[Mcgyver]

I did not understand the last part.Are you talking about filling the coloum with stones and pouring in epoxy?The epoxy is mixed and the fillers are added and then poured in place.Larry

Larry,

Yes I'd envisioned a normalized steel fabrication filled with aggregate and then polymer poured in as oppose to the polymer/granite being mixed and then poured. When i posted that, I envisioned (rightly or wrongly) a largish (maybe 1"-2") size aggregate, if this was the right size to use then mixing first would seem to me messy, extra work and of limited benefit. This may make no sense to someone thinking a 4*8 router out of 2" tubing, I'm thinking more along the lines of a small but massive machine for metal, filling a much more boxy shaped cavity...maybe welded from 6 or 8" column steel with the total machine being less than a couple of feet in each direction.

This idea of pouring the polymer with granite in place may be a bad one, don't know, its just how how it occured to me to do it.

on the other hand, if sand is the right size, it would of course have to be premixed, else you'd have a puddle of polymer on top.

Maybe a more succinct way of expressing the question is,

-what is the effect of aggregate size on the strength of the material?
-what sizes of aggregates are commonly used for various applications?
- for a give size(s) of aggregates, what are the techniques & concerns so far as mixing and pouring goes

Mike

[the4thseal]

I am thinking about doing some experiments to get some shop truth.
I am thinking about putting the aggregate in all of its sizes into the mold and then using a vacuum to pull the epoxy through the mold, much in the way you do with composite fabrication. It works in that and the molds are much more complicated. I am going to make a test and will let you know how it goes. I will be using a combination or granite and steel fibers.

[Geof]

.... I'm thinking more along the lines of a small but massive machine for metal, filling a much more boxy shaped cavity...maybe welded from 6 or 8" column steel with the total machine being less than a couple of feet in each direction....

To some extent you are talking apples and oranges here. This idea depends on the steel for the structural properties and the aggregate/binder fill for the vibration damping properties. You are not worried too much about the mechanical strength of the aggregate/binder fill so you can tolerate very large voids between the aggregate that get filled with the binder.

In the technique being developed by the German chaps you are concerned about the mechanical strength of the epoxy concrete so you do need to worry about having a range of aggregate sizes so that you have a minimal volume that is filled by the epoxy binder.

I think the steel structure filled with something to damp vibration is feasible on a DIY level. I don't think the full epoxy concrete approach is feasible for DIY. If you look at the German pictures they appear to have steel ways with bolts screwed in the back side and mounted in their mold. It would seem the bolts are acting to anchor the steel ways in the epoxy concrete. Some of the other links also mention making highly accurate molds for casting the epoxy concrete to tight tolerances and they also mention that it cannot be worked once cured; all threaded attachments have to be cast in situ. This means that for epoxy concrete you need to make an accurate mold or some form of structure to hold and locate the attachment points, etc, which is then discarded after the epoxy concrete structure is cast. This is fine if you are doing production because the mold is reused many times; this point is also mentioned in some of the links. For DIY it seems to me to make more sense to build your steel structure, use large section tubing, get it stress relieved if necessary, do all the attachment of guideways etc on a structure that can be drilled and tapped anywhere and then fill the structure to take out the vibration.

[walter]

...I don't think the full epoxy concrete approach is feasible for DIY. If you look at the German pictures they appear to have steel ways with bolts screwed in the back side and mounted in their mold. It would seem the bolts are acting to anchor the steel ways in the epoxy concrete. Some of the other links also mention making highly accurate molds for casting the epoxy concrete to tight tolerances and they also mention that it cannot be worked once cured; all threaded attachments have to be cast in situ...

That actually was the original idea- all bolts, reinforcements/attachments, mounting "devices" build into the epoxy(picture)- which would create a "plug and play" table, frame part or even entire gantry.

Polymer/concrete/epoxy may not be the best solution, but it sure beats the alternative:

I am in the process of building a welded steel frame over 10' long for my catilevered mill.
The basis is a Steel I-beam 24" between webs, 5/8 thick flanges 10' wide, with lots of 4x4x.25 wall A36 steel tubing welded in a torsion box design on bot sides between the flanges.
The cost for stress relieving something this big and massive in Northern CA is going to be between $1000 to $1200 dollars.
Blanchard grinding the long axis is going to cost another $750.
When I look at the overall cost and affect on accuracy, it seemed like a good tradeoff vs other construction techniques.
If the frame isn't straight and flat, it will be useless, hence the stress relief and grinding. Al

[Geof]

That actually was the original idea- all bolts, reinforcements/attachments, mounting "devices" build into the epoxy(picture)- which would create a "plug and play" table, frame part or even entire gantry.

Polymer/concrete/epoxy may not be the best solution, but it sure beats the alternative:

But my point is you have to effectively build the alternative to hold all your bolts, reinforcements/attachments, mounting "devices" in the correct place within the mold in which you then cast the epoxy. And if you do not get everything in the correct place you are stuck because you cannot rework the epoxy.

[greybeard]

But my point is you have to effectively build the alternative to hold all your bolts, reinforcements/attachments, mounting "devices" in the correct place within the mold in which you then cast the epoxy. And if you do not get everything in the correct place you are stuck because you cannot rework the epoxy.

But I would assume that all the "bolt ons" would be adjustable in position anyway. Seems crazy not to do so.
Surely the whole point of the EG is to give a well damped, simplified(!!) constructional method for frames etc.

Just my groat's worth though.

John