A "Pancake Type" stepper motor mounted on the carriage to power the crossfeed for NC purposes. On the right the bracket used to hold the motor before painting showing the Silver Solder (Silver Braze) joints.
A few things were learned from this "first time" installation which I will pass on here. The idea of folding the motor close to the lathe with the pulleys on the outside to make an installation that is compact as possible is an idea that seems worth the effort if one takes the trouble to do it this way. It makes the installation look like a professional design rather than have the stepper motor "hanging way out out" as some less well thought out installations end up. This appears to be about the largest stepper motor that can be done this way since there is just barely 1/16" clearance between the back of the motor and the lathe headstock when the carriage is all the way to the left. In fact the clearance is so close that a 1/16" boss that appears on the back of these motors must be kept below the protrubing base of the headstock for clearance. It would be good to keep this in mind if one is duplicating this installation.
Unfortunately at the moment I don't know the official NEMA, ISO, ASA, EIA, ANSI, or any other official form factor designation for this type of stepper motor but will describe its overall dimensions. The diameter of the pancakes is 2.25" and their depth from very rear(excluding the boss) to the front of the mounting plate is almost exactly 1.0". The minimum spacing between the two mounting screws is 2.5" while the slots allow this to be increased to 3.0" maximum. The shaft on this motor was 3/16" diameter which made it a direct fit for the 12 tooth timing pulley with no fitting required except for setscrews. The slots in the motor front flange mounting plate were apparently made for 4-40 mounting hardware since 6-32 screws are too large for the slots.
Two changes over this installization would be recommended. This motor is an old 48 step/rotation motor which does not have enough torque to reliably drive the cross feed under heavy load conditions. It is felt that a 200 step/rotation motor of newer magnetic materials would very nicely solve this problem and make this a winning combination. Also the two bolts used to bolt the frame that holds the motor to the carriage would be replaced with a single 1/4-20 bolt mounting strategy. This would require only one mounting slot to be milled in the mounting frame and make fitting it to the carriage much simpler. The strategy would be to use a 1/4" diameter clearance hole in the carriage with a 1/4-20 nut on the inside of the carriage to pull the the frame tight to the carriage. This would give added strength to the mount and eliminate any chance of problems with a tapped hole in the carriage.
Also a simple solution to obtaining a good mounting surface on the sloped outside face of the carriage casting could be obtained by carefully mounting a 1/4" ID "fender washer" with epoxy glue to the carriage. Getting the surface of this fender washer "square" to all the appropriate lathe surfaces could be effected by temporarily orienting the lathe with these surfaces horizontal and vertical as appropriate and then gluing the fender washer to the surface using a small level to make sure the surface of the washer is horizontal in all directions. It might take some fiddling with some modeling clay or a few tooth picks as props but this would provide a very rugged mounting surface since the washer would only be loaded in compression against the aluminum carriage surface by tightening the 1/4-20 mounting bolt. One could mount this washer before drilling the 1/4" diameter clearance hole and thus use the inside diameter of the washer as a drill guide for this operation as well. Also using epoxy glue in an application such as this does not need to be done all at one time. The initial positining can be done with just enough glue to initially hold the washer in position, and then the props removed and more glue applied to make appropriate fillets. If the second epoxy is applied before the first has hardened completely it seems like a good chemical bond is made to the first glue surface since it is still in the process of forming chemical bonds itself. Similarly one would want to sandpaper the metal surfaces before glueing to clean them and give them some "tooth" for the glue to lock onto.
It might be possible to replace the "built up" brazed motor mount with a machined aluminum mount for anyone not comfortable with all the brazing (silver soldering) that was done in this process. Again it would be smart to make a "mock up" of this mount from corrugated cardboard so the the "first try" is made from easily "machineable" cardboard rather than the aluminum version which will certainly take alot of filing and fitting. The circular iron part in this version was made from some scrap water pipe that was almost the right diameter but had to be "opened up" slightly to fit nicely around the motor. Craftsmanship, craftsmanship, .... craftsmanship. Something at the opposite end of the metal working spectrum from NC machining.