[spikee]

Epoxy granite is a material that has been gaining a lot of attention in the DIY CNC community for its ease of use and dampening characteristics. However, there are some drawbacks to using epoxy granite that you should be aware of before you decide to switch to it for your next CNC build. How good is it? Should it be avoided?

Read further here:

https://cncrouterinfo.com/article/av...e-for-diy-cnc/

[castinite]

Granite has been used for years as the filler but is not as good as quartz and requires more resin in the system. It leads to air voids and unfilled sections. Our CASTINITE epoxy/quartz is precisely formulated for machine tool castings and will result in lower cost and high strength, along with excellent vibration dampening and chemical resistance.

[spikee]

How does it compare to Materials such as Nanodur?

[peteeng]

Hello Castinite - The statement that granite requires more resin then quartz does not make sense plus that granite leads to voids and unfilled areas makes even less sense. Can you explain this further please? What is your typical solid volume ratio of quartz in your system? Peter

Hello Spikee - After years of testing various epoxy mixes and now looking at engineering grout I feel that epoxy has drawbacks that grout overcomes 1) epoxy does not like water and aggregate of any kind will have heaps of water in it. This water will inhibit good bonding of the aggregate to the epoxy. This reduces the possible value of the modulus of the material. 2) Even if you vacuum cast the material of which all my test coupons have been vacuum soaked to remove the moisture then cast under the same vacuum they have achieved low modulus values (less than 30GPa) compared to grout and other materials 3) Using UHPC or grout, it comes as a specified material, it is a water based product so is not influenced by ambient conditions and is in general stiffer then epoxy based products. Here in Australia grout is cheaper then epoxy mixes ($/m3) unless you get the sand for free. Because I have used epoxy in many applications for decades, initially I thought this would provide the "best" solution. But I have found this is not to be the case. There are several grouts available here in the order of E=50GPa and even using high solid volume (>60% solid) carbon fibre (E=210GPa) and ALOX E=300Gpa I have not been able to get past 40GPa in an epoxy casting. So I think that engineering grout is the better solution than epoxy+stuff. My two key attributes are modulus and cost. Metals are still in the mix as cold casting materials are not a clear winner due to the requirement for machine finishing. Peter

[peteeng]

Hi All - Re: nanodur Here's a good summary of mechanical properties. I'd like to use the E80 material but the company would not supply me the material. I found that they use acoustic methods to determine the modulus which is a very good method. Peter

https://www.durcrete.com/material-characteristics

[Mr-MaW]

The modulus of elasticity is important, but the design is more important, so good structural design optimization can give full play to the performance of the machine tool.
If you have less experience, you can take a look at our company's products, I have uploaded some photos and drawings, if you have any questions, you can send me an email, I will reply to you as soon as possible when I have time. I wish you an early disembarkation.

[awerby]

Granite is composed of quartz and feldspar, with an admixture of various other minerals. In small particles, as used in these applications, it's very stable stuff. If anything in this mixture is going to flex, it's not the aggregate but the epoxy. If you're worried about whatever water it may have absorbed, it can be heated before mixing to drive it off. Coarser particles will require more epoxy to fill in gaps between them than finer ones, but jagged particles will make a stronger product than rounded ones because of the way they interlock. Cementitious grouts have some advantages over epoxy/granite, notably greater stiffness, but I doubt they have as much tensile strength, so which to use probably depends on the specific application.

[peteeng]

Hi Awerby - drying 100's of kgs of aggregate correctly is not an easy thing to do! Even small quantities that I place in vacuum take hours to dry... I can tell when its dry because steam stops coming out of the vacuum pump! If the particles have the same packing factor then the resin fraction added is the same. So the size of the particle is irrelevant. Where size does matter is where the particles are pushed up to a wall or solid. Larger particles then have more space between them and the object. Some articles call this perimeter space.... Strength is rarely an issue with machine parts and if the aggregate is jagged it does not pack well so the solid fraction goes down so the modulus goes down. Then a two size aggregate system is used; a large one and a small one. Everything is a compromise Peter

Oh Granite stability - Granite was made around 3 billion years ago. So its had adequate time to stabilise. Can't get my head around that. The block of granite on my desk is 3 billion years old. We are such a small thing in the universe...

[Mr-MaW]

Yes, if more aggregate - 2000KG, it is very difficult to dry. Because the base of the large equipment must weigh at least 2 tons, how to control the mixing process? How to control the humidity of the air?
Whether the mold also needs to be dried, heated, etc. There are also vibrations, exhausts with heavy vibration processes, etc. This all needs to be considered.
What would you choose?