Milling Krell Metal?

I recently bought an Eagle Rock scissors type knurling tool like this:
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The catch is that the shank is 5/8" high, and my 11" lathe has an Aloris
AXA sized tool post on it, which can only take up to 1/2". No big deal I
figured, I'll just mill it down.
I hit it with a file, and it was pretty hard, so I used a nice new 4-
flute 1/2" Fette carbide end mill I had (note past tense). This has a
small (0.020") chamfer on it to avoid stress concentration in a sharp
corner. It's not under tons of stress, but it's what I had.
I have a Clausing 8520 mill, which is small, but a nice matchine if you
don't push it. The speed was set at 1000 rpm, which I figured would be
OK. Not wanting to push things, I took 0.015" deep passes, with ~ an
inch a minute feed. This all seemed to work OK, but after a number of
passes, I noticed the amount removed didn't look right compared to my
total Z-axis feed. I measured it, and I was about 30 thou shallower than
I expected.
I figured, OK, the end mill is slipping in the collet. I took out the
end mill with the intention of cleaning it & trying again, but I noticed
that the lovely sharp edges of my end mill were no more. It had worn
down the cutting edge to a very noticeable degree.
I'm about 3/4 of the way down to where I need to be. Tomorrow, I can hit
the nearest MSC for another carbide end mill of some flavor. However,
before I trash another one, I'd love to know what the heck happened and
how to avoid it in the future.
There are two issues:
1) What the heck is this stuff?: At worst, I figured the shank might
have been case hardened. It's cut from bar/sheet stock, not cast. I
haven't taken a grinder to it because it's all set up in the mill, but I
suspect it must be pretty hard throughout.
2) Feeds & Speeds?: Am I babying the cutter & wearing it out? Work
hardening the material? What sort of depth, speed & feed should I use to
maximize tool life? I experimented with using cutting fluid (Mr. Cool
Tool II), and it didn't seem to make any difference, so I mostly cut dry.
Keep in mid that this ain't no Bridgeport, so I can't get too agressive.
Also, will the chamfer tend to make the end mill want to "climb" into my
This is the first time I have ever worn out a cutter (much less a carbide
cutter) is less than one job. It's annoying to trash an expensive end
mill, but more so if I don't learn something useful out of this (other
than don't try to cut mystery metal).
(If you are wondering what the heck Krell metal is, it's from the movie
"Fobidden Planet", and the stuff was nearly indestructable.)
Thanks for any suggestions.
Doug White
Reply to
Doug White
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Doug White fired this volley in news:Xns9FC7D58A54875gwhitealummitedu@
At an inch a minute, you're taking only 1/4-thou per tooth. You probably want to take two or three thou, at least.
I had the same problem with a cutoff tool that wouldn't fit my B toolpost. I had to mill it, and it was tougher than my wife's worst snarl.
I cut about 5-thou deep at 20 ipm, and it cut very cleanly with oil-free coolant using a carbide insert facing mill with zero rake inserts. (a few yellow and white sparks, though, even with flood!!)
Reply to
Lloyd E. Sponenburgh
I have the cheaper import copy of the scissors knurling tool and an 8525.
The shank sparks like a medium carbon steel with possibly some alloy content. A file barely cuts it.
Generally when my mill balks at a disreputable hunk of steel I toss it in the wood stove overnight to anneal. Finished pieces can be wrapped in a flattened tin can containing charcoal, sawdust, paper etc to partly protect them from scaling. If you have to pay for your heat source, like a propane torch, it seems adequate to heat the steel to a moderately bright red glow, let it cool to black and quench in water. That may leave some gummy steels just hard enough that they don't tear, opinions vary.
A tin can on its side, floored with charcoal, holds the heat in better than an open torch flame. Beware of carbon monoxide.
Scrap flame-cut steel thusly treated mills very sweetly on my little Clausing with 1/2" HSS end mills at 600 RPM.
Reply to
Jim Wilkins
Well, get indexable end mills. You can index the inserts a couple times when dull, then replace the inserts. WAY cheaper than chewing up entire end mills on tough jobs like this.
Reply to
Jon Elson
The Clausing mill is limited to 1/2" MT2 or B&S7 collets which restricts the choice of indexable tooling. Mine holds a single insert.
Reply to
Jim Wilkins
Kristian Ukkonen wrote in news:P_iKq.2040$
I thought about attacking it with my bench grinder, as I don't have an angle grinder. It actually works out better to remove the bottom of the shank, because that lowers the tool closer to the centerline of the lathe. As it is, it will probably be tipped slightly in use, but for a scissors style tool, it doesn't really matter much.
I suppose I could grind it down a ways, and clean it up in the mill. The grinding would presumbly take out some of the temper as well.
Doug White
Reply to
Doug White
Or you could make another shank the right size and center height, and leave your expensive tool intact for when your heirs sell it.
Reply to
Jim Wilkins
...for a penny because they don't know what it is.
-- [Television is] the triumph of machine over people. -- Fred Allen
Reply to
Larry Jaques
"Lloyd E. Sponenburgh" wrote in news:Xns9FC7D99474ABlloydspmindspringcom@
OK, it sounds like I should try a shallower cut, but with a much faster feed. I'm off to MSC to pick up a couple cheap carbide end mills.
I'll also grind off what I can, partly to remove as much metal to start with, partly to see what the sparks look like (crude alloy test), and partly to try to soften the area before I hit it with a cutter.
Doug White
Reply to
Doug White
Take the chunk of Mystery Metal to your local scrapyard. They have these fancy Laser Spectrography Metal Analysis guns that they put up against the sample and pull the trigger, and in a few seconds {Bada-Bing!} it tells you exactly what you are dealing with.
And if it says "Titanium Alloy" or something exotic and expensive... You machine a new one out of steel, and sell them your mystery gear for surprising amounts of coin. And bring in the shavings you've already made, too.
Reply to
Bruce L. Bergman (munged human
Martin Eastburn wrote in news:mAwKq.224872$
I have an Aloris AXA tool post. The Eagle Rock knurler used to come with a cast shank that would fit the standard AXA holders (a friend has one), but they changed the design of the shank. I used to have an Aloris AXA knurler, but it was a pain in the neck to use compared to the scissor design. In order to get the knurls even, you have to get the center height just right, and it doesn't have nearly the size range of the scissor design.
I ground down the bottom of the shank most of the way, and will clean it up when my new carbide end mill arrives (hopefully later today).
Doug White
Reply to
Doug White
Doug White wrote in news:Xns9FC98A2C118C7gwhitealummitedu@
My MSC order arrived, and within minutes I was cutting metal on the mill. I'm not sue what did the trick, but the stuff cut just fine. When I was done, the end mill was still scary sharp.
Things that were different:
1) Ground down the metal most of the way, and beveled edges on grinder. This removes any surface hardness from the area of interest, and the grinding may have drawn the temper a bit.
2) Used a shallower cut (5 thou instead of 15) and a faster feed, with cutting fluid.
3) End mill. This one was a Hertel, the previous one was a Fette. Shouldn't matter, but who knows.
No sign of strain on the machine, nice finish, and the job is done. I blued the shank, reassembled the knurler, and mounted it in a tool holder.
I did my first knurl with it. I installed straight knurls, and I think I need some practice with them. They did the job, but I think the two knurls got out of sync, and I ended up with a finer knurl than I expected. I didn't bother checking the diameter, but I suspect that is much more crucial on a straight knurl than a diamond. The forces were also enough to move the cross feed around, so I need to lock that down. This was in 303 SS, and I suspect that it work hardens fast enough to make knurling it a pain.
Thanks for all the suggestions. On to the next project...
Doug White
Reply to
Doug White
I counted 48 teeth on a 3/4" diameter knurl, which if it were a gear would mesh with a 1" gear with 64 teeth. To me this suggests that the workpiece has to be an integral number of 64ths in diameter. Many even and a few odd millimeter sizes like 19 and 25 are very close to x/64"
Reply to
Jim Wilkins
"Jim Wilkins" wrote in news:jdg6ut$ru5$
Hmm. In this case the rod was 5/16" OD, so it should have been OK. I'll have to count the teeth. I bought the knurls quite while ago, and I thought I ordered "medium", but the Eagle Rock web site doesn't list them that way. They have quite a range of pitches.
Doug White
Reply to
Doug White
What you really want is an AXA-19. (I've got the BXA-19 on my lathe.) It is a scissors style knurling tool made for the quick-change toolposts. It has two parallel arms traveling on a vertical dovetail, with a knob on the top and a leadscrew which is right-hand thread on one end and left-hand thread on the other end to move the arms together or apart. This design maintains the center point between the arms, so all you need to do is take the time *once* to adjust the height adjust nut on the main body, and it will be centered every time you use it (presuming only a single lathe, of course). Since it is a scissors style in function, it relieves the cross-feed leadscrew of the excess load which a bump style knurler imposes.
O.K. I do have an Eagle Rock which came with a 1/2" shank and even works on my little Compact-5/CNC lathe (5" swing.)
But I have modified quite a few 3/4" shank tools to fit my BXA 5/8" holders. The first, after burning out endmills, I did with a surface grinder, but later, I got a horizontal spindle mill, and that, with a nice wide milling "wheel" does a nice job on all the tool shanks I've tried it on. Low spindle speed, lots of Ridged high sulfur threading oil, and lots of depth of cut with feed manually controlled to "feel" right. :-)
Enjoy, DoN.
Reply to
DoN. Nichols
I haven't done any straight knurling of stainless in a number of years, and I would expect that trying to use 2 straight knurls at the same time would be problematic.
I was able to straight knurl 316 SS with a single knurl (just crossfeed pressure) fairly consistently at low RPM on workpieces of about 1/2" dia. without traveling along the workpiece. Straight knurls should be capable of travel, but probably only easy if the knurl ID holes and the pins are very smooth, and well lubricated (not just flooded with watery coolant-type cutting lube).
Diamond pattern knurls need the same characteristics and lubrication to be able to track properly.
Attempting to see how well 2 straight knurls can sync is probably easier done with some aluminum or leaded steel material.. if they won't sync easily in these materials, the best choice may be diamond knurls, otherwise the anticipated results may be a matter of luck rather than skill or method.
There are the common metal-displacing type knurls and less common cutting knurls
Displacement-type diamond pattern knurls should be able to work properly without concern for matching the pattern size to the diameter of the workpiece.. that's where the good bearing surfaces of the pins and proper lubrication come into play, as the knurls can creep a little to keep falling into/track the same pattern. The helical shape of diamond pattern knurls helps them track because they can slip sideways a little while they're working.. if they don't have a gap between the knurl and the holder (and good lubrication), thay can't slip which will most likely produce poor results and lots of frustration.
The method taught when I was in high school was to carefully bring the knurls into light contact with the workpiece and rock the chuck back n'forth by hand, adjusting one of the knurls until the pattern was properly spaced to produce full diamonds (not smaller parallelograms).. then bump the cross feed in a bit and rotate the workpiece over a wider arc while establishing a bite into the workpiece with the correct pattern. After applying adequate cutting lube, it was a matter of feeding into the workpiece as soon as the spindle motor was switched on. The knurls would displace the material and establish a pattern to track, so the operator could travel the workpiece and continue to feed until the desired results were attained. We didn't have scssor-style knurling tools back then.. but the same principles apply. We were students.. I'm sure experienced machinists develop/utilize different methods.
Straight knurls should also track an established pattern, although this could be a little more difficult when working with work-hardening alloys.. it may require the operator to make CNC-like movements to be able to attain consistent results for a large number of workpieces.
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