WHICH AIR SCRIBE IS CORRECT FOR ME?
(some basic information on airscribe and stylus selection)
By Bill Murray, Paleo Tools
There are several pneumatic engraving units generally available
on the U.S. market today which are used for fossil preparation work. The model
CP-9361® is manufactured by Chicago Pneumatic and their registered name for it
is an "Airscribe", which is the name most people use to describe this type of tool.
There are several manufactures making exact replicas of the
CP® such as "Michigan Pneumatic" Tool Co. Ingersol Rand builds a similar tool, the
"EP-50® Engraving Pen". Another tool was manufactured under the
name of "Aro". This tool has been copied by four or five other manufacturers but
is commonly known as an Aro model 8315 Airscriber.
Paleo Tools has designed and is manufacturing four tools - the Mighty-Jack, the Super-Jack, the
ME-9100, and the Micro-Jack. We also do an "extreme makeover" on the Aro tools and call these
the "Paleo Aro."
I have been involved with some of these engraving tools for over
fifteen years now and the following information is based on the experiences I
have had with each.
THE Paleo
Tools "MIGHTY-JACK"
The Mighty-Jack came to life when a Paleontologist friend of mine asked if I couldn’t
develop an airscribe that was in between the CP and the pistol grip air chisels. The small
airscribes take forever to get down through a large block of matrix and the pistol grip air
chisels destroy everything in the block. So I took some of the better attributes from several
airscribes, sized it up by a factor of three and developed the Mighty-Jack. This tool works
like a very large airscribe in the sense that you have to let the tool do the work. If you bear
down hard on it, it just stalls out. It runs at about 8,000 to 10,000 CPM. It seems to work best
in the 100 to 120 PSIG (6.9 to 8.3 BAR) range and it takes somewhere around a 5 Horse Power
compressor to keep it going. If your air pressure gets down to 80 PSIG (5.5 BAR), shut the tool
off and let the compressor pump up again as the Mighty-Jack gets very wimpy at this and lower
pressures. Using the Mighty-Jack with two hands, it is very controllable and we have worked
within 1/8" (3mm) of the bone or fossil. This tool is designed to work on large blocks of matrix
containing fairly large bones. We have used it on a 1500 lb. (680 Kg) block containing a
vertebral column from an Allosaurus and worked right up to the vertebra and ribs.
The important point about the Mighty-Jack is that it doesn’t have "rock shattering" power.
It comes with a solid tungsten carbide
stylus that is ¼" (6.35mm) in diameter and protrudes from the bushing about 3" (76.2 mm).
I found in testing that a chisel type point, either three or four sided was the best for rock
removal. A round point just wanted to bury itself into the matrix without breaking it loose.
The stylus is free to rotate in the tool so a two-sided chisel will not work as it wants to roll
up on its edge instead of staying flat. Using a three or four-sided chisel eliminates this problem.
The air valve is similar to that of a Ingersol Rand and you rotate and slide the valve forward
to turn it on and backwards to shut if off. The Mighty-Jack comes with an 8 ft. long flexible
hose with standard ¼" NPT (national pipe threads).
The Mighty-Jack needs to be lubricated as it has reciprocating parts in it. I use
8 drops of a good air tool oil in the end of the air hose every three or four hours of operation.
The Paleo Tools Super-Jack
The Super Jack was developed to fill the gap between the ME9100 type of tools and the Mighty Jack.
At some point, preparators that use the ME9100 begin asking for more power. The Super Jack was designed
with a piston having twice the area of a ME9100 thus giving it twice the power of a ME9100. It operates well
between the pressures of 100 PSI and 120 PSI.
There are two styluses available for the Super Jack, a flat chisel and a four sided pointed one.
The chisel is best if you are just planing down a large block of matrix that isn’t too hard. When you get into really
hard matrix, there are several other shapes of styli which work better and don’t have a tendency to break the point.
Special grinds are available at no extra charge. Some preparators prefer the four sided pointed stylus as they can
get in closer to the fossil and not take off too much matrix at once.
The tool is quite controllable. It’s like using a large airscribe rather than a Jackhammer. I walked into a prep lab
one day and found a young lady using the Super Jack one handed, so that attests to its controllability.
The Super Jack has a throttling type air valve built into it. You can control the speed of the tool from 0 to wide open.
Most folks run it full open as they are trying to get the most work from it.
Paleo Tools"Micro-Jack"
There are many of you that work on small delicate fossils, from small insectivores
to micro-vertebrates and other tiny fossils. Most of this type work has been done using pin vises
and needles. Now, I have an alternative to offer you. Paleo Tools has developed five (5) airscribes
that begin one step smaller than the Aro and go down four sizes. We have named these small
airscribes the "Micro-Jack" series. They are the "Micro-Jack 6", "Micro-Jack 5", "Micro-Jack 4",
"Micro-Jack 3" and the Micro-Jack 2 in descending order of power. These airscribes all use a 1/16"
(.063") diameter tungsten carbide stylus ground to a fine point. They operate at 40,000 cycles
per minute except for the Micro-Jack 2 which is above 55,000 CPM. So, now you have the opportunity
to match an airscribe to the job you have at hand. Please keep in mind when using them that if the
amount of matrix you have to remove is overpowering the abilities of that Micro-Jack, then you need
to go to a larger airscribe or Micro-Jack. Once you have worked the heavy matrix off, go back to
a smaller and smaller airscribe to do the detail work.
These airscribes are mostly intended for use under a microscope although the Micro-Jack 6, 5, and
4 can be used with the unaided eye. The Micro-Jack 3 and 2 are best for use under a microscope
for doing the very finest work. The Micro-Jack 3 through 6 all chip the matrix away. The Micro-
Jack 2 turns anything the stylus touches to dust. However, keep in mind that it is removing
very small amounts of matrix. But with a steady hand and with the EXTREMELY sharp stylus I send
these with, you can work the toe bones of a mouse. It is an unbelievable tool if you're doing that
delicate of fossils.
In order to make them as light and easy to use as possible, the handle is manufactured
from aircraft grade aluminum, and then hard anodized to make it durable. The front end that holds
the stylus is tool steel, heat treated to 50 Rc. The air valve is attached to the quick disconnect
end of the hose so it doesn’t add any weight to the Micro-Jack. The Micro-Jack is supplied with a
six foot long medical grade hose made from polyurethane so it is very flexible and light. An air
filter is also supplied with the assembly as the orifice in the Micro-Jack is either .016" or
.020" in diameter and a tiny piece of lint or dirt would easily plug it.
Unsure which Micro-Jack to order for your needs? My suggestion if you can only
purchase one is to start with the larger sizes and then work down. If you purchase one that is too
small, you may not be able to use it to your advantage on your prep job. But if you purchase one
and it is too big for your current project, you will always have future projects come through your
prep lab where it can be used.
Air Pressure requirements.(VERY IMPORTANT!!) 100 PSI minimum! They work best up at
the higher pressures.The preparators that did testing for me report that they work best at
higher pressure. Some times they are reluctant to start and run when the pressure is below about
100 PSI. So if need be, my suggestion is to purchase a small one or one and a half horsepower
compressor that will run at 100 psi MINIMUM PRESSURE to operate the Micro-Jacks on. The Micro-Jack
consumes less than one CFM of air so a small compressor that can be plugged into a wall outlet is
sufficient. If you need such a compressor, please contact us as we can supply them.
Just as a note to show the power of the Micro-Jacks, with the size 4 , 3, and 2
you can write your name on your finger nail with no fear of puncturing through. That is something
you would never try with a CP or even an Aro with a sharp stylus! I also have customers that
are using the Micro-Jack 3 and 2 for doing "Scrimshaw" on ivory as they can etch their pictures
much easier with this tool than by hand.
Sears has a small compressor that they are selling right now for
$189.99. It is a Model 919.152140. If you order or call about one, the catalog number is 15214.
It's description is, 2 horsepower, 4 gallon Pan Compressor. It draws 10 amps so will work with
most circuits as almost any circuit is 15 amps. It comes with an air pressure regulator and
quick disconnect. It is 150 psi max pressure so works well with the Micro Jacks. It should
also be able to run an Aro with no trouble.
Here's something new we have learned about the Micro-Jack 5 & 6 and I've seen it
on one #4. If you try to rush and push the tool past it's capabilities, it will "buck" or jump
in your hand. What is happening is that the stylus stalls as it's pushed back against the "O"
ring in the stylus drive plate. Then the air pressure builds up to a point where the stylus is
forced forward and this is that bucking or jumping that you might experience. If this happens,
back off and let the Micro-Jack do the work. What happens if you don't ease up, is that it will
break the drive plate off of the stylus and then your out $30.00 for a new stylus.
THE
CHICAGO PNEUMATIC® CP-9361, Michigan Pneumatic
MP-9361 and MP-9100
The Chicago Pneumatic (CP) type airscribe has been the standard for
fossil preparation for many years. The volume of air going through the tool is
adjustable so the frequency of strokes (cycles per minute, CPM) can be adjusted
easily. The tool is very reliable for the most part, and is easily repaired,
although sometimes getting parts can be difficult. The biggest drawback has been the
factory stylus, which has a life of somewhere between a couple of minutes to a few
weeks. The stylus is the sharp pointed chisel part that makes contact with the matrix
around the fossil and chips the matrix away. The CP is a moderately powerful tool.
The factory recommends a maximum of 90 PSIG (6.2 BAR) air pressure. My own experience
is that they are pretty wimpy at 90 PSIG (6.2 BAR) and I run my own at 100 to 110
PSIG (6.9 to 7.6 BAR). I probably shorten the life of the airscribe somewhat by
running at the higher pressure, but I can remove a lot more matrix by doing so.
The CP has a frequency of somewhere around 15,000 CPM. I don’t have any literature
on the volume of air required to run a CP, but I used to run two of them off of a
¾ HP compressor at the same time. The CP has typically been used to remove the bulk
of the matrix from around the fossil and then the finish work has been done by other
means. If working on large dinosaur bones, you may be able to do all of the prep with
the CP. The CP normally has too much power to be used on anything delicate but some
tuning can be done to make it better. The length of the stroke of the stylus is
controlled by the "O" rings that fit under the stylus and act as a spring. Normally
there are two "O" rings. By putting a third "O" ring under the stylus and then
screwing the "sleeve" with the stylus down against the "O" rings, you can shorten
the stroke of the stylus down to a point where it stalls and doesn’t move at all.
So depending upon how far you screw it down, you can "tune" the stroke to do finer
work. Going the opposite direction, it is possible to get about 25% more power from
the CP type airscribe by making some modification so it gets more air through it.
This "hop-up" is a service provided by Paleo Tools if you need it. One reason
you might need more power would be if you are using our 3" and 4" solid carbide
styluses. These styluses are heavy enough to absorb a lot of the impact of the piston.
Increasing the power of the airscribe really helps make these heavier styluses work
better. And again, the life of the Airscribe is probably shortened somewhat as it is
working harder and it does vibrate slightly more.
Since the CP has a reciprocating piston in it, it does need lubrication.
I use a good "air tool oil". The method I use to lubricate it is to disconnect the 8-ft. hose
from its quick coupling and put six drops of oil into the hose for each 8 hours of work. The oil
will very slowly migrate down the hose as it spreads out and is wiped down the hose. This allows
a continuous but very minute amount of oil to go through the airscribe. This is enough to keep
the piston lubricated and reduce the amount of wear.
STYLUS
AND BUSHING SELECTION FOR THE CP-9361, MP-9361 & ME-9100
We offer four different lengths of styluses and two lengths of bushings
for each of the different airscribes. The bushing is the end piece that the stylus fits through
and supports the stylus.
- The short bushing (1") is normally used with the two shortest
styluses, although I have had customers use the longest stylus with the
short bushing. This is not recommended, but sometimes it may be all that
will work for you.
- The longer 2" bushing is used for the two longer (3" and 4")
styluses.
- The shortest (1 ½") stylus is designed for close work. It protrudes
about ½" from the bushing and can be re-sharpened a number of times. It
isn’t the best stylus if you have a lot of matrix to remove, as the
angle you use it at (in relation to the fossil) is pretty steep. For
close work though, it has the best control being the shortest.
- The 2" stylus is much better for matrix removal. You can get a much
shallower angle and it will peel the matrix off much quicker. It can be
used in moderately deep holes etc. and works well for all around prep
work.
- The 3" and 4" long styluses are for use in cranial cavities, working
out the neural canals of large vertebra and sometimes for even getting
between bones to remove the matrix so they can be separated. These long
styluses are surprisingly strong and do not easily break, however, if
pushed down into a hole and pulled sideways, they will snap (of course).
PRICE FOR THE CHICAGO PNEUMATIC
The CP can usually be purchased from a low of about $225.00 to something over
$300.00 (USD).
THE INGERSOL
RAND® EP-50
The Ingersol Rand (IR) is similar to the CP in its power, size and feel. The air valve is
not as easily adjusted for intermediate settings. The air valve is more of an off/on affair.
The IR makes about the same "cycles per minute" as the CP and the power is about the same.
I believe it may have slightly more power than the CP. It is a simpler constructed tool than the CP.
Prep Labs that are using the Ingersol Rand report to me that they find them more reliable than
the CP. The IR is listed as needing 2.5 CFM of air at 90 PSIG (6.2 BAR). This is about the same
as the CP. I have not used the IR much but its matrix removal is about the same as the CP. The
IR comes stock with a fairly fat, stubby stylus. The stylus is built similar to the factory CP
stylus, but doesn’t break as often. However, it is too short to be of much use. A slightly longer
factory stylus is available from Ingersol Rand.
The EP-50 is similar to the CP in that it has a reciprocating piston and should be
lubricated. Use about 6 drops of a good air tool oil for each 8 hours of operation, putting the oil in
the end of the air hose, the same as for the CP.
STYLUS AND BUSHING
SELECTION FOR THE INGERSOL RAND
The Paleo Tools replacement bushings and stylus give a much better selection.
In doing development I found that reducing the diameter of the stylus to .125" gave much better
performance. This necessitated that a new bushing be built to handle this smaller diameter stylus.
So just like the CP, we build two lengths of bushings and four lengths of styluses. Selection of
the bushing and stylus length is the same as for the CP type tools. The Ingersol Rand EP-50
generally costs a little more than the CP. The "Grainger industrial supply book" lists them at
$305.00 for the tool with the shortest stylus and no air hose. Their "kit" with air hose, three
assorted styluses and plastic case is $375.00 (USD)
ARO® MODEL 8315-B AIRSCRIBER
The Aro runs at about 30,000 CPM. As can be imagined, each stroke is very tiny.
Unlike the CP and IR, the Aro has no pistons, etc. in it. On the end of the stylus is a "stylus
drive plate" that is cup shaped. An "O" ring fits inside the cup and a spring pushes the stylus
driveplate back against the body of the Airscriber where the air inlet hole is. When air is turned
on, the "O" ring in the stylus drive plate acts as a seal and the stylus drive plate is pushed
forward until the air is released when the "O" ring seal is broken. The stylus return spring
pushes the stylus drive plate back creating the seal again and the air pushes the stylus driveplate
and stylus forward again. So it becomes a balancing act of the diameter of the cup of the stylus
drive plate, the strength of the stylus return spring and the amount of air pressure and volume
of air going through the tool. This makes for a very simple engraving tool. Instructions given
with the tool say to turn the air on full to get the tool going and then begin closing the valve
just to the point where it is running the way you wish it. Reducing the air volume increases the
CPM and decreases the stroke. Sometimes the tool will stall and has to be bumped against something
to get it going again. I usually tap the tip of the stylus against the table or something convenient
(but don't hit it sideways as this may break the stylus!). I think a lot of the stalling
is caused by the air pressure fluctuation. When you first start and adjust the air valve on the tool,
your air compressor is at some pressure. As you use the air in the reservoir on the compressor and
the pressure drops, the tool has a tendency to stall. This can be overcome by use of an air pressure
regulator to keep the pressure constant, but the minimum pressure that the compressor puts
out has to be higher than the setting of the regulator.
The Aro type of tools are capable of doing relatively fine work. They won’t remove
near the amount of matrix that a CP or IR will, but the Aro transfers very little energy into the fossil,
so work on some pretty delicate fossils can be done. Recommended air pressure from the factory is
90 PSIG (6.2 BAR) and air consumption is shown to be 2 CFM.
Even though the Aro doesn’t have a reciprocating piston, a little lubrication helps
keep the stylus and the "O" ring in the stylus driveplate lubricated. Three or four drops of oil
in the end of the air hose should be sufficient for each 8 hours of operation.
Paleo-Aro Tool
We are making an up-graded version of the All Air Products model 8315-B Aro type
tool. We call it our "Paleo Aro". We have had numerous complaints about the stock tool having the hose
come apart and the front end unscrewing itself from the tool while using it, etc, etc.
So...... I now take the 8315-B when received and completely disassemble it. I only keep three
pieces of the tool. The body, front end (minus the bushing) and the air valve. I throw away the
5 ft. air hose that comes with it and install an 8 ft. long American made hose. The hose is a 1/4"
200 PSI nylon type hose. It comes with the quick disconnect type fittings so if anything happens
to the hose, YOU can now just slip the old hose out and either shorten it and then plug it back
in or purchase a new piece of hose and plug it in. The reason for going to this new setup is
that the factory method of installing the original hose makes it almost impossible for a person
in the field to ever install a replacement hose. And although I have been installing hoses at no
charge, it is an inconvenience for you to have to ship your Aro to me. I install an air filter
which not only keeps dirt from getting into the tool, but it gives something to grip when trying
to couple the hose into a quick disconnect and I supply a standard male quick disconnect coupling.
Next I machine an "O" ring groove in the body of the tool right where the front end seats against
it. Now when I screw the front end back on, the front end seats over the "O" ring. This is a
friction fit and keeps the front end from unscrewing off of the tool. You don't have to tighten
is any more than finger tight and it will stay there. I hate seeing airscribes that have obviously
had pliers use on them to tighten and then loosen the front end. For those of you who would
like this "O" ring up-grade, send me you Aro and for $10.00 plus shipping I'll be happy to machine
it. The old bushing is pressed out from the front end and our bushing installed. All new bushings
beginning about the middle of 2003 will come so you can use either the non-rotating chisel stylus
or the standard 2" long PaleoTools stylus. The new stylus the tool comes with protrudes from the
end of the bushing about 1/2". When we get through, you have a good tool designed for fossil
preparation and not engraving. If you purchase one of these tools, you'll be happier and you
won't have need to complain to me which will make me happier too.
STYLUS AND BUSHING SELECTION FOR THE ARO
As with the CP and IR, Paleo Tools
manufactures two bushing assemblies and four different lengths of styluses. Selection of the length of stylus
is dependent upon your needs.
- The original stylus is .078" (2mm) in diameter. By going to the
longer lengths of stylus, I increased the diameter to .093" (2.38mm) to
increase the column strength of the stylus. This means that the Paleo
Tools stylus will not work in the stock factory bushing as it is
about .016" too small.
Note: Everyone from Aro to Suhner to Dayton to the Taiwanese are making copies of
the original Aro. In measuring them, I found that the internal dimensions where the bushing fits in
the front end are all a little different. A bushing that was perfect for one tool either wouldn’t
go into another or would fall into the hole in the front end. I finally decided that the best
solution would be to provide the front end with our bushing installed. This front end will screw
onto ANY of the Aro and the Aro knock-off tools and work satisfactorily. So this is why Paleo
Tools sells the front end with the bushing as an assembly.
ARO PRICING
The Aro type tools sell from about $70.00 for the Taiwanese copies to over $300.00
for the Original Aro. In my opinion, since there aren’t any moving parts in the tool other than the
stylus, the inexpensive ones seem to work about as well as the expensive ones. The heat-treating
seems to be better on the expensive ones, but I’m not sure that makes a difference.
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