sample calculations. It's also less than the 4.5 e5 psi incorrect modulus from accures as well as the 4.5e6psi correct modulus.

My formula for modulus based on walter's jig estimated 170psi as the flexural modulus of Walter's sample which is somewhat discouraging and means that it is likely only applicable as a vibration dampener in a steel structure due to what will likely be large deflections.

Given the US Composites 635 epoxy we have and aggregate designs that aren't made of a single type of round sand, the numbers ought to be better than that. I believe that the fact that they aren't, combined with Walter's descriptions of gumminess, indicate that there is either an error in the epoxy mix ratio or some other problem with the epoxy curing correctly. It is also possible that there is some issue with the reactive dilutants in the epoxy.

Based on the data currently available, I would think that it would be wiser to design a router with metal load carrying members filled with E/G (or rubber bagged portland cement) as I said in my first post on this thread and Andrew has said all along. I say this because casting a bad beam or table could be expensive and the reasons for the poor performance in the epoxy tests on this thread are not yet understood.

I realize from Andrew's comments that people might be unsure of my position so I will answer that my idea is to build gantry routers out of whatever works best be it E/G or not. Unlike some in the thread readership, I was interested to explore the idea of E/G gantry router top beams and also, what is ultimately possible for the material itself.

In general, assuming that the epoxy setting issues are solved and 2000ksi modulus E/G is achieved, I see unreinforced E/G as a possibility for 24 inch and smaller router beams (for .0001 deflection with beam weight carrying 100 lb live load) though I still need to do a shear deflection computation. Between 24 and 36 inches, a hollow gantry router beam that weighs around 150 lbs and has a 4x12 inch cross section with 1.5 inch thick sides and 2 inch thick bottom and top seems possible (with .0003 or so static deflection with beam weight and 100 lb live load) although perhaps not desirable. In pieces like gantry beams longer that 36 inches, unreinforced E/G likely qualifies as a complete waste of time.

<B>
In all cases, the risk will be a lot lower to make the load carrying parts steel and use E/G to add mass and vibration damping.
</B>

I'll continue to post what I determine about the material properties achievable and I'll post formulas as I learn more in case anybody is still interested. For all of you out there building routers, sorry if I've led you astray. I still think it will be possible to build most beam like parts under 24 inches in length from E/G once the issues with epoxy setting are resolved. I seem to be posting materials science on a router forum which some people seem to frown upon so I'll make the offer once again to relegate myself to another thread.

Best of luck to all those out there building routers!

[walter]

Given the US Composites 635 epoxy we have and aggregate designs that aren't made of a single type of round sand, the numbers ought to be better than that. I believe that the fact that they aren't, combined with Walter's descriptions of gumminess, indicate that there is either an error in the epoxy mix ratio or some other problem with the epoxy curing correctly. It is also possible that there is some issue with the reactive dilutants in the epoxy.

Gumminess is probably caused by carbon black- I'm sure the latest batch will have the same problem. It dramatically affects the curing time..

Samples made with straight sand and 15-20% epoxy didn't have any of that- they ring and feel like real granite.
_

[ckelloug]

Walter,

Thanks for the comment on the carbon black gumming up the epoxy. That's good data and I'll work on a fuller understanding of it just as soon as I have somewhere to do lab work. I had the impression you were having general problems with the epoxy, not just with the carbon black. I don't know whether it interferes with the epoxy chemistry or it's just such fine particles that they get in the way of something. To figure this out, I'd personally try with something like silyated silica fume like cabot TS-530 or TS-610 though I doubt you're interested in that experiment right now.

Responding to your comment about accurately controlling the curing temperature, it's really not absolutely necessary. The main difference it makes is that epoxy that is cured at higher temperatures appears to crosslink more and have a much higher hardness and lower creep as it is exposed to higher temperatures.

DAK3333 do you have any comments on carbon black hosing up the epoxy setting?

[walter]

I don't know whether it interferes with the epoxy chemistry or it's just such fine particles that they get in the way of something. To figure this out, I'd personally try with something like silyated silica fume like cabot TS-530 or TS-610 though I doubt you're interested in that experiment right now.

I don't know.. I sort of liked my early results.

I might go with a barebone system just to get it off the ground. I'm thinking Quartz only, three sizes, zeeospheres for color.
I need to visit Agsco and see what's in their 'Quartz' department.
_

[ckelloug]

Walter,

I realize you're interested in bare bones at this point and I don't want to distract you so I'll be succinct. Puffed wheat (Malto-Meal Brand of course) would almost work as aggregate except the strength is a bit low. The mix of stones you showed in your last pictures looked great regardless! My cabosil suggestion was just my idea for figuring out if carbon black hinders the mixture setting, not advice to you necessarily.

I can say that you're on the right track using multiple sizes of aggregates. If you're not aiming for a heavily graded aggregate approach like calling agsco, just use several sizes available from your favorite sources. The guys at Huntsman use 3/8 gravel, #100 sand and fly ash which is probably as fine or finer than zeospheres.

As harryn pointed out in post 1150, washing the aggregate in 91% denatured alcohol from the pharmacy and drying it ought to do quite a lot in terms of making the epoxy stick better and may turn out almost as good as silanes.

In short, if the epoxy sets correctly, you should have reasonably good luck with a mixture that uses multiple sizes of aggregate. A higher percentage of larger aggregates will have less chance of having mixing or adhesion difficulties though it will be harder to cast into complex shapes.

In short, getting reasonable strength should not be hard with multiple aggregate sizes and the US Composites 635. Getting the highest possible strength will be harder than reasonable strength but likely unnecessary.

The CNCZ-1 formula I posted was my attempt at the most advanced formula reasonably possible. I thought in those terms because if that formula fails to show serious strength after carbon black and epoxy are optimized then the whole approach may be wrong. If it works, then it is time to see what must be subtracted or changed to make it easier for everyone to do.

In short, Walter, in a stroke of brilliance, you extracted the exact right lesson with your comments about aggregate: aggregate isn't as important as getting the epoxy to stick. Bigger aggregate should have fewer problems.

Also, take a skewer or some small rod and poke it into the the mixture in the mold after it has been poured every few inches to help consolidate the mixture.(rodding) You might also try pouring only an inch or so and then vibrating before pouring the next inch. These are two techniques mentioned by one of the experimentalists in the the 1975 conference proceedings.

I'm anxious to hear how things turn out and I hope I haven't wasted your time with any of my ideas and suggestions.