Chasing I.D. threads in a blind bore...

[toolznthings]

Nothing like chasing I.D. threads on the lathe into a blind end bore. Especially where the bore is either small or larger, but deep into the parts. Here, I'm chasing a 1 3/8-16 thread into a blind bore about 1 1/4" deep. There is a thread undercut to run the thread into, but at the bottom of the bore.



The easy way to do this, even if you can see what you are doing is a simple pointer attached to the lathe carriage. It this case mine mounts when needed to the way wiper.

Position the tool at the point in the bore where you need to dis-engage the half nuts and apply a piece of tape to the ways and mark the tape at the pointer.



Now the only thing you need to watch is the pointer lining up with the mark.
Takes the fun out of running into the shoulder !

 

[10K Pete]

Very nice. Beats the heck out of a piece of tape on the boring bar and
eyeballing it across the face of the part!:wall:

Pete

 

[ChrisLister]

Nice idee. Thx

 

[toolznthings]

Very nice. Beats the heck out of a piece of tape on the boring bar and
eyeballing it across the face of the part!:wall:

Pete

Hi,
I've done that ,too ! No luck. ;D

 

[Nick Hulme]

There's always the option of running the lathe in reverse and using a left hand tool to start at the bottom and cut out into free air with no worrying about collisions ;-)

- Nick

 

[Ken I]

There's always the option of running the lathe in reverse and using a left hand tool to start at the bottom and cut out into free air with no worrying about collisions ;-)

- Nick

I always screw cut in reverse in a bore or to a shoulder - there is no way to muck it up - engage stationary (in undercut) - turn by hand to make sure you haven't crossed it - engage and go like a bat out of hell - there is no downside and you can screw cut at much more appropriate speeds.

Also I have screwed up more threads than I care to remember on mis-engaging the half nuts (either wrong division or nuts did not fully close creating an error - especially with metric threads off imperial screws and vice versa) - with this method I never disengage the nuts until the job is finished - I run the machine backwards and forwards to get the tool into position - a little time consuming - but absolutely guaranteed no catastrophes (well almost).

You don't need left hand tooling - it is still right handed - put the tool in upside down (you might have a toolpost height problem though - it still has to be on centre). In a bore you work on the back (away) side of the bore.

Regards,
Ken

 

[Nick Hulme]

You don't need left hand tooling - it is still right handed - put the tool in upside down (you might have a toolpost height problem though - it still has to be on centre). In a bore you work on the back (away) side of the bore.

Regards,
Ken

If you put your right hand tool upside down and work on the far side (back) of the bore you still have to have the lathe turning in the same direction as you do with the tool the right way up and working on the near side (front) of the bore.

This being the case, moving the tool in (towards the head-stock) whilst cutting will yield a right hand thread, if you start at the bottom of the bore and cut outward (away from the headstock) you will generate a left hand thread.

To generate a right hand thread whilst cutting outwards from the bottom of the bore (away from the head-stock) you need to cut with reversed rotation, this requires left hand tooling.

- Nick

 

[Ken I]

Nick,
I think we may be talking at cross purposes - I was referring to single point tools.
However RH threads are cut with RH tips and vice versa - the rotation direction doesn't change anything.
However there is a problem with internal threading bars - you can't turn them over the way you would turn over an external tool - if you did the butt end of the bar would be leading.
To be perfectly honest I have never seen an off the shelf internal threading holder that can be used to internally screw cut a RH thread out.
LH thread boring bars normally screw cut out in any case.

In the above image the tool has been turned upside down - you now cut out in reverse with the same tool. (Rotate the image through 180° - it remains the same.)

Internally the exact same thing happens - good luck finding a tipped tool holder though.

And as an afterthought - where the helix angle is incorporated into the tip then internal tips for RH threads will double as LH tips when used externally if you have a suitable holder - and vice versa.
Depends on the configuration - sometimes the helix angle is on the holder and the profile runs square to the tip then you need the correct holder.

Regards,

 

[Nick Hulme]

Ken,
We are definitely talking at cross purposes, the thread is titled Chasing I.D. Threads In A Blind Bore, all my responses are on topic, thus reflecting this and referring to internal threading.

Most manufacturers of internal threading bars make LH and RH bars and inserts, the ones in the photo are a couple of mine, for smaller jobs I have an ISCAR MCGH 06 which takes GIQR and GIQL inserts allowing work in bores down to 8mm,

Regards,
Nick