Lathe tool inserts

[SouthernChap]

I recently saw someone say the following:

Raise the tool height...carbide cuts better above center.

Is this good advice?

From my cursory knowledge of how a lathe tool cuts (HSS or carbide insert) that sounds off but eh, I'm greener than the fresh paintwork on a 1970s English park keepers shed!

 

[Nesse1]

There is one way to know...

 

[Just for fun]

That doesn't sound right to me either. I'm pretty green also but out of all the YouTube video's I've watched I have never seen anyone recommend cutting above center.

 

[55fairlane]

30 plus years as a tool maker...... OD tools run on center .....ID tools run a bit above center.
As a side note....I have yet to meet and engine lathe (especially a hobby lathe) that will hold up to the extreme pressure (speeds & feeds) that a carbide insert tools needs.....now if you are running carbide that has been ground like HSS....run at HSS speeds & feeds you good to go

 

[RaisedByWolves]

30 plus years as a tool maker...... OD tools run on center .....ID tools run a bit above center.
As a side note....I have yet to meet and engine lathe (especially a hobby lathe) that will hold up to the extreme pressure (speeds & feeds) that a carbide insert tools needs.....now if you are running carbide that has been ground like HSS....run at HSS speeds & feeds you good to go

This, all of it.

I wouldn’t try using anything other than ground inserts on a mini lathe if even that.

 

[benmychree]

30 plus years as a tool maker...... OD tools run on center .....ID tools run a bit above center.
As a side note....I have yet to meet and engine lathe (especially a hobby lathe) that will hold up to the extreme pressure (speeds & feeds) that a carbide insert tools needs.....now if you are running carbide that has been ground like HSS....run at HSS speeds & feeds you good to go

I quite agree with your comments, running carbide (especially) above center would decrease clearance and increase tool pressure, neither situation would be productive.

 

[SouthernChap]

This, all of it.

I wouldn’t try using anything other than ground inserts on a mini lathe if even that.

Which are the ground inserts.?

I've found I can get 'acceptable to me' finishes on mild steel with DCMT inserts that are intended for aluminium with small nose radii like 04 or 02 (which to be fair, are the only ones I use now, apart from one teensy one that I think is a CCMT in a boring bar that I've been using on brass).

I mean, it's true that trouble arises with the finish for anything more than about a 0.010" DOC.

I can get up to about 0.020" if I don't mind a bit of ugliness to the finish (So the mini lathe equivalent of roughing out on steel ) but that's at a pretty slow manual feed (mini-lathes with the change gears supplied don't really do fine feeds) or else it's howlin' cow in chattersville.

 

[WobblyHand]

Which are the ground inserts.?

I've found I can get 'acceptable to me' finishes on mild steel with DCMT inserts that are intended for aluminium with small nose radii like 04 or 02 (which to be fair, are the only ones I use now, apart from one teensy one that I think is a CCMT in a boring bar that I've been using on brass).

I mean, it's true that trouble arises with the finish for anything more than about a 0.010" DOC.

I can get up to about 0.020" if I don't mind a bit of ugliness to the finish (So the mini lathe equivalent of roughing out on steel ) but that's at a pretty slow manual feed (mini-lathes with the change gears supplied don't really do fine feeds) or else it's howlin' cow in chattersville.

Typically the inserts end with GT instead of MT, so as an example, DCGT, TCGT, and CCGT. I have used a lot of ground inserts on both my mini lathe and my G0752Z 10x22. Generally they work very well.

 

[SouthernChap]

Typically the inserts end with GT instead of MT, so as an example, DCGT, TCGT, and CCGT. I have used a lot of ground inserts on both my mini lathe and my G0752Z 10x22. Generally they work very well.

Ah, I just checked, the inserts I'm using for turning are DCGT, not DCMT. Thanks, that makes sense.

 

[WobblyHand]

Ah, I just checked, the inserts I'm using for turning are DCGT, not DCMT. Thanks, that makes sense.

I haven't used DCXT tooling, but do have TCxT and CCxT inserts and tools. Most of the time I use the xxGT inserts. I buy them from eBay or AliExpress, good enough for my applications. I've gotten longer life from them than expected. Buy a pack of them to try out, if they work, buy a bunch more from the same vendor. That you will get some decent inserts that will last a good long while.

The GT inserts do wear or chip faster, but that's how it goes. If your finish suddenly gets bad, on the part, it's time to rotate the insert to a new edge, even if you can't see anything. At >10x magnification, you will clearly see the chip or crack on the cutting edge of the insert.