PM-1640TL problems getting reasonable surface finish

[Lo-Fi]

I use TCMT with my Myford. 20 thou DOC, highest RPM I can set it to and a feed rate that gives decent chips leaves a great finish:



That's a bit of hot rolled plate I machined this afternoon. Baby it with shallow cuts and it ends up with the same awful finish you were struggling with.

Sorry I can't give numbers for speed and feed, it's belt drive, who knows what pulleys it's got, and no QCGB means I rarely change the feed rate or know what it actually is. Blue curly chips that break is what you're aiming for with carbide, though it's not always comfortable to be around.

If you want to hit accurate diameters and get a nice finish (no sneaking up with tiny cuts), all you need to know is right here:

I literally can't tell you how grateful I am to Stefan for that video. Was a lightbulb moment for me and I've never looked back.

Happy machining

 

[jeremysf]

Awesome, thanks!

 

[erikmannie]

Referring to your first picture (Post #1 in this thread), I would use tail support.

I have a PM-1660TL. Files, emery paper and Scotch-Brite are very often used.

You can rough finish with carbide, and then switch to HSS for the last .005” or so. You can do the last .001” with emery paper and smooth files. Of course, you have to make sure to move the emery paper and files evenly across the work surface.

I am always finishing things off with a green Scotch-Brite.

 

[BladesIIB]

Little late to the party here but as a TL owner, figured I should jump in. Skimming through, you have been given some great advice. The mild steel I think is your main issue. If I was turning that dial of mild steel I would max the RPM about 2000 for me. I would take .075 to .100" roughing cuts and feed at a minimum of .011. If the tolerance allowed, I may even bump that feed up a little more. Finishing, I would use a brazed carbide and run it the same speed and maybe down to about .008" feed.

 

[jeremysf]

Referring to your first picture (Post #1 in this thread), I would use tail support.

I have a PM-1660TL. Files, emery paper and Scotch-Brite are very often used.

You can rough finish with carbide, and then switch to HSS for the last .005” or so. You can do the last .001” with emery paper and smooth files. Of course, you have to make sure to move the emery paper and files evenly across the work surface.

I am always finishing things off with a green Scotch-Brite.

Great advice! Not evident from the photos but I have been using tail support on everything (except for a few tests without just to confirm I wasn’t messing up my tail support).

That does bring up another issue which is with a CXA quick change tool post and larger tool holders, I find it challenging to sneak the tools in on such small diameter parts with the live and dead centers that came with the lathe.

 

[jeremysf]

It’s mentioned above, but for anyone coming to this thread in the future, [mention]davidpbest [/mention] ‘s book is awesome.

I have been collecting and reading lots of classic machining materials, and I feel like his book is the “missing manual” filling in some major gaps for me.

 

[BladesIIB]

Great advice! Not evident from the photos but I have been using tail support on everything (except for a few tests without just to confirm I wasn’t messing up my tail support).

That does bring up another issue which is with a CXA quick change tool post and larger tool holders, I find it challenging to sneak the tools in on such small diameter parts with the live and dead centers that came with the lathe.

A long nose center is a great addition to your work holding. I have this one from Shars for my TL and use it all the time on small parts.

4 MT Morse Taper Long Nose High Performance Heavy Duty CNC Live Center

www.shars.com

 

[erikmannie]

…That does bring up another issue which is with a CXA quick change tool post and larger tool holders, I find it challenging to sneak the tools in on such small diameter parts with the live and dead centers that came with the lathe.

You can use a HSS tool bit with a custom (as in “You grind it”) “long reach” grind.

This is AXA (and it is in need of sharpening), but it provided me extra reach in to a tight area.

David Best’s book is AMAZING. It is truly a must have.

 

[macmccaskie]

For you HSS gurus: Is there any differences between grades/brands and quality of cut? I’ve been trying a brand of old stock T-15 and got BUE (now that I know what that is). Would backing down to M2 or something finish better at .002” DOC?

 

[erikmannie]

For you HSS gurus: Is there any differences between grades/brands and quality of cut? I’ve been trying a brand of old stock T-15 and got BUE (now that I know what that is). Would backing down to M2 or something finish better at .002” DOC?

At home (as opposed to school), I have only ever used cheap import HSS tool bits. It does the job for a while, & then requires resharpening sooner than I would like.

At the one school I went to, they used the good stuff. It was rare to see a tool bit require a trip to the grinder.

I should change to quality HSS tool bits. If the tool bit is getting smaller (i.e. “dulling”) during a single pass, then you would get a slight taper.

Is anybody else doing the roughing with carbide & then switching to HSS for the last .005” or so?