How big of a cut 9x20 import

[durableoreo]

How is my little lathe doing compared to other machines? Am I impatient or is my lathe too small?

I'm turning a bunch of parts, about 2" in diameter, material is 4140. It's taking forever. On my import 9x20 lathe, my maximum depth of cut is around 0.025. Other parameters are 300 RPM, 0.005 in/rev, new TPGT-321 insert with 0.015 tip radius. As I write, I realized how low that surface footage is... OK, much better cut and finish at 600 RPM but similar depth of cut. Getting a little vibration. My next speed is 1000 RPM, which left a nice finish but the belt slips if I take more than 0.012 deep.

Is there anything I can do to take off more material in a pass? Or should I be happy with this performance?

I've probably just watched too many videos of Hardinge HLV-H, Monarch 10EE, and Okuma LS. An upgrade feels certain but it's years away.

 

[markba633csi]

Welcome to hobby machining! These smaller machines have limits; takes horsepower to move steel- you might have better results with a HSS tool or razor sharp high-positive rake insert to reduce the cutting forces
I like Kennametal CCGT3251HP- KC730 for ferrous metals
They work well with my Atlas which is a smaller machine than yours

(Homebrew holder)

 

[durableoreo]

Welcome to hobby machining! These smaller machines have limits; takes horsepower to move steel- you might have better results with a HSS tool or razor sharp high-positive rake insert to reduce the cutting forces

I like Kennametal CCGT3251HP- KC730 for ferrous metals
They work well with my Atlas which is a smaller machine than yours

When you're turning steel, what feed/speed do you use? Just for comparison. I think most of use understand that lighter machines want lighter cuts but let's be specific.

 

[Ultradog MN]

How is my little lathe doing compared to other machines? Am I impatient or is my lathe too small?

I'm turning a bunch of parts, about 2" in diameter, material is 4140. It's taking forever. On my import 9x20 lathe, my maximum depth of cut is around 0.025. Other parameters are 300 RPM, 0.005 in/rev, new TPGT-321 insert with 0.015 tip radius. As I write, I realized how low that surface footage is... OK, much better cut and finish at 600 RPM but similar depth of cut. Getting a little vibration. My next speed is 1000 RPM, which left a nice finish but the belt slips if I take more than 0.012 deep.

Is there anything I can do to take off more material in a pass? Or should I be happy with this performance?

I've probably just watched too many videos of Hardinge HLV-H, Monarch 10EE, and Okuma LS. An upgrade feels certain but it's years away.

4140 is hard to machine so your lathe is probably doing okay.
If you have to remove a lot of metal, don't worry about the finish till you get close to your finished diameter. Just hog it off.
As the others have said, it takes horsepower to make chips. The only alternative to horsepower is patience...

 

[mac1911]

Welcome to hobby machining! These smaller machines have limits; takes horsepower to move steel- you might have better results with a HSS tool or razor sharp high-positive rake insert to reduce the cutting forces

When you're turning steel, what feed/speed do you use? Just for comparison. I think most of use understand that lighter machines want lighter cuts but let's be specific.

Its hard to be specific as what works on my small lathe might not work for you
Since you dont have variable apeed control ( I have a 12x20 2hp rated motor ) im stuck with 6 speeds so you have to choose the better of the options even know its not always great.
What 4140 do you have?
Bhn?
Hot rolled? Annealed ? Quenched and tempered?
Im just getting into all this myself
The more I know about what im cutting the more useful these book become . 4140 is some what hard for a mini lathe I think? Some of these mini lathes are for soft material , which is no easier to cut , lol.
We also have to factor the small lathe ….speeds and feeds are/where figured out for large production .
You can use basic feed and speed calculations to get a ball park.
There are more complicated calculators asking for cutting tool geometry also .

 

[mac1911]

A quick look and my not so great math ( book min cut is .040)
Your probably going to have to go 1000-1200 rpm spindle speed.
For what its worth my 12-20 2hp maxs out at .030” on almost all material before the clutch kicks out.

 

[mac1911]

How is my little lathe doing compared to other machines? Am I impatient or is my lathe too small?

I'm turning a bunch of parts, about 2" in diameter, material is 4140. It's taking forever. On my import 9x20 lathe, my maximum depth of cut is around 0.025. Other parameters are 300 RPM, 0.005 in/rev, new TPGT-321 insert with 0.015 tip radius. As I write, I realized how low that surface footage is... OK, much better cut and finish at 600 RPM but similar depth of cut. Getting a little vibration. My next speed is 1000 RPM, which left a nice finish but the belt slips if I take more than 0.012 deep.

Is there anything I can do to take off more material in a pass? Or should I be happy with this performance?

I've probably just watched too many videos of Hardinge HLV-H, Monarch 10EE, and Okuma LS. An upgrade feels certain but it's years away.

As for your belt slipping, I would clean your pulleys really well and get a new belt of the better quality you can find and then tighten the belt per instructions. I don’t know how new this machine is to you, but they put that anti-corrosive grease and spray all over everything and other than protecting from rust. It really has no other benefit so make sure you remove it. And I’m guessing maybe the belt is of lower quality.

My lady is old well not old older it has a clutch mechanism. I don’t know if I’m getting more aggressive or if the clutch is wearing out or needs adjustment. I’ll have to dig in that later.

As I mentioned, though, you’re just gonna have to find what works for what you have.

I also have made the mistake of setting my lead up to the diameter stock. I’m using removing a good amount of material enough so that I should’ve change the spindle speeds.

The book I pictured is a machinery handbook, but it’s a data it’s not the typical machinery handbook. They were given to me by an old machinist who’s told me this will be a little easier on you in the machinery handbook and it’s helped quite a bit, especially with speeds and feeds. I have just started buying more appropriate cutting tips for material and task at hand and right away. It’s a huge difference.

 

[Ischgl99]

I started out with a 9x20 lathe, it can’t do deep cuts in steel in most cases, and 4140 is more difficult to machine than freer cutting grades. The machine lacks power, but also rigidity. The compound is very weak and will cause chatter problems if you take too deep a cut. You can replace the compound with a solid plinth, that should help significantly. I made a bigger clamping bracket for the compound to replace the small one that came with the lathe that helped. If you haven’t done those upgrades, you might want to try that. Here is the link to what I did to mine: http://bedair.org/clamp/9x20clamp.html

 

[jcp]

Removing large amounts of material is not about speed, it's about power. While I do have some insert tooling, when I need to take off a large amount of material on my Southbend 9"A, I use a tool ground from high speed Rex 95. This is a .125 depth of cut in 1018.

View attachment My Movie.mp4

 

[Larry$]

Just curious, why 4140? If it isn't really required there are lots of free machining steels that are much easier to deal with. 12L14! Constantly pushing a machine to its limits is likely to shorten its life, a lot! As someone said, use sharp inserted tooling normally sold for aluminum or softer alloys. HSS that you can easily grind to any pattern you need is also a good option for reducing forces. Cutting fluids can also help.