Is it considered impolite, or just gauche to turn the cutting tool upside down, put the lathe drive into reverse and thread from the barrel shoulder to the muzzle to avoid needing a clearance cut?

Every bit of thread contact helps,etc.

Opinions appreciated.

That's how I do it on my little 9x20 since its slowest speed is still to fast to thread
up to a shoulder.

lawndart mostly you cannot see what the tool is doing. if you practice a few blanks and can cut a good thread like that it is no big deal

Can't those small lathes be slowed down by changing drive pulleys?

Sometimes you can replace a 3450 rpm motor with a 1725 rpm one. I've found that many foreign machines have 3450 rpm motors and so they run too fast.
Regards, Joe

quote:

Originally posted by lawndart:
Is it considered impolite, or just gauche to turn the cutting tool upside down, put the lathe drive into reverse and thread from the barrel shoulder to the muzzle to avoid needing a clearance cut?

Every bit of thread contact helps,etc.

Opinions appreciated.

Never ran a CNC lathe then? Upside down gets rid of the chips

quote:

Originally posted by lawndart:
Is it considered impolite, or just gauche to turn the cutting tool upside down, put the lathe drive into reverse and thread from the barrel shoulder to the muzzle to avoid needing a clearance cut?

Every bit of thread contact helps,etc.

Opinions appreciated.

John,

You would still have to have a groove of some sort doing it that way. You have to be able to advance the cutter with each pass to the correct starting depth before engaging the half nut as it is so you are much better off threading in the traditional manner where you can advance the cutter away from the spinning barrel.

I use a 1" travel, dial indicator attached to the bed to let me know when the carriage and tool are at my predetermined point of withdrawal. I set the indicator so the needle has to make one complete circle before I have to withdraw the cutter from the groove. This one free spin allows me to prepare to disengage the half nut and retract the cutter so as not to crash the cutter into the shoulder. When the needle hits zero, disengage the half nut, and quickly withdraw the cutter.

My reflexes are a bit off from what they were 30 something years ago so I keep my foot near the brake, just in case. The dial comes in real handy when the area is covered with cutting oil and chips and I cannot see exactly where the cutter is.

Once the half-nut is engaged you never take it out is how you always enter the same point.

I have cut threads just a couple thou-at-a-time without ever turning the machine power on. I just turn the chuck manualy.....but I've worked with many talented old-school toolmakers in the past 26 years and took notice every chance I could. I am now called old-school by the new guys.

quote:

Originally posted by ted thorn:
Once the half-nut is engaged you never take it out is how you always enter the same point.

I have cut threads just a couple thou-at-a-time without ever turning the machine power on. I just turn the chuck manualy....

That would be okay if you were charging by the hour.

That is a perfectly acceptable technique. I've used it many times and for the same reasons.

The bad part of threading in reverse with an upside down tool is if your machine has a screw on chuck. It may just unscrew on you.

Oh and an FYI set your compound to one full degree less then the cutter angle. If you are cutting 60 degree threads set it at 29 degrees if cutting 55 degree threads set it at 27.5 degrees
This allows a little bit of side clearance on the tool and will prevent tearing of the material.

Have to agree with Westpac here. It's no fun watching the thread dial and cross slide dial at the same time with out a run out groove.
Try speeding up the rpm's. With carbide tooling you should be using about 300 rpm's for a 10 pitch. 500 rpm's for 16 pitch.
Once you get the hang of it you can kiss the shoulder every time with out a run out groove or crashing.

quote:

Originally posted by kcstott:

Oh and an FYI set your compound to one full degree less then the cutter angle. If you are cutting 60 degree threads set it at 29 degrees if cutting 55 degree threads set it at 27.5 degrees
This allows a little bit of side clearance on the tool and will prevent tearing of the material.

I am intrigued with what you are saying here but am not sure I am following. Can you elaborate a little bit. Are you using the compound to advance the tool at an angle?

It's how I was taught also 29 deg on the compound rest on 60 deg threads....fish tail anyone?

I was taught to come in at 29 degrees also. I was also taught with Rex 95. Actually, the China version of Rex 95.
For the last 20 years I've come straight in on a manual machine. HSS tools couldn't take coming straight in. Carbide no problem.
When I opened my own shop I went with topping off inserts. A little more investment up front, but they last a lot longer and do a better job.

quote:

Originally posted by J.D.Steele:
Sometimes you can replace a 3450 rpm motor with a 1725 rpm one. I've found that many foreign machines have 3450 rpm motors and so they run too fast.
Regards, Joe

That's why I put a 2 hp DC motor with a speed control on my little pos. World of difference.
Don

quote:

Originally posted by Brad Hinn:

quote:

Originally posted by kcstott:

Oh and an FYI set your compound to one full degree less then the cutter angle. If you are cutting 60 degree threads set it at 29 degrees if cutting 55 degree threads set it at 27.5 degrees
This allows a little bit of side clearance on the tool and will prevent tearing of the material.

I am intrigued with what you are saying here but am not sure I am following. Can you elaborate a little bit. Are you using the compound to advance the tool at an angle?

Yes I'm advancing 90% of the cut with the compound as I was taught in trade school 22 years ago. The reason is if you dial straight in with the cross slide you are cutting on both side of the tool. Set at 29 degrees and dialing in with the compound (Remember the compound is a radius dial not a diameter dial when used like this so dial in half of what you want to take) the tool will have one degree of clearance on the right side of the tool when cutting from right to left. (Right hand threads conventional)
Then when you are approaching your finish diameter you dial in the last two or three thou with the cross slide to clean up.

Leaves a very nice finish.

John, threading away from the headstock with the tool upside down is how I was taught almost 40 years ago and it is how I do 99% of my threading. I set the compound at 29.5 degrees and feed just with the compound. I use my DRO to ensure I start at the same place each time.

I use a dial indicator like Westpac, I can make the thread stop next to a shoulder at the same spot every pass. Takes a little planning and set up but gives professional results, looks much better than a big ole groove, especially on muzzle brake threads. When you are truing up receiver threads the dial indicator method is a must.

Using the compound to advance is the correct textbook method and taught by nearly all skilled tool and die makers. I use 29 1/2 degrees for 60 degree threads and 27 degrees for 55 degree Mauser threads. Feeding straight in with the cross feed gives a rougher finish and creates more heat.

quote:

Originally posted by kcstott:


Yes I'm advancing 90% of the cut with the compound as I was taught in trade school 22 years ago. The reason is if you dial straight in with the cross slide you are cutting on both side of the tool. Set at 29 degrees and dialing in with the compound (Remember the compound is a radius dial not a diameter dial when used like this so dial in half of what you want to take) the tool will have one degree of clearance on the right side of the tool when cutting from right to left. (Right hand threads conventional)
Then when you are approaching your finish diameter you dial in the last two or three thou with the cross slide to clean up.

Leaves a very nice finish.

Interseting I have always gone straight in, but have noticed that sometimes I get some chatter. I will give this a try next time. Thanks for the heads up.

quote:

Originally posted by Brad Hinn:

quote:

Originally posted by kcstott:


Yes I'm advancing 90% of the cut with the compound as I was taught in trade school 22 years ago. The reason is if you dial straight in with the cross slide you are cutting on both side of the tool. Set at 29 degrees and dialing in with the compound (Remember the compound is a radius dial not a diameter dial when used like this so dial in half of what you want to take) the tool will have one degree of clearance on the right side of the tool when cutting from right to left. (Right hand threads conventional)
Then when you are approaching your finish diameter you dial in the last two or three thou with the cross slide to clean up.

Leaves a very nice finish.

Interseting I have always gone straight in, but have noticed that sometimes I get some chatter. I will give this a try next time. Thanks for the heads up.

It chatters because you have to much surface area making contact.

Try cutting a 6" 4 TPI. I did that on a 24X60 Graziano lathe

Now as for the correct angle. Swing the compound so it is pointed straight away from you 90 degrees to the bed ways then swing it to the right 29, 29 1/2, what ever. And only take about .005" depth of cut .010" at the most in the beginning but you'll have to dial it back quick. When I'm finishing up i'm only dialing in .002" on the compound. then finish with .001" increments till I hit the pitch diameter or the nut fits

That is where you want to start. You won't believe the difference.

The groove I cut for relief does not have to be big; it is proportional to the size of thread I'm cutting, and in my opinion gives a clean finished look. Once again we see "there is more than one way to skin a cat."

There's a video on youtube by tubalcain showing threading from the shoulder with the cutter inverted.

I prefer to not cut any relief groove at all on almost all my installations. Rather, instead I remove the first thread in the receiver itself if it's not already removed. I rely on manual dexterity to work the clutch and crossfeed screw simultaneously as the tool approaches the barrel shoulder. Tool is of course ground very short and close to the left edge so as to be able to approach the shoulder as closely as possible before withdrawal. 29.5 or 27 degrees on the compound, advance 0.005" at first and gradually transition down to 0.001" advance with occasional chasing passes.

Not the best method, not the worst method, just another method. One of Paul Simon's 'Fifty Ways...' (grin).

The 'no relief groove' method is not a critical thing except with rifles having very small-dia thread tenons such as the Martini Cadet and various other early lever and single shot rifles. With the Cadet it can be a VERY CRITICAL thing and so it's my invariable practice to leave these tenons full diameter with no relief groove at all, ever, in the CF Cadet.
Regards, Joe

I always cut a relief groove.

And my lathe has a foot break so you zero out your cross slide and whip it out as you jam on the breaks

I never cut a relief groove when threading towards the shoulder. Being able to pull out smoothly and quickly without breaking the tool is a basic machining skill. At 360 RPM and 16 tpi your carriage is not moving very fast.

quote:

Originally posted by rembo:
I never cut a relief groove when threading towards the shoulder. Being able to pull out smoothly and quickly without breaking the tool is a basic machining skill. At 360 RPM and 16 tpi your carriage is not moving very fast.

Is 360 RPM a typo? The tool would be moving toward the shoulder at what I would consider a frightening speed. Cutting 16tpi threads into a shoulder @ 80rpm is as much excitement as I need. Maybe I just need some stronger coffee.

360 is not that fast at 16 TPI but to each his own.

That is pushing it though for a HSS tool.

quote:

Being able to pull out smoothly and quickly without breaking the tool is a basic machining skill.

Maybe in your neck of the woods but not down here. We were taught to cut a relief groove to the minor diameter +5% and 1.5 to 2 threads wide