DEEP THREAD CHATTER

[shoplady#1]

HI GUYS,
GETTING READY TO USE A SPECIAL MAKE I.D. BAR FOR AN I.D. GROOVE. THE BAR IS 1 3/4 DIA X 16" OAL TO GO 12" DEEP INTO I.D. THE GROOVE WILL BE .130 w X .435 DEEP. THIS IS MORE THAN 4:1. THE INSERTS ARE ALSO SPECIAL MAKE. THIS WILL BE SET UP ON THE SH403. I JUST KNOW THIS IS GOING TO CHATTER LIKE CRAZY...ANY SUGGESTIONS? ALREADY LOOKED FOR A CARTRIDGE HEAD FOR OUR KENNAMETAL DEVIBE BAR D28TTB25. DO NOT HAVE WHAT WE NEEDED. READY TO LOCK AND LOAD....HELP!!

[AMCjeepCJ]

You're not going to believe me but instead of clamping your bar down super tight, try loosening it until all you're doing is keeping it from pulling out of your holder. I ran Mazaks in Tulsa for quite awhile and I'd have NEVER believed this would work except we'd do this all the time on extremely long overhangs of 12:1 plus... It goes against popular convention but it works like a charm with a little experience. Just keep the RPM's low if doing this and we regularly dulled the insert ever so slightly before use. Trying this technique is dangerous if done wrong so please keep your door closed when running and DO NOT EVER show inexperienced operators this trick, IT IS POTENTIALLY DANGEROUS IF NOT DONE WITH CARE!!!!!!!!!!!!

On one extremely long bore we completely loosened our bar until it would literally pull out by hand, so you have to keep your feeds and speeds reasonable. Also, doing this runs the risk of chips catching inside your I.D. and sliding your tool out and wrecking everything on a tool change. USE CAUTION!

Hope this helps... BTW, try it rigid first, this is a last resort for the 'impossible' bores you cannot do ANY other way~

[AMCjeepCJ]

I forgot to mention, we were NOT using carbide boring bars so these were insanely long overhangs... Our dimensions were very simlar to yours but our tolerance was kind of wide open at +.003" -.000

Also, too light of a cut per rev will cause a LOT of chatter too, you end up rub-rub-CUT, rub-rub-CUT, rub-rub-CUT... Not good for holding a dimension nor having a good finish if you're looking for a sealing surface like we needed in the deep hole oil well tips we manufactured~ Can't think of anything else at the moment, let us know how it goes!

[WOLOG]

Would a Sandvik Devibe bar be out of the question? They are insanely expensive but they work for long overhangs like that.

[AMCjeepCJ]

I was thinking about this some more this morning and remember an important question I forgot to ask. I assumed this is a production job and since we're in the Mori forum that you're doing this on a ultra rigid CNC lathe. (I'm not familiar with the model of your machine.) Either way, the loose bar thing seems to work best on CNC's.

To rather simply explain, put either the bony part of your forehead on a rigid part of your machine while it's turned on but not cutting or lightly put the second joint down from the tip of your finger on the tool changer, you'll feel a lot of vibration although its almost imperceivable to your touch. Now do the same with the on the tip of your boring bar at full extension. (On second thought, don't use your forehead on the bar, lol, good way to get decapitated. I use my forehead because if you do it right you can feel AND here the vibrations because your head acts like a big resonance chamber and amplifies those vibrations into an audible sound. Also, since you're not listening to airborne sounds at this point, you'll get an extremely accurate feel over time for chatter, tool break down, etc. if done on the same part of the cabinet during actual cutting.)

When your tooling is clamped down rigid, you'll feel those vibrations amplified at the cutting tip compared to the tool changer base. Now loosen the bar in small increments but make sure you put torque on the set screw in the tightening direction so they don't vibrate loose and fall out. Do the knuckle test again, do you feel the difference? If not, experiment a little, this always works given enough experience.

I really hope folks can get the gist of what I'm saying because you can use this technique to monitor cutter wear or chipping just by closing your eyes and lightly setting your forehead against the rigid structures on ANY CNC while it's running. I like using this technique on my mill when the flood coolant is obscuring any chance of seeing inside the machine and the noise is too loud to make out any discernible patterns.

Remember your eyes will lie to you during cutting but your ears usually won't.

I know the guys who run manual equipment get a 'touch' or a 'feel' for how the work is cutting but many people don't realize just how much of that is actually hearing. I know some of those guys have trouble adjusting to trouble shooting CNC equipment because the 'touch' is gone and the ability to make instantaneous corrections to tool load based on physical feedback in the handles has been removed. By learning this method, much of the 'feel' of older manual equipment can still be used on modern high end CNC's...

Let us know how it goes and at the risk of being redundant, please try it rigidly mounted first, this is a last resort but it WILL usually work if all else fails... (overhangs of 50:1 will probably still be impossible, but who knows, lmao

[HuFlungDung]

What AMCjeepCJ said may work. I wouldn't be trying this in a cnc, but on a manual 40 position toolpost, it does sometimes work to loosen off the toolblock clamp slightly. This style of toolpost minimizes the risk of anything getting away on you. Basically all we are doing is detuning the setup by introducing a 'soft interface' that seperates the bar from the machine. The toolblock vibrates non-harmonically with the bar. Its the kind of thing where you have to ride the toolclamp while the cutting is going on.

The clamped length of the bar seems to have a lot to do with vibration sensitivity, too. 6" of clamped length is better than 4". You may even find some advantage in extending the amount of bar hanging out behind the toolblock.

But, all that aside, I have wondered if it would be possible to make a 3 point support for a larger diameter bar. What this support would be is 3 floating pistons extending out the side of the bar. Each piston tip would float on the bore of the hole, spaced roughly at 120 degrees phase angle. The piston could have different dead lengths, depending on which way they extend from the bar. The 3 pistons would share a common chamber filled with hydraulic fluid, which you could pressurize with a setscrew, after you had gotten the three pistons and bar inside of the bore.

The pistons would not have to lie in one radial plane, you could offset them a bit so as to give yourself room to install them without interfering with one another.

My theory is that the 3 pistons would be able to float as the bar advances, because whatever amount one piston must retract, the others would advance and so the fluid volume displaced would be constant.

Hopefully at some point in this system, there would be some kind of inefficiency to the hydraulic system that would tend to absorb some energy and dissipate it. Maybe a heavy spring damper would be required in conjunction with the preloading setscrew.

[Geof]

Originally Posted by HuFlungDung ...Hopefully at some point in this system, there would be some kind of inefficiency to the hydraulic system that would tend to absorb some energy and dissipate it. Maybe a heavy spring damper would be required in conjunction with the preloading setscrew.

You may be able to substitute flexible polyurethane for the hydraulic fluid; something like is used on vibration mounts for motor.

And I just had a brainstorm related to extending the bar out behind the toolpost. Are you familiar with sound-dampening headphones? They synthesise a sound the same as the ambient noise but 180 degrees out of phase and add it to whatever is be played over the headphones. This mostly cancels the ambient noise so you hear your music better. On the end of the rear overhang you would mount a transducer that could vibrate the bar out of phase with the signal from an accelerometer at the other end. Complicated, probably expensive but it could work.

[AMCjeepCJ]

I agree completely that it isn't safe!! I'm only giving it as a last resort suggestion... Actually if a few people read this and feel it is too dangerous to even mention, I'll gladly remove my posts completely... Making a part isn't worth an injury!! Just for the sake of argument, I'm NOT suggesting anyone do this except as an absolute last resort if nothing else works. When I say nothing, I don't mean you tried with what you had and were just to cheap or lazy to buy better tooling or contact a tooling rep to help trouble shoot your application~

Use common sense here people, doing what I said is like shooting a 12 gauge, holding the shotgun with one hand at your hip standing on a folding chair on one foot... Is it possible?? Yeah... Is it safe?? ABSOLUTELY NOT AND AGAIN I SAY NOOOOOO!!

(((But just the same, I'm not going to say there would never be a reason to shoot a shotgun one handed standing on a folding chair off balance because I HAD to do it once but it nearly broke my thumb!!)))

[AMCjeepCJ]

Originally Posted by Geof You may be able to substitute flexible polyurethane for the hydraulic fluid; something like is used on vibration mounts for motor. And I just had a brainstorm related to extending the bar out behind the toolpost. Are you familiar with sound-dampening headphones? They synthesise a sound the same as the ambient noise but 180 degrees out of phase and add it to whatever is be played over the headphones. This mostly cancels the ambient noise so you hear your music better. On the end of the rear overhang you would mount a transducer that could vibrate the bar out of phase with the signal from an accelerometer at the other end. Complicated, probably expensive but it could work.

Since the pivot point is in the middle wouldn't it have to be in phase if you're looking at the Z movement going away from the operators sight? (Think teeter totter.) In other words, if the tip of the bar is at a moment in time moving Z+ wouldn't the back half also need to move in Z+ and have the identical same overhang length? Otherwise I think you'd get into some rather complicated math quite quickly that would depend on the boring bars material, etc. I like your idea, I wonder how practical it would be?!

One more thing I know you already know but it's worth repeating is that sound waves cancel each other out because you sync them out of phase just like you mentioned so that the inverse of your Y value of the sound wave is transmitted through the speakers to cancel out the noise. I just think the problem is going to be we're not dealing with two sign curves that need to add up to zero at all times... (Wait, i mean we are except there is a fulcrum in the middle making the opposite of the opposite the same, hows that for confusing?? It's a double negative equaling a positive.) We are dealing with an object resonating at one end and there is a fulcrum in the middle making the application of your idea a little more complicated... What are your thoughts?? I can picture the teeter totter example the best so if you could explain using that it would probably make the most sense to me~ I'm of the opinion at this point that resonating the back half that is overhanging would theoretically double the problem if done with the opposite wave like in those Bose headphones!!

[Geof]

Okay here is an extension of the idea to get around the fulcrum. Clamp the bar at two locations maybe 4 diameters apart. Now you have a system where the two ends move one way and the center moves the other; you are not teeter-tottering you are flexing the bar. Now you locate the sensor on the middle part, which simplifies things, and have the out of phase damping work between these two points. Probably the motion will not be sinusoidal but I don't think that matters. I think the way the Bose system works is that it digitises the incoming ambient signal, analyses it properties and then opposes it digitally before converting to an analogue output. They work best when the ambient sound has some regularity to it such as the background noise in an aircraft; they do not work as well or maybe not at all on true white noise which has a totally random wavelength distribution. The bar damper would be working on a regular vibration.

But taking the idea of two location clamping further it may be that if you had the space between the two clamps filled with lead shot or a polyurethane elastomer filled with lead powder you might get effective damping from this.

It would be expensive but custom made inserts for a particular job are probably expensive and time is money. Something that saves time and insert cost may be economically viable even if the upfront cost is a significant fraction of the machine cost. .

[AMCjeepCJ]

It just hit me, we might all be making this way to complicated. (Isn't that what we do best though? )

Why don't we just ask for the print to show that detail on the part and recommend tool path strategies that may minimize cutting with the full width, rubbing along opposing edges simultaneously, chip evacuation as in possibly doing pecking type motions in the groove to break the chip if need be. (Depends if the chip even ends up being a factor.) I'm going to bet a little creative tool path experimenting goes a long long way combined with some creative speeds and feeds.... Has anyone else ever wrapped piles of thick rubber bands on a boring bar?? I had a crazy foreman who used to do that and it worked!! Then again, he was the same guy who would unbolt the boring bars and that worked too... Fearless-crazy employees get all the breaks~ I've noticed that as an owner I'm only semi-fearless-crazy, lol, I don't need to gamble at a Casino, trying those tricks on my own equipment is adrenaline rush enough!!

My vote is to see the detail for the groove on a print and suggest a strategy from there! All in favor, say 'I' "eye" 'aigh', whatever!

[Geof]

Originally Posted by AMCjeepCJ It just hit me, we might all be making this way to complicated. (Isn't that what we do best though? ) .....

Isn't that what we do best??? You damn right; always come up with the complicated solution first

I have done the rubber band trick and yes it does work. Another one is a length of wood wedged between the boring bar and the part; this gets exciting when you slip and cram the wood into the spinning chuck. Strangely enough I still ten complete fingers and two eyes.

But, honestly, I think it is much more fun being complicated. Simplicity is for weak minds.