Cutting off in lathe.

[J Tiers]

Just did another little job of cutting off, and was again pleased with results. Also VERY pleased with the effect of oil.

After dealing with/fixing machine looseness, I had only cut off dry. Before dealing with it, I just had quit trying. This time, for various reasons, I thought maybe a little oil would be a good idea.

Well, it was...........as soon as the oil hit the groove, the tool quieted down even more, the "hiss" became a "whir" and the chips began just shooting out of the groove. Worked so well, I was done before I realized it. I am gonna rig a drip for future cutoff jobs.


I think it is worth paraphrasing and repeaating what Harold said in a different thread. "if you are having trouble cutting off, look for looseness in the machine or setup".

I will say that I had NO IDEA how easy and routine cutting off could be if the machine was right. I used to look at articles describing parting off washers and think, "yeah, right, like THAT's gonna work".

Well, I take it all back. It can work great. Even on a little machine (mine is a 10" Logan).

[JimGlass]

Parting off is one of the most challenging operations in a lathe.
Wish I new the number of parting tools I have broken off.
Threading a left hand internal is often easier than parting.

Oil is part of the secret. The point of cutting needs oil as well as the sides of tool and the kerf. Near "0" clearance between the kerf and tool. Start a little galling in the kerf for lack of oil and "SNAP".

The sound a cutting operation creats is an important indicator
of how well things are going. Turning, boring, parting one should hear the metal pealing off and the machine motor.
If you hear the same sounds comming from your machine that come from the bird section of a Zoo, something is not right.

Glad to hear you got it working,
Jim

[Jacin]

What kind of oil are you using?? I have found that the reccomendation to use a sulfur based oil works particular well for most ferrous materials I cut off.

Personally I think the "lube" quality of whatever you use is only 1/2 the story - keeping your cutter cool is worth it's weight in gold. That's my story and I'm sticking with it. [img]/ubb/images/graemlins/grin.gif"%20alt="[/img]

[Harold_V]

Nice going, J.

The only (metallic) material I've ever had success parting dry is leaded steel or brass, 2024 aluminum, and, naturally, cast gray iron. Trying to part without lubrication is an invitation to tool breakage. I can't stress enough, the importance of lubricating the cut when parting.

It doesn't take a lot of lubrication to make a difference, although the more the better. Parting with flood coolant is the best of all worlds, for it not only lubricates, but keeps things cool, as Jacin mentioned.

For the most part, I simply use an acid brush and keep the groove as well lubed as possible. Sulfur based oil for all the steels, and kerosene or used Stoddard solvent (from my cleaning tank) for aluminum. I've found that works almost as well as kerosene, and I have it readily available.

I often will have one brush in the groove while reaching for a second brush, so the cut never runs dry. From that, you might already understand I'm parting with power, not hand feeding. As scary as that may appear, you'll actually achieve better success power parting than doing so by hand. It does demand proper and constant lubrication, however.

Harold

[joel_k]

I had the similar machine looseness problems on a 12x36 Clausing, broken tooling, jams etc. Finally broke down and replaced the cross slide screw and nut. Went from about .080 backlash to about .005. It has virtually eliminated the problems. The play was allowing the tool to be sucked into the part with guarranted bad results.

[Harold_V]

I had the similar machine looseness problems on a 12x36 Clausing, broken tooling, jams etc. Finally broke down and replaced the cross slide screw and nut. Went from about .080 backlash to about .005. It has virtually eliminated the problems. The play was allowing the tool to be sucked into the part with guarranted bad results.

That's a very common problem on the light duty machines. There's usually not enough mass, nor surface area large enough to overcome the pressures of cuts. Your example is yet another good reason why parting on small machines can be troublesome. I can only imagine your sigh of relief when you replaced the screw and nut and found it worked as it should. Keeping the gib snug often eliminates the problem, even with a loose screw. That doesn't work when there's considerable wear, however. The center of the area of extreme wear will almost always be too loose.

Harold

[J Tiers]

What kind of oil are you using?? I have found that the reccomendation to use a sulfur based oil works particular well for most ferrous materials I cut off.

I don't recall for teh original, I grabbed the nearest oil can, and I have moved them since......could have been ordinary 20wt "erl", or it could have been way oil. Both cans are around there.

Used the 20wt for sure last nite, and it worked fine parting drill rod. Not sure it matters a heck of a lot.

[gglines]

The sound a cutting operation creats is an important indicator
of how well things are going.

Parting off should sound like bacon frying.

George

[J Tiers]

It did, dry.

With oil, it was quieter, and the chips were just shooting out of there silently.

[_pete913]

Parting with a HSS blade can sure be a pain at times alright. I use cutting oil, and most of the time I set my tool just a hair higher than center. To me anyway it's better to be a touch high than risk being too low which is a recipe for a broken cutter. I use the power feed as well. I find that if your setup is correct, and rigid enough, taking a wimpy cut just makes it easier for really thin chips to wedge the blade, while thicker ones roll up and find their way out of the cut. I do a lot of large diameter parting, some of it in a CNC lathe, and I find that with the indexable insert type cutoff blades, if I take a .005 or .006 per rev feedrate, it works a lot better than trying to baby it.

[standish]

FWIW ... One thing I've not seen mentioned here, but seems to work better for me (which could mean almost anything) is to use a lot slower speed for parting than for turning. For example, I have a lot less trouble parting at 60 rpm than at higher speeds. This applies to CRS and drill rod, at least for me. I've used power feed and hand feed with good results. It's important that your tool be parallel to the direction of the cut, so set it with care. To get the tip at centerline of the work, I take a freshly sharpened tool and use it to take light facing cuts on a piece of scrap or whatever, adjusting the height until there is no "tit" left on the work. A couple of thousandths higher than center is okay to allow for deflection of the tool under load, so that it doesn't go below center and break as it's advanced.

[J_Tiers]

Yeah, that's what I found also. Not back gears, but the slowest open pulley speed, for stuff under 1". For anything larger, I can see going slower.

Most people did say that faster was better, so I figured to keep a low profile on that. No sense starting an argument. Its working, and gives a good finish, and I'm not on a per-part schedule here.

At higher speed, I found that even after tightening up the machine, chatter wanted to start. slowing it down seemed to "tune it out". (Before tightening, nothing helped at all).