[js412000]

Has anyone considered using regular concrete with epoxy injected at high

pressure around the steel inserts, to mitigate the effects of shrinkage of the

concrete?

I have seen some information about epoxy grouting compressor bases.

In some cases the epoxy is injected into drilled holes at 300 to 1500 psi to

repair deteriorated machinery bases.

Post tensioning with tie bolts might also be useful to prevent cracks and

stabilize the base.

This approach might have a lower material cost, since only a small amount

of epoxy would be needed, and lower labor cost ,as concrete is readily

available and can be delivered pre mixed to your door .

I apologize if this topic has already been covered in the other thread.

[greybeard]

Has anyone considered using regular concrete with epoxy injected at high

pressure around the steel inserts, to mitigate the effects of shrinkage of the

concrete?..........

......I apologize if this topic has already been covered in the other thread.

Hi js412000.
While it is true that concrete has been touched on in the E/G thread, and possibly others, I wouldn't go so far as to say it's been covered.

With the coming spring, and planning to do quite a bit of concrete work in the garden, I don't think SWMBO will notice that I am also going to cast up a few experimental components.

One of my own ideas for reduction of the epoxy used was to glue together well matured concrete slabs as a way of getting round the slow shrinking with time that occurs with Portland cements. Other problems require other solutions, but I'm sure that some combination of these quite dissimilar materials might well produce a workable and useful result.

John

[js412000]

I am thinking that the concrete could be post stressed.

I would embed threaded rods in the mix and have them pass completely

through the part . The rods would be wrapped with something to keep the

concrete from bonding to them .

I would tighten the nuts on the rods after curing.

[The Blight]

I have been toying with this idea too, and after some drawing it turned out to be a 1500lb monster. I might even make it some day when I have enough space

I found a bunch of patents on concrete machine bases. If I remember that I have posted in this topic, I will come back with the numbers of those patents.

[The Blight]

Okey, here are the patent numbers I promised
2010557
3618432
4622194
3800636

This last one is just about machine bases in general.
4907478

[js412000]

Thanks for the links. Some of them I had not seen before.

For my machine base I am thinking that I don't want to rely on the bond

strength of the epoxy to keep the parts together. The epoxy would be just to

fill gaps and lock things in position.


My "monster" will take about five yards of concrete.

[martinw]

Dear js41200,

Concrete is a plastic material that creeps over time.

Look at any building that has RC cantilever floors built in the 1970s and you can see that they sag. That is just plastic behaviour exhibiting itself over time. I believe that this has nothing to do with the rebars sliding over the concrete, and is actually down to the material properties of the concrete.


Does any of this matter to you with your application? Probably not. If you want a few yards of "readymix" as a machine base, MVVHO is just pour it and forget about pre or post tensioning rods. It will shrink a bit for a couple of months (and years thereafter), but nothing that cannot be coped with by a few shims. Epoxy pressure grout is a bit OTT, again my VHO.

Best wishes,

Martin

[martinw]

Well, if you want a really good base, get a stack of granite tombstone stock from the people who supply the local Funeral Parlour. It will probably be polished, and you will need to rough it up a bit with a 60 grit wheel. Core drill holes for 1/2" tension rods and laminate the stack with some epoxy. Try and keep the epoxy layers as thin as possible.

Bingo. No need to worry about shrinkage or creep. Rock solid.

Best wishes,

Martin

[Geof]

....... My "monster" will take about five yards of concrete.

Monster is a bit of understatement; do you know how much 1 yard of concrete weighs? Not to mention the cost of 5 yards and the form work needed to retain it.

[js412000]

concrete weighs about 150 pounds per cubic foot - 4000 per yard!

[The Blight]

This is a machine that I want to build. I will create the base from concrete, and maybe even the table. All the big holes you see are for threaded rods so that I can post tension the concrete. I will also use rebar and all the threaded inserts will be welded to it.

So far without the linear rails, motors, ball screws.. it weigths about 500kg (1100lb). The table itself weights about 100kg (220lb).

You can sand concrete, so I will try to make some mounting surfaces on the concrete itself, and if that fails, I will just bolt some ground steel plates in between.

The mill will have 800mm X travel, 400mm Y travel, and 350mm Z travel. There is room at the back of the table for a rotary table, and maybe a lathe headstock.

I'm planning on using 25mm ball screws with a 5mm pitch. Combined with servos and a 5:1 ratio I will get around 100IPM rapids. I will be using 30 and 35mm rails with medium preload. Total cost for these components: $6000.

So far I'm looking into using the X3 spindle along with a 1000W motor. Was looking into one of those cheap high speed spindles, but I would like to be able to use bigger tools.

I have been thinking about how I want to make the mold for this, and I might just make it from fiberglass. All the surfaces used for mounting will have a metal plate to achieve some level of flatness (will have to sand afterwards).

Oh and this project wont start until I'm back in Norway. Might be this summer or it might be in 4 years. Lots of time for planning A bit of an insane project, but it might work. If it fails I will try to get my hands on some epoxy granite.

PS. I havn't drawn the linear rails because I can only have a limited amount of unique parts in the assembly. Alibre thing..

[BillTodd]

Blight,

Might be an idea to design-in some way of moving it around, to make it easier to handle.(i.e. slots for a pallet truck, lifting eyes etc.). Concrete will not take kindly to pry-bars or any point loading.

[The Blight]

Good idea! Will have to do that! Thanks

One more note on the machine. The base has 4 hollow rooms underneath it to reduce weight.

[The Blight]

A little update on the mill. (Picture has been updated above)

I was able to add the linear rails to the assembly. Looks nice

I will be machining a BT30 spindle for the machine. Found some nice cheap tooling, and I want to add an ATC to the machine later on.

There is a lot of room at the end of the table, so I will add a 4th axis which can be used as a lathe. Using the software to switch between the two spindles, I can use it as a lathe with live tooling or as a 4axis mill. I will also use servo motors on both spindles so that I can do some threading/tapping along with indexing (break on the 4th axis, or two gear setups).

The mill has also gotten taller. It's about 1000mm and it weights close to 700kg.

Edit: I have also decided that I want to use the CNC Brain for this machine. Closed loop and all

[podarok]

Hey
Any updates for the build?
Design looks promising

[Chazaxl]

Hey
Any updates for the build?
Design looks promising

You do realise the last post on this thread was in 2009?