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Potentiometer: Podolsky Roller-Contact Unit in a Moulded Casing
Podolsky's variable resistor (Wirt Company, US 2,060,114, 1936). The carbon strip is bent into a ring inside a moulded casing, and instead of a sliding wiper a small roller runs round it. A coil spring presses the roller out against the strip with even pressure in every position, even over slight irregularities. The patent gives no sizes; the parts are named by what they do.
The picture: the patent's drawing (Figs. 8 and 9).
Intermediate
2 hours
Instructions
1
1
Seat the strip in the casing
Seat the strip in the casing
Bend the resistance strip into a ring against the round inner wall of the moulded casing. A small rib across the wall stops both ends of the strip so it cannot shift; the thick part at the rib has a hole for bolting the casing to a panel. Ours: flat-nose pliers to ease the strip in.
Materials for this step:
Moulded Insulating Casing1 piece
Carbon Resistance Element1 pieceTools needed:
Flat-Nose Pliers2
2
Bolt the terminals
Bolt the terminals
Put two terminal bolts through the casing wall, one at each end of the strip. Under each bolt head a small contact plate rests on the coated end of the strip.
Materials for this step:
Terminal Bolt2 pieces
Contact Plate2 piecesTools needed:
Needle-Nose Pliers3
3
Fit shaft, sleeve, collar and yoke
Fit shaft, sleeve, collar and yoke
The shaft turns in a sleeve fixed in the base of the casing. A collar on the shaft rests on the outer end of the sleeve; on the inner end the shaft carries a yoke, with a spring washer between yoke and sleeve so the shaft cannot slide. Ours: pliers to seat the spring washer.
Materials for this step:
Control Shaft1 piece
Shaft Sleeve1 piece
Shaft Collar1 piece
Shaft Yoke1 piece
Spring Washer1 pieceTools needed:
Needle-Nose Pliers4
4
Fit the sprung roller
Fit the sprung roller
The yoke's slotted ends guide a flat stem. The roller sits in the stem's forked outer end. A washer on shoulders of the stem, pushed out by a coil spring, holds the roller on the strip with even pressure all the way round.
Materials for this step:
Roller Stem1 piece
Contact Roller1 piece
Flat Washer1 piece
Coil Spring1 pieceTools needed:
Needle-Nose PliersMaterials
13- 1 piecePlaceholder
- 1 piecePlaceholder
- 2 piecesPlaceholder
- 2 piecesPlaceholder
- 1 piecePlaceholder
- 1 piecePlaceholder
- 1 piecePlaceholder
- 1 piecePlaceholder
- 1 piecePlaceholder
- 1 piecePlaceholder
- 1 piecePlaceholder
- 1 piecePlaceholder
- 1 piecePlaceholder
Tools Required
2- Placeholder
- Placeholder
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