Single point threading

[MattM]

Here is a threading method an old time machinist taught me:

1. Lock in the thread dial at the appropriate number and leave it locked in until the thread is complete.

2. Take a few cuts using the cross slide.

3. At the end of each cut stop the lathe and zero the DRO in X.

4. Bring the cross out a few thousands and put the lathe in reverse.

5. Run the carriage back to the start of the thread.

6. Bring the X back to zero and crank in about .005.

7. Repeat for a few passes then switch to using the compound until the thread is complete.

The nice thing about this method is that it completely eliminates the tedious task of engaging and dis-engaging the lead screw. I use my Monarch 10EE running a carbide threading insert and Viper's Venom for lube. I am producing some excellent threads in the 20-30 TPI range. Haven't tried it on coarse threads but it should work just as well. Best thing about it is not having to deal with the thread dial on each pass.

 

[Norseman C.B.]

I have used carbide tooling for threading for many years and have
found that proper grinding and setup of the tooling is the key for success, no matter what cutting tool is used ........My $ .02

 

[Highsider]

From the before and after pictures of your threads, it looks like your problem is mostly that your compound is not truly set at anywhere near 30 Deg. from the cross slide. As mentioned by others, many hobby lathes are not marked in reference to the cross feed angle and you may have to set your compound using an angle finder accurately set at 30 Deg. and then make a new reference mark lined up with 30 Deg. Then always use a 29-1/2 Deg. setting for 60 Deg. threads

Your after pic, however reveals another problem with the finish you're getting. If you set the tip of your tool (accurately) to the centerline of the work piece and use a good cutting fluid/oil, on the work, your threads should come out shiny. The very tops of the threads might be a bit rough, but that is easily rectified by a short filing job after the fit of the thread passes muster.

I have single pointed 60 degree screw threads in an industrial machine shop for 40 years, in materials from Bronzes through all grades of Machineable steels to Aluminums and exotic alloys like the titanium's, using any cutting tool material from HHS through coated carbides and ceramics, to diamond faced tooling and .

 

[Downunder Bob]

When I was learning machine shop, I was taught, in part, by a bunch of guys that were making chips as early as just before the turn of the century. In their day, the material of choice was hot rolled steel and it WAS STRINGY. The technique was developed to grind the threading tool such that it cut on the leading edge only and sent the chip out of and away from the generated thread.... hence the use of the compound rest and the sainted and inviolable 29.5° setting. They were highly amused that the technique was applied to everything, rather than the task that it was specifically adapted to serve... They simply never used the compound to thread anything that would generate a non-destructive chip. (And, today, neither do I.)

When carbide tools came into wide acceptance, we found that the tips of those tools would fail using the compound rest. The carbide was simply not ground to accept a side load. So, abandoning the notion of the sanctity of the compound rest, threading was accomplished using the crossfeed, only, and the problem went away.

I realize that my position is anathema on this matter, but I was taught as much WHY as HOW and it has served me well. I believe that threading using the compound is so sacred, today, simply because it got a LOT more "press coverage."

My 2¢

I think what you are saying was quite valid in the early days of carbide tooling, but the new ones today that are specifically made for thread cutting don't seem to mind being used either way. BTW I find that using cross slide feed on small fine threads is ok , but much prefer compound set at correct angle for coarser deeper threads. Also don't forget 27deg for british threads.

 

[jamby]

It's been a long time since I stood at a w/s 32 nc turret lathe and cut threads but I seem to remember that the thread cycle feed in a 29.5 and the finish pass was a tool offset that went in normal to the compound. But the machine had no compound. I just rotated the insert to a fresh edge before finishing and used that to rough the next thread after backing off the offset. They usually repeated within .002 and were checked with a go/no-go snap thread gage. Most were 4.00 + in dia.

Jim

edit: funny how it makes sense when you write it... But the final cut was made straight in (nomal to the cross slide) cutting with both edges.

 

[darkzero]

Some great info here...thanks to all on this site..

One of the things about threading and feeding in with the compound that seems non-intuitive is that while we require that each pass be in perfect registration with the last, by feeding in with the compound set at an angle we are moving the tool in 2 directions (in relation to the work)... i.e. at 29 degrees feeding in 10 thousands results in the tool moving inward approx 8.746 thou and to the left 1.296 thou.
Which means our new starting point is not the same...

rich

Yes the starting point of the cutting tip will not always be the same when feeding with the compound but the start of the thread would still be the same. Feeding at just under 30° is doing most of the cutting on the left side of the cutter (talking external threads here, feeding right to left). Now the end of the thread will advance more to the left as you cut the thread. Most guys machine in a thread relief & as long as it's wide enough it won't matter. The left shoulder of that thread relief is what you measure thread length to when critical.

But there's times where you don't need to machine a thread relief which I sometimes do. If you need the thread to be a specific length when feeding in with the compound, it's easy to do. Someone posted a video earlier by Joe Pie & the method he shows will take care of that. I do it a different way but the result is the same. One example is when I need to make a short thread in a blind hole like for a cap. I prefer to have as much thread as I can get since the threads are short but I need to know how close I am to the bottom of that hole. If you don't account for that when feeding with the compound you'll get into trouble.

I like the 29.5 degree compound method. I have enough trouble remembering to return the cross slide to zero for the next pass, let alone trying to remember a different number to return it to for each pass with the plunge method.

Tom

Same here, kind of. When using the compound to feed, I don't have to bother remembering or writing down what to move the cross slide back to, just return to zero. I was also taught to set the cross slide handle at the 9:00 position for zero. This makes it really easy to not screw up when backing the tool out on the end of a pass, simply just push down on the handle to back the cross slide out, quick, easy, no thinking. Now the 9:00 position would be for external threads & 3:00 for internal threads. But since I thread internal threads with my tool upside down, I use the cross slide handle 9:00 & compound slide at 5:00 just like I would for external threads.

With modern tooling, as mentioned, you don't need to feed with the compound on fine threads, soft materials, or on a rigid lathe. But if you cut very coarse threads, thread hard materials, or don't have a rigid lathe, the compound is your friend. I rarely thread really coarse threads, but I still thread using the compound method for the reasons I mentioned earlier & because that's how I was taught. I have always done it that way, it's what I'm used to, so it's easier for me. It's also good practice for when you do need to use the compound for feeding.

 

[pstemari]

That's all good advice.

I'm not certain which carbide tools have problems with loading. I've been using 16 ER full-profile laydown inserts and they make gorgeous threads using the compound at 29 degrees.. My biggest problem is hitting the half nut lever consistently.

 

[MattM]

That's all good advice.

I'm not certain which carbide tools have problems with loading. I've been using 16 ER full-profile laydown inserts and they make gorgeous threads using the compound at 29 degrees.. My biggest problem is hitting the half nut lever consistently.

View attachment 228459

That's why I like leaving the half nuts engaged for the entire threading operation. See my comments above.

 

[Doubleeboy]

Matt, If you leave the half nut engaged, you might benefit from Joe P threading videos on you tube. He shows a way to take the drama out of engaging the half nut. 10EE has to be about the easiest lathe out there to engage half nut, check out Joes videos.

 

[pstemari]

That's why I like leaving the half nuts engaged for the entire threading operation. See my comments above.

In my case, the issue arises when threading up to a shoulder. The upside-down trick doesn't work with that sort of tool—you'd need a left-hand tool with a reverse helix shim.

Stopping the entire lathe or cranking out the cross slide is much slower than hitting the half-nut lever. You'd have to crank the cross-slide out at least two or three turns to avoid crashing into the shoulder, and the various retraction mechanisms don't have enough travel.

The one thing that does work reliably is the Hardinge-style single point dog clutch, but that's not something you can readily retrofit. You'd have to splice it into the gear train between the spindle and the threading gear box.

The Hardinge mechanism can be triggered by a carriage stop, and allows you to reverse the carriage and run it back without releasing the halfnuts or losing sync with the spindle.

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