Designing DIY CNC Milling Machine

Bummer about the marble.  Maybe try a different stone mason, or try to find a quarry nearby?

Marble and granite have about the same stiffness (Youngs modulus ~50), but marble is less than half as hard on the Mohs scale, and about 1/3 the compressive strength.

So I wouldn't use marble anywhere in a machine tool - not even as aggregate in concrete.

About the CSA - is this possible to add any stone fillter (like granite sand/rocks) to RapidSet Cement ALL to reduce the amount of cement needed? From what I see it does not seem like it should be possible, but wanted to make sure.

I don't see why not.  CTA sells other CSA-based concrete products, some with aggregate already mixed in.  The "DOT Concrete Mix" appears to be a mix of Rapid-set, fluidizers, fibers, and 3/8" aggregate.

Makes it harder to mix, of course.  Maybe mix up 1/3 of bag with maximum plasticizer and ice/water to get a feel for how it flows/works, and then do another test with using some  ~6mm to ~10mm angular gravel aggregate.  Last 1/3 of the bag, try fibers and aggregate together.

Cast yourself a few stepping stones for the backyard, or a couple of doorstops in the name of research.image missing /media/kunena/emoticons/wink.png

spumco wrote:

Cast yourself a few stepping stones for the backyard, or a couple of doorstops in the name of research.

+1
Experience is the best way to learn things.

Definitely won't go straight into final casting. But it's also great not to waste expensive cement on something dumb.

Thanks for all the tips!

Ok... for a 'not dumb' test, cast a simple beam.

Calculate the volume that 1/4 of a bag will fill, and make a mold for a rectangular beam with the same approximate volume.

Test the resulting cast beams for:

• Shrinkage (should be close to nothing)
• Deflection
  • Stiffness should improve if fibers with high Youngs modulus are added
  • Might do a couple tests with different aggregate loadings
• Edge stability (holes/features close to edge)
• Surface finish (may impact your design if you feel the need to 'finish' the casting cosmetically)

For the price of one bag, you should be able to get four different samples that will help you decide on fiber & aggregate loading, plus workability and mechanical properties.

You may find that the fibers are a huge pain to work with using limited tools, but that a 50% aggregate load will extend the cement without affecting the performance negatively. 

Or you may decide you hate the whole idea entirely because it's a mess.