Turning Fins

I use the micrometer carriage stop to keep the chuck and carriage apart. The previous users didn't, repeatedly, but the lathe survived.

You can also clamp a piece of scrap keystock to the carriage to limit longitudinal travel. Touch the cutter holder to the jaws with machine off, then clamp the rod so it touches the headstock at the back, with a .010 shim under the end.

Make a set of guides (both sides of the work) and use a hacksaw. A U-shaped piece with a slot mounted on the cross-slide - slot keeps the blade from wandering, bottom determines the fin depth.

I would recommend using coolant if possible. Make sure you have enough side clearance on the cutoff tool.

John

Can you mount the cylinder on an arbor? That would give you a more secure mount than a 3-jaw chuck, and you could get it away from the chuck. You could also stabilize it with the tailstock.

I guess this is aluminum? WD40 or kerosene works for cutting fluid.

Use a .045 cut off blade for a 4-1/2" angle grinder, mounted on your tool post grinder for the roughing-out. Then clean up with your itty-bitty tool. Or make a mount to hold your angle grinder & use it for the roughing.

I never said that I was a machinist, Bob

What kind of lathe are you using? Can you run backwards without causing the chuck to unscrew? Or, can you hold the workpiece in a collet?

Anyway, what I discovered in my long saga with chattering cutoff tools is that one big danger is self-feeding of tool into work. A very rigid machine limits this, but not all machines are all that rigid. One alternative is to turn the tool upsidedown and spin the work backwards, so the cutting forces instead tend to pull the tool out of the work. This will prevent grabbing due to self-feeding.

The other issue is to shape the cutting tool so it's max width at the cutting edge and tapers as one goes away from the cutting edge. In other words, the tool becomes slightly necked, prevent cutting on the sidewalls of the groove. Make sure that everything is square and locked, so the tool feeds straight into the groove without translating into either sidewall.

And ensure that the groove is flooded with cutting fluid. A brush will not do.

Now, I'm assuming that your lathe is tight. If not (and my lathe was not tight at first), you must first fix the lathe. I must say one stark moment was when I found that I couldn't make a 0.0625" wide slot in mild steel using my 1500# lathe. I knew that this cannot be right, and started the investigation. Everything that could be loose was loose. Search past RCM postings for "Clausing 5914 chatter" and "Trepanning and Parting Off" in the subject for the long sad saga.

Joe Gwinn

Tim Wescott wrote in news:DrudnexvHeuI0cjUnZ2dnUVZ snipped-for-privacy@web-ster.com:

While these may well be idiotic ideas, I'll offer them anyway.

1. Have you considered simply using a hacksaw while the part is spinning?
2. (A variant) Have you considered soldering the spine of a piece of hacksaw blade to a tool blank?

I've actually made those things before.... for guys racing model boats!

Anyway, what points to the problem is the chatter. How or with what did it "bind?"

What is loose? How big a lathe? How are you holding the part? Was the cutter properly lined up with the axis of the lathe? Proper clearances all around? Was the carriage locked? How much lost motion is in the compound rest (or was it locked)? What sort of tool holder? How close to center was the tool? Lotsa questions!

Unless this is a really tiny lathe you really shouldn't have any chatter with a .050 wide grooving tool.

Had a similar moment with my little 9" Logan, trying to part off a 1" rod. It finally dawned on me that something was shifting, so I started at the headstock mounts and worked my way through every joint up to the tool, cleaning, shimming, re-torquing. Took an evening, but it's still tight years later.

Shouldn't be a major problem. Make sure you have side relief on the tool. 2 degrees per side would be ideal, but one will do if it's consistent. That gives the back of the tool being 10 mils thinner than the front for 1 degree. Make sure the edge is perfectly square and sharp, with no more than 2 degrees of front relief (that'll help to stop it digging in). No top rake at all. you want a tool that can be fed very controllably and won't tend to dig in.

When mounting the tool, use a DTI or dial test gauge on the side to ensure that the tool is straight. The change in reading as the cross slide is moved should be the same for both sides of the tool.

Lock the saddle, nip up the top slide gib screws and ensure that the cross slide gib screws aren't slack.

If the cylinder has already been bored, then mount it against a shoulder on an arbor turned to a firm fit, drilled and tapped for a clamping screw and washer and then not removed from the chuck. Turn the clamping washer before doing the arbor!

You should be able to turn at normal turning speeds, just keep the feed under control if the tool post/top slide are a bit flexible.

Mark Rand RTFM

Once you get the chatter taken care of, you might be interested in this tip from people who make small engines with narrow fins: Make a disk that just fits between an adjacent pair of fins, and split it so you can place it in the last slot you cut. Tape should hold it in place.

When you're cutting fins with a slotting tool the previously-cut fin can get pushed out of shape by side force from the cutting tool. The filler should prevent the problem.

I have tried this but, frankly, I don't know if I would have had a problem without it, because I used the trick on the first cylinder I tried cutting. That experiment had some other problems but chatter wasn't among them. I haven't had a lot of chatter problems with cutoff or slotting. 'Lucky, I guess.

-- Ed Huntress

One of the problems with parting is that the work and the tool heat up and work grabs the tool. Coolant or some other way to get the heat out is advisable.

John

Parting is one of the few places where lubricating oil is sometimes recommended. I've tried it, and it works OK in steel. Since I use Buttercut lard oil for most of my turning I don't notice much of a difference. The lard oil works fine. I'm careful to have side clearance on my tools but there's still a lot of friction in that type of cutting.

I don't think that kerosene is lubricious enough for parting or deep grooving. WD40 might be, but it isn't much of a cutting fluid. It isn't much of anything, for that matter, except a good cleaning fluid. I've found that it's good for getting chewing gum out of your clothes.

-- Ed Huntress

It's steel. The Cox series of engines uses a one-piece cylinder finished on the inside for a piston, threaded at each end for crankcase and head, with 4 - 8 milling operations (one or two transfer ports, two or four exhaust ports, and two on no flats for removing the cylinder).

Cutting fluid. Ha. That'll be a pain on my minimalist lathe (but it sounds quite necessary).

On the cnc's with a lot of coolant I have no problem parting off 2.25 inch bars but on the manual machine not using coolant I have snapped a blade or two. With coolant on the manual machines the blades work fine.

John

Also a neglected machine.

More saga at "Clausing 5914 - Chatter and Self-Feeding Summary" and at "Clausing 5914 - Test Report Requirements". And so on. That lathe generated a lot of stories.

Joe Gwinn

Did you grind the nose so it isn't trying to push left or right?

Diamond hone it sharp. On center. Positive rake.

Minimize the stick out as in no extra tool protruding from holder.

Not sure this is a good idea but can you grind a valley in top of parting tool to fold your chip for clearance? I'd like to hear comments on that idea if it is good or bad.

Slitting blade, arbor, rotary table and mill also comes to mind.

Wes

When you say "coolant," if you're talking about conventional water-soluble (miscible) oil, the lubricating properties are those of the oil in the mix -- and they get lower as you dilute the oil with more water. Some of the real synthetics, like Blasocut, work differently; I don't know how they perform on a hobby-level or old manual machine.

On higher-power machines, including most modern CNC machines, the cooling properties of the water often are the dominant thing you need. On a smaller, older manual machine, it's the lubrication. But there are at least three different "lubricating" properties you're looking at, the tribology folks have told me, and motor oil, for example, can lead to skating of the tool.

Lard oil is pretty hard to beat on my old South Bend. It is pretty good in the high-pressure department but the film can be punctured, so it doesn't cause tools to skate. As a lubricant for the tool, where it might bind due to poor clearance, or the miniscule amount of springback that occurs just after the cutting edge passes a particular spot, lard oil is not bad. Not great, but you don't want more slipperiness there, or you may get skating with very light cuts.

I should point out that I have little direct experience with other cutting fluids, having used mostly lard oil, sulphated oils, and water-soluble all my life (plus kerosene, which I don't like, on aluminum), but I spent many hours with the cutting experts formerly at Carnegie-Melon, Purdue, and Master Chemical, and I picked up most of it from them -- including plenty of high-speed film that showed what was happening. (I never knew Gene Merchant but I've read much of his material, too.)

There is enough variation in performance between machines and tools that none of this is hard and fast, but it does give some guidance.

-- Ed Huntress