Re: 45.Thompson Submachine Gun - Waterjets
Posted by
Roland Friestad
on 1999-08-14 07:39:30 UTC
In reply to some points raised by Arne Jorgenson in Digest 132/Message 5 -
Thompson Gun might work but would produce unacceptable levels of what in the
CNC machining business is called "cusp height" unless horrendessly large
quantities of ammunition were to be used - (Tongue firmly in cheek)
Machining a small hole with thin wire using EDM - We also use both RAM and
WIRE EDM in our shop and the normal procedure for machining small diameter
deep holes using RAM EDM is to rotate a very fine electrode which is usually
either a piece of either hypodermic needle tubing or special molydbdenum
tubing - Small diameter brass tubing can be used but it doesn't last very
long - Tubing is used so that adequate flushing can be maintained - By
rotating the electrode the hole remains straight and while sparking will
occur on the sides of the tube, after the overcut value is reached the bulk
of the cutting occurs at the end of the electrode - I asked the FLOW people
how they made their carbide mixing nozzles for the waterjet machines and
they just smiled at me -
Roland Friestad is a scandanavian name (Norwegian) - Arne Jorgenson sure
doesn't sound Irish
Waterjet cutting force/mass momentum? - Yes, the force applied by the
combination of the velocity and mass of the water or water/abrasive is the
source of the cutting forces - The purpose of the high pressure is only to
accelerate the water to the high velocities required - I haven't done any
calculations on the cutting forces generated by an individual grain of
garnet at Mach 3 but it might be an interesting thing to know about -
Exploded view of nozzles - I have some of these that came with the FLOW
machine - Would be able to mail photocopies to those interested - Send a
SASE business envelope to - Roland Friestad - c/o Cardinal Engineering, Inc.
- Box 163 - Cameron, IL 61423 - USA -
Sapphire orifices - These are used for the water only cutting and also
upstream of the abrasive injection for the water/abrasive system - Water
condition is quite critical and must be maintained below certain levels of
iron and mineral content - In addition the water is filtered for
particulates to a 0.5 micron level using a two stage coarse/fine filtering
system - Particles in the water stream are accellerated to levels that can
fracture the sapphire orifice if they impact it - Incidentally the sapphire
orifices are made by the same people who make the jewels for watches and
other similar instruments - They are mounted in an aluminum or stainless
steel outer shell -
Need for 35 HP motor - Again, while I have not done the calculations I know
that an extremely large quantity of heat is generated by the act of
compressing the water (which is not incompressible at these levels of
pressure) - The source of that heat must be the energy supplied by the motor
- It is not unusual for our 200 gallon water tank to be raised to a
temperature that is uncomfortably warm just by the high pressure water
stream - That does not even take into account the waste heat that goes down
the drain with the pump cooling water and that generated by the pressure
relief valve - An intuitive analogy might involve attempting to inflate a
tire with a nail hole using a hand pump - (Something that we Norwegians
occasionally do for the fun of it) - It is quite easy to raise the pressure
to a certain level but as you attempt to go higher and higher the leakage
rate increases dramatically and soon you are unable to pump enough (supply
enough energy) to increase the pressure any more - At that point I
generally let my wife take over (She is Swedish) - A semi-educated guess on
my part would be that successful cutting of balsa and thin plywood could
possibly be done using a 5 to 10 hp motor but that is just a guess -
Our machine uses a reciprocating piston pump but many of them also use the
pressure intensifier approach mentioned in earlier messages - I have used
similar intensifiers myself for other applications in the past - The concept
is quite workable but, as has been speculated, the commercial waterjet
machines normally utilize an accumulator to reduce the pulsations in the
flow stream -
My suspicion is that the small motor/pulsed output approach would be
questionable in its efficacy but I certainly couldn't prove it at this time
- If I were to attempt a design such as this myself I would consider using
the small motor to run a relatively massive flywheel up to speed and then
use the flywheel to run an intermittent (clutch operated) pump with check
valves in the input and output lines - That is the basic way that a punch
press can provide many tons of punching force using a relatively small motor
- Of course a punch press is an extreme example of a pulsating type of
machine and if you have ever attempted to exceed the rated strokes per
minute capacity of a punch press and seen how dramatically the flywheel
slows down you will appreciate that the energy in must equal or exceed the
energy out over the long term -
Roland Friestad
Thompson Gun might work but would produce unacceptable levels of what in the
CNC machining business is called "cusp height" unless horrendessly large
quantities of ammunition were to be used - (Tongue firmly in cheek)
Machining a small hole with thin wire using EDM - We also use both RAM and
WIRE EDM in our shop and the normal procedure for machining small diameter
deep holes using RAM EDM is to rotate a very fine electrode which is usually
either a piece of either hypodermic needle tubing or special molydbdenum
tubing - Small diameter brass tubing can be used but it doesn't last very
long - Tubing is used so that adequate flushing can be maintained - By
rotating the electrode the hole remains straight and while sparking will
occur on the sides of the tube, after the overcut value is reached the bulk
of the cutting occurs at the end of the electrode - I asked the FLOW people
how they made their carbide mixing nozzles for the waterjet machines and
they just smiled at me -
Roland Friestad is a scandanavian name (Norwegian) - Arne Jorgenson sure
doesn't sound Irish
Waterjet cutting force/mass momentum? - Yes, the force applied by the
combination of the velocity and mass of the water or water/abrasive is the
source of the cutting forces - The purpose of the high pressure is only to
accelerate the water to the high velocities required - I haven't done any
calculations on the cutting forces generated by an individual grain of
garnet at Mach 3 but it might be an interesting thing to know about -
Exploded view of nozzles - I have some of these that came with the FLOW
machine - Would be able to mail photocopies to those interested - Send a
SASE business envelope to - Roland Friestad - c/o Cardinal Engineering, Inc.
- Box 163 - Cameron, IL 61423 - USA -
Sapphire orifices - These are used for the water only cutting and also
upstream of the abrasive injection for the water/abrasive system - Water
condition is quite critical and must be maintained below certain levels of
iron and mineral content - In addition the water is filtered for
particulates to a 0.5 micron level using a two stage coarse/fine filtering
system - Particles in the water stream are accellerated to levels that can
fracture the sapphire orifice if they impact it - Incidentally the sapphire
orifices are made by the same people who make the jewels for watches and
other similar instruments - They are mounted in an aluminum or stainless
steel outer shell -
Need for 35 HP motor - Again, while I have not done the calculations I know
that an extremely large quantity of heat is generated by the act of
compressing the water (which is not incompressible at these levels of
pressure) - The source of that heat must be the energy supplied by the motor
- It is not unusual for our 200 gallon water tank to be raised to a
temperature that is uncomfortably warm just by the high pressure water
stream - That does not even take into account the waste heat that goes down
the drain with the pump cooling water and that generated by the pressure
relief valve - An intuitive analogy might involve attempting to inflate a
tire with a nail hole using a hand pump - (Something that we Norwegians
occasionally do for the fun of it) - It is quite easy to raise the pressure
to a certain level but as you attempt to go higher and higher the leakage
rate increases dramatically and soon you are unable to pump enough (supply
enough energy) to increase the pressure any more - At that point I
generally let my wife take over (She is Swedish) - A semi-educated guess on
my part would be that successful cutting of balsa and thin plywood could
possibly be done using a 5 to 10 hp motor but that is just a guess -
Our machine uses a reciprocating piston pump but many of them also use the
pressure intensifier approach mentioned in earlier messages - I have used
similar intensifiers myself for other applications in the past - The concept
is quite workable but, as has been speculated, the commercial waterjet
machines normally utilize an accumulator to reduce the pulsations in the
flow stream -
My suspicion is that the small motor/pulsed output approach would be
questionable in its efficacy but I certainly couldn't prove it at this time
- If I were to attempt a design such as this myself I would consider using
the small motor to run a relatively massive flywheel up to speed and then
use the flywheel to run an intermittent (clutch operated) pump with check
valves in the input and output lines - That is the basic way that a punch
press can provide many tons of punching force using a relatively small motor
- Of course a punch press is an extreme example of a pulsating type of
machine and if you have ever attempted to exceed the rated strokes per
minute capacity of a punch press and seen how dramatically the flywheel
slows down you will appreciate that the energy in must equal or exceed the
energy out over the long term -
Roland Friestad