Repairing Cracked Chime Tubes

Randy A. Bergum


Keeping an older organ maintained properly can be very rewarding, although sometimes challenging, especially when many of the original vendors have gone out of business. Because some of the repairs required of any installation require parts that are no longer made, the technician must seek creative solutions.

Problem Statement

A few years ago Bob Trousdale faced the problem of repairing several large scale chimes at Plummer Auditorium in Fullerton, California. Each of these chimes had a vertical crack about six inches long starting at the top end near the plug and catgut hanger, adversely affecting the sound quality. Bob had asked members of the Plummer crew if anyone knew of a solution to this problem. There had been a few articles published in Theater Organ magazine, as well as the Glue Pot newsletter, but these repair schemes yielded various results, from Pretty Good to Not so Good.


There have been many attempts at restoring the sound of cracked chimes. Hose clamps have been installed on the crack to pull it closed, but this does not work completely. The tone is not fully restored, and a low frequency undulation can result. Filling the crack with epoxy and wedges has been tried, although this still permits a discontinuity along the crack surface, which interferes with the vibrations.

The original chimes used by Wurlitzer and other makes were supplied by J. C. Deagan of Chicago. They were made of nickel-plated brass, and they tended to crack during the 60 to 70 years of hard use. The typical crack occurs at the end of the tube in a longitudinal direction, and tends to dull and shorten the strike tone by interfering with vibration propagation.


A possible cause of cracking could be found in the way the tubes are formed during manufacture. The better grades of chimes - Class A, B, and C were drawn, but the Class R tubes were rolled from a brass sheet, shaped into a tube and joined at a seam. Solid plugs are then pressed into one or both ends, which affects the tone quality of the chime. This added mass acts to lower the pitch of the fundamental and the first few harmonics, effectively stretching the perceived pitch to one that is more pleasant to the ear. Pressing the plugs into the tube with an interference fit is necessary to match the impedence between the tube and the plug, making the assembly behave like one solid system. However, this interference fit causes a tensile hoop stress in the tube, much like that found in a rain barrel full of water, where the weight of the water places a bursting force in the outward direction. Steel hoops are usually installed around the circumference to contain these outward forces.

Local stress at the tip of a crack is extremely high, and easily exceeds the tensile strength of the base metal, causing the crack to propagate quickly once formed. In addition, microscopic imperfections in the base metal and seams made during manufacture cause local stress risers, which encourage the formation of cracks. Furthermore, the typical chime is struck repeatedly by a hammer, encouraging crack growth.

Previous Solutions

One method of chime tube repair has been to cut off the offending part and turn the tube into a higher note. This is not usually the best way to solve the problem for two reasons: First, the scale of the trimmed tube usually won't match the rest of the original set, and second, there are no guarantees of finding a larger set that is close in scale.

Solution and Metallurgy

We have found that the chimes can be repaired by welding with a TIG welder (Tungsten Inert Gas). Silicon Bronze rod is used as the filler metal because it closely matches the parent metal mechanical properties, and it has very good welding characteristics.

First, a bit about brass. Made of varying parts of copper and another element, such as zinc or sometimes silicon, brass is easy to machine and finish. The zinc contained in the brass will vaporize at an amazingly low 1,663 degrees F, and is very toxic, so you'll want to have adequate ventilation or the proper respirator for metal vapors.

The chime shown in this article is cracked at the bottom end, and has a recessed bottom plug inserted. Double plugged tubes usually have a very small hole drilled to allow for pressure escape during manufacture.

The Repair Process

  1. Remove the catgut hanger if it is near the weld site.
  2. Fig. 1. Crack in tube before preparation.

  3. Mark the radial location of the top plug if welding that end, since it will need to be realigned back to its original position after the welding. A small pair of punch marks will suffice. If removing the bottom plug, you will need to measure the depth if recessed, then drill and tap a hole through it in order to thread in a removing tool. I use a tap of 1/4"-20 size, then insert a bolt for knocking it out with vise grips and a hammer. Notice the silver paint on the tube in Fig. 2 - electroplating does not work very well in a recessed hole, so the factory painted the area to make it blend with the rest of the nickel finish.
  4. Fig. 2: Tapping the Bottom Plug

  5. Remove the plug by first heating the end of the tube with a propane torch. While the tube is hot, drive out the plug by placing a long bar in the chime from the other end, and gently tapping it with a hammer, or if pulling the Bottom Plug, extract with a threaded puller. Because there is an open crack in the tube, the interference fit of the plug will be reduced, and at this point the plug may simply fall out.
  6. Fig. 3: The Bottom Plug

  7. Using a fine file, gently file off the nickel plating on the outside of the tube back to about 3/4 inch away from the weld area. During the welding process the arc temperature can reach 6,000 deg. F, hot enough to vaporize almost all metals. Any plating should be removed around the weld area to prevent contamination of the weld, and also to limit any heavy metals from being vaporized into the air, posing a health hazard.
  8. Drill a 1/8" hole in the chime about 1/2 of an inch beyond the last visible part of the crack. This gives the crack a "friendly" place to end its travel, and will prevent further propagation during welding and while in use later.
  9. Chamfer the crack to about 80% depth at 45 degrees using a rotary file, such as a Dremel tool or die grinder. This will provide for proper weld penetration.
  10. Fig. 4: Prepped tube showing stop drilled hole and chamfered edges

  11. Place a hose clamp at the end of the tube and tighten it to close the crack completely.
  12. TIG weld the crack closed using Silicon Bronze rod. I use a Hobart TigWave 250 with the following settings:
  13. Fig. 5: The Welder

    Fig. 6 - Completed weld bead

  14. After the weld cools, dress the interior bore using a rotary file. Before driving the plug back in, this area will need to be smooth and as close to the original bore as possible - do not increase the diameter!
  15. Heat the tube end with a propane torch and drive the plug in the same position as it was originally. If inserting a Bottom Plug, replace it to the same depth as measured earlier.
  16. The bottom plug will need to have its threaded hole filled with the same amount of mass as was removed during drilling and tapping. Countersink the bottom of the the hole to accept a brass flathead screw. Place a drop of Locktite on the screw threads to keep the screw from vibrating loose, and install to a tight fit.
  17. File, sand and polish the weld area. This step is best done after replacing the plug because the interference fit will cause a local waviness in the tube, which will need to be polished out again. If you really want a clean tube, polish the remainder with Chrome cleaner, clean off with a surface prep, then clear coat with lacquer.
  18. Fig. 7 - Bead filed off and tube polished.

  19. Replace the catgut hanger if it was removed.
  20. Check for sound quality.


The completed chime has the tone restored, and matches the timbre of the other tubes in the set. The appearance of the chime reveals that the repair site is visible, but not overly noticeable. The nickel plate has been removed in the area adjacent to the welding, and the underlying brass has been polished. This may not be a problem since many chimes are hung vertically with the tops hidden by the hammer action, so your handy-work might be covered up in the end. The actual weld bead can be distinguished by its color, which has slightly more copper in it than the native brass in the tube, since some of the zinc has boiled off during welding.

Fig. 8 - Installed Chime Tube back home with the others


To date we have about 10 chimes in service, the longest one being in use since 1997 with no observable failure. The projected service life is not known, but it seems that the repaired area should be stronger than the original seam.

Many thanks to Bob Trousdale, John Ledwon and Al Sefl for their help in preparing this article.


  1. Mark's Standard Handbook for Mechanical Engineers - 8th Edition
    Baumeister, Avallone, Baumeister
    ISBN 0-07-004123-7
  2. Welding Handbook
    Finch, Richard, & Monroe, Tom
    HP Books
    ISBN 0-89586-257-3
  3. The Science of Sound
    Rossing, Thomas D.
    Addison-Wesley Publishing Co.
    ISBN 0-201-15727-6

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Copyright © September 1997 and Beyond. Randy A. Bergum - All Rights Reserved