# Ultrasonic Drill Suggestions Needed

J

#### jimbo

Jan 1, 1970
0
Greetings,

The way the device works is that the drill bit is a soft metal
tube driven by the piezo unit in a slurry of cutting grit (~100
grade silicon carbide) in liquid (mineral oil or water). The
action of the tube pounding grit against the substrate (jewelry
bead, gem, or anything with a hardness lower than that of the
grit) simultaneously eats away at the bit and the substrate, thus
drilling the desired hole.

From the design specs of manufactured multi-thousand dollar
units, it appears that I want something that drives a
piezoelectric transducer at around 40kHz.

I'm starting from square one. I can wield a soldering iron and
have played with the 300-in-1 type electronics kits a bit over the
years, but am not at the point of being able to design a circuit
for anything like this.

It appears that I need suggestions for:
1. a signal generator capable of operating at 40kHz (am willing to
experiment with different waveforms to see which is most efficient
at cutting)
2. an amplifier
- capable of good slew rates at 40kHz
- high input resistance matched to the piezo transducer
3. good candidate piezo transducer

Thanks for any help in advance.

--jim

B

#### Bob Masta

Jan 1, 1970
0
Greetings,

The way the device works is that the drill bit is a soft metal
tube driven by the piezo unit in a slurry of cutting grit (~100
grade silicon carbide) in liquid (mineral oil or water). The
action of the tube pounding grit against the substrate (jewelry
bead, gem, or anything with a hardness lower than that of the
grit) simultaneously eats away at the bit and the substrate, thus
drilling the desired hole.

From the design specs of manufactured multi-thousand dollar
units, it appears that I want something that drives a
piezoelectric transducer at around 40kHz.

I'm starting from square one. I can wield a soldering iron and
have played with the 300-in-1 type electronics kits a bit over the
years, but am not at the point of being able to design a circuit
for anything like this.

It appears that I need suggestions for:
1. a signal generator capable of operating at 40kHz (am willing to
experiment with different waveforms to see which is most efficient
at cutting)
2. an amplifier
- capable of good slew rates at 40kHz
- high input resistance matched to the piezo transducer
3. good candidate piezo transducer

Thanks for any help in advance.

Many industrial piezo devices typically run at high voltages
(1000 V is not uncommon), which makes the amp design a
problem even if you are a pro. One alternative might
be to tear apart a plastic piezo horn tweeter. Some of
these have decent response up to 40 kHz, although the
response has many dips and peaks. You'd want to
tune to the nearest peak, whatever the frequency.
That will depend on the mechanical structure that
you come up with to couple it to the cutter bit.
My guess is that despite herculean efforts to reduce
mass, this is not going to be in the same ballpark
as the commercial units as far as cutting speed.
The piezo tweeters just can't handle all that much
power. But it might be fun to experiment with!

Best regards,

Bob Masta

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Home of DaqGen, the FREEWARE signal generator

J

#### jimbo

Jan 1, 1970
0
Bob said:
Greetings,

The way the device works is that the drill bit is a soft metal
[...snip...]
Thanks for any help in advance.

Many industrial piezo devices typically run at high voltages
(1000 V is not uncommon), which makes the amp design a
problem even if you are a pro. One alternative might
be to tear apart a plastic piezo horn tweeter. Some of
these have decent response up to 40 kHz, although the
response has many dips and peaks. You'd want to
tune to the nearest peak, whatever the frequency.
That will depend on the mechanical structure that
you come up with to couple it to the cutter bit.
My guess is that despite herculean efforts to reduce
mass, this is not going to be in the same ballpark
as the commercial units as far as cutting speed.
The piezo tweeters just can't handle all that much
power. But it might be fun to experiment with!

Best regards,

Bob Masta

Bob,

Thanks for responding!

Big voltages but relatively small current?

The suggestion of the horn tweeter appeals to me. Looks like 50W
tweeters can be had for about $5 a piece from surplus sources. A cheap op-amp delivering less than 50W over a good frequency range might do the trick for initial testing--since I don't know what drilling rates commercial setups are achieving, I won't know how much better it could be. Apologies for this naive question: Big voltages ... can they be done using voltage multipliers after the amplification stage? Um, a cursory glance at simple voltage multipliers gives a few questions: 1) At what point (frequency and/or voltage) does the cost of suitable caps leave practical reality. 2) Are there diode issues, i.e. noise or voltage, that will impact the system at higher voltages? 3) Am I looking at voltage multiplier circuits that are too simplistic? 4) For boosting the voltage (also at the expense of the current) what about a good old transformer operating in the low ultrasonic range? The smaller form-factor, the better, I'd assume. Further down this road, another possibility that comes to mind is using another piezo transducer as a sensor that gives feedback so the circuit can drive itself to an (albeit probably local) maximum efficiency in terms of internal physical resonance. UGH, I'm going to have to find someone to lend me a scope. Thanks again, --jim R #### Rich Grise, but drunk Jan 1, 1970 0 Greetings, The way the device works is that the drill bit is a soft metal tube driven by the piezo unit in a slurry of cutting grit (~100 grade silicon carbide) in liquid (mineral oil or water). The action of the tube pounding grit against the substrate (jewelry bead, gem, or anything with a hardness lower than that of the grit) simultaneously eats away at the bit and the substrate, thus drilling the desired hole. Something like these? http://www.lauralee.com/chrisdunn/article.htm Scroll about 1/3 of the way down the page for s 6,000 year old example of this. Cheers! Rich R #### Rich Grise, but drunk Jan 1, 1970 0 Greetings, The way the device works is that the drill bit is a soft metal tube driven by the piezo unit in a slurry of cutting grit (~100 grade silicon carbide) in liquid (mineral oil or water). The action of the tube pounding grit against the substrate (jewelry bead, gem, or anything with a hardness lower than that of the grit) simultaneously eats away at the bit and the substrate, thus drilling the desired hole. These days, if you want to bore a hole in hard stuff using a copper tube, they just typically chuck the tube in a drill press and suspend the grit in the coolant stream. Have Fun! Rich J #### jimbo Jan 1, 1970 0 These days, if you want to bore a hole in hard stuff using a copper tube, they just typically chuck the tube in a drill press and suspend the grit in the coolant stream. Have Fun! Rich Not if you want the option of non-circular holes. --jim J #### Jasen Betts Jan 1, 1970 0 Big voltages but relatively small current? yes, if operating at 5W The suggestion of the horn tweeter appeals to me. Looks like 50W tweeters can be had for about$5 a piece from surplus sources. A
cheap op-amp delivering less than 50W over a good frequency range
might do the trick for initial testing--since I don't know what
drilling rates commercial setups are achieving, I won't know how
much better it could be.
Apologies for this naive question: Big voltages ... can they be
done using voltage multipliers after the amplification stage? Um,
a cursory glance at simple voltage multipliers gives a few
questions:

a transformer would be ideal. for working at 5W a 40KHz transformer
could probab;y be wound on a toroid from a dead computer PSU.
1) At what point (frequency and/or voltage) does the cost of
suitable caps leave practical reality.
2) Are there diode issues, i.e. noise or voltage, that will impact
the system at higher voltages?
3) Am I looking at voltage multiplier circuits that are too
simplistic?

yes, you need AC to drive the piezo, those capacitor-diode devices
produce DC. use a transformer.
4) For boosting the voltage (also at the expense of the current)
what about a good old transformer operating in the low ultrasonic
range? The smaller form-factor, the better, I'd assume.

aha.

Bye.
Jasen

B

#### Bob Masta

Jan 1, 1970
0
Big voltages but relatively small current?

The piezo material looks like a capacitor, so
it only draws current when the voltage changes.
The currents are "low" compared to typical
magnetic-type transducers, but at 1000 V
there is still a lot of power.
The suggestion of the horn tweeter appeals to me. Looks like 50W
tweeters can be had for about \$5 a piece from surplus sources. A
cheap op-amp delivering less than 50W over a good frequency range
might do the trick for initial testing--since I don't know what
drilling rates commercial setups are achieving, I won't know how
much better it could be.

Note that "consumer" tweeters are typically
rated for the power of the overall music program,
not the power actually handled by the tweeter itself.
In a 50W system, most of the power is going to the
woofer and midrange. The tweeter itself is
probably seeing well under 10W. So don't
expect you can put anything close to 50W into this
tweeter.
Apologies for this naive question: Big voltages ... can they be
done using voltage multipliers after the amplification stage? Um,
a cursory glance at simple voltage multipliers gives a few
questions:
<snip>
One problem with voltage mutipliers (besides efficiency)
would be that they rectify while multiplying. So you would
need to impose your 40 kHz on a much higher carrier,
and do some tricks if you want a bipolar response.

Also, remember that the load is a capacitor, so whatever
you drive it with has to remove the voltage as well as
supply it when the input voltage changes. It's not like
a power supply that mostly runs at a fixed voltage and
just uses a bleeder resistor to discharge the output
caps on shut-down.

A simple transformer would make much more sense.
Electrostatic speakers use high voltages at low
currents, and they typically use transformer drive.

But all that assumes you can get hold of industrial
piezoceramic materials that need the high voltages.
The horn tweeters don't need (and can't handle) any
of that.

The industrial piezo material I messed with many years
ago was tubular, about 1/4 inch in diameter, designed
as a linear actuator. Seems like it would be ideal for
your project, except that the original device was not
intended for high frequency use: It was for positioning
microelectrodes under a microscope, so the power
supply wasn't anything too fancy in the response
department. The whole instrument was from a
company called Burleigh, which may not be in
business any more, and they bought the piezo
material from somebody else. (I got some
samples from a Burleigh engineer, but never
really got them to do anything on my own.)

Best regards,

Bob Masta

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Home of DaqGen, the FREEWARE signal generator

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