On Sat, 02 Mar 2013 15:41:48 -0600, Ignoramus22609
wrote:
On 2013-03-02, Ed Huntress wrote:
On Sat, 02 Mar 2013 14:25:29 -0600, Ignoramus22609
wrote:
On 2013-03-02, Ed Huntress wrote:
On Sat, 02 Mar 2013 13:46:48 -0600, Ignoramus22609
wrote:
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
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
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
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/fabs...ruary2012/#/48
I have that photo and more in higher-res versions. If you want, I'll
e-mail them to you.
--
Ed Huntress