When would it be used, and why? How did it come to be invented in the first place?

I can see that it has the advantage of minimal teeth wear and (with air jets into the centre) good self-cleaning.

But it only works by pressing on rock, not shearing/tearing it, so must be awfully slow, and irregular in back pressure. Because rocks are strong under compression.

And those three bearings must be under enormous strain.

mollwollfumble said:

When would it be used, and why? How did it come to be invented in the first place?

I can see that it has the advantage of minimal teeth wear and (with air jets into the centre) good self-cleaning.

But it only works by pressing on rock, not shearing/tearing it, so must be awfully slow, and irregular in back pressure. Because rocks are strong under compression.

And those three bearings must be under enormous strain.

Might it feed something down into were the three thingies meet

mollwollfumble said:

When would it be used, and why? How did it come to be invented in the first place?

I can see that it has the advantage of minimal teeth wear and (with air jets into the centre) good self-cleaning.

But it only works by pressing on rock, not shearing/tearing it, so must be awfully slow, and irregular in back pressure. Because rocks are strong under compression.

And those three bearings must be under enormous strain.

https://www.youtube.com/watch?v=4BhSPKl3vMY

we would use it on Murdoch videre licet

roughbarked said:

mollwollfumble said:

When would it be used, and why? How did it come to be invented in the first place?

I can see that it has the advantage of minimal teeth wear and (with air jets into the centre) good self-cleaning.

But it only works by pressing on rock, not shearing/tearing it, so must be awfully slow, and irregular in back pressure. Because rocks are strong under compression.

And those three bearings must be under enormous strain.

https://www.youtube.com/watch?v=4BhSPKl3vMY

I saw that. All it does is confirm that the cones are rotating counter to the shaft rotation, which just about zeros out the shear of the tool against the rock.

I wonder if a tricone drill bit is only suitable for coal. ie. a rock that is brittle, soft in compression, but abrasive and with a tendency to clog.

mollwollfumble said:

roughbarked said:

mollwollfumble said:

When would it be used, and why? How did it come to be invented in the first place?

I can see that it has the advantage of minimal teeth wear and (with air jets into the centre) good self-cleaning.

But it only works by pressing on rock, not shearing/tearing it, so must be awfully slow, and irregular in back pressure. Because rocks are strong under compression.

And those three bearings must be under enormous strain.

https://www.youtube.com/watch?v=4BhSPKl3vMY

I saw that. All it does is confirm that the cones are rotating counter to the shaft rotation, which just about zeros out the shear of the tool against the rock.

I wonder if a tricone drill bit is only suitable for coal. ie. a rock that is brittle, soft in compression, but abrasive and with a tendency to clog.

Tricone bits are mostly used for sedimentary rocks (especially in the oil and gas industries). Cuttings are carried back by water, not air. There is a slight twisting of the gear-teeth on the rock. This cuts the rock, effectively by gouging out grains. They are very slow bits in igneous and metamorphic rocks.

Their real advantage is the low rate of wear compared to down-hole hammers. And their hole steerability compared to spade bits. And they are cheap compared to hammers. Low rate of wear means you are not pulling rods so often to replace the bit. (Think petroleum holes that can be thousands of metres deep.) They are not commonly used in drilling for coal, because the holes are much shallower.

The most interesting down-hole cutting arrangements I’ve seen are the ball-grinders (like large die-grinder bits) used on steerable down-hole motors.

Michael V said:

mollwollfumble said:

roughbarked said:

https://www.youtube.com/watch?v=4BhSPKl3vMY

I saw that. All it does is confirm that the cones are rotating counter to the shaft rotation, which just about zeros out the shear of the tool against the rock.

I wonder if a tricone drill bit is only suitable for coal. ie. a rock that is brittle, soft in compression, but abrasive and with a tendency to clog.

Tricone bits are mostly used for sedimentary rocks (especially in the oil and gas industries). Cuttings are carried back by water, not air. There is a slight twisting of the gear-teeth on the rock. This cuts the rock, effectively by gouging out grains. They are very slow bits in igneous and metamorphic rocks.

Their real advantage is the low rate of wear compared to down-hole hammers. And their hole steerability compared to spade bits. And they are cheap compared to hammers. Low rate of wear means you are not pulling rods so often to replace the bit. (Think petroleum holes that can be thousands of metres deep.) They are not commonly used in drilling for coal, because the holes are much shallower.

The most interesting down-hole cutting arrangements I’ve seen are the ball-grinders (like large die-grinder bits) used on steerable down-hole motors.

Oh, and the steerable down-hole motor had built-in, real-time down-hole geophysics only centimetres from the bit – short-spaced density, long-spaced density, natural gamma, and direction measurements along with other bore-hole information like caliper etc.

Michael V said:

Tricone bits are mostly used for sedimentary rocks (especially in the oil and gas industries). Cuttings are carried back by water, not air. There is a slight twisting of the gear-teeth on the rock. This cuts the rock, effectively by gouging out grains. They are very slow bits in igneous and metamorphic rocks.

Their real advantage is the low rate of wear compared to down-hole hammers. And their hole steerability compared to spade bits. And they are cheap compared to hammers. Low rate of wear means you are not pulling rods so often to replace the bit. (Think petroleum holes that can be thousands of metres deep.) They are not commonly used in drilling for coal, because the holes are much shallower.

The most interesting down-hole cutting arrangements I’ve seen are the ball-grinders (like large die-grinder bits) used on steerable down-hole motors.

Oh, and the steerable down-hole motor had built-in, real-time down-hole geophysics only centimetres from the bit – short-spaced density, long-spaced density, natural gamma, and direction measurements along with other bore-hole information like caliper etc.

Brilliant, thanks. So, suitable for very long bore holes because of the very low rate of wear, and the slight shear removes individual grains from sedimentary rock. Nice.

Water slurry rather than air, good. Air wouldn’t work well for long bore holes because of the pressure.

I hadn’t thought of the relationship to steerable motors and sensors, that would be great.

Looking up ball-grinder bits. Like this but larger?

Or like this?

mollwollfumble said:

Michael V said:

Tricone bits are mostly used for sedimentary rocks (especially in the oil and gas industries). Cuttings are carried back by water, not air. There is a slight twisting of the gear-teeth on the rock. This cuts the rock, effectively by gouging out grains. They are very slow bits in igneous and metamorphic rocks.

Their real advantage is the low rate of wear compared to down-hole hammers. And their hole steerability compared to spade bits. And they are cheap compared to hammers. Low rate of wear means you are not pulling rods so often to replace the bit. (Think petroleum holes that can be thousands of metres deep.) They are not commonly used in drilling for coal, because the holes are much shallower.

The most interesting down-hole cutting arrangements I’ve seen are the ball-grinders (like large die-grinder bits) used on steerable down-hole motors.

Oh, and the steerable down-hole motor had built-in, real-time down-hole geophysics only centimetres from the bit – short-spaced density, long-spaced density, natural gamma, and direction measurements along with other bore-hole information like caliper etc.

Brilliant, thanks. So, suitable for very long bore holes because of the very low rate of wear, and the slight shear removes individual grains from sedimentary rock. Nice.

Water slurry rather than air, good. Air wouldn’t work well for long bore holes because of the pressure.

I hadn’t thought of the relationship to steerable motors and sensors, that would be great.

Looking up ball-grinder bits. Like this but larger?

Or like this?

Like the first one, but steerable.

The second one is a downhole hammer bit. Probably reverse circulation.

Have a look around this site and all it’s related pages to get an idea about real-time downhole geophysics and steerable down-hole motors. Ignore my mad mate Davo staring at you from the bottom of the page. But don’t ignore the development of these amazing tools in Australia.

https://reflexnow.com/solutions/driller-operable-geophysics/

Also:

https://www.glossary.oilfield.slb.com/en/terms/s/steerable_motor

Michael V said:

mollwollfumble said:

Michael V said:

Tricone bits are mostly used for sedimentary rocks (especially in the oil and gas industries). Cuttings are carried back by water, not air. There is a slight twisting of the gear-teeth on the rock. This cuts the rock, effectively by gouging out grains. They are very slow bits in igneous and metamorphic rocks.

Their real advantage is the low rate of wear compared to down-hole hammers. And their hole steerability compared to spade bits. And they are cheap compared to hammers. Low rate of wear means you are not pulling rods so often to replace the bit. (Think petroleum holes that can be thousands of metres deep.) They are not commonly used in drilling for coal, because the holes are much shallower.

The most interesting down-hole cutting arrangements I’ve seen are the ball-grinders (like large die-grinder bits) used on steerable down-hole motors.

Oh, and the steerable down-hole motor had built-in, real-time down-hole geophysics only centimetres from the bit – short-spaced density, long-spaced density, natural gamma, and direction measurements along with other bore-hole information like caliper etc.

Brilliant, thanks. So, suitable for very long bore holes because of the very low rate of wear, and the slight shear removes individual grains from sedimentary rock. Nice.

Water slurry rather than air, good. Air wouldn’t work well for long bore holes because of the pressure.

I hadn’t thought of the relationship to steerable motors and sensors, that would be great.

Looking up ball-grinder bits. Like this but larger?

Or like this?

Like the first one, but steerable.

The second one is a downhole hammer bit. Probably reverse circulation.

Have a look around this site and all it’s related pages to get an idea about real-time downhole geophysics and steerable down-hole motors. Ignore my mad mate Davo staring at you from the bottom of the page. But don’t ignore the development of these amazing tools in Australia.

https://reflexnow.com/solutions/driller-operable-geophysics/

Also:

https://www.glossary.oilfield.slb.com/en/terms/s/steerable_motor

Ta for the reads.