Negative carbide insert on old and slow
Negative carbide insert on old and slow
This subject is difficult to search. Many times I’ve read a negative carbide insert on low HP lathes won’t work. Stay with a positive rake and use HSS. I am using the lantern post with Armstrong tool holder with HSS. Before ordering a QCTP I purchased a tool holder with insert to try but by mistake I ended up with a negative style insert. TN__? Something. Before sending it back I gave it a go. To my surprise I was turning 1018 into chrome. WOW! I’ve got the bug now. Lathe is an old Sheppard 15 x 40” the work piece was approx 1.25” d and DOC was anywhere from a few thousand to .030” at 600 rpm with very satisfying results. I couldn’t say about travel speed but to say it is my fastest setting. Before committing to more tool holders what suggestions does anyone have about insert style, shape etc ? This lathe top speed is 600 rpm. I like the versatility of CNMG if I had my choice but I’m not able to find holders in 5/8” shank for CNMG that fits my old lantern post. My other concern is I’d like to stay with tooling that is the most versatile and cost effective if I needed to switch back too HSS. I’m moving slow and the least expensive approach to try things out first.
Re: Negative carbide insert on old and slow
What you'll discover as you progress is that it is far more difficult to control size with negative rake. Sure, you get a nicer finish, but the guy with a 9" lathe, powered by a fractional horse power motor, isn't likely to duplicate your results. You'll also struggle endlessly if (when) you must hold a tight tolerance. If all you're doing is turning manhole covers, yeah, no big deal.
Before you get too excited about the use of insert tooling, do a soul search. Is it because you don't have the required skill to grind HSS tools? Do you, possibly, think that that isn't something you need to be successful in machining? If so, you're doing yourself a serious injustice. If you assume that posture you'll find yourself held hostage by your inability to create a needed tool for a one time use, and end up spending a huge amount of money buying tools that you won't need again. That's assuming you can find what you need. Far worse, you'll find yourself stopped on projects, time and again, while you wait for a tool that you could have hand ground in minutes.
There is nothing wrong with carbide insert tooling. It has proven to be a boon for shops, especially when applied to production. It is a luxury for the home shop unless such a shop has a legitimate need, or the owner has exceedingly deep pockets and doesn't mind waiting for needed holders or inserts. Keep this in mind.
H
Before you get too excited about the use of insert tooling, do a soul search. Is it because you don't have the required skill to grind HSS tools? Do you, possibly, think that that isn't something you need to be successful in machining? If so, you're doing yourself a serious injustice. If you assume that posture you'll find yourself held hostage by your inability to create a needed tool for a one time use, and end up spending a huge amount of money buying tools that you won't need again. That's assuming you can find what you need. Far worse, you'll find yourself stopped on projects, time and again, while you wait for a tool that you could have hand ground in minutes.
There is nothing wrong with carbide insert tooling. It has proven to be a boon for shops, especially when applied to production. It is a luxury for the home shop unless such a shop has a legitimate need, or the owner has exceedingly deep pockets and doesn't mind waiting for needed holders or inserts. Keep this in mind.
H
Wise people talk because they have something to say. Fools talk because they have to say something.
Re: Negative carbide insert on old and slow
I don’t follow holding tight tolerance. If you’re referring to the heat build up in the work piece using carbide I can understand that. Or possibly taking a very fine cut with a clean finish? I’m perfectly fine with inserting the insert style tool holder in my old lantern post with out having to adjust the rocker every time I resharpen HSS. I’d be willing to bet a vast majority of those rocker lantern post are sitting in a drawer for most. A QCTP isn’t so Quick every time the HSS tool needs sharpened. Maybe I expressed moving slow and not spending money was overstated. I’m stating my surprise that a negative insert performed so well on a very old and slow lathe, contrary to so much I’ve read. My question is more of what issues I may have using negative inserts (carbide) vs HSS blanks or if I wanted convenience of using HSS insert tooling on a slow lathe. No admittedly I have very little time with carbide inserts so perhaps the problems will reveal themselves but I’m asking here. I don’t know you and you don’t know me so no harm no foul but If I could I’d post photos of machine tools I’ve built to demonstrate my level of patience. Honestly as my eye sight has diminished I sure like the speed and convenience of inserts.
Re: Negative carbide insert on old and slow
You clearly do not understand the principles by which negative rake tooling works. For starters, while a scratch cut results in the tip making contact with the work, a serious cut (for which negative rake was intended) it does not. When negative rake is applied as intended, the cutting occurs well back of the tip, which is easily observed if you pay attention to the developed pattern on top of the insert.
Because of the negative rake, cutting pressure is increased dramatically, which is the reason a more robust and powerful lathe is required. You are fortunate to have a reasonably robust lathe, so you are avoiding some of the pitfalls of small machines.
The increased cutting pressure is the problem for finish cuts. A given load must be applied before a negative rake insert will generate a chip. A new one, right out of the package, usually has a slightly rounded cutting edge (which is intended to protect the edge from degrading). In the early years of negative rake usage, one was admonished to hone a slight (.005") 45° angle on the edge, for that very reason.
If you still think that negative rake is perfect for tight tolerance work, try machining a fit for a bearing, then tell me how well it went. I'll be interested in hearing how you managed to remove a few tenths, especially in mild steel.
Do not misunderstand my comments. What I tried to do is point out to you the things you will experience when using negative rake. This is not my first rodeo, as I've been on the machines, commercially, since 1957, although I spent several years away, refining precious metals. That said, you can profit from my comments, or you can ignore them.
Do not confuse the use of negative rake insert carbide tooling with the use of a quick change. A quick change is every bit as effective with HSS as it is with inserts. It has nothing to do with the type of tooling used, with the only real difference is one need not grind excessive front clearance, as is required by a rocker toolpost using a tool holder for HSS. The real value is that dials can be marked (or a DRO used) so tools can be changed without losing orientation with the dial (or DRO). Once set, you need not worry about finding center, or losing orientation. For more than one off, those features are important if you hope to get anything done. I strongly recommend a quick change. I do NOT strongly recommend carbide insert tooling unless you have a real need. If you wonder why, simply re-read my comments in my previous post. They were not intended to offend you, but to offer some insight, which is what you requested.
H
Because of the negative rake, cutting pressure is increased dramatically, which is the reason a more robust and powerful lathe is required. You are fortunate to have a reasonably robust lathe, so you are avoiding some of the pitfalls of small machines.
The increased cutting pressure is the problem for finish cuts. A given load must be applied before a negative rake insert will generate a chip. A new one, right out of the package, usually has a slightly rounded cutting edge (which is intended to protect the edge from degrading). In the early years of negative rake usage, one was admonished to hone a slight (.005") 45° angle on the edge, for that very reason.
If you still think that negative rake is perfect for tight tolerance work, try machining a fit for a bearing, then tell me how well it went. I'll be interested in hearing how you managed to remove a few tenths, especially in mild steel.
Do not misunderstand my comments. What I tried to do is point out to you the things you will experience when using negative rake. This is not my first rodeo, as I've been on the machines, commercially, since 1957, although I spent several years away, refining precious metals. That said, you can profit from my comments, or you can ignore them.
Do not confuse the use of negative rake insert carbide tooling with the use of a quick change. A quick change is every bit as effective with HSS as it is with inserts. It has nothing to do with the type of tooling used, with the only real difference is one need not grind excessive front clearance, as is required by a rocker toolpost using a tool holder for HSS. The real value is that dials can be marked (or a DRO used) so tools can be changed without losing orientation with the dial (or DRO). Once set, you need not worry about finding center, or losing orientation. For more than one off, those features are important if you hope to get anything done. I strongly recommend a quick change. I do NOT strongly recommend carbide insert tooling unless you have a real need. If you wonder why, simply re-read my comments in my previous post. They were not intended to offend you, but to offer some insight, which is what you requested.
H
Wise people talk because they have something to say. Fools talk because they have to say something.
Re: Negative carbide insert on old and slow
Just because it is a negative rake tool holder or insert doesn't mean that it can't have a positive cutting edge. There are both roughing and finishing type inserts available, although normally, negative rake tooling is for use as Harold describes.
Perhaps what you have is a sharp edge finishing type insert.
Perhaps what you have is a sharp edge finishing type insert.
Glenn
Operating machines is perfectly safe......until you forget how dangerous it really is!
Operating machines is perfectly safe......until you forget how dangerous it really is!
Re: Negative carbide insert on old and slow
I have read and re read your comments. A format like this can make words have strong personal flare and is not mine or your intension.
Before my purchase I have read many post and understanding of negative inserts. Thus my first comment about not using them on smaller lathes. I got it. I’m not an engineer or work professionaly in this trade and all my work is as a hobbyist. Appliying exacting useage and specifications in a production shop is important but I’m not doing that. Perhaps if I ask my questions this way. Since my lathe has demonstrated neg carbide inserts will work far better than almost everyones comments it won’t and knowing it’s not functioning as found in a modern robust machine. Question: 1- as stated old and slow. Is my lathe really that slow for carbide? Am I going to benefit using carbide inserts? 2- my goal is to turn out rough in work faster by reducing the diameter faster than running at 325 rpm with HSS. Size of work and materials used of course. 3- I think your stating a negative rake will never perform quality work on my lathe as described due to the force of cut but My intent is not to use this insert for fine work. As stated I will switch back to HSS. Given that am I better off to use positive inserts? 4- the purchase of QCTP is a big investment and for hobby work I believe to be completely a luxury after all we won the war using old and slow manual lathes. I don’t understand how center height is maintained using a QCTP and using HSS secured. Understanding that with words may be futile. Thus my wanting to move into a faster nicer set up. If carbide will work on my slower running lathe great and maybe not as designed and would make professionals laugh, however hobby work is often done somewhat crude but as long as it satisfies the operator. 5- to my understanding an insert tool holder is made specifically for either neg or positive insert only. Rake angles if not carefully observed when replacing them can be a problem. I’m not understanding the last comment by Glenn. I don’t want to get to deep into inserts as that’s a maze of options. Hopefully my questions can be answered in a general way.
Before my purchase I have read many post and understanding of negative inserts. Thus my first comment about not using them on smaller lathes. I got it. I’m not an engineer or work professionaly in this trade and all my work is as a hobbyist. Appliying exacting useage and specifications in a production shop is important but I’m not doing that. Perhaps if I ask my questions this way. Since my lathe has demonstrated neg carbide inserts will work far better than almost everyones comments it won’t and knowing it’s not functioning as found in a modern robust machine. Question: 1- as stated old and slow. Is my lathe really that slow for carbide? Am I going to benefit using carbide inserts? 2- my goal is to turn out rough in work faster by reducing the diameter faster than running at 325 rpm with HSS. Size of work and materials used of course. 3- I think your stating a negative rake will never perform quality work on my lathe as described due to the force of cut but My intent is not to use this insert for fine work. As stated I will switch back to HSS. Given that am I better off to use positive inserts? 4- the purchase of QCTP is a big investment and for hobby work I believe to be completely a luxury after all we won the war using old and slow manual lathes. I don’t understand how center height is maintained using a QCTP and using HSS secured. Understanding that with words may be futile. Thus my wanting to move into a faster nicer set up. If carbide will work on my slower running lathe great and maybe not as designed and would make professionals laugh, however hobby work is often done somewhat crude but as long as it satisfies the operator. 5- to my understanding an insert tool holder is made specifically for either neg or positive insert only. Rake angles if not carefully observed when replacing them can be a problem. I’m not understanding the last comment by Glenn. I don’t want to get to deep into inserts as that’s a maze of options. Hopefully my questions can be answered in a general way.
Re: Negative carbide insert on old and slow
I'm short of time, but I'll try to address your questions. We may have to kick this thing back and forth a few times, but answers to your questions are available, although you may or may not like what you read.
First, lets talk about a quick change. As I said previously, a quick change does not care what type of tool is used. Each holder, assuming you have one that has holders (not a square block, which I prefer for production work), is adjustable for tool height. The advantage in using one is that you can have a series of tools already set for use, and will be on center when the holder is dropped on the quick change post. I recommend one high above a rocker tool post. I'll address that this way. I purchased my Graziano lathe, new, back in 1967. It came with a rocker tool post. It has NEVER been on the machine.
Carbide inserts and holders, both negative and positive.
Glenn mentioned inserts for negative rake holders that are actually positive rake. They accomplish that by grinding the insert after it is formed. They are ground with diamond wheels, and have keen cutting edges, so carbide, today, is often sharper than HSS that has been hand honed. It performs exceedingly well for finish cuts, but tends to fail quickly if used for roughing. Depth of cut is limited, as is feed, as the heavy chip that develops from such cuts damages the insert edge, then it quickly fails. Even with modern micrograin carbide, inserts are relatively fragile (in the scheme of things). It is for that reason that one would rough with negative rake, then finish with positive rake. With a quick change holder, you can have both tool types mounted and coordinated with the dial (or DRO), so it makes it easy to produce more than one of any given item. It's all in learning how to run machines efficiently. Even as a hobbyist there will be times when you are called upon to make several identical items. The shine goes off running machines real fast when you are faced with that scenario, so it's important to be able to get through the task in reasonable time.
No one can answer your question about the machine you have and the speed it offers. That depends on the work you intend to do. If the vast majority of work you intend to do is under 1", you're kidding yourself if you think you'll be ahead with carbide. By sharp contrast, if everything you intend to do is over 1", and is often as large as six inches, you could benefit nicely (assuming you have enough horse power). Also, if the work you do is generally abrasive, or hard, carbide may offer an edge.
Your argument (not meant to be an argument) about not being able to remove much with HSS simply isn't true. If you understand good tool geometry and are able to grind a proper chip breaker, you should be able to take deep roughing cuts with reasonable feed. Sure, they're done at a lower rpm, but the coarse feed and depth of cut compensate for the faster spindle speed generally used for carbide. On modern machinery that most likely would not be true, but for older machines, often of limited horsepower, it certainly is. In your case, I strongly suspect that you'd be able to produce work in equal time by either method, but suspect HSS would be somewhat faster as you'd be restricted by power unless your machine has at least two horsepower. If it is powered by a fractional horse motor, there is no doubt in my mind, HSS would out-perform carbide.
One thing you must understand. Stopping a lathe in the cut will usually damage the cutting tool. If you attempt heavy cuts with carbide on a machine that isn't capable, you most likely will stall the spindle. That will spell the demise of the insert, and can damage the holder, depending on what happens to the seat when the spindle stalls.
H
First, lets talk about a quick change. As I said previously, a quick change does not care what type of tool is used. Each holder, assuming you have one that has holders (not a square block, which I prefer for production work), is adjustable for tool height. The advantage in using one is that you can have a series of tools already set for use, and will be on center when the holder is dropped on the quick change post. I recommend one high above a rocker tool post. I'll address that this way. I purchased my Graziano lathe, new, back in 1967. It came with a rocker tool post. It has NEVER been on the machine.
Carbide inserts and holders, both negative and positive.
Glenn mentioned inserts for negative rake holders that are actually positive rake. They accomplish that by grinding the insert after it is formed. They are ground with diamond wheels, and have keen cutting edges, so carbide, today, is often sharper than HSS that has been hand honed. It performs exceedingly well for finish cuts, but tends to fail quickly if used for roughing. Depth of cut is limited, as is feed, as the heavy chip that develops from such cuts damages the insert edge, then it quickly fails. Even with modern micrograin carbide, inserts are relatively fragile (in the scheme of things). It is for that reason that one would rough with negative rake, then finish with positive rake. With a quick change holder, you can have both tool types mounted and coordinated with the dial (or DRO), so it makes it easy to produce more than one of any given item. It's all in learning how to run machines efficiently. Even as a hobbyist there will be times when you are called upon to make several identical items. The shine goes off running machines real fast when you are faced with that scenario, so it's important to be able to get through the task in reasonable time.
No one can answer your question about the machine you have and the speed it offers. That depends on the work you intend to do. If the vast majority of work you intend to do is under 1", you're kidding yourself if you think you'll be ahead with carbide. By sharp contrast, if everything you intend to do is over 1", and is often as large as six inches, you could benefit nicely (assuming you have enough horse power). Also, if the work you do is generally abrasive, or hard, carbide may offer an edge.
Your argument (not meant to be an argument) about not being able to remove much with HSS simply isn't true. If you understand good tool geometry and are able to grind a proper chip breaker, you should be able to take deep roughing cuts with reasonable feed. Sure, they're done at a lower rpm, but the coarse feed and depth of cut compensate for the faster spindle speed generally used for carbide. On modern machinery that most likely would not be true, but for older machines, often of limited horsepower, it certainly is. In your case, I strongly suspect that you'd be able to produce work in equal time by either method, but suspect HSS would be somewhat faster as you'd be restricted by power unless your machine has at least two horsepower. If it is powered by a fractional horse motor, there is no doubt in my mind, HSS would out-perform carbide.
One thing you must understand. Stopping a lathe in the cut will usually damage the cutting tool. If you attempt heavy cuts with carbide on a machine that isn't capable, you most likely will stall the spindle. That will spell the demise of the insert, and can damage the holder, depending on what happens to the seat when the spindle stalls.
H
Wise people talk because they have something to say. Fools talk because they have to say something.
Re: Negative carbide insert on old and slow
Thank you for your write up. Again I may sound a bit argumentative or sound like a know it all. Yes I’m fully aware how a QCTP works maintaing center hieght and repeat work. However I don’t understand how a 3/8” HSS ground blank in a QCTP holder that needs sharpened maintains center height. Yes if one is good at grinding and I am but not good enough to keep center height escpecially with my vision. I tend to cut the relief down to make the edge I’m looking for. This is my handicap thus is my desire to move away from grinding every tool I own. I have considered grinding the negative carbide inserts to a positive with green stone or diamond but fully aware of creating a weak cutting edge doing so. My thought of using carbide for faster removal vs HSS for me is more a convenient than anything if it works (IF). My other hope was turning harder steel AND where I have a weld that draws the carbon in that makes that area harder. I have always struggled with weld areas on my lathe with HSS. The bit bounces off and back to the grinder I go. Center height is again lost particularly when diameter is less than an inch as you know the center height becomes very critical vs say a 4” piece. Yes I’m aware of carbide being more brittle in your last statement as well. Again not to sound like ya I knew that but yes I’ve done a fair amount of homework. I guess to my astonishment after my first few passes using a negative carbide insert on a non ridged slow lathe I wanted the world to know it will work. To what expense, well to buy one tool holder with insert is satisfactory for me. I will have a future use for this purchase and suggest others to try it as well for the reasons I’ve given. I agree for those that own a Chinese 6” or SB 9” I’d say no. I’m thrilled with how it performed. I think only the operator can decide if it’s right for you and your lathe. I suggest to anyone that finds this thread informative is to not shy away from pushing the limits of your machine short of creating damage of course. Hopefully you will find creative ways to make your hobby work better.
Re: Negative carbide insert on old and slow
Not to steer your thread OT, but resharpening a HSS tool and getting it back on center quickly is pretty easy. I made up an indicator stand that has a fairly heavy steel base with a vertical rod screwed into it. It's placed on my cross slide, a simple indicator snug is added to attach an indicator to the stands vertical post, and then replaced the standard indicator tip with what's known as an Elephants foot dial indicator tip. It's just an enlarged flat tip that screws onto the indicator. Set the indicator so it's zero point is at your correct tool tip height for your lathes head stock C/L. Obviously it can only work with a positive or neutral rake tool so the indicator tip measures the tool point elevation. Yes there's other tricks that can be used such as a steel scale against a chucked piece of material and gauging the tools elevation position by the scales tilt angle when the tool tip touches the vertical scale and lightly holds it against the side of the part in the chuck. That should get you within a few thou. But for some tools or materials it can be helpful to set them slightly above or maybe even a bit below the lathe C/L. A boring bar as one example for going a bit above the lathes C/L. That dial indicator allows a fairly accurate measurement to do that and gives an idea of how much above the lathes C/L that particular tool needs to be to give the best results with a few try's at it. For the time saved and the price of a cheap indicator it's well worth dedicating one to this job. Obviously this tool needs careful handling and storage so the indicators position doesn't get changed. I also machined a setting rod so if the indicator does get bumped that simple rod can be used to properly reset the indicators zero point. It also depends if your lathe has a large enough flat area on it's cross slide to use it the way I do. If not then using your bed ways as the datum surface will still work.
Those are some surprising results you got with a negative rake tool. And even more so with an old school lantern tool post. My lathe is a fair bit smaller and lighter so it's not really something that's worth trying out for me. But interesting to know that negative rake can sometimes work where many forum posts say they won't.
Those are some surprising results you got with a negative rake tool. And even more so with an old school lantern tool post. My lathe is a fair bit smaller and lighter so it's not really something that's worth trying out for me. But interesting to know that negative rake can sometimes work where many forum posts say they won't.
Re: Negative carbide insert on old and slow
It should be made clear that I've not said negative rake doesn't work on light duty machines. What I've tried to make clear is that the results don't live up to the potential of negative rake, and that only when one lacks proper spindle speed (a function of the horse power) and rigidity. If your machine happens to suffer from a lack of torque, when you attempt to take a respectable cut, the spindle is likely to stall. If you gear down to increase torque, you're moving towards the loss of performance that makes carbide desirable.
You can kick this thing around endlessly, but in the end when you've had enough experience to understand what I'm talking about, you may just see things the same way. Or not.
As far as centering a re-ground tool goes, I can't help you with that. I have always considered it a part of running a lathe, much as I see steering my truck is a part of driving. For me, it's no big deal, not even when I have to sharpen a threading tool in the middle of a thread. Again, very much a part of running a lathe.
In regards to hard spots due to welding, carbide may improve that to some degree, but I think you're going to come to the conclusion that the hard spots are going to influence the cut, carbide or not. That means that something that is intended to be round (or flat) won't be, due to tool deflection. That's particularly true on small, light duty machines, which are well known for a lack of rigidity.
So you don't pass along less than desirable information that has the potential to lead the unknowing in to a trap---it might be a good idea to describe in better detail what your machine is about. Detail the power of the motor, and, perhaps, and approximate weight of the machine. It's clear to me from your comments that a guy with a little Craftsman 109 lathe will get the idea he can benefit from carbide. He can't.
By the way, in your first post you made mention that there is precious little information to support the use of negative rake carbide on small machines. The bulk of what you've found suggests it's not a good idea. Ever wonder why?
H
You can kick this thing around endlessly, but in the end when you've had enough experience to understand what I'm talking about, you may just see things the same way. Or not.
As far as centering a re-ground tool goes, I can't help you with that. I have always considered it a part of running a lathe, much as I see steering my truck is a part of driving. For me, it's no big deal, not even when I have to sharpen a threading tool in the middle of a thread. Again, very much a part of running a lathe.
In regards to hard spots due to welding, carbide may improve that to some degree, but I think you're going to come to the conclusion that the hard spots are going to influence the cut, carbide or not. That means that something that is intended to be round (or flat) won't be, due to tool deflection. That's particularly true on small, light duty machines, which are well known for a lack of rigidity.
So you don't pass along less than desirable information that has the potential to lead the unknowing in to a trap---it might be a good idea to describe in better detail what your machine is about. Detail the power of the motor, and, perhaps, and approximate weight of the machine. It's clear to me from your comments that a guy with a little Craftsman 109 lathe will get the idea he can benefit from carbide. He can't.
By the way, in your first post you made mention that there is precious little information to support the use of negative rake carbide on small machines. The bulk of what you've found suggests it's not a good idea. Ever wonder why?
H
Wise people talk because they have something to say. Fools talk because they have to say something.
Re: Negative carbide insert on old and slow
I do have a better understanding now about undesirable results with negative inserts on machines not designed for them. A stick welder wasn’t really designed to cut metal but it will provide that function if no other solution can be found. I’m simply stating that I was always of the belief that my lathe would either chatter, stop the chuck or produce a horrible finish. You mentioned your lathe has never seen a lantern post. Perhaps I should start a new thread about switching over and what if any inserts I could use on my lathe. I’ve done plenty of reading about USA vs import. For my lathe BXA or CXA ? HSS inserts or HSS blanks? Positive carbide tools and holders recommended at all ? As moderator let me know if I should move this or answer briefly here. Thanks for your knowledge.
Re: Negative carbide insert on old and slow
No harm in that, but the information that accumulates will have little value to anyone but you, as they have no idea how their machines relate to yours. Like I said, until such time that readers have an idea of how robust your lathe may be, how it deals with carbide, negative or positive, doesn't equate to how THEIR lathe will respond. Even then, they may have individual issues that dictate differently. One thing is for sure, and applies to any lathe. HSS tooling will work just fine. Carbide may or may not.
As this is the lathe forum, and that quick change holders are commonly used on lathes, this would be the correct location for any discussions that relate to rocker and quick change tool posts.
H
Wise people talk because they have something to say. Fools talk because they have to say something.