poor finish with OD grooving tool

Ukraine Train · Mar 30, 2015

I'm making some .25" deep x .390 wide grooves in heat treated 4140 using a top notch 1/8" wide groover with the coating that the insert supplier recommends (Horizon). Finished diameter at the groove is 5.0". I started at 400sfm and .003IPR but was getting a lot of chatter on the finish passes so I slowed down the finish passes to 200sfm. This got rid of the chatter but the finish is still pretty rough and I need to be hitting 32Ra. Any suggestions? The insert lines up right on the tangent of the stock, or maybe .015" high. There is no chip breaker. I'd like to be using a wider insert but this is the widest one they have with a sharp corner radius.

Thanks!

TeachMePlease · Mar 30, 2015

.015 above center?

I'd start there.... I don't do much grooving, but I like it when my tools are set on center, or just a smidge below, definitely not high. Much like a cutoff, being high causes the face of the insert to rub, possibly even drag/catch/snap. I'd start just by bringing the tool on center and see where that gets you?

drewboyer · Mar 30, 2015

Try going the other way. Go with 600-650sfm just for the finish pass and feed it around .006-.007 ipr, leave about .003 to .005 for a finish cut.

Red James · Mar 30, 2015

TeachMe is right about the tool height. What do you mean by 'sharp corner radius'? If you wanted a good finish on an OD, would you use a dead sharp tool? Use a diamond file and break the sharp corners a bit.

Ukraine Train · Mar 30, 2015

So I got the tool on center (had to mill the holder) and it's working much better, though still leaving a hazy finish and it's not completely smooth. Any more tweaking I can do? I'm using 400sfm for full operation now. Should I try faster on the finish pass? As for the sharp corner radius, I have to have a .005-.010 radius in the corner of the groove, hence the sharp radius on the insert; I think it's a .0075".

palr717 · Mar 30, 2015

Red James said:
TeachMe is right about the tool height. What do you mean by 'sharp corner radius'? If you wanted a good finish on an OD, would you use a dead sharp tool? Use a diamond file and break the sharp corners a bit.

I was under the impression a sharper radius gave a better finish in exchange for tool life?

anyway, i'd play with the feeds and speeds more, and maybe give your final pass less stock to cut.

Utry2win · Mar 30, 2015

palr717 said:
I was under the impression a sharper radius gave a better finish in exchange for tool life?

Less tool pressure generally yes, but not always better surface finish.

toolsteel · Mar 30, 2015

Whenever I am trying new things and they are not working and I am not certain why........I will try ridiculously fast....then ridiculously slow......see if one of those things affected your outcome...did one sound better than the other?....did one feel better than the other? Then at least you can narrow down what direction to head from your initial calculations........only other thought I have is how hard did the 4140 get?......we turn quite a bit of it at 58RC.......but we are using CBN......I am not familiar with the tool you are using.

yardbird · Mar 30, 2015

toolsteel said:
Whenever I am trying new things and they are not working and I am not certain why........I will try ridiculously fast....then ridiculously slow......see if one of those things affected your outcome...did one sound better than the other?....did one feel better than the other? Then at least you can narrow down what direction to head from your initial calculations........

^^^^^^ This is good advice no matter what your doing or having fits with.

Only other tid bit I might add is when trying to turn a diameter with a square or flat tool I double maybe triple the when feeding across the diameter. Also I wouldn't leave much for finish. Roughing stabs at maybe 350sfm finishing at 600sfm or a little more. Its been my experience with 4140PH 28 to 32RC the faster the feed the more shiny it is. Doesn't mean good surface finish its just more shiny. Do like he said and find the best combination, then remember what it was. Good luck...

Brent

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poor finish with OD grooving tool

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