Strange steel that is very hard to cut with a bandsaw

Ignoramus9672 fired this volley in news:b6qdnTmGg7C5qqzMnZ2dnUVZ snipped-for-privacy@giganews.com:

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

Or 15-5 or 17-4.

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

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

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.

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?

I am keeping my fingers crossed, and hoping that the blade did not become dulled. I have 3 more tons of rounds to cut down.

i

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

A sharp saw blade (or any sharp tool) will grab your thumbnail as you slide it lightly over the cutting edge. It will just slip on a dull blade.

MikeB

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

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:

I have that photo and more in higher-res versions. If you want, I'll e-mail them to you.

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.

Mart> >

THATS what they make plasma cutters for!!

My first project when I got my Miller was some AR500 doodads

The methodology of the left has always been:

1. Lie
2. Repeat the lie as many times as possible
3. Have as many people repeat the lie as often as possible
4. Eventually, the uninformed believe the lie
5. The lie will then be made into some form oflaw
6. Then everyone must conform to the lie