By Jose F. Rodriguez

The TAIG Tool Company sells blank arbors that are in an unmachined condition other than the fact that they are threaded 3/4-16 to directly screw to the head spindle. As they are offered, they measure 1" in diameter and about 2-1/2" in length and the only visible machining sings are on the 3/4-16 threaded end and the front face where it was originally parted off the parent bar stock. The opposite end is cleaned off with a couple of light facing cuts to make it perfect. The perimeter is in the factory cold rolled condition and could also benefit from a couple of light turning passes. The material seems to be 12L14 steel, probably the best grade of machining steel currently available. This alloy is rated at 100% machinability and it is against this that all other grades of steel are rated. They are very cheap to buy in that condition, costing only about $1.40 each. This is one of those items better purchased that made, recognizing that I couldn't produce them for twice that. I always buy them by the bunch so I'll always have some on hand for any special arbors and holders I might need to make. Screw the arbor tight to the spindle and make a turning clean up pass along the whole length and a facing cut across the front face. The arbor will be running at its truest to the spindle at this point. Most of the end mills I commonly use have 3/8" or 1/2" diameter shanks with a flat spot for a locking set screw. The end of the blank arbor will now have to be drilled slightly undersize and reamed to a final bore of .375" or .500" to create a nice suction fit for the end mill or any other tooling that will be used with it. Screw the drill chuck to your threaded drilling tail stock on your Taig and chuck a #2 center drill. Loosen the tail stock lock and slide it along the bed so that the tip of the center drill is about 1/4" away from the arbor when the drilling lever is fully retracted. Run the lathe at a fairly high speed and paint a bit of cutting fluid for steel to the area being drilled. Drill a center hole about 1/8" deep and replace the center drill with a 1/8" twist drill bit and drill all the way through. Gradually enlarge the hole until you are about .010" shy of the final diameter. The final sizing of the hole is by using a .375" or .500" diameter reamer. The reamer is installed on the drill chuck but it is used at a much slower speed than equivalent size drill bits. If you would rather bore it to size you should find a boring bar that is narrow and long enough to do the job. The problem in boring such a hole is that it may turn out with a bit of a taper along its length with the rear portion being a bit narrower due to tool flexing. If you do chose to bore, you should only enlarge the opening in .005" passes and constantly check it for fit. When it looks like you are getting close, reduce the depth of cut to .001" per pass and finish with .0005" cuts until you have achieved a perfect sliding fit. If you goof and bore the hole too big, just start over again and save that arbor for one that will hold a larger bit later. Reaming to size will keep you from goofing up.

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