I am trying to teach myself old school methods of hand working metal, including filing flat and parallel surfaces, chiseling and hacksawing to a line. My first project is to cut a piece out of an old cast iron dumbbell weight I have. Should I invest in a high tension hacksaw at this point? How long does it take to get the hang of this?
I am actually probably going to cut it with a torch since cutting with a hacksaw wore all the teeth off a Nicholson bi-metal blade before I had cut two inches into it. Hopefully it won't damage my files and chisels.
High tension frames are nicer, but they are of most value when using all-hard blades rather than the bimetal ones. Get one if you can find one whilst you are buying the 14tpi blades that will really help you when cutting larger pieces of metal. For some reason, most shops think that 18tpi is as course as hacksaw blades need to go. I find that I use 14tpi blades more often than the finer sizes.
Rob, Don't forget to lighten up slightly on the back stroke, do all the cutting on the "push". Get ready to see how we cut a lot of materials in the "old days" :)
No matter what you are cutting, if you feel the teeth slide across the metal without cutting, you are trying to saw through too hard a material to use a hacksaw. I'm not sure... gray matter getting soggy... but flame cutting through castings? Maybe plasma cutting would be better. But then you defeat your purpose. Go to a local machine shop and scrounge the drop bin for a piece of good steel to start with. Cold rolled, low carbon, even leadloy is good to start. Then migrate to tool steel for later heat treating. Plan on making a first class machinist's vice as a project. Plan on using bearing scrapers and bluing to finish.
Reminds me of the first day in metals class in Jr High. The teacher pulled out two hacksaw frames, and put in two new blades. He put a piece of bar stock in two different vices. He took the first volunteer and instructed him, "when I say GO, you saw as absolutely fast as you can in attempt to cut thru the stock".
He took the second volunteer and instructed him, "When I say GO, You try to take one stroke per second, slightly pushing down on the forward stroke and lightening up on the return stroke".
The "one stroke per second" kid cut off the bar stock, the other kid never did. He burned off all the teeth !
Cast iron does not oxy-acet torch cut. Your options are to grind or saw the material. If sawing is ruining blades, the material may be slightly chilled---or has considerable sand in the skin. Cast iron, unless dead soft and free of sand is not a fun material without using carbide, and then only when the proper grade is applied. C2 is the grade of choice.
Mr. Anderson 9th grade shop teacher 1965, "Work in the vise, left foot forward, right foot back, left hand forward, right hand back, one stroke per second, do not drag the saw on the return stroke."
Later, at home in our garage, when hack sawing was needed, I showed my school learning to my little brother and my father, who were impressed with my effectiveness.
A good high-tension saw frame is a very worthwhile investment, but it won't make a blade cut what it won't cut. If you want to hand saw this cast iron piece, go get a grit-edge (carbide, I believe) rod-saw blade or hacksaw blade, depending on whether you want to cut straight or curved.
It's probably too hard to file or chisel if it's too hard to cut with a normal saw, so you may need a less obnoxious hunk of metal to start with. Weights are notorious for being mystery metal, and you need stock you can actually work on with normal tools.
it pays to understand the dynamics of cutting in steel.
if you saw away at a good fast cutting speed you will actually make slower progress than if you saw at a slow rate. sounds counter intuitive...
what happens in the workpiece of the average steel is that the cutting action heats the area of the cut in the material directly below the cut. since the cutting action isnt continuous the material heats then cools, heats then cools etc which sounds like the type of thing you do in heat treatment to harden the metal. the sawing often hardens the metal that you are trying to remove in the next cut.
what this will do is blunt your saw blade quick smart.
the way to avoid this is to cut slowly so that the heat dissipates before it has the opportunity to heat the metal to anything like a critical temperature.
coolant wont stop this overheating occurring.
I experienced this while cutting out the undercarriage legs for my (then) corby starlet project in half inch thick spring steel. the first blade lasted 2 inches before all the teeth were worn off. I slowed my stroke rate down by half and used the next blade to cut a further 6 ft of cut.
slow down and get the cutting speed right and the rate of cut through the material will increase.
Thanks to all of you for your help. I think I will lay my hands on some bits of mild steel. I have been trying to practice a good stance, release pressure on the back stroke, etc., but I am having trouble drawing the blade back without it binding in the kerf and also following a scribed line. I don't quite know how to get around those problems. Any thoughts?
The problems are probably interrelated. If you don't make a clean, straight kerf, you'll find a clean, straight blade binds in the cut.
You already mentioned one issue -- you can't hold a blade true with a wimpy, flexible saw frame. You don't necessarily need a high-tension frame, but you need a good rigid one with _absolutely_ no tendency to twist when you apply cutting pressure.
You must (as my day harped on me day and night...sigh) "let the saw do the work". You should only apply as much down pressure as necessary to allow each tooth to take chips. Too little pressure, and the saw will skate and work-harden the surface you're trying to cut. To much pressure, and you'll warp the frame or the blade, and cut off-line and crooked.
Take long strokes and use all of the blade. If you concentrate your sawing in a 2" section of blade, that section will become dull before the rest.
It's been said already, but saw at a fairly low stroke speed. You're supposed to cut the steel, not polish the kerf.
Develop a good eye for how perpendicular the blade is to the material. You cannot make a vertical cut with a blade that's held off the vertical. Worse, an off-kilter attack will cause the kerf to curve, not just cut diagonally.
Work with "polite" materials while you're learning; and only move to tougher-to-cut stuff after you've developed some technique. Some of the nicest metal to cut for practice is that cheesy Chinalloy semi-steel/cast iron they use for making import machine tools. "Cuts like butter" comes to mind.
Change your blade before it becomes so dull you have to fight it. You fight with more pressure. It fights back with crooked, difficult cuts. Even with the _right_ amount of sawing pressure, a dull blade tends to cut off-line. Hacksaw blades are cheap compared to your labor and frustration.
Cutting along lines requires that you keep the tooth area of the blade adjacent to the line. But the back of the blade is thinner. If you don't keep the back _centered_ in the kerf, you'll drift off the line. Go too far that way, and the blade becomes "self-guiding" off-line.
This is purely a manual skill anyone can develop. It's a lot of work, too, so most people never take the time to do it. Days gone by saw a beginning machinist spending his first year at a filing bench. Good manual cutting and filing can be really enjoyable. If you're fighting the work, though, it becomes about the most tiring, frustrating job in the shop.
Some other materials that don't cut reliably or predictably are old cast iron window weights and old bed frames (OBF). These materials will have lots of hard spots in them, and will dull cutting tools such as drills, taps and saw blades.
You might scrounge some scrap steel or used automotive, machine or appliance parts that are/have been machined during manufacture. Many of the materials used to manufacture "things" are selected because of their machining properties.
The file test will often reveal if materials cab be cut effectively. If a corner of the tip of a file will gouge/score a material, it's likely to be soft enough to cut by other methods.
Reminds me of my experience in the high school shop. Every class of kids I have to remind at least half a doz. that a hack saw only cuts on the forward stroke and a file does the same. ...lew...
A little tip that makes a huge difference in cutting accuracy: Lay your index finger (on the hand that is on the handle) straight out along the saw frame. Sounds strange but you will notice an immediate improvement.
That's because it isn't true----as long as you don't exceed the maximum surface speed
Blink. Blink.
That's an interesting theory---but nothing near the truth. The conversion from martensite to austenite occurs only at elevated temperatures, far beyond anything that would be created by hand sawing. Therefore, heating and cooling plays no role in the material being sawn, but that isn't true of the effects *on the blade*. A combination of pressure on the return stroke and rapid sawing motion draw the temper (carbon blades only) and dull the edges of the teeth, rendering them a poor cutting tool. That condition may induce work hardening in some materials, but there is no heat treat involved in sawing materials at hand speed------none!
Exactly----but for reasons I mentioned. It has nothing to do with the base metal, and everything to do with poor technique and blade metallurgy.
True---but in the blade------not the base metal. Critical temperature in base metal, to convert to martensite, is in the vicinity of 1500° F, and require a rapid quench. That condition is impossible to achieve by hand motion, but temperature enough to draw temper in a carbon steel blade is easily achieved by poor technique and rapid motion.
Not true------to some degree-----but remember that cutting teeth on metal cutting tools are very sensitive to reverse pressure. Tips of teeth are generally chipped off with reverse action. Those that have the greatest success hacksawing are adept at not just relaxing pressure on the return stroke, but lifting the blade a tiny amount. The greatest possible blade life and cutting speed is so achieved. Or, you can use a band saw! :-)
Another effect of raising the blade on the back stroke is to reduce the amount of chips that are dragged back with the blade. This in term increases the amount of metal that can be cut on each stroke before the gullets are clogged.
These observations aren't based on teaching or theory, just on me seeing what happens when sawing things :-)
PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.