Noob Lathe Q: Turning between centers

For class I'm turning an aluminum flywheel. 3" diameter. The steps are: face the sides, drill & ream the center, press onto a mandrel, turn
the outside and sides. Anyway, after pressing it onto the mandrel (yes, I cleaned out the cutting oil) I've found that I have to go very slowly or the cutting tool will grab the wheel and spin it on the mandrel. What are some good ways to deal with this problem? I already crammed it as far onto the mandrel as I'm comfortable with. I'm tempted to just loctite the damn thing.
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Wow!
Without seeing it, it's hard to second guess the problem. Can I assume the mandrel is ?" Pressed with an arbor press? Tapped in with a hammer? Cast aluminum, or bar stock?
That's not much to drive a large diameter cut. A couple things can help. Make certain that your cutting tool is sharp, with a slight radius (1/64" max) stoned on the tip so it cuts smoothly, but not too large, so you increase surface area in contact with the cut. That can lead to chatter, and increases cutting pressure, often overwhelming the friction fit of the mandrel. A little positive rake will lower cutting resistance, but too much will encourage hogging or chatter, so you have to walk a delicate line. Take a lighter cut and finer feed. Do what it takes to lower cutting pressure, but don't allow chatter to start. Once you get it, it can be difficult to eliminate. Higher speeds encourage chatter, but improve machining.
Harold
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Heat it, then quickly press it on--to remove, heat it up again.......~350 degrees F. should do the trick....remember, aluminum expands at a greater rate than steel....
Oh, and take lighter cuts, use a sharp tool, etc....cause if it heats up........
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On Wed, 02 Mar 2005 22:25:40 -0600, "B.B."

Superglue works quite well as long as you dont have any tool chatter. So does regular fingernail polish.
I make my own mandrels by turning a rod to diameter, drilling and tapping the end, then slitting with a hacksaw or slitting saw. Slip over the workpiece, then installing a socket head cap screw in the tapped hole to expand as needed.
Best if done in a collet of course. but works fine in a three jaw if you dont remove it during any of the process.
Cheap and easy to make, grabs well.
Gunner
Lathe Dementia. Recognized as one of the major sub-strains of the all-consuming virus, Packratitis. Usual symptoms easily recognized and normally is contracted for life. Can be very contagious. michael
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wrote:

Works real well with a pipe plug, too. It's a good idea to try to make your cuts at 90, so when you expand the mandrel it does so uniformly and retains concentricity. Rough turn, drill, tap, split, deburr the threads with your pipe tap, then finish turn with the pipe plug tightened ever so slightly. You can do surprisingly precise work with a mandrel so made.
Harold
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wrote:

turn
(yes,
crammed
just
The "splitting" part is what becomes the problem here--it's best done in this case with just a plain ole hacksaw....with the mandrel still firmly chucked in the lathe....
From start to finish, once you chuck your mandrel blank you should forget that you even *own* a chuck key--throw the darned thing out the bay door and retrieve it later......cause if you unchuck the work and have to re-set it then all bets are off....
== Never forget that turning or milling, makes no differance--your primary axis is always gonna defined by your spindle bearings, and all other planes are defined from that referance.
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Nothing says the chuck has to remain on the lathe, just the mandrel stays in the chuck.
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wrote:

in
forget
and
it
While most mounts are pretty darned accurate, I wouldnt bet on it without having some familarity with the actual lathe thats being used.
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wrote:

firmly
door
re-set
Agreed!
While the error is usually minor, even with a D type spindle, orientation affects concentricity in many instances. Many of the D type spindles have a witness mark for that reason.
Harold
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wrote:

done
without
have
Or there might have been a little dirt or chip someplace from the last guy that installed the chuck....
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On Thu, 3 Mar 2005 00:56:06 -0800, "Harold and Susan Vordos"

Ayup. Mine are threaded for 1/8" pipe plugs..but most folks dont have em, so suggested the standard bolt. The threaded and Tapered pipe thread is the best way to go.
I slit mine on the Mastermill with slitting saws and the mandrels held in a 5C indexer.
Sometimes I have to think hard on how to do things when the other guy may not have Stuff.
Gunner
Lathe Dementia. Recognized as one of the major sub-strains of the all-consuming virus, Packratitis. Usual symptoms easily recognized and normally is contracted for life. Can be very contagious. michael
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says...

Change the order in which you perform the operations.
1) clamp via the OD on the rough blank, and turn one side and the part of the OD that is extending out from the chuck jaws, but leave 20 thou or so for cleanup later on the OD.
2) in the same setup, rough drill the bore.
3) Flip it around in the chuck, so that the jaws are now grabbing on the finished OD from the previous step. Profile the second side and the OD again to a 20 over size. Finish bore and ream the ID dimension. (when you seat the part for this step, be sure it is bottomed in the jaws and that there are no chips under it)
4) use a stub mandrel in the headstock, with the stub turned in place - at a diameter one thou under the bore size. Also put a pusher block in the tailstock, a live center makes this run easily.
Then your flywheel goes over the stub on the mandrel (which picks up the finished bore) and the pusher block forces the part up against the face of the mandrel, which now drives the part for taking the final OD cut on the part.
You can glue some sandpaper on the mandrel face (which should be only slightly smaller then the part's diameter) to assist with driving it.
The benefit of this approach is:
The OD of the part is dead concentric with the bore, which is the most important issue.
The OD is turned with the part held rigidly between two large driver blocks - so there is much less chance for ringing or chatter.
You can take as big a cut on the OD as you want because it *will* drive.
How do I know all this? Because I spent a few years making crane sheaves out of nylon. This is the way it was done, and the OD cuts were often done with form tools, which require large cutting forces and are very prone to chatter becaue of the amount of tool engaged in the workpiece.
Make a stub mandrel and a pusher block, you could turn 20 flywheels from blanks in a half hour.
Jim
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hold the mandrel short so the flywheel is touching the jaws and center drill a piece of 1 x 1 x 4 in the center of the length and use the tailstock to press the flywheel up against the jaws .......
or
just turn it backwards and turn your tool upside down, so the nut will tend to tighten instead of loosen
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In article

Replying to all:
I like the method jim described since it's sturdy, but I can't use it since I've already done just about all of it except for turning the grooves in the sides. Of course, if I ruin it.... However, I believe we're doing this part mostly for the sake of turning something between centers as part of the class. I'm nearly done with the assigned project and have a half a semester to go for whatever, so I can probably try this at some point. Harold, When you wrote "Can I assume the mandrel is ?" that last character came out as Pi on my screen, and I have no idea what you meant by it. But, bar stock, pressed the mandrel in with an arbor press. We're using general-purpose indexable carbide tools on all of the lathes, but I have a fresh bit of tool steel and I'll see about making my own tool to play with. I did find (counter-intuitively) that running on the high side of the cutting speeds helped. I'll likely settle on the heat & press method suggested by PrecisionMachinist. Class is on monday--I'll let you know how it goes.
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    [ ... ]

    It comes out as "1/2" on some screens, but since it is a part of the extended ASCII character set, there are no promises that it will show up the same on all. This is a primary reason for sticking to only the characters which show on the tops of your keyboard keys. Anything which requires fancy keyboard tricks to generate (e.g. Compose-1-2 on my Sun keyboard) will not mean the same to everybody in this newsgroup with mixed systems in mixed locations around the world. (And it even chances on some of them when you change the characterset used by the program.

    Hmm ... bar stock? Not turned to have a very slight taper? That could be part of the problem. I think that the typical taper on an arbor for turning between centers is 0.001 inch/foot, but I'm sure that Harold will correct me if I am wrong.

    That could help, as typically a carbide insert is not as sharp as a frechly ground and honed HSS bit.
    Note that I have some very nice sharp solid carbide inserts (1/4" IC 55 degree diamond *without* TiN coating or the like, which I use when I want a sharp tool but am too lazy to grind my own. :-)

    If your arbors *do* have a taper, it should get it that much tighter. (Also note that the heat generated by turning could expand the aluminum and loosen the grip on the steel arbor, which would make the typical carbide insert the poorer choice here.)
    Enjoy,         DoN.
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wrote:

That's one thing I need to try to keep in mind. I'm fairly comfortable with a half dozen characters so generated and use them routinely. Probably not a good idea when posting! Thanks, DoN.

His answer is likely no, and it shouldn't have. Arbors have a gentle taper and will hold an item squarely, assuming the mandrel is pressed properly and the item held isn't very narrow.

Close, but no cigar. Standard taper is .0005"/inch. A tiny taper like you propose would necessitate a huge array of mandrels to be useful for run-of-the-mill parts, unless a very tight tolerance was imposed. They would also have the ability to swage holes effortlessly, which could be a bad idea depending on circumstances at hand. Mandrels are often used on grinding machines, where one is grinding the likes of bushings that must be dead concentric. Hone first for size and finish, then grind. I've ground literally thousands of bushings in that fashion.

Yep! Rarely do you find inserts that rival honed HSS tools, but they do exist. I use RB inserts that are diamond ground. Very nice inserts, and sharp, so long as you don't buy them coated. Even the coated ones are fairly sharp, however.

Yeah, all a part of that delicate balance one must achieve. In practice, one might never use a mandrel. They are slow, cumbersome devices that limit the ability to machine anything. Soft jaws are often used instead, or any of a myriad of setup variations, anything to improve driving capability and cutting ability. Still, they're a very important part of learning to run machines, exposing the newbie to precise ways to achieve certain functions. Learn any and all of these procedures, and learn them well. Later on, when you have better processes at your disposal, you'll incorporate them when appropriate. Right now you're learning the basics, and that's the best way to progress.
Harold
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snipped-for-privacy@d-and-d.com (DoN. Nichols) wrote:

Oh, the mandrel itself is tapered--it's a pre-made mandrel out of a box. I thought Harold was asking if I was turning my part from either cast or bar stock. I'm turning from bar stock, and the part is pressed onto a mandrel. Hope that clears it up.

Yeah, maybe I'll just turn it until it starts slipping and then run it over to the press while still hot.
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snip---

Ooops!! Sorry about that----I hit the keys in the wrong sequence, and didn't notice. It was intended to be " ?----asking the size of your mandrel. My concern is that the more slender is the mandrel, the more likely you would experience chatter.
But, bar stock, pressed the mandrel in with an arbor press.

If you understand rake and clearances, you'd be far better off, especially if you're using negative rake inserts. If you're using positive rake and they're sharp with a minimal corner radius, it may not make a big difference. Regardless of what you have, I'd strongly encourage you to learn to hand grind toolbits while you have someone looking over your shoulder (assuming you do have, and they understand the concept themselves), for it will serve you well for ever. It really is nice to not have to buy each and every special type tool that you need when it may get used only once.
Now that we understand you're using inserts, make sure you're not running a C5 or C6 grade, especially if the insert has looked at steel first. It's the wrong choice for non-ferrous materials to begin with, lacking the proper edge hardness to withstand cuts. It really does make a huge difference.

All metals have what you might call a "sweet spot", where they machine better than at other speeds. Aluminum really responds well to high speeds, and rarely is a problem as a result, assuming you use the right tools. Armed with that knowledge, try to run as fast as possible, which generally yields far better finishes and improved chip flow. You risk chatter, so you must achieve a balance for conditions at hand. You can't always use the speed you might desire. Run as fast as possible for conditions. The larger the area of contact your part has with the tool, the more likely you'll have chatter. Broad tools make for difficult operations unless you have *very* rigid machines. If you were to compare the likes of a 17" Axelson, for example, with a 10" Southbend (not a fair comparison, but it really proves the point) it would jump right out at you. When you run a lathe, try to keep everything choked up as close as possible. Material short in the chuck, tailstock quill extended only as far as absolutely needed, and cutting tools held as short as possible. When you keep everything close, you can usually run faster, which yields better results and shortens machining time. That can be real critical if you're making lots of the same thing.

Good luck! Hope you can give us a good report.
Harold
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It's a skinny little 3/8 mandrel and 6" long while my part was only 3/4" long. I had a chatter problem at first (I did kinda like the funky looking finish, though) but it went away as soon as I limited myself to passes of .010 or less. Not a problem since I'm only making one wheel and only needed to shave off about .070 anyway.

How would I check a carbide for its grade? Would it be embossed on the inset itself, or would I simply have to check the package it came out of?

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wrote: snip------

That's even worse than I had expected. While I realize that the number of passes you may have to take isn't of importance at this point, I think you can understand that if you were engaged in doing this for gain, you'd be out of business before you got started. Again, you're in a learning phase right now, so it's important to experience these things so you understand them.
Holding by other means, you'd have roughed the flywheel within .03"/side, then taken appropriate finish cuts of equal sizes for consistent tool load. One to determine size, the balance (2 passes) splitting the remaining material, half for each pass. That way you can better control diameter when it's critical. Certainly, the outside of a flywheel isn't, but it's a good method to learn for when your project demands precision.

Depends on the maker. Some carbide is identified on each piece, but you can't rely on that. The C2 designation might appear as something else, so you have to understand carbide markings for it to make sense. For example, if you're using Carboloy, their C2 grade would be marked 883, and C5 would most likely be marked 370. Understand that any carbide will cut any material, but how they hold up is determined by the grade. C2 has excellent edge hardness, but is brittle and chips easily. Not a problem when machining aluminum, but when you machine steel, unless you're taking very light cuts, it tends to chip the edges around the point of contact, the result of chips acting against the carbide. The point may very well stay intact and still cut fine, but if you use the tool for a deeper pass than the previous one, it often breaks because the tool has lost proper configuration because of edge erosion.
In the old days, (carbide) makers talked about a triangle. If your choice gave problems, you moved around the triangle. As you gain one feature, you give up two others. There's usually a balance of the three features that will provide good tool service and life. I'm not sure they even talk about that today, it's been years since I last had to worry about carbide grades. If you can find some old Kennametal data, they used to include the triangle, and it would help you understand how it works. It's been too long for me to recall it correctly.
What's important here is that your insert hasn't been machining steel before using it on aluminum, even if it's the right grade. The keen edge will be gone, and without that you're likely to have problems. Finish often speaks volumes about the condition of the cutting edge, even when you think everything is OK. If you're machining 6061-T6, you should expect the surface to show feed marks, but otherwise cut quite cleanly, with no fuzziness on the surface, assuming you're using a lubricant. If you get the slightest signs of fuzziness, the edge is likely experiencing some chip welding, maybe at the microscopic level. That makes for poor machining and increased cutting pressure. That works against you when using a mandrel, especially when you're driving with such a small diameter. Knowing the size you're using, I'd suggest what you're experiencing is more or less normal. That's why you try to avoid using mandrels. I also avoid turning between centers as much as I can. Same problem. Too much chatter and the cuts demanded can't be accomplished. Soft jaws answer the vast majority of the problems. It's a little too early for you to worry about them at this point. Besides, the chuck you're using may not accommodate them. Not all chucks do.
Harold
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