Friday, January 22, 2010

Finishing up the truck - commutators and cleat blocks

No, this is not a new traction motor.

It's not even a "serviced" traction motor.

How does it look so good?

  • New fibreglass insulating cloth above the brush holders.
  • The armature was "stoned". That means it was machined down with an abrasive material (the stone). It was "turned on a lathe" - except in this case the lathe was the traction motor itself. The axle was jacked up so the motor could turn free, and the motor was energized with power from a welder.
  • The commutator bars were notched. Each of those little bars in the picture connects two adjacent windings in the armature. There is typically 10 or 20 volts between each bar. This is insulated by mica between the bars. The mica cannot be allowed to get above the commutator copper, or it can damage the brushes. Therefore it is notched down 1/16" or so, while foreign matter is also cleaned out of the grooves to prevent short circuits between them. There is a special tool made for this; however in skilled hands a hacksaw blade can do fine.
  • The commutator sides were painted with orange "Twin Pack" epoxy, discussed here.
  • The insulated mounts for the brush holders (off screen) were hand cleaned and painted with Awlgrip primer and topcoat.
  • The brush holders were removed and bead-blasted.
  • Brand new springs. You can't see them, but the fingers which press down on the brushes get their motive force from springs behind. The thing with custom springs is "it's $1000 to set up, then 50 cents a spring." Despite these four motors being the only known such motors in preservation,WRM got plenty of spares.
  • Yup, those are brand new brushes.

The black hole on the left of this picture is where the previous shots were taken. The armature is covered with black cloth to protect it. There you see the insulated brush holder mounts. Those have since been removed, cleaned up and painted. They look great. Click on any picture to zoom in.

The motor leads were re-sleeved with new cloth sleeves. This is not the insulation; they are also insulated inside. The sleeves protect the leads from abrasion. Despite the advanced age of the leads, the insulation was OK - partly because they had been in sleeves. In this picture you see the motor leads from both motors, so eight leads in all. All eight leads will loop upward at this point, you can see where they want to bend. The square sheet of material is "hard fiber" or "bone fiber", varnished, and protects the leads from the rough motor case, and the motor case from a possible short from an insulation-damaged lead.

You also see one of several cleat blocks. An earlier blog posting showed these in paint. Here they are on the car. You notice the the "lower" cleat block is longer, and is bolted onto the car separate from the "upper" cleat block. Why not just bolt them together onto the car?

Ah -- because we are upside down here! Normally, a cleat block is found on the bottom of the car, where gravity works against you. The longer, "lower" piece here would ordinarily be the upper piece. Bolting it to the car separately makes it a lot easier to work with, when you're under the car trying to push the heavy cables up into it, while also pushing the lower (here, upper) block onto them, and with your third and fourth hands, spinning on the nuts. You can imagine why they bolt them separately!

Speaking of bolts, those are not studs coming out of the upp-- wait, lo-- hrm, let's say longer cleat block. Those are square head bolts embedded in the block. The wood shop had notched out a square shaped space in the hardwood, so the bolt head is captured.

Cleat blocks are not standardized. Each one is made custom. This one started with a 2x2" stick of wood. Eight big holes were drilled for the wires. Five bolt holes, then the block was ripped edgewise. Unless the woodworker is very consistent, this cleat block will only mate with itself. That's something the paint shop needs to keep in mind when painting a bunch at once! Often a number is set into each half using a number die.

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