why do we set the compound rest at 29 

I have been a machinist for 11 years, and thus is the best explanation of why 29⁰. I'll admit, i infeed at 0⁰ because I dont want to mess up my tool offsets on my DRO. Thanks for the video. Short and simple.

The best part about RU-vid. People who are prepared to share Information. Your Information is correct. But, rarely do I cut threads on a Manual Lathe with the Compound set to any other angle besides 90 degrees. It's not to say that this is the way to do it ?? But, it works very well when you're Not using High Speed Steel to cut Threads ?? It's not to argue the point. Just what works for me. I cut all types of Threads on a Manual Lathe from Metric Fine, ACME to 4.5 tpi UNC. All cut at 90 Degrees. I back this up with videos showing the process. Not trying oversell myself. Just sharing information that works for me 👍

Been a machinist for over 50 yrs. Never turned the compound to cut a thread. Fed the tool straight in and advanced the compound .005” or so each pass. Produced a fine looking thread on all pitches and materials.

👍 excellent explanation! My old shop teacher taught us to take the last few thou off by feeding straight in to let the tool final form the thread.

Great explanation. I notice that a guy in Australia who does you tube videos does not set his compound to 29 degrees but shifts it sideways a bit each pass.

I just did 1/2 -13 with cheap threading insert at 0°... fed in total of 0.116 on cross slide came out perfect ...also tried from left to right with insert upside down at higher speed again turned out great love working out in the shop when its to cold to fish

I just use 0 deg. on manual as well CNC, no problems. As you go deeper take smaller cuts and always use sharp tools.

Hello, I really like your channel. I have been machining for quite sometime now and I am always up for learning something new and YOUR channel does exactly that. Cheers. Wylie

Ive been a machinist for 25+ years and i cut threads using 29 degrees method and using the parallel method. Both produce the same thread without any problems or difference. The only difference is that when cutting threads by the parallel method you need to move the compound slightly for every infeed / pass you make. The exact amount you have to move the compound is given in charts that are specific for parallel thread cutting. I also noticed that in Europe most machinists learn the parallel method and usa machinists learn the angle method. For the end result it doesn't make a difference , it's more what method you like to use and find convenient 😀. I can use both methods and I will end up with exactly the same result .

You answered a bunch of questions, well done video, I've never done any threading before, but know I know how.

this is a wonderful video, thank you so much....Paul in Florida

I feed in with my cross slide when threading. However I still set the compound to 29 degrees so I can shift the cutter if I need to tweak the thread a bit. Still enjoying your videos!

Wow, it makes sense if the compound angle is set improperly that the thread form would be incorrect but I've never seen it so obviously before. Wonderful example. But I stopped using compound in-feed on manual machines that kick out the leadscrew engagement with carriage stops like the Hardinge HLV-H and Monarch EE. Losing absolute tool position and potentially gouging into a shoulder didn't seem like it was worth the additional setup planning/foresight. With modern carbide tooling, basically all common materials are 'easy' to finish just with plunging but I still do end up using compound infeed with superalloys and exotic stuff. Great video and thank you for making this accessible!

Should be 29 1/2 degree, not 29, this is so the right side of the tool will lightly skim the "back side" of the thread and the left side will be doing the majority of the cutting. But what do I know, I've only been doing this for 40 years! Lol

The Mazak CNC lathes in the shop where I worked did, indeed, cut threads with a 30° feed. The argument is usually that a big, pro lathe has the rigidity to handle a plunge cut, but that's not the point. Often the part rigidity cannot.

The video covers an issue that has created lots of conversation and sometimes heated arguments. As I have always worked in tool rooms and had access to a surface grinder, I machined a “tumble” fixture to form, or resharpen a hss tool bit. By changing which face goes down on the chuck, I can grind the left side angle, with a minimum of side clearance, followed by the top rake angle perpendicular to the left edge, which keeps the left angle proper, followed by another fixture face change to grind the right side angle and clearance to 29.5 degrees, giving me a clean flank cut. The compound is set at 30.0 degrees. Years ago I learned many of these lessons from my elders in the shops of my youth. “I took the path less traveled by.” Another advantage that I have found in using hss tools, ground in a fixture, is the ability to better control the left side length, which when held to a minimum, allows threading closer to a shoulder, without an ugly groove for run out. This just another way to skin that cat, that is always running around.

I've seen some thread like your photo; it's usually after some gorilla over torqued a nut & it re-modeled the thread during it's one way departure. Also seen in on a gear/pulley puller, too, now that I think about it. Very well done vid.

G92 canned cycle is a zero degree feed in threading cycle (Fanuc). G76 can also be utilized by specifying the angle of infeed to 00.

Excellent video. Thank you.

~29deg is used because 1) tools can be ground with a small error and/or mounted slightly off angle and we want to make sure the back side will always conform to the proper V shape. 2)It reduces the total load on the tool which can wear or break off the tip where it is weakest if two large chips collide there. 3)The compound angle cannot be perfectly set at 30 deg so we want to err on the side of safety which will keep the back side cutting the full V shape. 4)The chip from the leading edge erodes away the surface of the back side so by ensuring it is always being skimmed we automatically correct that erosion as it develops. 5) By placing the majority of the load on the leading edge you maintain a high and consistent pressure on the lead screw/nut assembly and all the ways to assure it does not advance erratically causing a drunken thread. Pro tip. Once you decide your first cut depth (20-50% of total depth) the each pass is the previous pass X the square root of the current pass number. EX start pass selected ..015 second pass of equal volume will be .015 x square root of 2 = .0212 or .0062 more. The 3rd pass would be .015 x square root of 3= .026 or another .0048 deeper and so on ....until full depth is reached.

What you say about flank versus radial feed could be said to have some relevance for a home ground form tool, but if you look at a modern full form threading insert it has a rake angle on the leading and trailing edge. Surely this implies the intention for it to cut on both sides.

That's not an incorrect thread, it's a proprietary thread that only works with proprietary nuts that cost 50x what normal nuts do... some would call it an "apple" thread.

Here is very common the parallel method. I set the angle at 90, effectively getting a 60 degrees point. After several pases, lets say somewhat around 25% of the depth, i advance the compound about 0.05 mm in each subsequent pass, this results in the leading edge doing the cutting. This technique is nothing new and is taught here in Spain in the first semester of professional training.

Interesting...as always.

actually the 60 degree thread looks very much like a sawtooth buttress thread . i did one once on a large nut 300 mm id for a tierod on a 2500 ton press . the thread was 33 degree total instead of 60. 3 degree on one side and 30 on the other. used a 35 degree insert cutter mounted to a shank and angled on the shank to give the 3 degree on one side but 32 on the other which still worked because all force was on the 3 degree side and it was internal thread so the 32 degree just gave extra clearance on the back side.. did this on a vertical cnc machining center as a thread milling operation. looked like what you showed as wrong except it was 35 degrees total included angle .

nice job

I must be missing something here, but where does your magic factor of 0.708 come from in calculating the infeed? A full V form thread has height H, but in the unified system the outermost H/8 and the innermost H/8 are removed (some sources suggest the innermost H/4) so the thread depth perpendicular to the axis of the thread is 3/4.P/2.tan(60), which would be your infeed if plunging at 90deg, not allowing for to radius on the end of the tool. With the compound set at 29deg to the perpendicular this will be increased by 1/cos(29), so I make the magic factor 0.7426 . Pitch, or 0.7426/TPI

Don't they teach compound and supplementary angles in school anymore? That's what most of this discussion seems to be addressing. Carbide tooling does not last very long with this 1 degree drag angle on infeed. It will chip the side of the insert that barely does any work! As a professional machinist, I would never teach the traditional angled infeed. If your lathe is set up with a DRO, you don't want to cancel the validity of your tool reference points with uncontrolled movements in an angular axis. Leave the compound alone! If it's at 90 degrees, you can tweak it forward and back to give single edge cutting on large threads. This technique is what I use. Modern laydown thread inserts with chip forming designs cut just fine on both edges with straight infeed. As for how deep to cut, thread measuring wires are cheap and accurate. Start measuring before you've gone too far 😁. The difference between the measured PD and theoretical is how far you've got to go on the cross slide. No compound miscalculations need be remembered. It's all guessing anyways until it measures right, and theoretical PD is an ideal, but it's not best, because tolerances are a real thing. Some tolerances are one way, not the other. A too big thread for an "ideal nut" will not make you any friends with the mechanic putting your stuff together. CNCs can cut with a staggered infeed that keep both sides of the insert engaged at slightly different chip thickness. Cleaning passes are straight infeed.

I honestly don't know anyone that changes cross angle to cut threads. Mainly because it changes the tool offsets when you rotate the cross slide. I converted my bench top sized lathe to CNC though and use a python script I wrote to generate gcode for the thread parameters I am cutting. Maybe they teach this in trade schools but threads can be cut without doing that easily even on a non cnc lathe. I think that the method should be taught from the start to preserve your DRO values and tooling offsets

Looks like those "incorrect" threads are buttress type threads used on antique firearm barrels

very informative and helpful thanks

At 1:20 and 5:50, the thread formed would be useful in a device designed to push the bolt and nut, or slide, or device away from the bolt, if the matching profile was made complimentary, 61Degrees the other way. This would now be a 'Bolt Press", to separate the ball joints of a car spindle or some other thing needing to be pushed apart, it would not be good for pulling things together--(Clamping Force).

I’ve noticed some lathes have 0° on X and some have 0° on Y. My lathe needs to be set at 60° to do 30°. If you set it at 29° you’ll infeed 60° and get the buttress looking thread.

At 4:02, that number, 0.708, is a very close approximation of the 'Square Root of 2'?

29 degrees is only appropriate for American and Metric threads with a 60 degree angle, An adjustment needs to be made if cutting a Whitworth thread.

Proper Threading inserts are designed to feed in a Zero Degrees, those designed for this collapse the chip, much the way a Carbide parting/ grooving insert does. A CNC program written this way only shows a succession of deeper cuts with no angle. This can be altered to several different thread cutting techniques, that only CNC machines can allow. When Using carbide for threading in a manual lathe, surface speed is more of problem, so much depends on the operators skill. HIGH SPEED STEEL threading tools are RARELY ground to produce the correct thread form, and they are never ground for the ultimate in threading topping.

for the little threading I do, 0 deg and carbide inserts has been working great, and lets me rely on the DRO for the exact thread cutting depth. i think the 29 deg rule was very applicable for HSS tooling, but carbide tooling is far more forgiving with both sides engaged. and since the carbide is idexable, it is easy to turn the insert for a fresh tip. the video is also showing a bit uncommon insert for threading?

More contact with one side of the thread than the other, less load resistance... less heat generated.

I'm not understanding this. The shape of the thread is determined by the tool profile, and you don't feed with the compound rest, you feed with the compound slide. It seems to me that it doesn't matter what angle you set your rest to. If the tool is perpendicular to the work, and you're feeding the slide in X, then the tool will be cutting on both sides. What am I getting wrong here?

I happen to own a micrometer dating from 1888 that has this peculiar ‘non-existing’ thread with one flank at 90 dg to the axis of its spindle.

That looks like a reverse buttress thread, how did you grind the tool

I thought you were going to explain the amount of actual infeed per thousandth you get with the compound set at 29 degrees.

if thread is left or right, does it change in this math something?

what multifix are you using?

Looks almost like a butress thread

Those threads look like hell

People don't get it right. When use carbide thread insert, which most people do then use only cross slide (0 degree), it will not give you anything good when trying to use the compound too. So why are people using compound ?, it is a leftover when machinist making their own HSS grinded tool. The HSS Tool was grinded in two different angles. prefect 30 degree angle on the left hand side and 27-28 degree on the right side hand. Still the 30 degree side was aligned perpendicular to the workpiece. If the HSS tool has this shape non symmetrical shape then of course you must set your compound to 29.999 degree angle and only progress with the compound slide. If you insist to use carbide and compound angle then you can modify the carbide insert similar to HSS tool. Grind the right-side angle to 27-28 degree and keep the fine nose radius intact (do not touch the nose radius) on the carbide insert.

Keep the compound slide parallel with the bed and advance the tool half the depth of cut to simulate feeding in at 26.6 degrees, This gives a desirable 93% of the cutting load on the leading edge. There is no calculation for the compound feed in distance as the thread depth is simply on the cross slide. My CNC has a default feed in angle of 29 degrees not 30. You have asked for links to other threading videos. Here is my offering of 12 ways to cut threads. SINGLE POINT THREADING 12 EASY WAYS - ZERO DEGREE COMPOUND, NO PLUNGING, NO TOOLS SET UPSIDE DOWN. I hope your students gain something from the video. There are several others for multi start - tapered & generating knuckle form threads.

I don't. I feed straight in. And don't care what angle my compound is set.

chinese machines use that oddball protractor. PITA

No offense, but this could have been explained a lot better. While i applaud your foray into RU-vid and education, you should refine your approach. Take a minute to breathe and for things to sink in. Use better images that sit for a little bit. Let your audience digest. I got it at the end, but i didn’t catch 90% of what you were saying to me.

61-90 = -29, not 29. If you are going to do math, do it correctly.