Boring a flat bottom hole

Jonathans said:
Thanks. I'll look into getting a boring bar for the mill. I'll try the tap guide method. Do you think it possible to drill the tap shank to insert a 1/2" rod for mounting in the mill chuck, or will it be too hard?
I also thought it a good idea to run a standard tap prior to the bottoming tap, but at 1.5" these baby's get spendy!
The plate I'm boring and threading goes onto my forging press. I could through bore it and forget the blind hole altogether, but then my problem becomes how to tighten the plate to the hyd rod. The plate is 1" thick 6x6". No way to use a setscrew
Click to expand...
Maybe I'm reading this wrong but is the only reason for the blind hole to jam the thread at the bottom of the bore to hold the rod tight? If that's the case, turn a shoulder on the shaft to tighten against and thread the hole right thru but one size smaller.
 
I’m agreeing with davidh. That’s a BIG tap! It will take different methods to get the job done. A little spring pointy thing for tap alignment ain’t gonna hold up IMHO. I think you will need a dead center type arrangement nested as close to the quill as possible and then feed the quill as you tap. As for the flat bottom hole. You can set-up a boring head to stop at a preset depth. So as you feed out for the next cut you continue to stop at that preset depth. The finish at the bottom will look kinna phonography but maybe that’s OK?…Good Luck, Dave.
 
Well, this is what I decided to do after so many great suggestions. I will through bore the plate and run the tap all the way through the hole. I'll run some rod from the corners corners of he plate/die holder that will be guided against some uhmw on the supports of the press. This will prevent any twist at all under high pressure, and provide me with good working room.
I'm going to attempt to hand tap the threads with the 1.5" 12 TPI tap I picked up using a guide on the mill. I'll have a friend keep pressure on the tap while I turn it.
 
Why not do it in the lathe with a four-jaw chuck and boring tool. You could also cut the threads instead of tapping them. I didn't read it all, so I may have missed something. But I just don't like hand tapping that big of a tap.
 
image.jpeg image.jpeg image.jpeg I thought I'd do a follow up on this string.
I did hand tap the 1-1/2 12 nf in my 1" plate.
The key was to position the plate and the no move it in the x or y axis until all the process was complete.
I drilled it out progressively to 1-13/64 and then used a Criterion boring tool to bring it right to 1-27/64.
I then mounted a dead center I made in a collet on the mill. There was a factory hole in the top of the tap
And the dead center kept it aligned while I turned the tap with a twisting wrench I had made up from an
Antique wrench. Keeping light pressure on the tap and turning it a quarter turn at a time did the trick.

Needless to say, I decided to abandon the blind hole concept.
 
It looks good, Now let us see it in action on that forging press you mentioned.
 
1 1/2-12 shouldn't be too bad, with the right wrench. I have done some 1 3/4-5 that was downright hostile though. I don't relish having to do any more of them now, especially with a damaged back.

I probably would have just made a jam nut for it to lock it in place.
 
Well, at long last I got her done. I think The next dies I make will be thicker to allow for greater visibility.
These should do the trick for setting a weld on a Damascus stack and drawing it out.

Here's the press next to its brother
image.jpeg image.jpeg image.jpeg image.jpeg
View of the 1.5" tapped hole threaded onto the ram shaft. It's on tight to the shoulder and secured from unthreading with a set screw.
 
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