NPT tap driver design

[aaron p]

I drew these up for a 1" NPT bridgeport hand-tap driver. The 1/2" side hole is for a handle. Made from 17-4PH. What are yalls thoughs on this design, good or bad?

[Superman]

---Move the 1/2" hole further to the back, this allows for tapping near higher features and keeps knuckles from being skinned.

---C'drill the end, allows for use in a manual lathe with tailstock and in a mill with a spring-loaded pointer to hold true to hole.

---Small grub screw thru wall to hold tap in, little gash on square drive would be needed.

[Geof]

Have you ever hand tapped 1" NPT?

I doubt very much that a 1/2" bar through your cross hole will be strong enough for the torque needed. Also the OD of the head may be a bit small and the material about the overcut corners of the pocket too thin, these will very likely split.

[aaron p]

My concern is that if I make the bar a 3/4", the walls will be too thin around the hand bar. I have tapped 1" NPT and its a whore. I guess I could make it a bigger O/D at the head AND at the hole, then neck it down for the collet size. Needs mo' heavy duty!

[aaron p]

heres revision 2. Made the O/D 1-5/8" and put a 3/4" handle hole in it. And noted a #5 center drill .125" deep.



The tap I have here, the square measured .835", so I made the square .840" with a .002" tollerance. If I put screws on the flats, it might put the tap off center, id rather have a slightly "floating" square so it can follow the drilled hole. Does this make sense?
12" long handle should work.

[Geof]

That's more like it, and if you can turn a 1" NPT tap with only a 12" lever I am not going to arm wrestle with you.

[aaron p]

lol. I might make it 18". Its just money right?

[youngjim]

If you start with square stock and put the socket 45 degrees to it you'd have a little more material around the corners.

Jim

[307startup]

Originally Posted by youngjim If you start with square stock and put the socket 45 degrees to it you'd have a little more material around the corners. Jim

Incorrect. If he started with a piece of square stock that has the same width as a piece of round material in diameter, the amount of material near the corners of the internal square would be the same, with the internal square being turned 45*. Only by going to an appreciably larger width piece of square stock would he gain any material there. He would actually have more material at the corners by making the internal square concentric and parallel with the stock.

Don't believe me? Draw a 1"x1" square. Draw lines diagonally from the corners. Set a compass to a 1" diameter (0.5" radius). Put the point where the lines intersect in the square and draw your circle. Same amount of materials in the corner!

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[youngjim]

You are of course correct.

Jim

[aaron p]

Round bar is cheaper than square, and easier to keep centered.

[fatal-exception]

Wow, that's a flashback to high school, which was a long time ago.

DesignCAD right?