Grinding chip breakers on HSS toolbits

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Harold_V
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Grinding chip breakers on HSS toolbits

Post by Harold_V » Thu Jan 11, 2007 3:33 am

I had offered to talk about HSS tool grinding, and did so with hesitation. My reservations were well founded. It's interesting how a person can do things on a routine basis, with success, and be at a loss to explain how or why, but that's where I find myself. It's nothing short of shocking to be without words, particularly when I rarely have a clue that it's time to shut up.

Grinding toolbits, for me, has been routine for so long that I have no memory of not being able to grind them. The skills involved were accumulated in practice, over a period of time, with the tools put to use in a production environment. By applying the tools under demanding circumstances, tool design was determined and performance evaluated on the machine. From this, I'd like you to understand that there is no substitute for experience. You can not learn the things that make one a good tool grinder from reading, you must experience them, and see the end result in order to understand the effects of subtle changes in tool design that spell success, or failure.

Functional turning tools are ground to a mental picture, with relief angles ground to fit the requirements of the task at hand. While these angles are important, they are not carved in stone, and vary with circumstances. It becomes a matter of course to grind in such a fashion, so no guides, aside from profile gages, are necessary. That's not to diminish the importance of relief angles, but they are flexible enough that they are not a serious concern unless one finds himself in a production environment, where a maximum performance over a long period of time is a requirement.

Often times, an alteration of an angle, particularly a rake angle, will allow for better performance for the short haul, often long enough to complete a rather unpleasant task. Turning the corners off a stainless plate cut from a square is a good example. Excessive positive rake, coupled with a very light feed, using a plunge turning technique changes the job from one of misery to one with few, if any, problems. It's easy enough to achieve functional angles without gauging, so the eye should be trained accordingly.

Having said that, I still need to say enough to help those that struggle. Which ones, and for what reasons, remains a mystery, so I'll start the ball rolling and try to answer questions if there are any. Best thing for me to do at this point is to talk about basic machining concepts, and what influences performance. The principles remain pretty much the same as you move from one type tool to another, taking into account that working in bores requires a serious rethink of front relief angles, which are influenced by bore size.

Tools that are ground with simple angles perform reasonably well, but often with higher cutting pressure than might be desired, and they rarely have any features that manipulate the chip. Surface finish and production, under those circumstances, can suffer. Chip control is often just as important as the cut itself----and must be dealt with accordingly. Faster operations are one of the benefits, as is safety through the elimination of stringy chips.

The mechanism by which this occurs is a ground chip breaker. Such an addition to your tool opens the door to greater rake angles, lower cutting pressure, and chip control Chip breakers can be ground with sufficient positive rake to seriously improve cutting characteristics and still have excellent edge strength, due in part to reduced heat at the point of cut, a result of positive rake. An offset to the positive rake is accomplished by grinding a cylindrical breaker, in which the chip reverses direction quickly after leaving the cut, more or less counteracting the effects of positive rake (hogging). The radius of the chip breaker, in conjuntion with the proper amount of front relief, tends to control hogging and chatter. Properly ground, the breaker will roll the chip, yielding either C's, 9's, or an endless coil. The coil isn't as desirable, but from the standpoint of safety, is much better than strings, and is often much easier to dodge than hot C's or 9's. There are times when a coil becomes the chip of choice, such as when boring a hole that has minimal bar clearance and it's desirable for the bore to not accumulate chips.

Metals, for the most part, respond to being "peeled" (shorn via positive rake) much better than they do to being displaced by brute force (negative rake). For those that use HSS, not carbide, the advantages to using reduced rake are few. It is not an option when machining steel, and offers no advantages when machining aluminum, so it's pretty much restricted to use in soft cast iron and free machining copper alloys, in both instances to control hogging, with no real advantages in machining aside from a prolonged edge when machining cast iron. In those examples, it is generally accepted that rake be reduced to 0, with no real need to go negative. Chip breakers, by sharp contrast, can be applied under almost all circumstances with huge benefits, except for machining free machining copper alloys, and, once again, soft cast iron.

Chip breakers are sensitive to speed, depth of cut and feed rate. Therefore it's nearly impossible to describe one that suits all purposes. Again, the basic principle remains a constant, so all one need do is make subtle changes to the breaker to improve performance when it does not perform to expectations. Likewise, a change of feed rate, spindle speed or depth of cut often will yield good results with an existing grind.

A narrow, deep breaker will usually yield poor performance, although it might serve for finishing cuts. Armed with that idea, one would widen a breaker that did not permit free flowing of the chip. It is also desirable for the chip to have the ability to flow freely, with a subtle change of direction such that there are no corners to trap the chip and prevent flow. A gentle radius is the most preferred design, although other configurations can work. By choosing a radius, positive rake can be introduced to the cutter without building any traps, with minimal effect on heat transfer. .

Please take note: The information I'm providing is pretty much useless for rocker tool post use. Between the included positive rake of the post, and the angle necessary to keep the post away from the cut, the geometry is totally different. Tools I recommend are intended to be mounted in a holder without rake, and at right angles, or very near right angles, to the turn. Both of those features become impossible with a rocker post. The details on chip breakers can, indeed, be applied to tools ground for use in a rocker tool post, but the extreme angle differences must be taken into account. In general, poorer performance can be expected as compared to holding cutting tools in a different post.

In order to facilitate the presence of a chip breaker, tool design is usually slightly different form conventional grinds. Where the included angle of the top of a right hand turning tool might have been in the vicinity of 60° for conventional grinds, an angle of 80° is more desirable, assuming it isn't in the way of the use of a center. In such a case, the tool is generally relieved to clear the center, leaving the bulk of the material that isn't in the way. By providing the greater angle, there is room for the full chip breaker to be ground without sacrificing much, if any, of the rear portion. That keeps the chip breaking properly, but plays no role in how the cut behaves otherwise. The bulkier tool is somewhat better at handling heat, so that is a side benefit.

For starters, lets consider the tool, below. It's a boring tool, one that is very useful in removing stock rapidly. The cutting edge is ground at a slightly less than 90° to the shank, so that the tool is able to bore to depth and face. For through bores, the tool can be mounted at a slight angle, so the cutting edge has a minor amount of lead. This design works exceedingly well in both circumstances, so there is no need for two different tools for boring. The cutting edge in this case is the end of the bar, which I will reference as the front. The relief angle will work as low as 5°, and up to 8°, and is affected by feed rate. You'll notice as you alter the angle, the tool will have more or less tendency to hog, and often chatter. You can use that feature to help control the performance of the bar.

Side clearance is in keeping the requirement for the tool of choice to enter the hole for which it's intended. There is no point to giving specific guidelines, for each hole has it's own demands. Just make sure that the heel of the tool, with the cutting ege in contact with the bore, has clearance. 5° or more beyond the radius of the part is very acceptable.

Pay particular attention if the tool is very close to bore size, so the back bottom edge of the bar doesn't drag in the bore. Remember, none of the angles are critical, so long as the tool is kept within reasonable boundaries, it will function very well. Avoid extreme clearance angles to help control hogging and to provide the maximum edge strength possible. If, by chance, you find the tool does not cut freely, inspect the tool for signs of dragging in the bore------and check the chip breaker to insure that the chip being generated is flowing freely. Chip stack up will quickly snap a tool if left unchecked. Chip welding alone can be the source of much grief. Use a tool of this design with lubrication. Brush application is adequate, just don't run a chip breaker dry. If, when machining aluminum, you find it has a tendency to streak off on the breaker, it's always a good idea to spin a small cylindrical stone in a chuck and apply the breaker to the stone to polish the surface. The smoother the better. Be careful to not round the cutting edge should that be necessary.

The chip breaker is ground freehand, using a standard grinding wheel with a radius dressed on the corner. Alternately, an old wheel can have a radius hand dressed and used exclusively for such grinding. That eliminates rounding the corner of your wheel, prolonging the useful life. The radius on the wheel can be smaller than the one you desire, but it is not as easy to get a uniform grind.

I also suggest that tools be ground without the use of a rest, which I will address in a different post. Lets see if this has helped anyone, or if it has raised any questions that may need to be addressed. The next tool will likely be a right hand turning tool. Once you have seen a couple designs, you should be able to envision a tool of almost any design, and grind accordingly.
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Last edited by Harold_V on Wed Apr 15, 2009 11:48 pm, edited 1 time in total.

torker
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Post by torker » Thu Jan 11, 2007 4:30 am

Harold...I just got off night shift (four months of it...yukk) and my head is a bit fuzzy but I'm glad you took the time to write this. I've been battling with a couple of thinwall 3 1/2" deep bores all week in my spare time. It hasn't gone well. I normally use brazed carbide boring bars and when sharpened right they aren't bad but they require a lot of pressure and high rpm. I've got one of the bars for HSS that uses a short piece of 1/4" toolbit sticking out at 90*. I've tried a lot of different profiles but haven't had the success I should. I think I know what you will say...I should grind a narrow chipbreaker groove along the length of the short bit...correct?
That's what you told me for a facing tool for alu and it worked well. I never thought of doing this with a bit for steel. Or do you have another trick up your sleeve for this type of bit?
I'm getting a very rough finish....my point is too sharp. I keep getting the nose a bit rounder but it's still not nice. I theenk I'm going about it all wrong. I've been using a typical 60(ish) deg profile with the point sticking out the side. Have a decent chip breaker ground in it but it's looking wrong now that I see your.
Thanks again!
Russ

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Post by Harold_V » Thu Jan 11, 2007 5:32 am

torker wrote: I've been battling with a couple of thinwall 3 1/2" deep bores all week in my spare time. It hasn't gone well.
Material? Thickness of wall? Diameter of bore? Tolerance? Fighting chatter? Through bore, or to a shoulder?
I normally use brazed carbide boring bars and when sharpened right they aren't bad but they require a lot of pressure and high rpm.
That's because they generally lack proper geometry for free machining. If readers come away with nothing more than the understanding that a proper chip breaker changes the way a tool performs, almost always for the better, each will have learned a valuable lesson. Relief angles on tools play a far less important role than some may have you believe. What really matters is how the tool sees the work-----rake. It also often dictates tool life----so there are times when one must compromise.
I've got one of the bars for HSS that uses a short piece of 1/4" toolbit sticking out at 90*. I've tried a lot of different profiles but haven't had the success I should. I think I know what you will say...I should grind a narrow chipbreaker groove along the length of the short bit...correct?
I'm inclined to say yes, but without knowing more, I hesitate. Thin wall work can be exceedingly tricky---whether you're turning or boring. I'd want to know a lot more about your setup, including the nature of the bar, diameter (of the bar) , if you're running on center, speeds and feeds, and, of course, what material, what tolerance, and what kind of surface finish you're trying to achieve. Sort of a repeat of the above things I mentioned. It's all important if you're trying to solve the mystery. Some things can be unreasonable and make the task border on the impossible without addressing the job from a different perspective.
That's what you told me for a facing tool for alu and it worked well. I never thought of doing this with a bit for steel.
That's the beauty of chip breakers. They work on almost everything----although hard materials shorten their lives considerably. Tough materials can yield surprising results, however. It's important that you understand the difference between hard and tough. They're not the same thing.

The nature of chip breakers for steel as opposed to aluminum would be a slight reduction of rake angle----and if the machine is light duty, width and depth may have to be adjusted accordingly. A shallow cut with fine feed would require a narrow breaker, and shallow, in order for the chip to curl. By contrast, a deep cut with heavy feed would require a wider and deeper breaker. Rake angle may have to be altered to prevent edge failure----which can be accomplished by using a larger radius for the breaker. As the radius increases, the angle diminishes, and it isn't nearly as deep. These features are best determined by trial and error, so the tool suits the exact conditions in which it's being employed.
I'm getting a very rough finish....my point is too sharp. I keep getting the nose a bit rounder but it's still not nice. I theenk I'm going about it all wrong. I've been using a typical 60(ish) deg profile with the point sticking out the side. Have a decent chip breaker ground in it but it's looking wrong now that I see your.
Thanks again!
Russ
If you try something that resembles a tool in my post and are still having trouble, post a picture of your tool and lets see if we can figure out what the problem is. I agree----you're probably going about it wrong, but that's how we learn. You should build a strong, lasting impression of what doesn't work from this experience. It's all part of arriving as a machinist.

Harold

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Hyper
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Post by Hyper » Thu Jan 11, 2007 7:29 am

You're not going to give us a test on this, are ya ? LOL

But seriously, very interesting write up you have there Harold.
And, nice looking hand done grind on the chip breaker !

Here's my questions for ya on this subject.....

Which do you grind first, the chip breaker or the cutting edge.

Also, do you have any suggestions for chip breakers when working with something like Delrin? (for turning & boring)
I had thought about a chip breaker that was more angled instead of radiused, but haven't tried that yet.

Thanks

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Marty_Escarcega
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Post by Marty_Escarcega » Thu Jan 11, 2007 8:09 am

Thanks a bunch for the write up Harold! Can you show (when you have time of course) examples of left/right bits and threading bits as the way you would sharpen them? Thoughts on the Aloris threading bit that comes with their QC sets?
"Jack of all Trades, Master of None"

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Post by kapullen » Thu Jan 11, 2007 10:28 am

I like to imagine the action of a cutting tool like
an icecream spoon at work.

When you have a light depth of cut on hard frozen
cream, the spoon skids over the icecream
digging here and there.

A bit heavier depth will make a nice curl out of
the spoon that you can continue forever.

Deeper, and the spoon will choke, and bind, plowing
the icecream out of the way on both sides.


Torker, your problem may be the chips binding between
the bore, and the boring bar it'self.

Sometimes I will grind chip clearance on the bar
to help curl the chips foreward out of the way.


When using heavy industrial machinery, varying the
depth of cut, and feed, can control chip formation
on some materials.

I will lower the depth of cut, and increase the feed
to produce the curl Harold talks about, or with a bit
more feed, form the c's and sixes.


I found that a tool as Harold pictured, with a couple
thousants wide flat on top of the edge, will cut freely, as well
as last a long time for roughing.

That knife edge is prone to chipping and over heating.


Kap
Fadal Turn, Fadal Vmc 15, Prototrak 16 x 30 Cnc Lathe, Pratt and Whitney 16 x 54 lathe, Pratt and Whitney Vertical Shaper, G & E 16" Shaper, B & O Electric turret lathe, 36" Doall band saw,
Enco B.P. Clone, Bridgeport CNC Mill, Delta 12" Surface Grinder.

OneOldCat
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Post by OneOldCat » Thu Jan 11, 2007 10:47 am

Harold,

Thanks for an excellent start-off on what I hope will be an extensive series of threads on lathe tool forming and sharpening (and, perhaps, will eventually extend to similar work on other types of cutters).

Funny how memory works - roughly 25 years ago, I knew at least some of what you're discussing here, from teaching metalworking and machine shop practice and from working on the machines every day. However, in the intervening years, I thought I'd forgotten it all - and, on a conscious, usable level, I had.

When you don't work with it every day, knowledge corrodes away, just like any other tool.

Thanks very much for bringing it back, and for extending and enhancing the relatively little I knew back then.

I hope, when you discuss grinding/shaping tools <i>sans</i> rest, you will also include some discussion of proper grinding wheel types, sizes and speeds, and the proper dressing of the wheels. :)
Making little ones out of big ones, and then trying to assemble big ones out of little ones...

"Engineering, after all, is determining the correct wrench to bash the proper screw into the appropriate size and shape slot..."

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Lew Hartswick
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Post by Lew Hartswick » Thu Jan 11, 2007 12:30 pm

Harold, Could you show a sketch of how the bit is orientated wrt the the
work? I guess the bit is parallel to the axis of rotation of the part , due to
the curve on the side but is it also "tilted" sidewise? For a deep bore how
does this work?
Thanks.
...lew...

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Post by Harold_V » Fri Jan 12, 2007 1:42 am

Hyper wrote: Which do you grind first, the chip breaker or the cutting edge.
My approach is to grind the entire tool first, leaving room for touchup.

Reason? Even when using a grinder that I recommend, you can't always see what you're grinding when you're grinding the chip breaker. You run the risk of rounding the cutting edge, or generating a breaker that doesn't parallel the edge as you might like. By leaving a small amount (locating the breaker slightly back from the desired cutting edge), you can then grind the cutting edge to the chip breaker. It's clearly visible, and easy to follow.

By the way, the tool that Kap mentioned for roughing steel, would be ground exactly that way, and it was an excellent tip from him. I rarely grind my (turning) tools that way, but only because I usually go to negative rake carbide, using molded breaker inserts. Interestingly, they are made the same way---with a shallow breaker behind the edge. It need not be at the edge to function----I do that only to increase positive rake and reduce cutting pressure. It can work against you in steel, as Kap so kindly mentioned. Should I use my design in steel and have a problem with edge life, I usually reduce the rake angle instead of move the breaker. Not better or worse, just my way of working.
Also, do you have any suggestions for chip breakers when working with something like Delrin? (for turning & boring).
Absolutely! Duplicate what you see in the posted pics, and, if anything, increase the rake angle. Make sure the chip can flow freely, and run the machine flat out, assuming that doesn't present any problems. Delrin is one of the finest of all plastics to machine and responds to positive rake in ways that are hard to understand. Keep the tool exceedingly sharp to avoid chipping the material. It's not uncommon to have a string chip flying over your shoulder, landing behind you. It may or may not break, but that is of little consequence with Delrin. If you insist on breaking it, reduce the width of the breaker (or deepen it), but stay with all the positive rake you can achieve. There are no heat issues with turning or boring Delrin, so the fragile edge isn't a problem.
I had thought about a chip breaker that was more angled instead of radiused, but haven't tried that yet.
Regardless of the nature of the breaker, you need a slight radius at the point of contact that determines the diameter of the cut. The radius should be a function of the feed rate, to help blend the feed lines. The angle you spoke of can work for or against you, depends on circumstances, but a sharp corner will still yield a relatively poor finish. Only with a narrow trailing straight portion or a radius would it not.

Because of the serious amount of positive rake, the compound angles you generate when applying a radius to your tool can create problems. The cutting edge tends to fall well away from center. If you keep the tool sharp, and the radius to a minimum, you should have excellent results. Unless you're machining a material that is notoriously bad for finish (C10108, for example), this machining procedure should yield good to excellent finishes. It stands to reason that you should select proper feed rates for finish cuts.

Should you fail to get a decent finish, a quick look at the tool will usually tell you what's wrong------and if it doesn't -------you need to keep studying until it does. Remember---you will not learn to grind functional tools by reading---that serves only to guide you while you learn to apply the geometry. You can follow the recipe and still get a non-functioning tool. Experience helps identify why.

Hope this helps

Harold

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Post by Harold_V » Fri Jan 12, 2007 2:53 am

Marty_Escarcega wrote:Thanks a bunch for the write up Harold!
You're very welcome, Marty. I hope that something useful comes from it----it's been an interesting experience for me---finding myself without words. :lol:
Can you show (when you have time of course) examples of left/right bits
I will likely grind and discuss a second tool, a right hand turning tool. By then, if the reader is still having trouble, all the discussion in the world won't help. Grinding toolbits is no different from playing the piano. You can read and read, but until you tickle the ivories, you won't know how to play the instrument.

The guidelines I've set forth, and will mention again when I get to the next tool installment, rarely change. The basics of cutting tool geometry repeat, regardless of how the grind is applied to the tool. Armed with that idea, you should understand that if you desire to grind a tool that has not been discussed, the only decision you need make is how you want the breaker ground on the tool. The rest is up to the circumstances at hand----material type----depth of cut, feed rate, spindle speed----all of which drive the design. Again, this is something that comes from experience, and the only way you can get that is to get your hands dirty. Once you understand the concept, grind away and look for the results you desire. If you don't get them, alter features until you do. It's something that you learn quickly if you have the opportunity to use it long enough -------which was the real advantage in learning on the job. Some jobs we ran would last for a few days-----an ample learning curve, which provided knowledge for the next job. You'd be surprised how quickly this thing comes together if you give it a go.
and threading bits as the way you would sharpen them? Thoughts on the Aloris threading bit that comes with their QC sets?
I am not familiar with the Aloris threading bit, so I hesitate to provide the slightest input. I don't use an Aloris type holder, and haven't for more than 39 years. My preference is a specific (OK Rubber Welders) square indexing block. Perhaps someone like Kap could provide some useful information. Kap has some serious experience to his credit and is very knowledgeable about the ways of good and proper machining.

I've always hand ground my threading tools, no work rest, using a fishtail as a guide. In order to see the true profile of the tool, it should be viewed with a light behind the tool and gauge, looking for light that spills through any gaps that are found. Trusting a view without this process tends to yield forms that are not true.

The sole exception to my hand grinding threading tools would be those rare times when I had a surface grinder at my disposal, with a threading tool block that established the proper angles and clearances. That makes the task real easy, although it does nothing toward promoting your skills. When my shop is setup and running, I fully intend to make such a block. I don't need any more practice. It's time for my tired eyes to do some things the easy way.

Know one thing about threading, or any form tool that is not a right angle. The moment you introduce rake, you move away from the proper configuration, and risk losing acceptable form. With threading, that is a particular problem, due in part to the rather narrow band of tolerance, plus there are some trick things you can do to end up with a very nice thread, but plunge cutting is very much a part of it-----so any rake ground on a threading tool not only affects form, but limits the way you can use the tool. Unless you're using insert threading tools that are ground with compensation for any deviation from 0 rake, never use a threading tool that has rake applied if you expect proper results. The tool may function, but the results will be questionable.

Harold
Last edited by Harold_V on Fri Jan 12, 2007 3:58 am, edited 1 time in total.

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Post by Harold_V » Fri Jan 12, 2007 3:10 am

OneOldCat wrote:Funny how memory works - roughly 25 years ago, I knew at least some of what you're discussing here, from teaching metalworking and machine shop practice and from working on the machines every day. However, in the intervening years, I thought I'd forgotten it all - and, on a conscious, usable level, I had.

When you don't work with it every day, knowledge corrodes away, just like any other tool.
I'm suffering from the same condition. I closed the doors on my commercial shop in '83, and hated the machines. So much so that they sat idle for several years, being used only when absolutely necessary.

Were it not for the mental exercises I go through trying to help by posting, I'm afraid what little I had learned would have long ago been relegated to the trash bin. It shows sometimes in the things I say-----where I have lapse of recall and don't remember things as they were. Still, my poor guidance is probably better than no guidance. The things I've discussed are not generally found in text books-------they come from hands on experience, with the added benefit of having worked under some heavily skilled and talented tutors. They showed me the way, but fully expected me to pick up the ball and run-----which I did.
Thanks very much for bringing it back, and for extending and enhancing the relatively little I knew back then.
Coming from one that used to teach, I especially value and appreciate your comments. It's nice to know that, perhaps, I'm providing information at some level of usefulness. As is often the case, we encounter people that have skills, but can't pass them on to others. My years on the machine were very successful, but I had no idea if I had the ability to pass to others the knowledge I had accumulated. Writing has never been one of my claims----so I consider myself fortunate to be able to convey my thoughts, such as I do.
I hope, when you discuss grinding/shaping tools <i>sans</i> rest, you will also include some discussion of proper grinding wheel types, sizes and speeds, and the proper dressing of the wheels. :)
I fully intend to address those issues. I have a precision grinding background, and while my experiences are quite old, I am very familiar with wheels and how they perform. I'll make specific recommendations as to wheel types, how they should be mounted, and how to judge a wheel when it isn't performing to satisfaction. Dressing is all important, as you know, so I'll address that issue as well. All I need is time. It may well be a week or so before the next installment, but I will get it done.

Thanks for you very nice comments.

Harold

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Post by Harold_V » Fri Jan 12, 2007 3:57 am

LewHartswick wrote:Harold, Could you show a sketch of how the bit is orientated wrt the the
work? I guess the bit is parallel to the axis of rotation of the part , due to
the curve on the side but is it also "tilted" sidewise? For a deep bore how
does this work?
Thanks.
...lew...
Lew,

As you alluded, the tool that is posted would be mounted very close to parallel to the bore, with no lead if boring to a shoulder. The tool shown addresses this issue, considering the included angle of the tool is less than 90°, which allows for facing. My usual practice is to mount the tool so it is not quite parallel to the intended face, with the tip the highest point. That permits machining a square corner and a facing cut towards center. By proper configuring the tool, that allows for a slight angle when mounting the tool in the post---with the heel farther away from the operator than the point. That helps prevent chip accumulation by providing additional clearance between the bar and the bore towards the shank.

Through hole boring is a different matter, but can be accomplished with the same tool. Depending on bore size, you may or may not be limited by the relief ground on the tool. Often the angle can be set such that the tool can enter the bore past the relief, but that is determined by bore size. A large bore that provides ample clearance makes that possible, whereas a bore that is small as compared to bar size would not allow for the same setup. Setting the tool in this manner provides a lead that is quite desirable when moving metal. It also often helps direct the chip forward of the cut, a very desirable thing if you don't want chips in the bore. Sometimes you just have to tough it out-----chips are known to do as they please.

You should have total flexibility in the way you use a tool of this nature. As long as it will accomplish your goals, there are few restrictions. One important thing to keep in mind is to keep the tool on center at all times, but if you must deviate, go above slightly, never below. Boring above center often yields a few benefits, especially when the bar is a tight fit in the bore. Use it with restraint-----you're always better off on center. And don't hesitate to experiment-----that's how we learn.

Boring tools such as I have posted have limited depth capabilities, and are in no way intended to replace a long boring bar-----but they replace them with far better success when the work allows for their use. They also often open up a position on an indexing block that otherwise would be covered by a too-long boring bar. The design of tools of this nature are famous for moving metal. That's particularly true for the guy that has a fractional hp machine that isn't otherwise capable of serious cuts. Small machines benefit from this tool design to a huge degree. The only caveat is if the machine is too light and the positive rake creates hogging. Guys with small machines should approach the use of this design much the same way one would when machining brass. If hogging is a problem, it can often be corrected by altering front relief, and a lessening of rake angle and width of the breaker*. As I said, experiment. You won't learn much from reading.

Harold

*Comment added for clarification.
Last edited by Harold_V on Fri Jan 12, 2007 4:43 pm, edited 1 time in total.

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