Don't want that taper

[rexcsmith]

I'm cutting a 2" of a 3/4" round rod down to .7200" on my Monarch 10ee. I've had the lathe less than a year, but this is the first time that I need to go for sub-thousands accuracy. The .7200" section I'm cutting is 2" long. I'm seeing a taper along the 2" of 1.5 to 3 thou diameter (diameter always smaller at the spindle end). This happens whether I use the auto feed or the manual feed handle, whether I'm going toward the spindle or away from it.

At first I thought that maybe the ways were not square with the spindle. So, I got my dial indicator out; mounted it to the compound and slid it along a 3/4" rod in the spindle. No discernible change over many inches. The ways seem to be square with the spindle.

Then I secured the end of the rod with a live center (even though there is only 2" of stickout on a 3/4" rod). Same result... 1.5 to 3 thou of taper.

At this point in time, I don't know what the heck is going on. It seems like the cross-slide is moving such that it cuts small diameters the closer the cutter gets to the spindle. There is no cross-slide lock, but I wouldn't expect creep to happen on a 10ee. I got this as a refurb from the Monarch factory less than a year ago, and it's supposed to be good as new. I would expect the taper to be within a couple of 10ths over a few inches (or better).

Anyone have to deal with this before? I'm a novice/hobbyist machinist, seemingly in over my head.

thanks, rex

[John Evans]

Your material is deflecting away from the cutter. Use a live center to support the free end. Not enough info really as to type of cutter-material etc for better answer.

[BadDog]

Getting smaller at the spindle is pretty much always the case due to deflection. Depending on cutting pressures, even with your relatively short stick out you would expect measurable defection. And if you haven't set your tail stock, that may not be true. Or using a loose or improperly seated live center, you can still get get taper even with the TS properly set. But with everything sorted, that 10ee should be easily capable of better than you describe. I wish I had it to find out!

[Harold_V]

You've not provided a bit of information that may be critical to the answer you receive. What type of cutting tool are you using, and what feed rate? What is the material type you are machining? How fast are you running the spindle? Is the machine properly leveled? (That may not be ultra critical for an EE, as they have a very rigid base).

How far are you projecting the material from the end of the jaws? Have you inspected the chuck to determine if it has been sprung? It's not uncommon for a three jaw to grip only at the rear, so you exceed the rule of thumb for not attempting to machine any material that is extended more than three times the diameter.

Harold

edit: I reread your post and now understand you have extended the material only 2".

[rexcsmith]

More information...
- I'm using an HSS tool that I ground myself.
- Spindle speed is 500rpm. Feed rate tracks with spindle speed, but chips are far from looking burnt. I'm seeing this while taking very small cuts. Feeding manually at very slow speeds; the tool still tracks at a taper.
- I'm having the same problem with live center.
- Cutting 1018 steel
- I'm not using 3 jaw. I'm using a 3/4" 5C collet with a Monarch draw bar assy.
- The machine has not been leveled; however, I've found the ways to be properly aligned with the spindle by mounting a dial indicator and running it several inches down a straight dowel held by the collet.

[shootnride]

Possibly that 5C collet is where the run out is.

Ted

[rexcsmith]

I would think that run out would cause a smaller diameter at the end away from the spindle. This is a smaller diameter toward the spindle.

[tornitore45]

So, I got my dial indicator out; mounted it to the compound and slid it along a 3/4" rod in the spindle. No discernible change over many inches. The ways seem to be square with the spindle.

This is good. HeadStock and spindle parallel to ways.

Then I secured the end of the rod with a live center (even though there is only 2" of stickout on a 3/4" rod). Same result... 1.5 to 3 thou of taper.

This means the tail-stock is OFF forcing the end far from the tool.

[rexcsmith]

Still get the taper without the tail stock and 1" stickout with 3/4" rod.
When I used the dial indicator, the tail stock was involved. Indicated ways parallel to headstock.

I'm beginning to wonder if the live center has some slop in it. It's a cheap one I've had for a long time. I'll check that out.

[GlennW]

Can you post a pic of your cutting tool?

That would be a good place to start.

[rexcsmith]

Here's the tool.

[GlennW]

As long as it is on center, it doesn't look like it should be causing you that much trouble.