Sometimes is smart to change approach

All discussion about lathes including but not limited to: South Bend, Hardinge, Logan, Monarch, Clausing and other HSM lathes, including imports

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tornitore45
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Sometimes is smart to change approach

Post by tornitore45 »

I have to remove a lot of metal from a 2.5" diameter x 10" long 4140
Is a tall order for my 9x20 Chinese hobby lathe

One end in the 4 jaws held up on a live center in the tail stock
Try brazed carbide C5 and C6 ... chatter city at all speed and feeds with lube 0.025 DOC max

Slog along until decided to quit, have a hunch that the minimal relief and rake of a brazed carbide may be the culprit, forces are just too high.
I do my best thinking in the morning in the twilight zone between sleep and consciousness and resolved to try a different tool.

I ground a classic HSS shape. The one where a single gutter perpendicular to the axis forms a high rake cutting edge and a chip breaker at the same time.

Well the chip comes out long but the chatter is gone, will try feeding harder and see how far can be pushed but just getting rid of the racket is good for now.
Mauro Gaetano
in Austin TX
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Harold_V
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Re: Sometimes is smart to change approach

Post by Harold_V »

That's the lesson I've been trying to convey as long as I've been on this board. A properly configured and ground HSS toolbit will generally outperform carbide on light machines. I'll never understand why so many resist its use.

If the chip is coiling, but doesn't break, that's acceptable. If, by chance, it isn't coiling, or if you hope to have it break, even if it's coiling, simply narrow the chip breaker, so it forces the chip to form a tighter coil.

Avoid using a sharp corner on the wheel used to create the chip breaker. The chip should be free to flow without hitting an abrupt wall.

H
Wise people talk because they have something to say. Fools talk because they have to say something.
Glenn Brooks
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Re: Sometimes is smart to change approach

Post by Glenn Brooks »

Harold, you said “narrow” the chip breaker. Do you mean a shorter length from the front, cutting edge back onto the length of the tooling?

I often have these loooooongosh chips also. 5’ is my record I think...

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SteveM
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Re: Sometimes is smart to change approach

Post by SteveM »

Good video of speeds and feeds with steel:
https://www.youtube.com/watch?v=NpuZFCG2JBg

Amazing how a small change in speed or feed, sometimes in a different direction than you'd think, can make going from long stringy chips to nice curls breaking off.

Steve
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Harold_V
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Re: Sometimes is smart to change approach

Post by Harold_V »

Glenn Brooks wrote: Fri Oct 02, 2020 6:03 pm Harold, you said “narrow” the chip breaker. Do you mean a shorter length from the front, cutting edge back onto the length of the tooling?
No. The width of the breaker, so it turns the chip in a tighter circle. You can often accomplish the same thing by deepening the chip breaker. Increasing feed rate is always helpful, as is depth of cut.
I often have these loooooongosh chips also. 5’ is my record I think...
If you're making reference to coils, yeah, they can really stretch out so long as they are free to twist as they come off the machine. I've seen then ten feel long or more, all depends on the nature of the cut and material. Those coils are pretty easy to clean up, and they're leaps and bounds safer to handle than strings.

If you're talking about strings, they can be exceedingly dangerous. When a string gets long and is still near the work, if it happens to get caught in the chuck, and it does happen, it rapidly returns to the machine and will drag along with it anything that happens to get attached. Beyond that, there's usually a razor edge on the chip, so you're at risk of being badly cut. I try to avoid strings always--but some types of material make that difficult. Some materials simply don't break easily, while others cooperate perfectly.

H
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RMinMN
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Re: Sometimes is smart to change approach

Post by RMinMN »

Harold_V wrote: Thu Sep 24, 2020 4:15 pm That's the lesson I've been trying to convey as long as I've been on this board. A properly configured and ground HSS toolbit will generally outperform carbide on light machines. I'll never understand why so many resist its use.
I can buy an insert tool that will already have the proper shape. If I destroy the insert, it is only a small outlay to purchase another and seconds to replace it so I can get back to work. Grinding takes both skill and time. I don't always have both and sometime neither. The latest insert tool I bought puts a better finish on my stock than any of the hand ground ones. Notice that I didn't say brazed carbide, the last of those I had just got replaced.
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Harold_V
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Re: Sometimes is smart to change approach

Post by Harold_V »

All well and good so long as your machine can benefit from carbide. Many can not. If yours is one of them, until you've experienced the difference to which I've made mention, you'll never understand.

H
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mcostello
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Re: Sometimes is smart to change approach

Post by mcostello »

It is good to learn the skill of grinding tool and drill bits. If You don't have a Plan B, or, Plan C, etc...., You might be in trouble. You don't have to learn it all in one afternoon, just a little now and then and build upon it.
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Harold_V
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Re: Sometimes is smart to change approach

Post by Harold_V »

mcostello wrote: Sat Oct 03, 2020 7:27 pm It is good to learn the skill of grinding tool and drill bits.
That's something I've tried, occasionally in vain, to communicate to those who are not well experienced in machining. Some don't seem to agree.

I wonder what the guy who lacks these qualities does when it's Saturday morning, the supply stores are closed, and they have need for a tool that can easily be created by hand, yet the necessary skill to do so has never been acquired.

It's pretty simple. If you hope to learn to machine, learning the art of fashioning cutting tools is very much a part of that experience. If one choses to ignore the learning curve, it's a serious disservice. Until one fully understands cutting tools, how they cut, and why each feature is important, one most likely will not have a clue in solving a cutting problem.

Worst of all--it borders on the impossible to help a guy who doesn't understand cutter geometry.

As you said, it need not be learned in a day. One can peck away at it each time there's a project, and in due time the skills are acquired. Ignore it and they never will be.

Nothing sets a guy free like having the ability to fashion a tool when it's needed, or to be able to troubleshoot a problem when it is cutter related. Hard to do without learning the basics.

H
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tornitore45
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Re: Sometimes is smart to change approach

Post by tornitore45 »

So much is being made of grinding tools, is no rocket science. Unless one has uncontrollable tremor in the hands it can be done without a rest and even a if one can trust himself with a steady hand one can resort to a rest.
After the main shape is obtained, removing most of the metal, putting on the angles and the chip breaker takes no more than 2 minutes.

If you have a friable wheel good. If you don't it may not be ideal but one can grind a serviceable tool on a gray wheel.
If you have a stone touch it up, if you do not the tool will work. Not as well but will cut.
On a delicate part use more rake and smaller tip radius
Learn to sense a tool rubbing, it is squealing at you.
A parting tool likes to be a bit below center, otherwise it will not plunge until pushed too hard and then you know what happen. Some people will not agree with me on this but is what my little lathe wants.
Big radius tool tend to chatter so if you have a large fillet move in and move sideway to engage a smaller portion of the cutting edge until you are almost done, then polish up the fillet with full engagement and nearly zero DOC

Is all geometry, yes, but even one that flunked HS geometry can master the process.

In a pinch a drill rod can be machined precisely on the mill, hardened and tempered and will work.

If you are in this business to make money, than in these day we are talking CNC and repeatable tool position. In that case the practical and economical solution is inserts all the way, BUT there will always be that Sunday morning emergency.
Mauro Gaetano
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pete
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Re: Sometimes is smart to change approach

Post by pete »

Chatter and the materials natural resonance frequency that are the cause of that chatter probably takes a university degree to fully understand. Lucky for us it's not needed, we only need to understand it happens, some of the reasons for why it does, and a few tricks that should work most times, but not always. I got bit by it a long time ago and it was pure luck I tried upping the feed rate. Since then I learned it's standard practice to increase the feed, drop the rpm, or change the depth of cut, or a change with all three. That chatter is a combination of the machines rigidity, tool rigidity and the same for the materials natural resonance while it's being machined in those current conditions. Most times if you can change at least some of those parameters it disappears. So dropping the speed, and/or upping the feed rate loads the machine, cutting tool and material differently. In rare instances I've read that raising the rpm can sometimes work. Deep hole boring is something where that chatter can happen easily. Long tool extensions work much like a tuning fork for visulisation purposes. Even wrapping the end of the boring bar with a length of solder or slapping a lump of plumbers putty on it can be enough to change the boring bars natural resonance. I've read more than once about wrapping a part like a brake drum with a rubber bungee cord to stop chatter on a thin walled large diameter part. So that feed rate, rpm or depth of cut changes still aren't the only solutions. But there usually the first things I'll try.
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Harold_V
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Re: Sometimes is smart to change approach

Post by Harold_V »

tornitore45 wrote: Sun Oct 04, 2020 7:31 am A parting tool likes to be a bit below center, otherwise it will not plunge until pushed too hard and then you know what happen. Some people will not agree with me on this but is what my little lathe wants.
The one thing to remember with a parting tool is that on light duty machines with the tool below center, the stock can climb the tool as it approaches center. That often leads to a broken tool and a scrapped workpiece. For that reason, it's very best to keep the tool on center. If it won't cut without being below, you'd be well served to investigate the front relief. If it's too shallow, a tool can be difficult to feed. Too much relief can be the cause of hogging (self feeding).

H
Wise people talk because they have something to say. Fools talk because they have to say something.
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