Shop Note

Harold Hahn, in his book Ships of the American Revolution and their models, published a table (page 195) showing the standard dimensions of guns and gun trucks in the 18th century. The drawings shown below are taken from that table, All of the truck dimensions are based upon the caliber (C).

All dimensions are based upon the gun's caliber; here's a table (from Hahn's book) of calibers listed by weight of shot, including the corresponding dimension at various popular scales:

Weight	Caliber (C)	1:96	1:64	1:48
4 pdr.	3.053"	.03180	.04770	.06359
6 pdr.	3.494"	.03640	.05460	.07279
9 pdr.	4.000"	.04166	.06249	.08332
12 pdr.	4.403"	.04568	.06879	.09171
18 pdr.	5.040"	.05249	.07874	.10498
24 pdr.	5.547"	.05777	.08666	.11554
32 pdr.	6.105"	.06359	.09539	.12717
42 pdr.	6.684"	.06962	.10443	.13923

The Frigate HMS IRIS ex. Hancock (1776) was armed with 24 12 pdr. and 10 6 pdr. cannons. In 1:48 scale, these correspond to .09171" and .07279".

I'll provide dimensions for the 12 pdr. gun truck parts, both as decimal inches (e.g., .092") and fractional to the nearest 1/64" (e.g., 3/32").

All of the truck dimensions are based upon the caliber (C). Many of the timbers are exactly 1 C (.09171 = 3/32") thick (bracket, trucks, bolster and transom); the fore and hind axtrees are 1.226 C (.124" = 1/8") stock, and the stool bed is .721 C (.065" = 1/16"). I began by thicknessing stock to these dimensions. In all cases, it doesn't hurt to make a couple of extra pieces of each part, in case one splits or is otherwise damaged.

F 02 Start with the bolsters. These need to be 1 C x 1.25 C x 2.974 C (.092" x .114" x .273" = 3/32" x 7/64" x 17/64").

(All instances of each piece go into a compartmented box to help keep then separate from one another).

Next you can make 25 transoms, 1 C x 3 C x 3 C (.092" .275" x .275" = 3/32" x 9/32" x 9/32"). Normally the grain of these would run from one side to the other to help keep the brackets apart. Don't forget the bevels top and bottom, and the barrel-relief cutout at the top. (Each instance went into another compartment of the box).

Wood piece, Stacking, Bar with profile on end.

The bracket stock needs to be 12.522 C (1.148" = 1 9/64") long and 4.686 C (.430" = 7/16") high. We'll need 48+2 of these, cut slightly oversize (1 3/16" x 1/2") for later finishing. I then glued these into a stack using model airplane cement. This gave me a "bar" of laminations (50 x .09171 = 4 5/8" long) which was much easier to work with. When the glue had dried, I thicknessed the bar to the overall dimensions of the brackets (1.148" x .430"). I could then make repeated passes with my Preac (TM) table saw, cutting longitudinal grooves for the axtrees (verifying the axtrees fit into their grooves), trunnion, "steps", and the curved area at the bottom of the bracket. Files quickly finished the profiles of the trunnion groove and bottom curve. After a final check, I separated the pieces by soaking the bar in acetone (Acetone will completely dissolve model airplane glue, leaving bare wood behind). Drill holes for the stool-bed support rod, and the various eye-bolts in the sides of the brackets.

Stool

We also need to cut out 25 pieces for the stool bed. The stock needs to be .721 C (.066" = 1/16") thick. These need to be 5.822 C (.534" = 17/32") long, and 1.803 C (.165" = 5/32") wide. Glue these into a stack and cut the taper on the sides - the narrow end is 1.082 C (.099" = 3/32"). Soak apart and add the two cross-wise grooves in the bottom of each.

Axles and Trucks

I then cut out the axtrees' stock (1.226 C =.124" = 1/8" thick) as long strips of the appropriate widths – 1.659 C (.152" = 5/32") for the fore axtrees, 2.163 C (.198" = 13/64") for the hind axtrees.

The axtrees are rectangular except for the round axle at each end. I cross-cut 25 pieces to length (9.735 C = .893" = 29/32") for each of the fore and hind axtrees. These were also glued up into bars as before. I then cut rebates in each edge, leaving a (still square) projection for each axle stub. The acetone separated these into individual pieces as well.

External Reamer

These now had to be rounded. I decided to make a special "external reamer" for this process.

External Reamer Detail

The fore and hind axles are 1.118 C (.103" = 7/64") diameter. Taking a hint from the trunnel-making cutters available commercially, I took a 1" length of a common nail that happened to be exactly 1/8" diameter and drilled an axial hole (#37 drill, = .104"d) 7/32" deep.

I then cut a slot through one side of the cutter's hole to form a cutting edge. It was now an easy matter to place this tool in my Dremel MiniMite™ and "ream" all of the axle stubs to the correct diameter– with the appropriate thickness washer in place.

Each axle has a "root" at the rectangular part. Since the length of this is different for the fore and hind axtree, make a spacer .605 C (.055" = 3/64") for the fore axtree, and a second .253 C (.023" = 1/64") for the hind axtree (this is basically a washer that you slip over the axle stub that the cutter can bottom out onto and leave the "root" intact.

The fore wheel is 3.245 C (.296" = 11/64") diameter; the hind wheel is 2.884 C (.264" = 17/64"). I cut out the appropriate number of (square) blanks (plus spares) and drilled a 7/64" hole in the center of each. These were then glued up into another "bar", with a length of 7/64" music wire first threaded through all of the holes (the wire is available in the model airplane section of your hobby store – it's available in straight pieces; don't use a piece cut from a roll – you'll never get it straight!). I could then chuck one end of the wire in the lathe (supporting the other end in the tailstock) and turn all of the wheels to the proper diameter.

Unfortunately, this proved impossible, as the force of the tool caused the wire to "whip".

Undaunted, I took a scrap piece of 2x3 lumber, cut it 4 1/2" long, and drilled a 1/4" hole near one end. I could then use a 1/4" bolt to hold this to my lathe saddle. Putting a center drill in the lathe headstock, I then used it to mark this block about 1 1/2" from the end opposite the bolt. Measuring my MiniMite, I found that the round section was 1 1/2" diameter - I drilled a hole of this diameter through the block, and then sawed the block in half through the center of this hole. I could now reassemble the block, insert the MiniMite into the hole, and be guaranteed that it was on center.

Setup for "Turning" Trucks

After setting this up, I installed a small circular saw in the MiniMite, and the wheel bar in the lathe. It was now an easy matter to use the saw as a grinding tool to cut the wheel bar to the correct diameter. Because of the high speed of the tool, it cut without deflecting the bar, and stopped cutting when it had reached the proper diameter. After completion, the resulting rods can be separated into the individual wheels.

Attach the Bolster to each hind axtree, and the transom to the fore axtree (that will also make it easier to tell them apart!) Glue the brackets to the axtrees and transom. Insert the stool-bed support rod, and then the stool-bed. Apply the eyebolts. Finally, slide each wheel onto it's axle, drill a hole through the axle outside the wheel, and add a splinter of contrasting wood for the pin that keeps the wheel from falling off.

I kept the boxes I saved the parts in. Since I didn't use them all, I have spares in case I ever need to replace one.

Collection of truck parts for the IRIS.
Collection of truck parts for the Caroline.

{John O. Kopf}

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