CNC metal C frame build

[Tristar500]

After posting a query regarding the possibility of building a mill from structural steel tubing and then filling the tubes with concrete I've taken the plunge.

Here the parts are mocked up in my shop with clamps to give me an idea of how the finished machine might look.
clamps to give me an idea of how the finished machine might look.

[Tristar500]

I got everything lined up and welded in place and readied the kiln to stress relieve the frame before grinding/fly cutting the mating surfaces true.

My wife built a pottery kiln some years back and I was in luck it fit in no problem.

Next I brought the base and upright to temperature or 1150 degrees for 5 hours.

When done, I shut off the gas and waited for it to cool.

It's done when a toothpick comes out clean right?

[Tristar500]

Here's a CAD file of the design.

[paulC]

Nice work. I'm a bit ignorant on the use of concrete in steel. Is reducing the strees a requirement for the concrete or for the grinding?
Paul

[saris]

Paulc: no expert, but i think you want to stress relieve the steel (or alot of materials) before you final machine the components true to get all of the movement out of the material. IF not stress relieved, if you machine something thinking ur gonna get acccurate parts, the material will move, or spring in some unknown direction, and ur parts won't be what u think ur getting.

1 So stress relieve

2 Machining

3 Sometimes for BIG parts, another round of stress relief

4 Final maching

5 inspection

[Geof]

When you do your machining I suggest you take everything down to within 0.020" of the final dimensions and check to see if things have distorted. You have welded together very different thicknesses and your first stress relieving may not have released all the stresses between these sections.

[Tristar500]

It looks as if I will have to have the mating surfaces to the bearing rails ground but will have to have the end of the base fly cut as it won't fit on any grinder in town. This shouldn't be a problem as it would be easy to shim if necessary the uprights to the base.

L

[Bill Johns]

Good idea.
Where is a good source for the ball screws etc.
Why not just use thicker cross section steel instead of the concrete?
Is there any info on here about using concrete?

[Tristar500]

The mill is reall coming along now. It's back from the ginding shop and I've had several days to work on it.

[Tristar500]

OK, gang, I'm really getting into it. Here's a shot of the z axis stand-off blocks coming together. Notice the sweet finish the facemill leaves on the aluminum!

Nice!

[Tristar500]

tolerances are looking really good, so far .00005 or better.

[Tristar500]

Originally Posted by Bill Johns Good idea. Where is a good source for the ball screws etc. Why not just use thicker cross section steel instead of the concrete? Is there any info on here about using concrete?

The concrete will dampen the natural resonance of the steel tubing.

When unfilled the tubes ring like bells.