This is the only threading lesson I've ever seen which actually explains and shows all of the situations clearly. In all of my years of machining, I finally understand why 29.5 is seen as the magic number.
FINALLY, someone who actually took the time to explain WHY and HOW to use 29.5. Beginning to thread, I read both through my machine's manual as well as several online tutorials and not one explained that the cutting tool/tool post needed to be at 0 degrees while the compound rest should be at 29.5. All I ever read was to set the compound rest to 29.5 and cut threads like that, so I was wondering why the heck anyone would do it like that.
I'm taking some machining classes now and I find a lot of the instruction wanting. Like you say, the books are quite lacking in thorough explanations and half the time I ask my instructors on the WHY behind something, they say "that's how I was taught" and admit they don't know the answer. Are there really so few machinists that ever bothered to learn the concepts behind the numbers they were told to memorize?
The chip action explanation really helps me understand why we should use the 30 deg or slightly less compound angle. And the white board drawings.... excellent!
Hi I want to congratulate you for the way you expose your themes. English is not my natural language and in many cases, in similar situations, I lose many words because the exposer doesn't realise that are people all over the world listening him. It's a please to learn with you. António Marques
I keep watching your older videos as well as the new ones. This was very well done, as usual. But there is one thing that I’ve always found to be in error about threading. That is, we do indeed cut on both sides of the bit when moving in at 30 degrees. South Bend, many decades ago, stated that in their own books, and I’ve confirmed it for myself a long time ago. Here, on RU-vid, Joe Pie did an excellent video showing that. He cut the trailing side of the bit away and threaded with it, moving in at 29-30 degrees. You could easily see the steps left by the bit not cutting away that portion of the thread that results as you step the bit in further each time. If you look at your own illustrations, you will see that the tip of the thread must be cut away on the trailing side. It doesn’t cut the entire length of the trailing thread, but only the new trailing part from the new cut. But it must do that too.
Wow ! it's a pleasure to learn from someone that really understands what they are talking about ,as you can describe how things work at the most fundamental basis . I am 68 yrs. old I was terrible in school largely because the teachers weren't that good , ( I'll it on blame them ) . I can remember only 2 teachers that really helped to learn , a math teacher and later in life at 55 yrs. old, an electrical teacher . I intend to watch all of your videos , your the best machining teacher i know of . Keep up the great work , I'm sure you are impacting many peoples lives & will do so even after your gone , great legacy to leave behind . Thank you Marc .
Good info Marc. @ 11:12 there is another reason for the 29-29.5 angle (and I think it is a main reason) is that it continuously cleans the right flank which gets eroded by the left flank chip rubbing against it. The 29 insures that it takes a skim pass on the right side every pass. 29 deg also guarantees the bulk of the force is against the pressure side of the lead screw which keeps the back lash firmly in check. Plunging straight in give the possibility of the right flank exerting more pressure and relieving the pressure on the backlash of the lead screw causing a drunken thread .
Thanks for explaining this very useful to know WHY these things are done most videos on here explaining threading say "set the compound to 29 degrees just because"
best tip from a 30 year experienced machinist i do this shit every day . use a full form insert they have a built in swath deflector .so just plunge in cutt that thread happy days....
WOW WOW WOW....Thank you so much for this explanation....I couldn't get my head around using the compound slide angle until you explained it in the way you have...I admit i'm a complete novice and learning all the time, but this has totally made me understand how it all works......Again....Thank you....I will follow any other videos you post from the past and now on....Ian UK
Perfect explanation. Thank you. My problem is that on my old, small lathe (EW Stringer), I cannot set a 29 degree angle, as the handles of the cross slide and compound slide clash together!
Thank you Sir. Very informative. I love your easy to understand instructions. My uncle has been a machinist for 50 years and still works one day a week at a machine shop. I asked him one time if a person could set the compound rest to say 5 degrees and cut his threads. Like you said, he said " sure you could " but he said the problem with having the compound at 5 degrees was the compound handwheel was almost right over the top of the cross feed rest and can make operating the handwheels awkward! Made since to me. Keep up the good videos. Tom
Marc, thank you for a _very_ _clear_ explanation of why the preferred compound angles for threading are close to 30°. I'm looking forward to your next video!
I had/have a problem with a lightweight 12" lathe. Using the compound to feed at even less than 30 deg I got sloped threads, similar to your stepped thread. I compensated using a mix alternating compound with cross feeding. It's still a mystery, it's like the tool is being pulled into the direction of cut even though having locked the cross-feed and compound. Just one of those quirks of lightly built machines.
Also less chatter at the 29° angle. After the cutter engages, the tool is forced in a single direction by the feed pressure and comes to rest; in a cut with both sides of the point doing equal work (0°), the tip can flex and overshoot, then flex and overshoot the opposite direction, back and forth.
As usual, a superb explanation! Just 2 comments: 1. I, and the rest of the diminishing number of other geezers who grew up with the Whitworth 55 degree threads, or the even stranger BA thread system, were taught to think in terms of "half the thread angle". I know you design your instruction for the novice, but sooner or later one of them will be brave (or foolhardy) enough to attempt an Acme or trapezoidal thread (yes, I know they are different), and the blanket "30 degrees setover" will let them down. 2. I have seen more than one RU-vidr blithely set their compound over to 30 degrees "because that's the formula", irrespective of where the angle is measured from. If they understood the basic principle of successive cuts shown in your 30 degree sketch they might not have made that mistake. There is no universal standard by which lathe manufacturers mark the degree graduations on their compound slides. Once again, great work, and thank you!
Hi Marc, Is this a re-post of an earlier video? The graphic looks very familiar. I am sorry to have to challenge you here, but on a 30 degree compound setup, the right side of the tool absolutely still cuts unless you take .0005 passes and a lot of them.
@@LESPRODUCTIONSMAL Hi Marc. I would be honored to get a shout out from you. Thanks. I remembered this video because it was one of my favorites. The colored marker demonstration was a perfect tool to illustrate the mechanics. Happy Holidays !!
When plunging straight in the tool only cuts on one side until the last few passes. I didn't believe it either until I observed it while watching the tool bit cutting under magnification.
Thanks Greg for the info! It is something that deserves looking into. Learning is an ongoing process and that is why I never get bored of doing it. Marc
Define "cut" on this. Do you mean that material is only removed from the work piece on one side of the cutting tool? Or do you mean material is coming off both sides of the tool, but one side is fully cutting/shearing and the other simply tearing off? For the former, that would only happen if the tool is deflecting when pressed into the workpiece.
A few years ago I was discussing this with if I remember right a retired Scottish machinist. He was taught to grind the tool to less than 60 degrees (at about 58), set the top slide to exactly 30 and only align the left cutting edge to 30. It was claimed it had the same effect as less than 30 on the top slide. Seemed weird to me but everyone to their own.
@@KK-tk8sk perhaps not so, the point of the cutting tool would still follow and cut a 30 degree path set by the top slide, but have clearance because of the 58 degree tool. Although I must say I have never tried it to confirm or deny the validity of the practice.
I prefer 25° when using a reasonably rigid machine. Even in tough materials I find I tend to get a nicer surface finish. Also, when cutting softer plastic, the pressure can be a problem too.. so I generally adjust the rake and clearance of the tool more than the angle of plunge. Just what works for me.
Said no respectable machinist leaves his lathe for the day without returning to 29.5 on the compound. ... the other guy in the shop should check before beginning work, but it’s just a good practice to return it to 29.5 when your done for the day.
At 30deg. plunge, it is not exactly true that the trailing edge does not cut, it does cut by an amount equal to the pass depth (on the compound dial). You almost mention this at the very end of the video, but not quite. Anyone who doubts this can make half a tool (no trailing edge) and try to thread... rough trailing side, stepped by the pass depth.
@@Okie-Tom ..or when an engineer puts a right angle borehole between two walls an inch apart with no way to get at it, and after pulling out half your hair for two hours trying to figure out what's going on he calls and says "oops, forgot the access hole, lol"
Simply keep the compound set at zero, parallel to the bed and advance the compound half the depth of cut on the cross slide for each pass. By moving the compound and the cross slide this closely simulates the 30 degree angle. This method also helps with the depth of the thread as the depth is directly on the cross slide dial ( dro ). The tool load is split 87/13 so the trailing edge skims the right hand flank and the leading edge does the majority of the cutting. Here is a link for a full explanation. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-uqm1-uEaE4c.html
When we cut 60' metric thread then we can set compound rest 29'/29.5' but for 55' withworth thread cutting how much we set the compound rest. Is it 27'/27.5'.pls advice 🙏
Thread feeding via the compound appears to be much an American based technique rooted in high speed zero degree rake cutting angle single point cutting tools. While feeding in at ~30 degrees with the compound increased the cutting forces on one side of the threading tool, that edge of the thread cutting tool will be more stressed and will tend to wear faster.. It is a fallacy that only the feed edge of the threading tool is cutting as threading is a form cutting operation. This mean Both sides of the threading tool is cutting, with one edge being loaded more than the other... And yes, Both sides of the threading tool is cutting.. Only the amount of forces on the cutting edges are different.. This will dull the cutting edge with the higher cutting forces faster.. Eventually resulting in uneven worn threading tool. In the case of modern carbide insert threading tools, makes zilch difference due to the threading tool geometry and rake that can be made uber precision during the carbide inert manufacturing process. Or, zero advantage to using the compound in-feed at an angle. Chip formations is determined by the carbide insert geometry (not easy on shop ground high speed threading tools with increasing difficulty as thread pitch increases), this can be controlled in ways not possible previously.. In real world single point threading, it is Far simpler and easier to feed direct in with the compound using carbide insert single point threading tools. This allows ease of cutting the required thread depth as it is directly related to feed on the compound.
Another example in this video @ 4:05 minutes, threading with the single point threading tool upside down_lathe spinning CCW, feed from the inside shoulder to the outside of the threaded area. Again direct feed using the cross slide only.. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-74lYv4X1i-M.html
In this video@ 11:00 minutes, Japanese machinist single point threading direct in using the compound only.. Note quality of the single point threads.. No regard for angle feed using the compound. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-khe-Iw2oScA.html
