Frequently Asked Questions

Foredom flexible shaft power tools have either Universal motors which can operate on either AC or DC power, or Permanent Magnet (PM), which operate only on DC power. Some PM motors incorporate a rectifier bridge, which converts the AC power to DC, permitting operation directly from the AC line. PM motors, which do not contain a rectifier bridge, can be operated from AC power if a rectifier is incorporated in the speed control. Universal and Permanent Magnet motors both have two magnetic components that interact to produce rotation of the motor shaft. The first, called the “Field”, is fixed to the motor case. The second, called the “Armature”, is the part that rotates and to which the motor shaft is fastened.

Universal Motors
The field in a universal motor consists of a laminated iron structure around which are wound many turns of wire. The line current flowing through the winding produces a magnetic field, which traverses the motor armature. In this type of motor, the current that flows through the field windings, also flows through the armature windings. The result is that the motor will rotate when connected to either AC or DC power. Series SR and SRH motors and older, discontinued Series S, SR (1/8hp), and CC are universal type motors.

Permanent Magnet Motors
In a permanent magnet motor, the field consists of ceramic or rare earth magnets, with no windings. The line power flows only through the armature. Since the magnetic polarity of the field is fixed, the motor will only operate from DC power. Series TX, TXH, LX, LXH and PGX are PM type motors. The speed controls that work with these motors – C.TXR, C.EMX, and C.SXR – have a built-in rectifier that converts the AC from the outlet to the DC required by the motor. These motors have special cord plugs that prevent them from plugging directly into an ordinary electrical wall outlet. The special speed controls have special female plug geometries that will allow the motor to plug into them and a normal male plug that will fit into your wall outlet. If you by-pass these special speed controls and plug-in an M.TX or M.LX motor directly you will damage and blow the motor and void the warranty.

All of our motors and speed controls have a label or motor label plate. The label states the model or series type along with maximum speed, voltage, amp or wattage rating and serial or code number.

A motor speed rating is typically the maximum no-load speed that a motor can achieve. A speed rating for accessories such as burs, drill bits and mandrels is the maximum speed that the accessory can be operated at with out danger of failure. Never operate any accessory at speeds greater than their maximum speed rating.

Low motor speeds can give users more control in certain operations such as milling, drilling and grinding. Low speeds help prevent bur and bit clogging when working with soft metals such as aluminum. Low speeds generate less heat that may adversely affect metal hardness and tempering.

The armature is a cylindrical laminated iron structure centered on, and rigidly fastened to, the motor shaft. The face of the cylinder has a number of slots in which the windings are placed. Since the armature rotates, a means of introducing the current into the windings must be provided. This is the function of the carbon brushes, which are mounted in the motor case in brush holders, and the commutator, which is mounted on the end of the armature opposite the shaft.

The commutator is a cylindrical structure, consisting of a number of copper bars, insulated from each other, to which the armature windings are connected in a specific order. The faces of the carbon brushes ride on the commutator bars. The function of the brush/commutator combination is two-fold:

1. It carries current into the armature.
2. As the commutator bars slide under the brushes, it reverses the direction of the current through the windings to maintain the proper relationship between the polarities of the motor field and armature.

This maintains the desired direction of rotation and produces maximum motor torque.

The inner shaft is a long thin flexible length of tightly coiled steel wires that slides and spins inside a shorter spring known as a silencer. The outer sheath is a reinforced rubber like or neoprene hose with a steel flat wire liner in which the shaft spins, transferring the power from the motor to the handpiece.

There are two types of flexible shafts
1. The standard shaft (Part No. S-93) is 39″ long and has a key tip on the end that connects to the keyway slot in the back end of the handpiece. It comes factory installed on all Series SR and TX motors and is perfectly suited for most applications. It is 1/8″ in diameter and can tolerate 12lbs. of torque. This key tip style shaft can use two types of outer rubber-like sheaths.

The first is made of neoprene and is very flexible. It comes on Foredom’s specialized motors – the Power Graver and the Series LX – but can also be ordered separately for use on any motor. The standard sheath (Part No. S-77) is just a little more stiff than the neoprene. Key tip shafts and sheaths also come in two longer lengths 46″ (Part No. S-93-43) and 66″ (S-93-66). 66″ long shafts are usually too long and cumbersome for most hobby/home use-type applications. Finally, key tip style shafts also come in optional, Non-Conductive versions.

A side note of caution when working with a neoprene sheath – it stretches when pulled, like a rubber band. This flexibility is great except when the user stretches it beyond the inner shaft which is not elastic. Since the inner shaft key tip is “free-floating” in the handpiece it will pull out even though the handpiece is still connected to the outer sheath via the catch ball and spring clip. When this happens, the user will think that the machine is not working even though the shaft is spinning in the sheath. The solution is to re-adjust the shaft so that it extends 3/4” beyond that sheath by moving the workpiece closer to the flex shaft to prevent future problems.

2. Square drive shafts are the second type of shaft. When a Foredom motor comes equipped with this style shaft, it is considered a “Heavy Duty” motor. Square drive shafts have a square drive tip (as opposed to key tip) on the handpiece end. This shaft is 3/16″ in diameter and can tolerate up to 28lbs. of torque. The sheathing for heavy duty shafts is stiffer than standard and neoprene sheathing.

The downside to heavy duty shafting is that it work ONLY with 4 handpieces (30H, 44HT, 25H, and the new H.28H). The square drive shaft (Part No. S-10823) that comes equipped on Series SRH, TXH and LXH motors is 63-3/4″ long. The companion heavy duty sheath (Part No. S-10801TX) includes a silencer spring. A complete Assembly of heavy duty shaft, sheath and silencer spring is also available (Part No. S-10816TX). Shorter and Non-Conductive versions of heavy duty shafts and sheaths are also available.

Vibration in the flexible shaft is usually caused by a kinked or bent inner shaft. If this is the case it will need replacing, straightening will not work. Bending the shaft too tightly at the handpiece or motor ends is the primary cause of shaft kinking. We recommend that you not exceed a 4” radius curvature of the flexible shaft. Avoid this problem by adjusting the height of the motor or moving your work piece.

Improper shaft to sheath adjustment will also cause vibration and kinking. The handpiece is held in place by the catch ball and spring clip to the sheath, with the key tip shaft free-floating in the handpiece keyway of the spindle. If the shaft tip extends to far it gets forced and jammed into the handpiece. This bends the shaft and causes it to rub in the handpiece connector and sheath, resulting in heat and kinks. To prevent this, the shaft key tip should extend 3/4″ out from the sheath tip. This measurement is important and can be done by loosening the sheath set screw located at the bottom of the gray plastic motor connector and sliding the sheath coupling up or down a little until the shaft tip extends about 3/4” out.

Over loading the tool will also cause vibration and “knotting” of the shaft. Let the tool do the work and don’t exert anything more than a firm but gentle application force of the tool. Forcing the tool will only result in damage to you, the tool, and your work piece. Sometimes the bur or accessory catches on an imperfection and stops rotating even though the motor doesn’t. This will cause the shaft to kink or break. Be sure to use caution when working around imperfections in your work piece.

Rarely the flexible shaft motor coupling set screw may loosen and fall into the space between the inner shaft and the outer sheath causing damage to both shaft and sheath. Lack of shaft grease and failure to periodically clean and re-grease the shaft may also cause vibration. Remember not to over-do it on the grease either. Over greasing the shaft is the primary cause of handpiece over-heating