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Re: insert profiles, as in tip radius/root width, the A60/A55/AG60/AG55 inserts support a range of pitches, but are not really great at the low or high end of their range. Esp at the low end the tip is too fat, and at the high end too narrow. If that is critical, then I grind the insert into submission (easy to verify on an optical comparator or USB microscope) or grind one out of 6 or 8mm round HSS on my d-bit grinder. And then plunge in incrementally to the correct depth. I might eventually buy some pitch specific inserts to save that hassle for common ones.
One critical thing hinted at earlier is to turn the outside diameter to correct dimension first. Generally that is .125*pitch less radius than nominal. (on the mtric videos I watched they do the math in head, using .1*pitch because, well things are simpler to do in metric) Any thread shape diagram has those factors drawn on them.
Great stuff Gerrit - right till the very end. You clearly don't know me very well. Curiosity and the pursuit of new knowledge are my basic Raison D'etre.
I didn't begin this thread with any intent to actually change what I do. I began it to understand why 29 is common practice in NA and 90 is common elsewhere. To do that meant understanding details and challenging assumptions. Of course, I may also change my own practice, but only because continuous improvement is always a worthy goal.
Unfortunately, I am not really significantly closer to understanding why the regional difference exists.......
And yes, I fully read your entire note. I don't speak Dutch or Flemish.
6 TPI internal in bronze is going different that 24 tpi external in 12L14. Obviously 29/29.5 (for a 60 degree thread) has a reduced chip width which I think is advantageous. Now I'm double thinking it....hmmm. if the chip is twice as wide but the removal rate the same....is there a difference in the forces? The other argument for it is the chips don't clear as well coming into the V from both sides. Does that matter? Maybe with heavy cuts, not sure.
There are lots of factors pitch, rigidity of machine, rigidity of set up, material and so on. I've viewed 29.5 as it should let you rough a little more aggressively, all things being equal. larger pitches (smaller leads) I sometimes won't bother, but always do on larger leads. For a really coarse thread, at the same DOC, you are imposing less force cutting at 29. I usually cut with the compound at an angle for most of the job, but the final few finishing cuts to take it dead on to size are done by feeding in the crossfeed, but by quite small amounts, probably thats textbook SOP
All great stuff Dabbler. I use my compound constantly, for many things other than threading. I like to lock the carriage and use the compound for more precise control of feed position. The carriage is way too course for many of my needs. So that bonus wouldn't really be there for me. But thank you so much for helping me see where you are and how you got there. I do love how you explain things.
See my reply to Gerrit a few moments ago. Anything you can do to answer that basic question will be appreciated - even speculation. Your experience may bridge time better than many.
6 TPI internal in bronze is going different that 24 tpi external in 12L14. Obviously 29/29.5 (for a 60 degree thread) has a reduced chip width which I think is advantageous. Now I'm double thinking it....hmmm. if the chip is twice as wide but the removal rate the same....is there a difference in the forces? The other argument for it is the chips don't clear as well coming into the V from both sides. Does that matter? Maybe with heavy cuts, not sure.
There are lots of factors pitch, rigidity of machine, rigidity of set up, material and so on. I've viewed 29.5 as it should let you rough a little more aggressively, all things being equal. larger pitches (smaller leads) I sometimes won't bother, but always do on larger leads. For a really course, the same DOC, you are imposing less force cutting at 29. I usually cut with the compound at an angle for most of the job, but the final few finishing cuts to take it dead on to size are done by feeding in the crossfeed, but by quite small amounts, probably thats textbook SOP
I think you are right on all counts. Both methods work with different modifications required to accomplish different goals. From an operational standpoint, I will probably start doing plunge threading more often. One more tool in my tool chest if you will.
Any idea how or why the two approaches evolved to be different common practice geographically?
Re: insert profiles, as in tip radius/root width, the A60/A55/AG60/AG55 inserts support a range of pitches, but are not really great at the low or high end of their range. Esp at the low end the tip is too fat, and at the high end too narrow. If that is critical, then I grind the insert into submission (easy to verify on an optical comparator or USB microscope) or grind one out of 6 or 8mm round HSS on my d-bit grinder. And then plunge in incrementally to the correct depth. I might eventually buy some pitch specific inserts to save that hassle for common ones.
One critical thing hinted at earlier is to turn the outside diameter to correct dimension first. Generally that is .125*pitch less radius than nominal. (on the mtric videos I watched they do the math in head, using .1*pitch because, well things are simpler to do in metric) Any thread shape diagram has those factors drawn on them.
The initial OD is something most hobbiests probably forget and then wonder why the thread doesn't fit. How many times have I taken a lathe file to an OD to watch someone's face light up with "huh"........
This thread profile thing is just another vote for HSS...... (Ducking for cover... LOL)
I'm not convinced they are, or at least that its so black and white. I'd think it a safe bet there are machinist here that have figured out it doesn't much matter at 32 tpi and that there's some guy in Germany who's figured out cutting a 10mm thread with the compound slewed over is easier. There may more here that default to one and vise versa there, but its shades of grey imo.
I also have two European publications, one British and one Austrian and both recommend slewing the compound over.
"The Amateurs Lathe" (great beginner book if you dont have one). It's a British publication from 1948 and recommends setting over the "topslide". I don't have German texts (and could not read them if I did) but did find this in an Emco manual I have (Austrian)
So yeah, things are different there...but they are also the same
I'm not convinced they are, or at least that its so black and white. I'd think it a safe bet there are machinist here that have figured out it doesn't much matter at 32 tpi and that there's some guy in Germany who's figured out cutting a 10mm thread with the compound slewed over is easier. There may more here that default to one and vise versa there, but its shades of grey imo.
I also have two European publications, one British and one Austrian and both recommend slewing the compound over.
"The Amateurs Lathe" (great beginner book if you dont have one). It's a British publication from 1948 and recommends setting over the "topslide". I don't have German texts (and could read them if I did) but did find this in an Emco manual I have (Austrian)
I have assumed that the difference was some shade of grey already. But it does seem like there is a significant shade difference.
It seems clear that the North American bias is toward skewing the compound. But even that sense might be a sample error. Regardless, it ought to be more obvious why. Unfortunately, all the really old machinists are long gone so I am left to mostly speculate based on discussions like this one with experienced machinists like you.
What intrigues me is my observation that skewing the compound is not an intuitive solution. I would have thought that SOP would naturally be the more intuitive approach with alternatives like skewing only arising when faced with challenging situations.
So what is it that drove the popularity of this old well established, non-intuitive practice?
I suspect the answer might be found in the old machines. With the old timers all gone, the only thing we have left is old machines and old text books to tell us their history.
How old is that Austrian EMCO manual? It's interesting that the manufacturer says "most machinists". This suggests that perhaps the rest of the world had the same bias as here in North America, but perhaps the old world was faster to change.
@Susquatch: Please refer to the attachments for your reading pleasure. There are "preferences" for how you set up and make threads, and indeed there are many different threads that are cut and the profile of the thread required will possibly dictate what set up is required. clearance for the tool, load, chip removal etc etc will typically dictate what is necessary for proper threading.
@Susquatch I don't know European things except from contemporary Youtube. However at least 2 machinists in Canada have independently shown me the plunge method of threading as a 'secret worth knowing'. Neither explained why, so I left it in consideration queue until Gotteswinter properly explained it.
So in summary, plunge is used here. 29.5/30 is used in Europe. Both sides have all kinds of weapons in the armoury.
@Susquatch: Please refer to the attachments for your reading pleasure. There are "preferences" for how you set up and make threads, and indeed there are many different threads that are cut and the profile of the thread required will possibly dictate what set up is required. clearance for the tool, load, chip removal etc etc will typically dictate what is necessary for proper threading.
I found two things of great significance to my quest in your documents.
In the first document, the author describes how we arrived at 29 vs 30. Basically he confirms what I had surmised earlier. On the earliest lathes it was not practical to set a precise angle of 30 degrees to cut perfect threads. But it was soon discovered that 29 degrees didn't need to be precise. 29 degrees solved the problem of precision by cutting the majority of the work on the leading face of the cutter and cleaning up the remainder on the right face with a very light 1 degree progressively deeper cleanup pass on the right face.
As @Dabbler said, a precise 30 works just fine. But 30.2 would not. In the absence of an easy way to set angles, machinists just fell into the practice of using 29.5 (or at least some slight angle less than 30).
The second source contains a reference section with information in it that I have never seen before. I "believe" it points to the reason for doing the 30 degree compound cut.
It is buried in the attached screen shot and discussed in the text.
Note the top rake on the cutting tool used for 30 degree method vs 90 degree in the top right drawing. The author claims that a single point tool that cuts on both faces must be flat with no rake and this results in chip clogging in many cases. A double rake tool is not possible with conventional grinding methods of that time. However, a tool with a top edge ground to cut primarily on the left edge never does this.
It is worth remembering the old lantern style threading tools of the day.
One can, easily imagine the process of cutting even moderate threads with a lantern post tool like that on an old lathe like my 1800s FE Reed.
At this point I can only speculate about a few things. Having done business in other parts of the world, I can say with certainty that there are many industrial practices in the old world and the new that were driven by the two world wars and especially the second world war.
I have almost no difficulty imagining that machine Shop practices on North America would survive the wars virtually intact. Old school (old lathes) machinists would teach the new machinists in the old school ways and that craftsmanship would stay engrained in machining practices regardless of changes in the machines and tools. Where once there was a reason for 30 degrees, the practice would continue even as the reason itself disappeared.
In the old world which had to be largely rebuilt from the ground up after the war ended, new machines, new tooling, and new practices would easily take hold.
Imagine then the arrival of carbide and multi-point threading tooling with none of the limitations of lantern style thread tooling and it is relatively easy for me to speculate about @Mcgyver s different shade of grey in the old world vs the new.
I don't personally believe that we are likely to find clear evidence to support or refute the speculation above. So I am ready to let it go (for now).
Nonetheless, there are some good outcomes from this exercise.
There are times and situations where both processes are advantageous. And while small modern machines are not as robust as new industrial machines, they are certainly orders of magnitude better than the old lantern style lathes that predominated before and after the wars. I believe in my heart of hearts that there is lots of room for both methods in any hobbiest workshop. Furthermore, I believe that learning from history is the best way to avoid repeating its negatives.
I am looking forward to learning to plunge thread and may even go buy some inserts to further facilitate that!
Although I will always be open to alternative explanations with or without evidence, I wish to extend a big huge thank you to everyone for ringing in and especially to @Brent H and his library for helping me bring this to a good comfortable conclusion in my own mind.
@Susquatch I don't know European things except from contemporary Youtube. However at least 2 machinists in Canada have independently shown me the plunge method of threading as a 'secret worth knowing'. Neither explained why, so I left it in consideration queue until Gotteswinter properly explained it.
So in summary, plunge is used here. 29.5/30 is used in Europe. Both sides have all kinds of weapons in the armoury.
When I was looking for inexpensive threading carbide inserts a while back I studied Carmex catalog literature. Mostly because that is one of the popular formats which are 'replicated'. From what I recall of documentation, straight-in feed is also prescribed. I recall another competitor system I looked at being the same. So my gut feel is its probably not a Sandvik thing or a European thing, its probably a more modern (current) tooling thing. This tooling relates to industrial/CNC machines which I would think is 99% of their target customer base. Now historically if hobbyists on one continent vs another had earlier exposure to these systems & adapted them earlier as a rub-off factor, hard to say. Back when an insert was $25 and a HSS blank was $5, the hobbyist decision probably favored the cheaper HSS solution that did the job to the standards required. But the tides have shifted. Currently, insert tooling is cheap & affordable for hobbyists either as typically Asian supplier/knockoffs or inventory sell-offs of otherwise more expensive systems. There is no disputing many fine examples of HSS threading both historically & current. I don't think its an either/or issue, its an overlap issue & what fits one (hobbyist) person may not fit another.
How adapting this insert tooling or setup methodology relates to a hobby lathe is a very open question with too many overriding variables IMO: machine condition, material choice, thread type, operator skill, operator bias... just to name a few. As a singular data point FWIW, so far I'm happy with Carmex clones & matching offshore toolholders on a typical manual mode Taiwan 14x40 lathe '98 vintage. Most of threading has been sub 12 TPI in materials like 1018, 12L14, O1, SS, aluminum alloys. I am hopelessly off the recommended charts, meaning lower speeds & feeds. But my takeaway point is thus far the world did not explode, no shattered carbide edges. But getting better threads than what I was achieving with my own grinds (or bad quality braze-on carbide tools which was another matter). So a lot of the insert handwringing I read about fortunately did not come into play, at least in my own experience. For personal R&D I did try straight in vs 29.5 & found no discernable difference to finish or accuracy. I have not done coarse thread lead screw like threading yet though. So on the basis of convenience & time I have become a straight-in guy.
Relating to geometry of tooling & setup, I can makes some guesses as to why hobbyists might have variable different results. The way I learned was hand grinding a HSS blank with relief angle set on grinder table, compare included angle to a fish tail template, set up to work piece... the classic method. Actually at school we put both the tool tip & thread on the big toolroom magnification projection device & that was quite revealing.
The 29.5 vs 30.0 compound discussion is interesting because it relates to cutting forces but also relates to implied theoretically perfect 60-deg pitch angle. Is a hand grind to a fish tail template really within 0.5 deg time after time? I'm not saying it cant be done, but its another variable that might explain different results. Similarly if the left/right relief angle is ground just a bit different or tool is presented to work just a bit different, then straight-in will see this difference & likely cut different. So if that is when chatter is observed the operator concludes straight in is bad. But correlation is not causation. The issue could be related to other factors outside of what can be easily identified. A molded carbide insert hopefully eliminates or at least reduces some of these variables. In addition, 'just because they can', molded carbide inserts can actually have different relief angles per side depending on the thread.
Lastly I have found that DOC passes are another thing to pay attention to, but I'm still learning there & is outside the scope of post.
When I was looking for inexpensive threading carbide inserts a while back I studied Carmex catalog literature. Mostly because that is one of the popular formats which are 'replicated'. From what I recall of documentation, straight-in feed is also prescribed. I recall another competitor system I looked at being the same. So my gut feel is its probably not a Sandvik thing or a European thing, its probably a more modern (current) tooling thing. This tooling relates to industrial/CNC machines which I would think is 99% of their target customer base. Now historically if hobbyists on one continent vs another had earlier exposure to these systems & adapted them earlier as a rub-off factor, hard to say. Back when an insert was $25 and a HSS blank was $5, the hobbyist decision probably favored the cheaper HSS solution that did the job to the standards required. But the tides have shifted. Currently, insert tooling is cheap & affordable for hobbyists either as typically Asian supplier/knockoffs or inventory sell-offs of otherwise more expensive systems. There is no disputing many fine examples of HSS threading both historically & current. I don't think its an either/or issue, its an overlap issue & what fits one (hobbyist) person may not fit another.
How adapting this insert tooling or setup methodology relates to a hobby lathe is a very open question with too many overriding variables IMO: machine condition, material choice, thread type, operator skill, operator bias... just to name a few. As a singular data point FWIW, so far I'm happy with Carmex clones & matching offshore toolholders on a typical manual mode Taiwan 14x40 lathe '98 vintage. Most of threading has been sub 12 TPI in materials like 1018, 12L14, O1, SS, aluminum alloys. I am hopelessly off the recommended charts, meaning lower speeds & feeds. But my takeaway point is thus far the world did not explode, no shattered carbide edges. But getting better threads than what I was achieving with my own grinds (or bad quality braze-on carbide tools which was another matter). So a lot of the insert handwringing I read about fortunately did not come into play, at least in my own experience. For personal R&D I did try straight in vs 29.5 & found no discernable difference to finish or accuracy. I have not done coarse thread lead screw like threading yet though. So on the basis of convenience & time I have become a straight-in guy.
Relating to geometry of tooling & setup, I can makes some guesses as to why hobbyists might have variable different results. The way I learned was hand grinding a HSS blank with relief angle set on grinder table, compare included angle to a fish tail template, set up to work piece... the classic method. Actually at school we put both the tool tip & thread on the big toolroom magnification projection device & that was quite revealing.
The 29.5 vs 30.0 compound discussion is interesting because it relates to cutting forces but also relates to implied theoretically perfect 60-deg pitch angle. Is a hand grind to a fish tail template really within 0.5 deg time after time? I'm not saying it cant be done, but its another variable that might explain different results. Similarly if the left/right relief angle is ground just a bit different or tool is presented to work just a bit different, then straight-in will see this difference & likely cut different. So if that is when chatter is observed the operator concludes straight in is bad. But correlation is not causation. The issue could be related to other factors outside of what can be easily identified. A molded carbide insert hopefully eliminates or at least reduces some of these variables. In addition, 'just because they can', molded carbide inserts can actually have different relief angles per side depending on the thread.
Lastly I have found that DOC passes are another thing to pay attention to, but I'm still learning there & is outside the scope of post.
I'm am actually quite happy with the way everything has unfolded. It's complicated but also quite simple. The history and the geographic differences all make sense to me now and I like that. I don't like things that don't make sense.
I had previously more or less settled on HSS and 29.5 degree threading as a way of life. In my humble opinion, my threading was excellent - although I accept that others might not agree.
Nonetheless, I am actually quite eager now to plow new ground and add inserts and plunge threading to my Toolbox of threading alternatives. I wish there fewer choices though so some of your recommendations are probably a good place to start.
I think it's time for me to move on to other areas of interest now and complete a few projects too. Way too much fun for an old man!
Your interest in indicators, measurements, and spindle alignment seems to have dropped off the planet. I've been waiting for you to reframe your question. But perhaps you got your answers or lost interest. That happens and it's ok.
I'm still waiting for the spindle test bar to arrive so I can qualify it and then go about the business of comparing the available alignment methodologies.
I'm a straight in kinda guy! I started all askew in my early life, but I've straightened up and fly right now.
I only use carbide inserts. Hopefully I can show my methodology properly in these pictures. I set up the compound so it will advance the cutter in the Z-axis when the time comes, dial set to zero, and backlash taken up. I have to cut 16tpi thread. According to the Sandvik chart my infeed (@90°) is 0.041". So I go ahead and thread that part to a depth of 0.041". Doing so does raise some burrs and the thread flanks are a little rough. I will use a file to remove the burrs and bring that part to the original OD. I try to screw the action in, and it starts, but stops within 1 rotation. I now use the compound, it was at zero, I back it up a fair bit and then advance it(taking up the backlash) to 99 (.001" before the zero). I move the cross-slide to 0.041", and make a cut. This cleans up the trailing flank of the thread. I test fit the part, it now screw is two rotations before it stops. I advance the compound towards the chuck +Z .001, move the crosslide to 0.041", and make a pass. This cuts on the leading flank of the thread. Test, and repeat moving the compound in 0.001" increments. I had to remove a total of 0.004" of material from the flanks of the thread for the action to fit perfectly.
On those cards: the one on the left shows how many passes, and depth of cut in the X-axis.
The card on the right:
According to Sandvik, a topping insert of 16tpi, has a nose radius of 0.008". The threading insert I use is non-topping, and has a nose radius of between. 002"-.004". So, when I cut the thread (before I used the compound), the root radius was between. 002-.004, and probably closer to the larger value since its been used many times. And the action wouldn't fit, because it was too tight, but by moving the compound in the Zaxis by 0.004, it now matches up with the topping value would be, and lo and behold, it fits.
My AliExpress Carmex 'style' insert & toolholder on 303 stainless. One nice setup aspect of this style of insert is you can pre-align quite quickly & accurately a few different ways because the pocket is already aligned within toolholder. Bring long edge of the insert up to end of work piece & daylight gap. Or daylight gap front of toolholder to side of work. Or set up an indicator on insert edge or toolholder shank side surface & advance cross travel.
Your interest in indicators, measurements, and spindle alignment seems to have dropped off the planet. I've been waiting for you to reframe your question. But perhaps you got your answers or lost interest. That happens and it's ok.
My AliExpress Carmex 'style' insert & toolholder on 303 stainless. One nice setup aspect of this style of insert is you can pre-align quite quickly & accurately a few different ways because the pocket is already aligned within toolholder. Bring long edge of the insert up to end of work piece & daylight gap. Or daylight gap front of toolholder to side of work. Or set up an indicator on insert edge or toolholder shank side surface & advance cross travel.
My AliExpress Carmex 'style' insert & toolholder on 303 stainless. One nice setup aspect of this style of insert is you can pre-align quite quickly & accurately a few different ways because the pocket is already aligned within toolholder. Bring long edge of the insert up to end of work piece & daylight gap. Or daylight gap front of toolholder to side of work. Or set up an indicator on insert edge or toolholder shank side surface & advance cross travel.
Or take a precision square placed on the tool holder with the blade against the side of the chuck. Perfect alignment. Snap off the tip, no problem rotate or replace the insert. I have threaded many, many, many parts with a single insert without having to dress it, or touch it up, or sharpen it (does that look like 60° or 58°?)
My AliExpress Carmex 'style' insert & toolholder on 303 stainless. I have several insert type tools that also provide convenient alignment so I get the idea.
I'm interested in gettng some carbide insert tooling for threading, but 'can't make head or tail' of all the choices. So I would really appreiate specific recommendations - not just the store, but the actual insert and insert holder/tool. Thanks in advance!
