The shipping is pretty good. it's about $15 from Oregon to British Columbia and that includes handling of customs/duty.
The shipping is pretty good. it's about $15 from Oregon to British Columbia and that includes handling of customs/duty.
So,
I was thinking about this again and while rounded aggregate is best in terms of total volume, there is a large downside. With rounded media, you're now more at the whims of fracture propagation. With sharp/jagged media, a fracture shouldn't propagate as far since the fracture should run into a perpendicular surface, unlike with round media.
The promise behind EG is that you take the innate strength of a compressed aggregate and ensure that you're locking it into place using epoxy. At this point, the youngs modulus for a structure is now mainly based on the strength of the compacted aggregate. So, at this point... you have the mix of aggregate sizes and shapes to take into account. I believe that regardless of the media used at larger sizes, the extraneous volume can be filled with smaller rounded media to take up gaps. But the larger media is what should be assumed as the strength point.
I also think that a gel coat with reenforcing fibers would make quite a difference in terms of fracture propagation from the surface (perhaps to the point where embedded features could be inlaid closer to edges.
Mark,
Did you have a look at the cost/pricing on the media available from the seller at all? I'm only able to get pricing on shipping to myself, but would be interested in hearing what it's like further afield.
Thanks,
--
Scott
Don' t fuss over strength.
It is extremely hard if not impossible to build a cnc that is rigid enough for milling and then to have it break because it is not strong enough.
Sven
http://www.puresven.com/?q=building-cnc-router
Sven, who said anything about CNC? =0)
Uhm, the url of this website : )
Sven
http://www.puresven.com/?q=building-cnc-router
heh... I was just going by "machine base". A lathe in my case.
Ah, had my own thinking cap on too tight.
For a lathe strength may have more importance...
Sven
http://www.puresven.com/?q=building-cnc-router
yeah... not killing myself in the process is definitely high up on my list.
I am making samples to find out if it is viable to make a "light weight" machine from EC. In that process I found out something that you should consider when working with epoxy percentages.
I am trying lean mixes, starting with 5% for a 0.8 mm grain batch of sand.
That was a bit too wet for my purpose so I decided to try and use 4% for the next batch of 0.5 mm grain.
It ended up super dry because I forgot that surface area of the aggregate doubles when particle size halves.
The first batch had 75 grams of epoxy for 1300 grams of 0.8 mm grain sand.
The second batch should have had about 100 grams of epoxy instead of the 50 grams I used to be slightly leaner....
Sven
http://www.puresven.com/?q=building-cnc-router
Hi Thread,
I'm dropping in 'cause I got a few PM's. Tenter asked if my aggregate simulator is available. I can make it available if somebody wants to maintain it. It's a pair of linux applications right now that communicate via a named pipe which probably isn't super convenient for most people. It also requires lab measurements of the packing factor which I made for all of my aggregates. The measurement involves vibrating the material under a weighted piston and measuring the volume of the vibrated sample.
Spherical aggregate is probably more resistant to fracture due to the Griffith equation term for stress intensity increasing with respect to the sharpness of edges. Spherical aggregate also usually achieves a higher packing density. The silicon carbide formula I published is all sharp aggregate and it is plenty strong and of high modulus. Silicon carbide has a higher fracture toughness than quartz.
There probably isn't a need to go to silicon carbide if you have cheap quartz available but it is the aggregate I characterized and did the work with. Since silicon carbide is available as an abrasive, the gradings tend to be accurate whereas with easily commercially available quartz, it is more difficult to match a grading curve made by simulation. My results for silicon carbide showed higher modulus and strength than the quartz formulas I worked with but rotary SMP is right that a machine designed heavy enough to work is unlikely to be anywhere near the loadings where the strength matters much. If you design the machine to be stiff enough to work well, it will be plenty strong. Also, Silicon carbide EG can be machined or ground with boron nitride inserts or grinding wheels however it will wear them out quick: much better to make your molds accurate.
I believe the formula I published is near the maximum achievable modulus with relatively cheap materials however it isn't necessarily optimized for maximum practicality.
I will reiterate the offer from earlier in the thread that I can test flexural modulus and strength of samples that are made to the size spec I published long ago. PM me if you have samples to test. I'm really busy so it may take me awhile to answer. I'm really impressed with the work that's gone on on this thread and I wish I had time to pay as much attention as I used to.
Cameron, is there a standard "box" that's common all over the place that can be used as a mold for the test pieces? That's probably the easiest for folks to send test samples.
Hi Konobi,
I have a very small test machine so the sizes I can handle are limited. The test I can do is ASTM D-790 flexural strength and modulus. This isn't as definitive as compressive stength and modulus or tensile strength and modulus but those require a test machine 10 times as expensive and it was well out of my hope of ever acquiring one. I can't find the test specification right now for more details. The size spec for the sample I can test is 7.5 x 3/8 x 1/2 inches. If folks can make a plate 1/2 thick by 7.5 long and 5 inches wide, I can diamond saw the 5 samples required for the test out of this piece.
Happy 2016
--Cameron
Hi Gang,
While looking for something totally different, I came across this excellent open access paper on polymer concrete.
http://dx.doi.org/10.4236/wjet.2013.13009
I think anybody who is interested in theory will like it.
Regards,
Cameron
Hey guys
I got a quarz mixture called sillimix 282 but unsure about type of resin to buy ?
I also want to introduse a dark black effect to it hope someone can help
Thanks
Well, I finally read this entire thread. Much of my reading was late at night and bleary eye-d, so I probably forgot lots of it. What a wealth of information! On the subject of vibration, has anyone tried speakers? I was also considering a orbital palm sander screwed directly to the mold. Any thoughts?
Heh, putting the bed to bed with a little Crystal Method!
https://www.youtube.com/watch?v=TQizAtoT8ac
Who is that suplier?
You need pretty violent vibration. I used a 3 phase concrete vibrator which weighed about 15kg to compact the M/G I used on the head support for my mill and it still took a fairly long time to compact. Also I still had some air bubbles. To do the vibrating accoustically, you would need to borrow the The Who's PA system.
If you have a nearly ideal packing density, this stuff is really still. An orbital sander won't impress it at all.
Mark
Regards,
Mark
The cheapest stable structure I can think of off the top of my head would be 12" cement blocks with machined aluminum plates bolted in between them (and maybe steel ones on the ends).