Gun Carriage Assembly Fixture
As they say, "necessity is the mother of invention"
How it all came about.
My website partner, Scott Bushnell is working on the Sergal/Mantua "Sovereign of
the Seas". The scale is 1:78. He asked me to make the Gun Carriages for him
because he was unhappy with his attempts.
They are to be made of walnut, and will be painted red. Note: Please keep
in mind that this Fixture could be made to suit any scale/model.
References at the bottom of the article page.
Calculations:
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The numbers:
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The dimensions for the locations of the axle trees and cheeks were taken from
the plans supplied with the kit.
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Make an accurate layout, to
scale, of the overhead view of the Gun Carriage in a large format. This is
useful because it pinpoints possible trouble spots when making the Fixture.
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I used the multiple of 14.
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The 1.048" length of the cheek
became 14.672"
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The .450" width of the axle trees at the front of the Gun Carriage became 6.300"
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The .508" width of the axle trees at the rear of the Gun Carriage became 7.112"
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The angle, when calculated, of the sides of the cheeks is one degree and thirty
five minutes.
I arrived at this number by applying the trig formulas using the .450" and .508"
and 1.048" dimensions of the respective parts. This helped when planning
the location of the containing dowel pins for the outboard sides of the
cheeks.
Cutting and preparing the parts for the carriages:
Axle trees and the cheeks:
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Cut some blank strips for the T-shaped axle trees with a Preac Table
saw. They were made to the following dimensions from the plans that Scott
calls "The Stupid Italian Plans":
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Front axle trees - strips were cut to .450" wide by 6" long out
of some 6mm stock
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Rear axle trees - strips were cut to 508" wide by 6" long out of
the same 6mm stock. Note:
I had to make about 24 carriages so cut plenty of extra material to cover
setups, goofs, etc.
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After the cutting of the blank strips, reduce
down from 6mm (.236") to
.197" using a Byrnes Thickness Sander.
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The cheeks are .085" thick by .329" high by 1.048" long. Note: I did not
have stock thick enough to make the .329" height. So, I glued up two
pieces at a suitable joint to make up the required dimension. Plus some
allowance for the thickness sanding after. The axle trees are also
.085" thick by .197" by .450" (front axle trees) and .508" (rear axle
trees) respectively.
Milling:
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The T-shapes are milled in a vertical
Sherline milling machine.
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The cheek profile is milled in the same milling machine, but used as
a shaper. Clamp a precision parallel to the table aligned with the
table travel (X axis). Push the blank strips through, against the
parallel fence while having a piece of spring steel bear against the
edge.
Slicing:
Making the Gun Carriage Assembly Fixture:
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Use the Sherline lathe to turn a piece of nylon to 1 1/2" diameter
(Nylon was chosen for the fixture because the glue will not adhere to it). Face
it off, and leave it in the chuck.
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Put the chuck with the nylon on the rotary table on the Sherline milling
machine. Make sure to align the center of the rotary table with
the center of the mill spindle.
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Do the math and center drill and ream for a total of 18 (eighteen)
.0625" holes for Stainless Steel (stainless won't corrode over
time) dowel pins. These hole locations cause the axle trees and cheeks to
be in the correct relationship. As you can see in the photos.
Twelve
Stainless Steel Dowel Pins to hold the axle trees and cheeks in location for
Assembly:
Now, to make a Gun Carriage:
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So, the procedure is to take a "set" of two axle trees .450" wide, two axle
trees .508" wide, and two cheeks. Note. Since
the gun carriage is narrower at the front, I calculated the angle and came
up with one degree and thirty five minutes. When applied to the thickness of the axle trees where they contact the angled
cheeks, there is a taper of .0022" along the .085" thickness. A small amount, but
I did "sand" it in. No unsightly gaps for me! Better glue job that way....
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One cheek is placed against the containing outboard pins.
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The axle trees are placed between the pins to locate them.
Use a
squared off ice cream stick to gently nudge the axle trees into place
against the cheek.
Axle trees in
position in Assembly Fixture:
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Using an artist's brush, apply glue to the vertical surface of the axle
trees and the underside of the inverted T.
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The second cheek is then put inside the outboard locating pins.
Note.
A really good fixture, which I like to think this is, also acts as a filter
to exclude bad parts. If they are too thick, they will not go into the space
between the pins. If they are too small, they are already sitting in my
reject bin, having been weeded out as I made them. I use a drop dial
indicator to measure the .085" thickness:
Cheeks added
to Assembly Fixture:
Two plastic
extraction forks in foreground:
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After the glue is set, remove the finished Gun carriage. To do so
safely, make two plastic extraction forks....using the principle of the
inclined plane. Note. Anoint the pins with a mold release (thin
grease) to prevent the glue from sticking to the pins.
If anyone wants, I can make a sketch with
dimensions that I used for my Gun Carriage Assembly Fixture. At the
present time, I am researching for the best glue to use....
Once I find that, I will make a few test assemblies to prove out the Fixture,
and then it will be "flank speed ahead"! :)
Jerry G (Glickstein)
Thread Reference:
Gun Carriage Assembly Fixture
Tool References:
Preac Tools
Sherline Products
Byrnes Model Machines
Ship Modeler's Desktop |
