What's a decent cut for a 9x20 import?

[RaisedByWolves]

I don't know why I responded like you're not right here. No offense intended. Thanks for adding to the performance conversation. You and @RaisedByWolves get the prize for video documentation of claims.

Regarding your video, when cutting steel, depth of cut is 0.020 in and feed is 0.005 in/rev. That's 0.30 cubic inches per min, if I calculated correctly. Not too shabby for a mini lathe.

For comparison, I was getting 0.4 cu in / min with a depth of cut of 0.030 in, 0.005 in/rev, and 600 RPM (average).

Here's the schedule for the bore, which starts 0.625" and is enlarged to 2.2. It's 28 passes at 0.030. Stepping up to 0.035, which feels like nothing when standing at the machine, brings it down to 24 passes. That's a savings of about 3 min per part. A cut of 0.040 brings the total to 21 passes, which saves 5 min per part. I'm doing another batch of 15 parts, so this saves 75 min.


Stock MMR
Pass diameter in^3/min
-------------------------
1 0.625 0.177
2 0.685 0.194
3 0.745 0.211
4 0.805 0.228
5 0.865 0.245
6 0.925 0.262
7 0.985 0.279
8 1.045 0.295
9 1.105 0.312
10 1.165 0.329
11 1.225 0.346
12 1.285 0.363
13 1.345 0.380
14 1.405 0.397
15 1.465 0.414
16 1.525 0.431
17 1.585 0.448
18 1.645 0.465
19 1.705 0.482
20 1.765 0.499
21 1.825 0.516
22 1.885 0.533
23 1.945 0.550
24 2.005 0.567
25 2.065 0.584
26 2.125 0.601
27 2.185 0.618
28 2.245 0.635
-------------------------
mean: 0.406


There's about 3.1 in^3 of material to remove, which should take 7-8 min if I was cutting continuously. Retraction, setting up the next cut, and maintaining the tool all add up to more than half the time spent on each part.

My thinking as to your OP is a lot of times the lathe gets a bad rap when in actuality it’s the user not knowing how to make his tooling do the work properly.

There’s quite a bit you can do with proper angles on your tooling that will overcome shortcomings of the lathe.

The lathe spins and slides, that’s it. The tooling is what does the work. Rigidity gets talked about quite a bit but looking at some peoples setups, bad setups probably account for half the issues blamed on rigidity.

 

[WobblyHand]

Long tool stick out usually causes trouble, generally one should choke up on the tool, so that the minimal amount extends from the tool holder. Poor grinds with incorrect angles increase tool deflection. There's a lot of good work that can be done with a small lathe, if it's properly set up. Of course, it can't do big stuff, but that should obvious.

If a new person has issues, most can be solved quickly by posting a few pictures online, here at Hobby Machinist. Often it's technique or set up.