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Parting Aluminum?

pak

Cast Iron
Joined
Oct 31, 2007
Location
Miami Fl, USA
I had a bad experience yesterday. I was parting a 2” aluminum bar in my lathe when all of a sudden the carbide parting tool snapped like a potato chip. Here is how I had it set up. The tool was dead on center and perpendicular to the part. My machine was at its minimum 70 rpm (23 SFM) and .0014 ipm on the cross feed. The tool was about .0375” into the work when it hogged in. Here is a picture of the tool I was using. The tool is designed to cut a maximum 5/8” radius, but I only needed to part the piece to a depth of ½” due to its hollow bore. I need to know what I did wrong. I think I’m going to hear that I probably should have used my bandsaw, but I had to ask anyway. Thanks.

Regards,

Drew
 

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Hi pak,
Cutting aluminum you want sharp tooling, usually HSS, you used "the carbide parting tool", I have the Seco carbide insert tool, it's inserts are made for steel. The blade is HSS but the insert is not razor sharp on the cutting edge, (not honed). When parting aluminum I always use a "sharp" standard HSS parting blade, with some back rake on the top of the blade, 3 to 5°, and use penitrating oil or fuel oil for cutting lube. For 2" dia. 70 RPM is a little slow, I prefer 200 to300 RPM. Also I use a dial indicator to check my parting blade along it's length is a perfect 90° to the work.
 
Nothing wrong with using carbide to part aluminum.

Maybe the bore was off center and the bar sprung through and caught?

What kind of lathe was it on?
 
I had a similar problem with some 6.5" 6061. I got an inch deep and it would chatter like mad and then snap the blade off. Did that twice and sawed it.

I tried numerous speed and feed combos as well as changing the HSS cutter geometry (I needed the piece parted in 5 spots - so I got the 1" grooves for all of them).

I'm thinking it was just too much overhang for the tool with the sticky nature of the material.
 
Next time hold a small brush dipped in cutting oil into the groove as you feed in. It keeps the aluminum from welding itself to the tool edge.
 
I have no problem parting off aluminium with carbide inserts; the secret is to use flood coolant. The narrow parting groove makes it very difficult to get coolant onto the tool if you are only using a brush or spray.

Regards,

Mike.
 
Looking at your photo again; that tool is meant for a 5/8 max. radius. The lower part of the tool with the radius cutaway is not going to go very far into a 2" bar before the lower part of the tool strikes the bar. Under power feed this will twist or bend the tool.
Could this be the problem?

Regards,

Mike.
 
Mike and Mike, the next tool order I make I'm getting a supply of

6536262-11.jpg


I'm tired of trying to get a flip-top on a bottle of cutting fluid to let me put that fluid where I want it, instead of "within 1/2" radius".

I've had a one of these bottles for a long time that I've kept filled with acetone and I don't know why it has taken me this long to realize that it would be good for cutting fluid too.

I think the TapMatic cans used to come with a small extension tube (like the red ones that come with spray cans) but it seemed like those always got chewed up/melted shut/lost, leaving me back with a short spout that required getting the bottle and my hand a lot closer to the work than I wanted.

These wash bottles seem like the way to go for "very small flood coolant" applications, like getting some lube down in a parting-off groove.

cheers,
Michael
 
Thanks for the input

vmil3:I thought I might get into trouble with carbide at that speed. I think I will go to the HSS cut off store now and bump my speed up a little. Good input. Thanks.

turnthis:

I don’t have coolant yet, so I will go with vmil3.

Macona:
Good thought, but I didn’t get close to the bore when it happened. The lathe that I am using is a PM 1330. Respectfully.

Jim Shaper:

Thanks for your input.

Mike72:

I don’t use a brush, but I use a syringe to flood the groove.

MikeJB:

I may have to start using flood coolant if this persists. With regard to the radius of the cutter, I was aware of the depth that I could go with this tool. However, after doing the math and observing the result when it snapped, it was nowhere near striking the lower part of the bar. Good thought though. Thanks.
 
This looks to be one of those self-locking insert type cut-off blade holders. Did the insert grab on one side and break off the support?

The ISCAR calculator seems to think you should be turning at several thousand rpm with coolant.

Chris P
 
See if this helps. Look between the ************

The Slitting Saw and the Woodruff Cutter

Slitting saws and Woodruff cutters work in much the same way; so we
can just call them saws for now. Saws have one big difficulty.
After we understand that difficulty we will solve it and increase
their performance. First a little background.
*******************
After you dig a hole in the ground to fix a water pipe you need to
put the dirt back. However all the dirt wont go back because it
doesn't fit anymore. The dirt has been "upset". That is, all the
little grains of soil and pebbles are no longer nestled together in
a compact form. This upset condition also happens in metal during
the cutting process.

Upsetting the metal increases its volume. So the metal in a chip
that is cut from a bar takes up more space after it has been cut.

Parting off steel in a lathe using a slender "part off" tool (The old style)
creates a long slender upset chip. This chips volume is greater
than when it was compact material in the parent metal. And greater
also are its dimensions. The chip is longer, thicker and wider.

The wider condition is what causes the problem. The kerf or groove
being cut has a width as wide as the part off tool. During the
cut, the emerging chip is actually wider than the groove being
formed. So the chip is in the groove under a "press fit"
condition.

As the bar rotates the press fit chip is being forced down against
the cutting tool. The tool has to support the pressure of the
downward cut in addition to the downward force created by the
emerging chip. The deeper into the bar the tool cuts, the greater
these forces multiply; because the chip grows longer before
exiting the groove.

The tool will break during this process unless the cut is shallow
or the feed rate is very light. A light feed rate will create a very
thin "ribbon" like chip with light forces; but this takes a much
longer time to do the work.
****************


The difference between a part off tool and a slitting saw is
slitting saws have many "part off tools" or teeth around their axes.
Manufactures of these saws make them with tooth forms which have
flat ends on the teeth like a part off tool. These teeth then cut
a chip which is as wide as the slot just like the lathe tool and
with the same problems of high destructive forces caused by the
"press fit" chip being formed.

Unlike the lathe tool the saw has many teeth. So if one tooth
misses cutting something the tooth coming right behind it can
scoop up the remainder. Now to the "fix".

A double cut saw blade has chamfers on alternate teeth. These
chamfers on one corner of the tooth are made by grinding away one
third of the tooth on the left side of the first tooth and then on
the right side of the next tooth and so on. This grinding is done
on each tooth at a 45 degree angle with a little relief.

Now when the saw cuts, it cuts a chip on the left and then a chip
on the right. These chips are only two thirds as wide as the slot.
The following tooth has its chamfer on the other side and so it picks
up the remainder of what the first tooth left. The forming chip
isn't wide enough to rub both sides of the slot so the slitting saw
can cut very freely and take a heavier chip load. Higher production
can then be the result.

Another saw geometry which I found very smooth was what is called a
triple cut blade. It works with a saw with a number of teeth which can
be divided by three.

The tooth width is about thirty five percent of the blade width. It develops
with a tooth on the right, then a tooth on the left, and finally a tooth in the
middle and repeat. It works with less pressure and almost feels like a rotary file.

Regards,

Stanley Dornfeld, San Diego
 
bcstractor: I'm not really sure what happened. I'm just trying to avoid it in the future. Do you have a link to the ISCAR calculator? I presume it would be useful to a novice like me.

Metalcutter: Interesting information, but I'm not sure how to use it. Are you suggesting that I use a slitting saw mounted to the lathe or cut the work off independently? If the former, I could use some direction. If the later, it's self explanatory.

Thanks

Regards,

Drew
 
MikeJB:

With regard to the radius of the cutter, I was aware of the depth that I could go with this tool. However, after doing the math and observing the result when it snapped, it was nowhere near striking the lower part of the bar. Good thought though. Thanks.[/QUOTE]



How deep did you calculate you could get before bottoming out ?
 
MikeJB:

I figured just over .4 from the finished diameter, but to be sure I drew a simple profile of my part and laid the tool over it to see if there would be clearance (Pic 1). Rather than try to explain the profile and how the tool was set up I attached a simple rendering (Pic 2). Pic 3 is a shot of the cut-off with the tool at the depth when it broke. Pic 4 is a shot of the tool at the depth at which it would have parted. From this we can see that there was plenty of clearance before bottoming out on the finished diameter. The diameter of the bar was 2.018 to begin with. I turned it to 1.71. I bored it out to 1.28. I then tried to part it.

Bcstractor: The tool is from ENCO:

317-3230 SGTHR 16-2 .087 5/8 RH ISCAR CUT-OFF TOOL HOLDER
317-3242 GTR-2 8DEG.IC-354 ISCAR CUT-OFF INSERT
 

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pak,
do you mean .0014 ipm or .0014 ipr? maybe I've missed it, but what kind of lathe are you using? how heavy is it?

You will likely need to increase the feedrate. take my opinion with a grain of salt, but for manual lathes, I've experienced that you often need to chuck the charts and technical information out the window. Since you can't blast coolant onto the cut, you won't be able to safely get the same performance out of the cutter.

Your lathe will let you know how heavy you can feed. I personally think you could feed heavier in the aluminum. I have often found too light a feed a cause of a great many parting ills. It seems to me that the heavier feed helps to "throw" the chip towards the middle rather than allowing it to pinch up into the groove.

Since you were not parting all of the way to the center, I would not put the tool right on center. I would elevate it just a little--it may keep your insert from trying to pull out if your lathe has any slop in the cross slide. (I do it this way even if I am parting to center on an older lathe. The part will either break off or you can twist it off if it is not a production situation.)

Tap magic always worked wonderful for me, you don't have to stick any nozzle right down in the groove...I've had good luck just letting it drip right over head. Mik-o-thread or other thread cutting oil also works fine. Some may prefer the thinner stuff like tapmatic or kerosene or wd-40...they will work fine but with good and bad consequences. they are thinner so they get righ into the cut, but they also don't stay there as long. That's why I like plain tap magic or cutting oil--it seems to stay in the cut better to me.

Also, if nessecary, you may need to "peck" with the cutter to let it clear the chips and get more oil into the cut
 
Regal13: I incorectly stated that it was 'ipm'. It was 'ipr'. Good catch. Unfortunately, the manual is worthless, so I am left to read between the lines. I am using is a PM 1330. Seems very substantial. I just don't know what happened here. Thanks for your input.

Regards,

Drew
 
Hmm - Iscar says that is for high speed cutting of steel. And when they mean high speed - I think they mean faster than your lathe can probably go. A PM1330 may not have the toolpost rigidity either depending on what setup you have.

What's the rake on top of the insert?

Chris P
 
bcstractor: The PM1330 has a top speed of 2000 rpm. As far as rigidity, I have nothing to compare it to. Its my first lathe since highschool. They were pretty rigid then. The rake on top of the insert is 8 degrees according to ENCO's specs.

Regards,

Drew
 








 
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