These mandrels are usually purchased in sets of 9 or 10 ranging in O.D. from approximately .425" up to .600" or so. They are relatively long (about 4') and are used as a back-up surface for burnishing dents or wrinkles out of straight-thin tubing (such as Trombone slides). Some inexperienced technicians mistakenly use them as they would rigid mandrels, and apply excessive pressure to them when attempting to rub-out dents. This technique will only result in bending the mandrel, rendering it useless unless restraightened.

This tool does with only 2 or 3 different sizes, what may be done with a complete set of 9 or 10 of the previously mentioned straight Trombone slide mandrels. There are situations, however, where each design of mandrel may be more effectively applied to a specific repair situation. It is for this reason that we list them concurrently. In shops with a limited budget, we would recommend that they first purchase the set of 9 or 10 straight mandrels, then purchase the expandable type of mandrel at a later time when the cost can be justified.

These mandrels are identical to the long expandable Trombone mandrels, with the exception that they are much shorter and utilized primarily for adjusting and removing dents from short straight tubing (i.e. tuning slides, Flute/Piccolo tenons, etc.)

Bell mandrels for the smaller brasswinds (Trumpet/Cornet, Trombone), are readily available from most distributors of musical instrument repair equipment. These form mandrels are particularly useful in shops that handle a relatively large quantity of Trumpet/ Cornets or Trombones. In any case, the expense of a bell mandrel can usually be justified after using it only a couple of times in the smaller repair shop, considering the ease and convenience this type of mandrel offers. As with all polished and buffed surfaces, these mandrels must be stored in a safe place and kept well lubricated to avoid corrosion. One technique that some repair technicians use to protect the face of their bell mandrels is to cut the flare off a scrap bell and place it over the mandrel when it is not in use.

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