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

I change HSS tools for sure. My roughers and finishers are different in geometry, so it's only natural to use a finer tool for the light work. With inserts, I like to rough with a less angled tool like a rhombus and finish with a finer tool like a diamond, all else held equal. That has more to do with tool type than specific inserts. I know there is good science behind insert selection, but just like ground tools, sometimes you find one that just works nice, so it becomes your finisher (or rougher or whatever) for a certain operation or material. I'm lazy when it benefits me, but I'm never too lazy to change a tool if it benefits the work.
 
I rarely use inserts; most of my turning is self-ground HSS. If I want a really smooth finish, I turn down to within a couple thou of my finished size, then use a shear tool to finish.
 
rabler said:
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.
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Okay, this is more what I was asking about. I've been doing most of my turning with CCMT, CCGX, TCMT and a bit of HSS. The post that got me thinking about this had several folks recommending CNMG based upon their results using the same material and similar sizes to one of my upcoming projects (likely an ongoing task).

That got me thinking...why not rough with something like the CNMG where you get twice as many uses per insert and have a stronger insert profile to start with, then switch to something like the CCMT/CCGX for finishing? It sounds like that's what you're doing so maybe I'm not completely off base :)

I know many machines won't run negative rake inserts, but I think both of mine can. I'm pretty sure my Clausing won't have a problem 14 x 48 with 3hp, so I went ahead and ordered a holder for CNMG and some inserts to try.
 
G-ManBart said:
Okay, this is more what I was asking about. I've been doing most of my turning with CCMT, CCGX, TCMT and a bit of HSS. The post that got me thinking about this had several folks recommending CNMG based upon their results using the same material and similar sizes to one of my upcoming projects (likely an ongoing task).

That got me thinking...why not rough with something like the CNMG where you get twice as many uses per insert and have a stronger insert profile to start with, then switch to something like the CCMT/CCGX for finishing? It sounds like that's what you're doing so maybe I'm not completely off base :)

I know many machines won't run negative rake inserts, but I think both of mine can. I'm pretty sure my Clausing won't have a problem 14 x 48 with 3hp, so I went ahead and ordered a holder for CNMG and some inserts to try.
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Yes, the 3HP is a consideration, most new hobby machines top out around 3HP, with many having less, so you have the HP to take a deeper bite and thus the array of usable inserts gets larger. I have 3, 5 and 10HP lathes so I'm not HP limited. I generally find the negative rake molded inserts work good for roughing. (Insert edge geometry can overcome toolholder negative angles though). Ground, smaller tipped for finishing or HSS for finishing, both for finish and less cutting pressure makes it a bit easier to hit a size specification, as the 'roughing' inserts especially tend to get much worse about finish when taking a lighter cut.

Getting a comfortable set of toolholders/inserts/HSS grinds as standard tools ready to go on my lathe has been a key learning experience. I've also ended up with a spreadsheet of toolholders and inserts that I have, so that I can keep the variety somewhat limited. For example, I overlap inserts between boring bars and turning. If I can do 90% of my work with the tools ready to go on my lathe I'm much happier than spending time swapping in new inserts into new tools, getting that tool into a holder, etc.
 
rabler said:
Yes, the 3HP is a consideration, most new hobby machines top out around 3HP, with many having less, so you have the HP to take a deeper bite and thus the array of usable inserts gets larger. I have 3, 5 and 10HP lathes so I'm not HP limited. I generally find the negative rake molded inserts work good for roughing. (Insert edge geometry can overcome toolholder negative angles though). Ground, smaller tipped for finishing or HSS for finishing, both for finish and less cutting pressure makes it a bit easier to hit a size specification, as the 'roughing' inserts especially tend to get much worse about finish when taking a lighter cut.

Getting a comfortable set of toolholders/inserts/HSS grinds as standard tools ready to go on my lathe has been a key learning experience. I've also ended up with a spreadsheet of toolholders and inserts that I have, so that I can keep the variety somewhat limited. For example, I overlap inserts between boring bars and turning. If I can do 90% of my work with the tools ready to go on my lathe I'm much happier than spending time swapping in new inserts into new tools, getting that tool into a holder, etc.
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I tried the CNMG 432 inserts on some 1144 today and it was a good combination. I didn't really push the DOC or feed rate, but my smaller lathe had no trouble with it at all. I'm hoping to come up with something like you're describing where I don't have to swap inserts constantly, or tools into holders, etc.

I've already told my wife that my retirement present at the end of 2025 is going to be a new, bigger lathe...you never know when you need more power :)
 
there are a heck of a lot of different grades, coatings and tip geometries for the same size insert, so it's next to impossible to say what will work best for what process and material. Typically the manufacturer will give the material the insert is best for, often with a ranking system, and will provide speed/feed/DOC (really, chip load) for each material for that insert. So you can get fabulous finishes with the right insert in the right material at the right chip load, but change any one of those things and the finish can look like garbage. Try a light DOC with a molded insert like CCMT at say 200SFM in steel, then try a much heavier DOC. You'll be amazed at the difference in the finish.
 
mattthemuppet2 said:
there are a heck of a lot of different grades, coatings and tip geometries for the same size insert, so it's next to impossible to say what will work best for what process and material. Typically the manufacturer will give the material the insert is best for, often with a ranking system, and will provide speed/feed/DOC (really, chip load) for each material for that insert. So you can get fabulous finishes with the right insert in the right material at the right chip load, but change any one of those things and the finish can look like garbage. Try a light DOC with a molded insert like CCMT at say 200SFM in steel, then try a much heavier DOC. You'll be amazed at the difference in the finish.
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No argument there. I wasn't looking for any specifics, i.e. "how to get the best finish on X" as much as wondering if anybody has different style inserts set up so they switch insert styles when going from roughing to finishing. It would seem that if the lathe will handle it, a negative insert has some benefits for roughing...if nothing else, it's stronger and you get twice as many cutting edges for the same money. Then switch to something like the CCMT or CCGX for finishing.

Initially I thought I was just going to have three different holders set up with CCMT and CCGX so I could go 32.52, 32.51 and then 32.50 but then I started looking at CNMG for another application and thought maybe it might make more sense to go CNMG 432, really hog off the material and jump to CCMT to finish. My thought was that it's faster and easier to change tools than change inserts in the same tool. At that point, if you're already changing tools, maybe a different style makes more sense. Maybe not....I'm experimenting with it, and figured I'd see if anybody else is doing something along those lines.
 
G-ManBart said:
No argument there. I wasn't looking for any specifics, i.e. "how to get the best finish on X" as much as wondering if anybody has different style inserts set up so they switch insert styles when going from roughing to finishing. It would seem that if the lathe will handle it, a negative insert has some benefits for roughing...if nothing else, it's stronger and you get twice as many cutting edges for the same money. Then switch to something like the CCMT or CCGX for finishing.

Initially I thought I was just going to have three different holders set up with CCMT and CCGX so I could go 32.52, 32.51 and then 32.50 but then I started looking at CNMG for another application and thought maybe it might make more sense to go CNMG 432, really hog off the material and jump to CCMT to finish. My thought was that it's faster and easier to change tools than change inserts in the same tool. At that point, if you're already changing tools, maybe a different style makes more sense. Maybe not....I'm experimenting with it, and figured I'd see if anybody else is doing something along those lines.
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Let's be honest we all take the last thou off with abrasive cloth anyway. :)
 
IMHO (I'm just a retired tool-maker/hobbiest) I spend my money on steel to make things with and use HSS tool bits to cut the steel. I don't get involved in production style moneysaving, 100 units per corner, etc., carbide.
 
I think it's worth simply experimenting and pushing your lathe to see what happens. Swapping tools can get you a great finish/ save more fragile cutting edges, but requires you to leave enough material to make a fresh cut, measure and re zero before making a final cut. Whereas pushing a tool harder to hit dimension on a final decent cut takes allot of practice and confidence. Still, it's always fun to experiment!
 
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