My small bandsaw with a Starrett blade works extremely well to cut
regular steel. I have been cutting a lot of 4-6 inch rouds without a
problem.
Everything else, that looks funky, I test with a file to see if the
file can easily scratch that steel.
So, today I took a piece of somewhat sniny, magnetic steel, tested it
with a file, and set in the bandsaw.
To my surprise, the bandsaw does cut it, but it works 10 times slower
than for the usual steel. The shavings are also longer in length than
usual. Again, this steel is somewhat shiny and magnetic. Any idea what
it could be, 416 or some such?
i
Shiny as-received usually means fairly high chromium or nickel content.
Those steels are tough, even when annealed. They're not necessarily
abrasive, though, and by annealing, not hard enough to damage your blade.
Annealed tool steels seem to cut as well as - albeit more slowly than -
any other steels; on the saw or on the lathe/mill. Most cut more cleanly
than low-carbon structural stuff.
LLoyd
On Sat, 02 Mar 2013 10:41:59 -0800, snipped-for-privacy@whidbey.com wrote:
Oh, jeez, I just realized what Iggy could be running into.
Please forgive this VERY long post. I don't have time to edit it and I
can't just extract the guts:
FabShop Magazine Direct
A Saw Blade That Gets Under The Skin
By Ed Huntress
Contributing Editor
Getting into production with his company’s new Amada bandsaw, Pat
Schisler was happily cutting 316 stainless barstock with the
recommended carbide-tipped blades when things started to go wrong. As
the blade wore, teeth chipped; teeth would give out on one side and
start cutting on angles up to 45 degrees; and blades snapped. It
didn’t all happen at once; when the blades worked, they worked great.
But when they failed, they failed catastrophically. They were giving
at least 25% more life than high-speed-steel (HSS) blades. But they
cost twice as much.
Carbide-tipped blades often need fine-tuning, but the economics didn’t
justify a lot of development time for Schisler. He was cutting through
full eight-hour shifts but only one or two days per week. What he
needed was some hassle-free, lower-cost blades.
Schisler is the CNC programmer, and half of the CNC machine-shop
staff, for Eagle Stainless Container. Eagle makes a range of formed
and welded containers for production pharmaceutical applications, and
a line of small bottles for pilot and testing work in the pharma
industry. Beautifully finished, almost art-like objects, the smaller
bottles are drilled and turned from solid 316 barstock, which begin as
slugs sawn on the Amada hydraulic-feed cutoff bandsaw.
Manufacturing medical and pharmaceutical products often involves
working with difficult or unusual materials, from aerospace
superalloys to foamed titanium. There are few characteristics that
these materials have in common but there is a dominant theme to them:
many of them are among the most corrosion-resistant, nonreactive
structural materials. And the most common among such materials is the
familiar range of austenitic stainless steels – the 300 Series – which
present some challenges in machining.
Work-hardening Is The Culprit
The machinability of the higher 300-Series grades averages around 45:
far from free-machining, but not demoralizing, either. The machining
challenges they present are based on their tendency to work harden,
and the higher grades of austenitic stainless, with their high nickel
content, are especially prone to develop a resistant, work-hardened
skin while they’re being machined. If not approached properly, it can
make machining especially difficult, stopping HSS drill and lathe
bits, and saw blades, dead in their tracks.
Grade 316 is one of the tougher ones, and also a popular one for
medical devices and pharmaceutical products. It passivates with a high
degree of corrosion resistance and it’s more resistant to pitting and
stress corrosion than lower grades, such as 304.
Schisler ran informal tests on a variety of saw blades before settling
on a special-purpose Starrett VTH (for “variable tooth height”)
bimetal blade, an electron-beam-welded combination of spring-steel
backing and a band of M42 HSS from which the cutting teeth are milled
and ground.
The M42 HSS used for the VTH is also known as “cobalt,” or “cobalt
high-speed steel,” due to its high, 8% cobalt content. It’s
longer-wearing than common M2 and Matrix II, and it can take more
heat, although it still falls short of carbide on both counts. Because
it’s tougher than carbide, it provides a good compromise in terms of
cutting speed, tooth life, and cost.
The story behind the VTH blade, however, is in the geometry and
configuration of its teeth. It’s an all-out effort to deal with
work-hardening and frictional heat. Austenitic stainless grades from
304 on up can work-harden even when cut cleanly with sharp teeth. When
a cutting edge begins to dull, it compounds the work hardening. A
normal sequence of even-height teeth in a conventional blade is always
on the brink of cutting hardened material, and if the feedrate is not
high enough, or if the teeth are not cutting cleanly enough, the blade
can overheat and quickly fail.
The VTH is based on a strategy to get around it. It begins by
minimizing the number of teeth in the cut, so each cutting tooth is
taking a deeper chip, getting under any work-hardening on the surface.
This it accomplishes by “ramping” the teeth. In any four-inch or
six-inch section of blade, tooth height progresses from highest to
lowest, at which point a new ramp of teeth starts with a high tooth.
That high tooth is a raker that cuts on the end of the tooth, straight
into the work in the direction of the cut.
If that’s all there was to it, the cutting would be exceedingly rough
and the blade wouldn’t be stable in the cut. So the VTH has another
tactic. While the first tooth is a raker that cuts straight down, the
following teeth have increasing amounts of “set” and cut the sides of
the kerf, using just the corner of each tooth to cut the kerf wider
than the rakers. There actually are multiple teeth in the cut at any
time, but they aren’t cutting in the same place. So the amount of
stock left for the next tooth that does cut in the same place is
greater than it normally would be, giving that follow-up tooth a
deeper bite into the work and helping to get under the work-hardening.
The series of teeth in one four- to six-inch progression actually
includes two or three more rakers – they’re placed at every fifth,
seventh, or sometimes every third tooth -- so it doesn’t rely on just
one raker in a progression. But the highest one does the most cutting.
By alternately clearing the sides and the bottom of the cut, friction
and heating are reduced.
“Eventually, as the blade wears, the top of the first set tooth will
start cutting on top,” says Gene Ramsdell, Starrett’s Production
Metallurgist and Mgr. of Saw R&D for North America. “But even if the
teeth are worn, provided they’re not overcome by frictional heat,
they’ll continue to cut. And as long as the teeth keep pulling a chip,
the blade won’t rub and create a lot of heat. Blade rubbing is the
kiss of death, especially in high-nickel alloys. You just have to
increase the feed pressure as the teeth wear to avoid it, until the
teeth wear excessively and you reach the point of diminishing
returns.”
Friction and heat, as well as work-hardening, are the enemies in these
alloys. Lubrication is especially important. Schisler’s machine is
running a mist-coolant system with a vegetable-based cutting oil.
“It isn’t ideal,” says Schisler. “We had to compromise on the drilling
of spray holes on the coolant manifold block, because the mist system
we used, on our machine, wouldn’t allow us to mist all the way down to
the teeth of the blade. So the blade runs a little hot, and it
probably shortens our blade life. But it was necessary to fit
everything into place.”
Starrett’s Ramsdell is not a fan of mist systems for these blades,
although he prefers to leave it to the coolant experts. All else being
equal, he prefers to see a flood of straight cutting oil or a rich mix
of water-soluble oil.
The mist system does have its advantages. Watching the machine cut, we
were struck by the lack of odor or fog, and the clean floor around the
machine. In one eight-hour shift, the mist system uses just one bottle
of oil, which appears to hold a liter or less. Sawn slugs were almost
dry to the touch.
After cutting, slugs are transferred to a large vibratory deburring
machine, and then into a pair of opposed-spindle CNC turning machines.
Short slugs, 0.350 in. long, become the lids of the bottles. Longer
ones, up to 8.25 in., become the actual bottles. They’re loaded into
the tail-end chuck, machined on one end, and the chucks swap the part
to turn the opposite end.
That’s it for machining. Only two operators, including Schisler,
handle all manual parts-handling, and there are no robots except for a
parts-handling robot on the parts washer. After turning, the bottles
are laser-engraved, sometimes mechanically polished, and then
electropolished. Finished parts are bright and mirror-like.
Starrett’s Ramsdell calls the VTH blade their “better,” mid-priced
solution. They offer basic bimetal blades and carbide-tipped blades,
as well. But the VTH, which has been in Starrett’s lineup for roughly
20 years, is an effective solution for many applications where the
material tends to work-harden and to heat the blade. Besides
stainless, it’s used on mold steels and other high-alloy steels, and
particularly on high-nickel alloys that work-harden excessively if
feedrates aren’t steady enough.
“It needs a robust machine, and it’s not a good choice on gravity-fed
machines,” says Ramsdell. But that’s true for any effective cutting in
work-hardening materials. A controlled feedrate that consistently gets
the teeth below work-hardened surfaces is the first key to success in
cutting high-end austenitic stainless, and it results in a
cost-effective, medium-priced solution for Eagle’s work materials and
work load.
-- end --
Ed, I am using those Starrett blades with variable teeth and they are
amazing, well worth the money. I can easily make, say, 20 cuts of 5
inch rounds on a given day, lately. The blades fly through regular steel.
i
On Sat, 02 Mar 2013 13:46:48 -0600, Ignoramus22609
Aha. Well, I haven't followed this thread very well, having given up
on having any helpful ideas early on, but the previous comment about
non-austenitic stainless steel plucked a cord.
FWIW, most high-nickel steels, which work-harden like crazy, are also
magnetic. Even 304 is highly magnetic if it's been heavily cold-worked
but not annealed, as is the case with cold-rolled bars.
Grade 316 won't be magnetic even if you beat it like hell. High-nickel
tool steels will be magentic, and they work-harden.
Work hardening causes a lot of surprises. Not that I'm sure what
you're encountering, but it's something to keep in mind.
I rechecked that steel round. Despite having been told that it is
magnetic, it was not magnetic, it was 300 series stainless. The
bandsaw cut it just fine, but it took an inordinate amount of time.
i
On Sat, 02 Mar 2013 14:25:29 -0600, Ignoramus22609
People who cut a lot of 300 Series and who know their stuff keep
telling me it isn't difficult or particularly slow. My experience with
it is that it can be difficult, and it's pretty slow.
Machinability for typical grades runs around 40%. But it seems to be
more extreme when you're sawing versus, say, turning it.
Don't hold me to it. I don't have a lot of experience with it, except
for drilling thousands of pieces in a Herbert turret lathe. Otherwise,
I haven't machined it much with other methods.
On Sat, 02 Mar 2013 14:25:29 -0600, Ignoramus22609
Just to recount this situation, the long chips support the idea that
it's 300 stainless. They also suggest that your feedrate is too low.
You have to be agressive when cutting work-hardening materials.
Have you cut 300 Series on that saw before? Is this bar behaving
differently than those did, if you've done it before? If it's a
cold-rolled bar and it's not magnetic, the possibility increases that
it's 310 or 316, or one of the special-purpose grades.
Aside from the free-machining types, they're all a bear to machine,
compared to 302 or 304.
One last question -- does your saw have hydraulic or gravity feed?
The saw has gravity feed, retarded by a hydraulic retarder. It does
not have any assist that pushes the blade down. It also does not seem
to need one.
Which brings up the next question.
I have two bandsaws, a smaller Wilton, and a larger Startrite H225 9
inch bandsaw.
The Wilton, with that Starrett blade, works great.
The Startrite, which I restored electrically due to burned out
control, cuts a lot slower than the Wilton, despite being larger and
running at what seems to be proper speed. I, obviously, compare both
saws with similar material, regular carbon steel.
I told my guy that the problem is, most likely, that it needs a new
blade. My question is, how can I ascertain that withuot spending $90
on a new blade? How do I assess "sharpness" of the blade? And, can
blades be sharpened?
i
On Sat, 02 Mar 2013 15:41:48 -0600, Ignoramus22609
If you're using the Starrett Variable Tooth Height blade, I think the
answer is "no" on resharpening. The teeth vary not only in height, but
also in set. I don't know how you'd sharpen that.
Based on what you're said, here's my assessment: You're using a blade
intended for cutting stainless and other high-nickel alloys with a
power-feed bandsaw. You're using it with a gravity-feed saw. When you
use it with a gravity-feed saw, it works fine on regular grades of
steel. When you use it on austenitic stainless, you're not getting
sufficient consistency in feed-per-tooth and you're cutting
work-hardened material.
When you run that blade on stainless with gravity feed, getting
sufficient feedrates puts you at risk of breaking the blade. The fact
that the work hardening occurs only in a thin layer of "skin" makes it
vitally important to get each tooth a consistent distance under the
skin. Gravity feed, which controls only feed pressure but not feed
distance, won't do it. That's why the Starrett guy I quoted in my
article says the blade doesn't work well with gravity feed.
This is analagous to drilling stainless with a manual feed drill press
or turret lathe, with which I have some experience. The difficult part
is converting that manual feed pressure to feedrate. I've
work-hardened many parts by just slipping on the feed for a fraction
of a second. Power feed overcomes that.
Put that into your computer and figure out what you want to do. If
your chips are long and thin, you're having trouble getting sufficient
depth-of-cut. If you crank up the pressure, you're risking breaking
the blade. Power feed avoids that by controlling actual feed rate
rather than pressure.
Here's a photo of what the chips should look like:
http://www.nxtbook.com/nxtbooks/fabshopmagdirect/february2012/#/48
I have that photo and more in higher-res versions. If you want, I'll
e-mail them to you.
I had a friend in college that told me that the secret to machining
stainless was "Low speed and High feed".
Over the years I have come to respect this sage wisdom. When combined with
"Wicked sharp" it has yet to fail me.
Paul K. Dickman
On Sat, 2 Mar 2013 16:19:58 -0600, "Paul K. Dickman"
Yeah, I think you've said that to me before, and I try to follow it. I
run into uneven cutting, I think because of work-hardening.
And I attribute that to two things: My old South Bend is pretty
flexible by today's standards, from the bed to the tool tip. So even
when I use power feed, the feed isn't all that consistent.
The second thing is that, like most hobby machinists, I'm probably too
cautious with depths of cut and feedrates.
I should practice it but I haven't had much occassion to cut stainless
lately. Mostly, I just make repeair parts these days, for the
environment that's falling apart around me. d8-)
I was cutting (foolishly) some AR400 - pre-hardened and fights
abrations... It was shiny and when it used up a blade I checked
the specs and shot myself into the foot... Chrome Molly and more
large body atoms.
Martin
On 3/2/2013 12:41 PM, snipped-for-privacy@whidbey.com wrote:
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