Preventing Deflection Without Live Center?

[Crashmaster]

I am running a very basic part. I am turning 1" 12L14 down to .866" I am having very slight deflection at the beginning of the cut, about .0015. Does anybody know if there is a way of preventing deflection without using the tailstock?

[Geof]

Use a Travelling Steady .

Alternatively you can sometimes program a taper to compensate for the deflection, however, as your tool gets dull the deflection increases and the original taper is no longer correct.

[cdlenterprises]

I'd typically try to program it out. You can either program the taper in or try changing your tool path to start cutting closer to the chuck and feed off on the free end. It could be that the shock from introducing the cutting tool to the part is causing the taper.

[307startup]

alternately, on your last pass, you can cut from chuck to workpiece end, as this makes the tool itself your traveling rest....

[Geof]

Originally Posted by WYLD alternately, on your last pass, you can cut from chuck to workpiece end, as this makes the tool itself your traveling rest....

How so?

No matter which way the tool is travelling it has to exert force against the workpiece in order to cut.

[307startup]

Geof

It has been my experience that when you have some overhang and are not able or unwilling to use the live center (usually due to cycle time) that cutting from chuck to workpiece face on the last pass will take care of the taper. I think it is due to the fact that the last pass is usually a much smaller depth cut than a roughing pass and the workpiece has a chance to settle down harmonically. Also, since the deflection is at the start of the cut, by cutting backwards, the cutter is at full depth on your way out, instead of trying to enter a cut that takes a number of revolutions before settling to depth, which is the cause of the taper initially. I respect both your opinions and your experience, I was only trying to contribute based on my own experiences and non-traditional solutions to problems I have encountered.

[HuFlungDung]

What is the length of this part?

What kind of chuck is being used?

What kind of tooling is being used?

Was the machine adjusted for 'level' lately?

Is this deflection a full length taper?

[Crashmaster]

The length of the cut is 2 inches, the part is chucked in a 5c 1" collet. I am using a CNMG431 9110grade kennametal insert. Just had the machine leveled a few weeks ago. The deflection is occurring within .25"-.45" from the end of the part. I have programmed the deflection out which is working 75% of the time, the part is not defecting all the time. So every 10-15 parts are measuring small. I can live with that if I have to, but would rather figure out a reliable solution. Does having your last pass traveling away from the collett really work as a "traveling rest?"

[KENNETH BROWN]

Use Cutting From Chuck To End Of Part With My Finish Pass On All Long Over Hangs, Most Of The Time With A Vnmg Or Dnmg Type Insert.got This Trick From A Old Programmer For Catterpillar.i Do This Even When Using A Tailstock.no More Than .01 Depth Of Cut And Most Of The Time With A Ghost Pass.

[g-codeguy]

Originally Posted by KENNETH BROWN Use Cutting From Chuck To End Of Part With My Finish Pass On All Long Over Hangs, Most Of The Time With A Vnmg Or Dnmg Type Insert.got This Trick From A Old Programmer For Catterpillar.i Do This Even When Using A Tailstock.no More Than .01 Depth Of Cut And Most Of The Time With A Ghost Pass.

I agree with using a VN or DN style insert. Personally I would go to a VNGP or DNGP insert. Use a positive rake insert instead of a negative one. Less tool pressure. Freer cutting. A ground insert also helps by cutting freer, thus exerting less tool pressure. KC9110 can run at 7000 RPM at that diameter in that material. A VNGP-331 KC730 needn't run that fast to give a good finish although I would be more tempted to use a VNGG-331R N1 XT3 or VNMG-331 ZF1 XT3 cermet insert in 12L14 material.

Although I have cut going away from the chuck before, I've never tried it as a means to straighten out a turned diameter. Thanks for the tip.

[Crashmaster]

Thanks for all of the advise guys. I programmed the finishing cut to go away from the chuck and it is working surprisingly well, so I am going to stick with that. Thanks again!