hacksaw blade and cutting oil

[J Tiers]

so does anybody have hard evidence of oil producing better finish on light cuts?

I find by experiment (and the plural of "experiments" can indeed be "data"), that oil helps a lot IF the cut develops a built-up edge on the cutter. Depth of cut isn't always important with regard to that problem.

The build-up tends to come off and stick to the work at unpredictable intervals, leaving a rough finish. Oil tends to discourage the build-up, so the problem is reduced.

Also, with "sticky" or "gummy" materials, like some aluminum alloys, oil can let the cut material slide away easier over the tool surface, which tends to reduce "tearing" of the surface, encouraging true 'cutting".

These problems are usually less with really light cuts, and if the problem is reduced, the solution is harder to observe working.

[Optics Curmudgeon]

My diagnosis is that the blade was cutting slowly because it had too fine a tooth pitch, and the oil finished it off by clogging the blade, as Carl said.

[dian]

so i found a blade exactly the same as the previous one and cut an other piece of silver steel dry (its not O-1 or W-1 but probably pretty close). no problems at all, cut went under a minute and blade was like new afterwards.

so what do we make out of this? in what is a hack saw different from a band saw, an end mill, face mill, drill or a lathe tool?

many years ago, when i knew nothing about machining, i found out, that i was able to drill spring steel with regulal drills by filling the hole with alcohol. i remember drilling a 12 mm hole into a sway bar with a hand operated drilling jig (used up three drills). later i was very surprised, that you were supposed to use oil when cutting metal. intuitively it was wrong, because it would prevent the tool to "bite". nevertheless, i have used cutting oil for many years when machining harder stuff, but i have never really seen any obvious evidence of it being any good. i always hoped it was saving the tool from damage. (i do most of my machining dry, its much less of a mess, you just vacuum it up.) i also tend to use cutting oil on the finishing cut, when a nice surface matters. just because you are supposed to.

so if you think about it, a light cut maybe 0.1 mm or 0.05 mm, you put oil on it and that makes the tool skid and rubb (like the hack saw)? on the other hand i can see how oil preserves the cutting edge on a deep cut.

so does anybody have hard evidence of oil producing better finish on light cuts?

i dont, but i also use several "cutting fluids" and many materials and have never bothered to investigate this matter (would need an awfull lot of experiments).

[J Tiers]

If it was sharp, but was cutting slowly, and then after the oil it didn't cut, and the blade lasted only a dozen strokes, the "silver steel", which is usually W-1 or O-1 maybe was somewhat hardened. Either just in the cut, or throughout.

Then also, about halfway through a piece of round is where in the bottom of the cut the edges change to be acute angles that can tear off teeth.

The oil with a hacksaw tends to make the teeth "skid", more so with any sort of hardening of the material. So what do you do? You tend to press the saw down harder.

if you then catch the edge, and the teeth are hard (and therefore brittle), you can strip off a bunch of them. More so if the material is somewhat hardened, but it can happen with regular materials.

If it wasn't cutting well to begin with, you were probably already forcing it into the material, and it just got worse when the material edge got sharper/a more acute angle.

A hacksaw should cut without much forcing at all. Like any cutter, if it skids, either it was dull, or else the material is hard and the saw is NOW dull from skidding over it.

Regular oils are not so helpful. Some materials DO help, kerosene or diesel is a "cutting" fluid, it doesn't have much lube capability. The last thing you want is a "lube" when cutting.... you want an oil that is NOT a good lube. You want one that has helpful properties....one that carries away heat and chips without lubing the cutter, or that "poisons" the surfaces to prevent chip welding, etc.

It's pretty helpful if the "cutting oil" (cutting compound) does not tend to act as "chip glue" to hold chips in the cut, to be re-cut and re-re-cut until the remains fall off or are pushed away

I think when you put oil under extremely high contact pressure it will tend to weld the contacting materials, and as you force the relative motion, both materials will shed.

Usually, oil "poisons" the surfaces so they don't weld. Sulfurized oil is even better at "poisoning" the surfaces than straight oil. Try tigging oily/greasy steel....

[caveBob]

I wonder if it work hardened a spot then simply plucked the teeth off. Instead of oil, try first running the blade into a candle as you go.

[darryl]

Without oil, the teeth have a greater tendency to bite into the hard steel. There's probably a fine line between having the teeth cut and having the silver steel shed each tooth as it passes. If the tooth bites, the silver steel yields. With oil, the advantage goes to the silver steel, and the teeth drag across the material. No doubt a fine powder that's a mixture of the silver steel and the tooth material begins to develop and act like a lapping compound.

But I don't believe that the lapping action is the only thing destroying the teeth. I think when you put oil under extremely high contact pressure it will tend to weld the contacting materials, and as you force the relative motion, both materials will shed. In this case the silver steel will polish up brightly in the bottom of the cut and the hacksaw blade teeth will flatten off. The point contact pressure will lessen, and both materials will polish rather than one always eating the other.

Seems reasonable to me anyway.

Something that has at times occurred to me- you could use any liquid on the blade, some made to lube and some made to cool. The properties of the particular liquid under extreme pressure would likely become predominant, so if oil turns into a 'weld material' under pressure and water does not, then water would be the fluid of choice for this type of application. Hmm- cutting fluid is mostly water, with only enough other stuff in it to prevent rust. If you were to clean up well after the cut, then why couldn't you use plain water instead of something else- it would be interesting to try that. Might cost a blade or two-

[CarlByrns]

I have to agree with Carl on this one. Any time I tried oil
on a hack saw, the cutting was worse. Yes, the chips stuck
to the blade and filled the kerf, making it more difficult.

--Doozer

And we have all tried oil at least once when sawing because it seems like a good idea (geez, it's taking forever for this thing to cut. What if...).

[Mark Rand]

The fact that the saw was cutting slowly when dry tends to indicate that the blade was worn before the cut was started. A 10mm section of silver steel shouldn't take very long at-all to cut (if it wasn't hardened).

cutting oil doesn't seem to help hacksaw blades. As Carl and Doozer say, it leads to the chips sticking to the blade rather than falling off cleanly.

In almost all cases, people use hacksaw blades that are too fine. 14tpi should be the normal blade except for anything smaller than 6mm.

[Doozer]

I have to agree with Carl on this one. Any time I tried oil
on a hack saw, the cutting was worse. Yes, the chips stuck
to the blade and filled the kerf, making it more difficult.

--Doozer

[Daveb]

Nothing to do with the oil. Once you cut halfway through the bar, the blade was cutting against a sharp edge which simply stripped the teeth off the blade.

[CarlByrns]

i wanted to cut a piece of 10 mm silversteel (115crV3), so i grabbed a hacksaw. it was cutting slowly, but it was cutting. about half way through, the teeth on the saw were still sharp. then, to make life easier, i put some cutting oil on the cut. after a dozen strokes the blade was done, almost all teeth were missing. i had to look for the angle grinder (which i should have used in the first place). looking at the blade, it seems it was a "wolfram (=tungsten)" blade (not hss).

so how do you explain cutting oil ruining a cutting tool?

The oil held the chips in the gullets and formed a tooth-destroying abrasive paste. Hacksaws and bandsaws need flood cooling to flush the chips away.

[Peter N]

Was it a Starrett blade?

[Richard P Wilson]

I can't, I've never known it happen. Having said that, I usually only use cutting oil when sawing larger sections, to reduce the friction in the sides of the cut. Anyway, power hacksaws and bandsaws use cutting oil all the time, and their blades last.
Richard

[dian]

i wanted to cut a piece of 10 mm silversteel (115crV3), so i grabbed a hacksaw. it was cutting slowly, but it was cutting. about half way through, the teeth on the saw were still sharp. then, to make life easier, i put some cutting oil on the cut. after a dozen strokes the blade was done, almost all teeth were missing. i had to look for the angle grinder (which i should have used in the first place). looking at the blade, it seems it was a "wolfram (=tungsten)" blade (not hss).

so how do you explain cutting oil ruining a cutting tool?