Home About USS Squalus About the diving operations Manufacturing the helmets Part machining & finishing Sub-assembly fabrication Final Assembly Progress Updates
Once sufficient parts are accumulated the assembly process can commence. Each helmet is produced as sub-assemblies. The breastplate and bonnet are made up individually but concurrently. What mates a bonnet and breastplate together (literally and figuratively) is the neck ring set. The neck rings are machined as sets and are kept together. In theory all Mark V helmets should be interchangeable, but in practice small variances in manufacture may interfere with a proper assembly of a helmet with new neck rings. As the helmets are used and wear the impact of any variances diminish to insignificance. It is not unusual to come across WWII Mark V helmets with a breastplate from one manufacturer and the bonnet from another.
In practice a helmet and breastplate will be started together with a shell being cut and a breastplate shell being pounded within a day or two of one another. Depending on manpower allocations one person may alternate between the bonnet and breastplate, or two persons may work on the separate assemblies. As this project is a series of helmets several helmets are in various stages of manufacture at any given time.
Generally all classic style helmets follow a similar pattern of construction. The bonnet shell is cleaned, buffed if necessary to remove excessive spinning marks, laid out and cut. Window, exhaust, spitcock (if applicable), and telephone cup (if applicable) holes are cut with hole saws. After the holes are filed to remove burrs from cutting the cast parts are fitted and soldered to the shell. The first cast part to be soldered on is the neck ring. The window frames are next, then the telephone cup, The exhaust valve and duct are now fitted. The exhaust duct has to pass between the top and side windows, and between the air and suit heater elbows, terminating at the back of the bonnet. After the exhaust duct is installed the air, telephone, and suit heater elbows are installed adjusted to the position of the exhaust duct.
The breastplate shell is pounded out of sheet Copper. The base ring is sanded, buffed, and media blasted. The breastplate shell is media blasted and it, and the base ring, are clamped to the male mandrel for peening. The outer edge of the breastplate is rolled over the outer edge of the base ring to bind them together. Now the breastplate goes to the solderer and the joint is soldered. The breastplate is then sanded to remove the excess Copper and solder on the top face of the base ring. The top of the base ring is the sealing surface for the dress collar and must be smooth. Now the stud holes are laid out and drilled. The neck opening is trimmed and the lower neck ring is installed. Once the neck ring is on the studs can be installed. The final part to be soldered on is the wire running along the outer edge of the base ring. This wire increases the sealing ability of the dress collar. At this point the breastplate is ready for media blasting in preparation for plating.
The canister casting is sanded, buffed, and polished, by a sub-contractor. The two necks are milled flat to accept the nuts and collars. Positioning of the collars is critical to proper fitting of the canister to the bonnet. The canister is jigged into a fixture and the nuts and collars are Silver soldered to it. The canister has a vent hole in the bottom which is now plugged. At this time the canister is pressure tested and any seam leaks are repaired.
Having the breastplate complete the bonnet can be placed on it and the canister can be fitted. To assure proper alignment the canister elbows are fitted to the canister and the assembly is positioned on the bonnet/breastplate. Measurements are made and the holes for the elbows are marked and cut. The canister assembly is put back on the bonnet/breastplate and the elbows have one rivet installed in each. The elbows are tack soldered and the rest of the rivets are installed. The canister is then removed and the elbows are finish soldered. The canister elbow installation completes the fitting installations. The interior ductwork for is cut from sheet Copper and formed. The window ducts are installed first. The ball lever for the lock is installed, the large recirculator duct is installed. Finally, the studs for the transceiver mount, and the wire tabs are installed. The bonnet is media blasted and is ready for plating.
The Copper canister tag is installed over the vent hole plug on the lower part of the canister.
The helmets will be held at this point until the fall when they will be sent two at a time for plating.
The sub-assemblies are now ready for fitting out. We will pick up the process in final assembly.
Bonnet
The shells for the top are made by a sub-contractor who specializes in metal spinning. The shells are spun using a DESCO mandrel on their spinning lathes. The shells are received without any holes other than the base. All window and elbow holes are laid out and cut in our shop.
Cutting out the shell. The shell is marked up using a pattern. Holes are cut in the shell using hole saws on a drill press.
Layout and fitting of parts on the shell.
Drilling the holes for the canister elbows.
Breastplate
Forming the breastplate shell. The Breastplate shell is formed from a sheet of Copper in a Steel (female) mandrel. The Copper is heated to soften and anneal it as it is pounded to shape.
Fitting the base ring. The formed breastplate shell is placed on another steel (male) mandrel to have the base ring fitted. The base ring provides rigidity and a solid anchor for the breastplate studs. The Copper is peened over the outer edge of the base ring while it is clamped to the mandrel. The neck is marked for trimming at this time.
After the base ring is soldered to the breastplate shell the top of the base ring is sanded smooth. The neck opening is trimmed and the neck ring is fitted. The stud holes are laid out and drilled. The neck ring is then soldered to the breastplate. The next parts added are the breastplate studs, then the wire seal bead. Finally the breastplate loops are installed.
Sub Assembly
Complete top and breastplate assemblies are required to fit the canister. Position and alignment are critical for the canister to easily mount to the elbows and to clear the breastplate.
Checking fit and alignment between the breastplate and top.
Fitting the Canister Assembly. To ensure proper positioning of the canister the elbows are riveted with all the components in place.
