First build, Attempt to stiffen it up and add some weight
Not going at this blind i did some searches on the web for information on building the frame out of a concrete or epoxy concrete mix. To my surprise I found the epoxy information used playsand and 2 part epoxy and the concrete option used a custom counter top blend. Without all the scientific reading on vibration the conclusion was not that one is better than the other (costs aside) but that including a frame inside is a big benefit on vibration absorption. Here is the AI result and other input I posted in the activity stream.
Decision on material has not been decided and it's possible i will make 2 using both methods
Another bit of info:
Evaluating countertop concrete mix for a CNC base instead of epoxy granite:
- Cost-effective: Concrete mix can be a cheaper option compared to epoxy granite, especially when considering the equipment required for epoxy granite production.
- Mechanical properties: Concrete has similar or better mechanical properties than epoxy granite, including increased dimensional stability and vibration damping.
- Customization: Concrete can be molded into any shape or color, offering more design flexibility compared to epoxy granite.
- Maintenance: Concrete requires less maintenance than epoxy granite, as it doesn’t need annual sealant applications and can be cleaned with soap and water.
Comparison to Epoxy Granite
- Thin-walled parts: Epoxy granite has limitations in producing thin-walled parts, whereas concrete can be mixed to achieve thinner sections.
- Curing requirements: Epoxy granite requires a large curing enclosure and high curing temperatures, whereas concrete can be cured at room temperature or with minimal equipment.
- Weight: Concrete can be denser than epoxy granite, depending on the mixture and curing process.
Recommendation
For a CNC base, a countertop concrete mix can be a suitable alternative to epoxy granite. Consider the following:
- Choose a high-strength concrete mix specifically designed for countertop applications.
- Optimize the mixture for the desired density and vibration damping properties.
- Ensure proper curing and finishing techniques to achieve a smooth, durable surface.
- Consider adding reinforcement materials, such as fibers or aggregates, to enhance the concrete’s mechanical properties.
By carefully selecting and preparing the concrete mix, you can create a reliable and cost-effective CNC base that meets your requirements.
4080 to attach to the new base, looks like a metal plate down the center 160mm wide would help distribute the 4080 beam load and give ample secure points. This was a question on where to place aluminum rails inside the concrete base in the middle, this way there will be 4 lengths of 2040 so far will probably attach them together with some 1010
lets look at some pieces
As far as the base the idea was to place the y axis on top of the concrete base and then mold the z axis tower and attach it to the concrete base but if the vertical tower is molded and attached to the base the y axis will need to be attached to it. The tower to the base bolted and the x&y assembly bolted to the base, will have to assemble the y axis first and see how to make sure all things align
These are the parts for the tower to get an idea of the size and requirements for a molded vertical component
z axis--- standard 60mm clearance build. A 120mm clearance build will have A & B be 60mm longer.
A: Openbuilds 4080x260mm C-Beam add 60mm 4080x320mm C Beam
B: Openbuilds 4080x260mm C-Beam add 60mm 4080x320mm C beam
C: Openbuilds 4080x250mm C-Beam
D: Openbuilds 4080x120mm C-Beam
Get an idea what the molded unit will look like
Mods:
https://github.com/MillenniumMachines/UserMods/tree/main/Millennium-Milo-V1.5-MODS/AramcoPhil
ball screws this is the y axis needs trimmed for screw clearance, to be considered in molded tower
It was recommended to upgrade the 8mm ball screw to 12mm and change out to servos. I can see the ball screws but I'm running duet control and that's stepper. maybe a larger stepper is being installed, If i go with servos it's a different os and control board. more research on this is needed
A number of concrete-only, or concrete-filled machines have been built by people over the years - there are even some YT vids available. I think the fundamental problem with using concrete is that Portland-cement based concrete shrinks and cracks. Using it to fill structures doesn't work well (far as I know) as the shrinkage decouples it from the outer structure and it just becomes a weight without adding any strength or stiffness to the assembly. Even if cast around internal steel reinforcement it still cracks and shrinks. Weight is certainly good, but it tends to be a by-product of a massive structure rather than the end goal.
Epoxy doesn't appreciably shrink when it cures, allowing it to stay in contact with the structure (or remain stable if it is the entire structure). But epoxy isn't stiff - compared to metals, ceramics, or rocks. So you add stiff fillers (which also reduce the cost) and, in theory, you get an improved bulk stiffness for the whole casting. Problem is that without some trial and error and fairly tight control of the mix and placement, you will wind up with a heavy, but not extremely stiff casting. Plus casting in really thick sections is a challenge without fairly specialized epoxy (i.e. overheating).
The deal with CSA cement is that it doesn't shrink like Portland cement. It can also achieve extremely high compressive strengths very rapidly. So can Portland-based UHPC, but those take rather a long time to achieve the high strengths and they still have the shrinkage problem.
CSA isn't extremely stiff (compared to steel), but adding stiff fibers to it improves things dramatically. Fibers are typically added to UHPC for crack control, but a side benefit is that steel or basalt fibers increase the average stiffness... something desirable for a machine tool frame.
So the 'ideal' frame uses a high tensile strength outer skin, and a high compression strength internal filler... and design the geometry so that the skin is in tension and the core is in compression. Then make sure the connection between the skin and core is intimate and will not dis-bond (or is mechanically coupled). Make sure both the filler and skin are very stiff and you've got a solid assembly.