Semi-hard turning boring?

[Matthew Hajicek - Singularity]

I'm trying to finish turn a tapered bore after heat treat. This is a short run situation, generally one to three parts at a crack. Material is H13 at 47RC, and I left .015" per side before heat treat.

 

Our current setup is a 5/8" boring bar in a tapered sleeve to maximize rigidity, about 4" long from the turret. Current insert is TiN coated carbide with a 1/16 radius. I was trying 120SFM and .002" chip load for a .005" deep finish pass after taking off the first .010" at .004" chip load. Finish is ok much of the time, but I keep getting gouges here and there. Cycle time isn't a significant consideration since quantity is so low.

 

Help please?

 

Thanks,

 

-Matt

[Del.]

Ceramic.

[Matthew Hajicek - Singularity]

I was afraid of that. Boss wants me to make it work with what we have.

[Del.]

I was afraid of that. Boss wants me to make it work with what we have.

 

 

Ahhhhh Make the old chicken salad out of chicken sh*t philosophy.

[K2csq7]

How is your finish after the .010/.004 cut?

You should really be burying the TNR, the "gouges" you see are most likely from chips being to small and getting stuck between the tool & the part... .005 DOC is to small IMO.

Maybe you can BLAST some coolant in there to keep them out of the way?

[Matthew Hajicek - Singularity]

For DOC should I try .010? The whole .015? Finish after the .010 at .004 isn't great, but no gouging. Are skim passes a good thing here or a bad thing? I don't have too much experience on CNC lathes, mostly a mill guy.

[T_MALENA]

Have you tried a finish pass only with a 1/32 TNR or try a 1/64 TNR. With a 1/16TNR you are probably "bouncing" during the cut. If you figure the radial DOC & your feedrate your chip is only a few tenths. Sugg. largest carbide bar that'll fit,1/64 TNR & adjust the feed to get the finish you need. 120 sfm sounds good to start. maybe cut .005 to rgh. then .01 for finish only if .015 is too much.

[Matthew Hajicek - Singularity]

Thanks, I'll give it a shot.

[K2csq7]

Have you tried a finish pass only with a 1/32 TNR or try a 1/64 TNR. With a 1/16TNR you are probably "bouncing" during the cut. If you figure the radial DOC & your feedrate your chip is only a few tenths. Sugg. largest carbide bar that'll fit,1/64 TNR & adjust the feed to get the finish you need. 120 sfm sounds good to start. maybe cut .005 to rgh. then .01 for finish only if .015 is too much.

 

Oh, crap.. you're using a .062 rad!!!

My bad, read it quick and assumed I read 1/64" not 1/16"

 

ABSOLUTELY use a smaller radius....

 

From a milling perspective, that's (using a 1/16" TNR) like trying to take .001 off a .010 thin wall with a 2.0" finish EM...

[Matthew Hajicek - Singularity]

Oh, that was my bad. It is a 1/64 (.016) radius, I typed it wrong.

[Mr. M]

Usually in hard turning you need to get the chips hotter to soften them and get the heat all out in the chip. In some 60rc steel I just did (boring and threading) we ran 600sfpm and .003fpr with a 1/64 radius cbn insert in a 5/8 carbide bar. If you like I have a power-point from a seminar we just did that I can e-mail you

[T_MALENA]

Definately agree with that. I've done the same thing(speed it up) after trying the lower stm's with hit or miss results. It seems with the CBN & a few coated carbides you get better & more consistant results at 500+ sfm, depending on rigidity.

 

Matt, try the suggestions above - per your boss "do it with what is in house" Then next run make sure you have some CBN in stock. Oh and use air pressure to push the chips where you need to NOT coolant. With CBN & the correct "dry " cutting carbide the idea is to keep the chip hot & move the cutting tip fast enough to keep the heat in the chip not into the part.

HTH

[Matthew Hajicek - Singularity]

So how well do the CBN inserts work with medium harness materials, like in the 45 - 50 range?

[mig]

We cut this kind of stuff often . Iscar

Insert works just fine

[Mr. M]

Good, but the edge prep is key. Hanging out that far, I would definatly want a solid carbide bar vs a steel or heavy metal bar. If I had a carbide bar, I would not hesitate to try it with regular inserts.