Cutting Metal

Hi all. I just got a new lathe for Christmas and I have been trying it out. I have been trying to turn a piece of unknown CRES from about 0.75 OD to
about 0.38 OD. I have tried various speeds and feeds but still keep getting a very rough finish. The finish is so bad that it looks as is the metal is being torn rather than cut. The surface is full of small slivers that would cut your hand i a heartbeat. I am having similar problems with an unkown carbon steel, although not as bad. I have checked the Machinery's Handbook, the Army metal working PDF, and some engineering reference books I have, but no help. I thought that I might even be using the tools wrong (cutting on the wrong face) but I can't seem to find the source of the problem. The lathe is a Grizzly 12 X 36. Any ideas?
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Kelly Jones wrote:

You are either using a really pointy tool or a dull tool or both.
A good finishing tool is rounded when you look at it from the top, and _sharp_ when you look at it from the side. If it's sharp when you look at it from the top and dull when you look at it from the side then somebody got things mixed up.
Is it the tool that came with the lathe? If so, it's probably too dull. I had to sharpen up the tools that came with my Smithy before they'd make decent cuts.
--

Tim Wescott
Wescott Design Services
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"Kelly Jones" wrote in message ...

it out.

to
getting
metal is

would
unkown
Handbook,
wrong
Hi Kelly; The speeds, feeds and the amount being cut will all have an effect on the surface but those are probably not the problem.
Do you have a bench grinder for your tool bits?
Two points: 1) line up the tool bit (where it is cutting) with the exact center of the piece being turned. You can see this by taking a "face cut" - if you are low you will see a little round "stub" when your tool bit passes the center and under it. Shim the tool bit up repeatedly until the cutting point passes thru (or almost) dead center. (better to be a few thousands low than high - if high the "relief" or under side will be "rubbing" rather than cutting)
2) Find a reference on the angles you should grind on the tool bit. In general the softer the material, the sharper the angles. Also check the rasdius at the cutting point - anywhere from a "hand stoned" very slight radius to large "form tool" for a radiused shoulder on the work.
What you ask is not really "simple" and you will still be learning these operations next year. You can learn about your "speeds and feeds" (for each material) from the colors (steel) on the continuous "chip curl" - or the small separate chips that fall to the bed... Aluminum will curl and spiral or be in ling straight "strings."
I suggest you find a machinist, toolmaker or modelmaker in your area that will let you watch and ask questions as he demonstrates - You will learn more it two hours that way than with all the instructions - then read the tables and instructions and play... You're going to love this... JHbs
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Phants wrote:

Sounds to me like your 'tool' is too sharp (read no radius).
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Wouldn't that be comparable to cutting a flat with a threading tool?
Tim
-- "I've got more trophies than Wayne Gretsky and the Pope combined!" - Homer Simpson Website @ http://webpages.charter.net/dawill/tmoranwms
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"Tim Williams" wrote in message ...

...
Yes - cutting a flat with a threading tool produces a "bad surface" but only if you are in a hurry and want to take a cut or two without changing the bit. If the tool bit is set correctly this will produce that bad surface, most likely with a spiral-like cut (a very fine and uneven thread), when the feed is too fast. A flat can be cut with a threading tool "point" by feeding really slowly and filing or stoning the surface afterward. Do this only on a non-essential surface - a shaft to provide sloppy clearance through a hole... (Called "mulyak machining")
BTW - I almost always take a very small radius on a threading tool... a pass or two with a fine stone or even a whitestone - absolute sharp makes for a possible fracture point under shear...
And, yes, too sharp with no radius could be a part of the problem but will not totally account for the problem being described as: "metal is being torn rather than cut"
That description is usually caused by metal being "pushed off" or "torn off" rather than cut off. The tool being too low (work attempting to "ride up" onto the top of the too bit) or too high (rubbing under the cutting surface) produces this. I have also seen this happen with a "negative rake" on the top of a fairly flat cutting surface.
Remember this for the time you want a (small o.d.) surface to grip with your fingers to turn and do not have a knurling tool... Tear it out (it's sharp) then file off the tops of the points ... Not for clients or others but quick and dirty in your own shop - and cheap...!
JHbs
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I ran into this by accident a few weeks ago. I was making a handwheel for an Atlas milling attachment from an aluminum blank. The OD of the wheel turned out with that 'torn' finish. But it was uniform, looked OK, and offered a superior grip that let me set the gibs a little tighter than usual. So I left it that way.
That description is usually caused by metal being "pushed off" or "torn

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You got a lathe for christmas?? shucks.. I'm so jealous :( all I got was $20 LOL
-Mike
-- A happy kid behind the wheel of a 98 Mustang GT Cold air intake FRPP 3.73 gears Steeda Tri-Ax Shifter Flowmaster 40 Series mufflers (self-installed woohoo) Hi-speed fan switch 255/60R-15 rear tires Subframe connectors Aluminum adjustable clutch quadrant

out.
getting
would
Handbook,
but
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On Tue, 28 Dec 2004 16:52:42 -0800, "Kelly Jones"

Fill in the blanks
1. What kind of tool are you using? 2. What is your feed rate in inches/rev? 3. What is your rpm? 4. How much material do you have hanging out of your chuck? 5. Have you tried a piece of aluminum?
Gunner
"Gunner, you are the same ridiculous liberal f--k you ever where." Scipio < snipped-for-privacy@actd.net
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wrote:

Thanks for the comments guys.
Answers to Gunner's questions:
1. Unknown tool. (I know this sounds crazy.) They are the tools that came with the machine. They are indexable inserts, but I don't know if they are carbide or simply HSS (although I suspect the latter).
2. I have tried a variety of feed rates, including the smallest available. Usually I have it set mid-range (I don't recall the precise setting at this time, but changes in feed rate seem to make no difference.)
3. I have tried all the speeds from 200 to 1000 RPM. I have been hesitiant to go faster.
4. About 4 inches.
5. I have not tried aluminum yet.
I know that I have damaged some of the tools (inserts) in my experimentation (chipped, dulled) but I still have this problem after rotating the insert to a fresh surface. Phants' comment about the tool height may have some bearing. I set the tool "high" to achieve the 5 degree offset described in chapter 7 of the Army training manual. Could it be that this only applies to square tools (not inserts)?
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came
are
If they are inserts they are probably carbide.

available.
this
hesitiant
Speed is a function of diameter. Smaller stuff runs faster than larger stuff.
Phants' comment about the tool height may have some

in
When turning, you want the cutting edge to be right on the centerline. What I do is (with the machine off) pinch a small scale (ruler) in between the bit and the work piece until it just stays without falling. If the top of the scale tips toward you your cutter is low. If it tips away your bit is too high.
--

Roger Shoaf

About the time I had mastered getting the toothpaste back in the tube, then
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you would want it very slightly high, so that under load it is near centerline, but never low, or so I was taught
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"yourname" wrote in message ...

centerline.
falling.
tips away

You are absolutely right, and were taught correctly. The phrase you use however (very slightly high) is also known as an RCH. Some think that this is the smallest measurement that can be made. ;-}
This is also "book correct" and, like so many things, is not really practical to achieve 100% of the time. This actually attempts to address the fact that under the force the cutting, the work will "raise itself" while being worked. The obvious part of this becomes "more correct" with smaller, more flexible material and cuts further out from the spindle. Diameters of the stock and heavy cuts come into play - the heavier the cut the more force attempting to "raise the work."
The less obvious part of this is that a cut that starts several inches from the spindle or Collette will allow much more "lift" in the material which will be less and less as the cut approaches where the material is being gripped in the spindle. As this happens your cutting tool will get "higher" until, if you started high it will become high on the work once again.
Start "dead on center" if you can - or a thousandth or two low... Being Highwill cut an RCH from where it should, but it cuts. Being Low cuts only at the start and then does not cut - it rubs...
JHbs
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    Carbide -- almost certainly.

    I forget whether you mentioned what machine you were using, but if your lathe has both power feeds and threading (threading controlled by the half-nuts lever, power feed by another), you want to use the power feed (which is slower) for turning, and keep the half nuts for threading only, to minimize wear on the leadscrew. If it has power feed, it probably also has power cross-feed, perhaps selected by the same control in a different position, or perhaps selected by a separate control. (Lathes which have three controls -- half-nuts, cross-feed, and longitudinal feed -- can often have both cross and longitudinal engaged at the same time to produce a taper. However it should not be possible to engage one of the power feeds and the half-nuts at the same time.

    With carbide, and with a 0.750" diameter workpiece, I would consider 300 RPM minimum, and probably 1000 RPM to be a reasonable choice in mild steel. (Without bothering to look up the proper SFM for that -- just going by feel.) As you reach smaller diameters, the speed can be increased.

    4 inches -- with only a 0.750" OD? That is likely to be a significant source of your problem. Before attempting to cut it, use a center drill ("drill and countersink") to make a center hole in the end of the workpiece, and then bring a "live" center (ball bearings) (if you have one for the machine) into the hole. If you don't have a live center, you'll have to use a hardened "dead" center and be careful to lubricate the hole with a good thick lube. What used to be used before all the hysteria about lead was white lead paste. Now, perhaps something like a molybdenum disulfide grease.
    This offers support to the free end of the workpiece, so it will not flex as much. With really long extensions, you will need more support than that -- with a follower rest if you are turning the whole exposed length, or a steady rest if you are only working on the end.

    Aluminum can be very nice to turn, or also be ugly, depending on the alloy. Pure aluminum is too soft to turn nicely. However, an alloy like 6061T6 can be very nicely turned.

    It could, indeed.

    It could be. Any insert tooling should have whatever angle needed built into it, so the shank can be level, as most quick-change and turret toolposts tend to hold the shank level, and the angle can only be easily set on one of the old "lantern" style toolposts, which is what was mostly in use at the time the Army manual was written.
    If you have an import 13x40 or similar lathe (Chinese or Taiwanese), it most likely came with a turret toolpost (four slots for tools on a rotatable device). These need stacks of shim stock under the tools to bring the cutting edge up to on center.
    If you have a quick-change toolpost, you have the ability to adjust the height of each tool individually without shims. Ideally, you should have a separate holder for each tool which you have.
    Note that many inserts can be totally level, and have a groove in them to make the effective angle correct.
    Cheap insert tooling (commonly sold in sets of five) tends to have inserts which are too thin, and are not properly supported. *Good* insert tooling has a secondary carbide anvil between the insert and the holder. And I tend to prefer insert tooling which fits a negative rake holder, but has a groove to make it into a positive rake cutting edge. I normally use these in an Aloris BXA-16N tool holder (the letter code changes for the size of the toolpost, with AXA being the smallest of the standard size, and BXA usually being a better fit for a 12" or 13" lathe. The "-16N" mounts two negative rake inserts, one on the turning end and one on the facing end, so a single holder handles most of the common operations. There is a plain "-16" (or is it called a "-16P"?) which uses positive rake inserts.
    Good Luck,         DoN.
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Thanks. Lots of good info. I spent the day playing with the machine. The first thing I did was to reset the tool height like Phants suggested and got an immediate improvement. Then I chucked up some 6160T6511 I got at the local scrap yard. It turns beautify. I also experimented with some internal turning / boring. Learned quickly that the thickness of the tool was greater than the width (i.e. it started rubbing). Thought I really screwed up, but I hit the emergency stop fast enough and everything still looks OK. I am surprised that the machine came with carbide inserts, but I am not complaining. Is there a way to tell by looking? I've got center drills and a cut off tool on order. Should be here within a week. The machine came with a quick change tool post. Thanks again for the info.
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    Yep -- you need a special format to use for boring. My own favorite is a 1/2" solid carbide bar with carbide inserts. (The benefit of the solid carbide is that it has less give than any steel of the same size, so it is harder for it to start chattering at a long extension.
    For shallow bores, get some of the brazed carbide insert boring bar sets for boring heads. Just make sure that the shank will fit into your tool holders. The BXA quick-change tool holders will accept 5/8" square shanks, and the one which you want has a 'V' bottom to the tool holder slot, so a round piece won't try to roll out under cutting loads.

    O.K. Good reflexes help a lot. :-)

    It may be cheap insert tools (which tend to have more expensive inserts. :-) A quick test for whether an insert is carbide or HSS is a magnet. HSS should be attracted, while the carbide should pretty much ignore it. (I think -- I would have to go downstairs to check it for sure.)
    Some of the inserts are TiN coated (Titanium Nitride, not the metal "tin"). Those will look gold. Though HSS can be (and is) TiN coated, too.

    Within a *week*? You need to learn about MSC. Check out:
    http://www.mscdirect.com/
and register for a catalog. (It is *big* -- over 4000 pages last time I checked.) While there are places which will charge you less, MSC is *very* quick. I don't know where you are located, but where I am, most things called in by about 6:00 PM or so will be here about 3:00 PM the next day. (The nearest warehouse is in Harrisburg PA, and I'm just a bit south of Washington DC.) They've got enough warehouses around the country so I would think that at worst you would only need one more day on top of that for most things.

    Great! Those are *so* much better than the turret toolposts. Any idea what size? Aloris and several other makers use the "AXA/BXA/..." markings, while Phase II and some others use "Series 100/200/...". The tool holders are interchangeable between them. I have the Phase-II Series 200 toolpost, and use a mix of Phase-II and Aloris tool holders.

    You're welcome.
BTW.    When commenting on the 4" stickout for 0.750" diameter situation     I forgot to mention that anything beyond 4X the diameter of     stickout needs support -- and if you're close -- use a center to     support it anyway.
    Good Luck,         DoN.
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"Kelly Jones" wrote in message ...

The
and got

the
For a "quick test" - You can tell carbide by attempting to sharpen (or to just grind) a spot on a "back surface" where it won't hurt the intent of the tool. If the grinding wheel breaks down instead of the tool - it is probably carbide.
You need a "green wheel," for sharpening carbide, a very soft wheel (counter intuitive) or a diamond (very hard) wheel... You can also sometimes tell by weight - if you have a comparative size in steel - carbide is noticeably heavier...
And You are "off and running" - congratulations..! Machining Beautifully is as exciting and gratifying as you can get in any hobby; the joy of actually producing a piece or a part that looks good and/or functions just the way you wanted it too only adds to the joy. That is why so many people that do this for a living choose to come home and do it as a hobby as well...
One caution in recognition of your status as a "newbie" - Be careful of taking advice from us "old farts" at face value, and remember that advice is restricted to only what you told us. There are sometimes valid reasons that the material is chosen, and for reasons other than the fact that it "machines better."
If this part you are making is a "pressure vessel" or must have certain hardness or even electrical properties, be careful when substituting one material for another. Probably not important in your first practice pieces, but a good opportunity to remind you that you are ultimately the only one responsible for the entire process; start to finish. Think it through...
Good luck and happy tooling... JHbs
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You might want to get yourself some free machining steel like 12L14. There is a lot of steel that does not machine very nicely unless you have everything just right.
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How about getting some "known" material for starters? Do you know what tool angles, speeds and feeds you need? What are you using for tool bits? Are they sharp? Do you understand how to set the tool to work? I'd get a "how to run a lathe" book if the answer to more than one of these questions is a "no". They can be had for about $10 on E-Bay. I don't mean to sound harsh, but with so many variables, it's hard to give any useful advice. If you don't want to do that, I'd at least visit a high school or vo-tech shop and ask the instructor for some help.
If you want to get some help over the phone, email me back off list. We can plan a time when you can be at the lathe and have a phone in one hand. Then we could start working through the issues.
Pete Stanaitis --------------------------------------------
Kelly Jones wrote:

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