1943 Sidney Lathe Partial Restore

[nickel-city-fab]

BTW forgot to add, Inconel TIG rod works really really good on CI long as the CI is clean enough. You don't even need any preheat or postheat -- the stuff is very stretchy and gummy. OK postheat if you want to relieve stress, but not an absolute requirement.

Nope, you'll NEVER hear that from an AWS instructor ,,, not an approved (certified) technique. No WPS for that even though the chemistry of it is pretty simple.

[The Metal Butcher]

A bit of a moneyshot for why a wornout lathe is worth keeping around if you have the space:



Just some weldprep on 1/2" aluminum plate, cutting vees. Using my chamfer tools (which were admittedly getting a bit dull) on the Lagun I could get about ~5/16 to 3/8" before chatter started. On the Sidney... well by my eye I'd say that is getting close to 3/4", and not even a hint of chatter. I'm not so sold on perfect scraping and contact patches. I think mass and rigidity is a larger contributor if chatter resistance is all one is after.

[nickel-city-fab]

A bit of a moneyshot for why a wornout lathe is worth keeping around if you have the space:

she's got some gonads....... BIG'uns !!!

yea mass and rigidity for keeping down chatter, but I think having everything scraped in nicely helps because poor fit == losing rigidity and losing accuracy (can be compensated out tho)

[J Tiers]

As for chatter, you can figure this out reasonably easily, but chatter involves a mass/spring system. Mass reduces resonance frequency, but a stiffer spring (rigidity) increases it. So doing both may keep the frequency where it is. Usually the resonance is "driven", i.e. something is inputting energy to the system. That may be at a specific frequency, or just inputting energy that will "find" a resonance.

To deal with a resonance, there are several methods: You can move the resonance away from the driving frequency, by changing the mass or the stiffness. You can deal with the driving frequency at the source. You can add damping (friction) that takes energy out of the resonant system.

When things are scraped in nicely, there is some increase in rigidity, but there is also a good oil film, which can act as a damper. With the parts not scraped-in well, there may be poor contact, with parts able to rock, twist, or otherwise move in ways that help a resonance.

It's interesting that one way to kill chatter is to add a gooseneck tool holder. That actually adds flexibility (reduces rigidity), but it does so in a way that tends to reduce the energy input to the system.... the tool moves away from the work without digging in, instead of digging in and being bent downward (storing energy).

So the rigidity is good if it prevents springiness that stores energy, but can be bad if it serves to move a resonance into the driving frequency range.

Flexibility is bad if it "winds up" and stores energy, but good if it allows movement in a direction that reduces energy input by not allowing a tool to dig in.

No absolutes as to rigidity of the machine. As usual in engineering, "it depends".

[The Metal Butcher]

she's got some gonads....... BIG'uns !!!

yea mass and rigidity for keeping down chatter, but I think having everything scraped in nicely helps because poor fit == losing rigidity and losing accuracy (can be compensated out tho)

As for chatter, you can figure this out reasonably easily, but chatter involves a mass/spring system. Mass reduces resonance frequency, but a stiffer spring (rigidity) increases it. So doing both may keep the frequency where it is. Usually the resonance is "driven", i.e. something is inputting energy to the system. That may be at a specific frequency, or just inputting energy that will "find" a resonance.

To deal with a resonance, there are several methods: You can move the resonance away from the driving frequency, by changing the mass or the stiffness. You can deal with the driving frequency at the source. You can add damping (friction) that takes energy out of the resonant system.

When things are scraped in nicely, there is some increase in rigidity, but there is also a good oil film, which can act as a damper. With the parts not scraped-in well, there may be poor contact, with parts able to rock, twist, or otherwise move in ways that help a resonance.

It's interesting that one way to kill chatter is to add a gooseneck tool holder. That actually adds flexibility (reduces rigidity), but it does so in a way that tends to reduce the energy input to the system.... the tool moves away from the work without digging in, instead of digging in and being bent downward (storing energy).

So the rigidity is good if it prevents springiness that stores energy, but can be bad if it serves to move a resonance into the driving frequency range.

Flexibility is bad if it "winds up" and stores energy, but good if it allows movement in a direction that reduces energy input by not allowing a tool to dig in.

No absolutes as to rigidity of the machine. As usual in engineering, "it depends".

No doubt about it, a properly scraped lathe with perfect bearing area would be better.

My argument here is that: "ain't no replacement for displacement". Even with horrendous contact patches and a saddle and ways shaped like a banana, it still well outperforms a lathe weighting 60% as much. Of course, it's situational, but for just hogging off stock, I think that worn, heavy, and with directly supported lines of action well outperforms lightweight, overhung, but tight machines.

[J Tiers]

.............. Of course, it's situational, but for just hogging off stock, I think that worn, heavy, and with directly supported lines of action well outperforms lightweight, overhung, but tight machines.

Totally agree. Rigidity through direct support is the "good kind" that acts to reduce energy storage as opposed to increasing it.

There may be replacements for displacement (there are), but there is no replacement for mass and rigidity that is correctly placed.

[nickel-city-fab]

Totally agree. Rigidity through direct support is the "good kind" that acts to reduce energy storage as opposed to increasing it.

There may be replacements for displacement (there are), but there is no replacement for mass and rigidity that is correctly placed.

Absolutely agree. Many times, heavier machines are easier to use. The ultimate is a heavy machine that is tight.