FACT CHECK: Threading Myth BUSTED !! You'll Find This Interesting...... 

Realistically the 30 degree feed trick does one thing, it reduces the minimum force required to cut a thread, for a big machine it may not matter, but for a smaller machine, or a less rigid part, it can make a difference.

To those wondering about the origin of the myth: Cutting using only the cross-slide instead of the compound set at 30 degrees (with a full 60 degree tip, of course) will cause the cutting action on both sides of the thread profile to make chips that collapse in towards each other on top of the tool as they are formed, which can tangle and jam and chatter. Cutting on one side of the thread OF COURSE will shear off a tiny bit off of the other side equal to the depth of cut, just like any other facing or turning does, but it lets the chips fly free and unhindered. The final light cut at full depth using the cross-slide will cut on both sides to clean up the small amount of stair-stepping you get if the compound is set 1 degree over* 30 (which was preventing you from constantly dragging the whole "unused" edge on your work while hogging the thread). *I originally said 1 degree under 30 leaves steps, which was incorrect.

I don't know if this is still a myth, but I was taught to step using the compound because the cutting tool is more prone to chatter if both sides of the tool are equally loaded. Cutting primarily with the leading edge puts force against the tool holder in the ordinary location and direction.

Interesting demonstration. I never even knew threading was a complicated thing until I got on the internet.

Is this a myth? I've never thought that anyone was literally saying they right side of the tool doesn't cut even a little tiny bit, just that *most* of the cutting happens on the left

Joe, firstly let me be clear that I have great respect for your immense skill and experience and I have learned so much from your excellent videos. So, with the greatest respect I think the issue here is that the original 'old school' teaching has been mis- interpreted and mis-quoted by generations of later day armchair experts. The old school technique was to set the compound at 'slightly less' than the thread angle so that the tool cut 'mainly' on one side, inorder to reduce chatter on small, primitive, non rigid, hobby lathes when cutting coarse threads . There was no mention of the tool not cutting at all one side. Somewhere over the passage of time 'slightly less' became the (incorrect) 'rule' that you had to use exactly 29.5 degrees (for a 60 degree thread). From this, it was a small step, to develop the incorrect belief (myth) that the tool didn't cut at all on one side. So, while you are totally correct to debunk the myth about only one side of the tool cutting if the compound is set at 30 degrees I don't think that undermines the value of the offset compound technique for small hobby lathes trying to cut coarse threads, but it's important that newbie lathe operators realise that '29.5 degrees'' isn't 'gospel' , it really means a few degrees less than 30. Regards Paul in NZ

"Only the left side cuts" That is true up to a point...

GASP Joe! you threaded towards the chuck!!! Nice demonstration, Pierre taught me to thread straight in plunge cutting and it has not failed me yet. the only time i have used the compound is to pick up an existing thread.

I never heard that the back side of the tool didn't cut but just that you wanted the leading edge to be performing most of the cut and the trailing edge to be performing a minimal cut. This was to keep the leadscrew pushing the tool under a constant pressure through the work. Not sure there's much effect on good material with a constant diameter. All that said I know good machinists who just plunge the tool straight in with acceptable results. I still use a bit less than 30 degrees and the compound since many of my tools have side rake.

Wow, Joe, great minds think alike; my machine shop instructor went through a very similar tutorial almost 50 years ago; thank you for the memories. I enjoy watching your tips, tricks, and how two’s, thanks for taking the time to share them with us. Play safe from Elliot Lake, Ontario, Canada.

I think that using the compound slide for the incremental infeed when threading has many advantages, A: reduces the load on the tool. only 51ish% of the total length of the tool actually engaged with the work, both sides, is really doing the cutting, Drastically reduces chatter B: this allows you to set the cross slide handle to a comfortable position for fast and easy retraction each pass and back to 0 every time, no number to remember real nice for large deep threads!! C: chip control, if all I ever did was brass not only would I be a happy camper and none of this would matter, BUT straight in feed large diameter internal threading in 304/316 stainless makes the shittiest chips you can imagine.......

Yes! The 29.5°/30° on the compound is meant to help reduce tool contact and chatter. PS Alternating flanking or ziz-zag threading on a cnc is awesomeness.

You’ve done a perfect job of explaining why cutting a staircase thread with a weakened tool would be stupid.

I’m happy you did this video, because I’ve never been able to convince people of this. It seems logical to believe that the tool only cuts in the direction of movement, so that’s why people believe it. But each time the tool is moved in, the rear is also moved in, so it cuts off the rear of the thread. It’s always been obvious to me, which you demonstrated extremely well. When you move the 30 degree tool in, either by using the compound, or the cross slide, you’re moving it in towards the center of the piece. With just 30 degrees, you have to leave a step on the rear of the cut, because there’s no edge to remove the step. No matter how the tool is moved inwards, it’s moved in step by step, which leaves a 90 degree back edge. It don’t understand why that’s hard to realize. Guys, no matter where you go, whether it’s people on RU-vid doing machining videos, some of whom who should know better, or even machining articles, say that moving it in 30 degrees with the compound just cuts on the leading edge, and supposedly is lessening tool pressure in doing so. I’ve read this innumerable times over the more than 50 years since I first started doing this. It’s so ingrained that nobody has ever tried it out publicly, as far as I know, until Joe just did here.

Indeed, the other side of the tool would need to be a minimum length of whatever your feed on the compound is. Love your technique of measuring thread depth btw. Been using it for a while now and it's super helpful, thanks! 😊

Joe anybody who doesn't understand this concept should not be anywhere near a lathe. Great video! 🤗

You only need as much on the second side of the tool as your depth of cut so it cleans up the step. Full profile on the second side is not needed.

Can't believe I missed this when it came out. Well demonstrated and explained, and it makes total sense.

Hi Joe! Nice to see you again. All your tips 'n' tricks are most interesting and very helpful! An awesome and very understandable demo. Thanks Joe!

Great demonstration of thread cutting using a compound angle tool vs a leading angle tool cut only... I suspect the trailing angle of the cutting tool is also stabilizing the torsional vibration being generated, when using only the leading angle of a cutting tool .

The back edge provides a wiper action on infeed. If infeed was some small fraction of the tip radius the finish would be great, like the V groove you cut with it.

Joe, again great content! I sure wish my dad was still with us, he was a humble self taught machinist and like you was a genious. I used to send him ytube vids on discs and would have sent him yours as well. Many things I'm certain he would have said "Ya, ya, that's how you do it" yet on other things he'd say "Oh, that's a good way to do it!" I've learned much from him and learn much from you. Thank you for your knowledge, experience and humble way of teaching, that is what keeps many of us coming back for more. God bless.

Excellent video and explanation Joe! Your verbal explanation in a previous video was easy to misunderstand, even though it was 100% correct. This demonstration really helps to clarify the issue. Thanks for taking the time. It would be interesting to see the same procedure, but with the tool having a small cutting edge on the right side about equal to the compound advancement. Again thanks for the video.

Excellent demo to prove a point....Thanks for Sharing....!

Joe, You are absolutely right Again !!! Thanks a bunch ! Joe , you are always there to help those of us who need to learn at home and on the job. Paul Kerst Glen Rock PA.

I’m mostly a mechanic, but yesterday I needed to lengthen the threads on a bolt to make a jack screw to pull out some flanged bushings. Anyway, I set the compound to 29.5°, or 59.5° on this lathe, like I was taught in school. Then I needed to square the tool, but I couldn’t do it against the face of the chuck because the tool had a weird offset, so I asked one of the machinists if he had a fishtail gauge. He didn’t know what I was talking about… but he just lined up the tool in the existing threads. I felt dumb. But he also asked me why I had moved the compound. He said he always cut threads by feeding directly with the cross slide. He said it’s a carbide insert and the lathe is strong, just go for it. And indeed I cut the best looking threads I think I ever made. The irony is that I learn to cut threads in school using the same exact carbide inserts, but I guess the teacher wanted us to learn the hard way… Or maybe he didn’t even think about it. The HSS tools were just cut from the program 3 months before I started. Still, the machinist was surprised that I knew how to cut threads, especially metric threads, and that I knew my way around a lathe. I pointed out that I know every machine in the shop literally inside and out because he breaks them and I repair them… haha.

Absolutely superb illustration of a problem I've faced in work many times Joe,& now have the correct ammunition to get my point across. Cheers for this!👍🏻👍🏻

The idea isn't that the tool doesn't cut on the backside. It's that the bulk of the cutting is done on the leading edge and all the back of the tool does is basically spring cut what is missed. That's why I never use the compound to cut fine threads....it's just not necessary. Now start cutting 4 tpi in 4140 ht and yeag compound all day long. The tool still cuts on both sides just not nearly as much when the compound is used. I run big machines and straight in works perfectly fine for most alll threads

Always good info! Thanks Joe!.

Awesome content and demonstration...many thanks

Set top slide at 90 to cross slide, use cross slide as accurate depth of cut (no guessing) and on each pass move the top slide towards the left 50% of depth, (right hand thread). (can vary from 50 to 80% depending on material & tool type). As an apprentice i was taught this & have been doing this for 50 years with out a problem. This takes the excess force of the back face, It has no chatter, the finish is perfect and the depth is very easy and much quicker

The only people that think the right side of the tool is not cutting have never ran a lathe.

I love this video ! I was taught to set the compound at 30 degrees, I never really thought about it. Early in my career I learned to cut double lead acme threads with no relief cut allowed. You had to time backing the tool out while cutting threads at slow rpm. I don't think i could do that these days.

I am just surprised to see Joe Pi. cutting threads toward the chuck. :)

This further illustrates the earlier video you did on thread cutting this way. Good job and thanks.

I've never heard that said. The reason for setting up at an angle is to reduce the load on the tool and work. It does cut a little on the back, but nowhere near as much as if you plunge straight in. When you're cutting a long coarse thread on a difficult material, you don't want the job climbing up over the tool. It also makes it more convenient on manual machines, using the cross slide to come back to zero. See how inconvenient it is, plunging straight into the work, having to keep track of the depth of cut each time.

I have no idea why anyone would imagine that the 'back' of the tool is just there for decoration ;-) Even a simple electronics guy can see that threading is a 'form tool' operation ...ah, well, myths have to come from somewhere, always fine to see another video from you, sir, even a 'myth buster' ?

Another great video. Thank you, Professor Pie!

Excellent clear demonstration of what is actually occurring during a single point threading operation. It is my understanding that the oblique approach was to reduce chatter by using the leading edge to remove more that the trailing edge. Thanks for sharing, best regards from the UK.

I began my machine shop training in 71 and was taught this fact entirely in the classroom. I've tested it more than once "accidentally" by less than a perfect 60 degree cutting tool. I was taught "threading is always with a form tool", we did have "NC" back then, even as CNC was only beginning to be mainstream in general service machine shops. We were also taught to take one last pass with the cross slide of a thousandth or two to ensure the form of the thread came from the tool form.

Greetings, I’m not a machinist but am addicted to your channel. Always good to learn new things, don’t know if I’ll ever use it but it keeps the brain working. Always a good thing 👍

Hi Joe, as a retired toolmaker I find your videos of a high caliber and informative for many wannabe engineers . As far as threading is concerned I thought all my Christmases came together when I got hold of full profile carbide inserts ( many moons ago ) from a reputable brand . I soon found out how accurate these inserts were by comparing the effective size with the OD and found that working to a tolerance you didn’t need to measure with those horrible screw thread micrometers and could solely rely measuring the diameter ( crests ) with a standard micrometer and as a bonus no burrs . I am sure you would be aware of this . Happy screw cutting !

Short, sweet and to the point with graphical proof. How simplier can it get. GREAT job Joe, you did it again !!!!!

Joe, great explanation and demonstration. I always wondered about how much the back side of the tool played a part in the thread formation in a single point operation. Seeing the result makes it as you demonstrated, makes it perfectly clear. Based on this demonstration, you don’t even have to set the compound on 29.5 degrees, because it only lightens the load slightly on the backside. It does not completely eliminate it, so it may improve the finish quality but does little to nothing in forming the thread. Thank you

Good stuff Joe! Its actually kind of nice to see it in real time and hear what it sounds like cutting. Sometimes when you speed up the actual milling/turning I wish you would play it in real time so we can get a feel for what good milling/turning should sound like. And if it doesn't sound like that, we would know something is not right.

thanks for that explanation your videos are always enlightening

Always enjoy your videos nice work.

Joe another good demonstration on thread cutting, I think its a matter of what you are use to doing that is easiest weather it is plunge cutting or compound cutting. The best advise I got from another of your videos was about the threading dial and how to close the half nut.

In the 1980s, I had an order for stock sling swivels and I had to make them with wood screw threads. Wood screw threads are tapered near the insertion end of the thread. I made these by two methods; form tool and form ground grinding wheels. I must say that I have never heard of this myth of half of a threading tool. It did as I expected; created steps on the trailing edge of the thread form. In finishing, my wood thread could not have been accomplished with half of the form and since I had to cut the threads on a taper half a thread form would have looked really bad. This was a very nice demonstration of a weird myth that has come into the machining business. Keep up the "Myth Busting" and I will await your next demonstration.

Never doubted you. Thanks for the look.

I have run large threads with part of the thread tool relived to help with chatter but you have to leave the nose of it in tacked. I've cut some extremely large threads (like 1/2 TPI) on some relatively small lathes with just a narrow grooving tool with only the v formed on the end. You just have to run the tool up and down both flanks of the thread, takes a while on a manual lathe but works.

Hi Joe, This was definitely one of the more interesting ones, I am slowly trying to learn and understand the whole turning art, and tool shapes have also been sort of a mystery to me ( I am not a machinist / fitter/turner). This showed quite a lot of things that I did not quite expect or know of before. Thanks again :)

That's a good demo Joe! I was taught to use the compound to rough out the thread and leave a thou or 2 for a cross-slide pass to "back-face" the thread and remove the steps. I almost always run a spring-pass as the last cleanup pass.

I’m lazy - I just plunge in on the cross slide - can’t be bothered moving the compound . I also find that not having to trig out the feed for the compound easier . With the compound set to half the thread angle it still cuts on the trailing side but the bulk of the cut is on the leading side which can help to stop chatter or a dig in on light machines , you also have to be careful threading up to a shoulder or in a blind hole as having the compound set to half the thread angle not only feeds the tool in towards the centre axis but longitudinally so the little bit of clearance you had at the start can disappear and you end up driving the tool into the shoulder or bottom of the hole . Threading away from the chuck fixes that problem ! Thanks for the fantastic video Joe , I know this has been picked up on one of the model engineering forums and I look forward to the ensuing squabble it will cause 🤣

Always learn from you, thank you sir.

Very well done and informative. Thanks!

My first attempt at cutting a thread produced the ugliest screw you can imagine but the nut didn't seem to mind so I used it anyway rather than spending another 5 hours trying again. Changing the gears on a mini lathe is a job in itself.

This whole series on single point threading is phenomenal. I very much appreciate you going to the effort to show what is really happening by removing one side of the tool - the facts are now on show for everyone. I've been cutting threads by just going in straight with the cross slide on my new lathe, but it's got decent rigidity and for small threads the load isn't too much I think. I suspect that as I get to larger threads - 1" and bigger at a guess - the chatter will start to get evident and I'll need to set the compound over. Cheers and best wishes for 2024 (and beyond).

When I got my lathe, I did the traditional 29+- compound method. After I saw Joe's video on inside-out/upside-down, I experimented in different metals, DOCs, feeds etc. Conclusion, Joe's method is faster, easier, and gives excellent results.

In theory the only part of the right side you need is equal to the amount of infeed, the size of one of those steps. The entire rest of the right hand edge is superfluous.

Another great piece of pie. Thank you sir. Great info and presentation

On a side note in cnc canned cycles for threading in several of the cases i have come across the tool path as far as the feed is concerned can be controlled as a right, left, or both sides with each pass. Left the right then left and right descending offset as to put a larger or smaller per chip load on the sides of the tool. Including a straight down feed as well perpendicular fo travel. In all things manual this is a user subjective approach and confidence. Final pass should always be both sides more or less and always with a full form tool. Joe you nailed it on this video. The fancy stuff is simply for tool life management and chatter control. I think Kimber commented his lack of a compound,. He may have less chatter than a 29deg angle with a compound in overall ridigity. The comment about chatter in plastics is all reduced to tool material and rpm. Super honed tooling is best for plastics with high positive geometry and a chip pocket, imagine a knife blade reaching up into the part.

Nice work! Thank you.

Thanks Joe. About time someone clarified this. Thanks !!

This is the way I learned to thread but I don't remember anyone claiming that only one side of the tool was cutting.

If you’re set up for high-speed photography, you could probably show directly that the right edge of the tool is cutting.

Simply Awesome Joe. Proves that there are those who theorize and then there are those who know. I guess at the time I posted my comment there were 13 theorists who didn't like having their theory busted by your great demonstration. Thanks for sharing Joe. Thumbs Up! Best Wishes & Blessings. Keith Noneya

I've always used a 60 degree tool sharpened at about 50 degrees, with a full radius on the point. Because of the radius, which cuts on the back side, I have never detected any stepping at all. Every thread that I've ever seen has a radius at the bottom--a Sharp corner creates a stress concentration which encourages breakage.

Agree completely, I was taught the 29.5 deg method long ago, but I plunge everything nowadays. For me results are the same or better in difficult materials as well. Perhaps it has to do with modern carbide tooling. Carbide does not like rubbing, in my mind a properly rounded 60 degree tool should actually perform better plunging since depth of cut will be more consistent around the tool. I can speculate that perhaps sharp HSS tooling and less rigid lathes may perform better the old way.

Great presentation Joe, as always. Your half tool made me wonder how buttress thread are cut. Is the tool advanced perpendicular to the spindle axis or the compound clocked the opposite as with a 60 degree thread form and incrementally advanced toward the perpendicular flank of the thread with each pass?

Love it joe! I learned something. Thank you.

Most of the time I ignore the compound for threading, simply because it's rarely on the machine anyway. Heck, I just cut a M42x2 thread in cast iron at 650 rpm, 'cuz that's as slow as my beast goes, with minimal issues, except the terror of a possible crash.

Excellent explanation and even better demonstration Fantastic video 👍

There is a very important distinction to be made here: the 30* compound setting is relative to the cross slide axis. I.e., it is the angle off of perpendicular to the spindle axis. If you're thinking "Duh, what else could it be?", on some lathes the compound angle is relative to the spindle axis. I.e., 0* is parallel to the spindle axis, not the cross slide axis. On these lathes the compound is to set to 60* for threading!! It's the same position in both cases, it's just the reading on the scale that's different.

Perfectly demonstrated Joe, thank you!

Enjoyed the video and reading most of the comments/replies….I book learned compound, never attempted a change as it works even though years ago I understood that plunge cuts also produces the same thread….time for me to modify my methods….tks

It would be fun to see you do something like special form threading such as light bulb sockets or buttress threads.

Hi Joe, another great, easy to understand informative video. You would make a great school teacher!

My Sherline actually does threading fine using only the cross slide. Of course, it doesn't come with a compound. I've never done coarser than 1/4-20 though.

Sweet Demo. Seen this topic discussed many times before I even knew what a single point operation even was. Both sides hold their ground is what I remember most.

Thanks for disabusing me of yet another falicy. And thanks for your usual thorough, clear explanation aided by lots of examples. For what it's worth, I'm pretty sure I picked up this one in a night class I took while I was in high school about 50 years ago. While there are those who might say that understanding this process doesn't have any real affect on the final outcome, my experience has taught me that acquiring a deeper understanding of any process generally pays off somewhere down the road.

I paused the video at the beginning to make a statement of fact. The compound is set @ 29.5 degrees so that the tool is whiping clean the back side of the tread, so when you advance the compound it keeps the following side of the tool in contact the following side of a 60° thread that is.

I was always trained to use a compound. We set it at 29 1/2 °, never understood why on a 60° tool? Great video as always.

I was taught to single point by several old timers and this is the first time I've heard this nonsense. We keep our compounds set at 30 all the time, when I asked why, they said it was so you could "pick up" an existing thread and fix it. I've been cutting single point threads for over 20 years in a production shop, both with and without a compound. If you have ever actually WATCHED the tool cut, you can easily see it's cutting on both sides.

Joe, Thanks for all of the vids you have made! Did you have to go to confession after threading toward the chuck? ;)

Great demonstration Joe, I was taught this in my apprenticeship but have run into many people who hold the view of single edge cutting. Cheers, Jon

Another great video, thanks Joe

But an interesting idea-- use your setup for this demonstration to thread both bolts AND nuts. Then have people try to put a standard nut on your custom bolt, a standard bolt into your custom nut.

Thanks for clarification Joe

Great demonstration thanks Joe. I’ve had many arguments over this point over the years. This video proves the point (no pun intended) stay safe.

Joe, could you do a video on the idea of tilting a threading tool to the thread helix angle, and explain how that does or doesnt work? I always thought if you did that one side being lower than centerline would smash, and the other being higher it would rub and not cut, but supposedly it's an advanced technique some would use, and I've always been curious how that actually worked or didn't work at the cutting surface. In fact it's one of the few things about cutting geometry that still confuse me when I can understand some otherwise very complex tooling. Can you cover that sometime?

Hey Joe thanks again great content.

Great observations and demo. Enough said.

Absolutely correct and again, beautifully explained.

Nice demo Joe, a picture says a thousand words. Thanks j

Is that one half of a threading tool what you would use to cut a buttress thread?

Great lesson, Joe. I'll take all the lessons that you can throw at me! Would you do a gear cutting lesson. I've been machining for a number a years but never did any gear cutting. Thanks Joe.

Always first class information, can't than you enough for all your videos

Thanks for the video Joe.

As always thanks for the Ed. God Bless. Ron