Tim, We don't know about this calendar thing, thought that was closed, but every once in a while we like to share more pics and tips on getting things done.
Victor, There aren't too many 12 inchers out there, but one we know about is right outside Admiral Dahlgren's Old Headquarters at the Washington Navy Yard. If you get a chance to go to DC, let us know and we will meet you there take a photo of you sticking your foot down the bore!
Tonight we will try to present a few photos using these tools to quickly and properly get some dimensions from a variety of features from a few different cannon. Also the done-in-the-field Rough Draft of the Field Drawing and a separate sheet showing actual shape transfers from a rifled siege gun of the type used by Confederate forces at Fort Pulaski, Georgia in 1862.
Regards, Tracy and Mike
The lowly penny can be used for more than a tire tread depth gage. This method for finding the width of a rifled cannon's rifling groove works, even if you have no measurement tools with you at all, just a bit of pocket change. We place a penny in the groove against the left edge. Then we take a photo of the penny and groove from the top. When we get home, we make a photo or photo copy of the penny/groove subject. We measure the penny's dia.; it is .750". Measure the penny's image dia. It was 1.375". Measure the groove's image. We found it to be 2.292". Place these values into a simple ratio formula like this:
X = Width of Rifling Groove
1 3 2
.750" : 1.375" = X :2.292"
X =
1 x 2 3
X = 1.250
pg
This measuement should be accomplished by looking down on these features, not across to the tape which is quite distant from the elevation screw feature. See the next photo for a better, more accurate method.
This photo shows a better method for getting this type of dimension. You can see the various features and where they lie along the tape.
A unique use of your smaller, flat steel tape is show here. You simply maneuver the flat tape until you have a nice circle of tape around the inside of the breeching hauser hole in this large Parrott cascabel.
Measuring a cylinder, in this case a reinforce on the British siege gun, is the specialty of the flat tape. It actually measures, not the diameter like a PI tape does, but rather the circumference which requires further coputation, although a simple one. Take the 83 and 17/32 inches and
subtract one inch, because you used the one inch mark to mark the total circumference and then divide by the value of PI on your calculator or 3.1416" which is close enough. So you get 26.27" Dia.
This method of trunnion dia. measurment is too inaccurate; use your smaller flat tape as we just did on the reinforce.
The radius on the rear top of the percussion lock boss is captured by the shape duplicator tool on this 9" Dahlgren Shell Gun.
Here the shape duplicator gets the large radius blend at the rear where the radius ends at the origin of the hemisphere on this tube's breech.
This is a whole page of shape duplications that we pulled from a British rifle we found in New England on this last trip.
As messy as it is, this rough draft field drawing will suffice to build a nice 1/4 scale siege gun if we ever get the time to make it someday.
Sure it's easier to just buy a drawing, but there is none available on this rifle and a bunch of others in the U.S. Besides, it's fun and there is a special sense of accomplishment when you really "Do it All" to build your own cannon!!
Have fun! M&T