Turning Fins

keeping all overhangs to a minimum, buth tool and workpiece, are good things to do. Possibly going to an even narrower grooving tool, and alternating taking a little off each side of the groove would work better.

You probably need to understand what was going wrong. Was the work too flexible, or the tool? It depends to some extent on the rigidity of the lathe, too. When I used Atlas/Craftsman lathes, any cutoff job was a nerve-rattling exercise, and bind-ups were VERY common. Now that I have a 3500 Lb Sheldon 15" lathe, I rarely have any problem with cutoff or grooving operations that would have been unthinkable on the Atlas. So, the total rigidity of the machine must be part of the difference.

Jon

Oh, one other thing for parting or grooving tools. Grind a slight groove in the top of the tool, so that the chip is forced to curl inward. What you need is the left and right edges of the tool to be higher than the middle, so there is a little bit of a valley coming out towards you. This curling inwards makes the chip narrower than the groove, eliminating the binding in the groove. When you get it right, the chips come off rolled up, and there is a clear barrel-shape to them.

Jon

This is the way that commercial cutoff inserts are made, and it works fine with those wider cutoff/grooving inserts. I haven't had any luck trying to do it with very narrow ones because the chips just jam against each other.

Have you tried it with narrow grooving tools? Tim says this one is only

0.050" wide.

-- Ed Huntress

Sounds like your tool isn't properly ground, Tim.

Did you provide side relief, both top to bottom and front to back? If the tool touches anywhere but at the tip, the point of the cut, you can expect terrible results.

Did you provide a small amount of positive rake? It often helps the cut, and provides additional relief when the tool is properly ground.

Did you try parting dry? That's a mistake unless you're machining 2024, and even then it's not the smartest thing you can do.

As for creating the fins, you'd be well served to use a long travel indicator to index the cuts. Measure the width of the tool, then determine how thick you want the fins to be. Make that offset after each one is machined.

if your tool cuts well, you should end up with a clean cut on both faces of the fin. If you find it doesn't, you might explore a tool that is slightly undersized, then face each side after you've taken the groove to depth.

Unless you have a pygmy lathe (not trying to be rude), you shouldn't have any problems with this little project. The grind of the tool is everything.

Harold

It is the lubricant of choice.

Harold

I thought it was aluminum, too. Forget the kerosene, it is restricted to use on aluminum.

If you have access, use some of the old formulation Tap Magic (the one with

1,1,1, trichloroethane). There is no better lubricant for such an operation. Same rules apply on the parting tool. If it makes contact anywhere but at the point of the cut, you'll never get through the job. You also won't have the same degree of success if you try to face the fins, but it can be done. Keep the tool exceedingly sharp.

Harold

FOR ALUMINUM, not steel.

In aluminum, yes. Not in steel.

This is a steel-cutting application, Harold.

-- Ed Huntress

Having read all the posts, I suspect that my problems are, in order:

• I let the tool get dull -- it worked for some cuts, then got worse and worse and ...

• Not enough positive rake, possibly exacerbating the sharpness. I knew this, but I was lazy.

• Heat. Coolant would be a real pain, but I can try flooding it with lubricant, and going slow.

There may be other problems, but when next I get the chance I'll go remake the tool and give it a try.

Yes, so I discovered after I posted my comments. Thanks, Ed.

Harold

That is likely a function of surface speed. The tool should have held up for the amount of cutting involved. Try slowing down ever so slightly. If the chips came off anything but a pale yellow or silver metal color, you ran too fast.

As you increase rake, the tool will tend to peel the metal instead of push it off. That lowers cutting pressure and often results in a cooler cut----although with the reduced mass at the point of cut, the result of the angle of rake, the tool may heat just as quickly as it did previously. Pressure will be lower, however, and that's a good thing.

Cooling is important, but not nearly as important as lubrication. It's virtually impossible to part dry---although a few metals will cooperate. Leaded steels and brass tend to part dry fairly well, as does 2024 aluminum, but you're never sorry for adding lubrication. If it doesn't do anything else, it helps chip evacuation, although there's far more involved. You limit or eliminate chip welding, and cut cutting pressure in ways that are hard to believe. You need not flood the cut----an acid brush (don't use a paint brush---it doesn't hold a supply of oil the way an acid brush does) held in the groove while cutting will make a remarkable improvement, plus the reduced friction will yield less heat. Overall, you'll see an improvement you can't believe. Give it a go. You'll be pleasantly surprised. If you don't have any of the 1,1,1, trichloroethane, try sulfur based cutting oil. It stinks, but it does a decent job.

One more consideration. The material you're using can make a huge difference. If you're using mild steel (C1018 up through any of the 1020 materials, hot or cold rolled), you can expect grief. You might consider making the cylinder out of Stressproof (1144). It machines beautifully, especially with HSS. It also has great properties.

Be certain to have relief properly ground.

It would have been interesting to hear about the lathe you're using. Did you make mention and I missed it?

Small machines are not the best scenario for parting, although with a narrow tool you should achieve excellent results. If you find you're having trouble, use a narrower tool, plunge the centerline of each groove, then, using a long travel indicator, step over and face each side. With a sharp tool you should be able to do so without problems, assuming the fins are reasonably thick.

How about a report on the project when you're finished? I'd be interested in hearing the outcome. Sounds like a good one to pursue.

Harold

I agree with all of your recommendations, Jim. And it's reasonable that if "I do this" works well, then that's definitely the way to go. Some of the other folks with different machines will need to adopt their own "I do this" procedures for whatever works best for them.

The parting tool I've been using is 1/8" wide x 1/2" high HSS, the tapered cross section type. The tool holder I use also holds the blade at an (upward) angle, but I haven't measured it. I was concerned that a chip breaker ground into the tip would be too much top/back relief, but it works well. The chip breaker might not be the ideal tool profile for power cross feed, but it's definitely been beneficial for manual cross feed. The chip breaker tip has worked well for all of my mild steel and aluminum parting operations up to about 1.5" diameter, and smaller diameters of stainless steel (just haven't had any need to part/cutoff larger SS yet). The very slight front relief made a dramatic improvement, completely eliminating any digging/grabbing in the workpiece. Of course variable spindle speed makes it easy to find a good relationship between spindle speed and manual cross feed rate.

For larger diameters, I use the band saw to cut sections, since the cutoff blade would be extended too far to complete larger diameters, unless the larger diameter would have an axial hole, then the parting/cutoff blade would probably work well. The problem with large diameter stock is that for parting, the tailstock center should never be use to complete the parting, so the section of large round stock would need to be short so that the parting groove would be near the lathe chuck.

Nearly any parting operation will go smoother if the workpiece is to have an axial hole in it, and the hole is drilled before the parting/cutoff operation.

The tapered type parting/cutoff blades provide good side clearances, but it's important to mount the blade as perfectly vertical as it can be. Some blade holders aren't machined properly to set the blade in the vertical position, so the operator needs to be aware of this.

I haven't used the T-shaped parting blades, but I've read good comments about their performance.

I would guess that you ground the parting tool from 1/4 square? If so your asking a lot for the tool to plunge .3" deep even if ground very well.

For a one off groove I'll use the compound set parallel to the ways and feed 1x to 1.5x the tool width then pull out, move the compound over and plunge again, etc.

Obviously, the tool must be ground narrower than the finished groove for you to do it this way.

Most folks part with the tool on or slightly below center with somewhere between "0" up to half the usual rake used for a given material. Side clearance is crucial for deep plunging, but less so for "pecking".

You've got lots of time, the part is precious.

Matt

I don't recall were on the web I saw this idea for making a grooving cutter for small fins but I drew up a sketch and placed it on the NEMES web site.

I think it is a good idea but have not tried it myself.

Errol Groff

Sorry -- it's a Smithy "3" in one (actually 2 + excuse in one, but the excuse is the milling section; the lathe seems to be pretty good). Other than the compound, which seems to have some taper in the dovetail, I can get good control of the rigidity by snugging down the jib screws.

Yes.

Well...

Actually, at this point the part has been through the wars. It's still clinging to "finish it and try it out but don't let anyone see it" -- any more stuff-ups and it'll attain the status of "the one I screwed up on so I could get the next one right".

Unless you are doing it for money, there's nothing particularly wrong with having to make the odd, difficult, part a few times as a "learning" experience.

At least, that's what I tell myself :-)

Mark Rand RTFM

Well, yes. But I take that to mean that I should continue trying to make the part until it is _completely_ hopeless before I start over again.

After all, if everything I did looked really good, people would think I'm a competent machinist. I don't want them to be deceived...

rote:

Even when you are it's common to make spares. Use the "sample" part to try each setup before risking the good one.