Trombones are not inherently more difficult or troublesome to repair than other instruments. Like any specialized job, successful trombone repair requires the right knowledge, tools and techniques.

Many excellent tools have been developed over the years to make hand slide repair easier and more accurate. Unfortunately, some have also been misused or used beyond their intended limits. The N11 Expandable Trombone Burnisher is one example. No tool can replace careful observation, sound judgment and an understanding of how the instrument reacts during repair.

Begin with a Properly Cleaned Slide

Straightening and alignment cannot begin until the hand slide has been thoroughly cleaned and all dents, kinks and creases have been removed. See the related trombone hand slide cleaning guide before beginning this procedure.

Dents and dent removal both affect alignment. When a dent is created, the impact frequently bends the surrounding tube. Removing the dent requires bending the tubing in the opposite direction, but the correction may not occur in exactly the same place or with the same amount of force.

A dent is highly localized, while a bend generally affects a larger area. A dent or crease can also cause the rail to become oval while producing other distortions. The N87A Trombone Pliers help eliminate many of the problems traditionally encountered during this stage of the repair.

Identify the Type of Repair Required

Trombone hand slide repairs generally fall into two categories.

Minor Dent, Straightening and Alignment Work

The first type requires minor dent removal followed by straightening and alignment of the slide rails. Most repairs will hopefully fall into this category.

The completed slide may not be theoretically perfect, but it can be accurate enough to satisfy even a very particular player. Unless the customer has a leveling stone and the necessary repair skills, practical performance is more important than pursuing an unattainable mathematical ideal.

Complete Disassembly and Realignment

The second type requires removal of the hand slide crook or end bow. This releases accumulated stress within the assembly and allows the technician to straighten and align each component independently before rebuilding the slide.

Removing the end bow allows you to start fresh, eliminate internal stress and complete a more comprehensive alignment. This procedure is more involved, more accurate and more expensive than a minor correction.

A technician must learn to recognize which type of repair is required during the initial inspection. This is essential for quoting the work accurately and avoiding a later conversation in which the customer questions the additional cost or the technician’s judgment.

A complete hand slide realignment is similar in principle to a full repad. You are taking control of the entire system, rebuilding it according to your standards and accepting responsibility for the result. That additional work is why a complete rebuild costs more.

Most customers will naturally want the results of the second procedure at the price of the first. Clear inspection, documentation and communication are therefore important before work begins.

Evaluate Slides That Appear Undamaged

Many hand slides have simply been mishandled, dropped or knocked around. They may show no obvious damage and can look nearly new, yet still fail to operate properly.

It can be difficult to justify a major expense when the customer believes the problem should be simple. A skilled technician should be able to complete these less severe cases as a minor repair whenever the condition of the slide allows it. The technician must also be able to explain when a more extensive repair is necessary.

Important Rules for Trombone Slide Repair

Do Not Twist the Slide

Do not grab the slide and attempt to change the relationship between the rails by twisting the assembly. Twisting usually does not correct the underlying problem and can introduce additional stress.

A very minor adjustment may occasionally respond to a gentle tweak. If it does not produce an immediate result, stop. Continued twisting is unlikely to help.

This is also a point at which a poorly soldered connection ring may reveal itself. Unless the original damage was caused by someone grabbing and twisting the slide across the rails, follow the normal straightening and alignment process.

Most bent slides are caused by being dropped and sliding across the floor. Many dents are caused by impacts with music stands. In either situation, twisting seldom provides the proper correction.

Remember that hand slide correction is primarily lateral, not rotational.

Do Not Unsolder the Slide Unless Necessary

Do not make disassembly your first response. Dent and alignment work should reverse the action that caused the damage whenever the slide can be corrected safely while assembled.

When removing a dent, the distorted metal is returned to its original position. It may need to be moved slightly beyond that position so the metal can spring back into the correct shape. Learning to anticipate and control this spring-back is one of the fundamental skills of instrument repair.

The same principle applies to a hand slide. Analyze the bent rail and move it back in the direction opposite the original damage.

When one rail is bent, the other will respond sympathetically because the two rails are connected by the end bow and, on the outer slide, the brace. A successful technician must anticipate this movement and use it to their advantage.

If the correction is unsuccessful or the damage is too severe, remove the end bow. Allow the assembly to relax, straighten each component independently and rebuild the slide with improved alignment. With proper heat control and careful technique, this can usually be completed without seriously damaging the lacquer.

Never Use a Hammer on a Trombone Slide

Hammering causes two significant problems. It work-hardens the metal and thins the tubing, often very quickly.

Modern dent removal is better accomplished by rolling the damage out over a smooth, straight mandrel with pressure-adjustable rollers. The recommended combination is the N87A Trombone Pliers with the correctly sized N53 Trombone Mandrel.

As a dent is rolled out, the tubing is pressed against a perfectly straight, round surface. This removes the dent while simultaneously re-forming, re-contouring and straightening the tubing.

Traditional Trombone Dent Removal Tools

Many effective tools have been used for hand slide dent removal over the years, including:

• N52 and N53 Trombone Slide Mandrels
• N12 3/4 Ring
• Chrome-plated N11-style expandable tools
• Original N87 Dual Roller Tool
• A bar of ivory soap at least five days old for lubrication when using the N12 ring

These tools remain valuable when used with the skill and care required by the procedure. Problems generally occur when a tool is misused, overexpanded or pushed beyond its intended capacity.

No tool can determine when the metal has reached its limit. That judgment belongs to the operator. With experience, the technician should recognize the limit before the tool or tubing approaches maximum stress.

Over approximately 40 years and thousands of rental-return repairs, properly used tools did not cause a slide to become so work-hardened that it cracked or split. Slide rails were not replaced because of supposed overhardening caused by proper repair procedures.

If a rail is damaged through expansion, the tool was likely overexpanded or the tubing was overworked.

In one experiment, an outer slide was intentionally worked for nearly an hour in an attempt to enlarge the bore by .001 inch so it would accept an inner slide from another instrument. Despite considerable effort, blistered hands and aching fingers, the total expansion achieved was zero.

These slides often continued through the remainder of a student’s marching band career without incident. Older, corroded slides occasionally split because the tubing was already deteriorated. Slides also broke where previous severe bending, cracks or poor earlier repairs had weakened them. Those situations are different from damage caused by correct tool use.

Of the few rails replaced in a typical year, most were damaged through marching use or had simply reached the end of their service life. Modern tools now make many of these repairs faster, easier and more dependable.

Removing Dents from the Hand Slide Bow

Until recently, dents in the hand slide bow were generally handled in one of two ways.

A technician could float a ball through the bow and attempt to smooth a minor dent, or remove the end bow and use a rod and ball to remove the damage before straightening, aligning and resoldering the assembly.

The P53 Trombone Dent Ball Driver and Retriever provides another option. It allows the technician to control the placement of the correctly sized N57G Ball inside the hand slide bow.

The fitted ball will still be approximately .010 to .020 inch smaller than the tubing because of shrinkage at the solder joint. Even with this clearance, the P53 provides significantly better control over ball placement and removal.

Once the dents have been removed, the actual straightening and alignment process can begin.

Straightening Versus Aligning

There are two distinct stages to this work:

• Straightening corrects each individual slide tube or rail.
• Aligning establishes the correct relationship between the straightened components before they are soldered together.

Quality slide repair requires a ground stone or another dependable flat surface. The accuracy of this surface will determine the final quality of the repair.

After cleaning and dent removal, there are approximately 12 areas to inspect for straightness and another eight to ten areas to evaluate for alignment, depending on how the inspection points are counted.

Straightening the Outer Slide Rails

Place the outer slide assembly on the stone with one rail contacting the surface at a time.

Roll the rail toward and away from yourself while watching the light between the rail and the stone. Changes in the visible light will reveal the direction and location of the bend.

Once the direction is identified, place the open end of the slide on a slightly formed support block and carefully push the rail in the opposite direction.

A radiused notch carved into a wooden block mounted lower on the P91 Stone Stand can provide appropriate support. This helps prevent unnecessary distortion of the tube during correction.

If a ball must be inserted merely to prevent the rail from collapsing during ordinary straightening, the tube is too fragile to provide dependable service. Replacing that rail is more responsible than spending the customer’s money repairing tubing that may fail immediately after leaving the bench.

Customers will not be pleased if the slide returns the next day with the same problem. The technician will also be performing the second repair without compensation. If the customer will not preapprove the necessary work, decline the repair. Completing inadequate work is generally more expensive than turning the job away.

Inspect Every Long Rail and Stocking

Check and correct each of the four long slide-rail sections. Next, inspect all four stocking areas using the same rolling method.

For the inner slide assembly, roll each stocking tightly against the stone and observe the elevation of the long rail. This reveals whether the stocking and rail are concentric and properly aligned.

For the outer slide, press the stocking firmly against the stone and observe the height of the long section as the assembly is rotated.

Every section must be straight and concentric. If the end bow remains soldered in place, some compromise may be necessary. Work carefully and achieve the best result possible without introducing additional stress.

The goal is to straighten and align the slide without disassembling it whenever the condition of the instrument allows. This is an acquired skill. Twisting the assembly only adds internal tension and creates additional problems.

Straightening the Inner Slide Assembly

The inner slide is generally easier to evaluate because it does not have an end bow connecting the rails.

Check the long, straight sections by rolling them forward and backward on the stone while observing changes in the light. No slide is perfectly straight, including a new factory-built slide. Make the linear corrections necessary for smooth operation rather than chasing an unrealistic ideal.

Use Extra Care Around the Venturi

The upper rail on the mouthpiece side contains the venturi and may resist correction differently from the other rail.

The venturi tube is slip-fitted inside the slide tube. Depending on how the instrument was assembled, the mouthpiece side may have been soldered before or after installation into the cork barrel. As a result, this section may not bend, move or react as freely as expected.

When straightening the first eight inches or so, the two tubes may move internally because they are connected at only one end. They may not slide smoothly against each other. This can make the rail move in an animated or jerky manner rather than responding with the smooth movement normally expected.

Even a small movement can produce a surprisingly large result. If this occurs, straighten the area carefully by hand rather than sliding your hand down the tube as you might elsewhere.

Corrosion can occasionally bind the interior end of the venturi to the rail and magnify these difficulties. Work slowly and make small corrections.

Check Stocking Concentricity

Place the slide tube on the stone with the stocking near one end. Because the stocking and long rail have different diameters, the free end of the stocking will be elevated above the stone.

Rotate the tube slowly and observe the light beneath the stocking. Determine whether the stocking rises and falls or maintains the same angle throughout the rotation.

The slide lock may interfere with the inspection, so work methodically. The stocking itself should already have been checked for straightness. If it is straight but the angle changes during rotation, carefully bend the stocking until it is concentric with the rail.

Complete this inspection on all four stocking areas.

Compare Rail Spacing with Calipers

Use calipers or dial calipers to compare the spacing between the slide rails. The exact measurement is less important than consistency.

Whether the calipers display thousandths of an inch or millimeters, compare the measurements until the rails are parallel and each position produces the same feel.

Do not become overly focused on achieving a particular number. What matters is that the measurements match and the slide operates correctly.

If the assembly remained soldered and each component returned to its original position, the inner slide may only need to be adjusted to fit the aligned outer slide. If no previous soldering or improper assembly is present, the components should now be close to their correct alignment.

Resoldering an End Bow

If the hand slide bow was removed, complete the straightening and alignment work before reinstalling it.

Check the rail spacing again with calipers. Place the slide assembly on the stone with the stockings extending approximately one inch beyond the edge.

Lightly press one stocking downward and observe which rail rises and how far it moves. Repeat the test on the other stocking.

If one rail lifts before the other, the assembly is not fully aligned. Adjust the hand slide brace in the appropriate direction to equalize the stress, then repeat the test.

When both sides lift equally, the hand slide is parallel in that plane. The calipers verify the plane positioned 90 degrees from this test. Once both tests agree, the slide can be considered straight and aligned. The same procedure can also be used on the inner slide.

Confirm the Complete Assembly

Install the aligned inner slide into the aligned outer slide and place the complete assembly on the stone.

Physically confirm that the rails remain straight, parallel and properly aligned. Check whether the end bow can be installed without changing any established dimensions.

If the bow does not fit naturally, adjust the bow itself until it can be installed without pulling the rails out of alignment.

Use Controlled Heat When Soldering

The end bow must be soldered without allowing heat to distort the alignment established during the previous steps.

Use only enough heat to melt the solder. Place the solder on the brass and move the torch near the heavier side of the joint until the solder flows into place slowly.

Apply heat away from the solder and toward the area where the solder needs to travel. This is generally the heavier side of the joint. Remember that solder follows heat.

This controlled method is sometimes called “cold soldering” because it minimizes the amount of heat introduced into the assembly and helps preserve the existing alignment.

Clean all affected surfaces before soldering. Apply liquid solder flux with an eyedropper for greater control.

Liquid flux can also be used to partially cool the solder joint without rapidly crystallizing the tin, which may weaken the joint and reduce adhesion. This theory can be demonstrated using a saxophone post and the L13 Slide Hammer while lifting a dent.

Avoid cooling the joint with water. Water cools the metal too quickly, which can change the relationship between the tubes and may weaken the solder joint.

Final Cleaning and Inspection

Complete any minor touch-up work after soldering. Perform one final inspection of the slide on the stone and confirm that it operates smoothly.

Finish by dry-ragging the slide rails under pressure to remove any remaining dirt, dust or moisture.

The slide should now be clean, straight, aligned and ready to return to service. A careful setup can be better than the original factory alignment because the technician has the time, tools and responsibility to evaluate the needs of that specific instrument and player.