deep hole tapping in SS 316 L

milindiliz · Sep 25, 2006

Dear All,
This is my first post in this forum, so please forgive any inadvertant mistakes...

we have a SS 316L ( hardness RC 33) tube with ID approx 6.8 mm and O.D. about 12.7 mm ( ~0.5"). I need to tap M8 threads internally to a depth of 130 mm (min 5") and a maximum of 230 mm ( approx 9")
THe threads have to be precision threads.
Queries:
1)is it better to use a cutting tap or a Roll / Form tap
2)should the tap be cannulated and have option of forcing lubricant/ tapping oil under pressure?
3) what sort of machine is ideally suited for this job?

Do note that we have spent a long time trying to get taps that are this long--folks at Emuge and Sandvik declined!

I am a little new to this & would be very grateful for any pointers, tips and pearls from the experts.
thanks
milindiliz

mmachining · Sep 25, 2006

If it were me I guess I would try to tap using a tap peck cycle. It sounds funny but if done right in a macro you can tap to any depth you want to using pechs like drilling. The only thing you ne to do is make sure you can program
the spindle to start at the same deg every time to match the lead thread in the part and the tap.
Also we us rigid tapping w/thru spindle coolant.
The taps we get we edm the center out for thru spindle coolant. Just my 2 cents..

Ox · Sep 25, 2006

What denotes a "precision" thread?

Think Snow Eh!
Ox

milindiliz · Sep 26, 2006

Thanks for your replies folks.

dear mmachining: pls be kind enough to elaborate on tap peck cycle--does it have to be done on a blind tube or can it be done on a thru tube ?
on a M8 tap what is the max dia of the hole that can be made on EDM for coolant without weakening the tap? ( it being about 150mm long --6")
thanks lots, for all your tips.

dear ox:the "precision" thread refers to the fact that this is to be a part of a mechanism in which there is a smaller threaded part which will travel down these internal threads in the tube--without jamming etc.
which SNOW you would recommend? place where we are working has an old horizontal CNC lathe and we hope to use it on this. the max length of this job will be 12 to 13 inches and threading size will be M8 max.
thank you all so much. I am really a novice and appreciate all your inputs,
milindiliz

Ox · Sep 26, 2006

Ifyou are cutting threads - you don't wunna run it horizontally!

Sounds like quite the challanging job for a beginner!

Think Snow Eh!
Ox

milindiliz · Sep 26, 2006

you kind of got me there!. Yes, it is a challenging job allright. I think we may be biting off more than we can chew

. We are absolutely new to all of this.
We have an old MASCH CNC lathe (horiz)with the tapping attachment with a SAGOR controller with a spindle speed of 4000 rpm. Are you saying that a horiz machine is an absolute no no?
OK, then I will start looking for a Snow or something similar.
thanks millions
milindiliz

Dave K · Sep 26, 2006

OK, then I will start looking for a Snow or something similar.

I think you're confusing his sig. line with his answer.

milindiliz · Sep 27, 2006

Oops!
Is that my first blunder or have there been more so far....?
milindpix

mmachining · Sep 27, 2006

milindiliz, blind or thru. I would go 2mm all you want is no chips and to cut down on heat thru the hole tap from top to bottom.

milindiliz · Oct 2, 2006

Dear mmachining,
edm worked for us. went to 1mm. Now need to figure how to hold the job/workpiece.what would be the ideal machine to do the tapping on? the length of the tube is about 210 mm (8")minimum.
thanks for all your tips & help
milindiliz

alphonso · Oct 2, 2006

You want extension taps with reduced shanks. These guys should be able to help out.

Rieff & Nestor

http://www.rntap.com/

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