[QuinnSjoblom]

I have a decent amount of experience with cnc milling, but now I'm about to go down the path of cnc lathe. After doing some reading, it seems that there are just SO many variables and opinions when it comes to choosing the proper tool. I work with mostly 7075 aluminum and for milling it was pretty simple. Most agree that 3 flute endmills are a good balance of chip evac, rigidity, and resists resonance, Zrn coating for aluminum. Thats what i use and it works excellent. Turning on the other hand seems like quite the mess with far more variables and inconsistent opinions. I want to do light to medium work on aluminum with a great surface finish and would prefer to use carbide inserted tooling. Many would say anyone learning lathe work should start by grinding hss blanks and learn about geometries, but I would really prefer to use tooling that's ready to go without having to hone my skills at grinding, even though it's obviously a good skill to have when you need a special tool fast. The other side of that, some say hss tooling is capable of taking a sharper edge and can actually give better surface finish with the downside of not lasting as long. Are there really not carbide inserts capable of giving just as good of finish in aluminum? Is it true that you need to go faster to get carbide to cut nice?
My spindle has a max rpm of 3000 and I'll be turning mostly around 1 inch diameter aluminum parts. Will carbide inserts do well in this scenario? Or do I really need to consider hss for best finish? I will also be running kool mist coolant.
So assuming I can stick to inserts and not bother with grinding hss, where do i start? Like i mentioned, ill be doing light to medium work in aluminum. I understand that the base shape of the insert is gonna depend on geometry of the part. C and d type seem most common, c type being preferred if geometry of part allows it. D or E if I need clearance in tapered areas with drawback of less strength in the insert. What about rake and relief? This is one of those things that everyone seems to have their own opinion on. Some say positive, some say negative. I understand it depends on the application, but in my case, what do i want for getting a great finish on aluminum with coolant, considering a max rpm of 3000, most turning at 1 around inch diameter, and no need for crazy removal rates? One thing people seem to agree on is polished uncoated inserts for aluminum. As for size of the tool, I don't see a reason to go small. Ill be machining my own tool post setup so I can design for larger tools to get best rigidity. I can also make adapters to hold round boring tools in the tool post, or separate holding all together. This is a mill turn spindle on a mill, so I can make use of both x and y for gang setups with multiple tools in different places.

So where do i start? I imagine I need a few different tools for different shape inserts and different orientations. Just want to make sure I pick tools that are compatible with readily available inserts that are proper for my application.

I know this is a really loaded question with many variables, just looking for a general idea of what to start with for what I want to do. I'm sure I will need to expand my collection of tools as I run into features that maybe don't have clearance with the common inserts.

[Jim Dawson]

We started out with one of these 3/4 inch sets from Accusize (Amazon) for our Hardinge, and have been happy with them with the exception of the parting tool. We replaced that with a Kyocera parting tool (that cost more than the whole Accusize set). The parting tool, 5/8 set, for the manual lathe has been OK. We get the inserts mostly from Shars, again with the exception of the parting tool.

https://www.amazon.com/s?k=accusize+...ref=nb_sb_noss

For aluminum, we normally use https://www.shars.com/products/index...ed_on=aluminum

Pick your size and nose radius to fit your tool holders and application. Available in nose radius of 0.004 to 0.032 as I recall

I haven't noted any cut quality difference in the Shars vs. Kyocera inserts, the primary difference is cost.

[rcs60]

you are correct when you say there are a lot of choices out there
hhs will give you a good finish but you will be doing the tool grinding

(generally)
small machine tend to use positive inserts(uses less hp) and larger machine tend to us negative inserts (more cutting edges per insert)
with carbide there are the polished hi positive tools these are good for finishing but don't like to break a chip
you can use carbide tools with chip breakers you may have to increase the ipr to get it to break the chip the coatings to stay away from are the ones with aluminum in it these tend to react with what you are cutting
also depth of cut will matter too a cut small may have the chip curlling into the material causing finish problems
there are also diamond tipped inserts that will give you very good finishes with chip breakers and with out
the reason for more choices is that there is as you said many variables to deal with
grade of material,cold drawn/extruded/cast, doc,sfm, ipr, hp of machine, finish you are trying to attain,how many pcs. to be made

[mcardoso]

I second the use of Shars aluminum specific inserts. They work well and give a good finish. They can break a chip, but your DOC needs to be moderately heavy.

[QuinnSjoblom]

Ok, thanks alot guys. Ill start off with a cheap set of accusize tools and shars inserts. Once I get the hang of things and start producing some parts eventually, is there much advantage to the higher end more expensive inserts? I've looked on ebay and sometimes you can find really good deals on name brand stuff. I watched a video on shars inserts vs more expensive version of same type and the shars insert gave out with much lower load. This was pushing to the limit in steel though. For what I'm doing in aluminum, this comparison is probably irrelevant, but what about things like chip breaking and surface finish? Is shars pretty much as good as the other more expensive stuff? I realize geometry can be chosen for better chip breaking or better finish, but considering exact same geometry, shars vs other brand, much difference? If I can get better results by paying an extra few bucks per insert, it's worth it to me.

[Jim Dawson]

I have not seen any real advantage of using the $20 inserts over the $5 inserts. I just inadvertently (I forgot to change the insert) ran 80 304 SS parts using a Shars aluminum insert, it lived through the run. I do use heavy flood coolant.

But once you get into production, experiment with inserts to see what works the best for you. I have both in my inventory, I keep SS, aluminum, and general purpose inserts around. I don't do much work in mild or alloy steel, mostly aluminum and 304 SS

[QuinnSjoblom]

I have not seen any real advantage of using the $20 inserts over the $5 inserts. I just inadvertently (I forgot to change the insert) ran 80 304 SS parts using a Shars aluminum insert, it lived through the run. I do use heavy flood coolant.

But once you get into production, experiment with inserts to see what works the best for you. I have both in my inventory, I keep SS, aluminum, and general purpose inserts around. I don't do much work in mild or alloy steel, mostly aluminum and 304 SS

Ok shars it is, at least for now

[QuinnSjoblom]

I have not seen any real advantage of using the $20 inserts over the $5 inserts. I just inadvertently (I forgot to change the insert) ran 80 304 SS parts using a Shars aluminum insert, it lived through the run. I do use heavy flood coolant.

But once you get into production, experiment with inserts to see what works the best for you. I have both in my inventory, I keep SS, aluminum, and general purpose inserts around. I don't do much work in mild or alloy steel, mostly aluminum and 304 SS

Hey jim, thought you might be able to answer something for me, I got my lathe tooling, went with the accusize 1/2 inch tools since most of my work is pretty small. The insert parting tool it came with looks like it will part off about 1inch diameter max. Is it ok to pull the insert out about 1/16 so I can part of 1 1/8 or is that a bad idea? The holder and insert is the type with v grooves that lock it in. Does it need to be bottomed out for proper support, or ok to pull it out just a bit? I could probably use a dab of green loctite on the mating surfaces if the insert sliding back in under load is a concern. Otherwise I'm gonna have to buy another parting tool justvyo reach in another 1/16

[mcardoso]

I would really recommend against pulling the insert further out of the holder. If you are using the kind that hold thin grooving inserts, you'll probably end up breaking the insert and holder. They are not particularly strong to start with due to the geometry of the cut and you'll lose a significant amount of support on the insert if it isn't fully seated.

Either buy a tool which meets your needs or go to HSS cutoff blades. I use inserts for everything on my manual lathe except for parting blades. I've tried the indexable ones and just haven't had the best process security with them.

[Jim Dawson]

Hey jim, thought you might be able to answer something for me, I got my lathe tooling, went with the accusize 1/2 inch tools since most of my work is pretty small. The insert parting tool it came with looks like it will part off about 1inch diameter max. Is it ok to pull the insert out about 1/16 so I can part of 1 1/8 or is that a bad idea? The holder and insert is the type with v grooves that lock it in. Does it need to be bottomed out for proper support, or ok to pull it out just a bit? I could probably use a dab of green loctite on the mating surfaces if the insert sliding back in under load is a concern. Otherwise I'm gonna have to buy another parting tool justvyo reach in another 1/16

What mcardoso said. I have used my Accusize parting holder (5/8) on my manual lathe without problems. On my CNC lathe the Accusize 3/4 parting holder did not live long, and we replaced it with a Iscar parting holder that cost more than the entire Accusize set.

[QuinnSjoblom]

Ok sounds good, I wont pull it out . After thinking about it, the parts I'm turning that are 1 1/8 have an 8mm inner bore so it will clear no problem. I do plan on swapping out the insert with a nicer polished aluminum specific one. They are the 2mm wide type.
Just so I know, if I eventually get another inserted parting tool, would i be better off with something wider like 3mm? From what i have read on the subject, it seems the wider insert is a bit more forgiving when it comes to chatter and some of these parts I do want to be finished in the one op, preferably no second op to clean up a chattery part off. Is a wider parting insert more likely to do well at this? Ive heard a clean chatter free parting in aluminum is a bit of a challenge. Couple approaches I've heard of to solving this, like parting most of the depth leaving a few thou on the back, then stepping in to final dimension and parting through with a full second pass.
Hss blade is another option, but I feel like a proper aluminum polished insert should do just as well right?

[mcardoso]

Quinn,

If you can find an aluminum specific grooving/parting insert, please let me know. I've never been able to source one. As the width of the insert increases, the strength and stability of your insert/tool go up dramatically, however the cutting forces do as well. For large stable workpieces, a wider 3mm grooving tool will perform better (assuming you have the horsepower to drive it), but with thin wall or slender components you may find the forces generated by the tool to be detrimental to your operation.

I have done very deep parting (5.5" Diameter) with a 2mm width insert but ended up wrecking the insert, tool, and workpiece after 10 parts or so. It was a good lesson that no single tool can do all jobs well.

I have never produced parting operations on my manual lathe which do not require a face cleanup for good final surface finish, however I have seen some CNC's running coolant through the tool produce excellent finishes even in very deep parting operations.

[QuinnSjoblom]

Quinn,

If you can find an aluminum specific grooving/parting insert, please let me know. I've never been able to source one. As the width of the insert increases, the strength and stability of your insert/tool go up dramatically, however the cutting forces do as well. For large stable workpieces, a wider 3mm grooving tool will perform better (assuming you have the horsepower to drive it), but with thin wall or slender components you may find the forces generated by the tool to be detrimental to your operation.

I have done very deep parting (5.5" Diameter) with a 2mm width insert but ended up wrecking the insert, tool, and workpiece after 10 parts or so. It was a good lesson that no single tool can do all jobs well.

I have never produced parting operations on my manual lathe which do not require a face cleanup for good final surface finish, however I have seen some CNC's running coolant through the tool produce excellent finishes even in very deep parting operations.

Here was one example, no idea on the quality of it. Could be cheap garbage, but I did find a few others searching Google and ebay. https://www.ebay.com/itm/MGGN250-V-2-5mm-Width-Parting-Grooving-Insert-for-Cutting-Aluminum-for-MGEHR/252348532081?hash=item3ac1250571:g:C1wAAOSw8RJXB4d N

I'll start off with the 2mm tool and some good inserts to see what kind of results I can get. Most of my parts have a bore through the middle so in most cases my parting tool doesn't need to go any more than 10mm deep or so. That should help me quite a bit. I can imagine things get much trickier as you go further in depth.

[Jim Dawson]

I corrected my post above to Iscar rather than Kyocera parting holder. Here is the insert we use, it's actually for SS, but also works fine in aluminum https://www.mscdirect.com/product/details/06259436

On deep parting I use ''peck'' parting, just like peck drilling, normally about 0.030 - 0.040'' per peck, with a 0.01 pull back. Seems to be easier on the system overall, and produces short curls that clear easily.

[mcardoso]

Ouch! $20 per cutting edge. Bet it works well though. Thanks for the links guys.

[Jim Dawson]

Ouch! $20 per cutting edge. Bet it works well though. Thanks for the links guys.

I get 2000 or more parts out of one insert so it's really pretty economical. At $150/hour, the down time to change the insert costs more than the actual insert.

[QuinnSjoblom]

Another lathe tooling question for you guys. I have a part i need to make multiples of. Not quite exactly like this example i modeled up real quick, but the inside features are basically the same. The part is 60mm long, 26mm od, the long bore in front is 19.5mm id stepping down to 19mm id for 6mm of depth, then stepping down to 15mm id for 8mm of depth, then opening back up to 19mm for 5mm of depth. The 2 19mm bores are for bearings and very important that they are perfectly coaxial and tight tolerance. Pretty straight forward turning and boring other than the 19mm bore at the back. Easy solution is 2 ops, flip it for rear bore, but i would like to do it in one shot if possible. Not only because i want to finish the part in one op, but also to keep those 2 bores perfectly coaxial. Can it be done and hold a tight tolerance at that rear bore? What is the right tool for the job? An id grooving tool, or is there something better? tool needs to reach in 60mm, fit through a 15mm bore, and back bore 2mm. One complication is the fact that i cant sneak up on it and check the progress. No way to measure until i part it off. thoughts?

[Jim Dawson]

An ID grooving tool would be my weapon of choice here. Making that bore on some test pieces without the length would allow you to dial it in as long as the set up looked the same from the tool's perspective. Once dialed in, it should be repeatable.

Also that drawing is an interesting optical illusion, my brain knows the bore is a concave surface, but my eyes insist it's convex at the top.

[QuinnSjoblom]

An ID grooving tool would be my weapon of choice here. Making that bore on some test pieces without the length would allow you to dial it in as long as the set up looked the same from the tool's perspective. Once dialed in, it should be repeatable.

Also that drawing is an interesting optical illusion, my brain knows the bore is a concave surface, but my eyes insist it's convex at the top.

Ha! Now it keeps popping out as a positive shape on me as well.

That makes sense, I can dial in the bore on a peice of stock that is easily measurable, as long as the tool is removing the same amount of material and has same stick out as it will for actual operation. I imagine solid carbide is a big advantage for long reach tight tolerance stuff like this. Been keeping my eye out on ebay for good deals on quality boring bars and id grooving tools.

[mcardoso]

Did a bunch of deep bearing bores similar to what you're talking about here. Dial in the starting diameter to be very consistent then your finish pass will have the same deflection from part to part. Take your one cut and be done.

A solid carbide bar will almost certainly be needed here unless you want to run your lathe at 50rpm to avoid chatter.