[jestah]

I have read most of the EG thread.... well a good chunk of it any way.

I think there has been 'nuff taking so time to get to casting!!!

No test batches for me... I am diving right in and going to cast a two 100kg blocks some time within the next few weeks. I have located all of my materials, found rented time on a big vibrating table and taking a few days off work to construct the casting form next week. All systems go!!

I have now found the resin I am happy will work but would like to ask a few questions about adding a small amount of steel rod inside the casting to provide a bit of strength.

Would rebar be better or would a few lengths of thread rod with a few nuts and washers to help recall lock it to the block be better.

lastly here is my current recipe: Stone, size mm, ratio

Quartz 0.1 – 0.3 0.13
Quartz 0.3 – 0.7 0.08
Granite 0.5 – 1.5 0.11
Granite 1.5 – 3 0.13
Quartz 4 – 6 0.16
Quartz 8 – 4 0.09
Quartz 14 – 22 0.3


the slabs will each be around 100kg and I will aim for a 9-10% resin ratio. I am going to cast aluminium pads into the block to be surfaced and act as pads for my linear rails.

[brunog]

Jestah,
It would be hard for me to confirm proportions of the items, not knowing the sizes and proportions within them, however one of my concerns is the 14-22 mm item: it is usually recommended the the thinnest wall be at minimum 5 times the size of the largest item. Not knowing what your design looks, 110 mm is quite large as a minimum wall size. Rebar and/or threaded rods will help only if your parts will work under tension, as EG, like concrete, is strong in compression.
Special care (processing) is required to make epoxy stick to aluminum, I suggest using steel instead.

Best regards,

Bruno

[jestah]

Jestah,
It would be hard for me to confirm proportions of the items, not knowing the sizes and proportions within them, however one of my concerns is the 14-22 mm item: it is usually recommended the the thinnest wall be at minimum 5 times the size of the largest item. Not knowing what your design looks, 110 mm is quite large as a minimum wall size. Rebar and/or threaded rods will help only if your parts will work under tension, as EG, like concrete, is strong in compression.
Special care (processing) is required to make epoxy stick to aluminum, I suggest using steel instead.

Best regards,

Bruno

Sorry for the lack of info, I was a bit put off by the task of once again rebuilding my entire design after deciding to cast both the base AND the tower. I expect the casting to be around 270-300kg cast in two or three parts (tempted to do the spindle standoff in MC too)

Here are some photos of my plan so far. The base is 1015x550x140 and the tower is 550 - 350 (base - top) x 710 x 200 thick.

My thinnest wall section is the feet of the tower at around 50mm at the tip but the rest of the design is more than 100mm thick and I am planning today to refine the design to eliminate most tight corners. I have also contracted a company to help me vibrate this whole thing to make sure I achieve as void free casting as possible.





I was worried about adding rebar as my main goal was to test the dampening factor and did not want to add ANY extra steel. I was considering casting in some full length pvc tubes that I could add threaded rod and post tension IF required. You can see the four holes for this on the top of the tower. I will add 3 or so tendons down the base as well but highly doubt it will need it but better to cast a few holes and not need them than be faced with having to add them after casting!

I am going to stick to aluminium rail pads as it has a closer thermal expansion to the epoxy/rock mix. I will talk to my resin guys and make sure the resin will bond to it but I was also planing on tapping and treading down the underside on 60mm centres to also mechanically lock the bar into place.

What are the ally bonding with epoxy trick you you?

[ckelloug]

Hi Jestah,

Congratulations on the design of a really sweet looking machine.

Sorry to be late noticing your post and saying something. Bruno is right that 22mm is a bit excessive for a small machine since the literature suggests you want features to be 5 times the size of the largest aggregate.

I've run my CPM model on your aggregate assuming that the density of all of them are the same and get a packing density of 78% aggregate by volume (90% by weight= 10% epoxy by weight) with the following percentages:

q8 0.06 (should the size listed for this be the size for q4?)
q4 0.44 (should the size listed for this be the size for q8?)
g1.5 0.08
g0.5 0.12
q0.3 0.10
q0.1 0.21

Since all the components have the same densities, you can use the percentages given as weight percentages of the total.

I note that the sizes you give suggest that q4 is bigger than q8 which might suggest the sizes of the fractions are transposed in what you wrote. The above analysis assumes the given numbers were correct.

Further analysis suggests that almost any combination of the listed aggregates should achieve at least 75% aggregate by volume (88% by weight=12% epoxy by weight). At these aggregate percentages, the difference between my predicted optimal mixture and any other mixture is negligible so all I can say is don't sweat the small stuff: whatever you do should work fine.

Regards,

Cameron