Trying to improve parting

[Aukai]

I have gotten things quiet, but the part looks distressed. My mystery 1.25 wants ~ 200 rpm, slow feed otherwise it starts singing, I could probably up the rpm as it progresses, as it gets quieter, but still looks smeared.
The 1" 12L14 can go a bit higher rpm, but ~300-350 has the better finish, something sounded bad, and went away on the picture. The center is how the other cuts looked. Center height, and squareness were adjusted over several cuts for both materials. If it's off the choir is in full song. The blade is an Empire P2 N, I tried low rpm, higher feed, and higher rpm, slower feed. There were several aborts trying these. I'm not sure how the face is supposed to look, so here is what I got, I'm adding oil as it's turning.

 

[Technical Ted]

Parting is not a "finishing" operation. If you want a good finish on a parted surface, plan on machining it somehow. Usually, you can turn it around and face it. If it's thin, you can face off a different piece of stock in your chuck and then either super glue the piece to it or use double sided tape and take a light finish cut.

For parting, use a quality cutting tool, use minimal tool stick out. Make sure your tool is sharp with ~ 5 degrees of clearance. Too much with cause chatter. Make sure the blade is square to the work piece. Use plenty of oil. I always use hand feed and try to keep a nice chip rolling out.

Good luck,
Ted

 

[kb58]

While this probably isn't your issue, I'll pass on what an old machinist once told me. Depending upon the metal (in my case it was mild steel) he said that unless the metal is certified, you can never know what you're getting because the steel mills throw all sorts of donor material in, and "most" of it melts. His worst-case example was half-melted ball bearings ending up in your "mild" steel. Just a few months later I had some mild steel on the lathe and dang if his example didn't ring true. It was cutting just fine, but then started running into something that was obviously much harder than the surrounding material. The cutter and lathe certainly didn't like it, "thumping" every time the part came around to the same point. Stopped the machine and examined the face of the material and couldn't see a darn thing, but something was there.

 

[WarrenP]

I noticed useing a "T" shaped parting tool helped alot for me, also making sure the holder , etc was rigid.

 

[mikey]

Mike, cutting mystery metal can get tricky because we don't know what speeds will work. However, this is what I would do.

I would try 400 rpm and feed manually. Assuming everything is tight and aligned, I would put the tip of the tool slightly higher than dead center. Use your tool height gauge and get it on center, then a tiny bit higher (a few thou). What we're doing here is to attempt to deal with tangential cutting forces that are pushing the tip down. I would manually feed it, with the goal of feeling the tool push back as you feed. You want to feel like you're consistently feeding or pushing the tip of the tool into the work. As the tool cuts you want to maintain that feel. As you get about 1/2-2/3 of the way in, slow your feed because your SFM will be slowing at that point. Be sure to keep things lubed up well.

You will find that for most materials the faster your speed, the lower the force required to feed the tool into the work. This gets a little tricky because we are not just talking about the tool or the work. Fits in the lathe, rigidity of the tool post and holder and who knows what else gets into this equation. This is why I usually feed manually when parting. My sense of feel will usually make up for a lot of other failings and I almost never have issues parting. Anyway, give this stuff a try.

 

[higgite]

Am I seeing raised, flat bumps in the center of the work pieces? If so, I believe your tool is set too low, which won’t help the process. In my limited experience, you’ll get less cutting and more tearing that way. I set my parting tool height so there is just a tiny bump or none at all left on the work piece. I’ll second Mikey’s recommendation of slower speed. I usually part even slower than 400 rpm. I found that aggressive feed is much less chatter prone than wimpy feed, but there is a medium fine line to be learned through experimentation on your machine.

Tom

 

[Aukai]

Thank you Mikey, Tom, I'm running out of the mystery bar stock. I have about 1/2 dozen cuts on it with the Chinese blade, and the Empire blade. I will hone the blade face, and give it a try. I may have gotten too high as it stops cutting near the center, and the clutch pops. I stayed with the cut, and dropped the blade through several adjustments, and it finished. That was with a just no go with the height tool. With these settings, and at 300- 350 rpm it made a lot of noise, and was better at 180-210 rpm. I'll see if real cutting oil makes any difference also. Thanks...

 

[benmychree]

REAL cutting oil? What have you been using? I use TapMagic for all my cutting oil needs, makes a difference !

 

[Aukai]

I have used Tap magic, but was trying more volume with this episode, and filled the can with #2 way oil.

 

[benmychree]

I use a chip brush and apply the oil constantly to the cut, you don't need to waste a lot of oil, just keep it on the cut constantly, stop the feed, er dip the brush and resume. I took a tuna can and glued a rare earth magnet to the bottom, and set it on the cross slide under the back side of the cut to make re dipping convenient.