doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Barrel wall thickness

I am familiar with the barrel wall thickness measuring devices we have now, having one myself. I'm wondering how this was done 200 years ago, before dial indicators? What's the conventional wisdom on this?

Jim, Google up the ancient Greek "clepsydra" or water clock. Not a dial of course but I'm thinking by 1810, there had to be not just a concept but also the micro-machining skill among clockmakers to easily fashion this contraption. Or, I'd think it's pretty easy to move a spring-loaded shaft (spring scale is a good example) and "read" the amount of travel of a pointer attached to shaft or simply the opposite end of the shaft against a graduated scale. You could certainly build a big "tuning fork" caliper with this simple "linear" readout in place of the conversion of linear movement to angular movement (circular) of the dial. Pure speculation as I have never seen a W/T gauge from back there around the War of 1812. I'd wager it wouldn't have had a digital readout.

jack

Also had the thought that you can easily make a "mirroring" caliper. I can't remember or find what these are called, but are based on registering angular displacement of legs joined by a pivot by extending the legs beyond the pivot--sort of a big "X". Looks like a pair of ice tongs on the measuring end and the "handles" become the "repeater" of the measurement by fashioning one arm of the "X" as a protractor-like scale and the other as a pointer. For a W/T gauge, I spitball that you'd need a straight columnar rod with an anvil to enter the bore much as does the internal leg of the contemporary gauge. The other "leg of the caliper would be a large "S" shape. These legs would pivot on each other at their exact centers and angular displacement (gap) at one end would repeat at the other end 1:1 and could be taken off with another measuring device or compared to a series of "standards". Varying the pivot point to some proportion of the whole would give a readout (movement of the repeater end) in a greater or lesser ratio to the the measuring end. I think the implications for accuracy of moving the pivot closer to the measuring end (movement of repeater much larger than that of measuring end) are pretty obvious. I made one of these yrs ago from aluminum sheet to measure boat planking where the use of a very small bent leg caliper ran into trouble from interference from the width of railcaps because the caliper could not simply be slipped off the planking with the leg gap maintained. This "ice tong" caliper had curved legs to clear the rail obstruction when the tips were in contact with the planking and opposite the pivot the legs turned in an S-curve and became on the measuring end a graduated panel and a pointer. The graduations were of course done "seat-of-the-pants" by setting gap to a known standard and scribing a line on the panel in line with the pointer. Again this is just a suggestion of what may have been.

jack

Whatever was used, it was good. I have a double flint gun from about 1810 whose walls don't vary more than a couple thousanths. And it hasn't been refinished/restruck. Absolutely amazing.

Jim,
Thanks for bringing up this subject. It's always fascinated me since I started working in machine shops in my teens.

The vintage machinist nuts, like the vintage gun nuts, are out there.
http://www.practicalmachinist.com/vb/ant...obinson-112172/

Most of the 19th century indicators I've seen were simple lever types with ratio multiplying (the pointer end longer than the contact tip). I suspect that design has roots as far back as the need for test indicators goes.

"Transfer" caliper is another possibility. Has limiter arm attached which can be fixed as a "stop" to allow repetition of leg position after legs have been opened (or closed) to clear an intervening obstruction such as a flange or thickening at the edge of the section measured.

jack

Clocks hit the scene in early 1300s, screw type micrometer designed in 1666, spring driven clock in 1475, watches in the early 1500s, Watts screw micrometer 1772, an instrument making lab/shop built in Nuremburg in 1450. So it's conceiveable that some form of test indicator and wallthickness gauge was around at least that far back. But, I'd go out on a limb and say that machinists are a innovative bunch and if they were boring barrels, they had some way to measure walls.

Say, Chuck, I suppose once you set up your boring rig and bored a few, you could "ticket" them up into calamari and measure them with the King's fingernail paring or whatever. But I'd bet you're right that there was a less destructive method of trying the accuracy of the boring machine and checking on struck tapers. I'd be surprised if the E.A.I.A. didn't have this paraphenalia in context in an old article? I'll try to find out.

jack

There are hanchons in the foreground.



The man to the right is holding a hanchon. This tool can be seen in armour's shops long before the age of gun powder. If you know the outer diameter and the bore....




Pete

That's a record of "stations" or tranverse sections on a stick, Pete. I doubt that it would guarantee forging (or later striking) the outer surface uniformly concentric to the bore. Would a uniform thickness of the damascus bundles or irons tend to ensure surface concentricity with the "bore" (hole created by the mandrel)?

jack