poor finish with negative top rake tool holder

[DeereGuy]

Hi guys, hoping someone can lead me in the right direction here. I can't seem to get a good finish using the negative top rake indexable carbide tool holder I just got. I have played around with feeds and speeds and depth of cut and the finish is alway rough. Note this is on 2" dia CRS. I have a 13 x 40 lathe. The cemeted carbide tools were doing ok. The insert is C6 TIN coated. Appreciate any feed back to help clear this up.

TIA
Bob Abbott

[dsergison]

it's only my opinion, but I wouldn't expect a good finish from a negative rake tool. Really aggressive removal rates on massive machines, but not a nice finish, especially on anything lesser in heft.

[wierdscience]

What speeds and feeds were you using?I run mine at no less than 450 feet per minute and .015" per rev.The negative rake tools need the speed to make a decent finish.

[This message has been edited by wierdscience (edited 04-01-2004).]

[DeereGuy]

Weird, thanks. Are you using these parameters for all depth of cuts? Also what rpm were you using? I tried pretty much everything last night and couldn't come up with a combo that worked. Maybe I was just tired.

Bob

[bspooh]

The only trick with using carbide inserts, is to take a deep enough cut...you might not be taking a deep enough cut..

Its hard to tell you exactly because each insert manufacturers have their own speeds and feeds for each type of insert and grade..

going blindly here, I would just suggest you go as high of RPMs as you feel comfortable with and go with a .005-.008 per rev. of feed..You need to go a depth of cut that is deeper than your insert radius...

Try going no less than .050 off of diameter per pass, if your machine can handle it..

I am assuming you are using positive style inserts on your negative style holder...

On my lathe, I am using a .015 radius and I never go under .030 off of diameter per pass..the deeper you go the shinier your finish will be...


Whatever your radius on your insert is, cut that number in half and thats your starting feed per rev..

example... .015 radius equals a .0075 in/rev.. .032 radius equals a .016 in/rev...this is the starting point for turning, this is where you start at and then you need to "fine tune" from here..

CRS machines fine if you take a deep enough pass...
brent

[This message has been edited by bspooh (edited 04-01-2004).]

[DeereGuy]

dsergison, I have seen some finishes that others have gotten with this tool on lathes simualar to mine and they looked pretty good. I think that I just don't have things adjusted yet. Perhaps I need to drop just a little lower than center. Don't know for sure.

Thanks
Bob

[Forrest Addy]

2" dia? Neg insert TiN coated? CRS? You should be running about 1000 RPM and taking at least 0.030 depth of cut at 0.006 to 0.010 feed depending on the nose radius.

A faint heart ne'er worked carbide to capacity. You have to laugh and dance as hot chips down your open collar as they infiltrate past your belt all the way down to your shorts there to ignite your pubes.

[dsergison]

Deer_x475guy

Yeah, I don't know what you were running.
and I'm no expert (or even much of a novice)to boot. I just figured most people don't have the horses to use negative rake carbide. I know I don't.

what are you making, just curious.

[DeereGuy]

bspooh, thanks for all the info. I am using a TNMG 321 TIN insert. I think but maybe wrong that this is a .032 radius. Am I correct in the radius? I was using 600 rpm with a 2" dia. piece. I was taking some smaller cuts trying to hit my dia. Do you suggest that I go to HHS for the finer finish cuts?

I have tried to figure out what all the insert numbers mean but still get confused.

Thanks again
Bob

[DeereGuy]

dsergison, I am making a ball turner using a boring head I have for the mill. I have the arbor completed and now want to make the part that will hold the arbor from sliding back and forth in the holder and will also have the handle screwed into it.

Bob