Anyone have any concrete grinding tips?

[Sveedy]

The cement its self isn't so bad; it's the aggregate / rocks that can stop you cold. On occasions I have had to drop a steel punch into the hole and wack it with a hammer in order to crack a piece of rock. Then back to hammer drilling.

[RickHaleParker]

In this case, it's the sheer amount of energy required to remove just a 2-inch deep (at center), concave amount of regular old concrete.

It looks like it might be High-Density Concrete ... the mix that is used for Radiation shielding and Blast-Resistant Structures. Are you feeling like it is?

[matthew1]

I'm feeling like it's made for plutonium casing purposes, so yes.

Or it's 50% granite chunks to deter backyard guys like me from messing with it.

It came from a public sidewalk in a high density area here in Denver, so I'm thinking it was poured meeting public works requirements.

Anyway, the chisel and hammer drill were good suggestions... many thanks to Sveedy. I was able to break some rocks and make good vertical progress today.

I think I'm done. The height x diameter is beginning to rear its head on how far I can go down with the grinding wheel.

It's not suitable for anything but small-medium plants, which is fine.

[RickHaleParker]

It came from a public sidewalk in a high density area here in Denver, so I'm thinking it was poured meeting public works requirements.

It is a Bollard. Its original function was to keep vehicles from crashing into pedestrians. That is why it is so hard.

[matthew1]

It's not a bollard. I think they were coring to make holes for new traffic lights. This was one of three I grabbed that they left on the sidewalk.

After doing all this work, I can appreciate the power and durability of whatever they use to get these holes cut. The machines must be incredibly powerful and heavy.

[RickHaleParker]

The machines must be incredibly powerful and heavy.

That nothing. They are still trying to figure out how the ancient Egyptians drilled cores in granite at 500 times the feed rate we can do today.

[matthew1]

But could they solve a P0442?

j/k https://www.pbs.org/wgbh/nova/lostempir ... ing07.html that is very interesting. The theory of relativity is difficult to understand, so I turn to Egyptology... which is also difficult to understand. In all seriousness I love reading about ancient Egypt. I hope to go there one day, but in the present.

It blows my mind that the Great Pyramid was once finished in fine white limestone... no jagged stair steps/blocks showing.

Anyway, here's today's work. I think I'm done for now. I planed the other two.

I just realized I made a 120-lbs planter for a 2-oz plant.

[volvolugnut]

Looks great!
volvolugnut

[matthew1]

Thanks lugnut

[RickHaleParker]

It blows my mind that the Great Pyramid was once finished in fine white limestone... no jagged stair steps/blocks showing.

What blowing everybody's mind on the Egyptian cores is. They measured the concentric cut lines on the cores. The feed rate works out to 0.100 inch per revolution of the drill.

Drilling granite with a modern diamond drill rotating at 900 revolutions per minute, penetrate rate is 1 inch in 5 minutes. This works out to 0.0002 inch per revolution. 0.100 / 0.0002 = 500. Meaning that the ancient Egyptians were able to cut granite at a feed rate 500 times greater then we do today.

Please don't try convincing me they had help from ET.