1940 Monarch Lathe - how accurate is it after 84 years?

[@edwinmuzzey7161]

Leveling the bed with a high precision machinist level is the main thing.

[@snicks50]

For sure

[@jimfiles3307]

What you are seeing in the center is deflection of the material from the tool pressure. Do several light cuts, then several passes without changing the depth of cut. This will show you where you are in alignment. Typically you should do a test cut of 3” long at the chuck, and the same cut at the tailstock. Both diameters should be the same. This way you don’t need to worry about bar deflection.

[@samuelwiltzius]

That’s a great idea. I think at this point I am punching above my skill and am content that this lathe is plenty accurate for my current projects. I will definitely keep this in mind.

[@dudleycornman1624]

You need to make you test bar differently. Relieve the middle part by say .125" and leave the ends (about an inch) so it looks like a dumb bell. This makes it a lot faster as you don't have to cut the whole length on your test and it reduces any wear on the cutting tool that may occur on the long cut.

[@Mike40M]

As Georg Schlesinger said in his works some 90 years ago.

[@snicks50]

Also for a true way to do it would be between centers ( on both ends also a dead centers)

[@RustyInventions-wz6ir]

Very nice video. Good job.

[@MegaRiffraff]

Also be sure to level it first before you spend any time adjusting it

[@samuelwiltzius]

I recently leveled it with the help from a local machinist. I may recheck in a year to see if it settled.

[@tompayton6778]

i've been a manual machinist for 40 years and you obviously don't know what you are doing, {no offence intended} leave the tail stock tight but not too tight and adjust the tail stock by tightening one side as you loosen the other side watching the indicator as you do so, if it has a one thousandth taper you only move the tail stock by a half thousandth, first you need to make sure the bed is leveled to within a half thousandth both in X and Y directions, you have wear in the ways, and good luck with that old dinosaur

[@samuelwiltzius]

Yeah… it was obvious to me as well that I didn’t know what I was doing (that has never stopped me though) but I’m getting there. A lot was learned on this exercise.

[@douglaslodge8580]

The ways are giving you a little and the bar gives you a little because of whip and preload on the bar.

[@petemclinc]

What you really need to do is remove the chuck and stick a precision ground test bar in the spindle bore. This eliminates any misalignment that might be in the chuck.