One needs to cut down a tap with a precise metal lathe. A lathe with tight gibbs and close tolerances. No offense to the Cueman, porper, unique, or clones out there. I have a deluxe and love it, I have three different Unique's and love them, but I give the devil its due for specific jobs: there is the right tool. A tool post grinder on a metal lathe would grind a tap down nice, I would think that with a spray of lubricant it would be the ideal way to go. But an appropriate carbide bit mounted on a solid post and carriage, with the proper speed, feed, and lubricant works nicely too. A little router running a small grinding stone may work with a deluxe that was carefully dialed in and tight, but not very wise as far as safety or dollar sense goes. It will take a lot of stones to get a nice square cut. And just think about all those grinding stone particles getting into every nook and cranny of your cue lathe, dooming it to premature failure in the future. Makes me cringe.
Funny and very good points. A toolpost grinder is an excellent idea but rather expensive if you're only doing a couple taps.
The dust could be a problem. Cover up what you can and use a vacuum up close.
I would rough grind it down close to size no matter how I did the final turn to size. For that I would either make a jig and spin it down on my tool grinder or maybe try holding the end of the tap with a center in one hand and spin it with the other hand to .030 or so oversize. You'll need a little dexterity for that.
A better way to rough might be to tap through piece of wood, run the tap through it so the end sticks out, if its loose lock it down by runnning a nut on it and tighten. Then you can hold the piece of wood and rough grind it. Unless you've done a fair amount of freehand grinding, I wouldn't count on keeping it concentric. You can always check your progres by chucking up a center and spin the end of the tap with your hand and look to see how much it runs out (or use an indicator but I wouldn't bother getting it that close).
The way I would do it at a machine ship:
Rough the tap down by hand
Put the tap in a Hardinge 5C collet holder.
Look it open so I can spin it
Dress the grinding wheel (White Norton wheel on a surface grinder)
Mount the hardinge on magnetic plate of the surface grinder
Lock the sliding table with the wheel directly above the center of the tap or slightly past... you don't want it jumping into the tap.
Spin the tap and bring down the wheel til it touches and move wheel off tap
Dial down maybe .005 don't think I'd try any more that .010 but its been a while.
Spin the tap and turn the handle for the cross slide slowly until you reach the end of where you want to grind
Mark with spot with tape, lines and the number on the dial
Move back out, dial down and repeat until I reach final size.
The method I described earlier with the Dremel will work but if you really don't understand how and why it will work, get someone to grind it for you. No matter which method you try, they are all somewhat dangerous.
Think Safe!!!
