Thread: Epoxy granite or mineral casting
I think the difference is that in the long thread on CNCzone they are (or were) trying to find a resin/aggregate mixture that would when set leave a surface smooth, accurate and stable enough to mount the linear rails directly to it, hence the suggestion of using a flame to remove bubbles. However if you're just making a base or frame with it and embed steel strips, or other means, to mount the rails, that can subsequently be machined or adjusted to obtain the required accuracy then you can get away with all sorts of things. There are quite a few examples of where people have not used fancy resin etc on their machine and got good results, such as this one.
The Following User Says Thank You to Jonathan For This Useful Post:
I could have brought home half a dozen bags of fast-setting concrete from site last night that would do a pretty good job. I don't know what it's proper name is but the track workers call it 'Boff' - it comes in small bags of about 15kg, mixes directly with water, pours, doesn't shrink and crack and you can run trains on it within an hour of pouring. Very fine aggregate in it but by God is it tough, I dread having to break it - even with the demo robot it's hard going.
Dunno what you mean...
Actually, the stuff does shrink somewhathaving thought about it as I have seen cracks in large pours - no getting away from it when it's mixed so as to be pourable I guessbut I bet if you mixed it dry enough it would be reduced to a minimum. If you cast it into a steel form why would it not be good enough to fix rails to it directly?
I've been catching up on things with the forum and found this thread to be very interesting. Many years ago i worked in the flooring industry. The type of flooring our company did a lot of was expoxy resin coatings and floors. We used to do a lot of sculptured floors which had to handle high loads.
Granite was used as a high density filler for the hi loads. Silica sand was used for general use and mixing both together gave a happy medium for general use. Do'nt ask me for quantities as i can not remember but a company we did use was Flowcrete. We could order the stuff with fixed curing times.
Looking at the other thread in that link with the French build, i would have considered concreate with the thicknesses he was pouring. The advantage of epoxy resin is that you can get away with thinner sections (reinforce with mesh).
Things to think of are:
All fillers must be dry
Pea shingle makes an excelent cheap filler (wash and dry it before use)
Silica sand (paving gap filler from wickes)
This stuff shrinks
Always use mechanical mixing
Pouring too thick in one go is bad (add mesh to key pieces together), do it in a couple of pours before removing from the mould.
This stuff gets very hot so pour into moulds outside to avoid the nastys
Clean all items with thinners that are being sed within moulds
we worked to a max of 60mm for screeds in one go
if you use a release agent in the mould then you could use a gel coat to give you nice surface to paint afterwards.
Hope this helpsIf the nagging gets really bad......Get a bigger shed:naughty:
I've done some composite work and make the odd flight case for people using sheets of a carbon/kevlar/glass mix - the easiest way I have found of getting a glassy smooth finish is to use vacuum infusion onto a rigid sheet of perspex "mould" on a flat surface - you get glassy smooth finish with no bubbles.
Not sure, but you might be able to pull a thin infusion type resin through large sized grains of "rock" of some kind mixed with chopped fibres (I keep all my carbon/kevlar/glass off cuts for this purpose). If you can't vacuum through the aggregate, then pouring into a box mould with a perspex bottom should achieve good results. All the bubbles and crappy surface will be on the top and the shiny flat surface on the bottom, which you can then demould and flip over.
Heat would be my only concern, as large volumes which don't have a matrix of some kind tend to go off with cracks in them, but a few sheets of glass or carbon layered in the mixture should help solve that.
(Eyes up the gallon container of resin on the other side of the cave ;-) ).
Edit - nearly forgot - this link might hel with ratios http://www.talkcomposites.com/11/Res...ge-calculation
Strangley the chap Xavier mentioned this relies more closely on the principles of precasting concrete than my field of expertise which is composites and as such its just a different binder which is low enough not to exotherm with slow ARADUR hardner
Will drop the details to you guys wanting to have a play on wednesday when i'm back at work even for us in industry its a damn sit cheaper than having a machine bed fabbed they are sending me some bags 5 of quartz for trials and the Resin we already have ,and its easily obtainable
the only thing that need to be scaled down is the vibrating table
By irving2008 in forum General DiscussionReplies: 7Last Post: 18-02-2014, 10:01 PM
By gavztheouch in forum Moulding MachinesReplies: 8Last Post: 18-02-2014, 06:28 PM
By woolley2002 in forum Machine DiscussionReplies: 4Last Post: 04-09-2013, 08:06 AM
By flanagaj in forum Gantry/Router Machines & BuildingReplies: 1Last Post: 23-10-2011, 09:54 AM
By AdCNC in forum General DiscussionReplies: 2Last Post: 16-05-2011, 11:04 PM