george wilson
01-31-2012, 10:07 PM
These closeup pictures turned up in my scanning of slides. Previously I had only the one overall picture of the compass in its box. I had no idea that I had other views of it. I'd have had no way of posting them anyway,before I got the slide scanner for Christmas.
The view of the back of the compass shows the housing for the counting device built into the original. The hole in the center for mounting to the tripod was a very close match to a #2 Morse taper,though the original was made in 1802 in Virginia. Those little slotted head screws were a nice detail: They each had "built in" washers turned on their bottom edges,1 piece to the screw. I'm not sure what to call the shape of these screw's heads,but they look like whole cheeses. I know the term "cheese head screws",but the sides of these screws are fairly convex. Not quite the same as more modern screws.
The needle is hardened and fire blued W1 steel. These were magnetized but would lose their magnetism over time. They had to be "re charged" by stroking over the glass with a lodestone when they got too weak. Hardened steel kept magnetism better than soft steel or iron.
I engraved the degree markings with a rotary table. I made a fixed,sharp scribe to put into the spindle of the milling machine. Then,I scribed each line,360 of them,one at a time.I had to be very careful to NOT scribe a line too long,where it should have been a short one. Every 5th.degree has a longer line. No doubt,the original makers also used some kind of an indexing device to perfectly engrave the degree marks.
The face of the compass can be seen better here. The engraving of the original was filled with black mastic. I filled this engraving with artist's acrylic paint,as time was VERY short in getting the compass ready for presentation. I just didn't have time to get into researching and making "mastics" used as fillers back in 1802. Plus,I couldn't take the chance that my rushed mastic filler wouldn't shrink,crack,or fall out. Personally,I'd have preferred to not fill the engraving,but this is a repro. They did use mastic filler on things like clock faces,too. Probably to make them easier to read. We must remember the poor lighting situation before electricity.
You can see the dead silver finish of the dial.It was done by making a medium size wad of cotton,and wrapping a wire in the wad,connected to a couple of batteries. The compass was grounded to the other wire. The wad was dipped in silver plating solution,and gently passed over the dial.
You can make out the stored upright sights in the case. They were secured by little swinging arms I made from ebony,and turned some nice little handles to swing them with,securing the sights in place. There were little arms also securing each end of the compass itself. You can just see one on the right end of an arm.
You can see the 2 little level vials,which I also made from glass tubing I slightly bent,filled with fluid,and melted the ends shut. There is a thin little brass line filed from the solid,to indicate when the bubble was on center. On the back of the compass,you can see the covers that enclose the vials.
You can now see the engraved scale where information was penciled in when using the compass. The hemispherical lines are not just solid lines. They were actually little,NEARLY connected punched dots. I mean nearly connected by a few thousanths of an inch. And ONE chance to get the dots perfectly placed!! Stuff like that makes me nervous!
I did make all of the number stamps,which are exact copies of the originals. I still have them. It is just not suitable to make a nice object,and use bad,Gothic,modern stamps on it. These are about 1/16" tall. The original "2" on the compass had a circle making the top portion of it. I did use that one because it was what was on the old compass,but I made another "2",which is still correct for the period,but has an open face,which I like better. The square W1 steel I made them from is 3/16" square. That gives you a scale for visualizing the size of the numbers.
The compass is made of 260 alloy brass. It was hand polished for 9 days with hand buffs,so as to not smear the details(like the scale engraved on the left arm),and was lacquered with a golden tinted metal lacquer. The original had more of a "working finish" on it,where you could see the lathe turning marks. It was not lacquered. What they had back then might have turned white if it got wet in field use. This was a presentation grade finish.
There is a thin brass rod seen sticking out from 1 side,going to under the compass needle. This can be screwed up under the needle so it is locked in place,and can't bang about and de magnetize itself during horseback rides from place to place. It is like the original. On the back,you can see the knob for tightening the rod GENTLY. The other knob is for indexing the counter. On the dial,there is a small hole through which you can read the number. It may have counted "chains",a measurement used in surveying.
You can also see the silver dedication plaque. David Brinkley was head of the Raleigh tavern society for several years,and wanted to resign. He collected scientific instruments. This gift persuaded him to stay another year. No doubt his presence induced the giving of much more donations than the cost of the compass. It was all high society.
The view of the back of the compass shows the housing for the counting device built into the original. The hole in the center for mounting to the tripod was a very close match to a #2 Morse taper,though the original was made in 1802 in Virginia. Those little slotted head screws were a nice detail: They each had "built in" washers turned on their bottom edges,1 piece to the screw. I'm not sure what to call the shape of these screw's heads,but they look like whole cheeses. I know the term "cheese head screws",but the sides of these screws are fairly convex. Not quite the same as more modern screws.
The needle is hardened and fire blued W1 steel. These were magnetized but would lose their magnetism over time. They had to be "re charged" by stroking over the glass with a lodestone when they got too weak. Hardened steel kept magnetism better than soft steel or iron.
I engraved the degree markings with a rotary table. I made a fixed,sharp scribe to put into the spindle of the milling machine. Then,I scribed each line,360 of them,one at a time.I had to be very careful to NOT scribe a line too long,where it should have been a short one. Every 5th.degree has a longer line. No doubt,the original makers also used some kind of an indexing device to perfectly engrave the degree marks.
The face of the compass can be seen better here. The engraving of the original was filled with black mastic. I filled this engraving with artist's acrylic paint,as time was VERY short in getting the compass ready for presentation. I just didn't have time to get into researching and making "mastics" used as fillers back in 1802. Plus,I couldn't take the chance that my rushed mastic filler wouldn't shrink,crack,or fall out. Personally,I'd have preferred to not fill the engraving,but this is a repro. They did use mastic filler on things like clock faces,too. Probably to make them easier to read. We must remember the poor lighting situation before electricity.
You can see the dead silver finish of the dial.It was done by making a medium size wad of cotton,and wrapping a wire in the wad,connected to a couple of batteries. The compass was grounded to the other wire. The wad was dipped in silver plating solution,and gently passed over the dial.
You can make out the stored upright sights in the case. They were secured by little swinging arms I made from ebony,and turned some nice little handles to swing them with,securing the sights in place. There were little arms also securing each end of the compass itself. You can just see one on the right end of an arm.
You can see the 2 little level vials,which I also made from glass tubing I slightly bent,filled with fluid,and melted the ends shut. There is a thin little brass line filed from the solid,to indicate when the bubble was on center. On the back of the compass,you can see the covers that enclose the vials.
You can now see the engraved scale where information was penciled in when using the compass. The hemispherical lines are not just solid lines. They were actually little,NEARLY connected punched dots. I mean nearly connected by a few thousanths of an inch. And ONE chance to get the dots perfectly placed!! Stuff like that makes me nervous!
I did make all of the number stamps,which are exact copies of the originals. I still have them. It is just not suitable to make a nice object,and use bad,Gothic,modern stamps on it. These are about 1/16" tall. The original "2" on the compass had a circle making the top portion of it. I did use that one because it was what was on the old compass,but I made another "2",which is still correct for the period,but has an open face,which I like better. The square W1 steel I made them from is 3/16" square. That gives you a scale for visualizing the size of the numbers.
The compass is made of 260 alloy brass. It was hand polished for 9 days with hand buffs,so as to not smear the details(like the scale engraved on the left arm),and was lacquered with a golden tinted metal lacquer. The original had more of a "working finish" on it,where you could see the lathe turning marks. It was not lacquered. What they had back then might have turned white if it got wet in field use. This was a presentation grade finish.
There is a thin brass rod seen sticking out from 1 side,going to under the compass needle. This can be screwed up under the needle so it is locked in place,and can't bang about and de magnetize itself during horseback rides from place to place. It is like the original. On the back,you can see the knob for tightening the rod GENTLY. The other knob is for indexing the counter. On the dial,there is a small hole through which you can read the number. It may have counted "chains",a measurement used in surveying.
You can also see the silver dedication plaque. David Brinkley was head of the Raleigh tavern society for several years,and wanted to resign. He collected scientific instruments. This gift persuaded him to stay another year. No doubt his presence induced the giving of much more donations than the cost of the compass. It was all high society.