[Geof]

....The idea of introducing a compound to release water into the mix just to counter shrinkage seems a backward step to say the least !!! John

Yes it does and in addition they say: "at temperatures above 100°C some of the hydration water is released, creating expansion forces," .... which counteract resin shrinkage. But the polymer aggregate has a fairly large coefficient of thermal expansion so it seems to me you are replacing curing shrinkage with thermal shrinkage.

[RotarySMP]

Geof, it is shame the thread on Nucky and Thomas's Mill is in german. This thread is the one that really opened my eyes that polymer concrete is not only viable but also possibly ideal for homebuilders.

To make complex mold forms they are laminating simple 2D shapes cut on a homebuilt CNC router. To mix the epoxy and aggregates they are just stirring hell out of it in a bucket, they are doing heaps of thumping the mix into the mold as I don't think the vibrating table is optimised, but the results look great. If you have access to a mill big enough, getting the linear slide mounting strips milled (preferably ground) would be perfect, but there is plenty of information about hand grinding and scrapping available in the gingery tooling world.

[digits]

If the concrete doesn't get too hot and doesn't shrink or expand during curing, has anyone considered setting an 80/20 frame in concrete, leaving the top-surface of the extrusion out of the concrete? The 80/20 is plenty strong but it is relatively light and the joints may not be the most rigid.

This way, wouldn't you get the rigidity and damping of concrete, but with the inbuilt accuracy of the profiles with the magic adjustability their slots provide?

[Geof]

If the concrete doesn't get too hot and doesn't shrink or expand during curing, has anyone considered setting an 80/20 frame in concrete, leaving the top-surface of the extrusion out of the concrete? The 80/20 is plenty strong but it is relatively light and the joints may not be the most rigid.

This way, wouldn't you get the rigidity and damping of concrete, but with the inbuilt accuracy of the profiles with the magic adjustability their slots provide?

For what it is worth I think this is a brilliant idea. It removes practically all my points of difficulty which are related to premaking and positioning the mechanical elements.

[Oldmanandhistoy]

Hi all,

Just a quick question; would this E/G be any good for small components such as bearing blocks?

Very interesting thread btw.

John

[greybeard]

For what it is worth I think this is a brilliant idea. It removes practically all my points of difficulty which are related to premaking and positioning the mechanical elements.

Geoff, didn't my posting #93 have the effect ?

Regards
John

[Geof]

Geoff, didn't my posting #93 have the effect ?

Regards
John

Then I was still thinking about having to make the 'bolt-ons'. Drill and tap strips of metal both for bolts to anchor them into the EC and to attach the bolt-ons and then drilling or slotting the pieces that attach to the embedded metal. If you do not have free access to fairly good metal working equipment this is difficult.

I had totally overlooked that the 8020 extrusion could serve as the embedment and provide adjustable attachment points. This also removes my criticism of the 8020 that it is not adequately rigid; embedding most of it in the EC means only small distances are exposed.

The other query from the historic old man is also (in my humble opinion ) in the correct direction for using EC on a DIY basis in a viable manner. For feedscrew mounting attach the bearings to each end, align everything and then make little molds where the mounting blocks are to be cast. In this case it might be best to make up a base for the block that would be bolted in place so that when the block is cast it is possible to remove everything.

It would also be a good idea to slip a plastic tube over the screw and make protective covers for the bearings.

[walter]

8020 frame in zero-shrink concrete- that is brilliant
(thanks Digits)

[atenman1]

If the concrete doesn't get too hot and doesn't shrink or expand during curing, has anyone considered setting an 80/20 frame in concrete, leaving the top-surface of the extrusion out of the concrete? The 80/20 is plenty strong but it is relatively light and the joints may not be the most rigid.

This way, wouldn't you get the rigidity and damping of concrete, but with the inbuilt accuracy of the profiles with the magic adjustability their slots provide?

Good thread, read daily...:banana:
But can some body tell me what is 80/20 frame, please?

[atenman1]

I got it!!! So sorry for being dumb

[digits]

8020 frame in zero-shrink concrete- that is brilliant
(thanks Digits)

Thanks, but someone has to actually try it and find out if it works first! I am not brave enough to bury £100 of aluminium extrusion in 50kg of concrete to find out whether the extrusion gets warped as the concrete sets!

This is a very interesting thread though - I'm really looking forward to seeing some finished results

[lgalla]

I know I have been posting lots on E/G and am embarrassed to admit my first project is a circuit board router built on a granite plate,drilled with diamond drills to mount 80/20.This is similar to the concrete 80/20 posts.
I assume the posts are meaning to fill an 80/20 frame with concrete as stated.We are talking here about polymer concrete or E/G.Two problems I see is the mixes are of trowel consistancy,which would prove difficult to force in to the slots.If one were to accept less filler and a pouring consisty,I would not see a problem.If an epoxy based filler is used we may have to consider the cofficient of thermal expansion of aluinium.Thick crossections of epoxy can have an exotherm of 150degrees C.I hope Geof can tell us how much the aluinium will expand.I don't know.Filling the hollows of the 80/20 is another interesting subject.
BTW granite sand or chips has been impossible to source.I found a possible source in Northern Ontario of black granite sand and screenings but the minium order is like 200tons.Chicken grit is usually granite and stocked in farmers co-ops or feed places.I will check it out on the weekend.Anybody else found a source?
lARRY

[Geof]

Igalla; I took digits' suggestion to mean the 80-20 frame is embedded in the EC not filled with EC. My mind has a picture of the frame members that would carry say the X axis guides buried up to their neck in EC with just enough exposed to attach things to the channel. I suppose one end would need to be fully exposed to get at the channel. With a bit of ingenuity I think it would be possible to build a gantry in a similar manner.

Regarding thermal expansion aluminum is around 25 x 10^-6 and EC varies at 10 - 30 x 10^-6 in/in degree C so you can more or less consider them equivalent. Actually the EC would tend to thermally contract around the aluminum. I also looked at the elastic modulus and aluminum is about twice as stiff as EC but of course because there is so much more bulk in the EC it would be the primary contributor to stiffness.

Your point about the EC mix being to thick to penetrate the aluminum is correct but it would embed it more than adequately I would expect.

[walter]

Larry, how about making a lenght of 4"x4" formwork with 2"x2" 8020 in the center (a core, if you will) and then pouring concrete?

CNC user would have to build a "complete" 8020 core-frame and then encapsulate it with a concrete. 8020 being just a core holding the entire structure. All concrete on the outside...:violin:

EDIT: Geof pretty much explained it

[lgalla]

Geof
Thanks for the input.I stated previously a total E/G or E/C machine was impossible for the hobbyist as per your opinion.Who am I to state the capabilities of the Members?Obviously good ideas are forming and growing from member input.We are on to something here for everyone,be it cast surface plates or improving existing structures.Previous Polymer concrete threads have died.Hope this one continues.A lot of members are viewing this thread and not posting.Any crazy ideas are welcomed as it results in refreshed or renewed thinking.I am just an epoxy guy and woodworker.The ZONE allows a marrige of different technologyies to produce new ideas.
L:arry

[walter]

With 8020 aluminum "core" we are using significantly less material. Would it be feasible to use the epoxy/sand instead of "polymer concrete"..?
.

[greybeard]

I wonder if there are "cheaper" sections than the one's poeple have been considering using up to now that might be embedded ? If you're going to bury 2/3 of the extrusion in the EG it seems a bit of an expensive way just to lock it in place.

John

[digits]

I wonder if there are "cheaper" sections than the one's poeple have been considering using up to now that might be embedded ? If you're going to bury 2/3 of the extrusion in the EG it seems a bit of an expensive way just to lock it in place.

John

I can't see why you'd need sections as tall as the ones in those pictures. Fully supported aluminium extrusions can't sag or deflect under load, so as long as they are surrounded on 3 sides by concrete, I would have thought thin profiles would be fine.

For my project I need a way to support two linear rails about 1m apart, but exactly and rigidly parallel down an 800mm length. To get the strength I need, I was planning to simply lie two 800mm long 80x80mm profiles on top of two 1200mm long 80x80mm profiles and then bracket the hell out of it - this allows me to get perfect parallelism without any need to be able to cut the profile at all accurately. However, I imagine that if it were all going to be embedded in concrete, I could switch to 80mm wide x 40mm deep profiles, and sink the whole lot in 60-70mm of concrete. Infact 40x40 would probably do, but I want two (perfectly parallel) slots per extrusion - so I need wide profile.

[lgalla]

I would hazard a guess.Depending on size or application,we probably want 3to4" of E/G which makes tall extrusions necessary.From posts I am seeing 2 different ideas.One where there is a frame of extrusion ,two where there is two pieces of 80/20 surrounded by polymer.Either case we need a mold.3/4 melomine may be a good cheap material.I we had a frame of extrusion we could simply attatch it to a melomine base and pour.In the other style one would build a box and pour allround.
Now we have to accept we need pouring consistancy so the polymer can flow into the 80/20 side slots.I would just use sand in the mix,pour1/2"and manually push stones or aggregate into the epoxy.
Larry

[walter]

Melamine mold sounds good and I like the "box" idea.

re: tall extrusions
There are multiple 8020 choices (esp on Ebay). The one pictured would be good for longer machine frames 8-16 ft. Anyone here interested in a frame longer than 8ft..?
.