Finish Question

[Shiseiji]

This uneven finish is common on my Logan 820. Bearings have always seemed to check out OK. Ideas? Saddle/bed? EDIT. About .0005 difference in the OD.
TIA

 

[WobblyHand]

Without knowing any details, like tooling type, it's hard to guess. But I've seen similar finishes simply due to microscopic chips or defects on the cutting tool. These defects can be really small but still cause this. Like nearly invisible under 8X magnification. Whenever I get this it's time to resharpen the HSS, or change the insert. It might be something else, but this most often fixes it for me.

 

[Ulma Doctor]

Are you using the tailstock for support?
If so you may wish to pull the tailstock half the error to you.

A slight nose radius on the tool would give a smoother finish in comparison to a pointed tool.

 

[compact8]

the rod is like strings on a guitar, depending on where you pinch it, the vibration frequency changes, the vibration of the rod interacts with that of the lathe results in complicated mechanical things like resonance happening, beyond a certain point, the overall vibration is reduced hence better finish ?

 

[Shiseiji]

Without knowing any details, like tooling type, it's hard to guess. . . . Whenever I get this it's time to resharpen the HSS, or change the insert. It might be something else, but this most often fixes it for me.

Thanks, I feel a little less dumb. And the voice in my head when I started the cut, tangential tool holder/HHS, "Probably need to hone that tool."

 

[Flyinfool]

It is hard to guess without more info.
material being cut
Cutting tool
speeds and feeds
These are all very important.

From a distance, looking at the end of the cut it looks like you may have a large R nose on your cutting tool. Taking a very shallow cut with a large R nose will not give good results.

 

[Shiseiji]

Are you using the tailstock for support?
If so you may wish to pull the tailstock half the error to you.

A slight nose radius on the tool would give a smoother finish in comparison to a pointed tool.

Thanks, and yes I was using the TS with a live center.
Nose radius is an ongoing challenge for me regardless of the tool. If I mess it up too much on the tangential the tip will end up at the wrong angle the tool will need a regrind. So I am probably too cautious. I've been using the crobalt that Gary/Eccentric Engineering provides with the tool that unfortunately I've not found a US retail source, even though it's made here. Makes me even more cautious. Time to go back and practice on key stock and Chinese HHS.

Thanks again.

 

[WobblyHand]

Thanks, I feel a little less dumb. And the voice in my head when I started the cut, tangential tool holder/HHS, "Probably need to hone that tool."

I'm not an experienced machinist, just a hobbyist. But whenever I see stuff like this 95% of the time, at least for me, it's the tool tip. Especially if the day before I had a nice finish on similar materials. If you try a piece of similar material with a short stick out (less than 2:1) and you get similar crap finish, there's a high likelihood the cutting tip has some damage. It doesn't take much damage to mess with finish. I've had poor finish on cutting tips that I can't see anything wrong at 10x, but replacing the cutting tip (or rehoning the HSS) fixes the finish problem. I use cheap inserts or HSS on most of my work. The cheap carbide TCGT can micro-fracture. I don't really care, at 33 cents per cutting edge, I just rotate the insert.

I do have some tools with more expensive inserts, and I take a lot better care of them, simply because they are more expensive to replace. At $10 or $15 each, (or more) it's worth your time to take very good care of them.

 

[Shiseiji]

It is hard to guess without more info.
material being cut
Cutting tool
speeds and feeds
These are all very important.

From a distance, looking at the end of the cut it looks like you may have a large R nose on your cutting tool. Taking a very shallow cut with a large R nose will not give good results.

Material is 1/2" O-1
RPM was 330
Feed with the lead screw is .0018 (224 tpi) or .554 ipm, slowest I have on the QCGB. Which is 11 fpm if I calculated it right. Not even close, but I "thought" slower could only be better. ??
Duh, dug out my chart. Looks like ~ 65 fpm is optimal, online calculator says 65 rpm is 5.41 ipm or ~ .0098 rev at 550rpm. Have to check my QCGB to see what's close.

And when I removed the tool holder to get a better picture of the tool, "Blinding Flash of the Obvious." Tool holder was loose. I use a rule to check tool height and obviously failed to tighten the tool holder after I removed the rule. And the tool was in worse shape than I thought. Slap forehead. Time to regroup, more to follow.

 

[itsme_Bernie]

How's it going Ron?