Sako M-591 barrel thread: 1" 16 tpi

[TRECustom]

Robert, Shortgrass's posts have always been very informative. I haven't seen many of yours, but will watch for them now. My impression is that both of you know what you're doing, just approach it differently. For instance, I also feed with the compound, and keep it set at 30 deg. I stop and try the fit a lot, because I want a very close fitting thread. I also zero the compound dial and the crossfeed dial with the tip of the tool just barely touching the work. I use the crossfeed dial on zero and back it out between passes, then run it back in to zero and advance the compound to cut the next pass. It does only cut on the left flank of the tool though. I know a gunsmith that does it like you do and only feeds the cross slide. He gets excellent results also. My lathe is not a toolroom lathe, and I think I get better thread depth control by using the compound to feed. I don't know that, I just think it. Something that helps me is that quite awhile back, I started recording the number on the compound dial when I finished a thread. So now I have a record of the depth I cut to on different pitch threads, and can start trying for fit well before I reach the number (an average) for that thread pitch. I haven't cut a loose thread since I started doing that. I know that this stuff is kindergarten for both of you, but I'm self taught, and unfortunately a very slow learner, so I pay close attention to people who know what they're doing.

Thanks again to both of you. Tom

 

[shortgrass]

Robert, I only posted my experience to show I'm not new at this. This is the way manual machinists, of my generation, were taught to cut threads with single point tools. My training came from OJT/apprentice type setting. I'll chalk-up the differences in methods to the different schools of thought on different continents.

 

[therifler]

to all those that posted on this subject . all the methods mentioned can and will produce a good thread . i have used different aproaches to produce threads with very good results . for the most part seems like it is up to the person behind the threading tool. cut my first thread on a south bend 9" lathe then moved up to a 16" LeBlond . not much difference between the two, they were both flat belt drive . just thought i would stroll down memory lane . keep on machining guys thanks for the interesting posts. T.R.

 

[Robert]

Robert, I only posted my experience to show I'm not new at this. This is the way manual machinists, of my generation, were taught to cut threads with single point tools. My training came from OJT/apprentice type setting. I'll chalk-up the differences in methods to the different schools of thought on different continents.

Shortgrass,

I understand your method, and respect you technical options on many subjects. No need to start arguments on points we should only consider the finals, whatever the individual methodologies and schools...

As Tom explaned his method, let me explain the one usually teached here: I will however be as short as possible, as this has lasted enough I think.

-The compound slide method was considered here as a production method. 30°, never less, as it may create uncontrolled problems in finishing the external thread face. This often appeared and was even shown in schools demos.

-The usual method for one-only operation is to use the cross slide and the compound set lenghtwise. The cross slide is used to cut the threads up to the specified depth (core diameter), moving at the same time the compound slide just to not touch the external face. (.57735 of 1/2 the penetration to go up to the last detail!!).

When the core diameter is reached, finishing cuts are made, first moving the compound slightly rearwards to finish properly the left profile, then forward to create the Norm (UN = 010825xP) flat at the root of the thread. Adjustment of the fit is done at this stage, although controls should have started earlier already…

IMHO, maintaining the core diameter as it is fixed in the profile is important as:

-It contributes to centering the assembly.

-Making the threads too deep would reduce the core section of the shank. This might be minimal, but maximal section counts h at his point.

-If a profile has been normalized, this was for good reasons, and maintining ptofiles and tolerances is a evidence of shill…

BTW; this was learned with dials slides, on a Le Blond lathe with imperial leadescrews. This is the hard way we were teached to machine on metrics … But the last I used was a Boxford with DROs..thanks to that marvellous aceessory making life and accuracy so easy!!!..and forgtting about conversions..

I have even once came across a lathe having L/H leadescrews…try to cut a thread on a lathe having reverse handles rotations?? A trick used in exams..
R.G.C