Designing a better bed

**Sven** · 15-08-2015

I' ve been reading up on EG as my own ideas are taking shape.
As far as I' read, vibrating EG does not work unless you use a mix with too much epoxy for a small size casting. Too much meaning it will yield an end result that has some shrinkage and maybe some warp.

The best seems to be a mix that is "very dry" compared to what most people on forums seem to be using: in the 4% area, or a bit wetter where it needs to adhere to another material.
Also, best to use various grain sizes, the next size 1/5th of the previous.

Put a measured amount in a jar, then add the smaller size and shake until the volume increases and you know the ratio.

A dry mix like that will need stamping.

And off course, make sure to do trials :)

**Robin Hewitt** · 15-08-2015

If all you want is to flow a flat surface, why not use Wood's Metal? That goes very runny and sets hard. You could even reflow it if you moved the machine.

**D.C.** · 15-08-2015

Originally Posted by Robin Hewitt

If all you want is to flow a flat surface, why not use Wood's Metal?

Not a bad idea but Wood's Metal / Cerrobend etc looks to be about £40 per kg, so it would cost a lot more than epoxy levelling I think?
Have you ever tried it if you have some lying around?

Originally Posted by Sven

I' ve been reading up on EG as my own ideas are taking shape.
As far as I' read, vibrating EG does not work unless you use a mix with too much epoxy for a small size casting. Too much meaning it will yield an end result that has some shrinkage and maybe some warp.
The best seems to be a mix that is "very dry" compared to what most people on forums seem to be using: in the 4% area, or a bit wetter where it needs to adhere to another material.
Also, best to use various grain sizes, the next size 1/5th of the previous.
Put a measured amount in a jar, then add the smaller size and shake until the volume increases and you know the ratio.
A dry mix like that will need stamping.
And off course, make sure to do trials :)

For larger aggregate This place does washed, graded and dried quartz specifically for resin bonding:
http://resinbondedaggregates.com/cat...ound-aggregate

For the smaller sizes I think it would have to be blasting grits:
http://www.stacey-processing.com/gla...ing-media.html

Then Aluminium Oxide powder and milled CF.

**Robin Hewitt** · 15-08-2015

10 kg Cerrobend £162

http://www.ebay.co.uk/itm/Cerrobend-Woods-Metal-Bismuth-alloy-10KG-/261983313460?hash=item3cff6c1e34

**Sven** · 16-08-2015

I may have had my expansion reasons mixed up...

A guy I know built an epoxy-concrete machine with steel bars at the surface to connect the rails to.
They were flat when casting started but the end result was not.

If you cast EC in a steel tub, it may end up not being part of the construction but just a liner and not a reinforcement.

**Boyan Silyavski** · 17-08-2015

There are many ways to not do it right. Apart from choosing the best epoxy for deep casting, is good idea to read the documents of the said epoxy and follow them instructions to the letter. best is to call the epoxy manufacturer and speak with them for the most suitable epoxy for the purpose.

Cause at the end of the day they know their stuff and even can mix a custom epoxy for your purpose. I have talked with one company technician and he knew exactly about that situation and explained me the differences between the 3 suitable epoxies they had.

**D.C.** · 18-08-2015

The http://durcrete.de is quite interesting.

What I was aiming for was finding a sweet spot between price/performance and ease of construction given that I only have not very accurate tools to work with.

The Durcrete site has some vibration damping data available and a demo:

**Boyan Silyavski** · 15-08-2015

Linear or volumetric thermal expansion coefficient is irrelevant in constucting a CNC.

First of all cement, steel and concrete have very similar thermal expansion. Even if the epoxy has higher thermal expansion its irrelevant at 1m and temperature changes. Plus the epoxy cement or epoxy granite will more similar expansion to the concrete

EG is same like all, do it properly and it will work well.

There are better options of course and not so expensive- purpose made epoxy concrete, especially made for the purpose. Problem is finding them close to you or in your country at all.

But those who search will find :-).

Key words:

epoxy concrete cast machine bed, ultra-high performance concrete

These guys http://durcrete.de/ can do machine bed design or cast inhouse for you or as far as i remember 1 ton of the stuff was like ~400euro

Gues what i will be bringing home if i go to Germany :-)