blasting smallish tunnels in hard rock

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This shows the speed of non-electric blasting cord:

IIRC primacord detonation head propagates at about 2000 meters/second . I only got to play with it once or twice but it sure was fun !

IIRC primacord detonation head propagates at about 2000 meters/second . I only got to play with it once or twice but it sure was fun !

Thanks. That's the sort of thing I was looking for.

For what it's worth - identified the rock-drill I used.

One of the volunteers was a driller and said this machine is only usable on hard granite. That on any other rock - which in Cornwall would mean the "killas" which is the "country rock" - is a metamorphosed sedimentary rock - it is difficult to control. Use the popular smaller "303" - which is easier to carry too, etc.

Rich S

For what it's worth - identified the rock-drill I used.

One of the volunteers was a driller and said this machine is only usable on hard granite. That on any other rock - which in Cornwall would mean the "killas" which is the "country rock" - is a metamorphosed sedimentary rock - it is difficult to control. Use the popular smaller "303" - which is easier to carry too, etc.

Rich S

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This looks to be a copy (something like a copy?) of the Holman Silver 303.

The expression in English about the drill is brilliant.

Air-powered, at one place it's got an internal petrol (gasoline) engine - in another it has an internal diesel engine ... (!)

I imagine "lofty quality" is excessive use of a thesaurus to find synonyms for "high" - "high quality"

Rich S

This looks to be a copy (something like a copy?) of the Holman Silver 303.

The expression in English about the drill is brilliant.

Air-powered, at one place it's got an internal petrol (gasoline) engine - in another it has an internal diesel engine ... (!)

I imagine "lofty quality" is excessive use of a thesaurus to find synonyms for "high" - "high quality"

Rich S

--------------------------------- I would be worse translating to or from technical French or German. I subscribed to the German language version of the Daimler in-house magazine and couldn't find many of the high tech words in a dictionary. Although much of English descended from Saxon German the modern usage is considerably different, they don't translate word for word the way French sometimes does.

The "Delmag" type pile-driver...

They work by the piston falling in gravity. For a horizontal cylinder there could be a spring or gas pressure.

The problem would be clean combustion. You wouldn't want sooty and tarry waste gases down a mine.

Maybe use something like propane, with spark-ignition. Would still need ventilation - would get through oxygen in the air.

Beauty of air-tool is exhausts breatable air and the tool gets cooler as it works - makes it handlable for hard work.

I think suffer the inefficiency of compressed air systems for the simplicity, robustness, safety, avoidance of environmental problems down the mine, etc.

My impression is compressed air systems are about 10% efficient. eg. 3kW into the compressor motor to get the equivalent of about 300W of electrical power in something like an angle-grinder.

I've never seen a diesel hammer in action. Seen air-driven and hydraulic.

I've seen diesel pile-drivers in action. Like this:

.

Joe Gwinn

From my experience about sixty years ago, the crew opperating a "Delmag" pile driver, wear black (beige when new) coverals!

From grease lubrication and from part-burned fuel?

From grease lubrication and from part-burned fuel?

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The video shows what I remembered, except for the smoke color. The firing rate is at or below once a second so the chamber walls may not warm to operating temperature quickly.

Last night I dreamed about being offered a very inexpensive batch of used lawnmowers with a strange electric drive, powered by a 2 cylinder rotary (like WW1) engine built into the rotor of the alternator, as simple to make as a model airplane engine, and cheap surplus 90V electric motors to spin the blade. The seller's explanations all made sense, but I woke up before he answered if it required unavailable carbon brushes or castor oil.

Speaking of weird lawnmowers, I helped restore an MTD Yard Bug.

My impression is compressed air systems are about 10% efficient. eg. 3kW into the compressor motor to get the equivalent of about 300W of electrical power in something like an angle-grinder.

------------------------------ I saw about 20%, comparing the metered 2.48KW of my air compressor to the claimed 500W of an electric angle grinder. The time to grind welds was similar for both tools. I didn't measure carefully because I can't fine tune the process, only choose between them.

I read an analysis of a proposed compressed air automotive drive that said the energy loss was mainly from compression heating and expansion cooling, and in the installation they proposed insulation and a heat exchanger would increase efficiency, for instance if the compressed air remained hot its energy would be retained. PV=nRT. Compound steam engines were developed to reduce the loss from steam cooling the cylinders as it expanded.

I've never seen a diesel hammer in action. Seen air-driven and hydraulic.

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Only saw one once mowing in a ditch... but thought the "Hover Mowers" were pretty unusual😉

See the Taylor Hydraulic Air Compressor for some interesting reading. A patent with some info and related pointers here:

My uncle had one of those back in the late 50's (?) or maybe early 60's . As I recall it did a reasonably decent job .

You know you might be overdoing arcane interests when you get strange dreams on the topic... :-)