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"Repositioning the Spider Truck Under a Grand Piano"

By Robert Callaghan, RPT

This article was published in the Piano Technicians Journal, a trade journal for professional piano tuners and technicians..

"Repositioning the Spider Truck Under a Grand Piano"
by Robert Callaghan, RPT

I was asked to service the spider truck holding a 9 ft grand. The problem being the piano was very difficult to move and the rubber casters were wearing out.

I found the large center plate to be overly turned (photo 1).

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One truck arm was short and the other two were longer than they needed to be, causing them to sag under the weight of the piano legs (photo 2).

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I felt this was the source of the problems.  My goal was to reposition the truck under the piano so that all the truck arms were of equal length, providing equal leverage for each arm, resulting in leveling the casters so they would rotate freely. Not having an assistant I devised a method where one person could reposition the spider truck in place.

Use a small floor jack to raise the truck arms one at a time. Then lower them onto two scrap pieces of 2x4, so that the casters were just off the floor (photo 3).

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This takes the pressure off the truck arm components.

Next, mark the center of the large plate on a piece of tape (photo 4).

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Measure the distances from the plate center mark to the three piano legs. Adding them and dividing by 3, the average length of the three arms in this case was about 46 inches.Â

Loosen all the set screws on the truck arms. Adjust the center plate and truck arms until each arm measures the average distance from the piano leg to the plate center mark. This repositioning can then be refined by taking smaller measurements from other places, such as from the edge of the truck arm sleeves to the first bolt of the caster mounts, and averaging them. Tighten all the set screws on the truck arms.

With the piano on blocks you can change the casters (not pictured). Jack up each truck arm again, remove the 2x4 pieces, and slowly lower the piano onto the casters.

Compared with photos 1 & 2, the truck arms now radiate more evenly (photo 5),

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and the arms at the casters are more level (photo 6).

 

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Publications

Robert Callaghan was the piano technician for the following CD recordings:

Robert Callaghan has published articles in the website
Piano Technicians Journal.

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