Anybody switch tool types between roughing and finishing on a lathe?

[G-ManBart]

A recent thread on another forum got me wondering about this, so I figured I'd ask here. Does anybody start out with one type of tool/insert type for roughing and then switch to a different tool/insert style for finishing? I'm talking traditional OD turning, nothing fancy.

I started thinking about this because the other discussion had a few folks getting really good results with negative rake inserts and I have a project with the same material in similar sizes, so I bought another tool holder and some inserts to give it a try. That got me thinking that there might be times when rather than just changing to an insert with a different radius, an entirely different tool/insert style might be a better option. Yes, no, crazy?

 

[benmychree]

I use positive rake tools for nearly everything, TPG style, only exception is using TNU for interrupted cuts.

 

[mmcmdl]

Yes , finish with a smaller radius insert .

 

[Mitch Alsup]

Exactly, use a larger radius tip for roughing, and a fast transverse rate
............... then use a small radius tip for finish, and a slow traversal rate (~¼)

 

[G-ManBart]

Yes , finish with a smaller radius insert .

That would be the same insert style though, which isn't what I was asking about. I'm talking about using one style for roughing, and another for finishing.

I've got one tool holder for CCMT inserts and have inserts in 1/32 and 1/64 radius along with CCGX that fit the same tool in 1/128 radius...all the same tool and style insert. I've also got a tool holder fro CNMG inserts and have those in 1/32 and 1/64 radius. I've got others as well, but those are two easy examples. One is positive rake, the other negative rake so significantly different.

I'm just curious if someone might rough with one style of insert and then switch to another for finish work. I would guess is that if anybody is doing that it's a more specialized application, or specific to certain materials, but maybe not.

 

[mattthemuppet2]

If I'm returning in steel, particularly one that leaves a crappy finish, I'll often do most of the roughing with a ccmt insert and then finish with a ccgt. Leaves a beautiful finish and can shave off tiny amounts of metal.

Now that I have a stiffer lathe I'm working on pushing the ccmt harder and practicing the cut cut measure compensate method. If you push those inserts hard enough to generate 6s and 9s they tend to leave a good finish. All part of the learning process

 

[Parlo]

If I am making several parts in a small batch manually on a centre lathe. I will often rough them all out to within 1mm on diameter including drilling. I can then finish them off once cooled and relaxed without having to hold them too tight in the chuck. Regarding tools, generally I will rough out with used a wnmg insert and then change the edge for finishing if required.

 

[Flyinfool]

I do not have many tools with inserts. But I do use different shapes of grinds on my HSS tools for roughing and finishing.

 

[erikmannie]

I start with a roughing insert (e.g. .035”-.090” DOC on mild steel), and then switch to a “medium/fine finish” insert (e.g. .015”-.035” DOC on mild steel). I would likely break the medium/fine insert if I took the deeper roughing cuts with it.

If I need to, I will go to HSS after the carbide. I use HSS for cuts from .015” down to .0001”. The HSS bits get a ton of use in my shop.

 

[rabler]

Typically I keep WNMG for roughing, smaller radius tipped CCGT or HSS for finishing. Or maybe that should be emory cloth and scotchbrite for finishing ?

This is one of those questions of how deep down the rabbit hole can you afford to go. With inserts there always seems to be a better insert for each particular job, but you can get by with a few general purpose inserts, and HSS.