Modified flank Inside threading away from the chuck question

[WobblyHand]

I made (and have used) a tool to cut inside threads. It can be either right or left handed by changing the HSS tool bit. Have cut threads with the plunge method and they came out ok, but that was in 6061. I need to thread 4140 and was thinking of using the compound and modified flank cutting. I know how to do this for external threading, but get confused when thinking about internal threading. Since everyone's lathe is a little different, let's use 29.5 degrees (rather than 60.5) as the reference. Is it the same set up as external threading? (Except adjusting the compound towards the back.) I will be cutting RH threads in reverse with a LH tool away from the chuck.

 

[benmychree]

So far as the angle of the compound is concerned, why not set it for 30 degrees off the centerline angle of the cross slide, I and everyone I have known in the trade has done so, so far as where the compound dial and crank faces, I have always swung it to the left front and have not had problems with it interfering with the chuck.

 

[3strucking]

Cut on the backside and you can leave the compound where its at.

 

[benmychree]

Cut on the backside and you can leave the compound where its at.

You want the subsequent chips to be driven at the front of the cut, not the back side, hence the compound to the left.

 

[WobblyHand]

Perhaps I need to rephrase the question. I think my question is Given that the compound is like \ and that angle is 29.5* from perpendicular to the spindle axis. And is twisted away from the chuck. Or @benmychree are you saying the compound is like / 29.5* towards the chuck? Guess it is the angle that is confusing.

Is the the correct order of doing things?
1. Insert bar into bore at correct depth. Set cross-slide origin.
2. Advance the compound into work by correct amount
3. Cut thread (making sure you are on the correct mark)
4. Back out cross-slide for thread clearance
5. Insert bar into bore at correct depth
6. Put back cross-slide to origin
6. Advance compound into work by whatever the correct amount is for this dept
7. Cut thread (making sure you are on the correct mark)
8. Repeat until done

 

[3strucking]

I have been internal threading that way using a left hand bar with a negative anvil installed. I have not had any problems as of yet. I always welcome advice as I am self taught.

 

[WobblyHand]

You want the subsequent chips to be driven at the front of the cut, not the back side, hence the compound to the left.

Guess, I'm a little slow on the uptake. Compound on the left means the crank handle is towards the chuck? Like / where the bottom is the crank and the top is the spindle axis? Oh, this is so hard in words. I'm going to make a sketch. Hope this is what you meant? Please confirm.

 

[benmychree]

Perhaps I need to rephrase the question. I think my question is Given that the compound is like \ and that angle is 29.5* from perpendicular to the spindle axis. And is twisted away from the chuck. Or @benmychree are you saying the compound is like / 29.5* towards the chuck? Guess it is the angle that is confusing.

Is the the correct order of doing things?
1. Insert bar into bore at correct depth. Set cross-slide origin.
2. Advance the compound into work by correct amount
3. Cut thread (making sure you are on the correct mark)
4. Back out cross-slide for thread clearance
5. Insert bar into bore at correct depth
6. Put back cross-slide to origin
6. Advance compound into work by whatever the correct amount is for this dept
7. Cut thread (making sure you are on the correct mark)
8. Repeat until done

Yes, I am saying that the compound is swung to the left (towards the chuck) i also said that in the 57 yeas that I have been working at the machinist trade, I have never seen any journeyman machinist use to plus or minus half degree setting of the compound; I was taught in school by a quite competent instructor who had apprenticed at the local navy yard and taught in their apprentice school that the proper angle was 30 degrees, and in my subsequent apprenticeship and journeyman status, everyone in the shop used 30 degrees for 60 degree vee threads.

 

[benmychree]

Guess, I'm a little slow on the uptake. Compound on the left means the crank handle is towards the chuck? Like / where the bottom is the crank and the top is the spindle axis? Oh, this is so hard in words. I'm going to make a sketch. Hope this is what you meant? Please confirm.View attachment 380454

In a word, yes!

 

[WobblyHand]

Yes, I am saying that the compound is swung to the left (towards the chuck) i also said that in the 57 yeas that I have been working at the machinist trade, I have never seen any journeyman machinist use to plus or minus half degree setting of the compound; I was taught in school by a quite competent instructor who had apprenticed at the local navy yard and taught in their apprentice school that the proper angle was 30 degrees, and in my subsequent apprenticeship and journeyman status, everyone in the shop used 30 degrees for 60 degree vee threads.

Thanks for confirming the swing to the chuck. Now I know what to do.

Point well taken on the 1/2 degree. To be very honest, I couldn't measure that 1/2 degree with any real certainty with the protractor I have. The protractor is neither large enough or clamps well enough for me to believe it to sub-degrees. For that matter, I don't have a great way of checking it. I'm afraid I was just parroting the "magic" number. Didn't mean to irritate you, especially over 1/2 degree. Peace.

I want to thank you for being on HM and your being willing to help out beginners with little or no experience. Your efforts to help out is greatly appreciated.