Barrel threading lathe question

[kawsam62s]

Good evening
When you thread a barrel, normally you use the compound dial to feed in
I watched a video tonight that showed a major name gunsmith feed in with the cross slide to cut threads it seems to work, but why? Or why not? Should you do this in threading.
Thx!

 

[jackieschmidt]

I thread feeding in with the cross slide, whether it’s a 18 tpi on a barrel or. 2 tpi on a 10 inch shaft.

I know it goes against all of norms that are taught in trade schools and books. I know the theory behind using the compound at 29 degrees.

I won’t go into the reasons why I choose to thread this way.. As a Machinist,, that’s just the way I do it.

 

[Doug Beach]

Either way will work. The resulting threads will be indistinguishable, all else being equal. It’s just something to argue with strangers about, not something that matters.

 

[Carl S]

You will put less load on you tennon-muzzel thread using the compound.reducing the chances of 'chatter 'on your thread if your set up isn't very rigid.in the grand scheme of things it doesn't matter which way you do it..do what gives you the best results.

 

[SKWERLZ]

On my smaller lathe I prefer the compound and 29-30 degrees, less tool pressure.
My last thread adjustment is often with the cross slide as that seems to clean up any chatter.

 

[Walt Krafft]

It is important that your tool is perpendicular to the work. If feeding with the compound, it must be at the correct angle. Feeding with the cross slide removes that possible problem. Many high speed threading tools are ground with a top rake angle that require feeding on the angle because they wont cut on the back side.

 

[GenePoole]

I like the "alternate flank cut" on the CNC G76 cycle (like the 29.5° compound cut, but alternates to either side with each pass), but I've yet to figure out how to do that on a manual machine so I just run a single flank cut at 29.5°.

 

[jackieschmidt]

I like the "alternate flank cut" on the CNC G76 cycle (like the 29.5° compound cut, but alternates to either side with each pass), but I've yet to figure out how to do that on a manual machine so I just run a single flank cut at 29.5°.

Gene, when threading really course threads on a big manual, a trick is in the final passes, you hold just a little back pressure on the carriage hand wheel, it takes just enough slack out of the entire lead screw thrust system to allow it to skim the back of the thread. The next pass, you do it as usual, and so on.

it takes a little learning, but works amazingly well and keeps the load off of tool for the final passes when cutting threads with a pitch of 4 tpi and courser.

This is a 4 tpi on a 6” diameter prop thread.

 

[kawsam62s]

Thx all!!

 

[boltfluter]

Lately I have just been plunging in with the cross slide, but have used both methods. Jackie seems to have some good tricks for this. All that really matters is that you end up with a nice thread!
Paul

 

[paperpuncher]

Done it both ways with good results. I prefer the compound because I can set my crosslide to 0 and advance the tool with the compound. This way after a pass I when I retract the tool I dont have to remember where the crosslide was set and add to that for the next pass. I could just reset the crosslide to 0 after each pass I guess

 

[Alex Wheeler]

Im my mind the cross slide makes sense because it loads the gears and screw. Think about what happens when internal threading. Straight in is probably not an issue on heavier machines. I just wonder about thread helix variation on light machines. The thread pushing the the carriage if you will.

 

[WSnyder]

On my smaller lathe (Rockwell) I compound feed just because the Rockwell has a selectable zero hard stop on the cross side for threading. When you pull the cross out at the end of the thread and you move back over to restart you can crank the cross slide back into the stop never having to look at the dial to zero or have to remember the last number of your feed. If I didn’t have that on that lathe I might do it differently.

 

[LVLAaron]

zero hard stop on the cross side for threading.

That's a nice feature.

 

[SKWERLZ]

That's a nice feature.

I thread an a hardinge HLV-h
That easily set stop reality spoils you.
I can easily thread one handed and sip coffee at the same time.

 

[ridgeway]

The purpose of feeding with compound is less tool pressure on the tool. It cuts on one side of tool. When close to pitch diameter, simply feed in on crossfeed for the last couple passes.

 

[ridgeway]

I guess to answer the question, crossfeed or compound. It would depend on the tooling/geometry. Straight single point 60° tool, feed in on compound. Full profile lay down tools, straight in using crossslide. Depending on geometry, full profile can be fed in at 30° no problems. I don't care much for laydown tools on lighter manual machines. Either way can make good threads.

 

[Randfal]

Only using the cross slide: because a lot of gunsmiths are not machinists.
Using the compound: Better machining practice performed by better machinists. I've been around tons of "gunsmiths" in 35 years of shooting and it wasn't until just a few years ago that I ever met one that even knew what Pitch Diameter was or even how to measure it. When suppressors became all the rage, I spent several years re-threading the area gunsmiths's muzzle brake threads because nobody could get their suppressors to thread on. They were all oversized or looked like someone tried to use a dull die. It's horrifying to see what some people hide under a muzzle brake lol. There are good and bad "gunsmiths" and there are good and bad machinists. Hopefully you all find a good gunsmith that is also a good machinist; that's the hard part.

 

[jackieschmidt]

Well, I am a Machinist, I am not a Gunsmith.

I prefer threading in with the cross slide.

 

[skeeljc]

I use the compound at 29.5 degrees. I run at 60 rpm and use a dial indicator on the carriage to pull out with the cross slide at the same carriage reading each time. That way I do not end up with a groove at the end of the thread.