THE CLASSROOM
CONTENTS:
New!
Damascus Tutorial
Bet You Didn't Know...
Hacksaw Information
File Information
Heat Treat
Information
In the heyday of the sailing ship, every ship had to have cannon for protection. Cannon of the times required round iron cannon balls. The master wanted to store the cannon balls such that they could be of instant use when needed, yet not roll around the gun deck. The solution was to stack them in a square based pyramid next to the cannon. The top level of the stack had one ball, the next level down had four, the next had nine, the next had 16, and so on. Four levels would provide a stack of 30 cannon balls. The only real problem was how to keep the bottom level from sliding out from under the weight of the higher levels. To do this, they devised a small plate ("monkey") with one rounded indentation for each cannon ball in the bottom layer. When iron was used to make this plate ("monkey"), the cannon balls would rust to the plate. As a result, these plates were made of brass to prevent this problem-- thus the name "brass monkey." When temperature falls, brass contracts in size faster than iron. As it got cold on the gun decks, the indentations in the brass monkey would get smaller than the iron cannon balls they were holding. If the temperature got cold enough, the bottom layer would pop out of the indentations spilling the entire pyramid over the deck. Thus it was, quite literally, "COLD ENOUGH TO FREEZE THE BALLS OFF A BRASS MONKEY." And all this time some of you thought we were talking dirty.
—Author Unknown
1) Apply pressure on forward cutting stroke only. Relax pressure as you drag saw back for next cut. Dragging teeth backwards under pressure will dull blade fast.
2) Keep control, let the saw cut don't force it. Too much pressure on ends of saw will flex blade, resulting in short blade life along with tiring operator.
3) About one stroke per second is top speed.
4) With proper technique, speed, & pressure a person can saw all day long without tiring or breathing hard.
5) Pick a blade (teeth per inch) so at least two teeth are in contact with work at all time. This prevents catching a single tooth tearing it off the blade.
6) Never put a new blade into an existing cut. Flip the work over and start a new cut opposite the first cut. A worn blade makes a narrower cut than a new blade. Placing a new blade into the old cut will ruin the "set" on a new blade during the first few strokes.
Suggested Blade Selections:
14 teeth per inch:
mild material, large cross sections
24 teeth per inch:
mild material, medium cross sections such as: angle iron, brass, copper,
iron pipe
18 teeth per inch:
tool steels, high carbon steels, high-speed steels
32 teeth per inch:
thin cross sections, conduit, thin tubing, sheet metal
Files come in six degrees of coarseness:
1) Rough, 2) Coarse, 3) Bastard, 4) Second cut, 5) Smooth, and 6) Dead smooth.
All bastards (for example) have the same number of teeth. This means a 6" bastard will have a much finer cut than a 12" bastard. This is true for the other coarseness too.
Files fall into five basic categories:
1) Mill & saw, 2) Machinists, 3) Swiss pattern, 4) Curved tooth, and 5) Rasps.
Pillar, square, warding, knife, three square, half round, round, and etc. are types of shapes/profiles.
Drawfiling:
Technique used when one wants a true flat surface. As with any skill requires practice to become proficient. When handle is in your right hand, file will only cut as you push it away from your body. When handle is in your left hand, file will only cut as you pull it toward your body.
Care of files:
1) Keep your files in a wood rack so their teeth never hit other tools or metal.
2) Cut in one direction only. Raise file off work to bring back for next cut. Dragging teeth backwards on work will dull a file fast. Also raising gives the cut chips time to drop out of the file teeth.
3) Keep your files clean by using a file card. Chips stuck in the file's teeth will make nasty scratch marks in your work surface.
4) About one stroke per second.
5) Keep control, let the file cut don't force it. Too much pressure on ends of file will flex it, resulting in a curved work surface.
6) NEVER USE A FILE WITHOUT A HANDLE
This is my heat-treat procedure for carbon and low alloy tool steels. It uses the following four steps: 1) annealing, 2) normalizing, 3) quenching, and 4) tempering in this order.
1) Forge to shape.
2) Put project in forge one last time. Take to non-magnetic and place in vermiculite to slow cool. This is called annealing. It will make metal as soft as it will get and relieve any stresses in the work.
3) Do any grinding, filing, drilling, and etc. that you wish to do.
4) Take work back up to non-magnetic and place it where it can cool naturally at room temperature. This is called normalizing. It will refine the grain structure of the steel and relieve any additional stresses from working the steel. DO THIS AT LEAST ONCE! Some people prefer to do this three times. I like to hang work by a wire while it cools. Do not lay one side on a cold bench or brick while it is cooling. This will create terrible stresses in the steel, undoing what you are trying to do.
5) Heat to non-magnetic again and quench to harden. This will make steel as hard as it can get but very brittle. I do all my quenching in oil heated between 120 to 150 degrees for consistency. If a person quenches in fluid (40 degrees in winter), (90 degrees in summer), or (several parts in succession - each raising the quench to a higher temperature) you will get poor consistency. A bucket of woodchips / sawdust works great to wipe oil off the part. No oily rags lying around in shop. I use cooking thermometer to monitor quench temperature.
6) Immediately temper after hardening. I heat in an oven between 250 and 500 degrees for one hour. Some temper three times allowing to room cool between each cycle. The higher the tempering heat the more tough the steel. For example: a razor at 250, a hunting knife at 375, an ax or sword at 500 degrees. If I want to leave the steel in a very hard state, I will boil it in a pan of water for 30 minutes guaranteeing a perfect temperature of 212 degrees.
This is only a guide as nothing is absolute. One needs to pick the procedure specifics based on the application, materials used, shop equipment, and the expected end result. However a person will be on their way to consistent predictable heat treating as long as the four steps: 1) annealing, 2) normalizing, 3) quenching, and 4) tempering are followed.
NOTE: Annealing and normalizing both relive stresses. Main difference is annealing softens metal for further working and normalizing refines the grain prior to hardening.