Turning Fins

Problem: A Cox 15 replacement cylinder, than needs fins.
I machined an itty bitty cutoff tool, about 50 mils wide and 300 mils
deep. It chattered. I gritted my teeth and kept feeding. It bound up,
wrenched the cylinder out of the chuck, and broke.
Fortunately the part looks to be recoverable, assuming that I can
finesse the spot where the chunks of tool dug into the steel.
But I still need to turn in those damn grooves between the fins.
Any pointers, or should I just make a new tool, do the same stupid
thing, and see if the laws of physics have changed since November? I
_did_
make sure that things were as rigid as possible, with the
exception that I probably had the cylinder sticking too far out of the
chuck, out of paranoia about hitting the jaws with the tool holder.
Reply to
Tim Wescott
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I use the micrometer carriage stop to keep the chuck and carriage apart. The previous users didn't, repeatedly, but the lathe survived.
Reply to
Jim Wilkins
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.
Reply to
RB
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.
Reply to
_
I would recommend using coolant if possible. Make sure you have enough side clearance on the cutoff tool.
John
Reply to
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.
Reply to
RB
I guess this is aluminum? WD40 or kerosene works for cutting fluid.
Reply to
RB
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
Reply to
Bob Engelhardt
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
Reply to
Joseph 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?
Reply to
RAM³
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.
Reply to
Gene
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.
Reply to
RB
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
Reply to
Mark Rand
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
Reply to
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
Reply to
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
Reply to
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).
Reply to
Tim Wescott
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
Reply to
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
Reply to
Joseph 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
Reply to
Wes

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