Need Help!- Deep and precise Hole, Please, need an expert on this...

[CNCenforced]

I have this part of Stainless 303, and I've managed to machine all the OD's on a CNC lathe (Diameter surrounding the hole is 3"), now the last operation is to make a hole of 4" deep and 1" in Diameter; tolerances are +-.001.

My problem is not about how to clamp it or hold it on to something.

It's only one part and I have no spare stock or extra parts for that matter, in other words, I can't try out different tools and approaches.

What's the best approach on making this particular hole that it's so deep, precise, yet in need of a nice surface finish????

I was thinking about roughing it out with a long drill that is less than 1" in diameter and then using a reamer to finish it off, but I need a nice surface finish, and a boring bar is out of the question (vibration, taperness even if it is a carbide one).

Should I use 2 reamers? Like one of .998 in Diameter and the last one at 1" Dia?

Hope some one who is been here in this situation can help.

Thanks in advance to you all!!

[zsinclair]

Ive done several lathe parts similar to what your describing. The best way I have found is to use a boring bar with minimal stickout. Make several passes starting .005 under and work out in .001 increments. You can do spring passes on you 1" finish. Spring passes should be no bigger than .999

[CNCenforced]

Thank you so much for the info!!

Something that I forgot to mention was: The hole is a blind hole, no brake through option; so, my biggest concerns are the finish quality of the surface and the diameter of 1" to be straight all the way in.

Once again,

Thank you so much for your reply!!

[Delw]

to add to what zsinclair said.

ccmt with a .004 or .008 rad on a ceratip insert run the SFM half-3/4 of what is called out or less.

A 1" hole running a 5/8 boring bar with a 3" cut length is NO Problem try running 5-7 inches a TG insert will also work, CNMGS trigons I wouldnt tough for that in that size of a bore. if you can get a 3/4" bar in there all the better.

Make sure your Bar is a tad above center, this way if it attempts to chatter when the bar flex's it wont dig in.

the hole key is SLOW and Sharp positive insert

[CNCenforced]

Go it!!

I was able to get this hole done with-out scrapping the part.

The key was to rough it out with a smaller drill and then bore/finish (carbide boring bar) the hole with small passes at .005 and about 3 spring passes to finish it off.

I was very skeptical at first about using a boring bar due to the length of the hole, but with some help (here at CNCzone) I was able to do it.

Many thanks to zsinclair and delw!!

I really appreciate the comments and help !!