# Erector set part number NH lamp socket unit



## BGHansen (Oct 7, 2018)

Yup, another string on a Gilbert Erector set part I reproduce.  This one is the part number NH lamp socket assembly.  First the obligatory history lesson . . .

Erector sets included an electromagnet in the larger sets starting in 1933.  The manual pictured a separate dry cell battery and a switch made from Erector set parts to power up the magnet.  In 1938 the electrical parts expanded to include a part number NJ battery holder (held a ‘D’ cell battery), an NI 1 ½ volt flashlight bulb, and an NH lamp socket unit.  The NH/NI/NJ parts were included in the mid to larger sets.

It seems like kids of the day repurposed these lamp sockets as they are often missing from eBay-acquired sets.  So, limited market but there is one out there.

I purchase the basic A10 lamp sockets off eBay (bulbs too).  Gilbert mounted the lamp socket to models through an 8-32 threaded base.  In 1938 – 1946 the base was a loose piece and set in the bottom inside of the screw-in lamp socket.  The base had a 5/64” hole drilled up the center to pass a power wire up to the bottom of the bulb.  This was soldered to an eyelet with a fiber insulating washer isolating the eyelet from the socket body.  The lamp socket body was grounded to the model through the base.  In use, the NJ battery holder was screwed to the model which grounded the model.  The positive terminal had a Fahnestock clip for hooking the NH lamp wire to.

In mid-1946, the threaded base piece was soldered to the bottom of the lamp socket.  No idea why the company changed the design.

I try to speed up the production process wherever possible.  I’ve made these bases in the past by center drilling, then drilling a 5/64” hole into a length of brass.  That requires a tool change in the tail stock, so I made a hardened steel bushing to skip the center drilling process.  In use the bushing slips over the 5/16” brass stock, then drill away.

Chucked up a piece of 1/2” drill rod, center drilled and drilled a 5/64” hole.  Then drilled a 19/64” clearance hole in prep for a 0.3135” over-sized reamer.  Parted and faced the opposite side.  Then flame hardened the drill bushing with an oxyacetylene torch.  In retrospect, it might have been better to have attached the bushing from either end of the part.  First, drill the 5/64” hole, and then part.  Flip the piece of stock and center drill, clearance drill and ream from the opposite side.  Reason being the 5/64” drill bit could have walked a bit off center.  Fortunately, it didn’t walk on me but I’ll flip it next time.

Turning was pretty straightforward.  Chuck up the 5/16” brass in a collet, slip the drill bushing over the rod and drill a 5/64” hole.  Then turn to diameter for an 8-32 die and cut a relief at the base of the lamp base.  File a lead in at the end of the base for threading and shut off the lathe.  I power thread with a die as the lathe is coming to a stop.  Finish threading to the base by hand, then reverse the lathe to back off the die, and part.

The commercial lamp sockets include a couple of details for soldering wires for power and ground.  These are peened in place, I peel the lamp socket apart, hold the socket with a piece of steel rod while sanding the bottom flat on a 2” x 42” sander.

I use a block of wood with appropriate sized holes for a holding fixture for soldering.  Cut 1/8” insulation off a length of bell wire and bend the end at a 90.  Feed the wire through one of the terminal details and solder.  I pull up on the insulation to force it to the base of the eyelet while it’s still warm, keeps from shorting out the terminal.  Then cut the soldered on detail to a rough circle with diagonal plier.

The brass lamp bases are tinned and allowed to cool.  Then set a lamp socket open end down, set the tinned brass base on top and hit it with my 300W Weller soldering iron.

The wire terminal is fed through an insulating disk reclaimed from the commercial lamp socket, then fed through the lamp socket.

Process for the non-soldered base version is similar, feed the wire through the insulating disk, then through the brass base, then the lamp socket.

Made a few repros today which usually sell for between $5 - $10 each on eBay.  Won’t buy me a new 6-jaw chuck, but maybe another Interapid indicator.  Thanks for looking.

Bruce


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