Ron Rapa
Rapa Electric, Inc. 
Allegan, Michigan
Technical Education Committee Member 

Over the many years that I’ve been in the electrical and mechanical repair business, I’ve learned a number of tips and techniques to help me work more efficiently. Time is a precious commod­ity, so making the best use of it can help you provide the best possible service to your customers.

Following are just a few ideas I’ve picked up that might help you out, too:  

• Tear down of small metric motors – Removing stubborn through tie bolts can be a chal­lenge.  I’ve found that a little heat goes a long way in making it easier. Have the appropriate tool handy, then use a torch to break down corrosion or rust at the boss where the threaded portion is seated. Then while still hot, work the torch along the length of the rod. The rod will grow in length sufficiently to remove tension and the bolt will back out easily. 
• Avoiding chuck jaw marks when shaft is in the lathe – Use a flat piece of copper sized to wrap the circumference to be held. Anneal (heat until cherry red, then cool). Now it will conform to size and shape easily. The chuck tooth may leave dents in the copper, but not in the shaft. Save the copper piece for future use. If it hardens from use, it can be re-annealed and used over and over. 
• Avoid over-shoot when mount­ing shrink fit couplings – Before heating, affix a flat bar across the outboard face. Then once the part is heated to the desired tempera­ture and the shaft has been coated with an anti-seize compound, slip the coupling half on with one motion and it will stop when the coupling is flush with the shaft end. 
• Superior brazed winding connections – Twist the conduc­tors to be joined together into a neat bundle. Torch heat the area to be brazed until the area is cherry red. Allow to cool, then continue to twist into a more solid, compact bundle. When satisfied, heat again and apply a brazing rod and allow it to flow into the joint. 
• Forming copper tubing without crimping – Some specialty coils and induction hardening fixtures require copper tubing to be bent into difficult radii and shapes. Without special equipment, this can be a daunting task. Here’s one effective method I’ve used. Tape one end of the tubing shut. Sift sand blast media or sand into the open end of the tube. Then shake it down to prevent air voids. When full, tape the other end closed. Now the tubing can be formed into a tight circle with­out collapsing the tubing wall. When the desired shape has been achieved, remove the tape from both ends and shake out the sand. 
• Better babbitt pouring results – A homemade bottom pouring pot reduces the amount of con­taminates in your babbitt melt (see Figure 1). We made ours using heavy wall tubing with a rectangular hole milled in the lower quarter. A rectangular tube is fitted and welded into place to serve as a spout. Two pins are welded to the outside top of the tube. This allows a pivoting suspension bale to be mounted. Weld the bottom of the tube with a heavy plate (3/4” to 1” or 19-25 mm). Using a thick piece helps avoid burn-through and helps distribute the heat. An appropri­ately sized pipe at the tail of the pot will accept a bar to tip and control the pot.

• Hot dam – I know this sounds like an exclamatory comment, but dental plaster actually is something that really works to contain extremely hot mate­rial such as molten Babbitt. It mixes easily, has a quick setting time, can be applied in layers to achieve the required dam and is relatively inexpensive. Always bake the part prior to pour to prevent moisture explosions. Af­ter the pour is complete and the material set, the plaster can be chipped away easily. The dental plaster withstands the heat with­out any effect. Anyone who has poured Babbitt knows that it is wet and hot, so extreme caution is required. I also use dental plas­ter to dam potting compound in magnets and submersible cable cord entries. It will hold the liq­uid epoxy until set and removes easily.
• Maintaining centered hole in end of shaft when shaft is short­ened – On occasion, a customer will require a special shaft. If the threaded hole in the end of shaft must be maintained after short­ening, try this: Pre-drill into the existing hole sufficiently deep so that it is beyond the called for depth. Then, using the original threads as a pilot, tap the hole deeper than needed. Now the shaft can be cut off, chamfered and the hole cleaned up.
• Remove stuck outer bearing races from end bell – Often the outer race of a roller or ball bear­ing will be stuck in the housing. The location and limited driving angles make them problematic as to removal. Using an arc welder, run a beat of weld around the inside center of the ring. When cooled, the race will usually fall out due to the shrinking caused by the weld.
• Inner race stuck on shaft – This method won’t work on a fully gall welded race but works great on just stuck or slightly galled bearings. It is easier and less damaging to the shaft than torch cutting. Support the bearing area underneath. Then spot heat a small area on top of the race until cherry red. Using a substantial ball pein hammer, hit the red area.  Repeat several times in the same area. This will normally cause the stuck race to grow in circumfer­ence and expand to the point of falling off. 

Categories: AC motors, Repair procedures & tips

Tags: Motor rewind/repair

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