[How-To] Lathe chatter

[gwklinger]

I bought a used atlas 10” lathe to convert to boring dirt bike cylinders. Everything works fine except I can’t get a good finish. Even when I use it like a regular lathe. Any tips?


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[Nogoingback]

It would be helpful if you tell us more about your setup, and pictures would help as well. Type of tool, speeds and feeds, how you secure
the work, type of material you're turning, lathe rigidity all play a part in the outcome.

 

[Nutfarmer]

Find a more rigid machine. You are asking why too much from an Atlas lathe. Need to know more on what type of tooling being used and the set up. I use a fresh lapped carbide tool bit on a Van Norman cylinder boring bar when reboring engine blocks. What I see most commonly used to bore small engine cylinders is a fixture with top and bottom plates with a standard engine boring bar mounted on the top plate. The main boring bar is more than a couple inches in diameter. It's going to be hard to duplicate that kind of rigidity on a small lathe. Not to knock an Atlas lathe ,but you need to have realistic expectations.

 

[mmcmdl]

Not understanding the need as to why you would have to convert a lathe to bore out a cylinder

 

[gwklinger]

I’m retired and I don’t have the money for a good machine. I just thought I could rig the Atlas up to do some boring. No matter how I use it I get lines in my finish. The finish isn’t smooth. It’s something I’m just fooling around with but it should at least give a decent finish. I just need suggestions as what to check. The table is tight and the spindle doesn’t seem to have any play. I don’t have fancy holders and I’m using carbide tipped single point bits.


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[mmcmdl]

Table ? Not sure what this table is ? Bore it and then hone it to finish size , that is pretty much the industry standard .

 

[markba633csi]

Are you boring cylinder heads? That's asking a lot of a small, wiggly Atlas; that's why they are sometimes derisively called "noodles"
You really should be using a milling machine with a powered downfeed
-Mark

 

[gwklinger]

I’m retired and I don’t have the money for a good machine. I just thought I could rig the Atlas up to do some boring. No matter how I use it I get lines in my finish. The finish isn’t smooth. It’s something I’m just fooling around with but it should at least give a decent finish. I just need suggestions as what to check. The table is tight and the spindle doesn’t seem to have any play. I don’t have fancy holders and I’m using carbide tipped single point bits.


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The lathe is the easiest cheapest method. I don’t have a 220v set up, only 110. I bored out the mounting plate and have to make the top torque plate yet. The finish doesn’t matter on them. Again it’s just something I’m just trying to see if I can do it, right now I just want a good finish. When I move the carriage I can feel the rack and pinion. Maybe that needs to be loosened up somehow!


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[pontiac428]

I like my little Atlas, but it is hard not to find its limitations constantly while working at the outer edge of its range. The carriage, compound, and tool post are very flexible, even with the gibs adjusted to perfection. Boring adds to that flexibility big time. I can't bore more than a couple inches without inducing taper and having to take a million spring passes to get an approximation of a parallel cut. Finish is typically less of an issue for me than deflection, but trying to reach the end of a 6" deep bore sleeve would certainly give me finish problems too. Cast iron has its own properties that make the job more difficult. Use a sharp tool, keep everything as short as possible for rigidity, and use feeds/speeds for manual equipment (use a good reference like machinery's handbook printed before color TV and passenger jets), not those for CNC, which are way too fast.

 

[brino]

I agree with @pontiac428.

What I find with my Southbend 9" is that chatter is always caused by movement; either slop or bending.
Find that source of movement and eliminate it.

Unfortunately, the potential source are many:
-top-slide dovetails and feed screw/nut
-cross-slide dovetails and feed screw/nut
-carriage dovetails and feed screw/nut
-slop in spindle bearings
-bending of the boring bar
-flex in the tool post

It requires some detective work.
Think about each and devise a test for it. Mount an indicator on one part(mag base) and put the indicator point on the other, either run it this way (if safe) or just push, pull and rotate the part to see the indicator reading.

Another approach that helps is to reduce the load on the lathe.
I find that sharp high-speed steel cuts easier than carbide. I believe it's because I can make it sharper than carbide.
Feed, speed and depth of cut also play into loading.

There are a couple good threads here on surface finish and chatter. Those should also have some techniques and tips.

-brino